ANNUAL AND SEASONAL DISSOLVED INORGANIC NUTRIENT BUDGETS
FOR HUMBOLDT BAY WITH IMPLICATIONS FOR WASTEWATER
DISCHARGERS
By
Charles R. Swanson
A Project Report Presented to
The Faculty of Humboldt State University
In Partial Fulfillment of the Requirements for the Degree
Master of Science in Environmental Systems:
Environmental Resources Engineering
Committee Membership
Dr. Brad Finney, Committee Chair
Dr. Matthew Hurst, Committee Member
Dr. Robert Gearheart, Committee Member
December 2015
ii
ABSTRACT
ANNUAL AND SEASONAL DISSOLVED INORGANIC NUTRIENT BUDGETS
FOR HUMBOLDT BAY WITH IMPLICATIONS FOR WASTEWATER
DISCHARGERS
Charles R. Swanson
Dissolved inorganic nutrient loading and uptake have been estimated for each of
the four major compartments of Humboldt Bay for the two major seasons characterized
by ocean upwelling (April through September) and watershed runoff (October through
March). Dissolved inorganic nutrient loading estimations include dissolved inorganic
nitrogen (DIN) as ammonium-N, nitrate-N, and nitrite-N, dissolved inorganic phosphorus
(DIP) as phosphate-P, and dissolved inorganic silicon (DSi) as silicate-Si. DIN and DIP
uptake estimations include phytoplankton, macroalgae, and eelgrass production, intertidal
sediment flux, and denitrification. A water budget including tidal flows, watershed
runoff, wastewater discharge, and direct precipitation on the Bay is also included as a
means for determining mass inputs from various sources using concentration data.
Humboldt Bay is a nitrogen limited system exhibiting stoichiometric N:P ratios
below the 16:1 Redfield ratio. N:P ratios decrease significantly inside Arcata Bay (the
inner-most compartment of Humboldt Bay) compared with water near the Bay entrance
during the upwelling season, indicating that denitrification is a major contributor to
nitrogen removal from the system during these periods. This also suggests that Arcata
Bay is more nitrogen limited than nearshore waters, as denitrification removes N and not
iii
P from the system. Annual estimates of denitrification in Humboldt Bay using areal
denitrification rates from a nearby tidal estuary indicate that denitrification may be over
five-times greater than the total wastewater DIN discharge, 768 Mg N/yr and 149 Mg
N/yr, respectively. Estimates of phytoplankton, macroalgae, and eelgrass production in
the Bay are also greater than wastewater DIN discharge loads.
Freshwater DIN and DIP loads to Humboldt Bay are minor in comparison with
estimates of nearshore nutrient loading. Average annual DIN and DIP loading to
Humboldt Bay from nearshore waters is approximately 14,363 Mg N/yr and 2,653 Mg
P/yr, respectively, with only 1.7% of the total nearshore load, 239 Mg N/yr and 44 Mg
P/yr, respectively, estimated to be directly loaded to Arcata Bay. DIN inputs to Arcata
Bay from freshwater sources including wastewater and watershed runoff contribute 40
Mg N/yr and 51 Mg N/yr, respectively, or 17% and 21% of the estimated load from
nearshore waters, respectively. DIP inputs to Arcata Bay from wastewater and watershed
discharges contribute 13 Mg P/yr and 6 Mg P/yr, respectively, or 21% and 10% of the
nearshore load, respectively. During the upwelling and runoff seasons, the Arcata
wastewater treatment facility (AWTF) DIN discharge to Arcata Bay makes up 5% and
18% of the total load to the Bay, respectively, and 16% and 25% of the DIP load,
respectively.
Eutrophication potential in Humboldt Bay increases during the productive
upwelling season as biological uptake of DIN and DIP increase by an estimated 250%
and 415%, respectively, and nearshore loading increases by 20% and 14%, respectively.
Watershed runoff DIN and DIP loads decrease during the upwelling season by an
iv
estimated 74%, and wastewater loads decrease by an estimated 32% and 20%,
respectively. Decreased DIN and DIP discharge from wastewater and watershed sources
during the productive upwelling season suggest that anthropogenic nutrient impacts to
potential eutrophication in Humboldt Bay are minor in comparison to nearshore
influences.
v
ACKNOWLEDGEMENTS
I would like to thank Professor Matt Hurst who introduced me to research,
provided years of guidance in the laboratory, secured grant money for our work, and got
me interested in Humboldt Bay. I would like to thank the Wiyot Tribe's Natural
Resources Department staff including Stephen Kullmann and Tim Nelson for their years
of high quality monitoring and sample collection in Humboldt Bay, and for maintaining
the data sonde on Indian Island that continues to provide the best and longest running
near-real time dataset in Humboldt Bay. I would like to thank Professor Bob Gearheart
for giving me the opportunity to learn from his lifetime of experience at the Arcata Marsh
and for providing material support for this project. I would like to thank Professor Brad
Finney for years of support in and out of the classroom as I endlessly over-committed
myself. I would like to thank Jeff Anderson, P.E. for his support in providing detailed
output from his hydrodynamic model and for taking the time to meet with me over the
years to teach my how to use the model software. I would like to thank Kenny Smith for
all of his help collecting, processing, and analyzing samples including some very windy
days on the Bay. I would like to thank the City of Arcata Environmental Services
department, in particular Erik Lust, Mark Andre, Karen Diemer, and Rachel Hernandez,
for their support of this project well in advance of any regulatory necessity. I would like
to thank Professor Jeff Abel for the use of his autoanalyzer to run all of our nutrient
samples. I would like to thank the Humboldt State University Telonicher Marine
Laboratory in Trinidad for the use of their facilities including the autoanalyzer and
vi
fluorometer. I would like to thank the Humboldt State University Sponsored Programs
Foundation for their financial support that helped us pay for laboratory supplies and
student labor. I would like to thank the City of Eureka wastewater treatment facility staff
for readily providing water quality data and their openness to letting me grab samples and
run independent nutrient tests on them. I would like to thank Jennifer Kalt at Humboldt
Baykeeper for providing their citizen monitoring dataset. I would like to extend a special
thank you to Juliette Bohn for her unending patience, love, support, and enthusiasm, and
most of all for the use of her Zodiac!
vii
TABLE OF CONTENTS
ABSTRACT ........................................................................................................................ ii
ACKNOWLEDGEMENTS ................................................................................................ v
TABLE OF CONTENTS .................................................................................................. vii
LIST OF TABLES ............................................................................................................ xii
LIST OF FIGURES ........................................................................................................ xvii
LIST OF ABBREVIATIONS ......................................................................................... xxii
LIST OF UNITS ............................................................................................................ xxiv
INTRODUCTION .............................................................................................................. 1
Geographic Setting ......................................................................................................... 2
Hydrographic Setting ...................................................................................................... 5
Watershed Characteristics ........................................................................................... 7
Arcata Bay ................................................................................................................ 10
Main Channel ............................................................................................................ 13
Entrance Bay ............................................................................................................. 15
South Bay .................................................................................................................. 17
Oceanographic Setting .................................................................................................. 18
Ecologic Setting ............................................................................................................ 22
Wastewater .................................................................................................................... 24
REVIEW OF LITERATURE ........................................................................................... 26
viii
Nutrient Cycling ........................................................................................................... 27
Nitrogen Cycle .......................................................................................................... 28
Phosphorus Cycle ...................................................................................................... 30
Silicon Cycle ............................................................................................................. 31
Nutrient Sources and Uptake ........................................................................................ 32
Atmospheric Fixation ................................................................................................ 33
Phytoplankton Production ......................................................................................... 33
Eelgrass Production .................................................................................................. 35
Macroalgae Production ............................................................................................. 35
Salt Marsh Production ............................................................................................... 36
Mariculture ................................................................................................................ 37
Sediment Flux ........................................................................................................... 38
Denitrification ........................................................................................................... 42
Humboldt Bay Flushing Times ..................................................................................... 45
Humboldt Bay Circulation Studies ............................................................................... 49
Humboldt Bay Nutrient Studies .................................................................................... 54
METHOD ......................................................................................................................... 65
Sample Collection ......................................................................................................... 65
Sample Analyses ........................................................................................................... 72
Data Analyses ............................................................................................................... 74
Tidal Volumes ........................................................................................................... 79
Watershed Runoff Volumes ...................................................................................... 81
Precipitation Volumes ............................................................................................... 83
ix
Ocean Nutrient Loads ............................................................................................... 83
Wastewater Nutrient Loads ....................................................................................... 84
Watershed Nutrient Loads ........................................................................................ 85
Phytoplankton Uptake ............................................................................................... 86
Macroalgae Uptake ................................................................................................... 88
Eelgrass Uptake ........................................................................................................ 89
Sediment Flux ........................................................................................................... 90
Denitrification ........................................................................................................... 92
RESULTS ......................................................................................................................... 94
Upwelling Season Response ......................................................................................... 95
Runoff Season Response ............................................................................................ 100
Nitrogen Limitation .................................................................................................... 108
Eutrophication Level ................................................................................................... 110
Climatic Anomalies .................................................................................................... 113
Intertidal Properties ..................................................................................................... 114
Chlorophyll-a .......................................................................................................... 117
Nitrate ..................................................................................................................... 120
Silicate ..................................................................................................................... 124
Ammonium ............................................................................................................. 127
Phosphate ................................................................................................................ 130
Nutrient Sources ......................................................................................................... 132
Ocean Influx ............................................................................................................ 132
Wastewater Discharge............................................................................................. 133
x
Watershed Runoff ................................................................................................... 140
Sediment Flux ......................................................................................................... 143
Nutrient Uptake ........................................................................................................... 144
Phytoplankton Uptake ............................................................................................. 144
Macroalgae Uptake ................................................................................................. 148
Eelgrass Uptake ...................................................................................................... 150
Sediment Flux ......................................................................................................... 151
Denitrification ......................................................................................................... 156
Water Budget .............................................................................................................. 157
Nutrient Budgets ......................................................................................................... 161
Annual DIN Budget ................................................................................................ 161
Seasonal DIN Budgets ............................................................................................ 167
Annual Phosphate-P Budget ................................................................................... 169
Seasonal Phosphate-P Budgets ............................................................................... 171
Annual Silicate-Si Budget ....................................................................................... 174
Seasonal Silicate-Si Budgets ................................................................................... 175
DISCUSSION ................................................................................................................. 178
Seasonal Responses .................................................................................................... 178
Budget Surpluses ........................................................................................................ 180
Budget Deficits ........................................................................................................... 181
Comparison with Other Systems ................................................................................ 182
Historical Changes ...................................................................................................... 185
FUTURE RESEARCH ................................................................................................... 188
xi
CONCLUSION ............................................................................................................... 189
REFERENCES ............................................................................................................... 190
APPENDIX A - SAMPLE SITE COORDINATES ....................................................... 201
APPENDIX B - WATER QUALITY DATA ................................................................. 202
xii
LIST OF TABLES
Table 1 - Surface area and volume for Humboldt Bay at various tidal data; note these data
are from a hydrodynamic model that includes portions of Mad River Slough, Freshwater
Slough, and Martin's Slough, so high tide values are slightly greater than listed
elsewhere............................................................................................................................. 5
Table 2 - Average monthly precipitation for the period of record (12/1/1886-1/20/2015)
at Woodley Island in Eureka. .............................................................................................. 6
Table 3 - Average daily flow rates for the two major wastewater treatment facilities
discharging to Humboldt Bay. ............................................................................................ 7
Table 4 - Humboldt Bay sub-watershed surface areas........................................................ 8
Table 5 - Water to watershed surface areas ratios for Pacific coast bays. .......................... 8
Table 6 - Surface area and volume of Arcata Bay at different tidal datums. .................... 11
Table 7 - Surface area and volume of the Main Channel at different tidal data. .............. 14
Table 8 - Surface area and volume of Entrance Bay at different tidal data. ..................... 16
Table 9 - Surface area and volume of South Bay at different tidal data. .......................... 18
Table 10 - Tidal data from the NOAA North Spit, Humboldt Bay station. ...................... 19
Table 11 - Phytoplankton assimilation ratios from three independent studies (g/hr/g Chl-
a); it should be noted that these values vary significantly, likely due to variations in
ambient nutrient concentrations that can influence phytoplankton uptake rates. ............. 35
Table 12 - Nutrient flux rates for microalgae-covered intertidal sediments in Yaquina
Bay, Oregon (mg/m2/hr); negative values denote sediment uptake. ................................. 41
Table 13 - Phosphate and silicate concentration ranges measured near the Bay entrance,
in Arcata Bay, and in South Bay. ...................................................................................... 55
Table 14 - Phosphate, nitrate, and ammonium concentration ranges (and medians)
measured near the Bay entrance and inside Arcata Bay between July 1979 and March
1980................................................................................................................................... 58
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Table 15 - Phosphate, nitrate, ammonium, and silicate concentration ranges (and means)
measured near the Bay entrance, in Arcata Bay, and in South Bay. ................................. 59
Table 16 - Dry Season phosphate, nitrate, and ammonium concentration ranges (and
means) measured throughout Humboldt Bay; note that low and high range values were
estimated from plots, whereas means were gathered from tabulated data. ....................... 63
Table 17 - Wet season phosphate, nitrate, and ammonium concentration ranges (and
means) measured throughout Humboldt Bay; note that low and high range values were
estimated from plots, whereas means were gathered from tabulated data. ....................... 64
Table 18 - Ranges (and medians) of phosphate, nitrate, nitrite, and silicate measured in
Humboldt Bay. .................................................................................................................. 64
Table 19 - Sub-bay and associated watershed surface areas. ............................................ 79
Table 20 - Surface area and streamflow characteristics for each stream entering Humboldt
Bay and nearby Little River. ............................................................................................. 82
Table 21 - Monthly macroalgae production rates measured in Coos Bay, Oregon; % RSD
is the percent of the standard deviation relative to the mean. ........................................... 88
Table 22 - Average monthly eelgrass production rates measured in Arcata Bay and South
Bay. ................................................................................................................................... 90
Table 23 - Monthly light and dark period intertidal sediment flux rates for nitrate and
ammonium; values in bold are actual measurements, values in italics are linearly
interpolated between measured values (bold). .................................................................. 91
Table 24 - Monthly light and dark period intertidal sediment flux rates for phosphate and
silicate; values in bold are actual measurements, values in italics are linearly interpolated
between measured values (bold). ...................................................................................... 92
Table 25 - Eutrophication classification system based upon maximum annual
chlorophyll-a concentrations in an estuary developed by the National Estuarine
Eutrophication Assessment (Bricker et al., 2003). ......................................................... 111
Table 26 - Eutrophication classification system based upon minimum annual dissolved
oxygen concentrations in an estuary developed by the National Estuarine Eutrophication
Assessment (Bricker et al., 2003). .................................................................................. 113
Table 27 - Total annual precipitation at Woodley Island during the sampling period was
between 50-84% of the average for the period of record. ............................................... 114
xiv
Table 28 - Average annual and seasonal chlorophyll-a and nutrient loading to Humboldt
Bay (and standard deviations). ........................................................................................ 133
Table 29 - Nutrient concentration and loading ranges (and means) for the AWTF and
EWTF; only one value for nitrate and phosphate were collected for EWTF effluent on
August 31, 2015. ............................................................................................................. 137
Table 30 - AWTF annual and seasonal hydraulic and nutrient loading to Humboldt Bay
(and standard deviations). ............................................................................................... 139
Table 31 - EWTF annual and seasonal hydraulic and nutrient loading to Humboldt Bay
(and standard deviations); note that only one measurement of nitrate and phosphate were
available so the uncertainty reported for these values is attributed completely to the
variation in flow rate used to calculate the mass discharge. ........................................... 140
Table 32 - Annual watershed hydraulic and nutrient loading to Humboldt Bay (and
standard deviations). ....................................................................................................... 142
Table 33 - Upwelling season (April-September) watershed hydraulic and nutrient loading
to Humboldt Bay (and standard deviations). .................................................................. 143
Table 34 - Runoff season (October-March) watershed hydraulic and nutrient loading to
Humboldt Bay (and standard deviations) ....................................................................... 143
Table 35 - Average annual and seasonal chlorophyll-a concentrations for sub-bay and
average volume of each bay. ........................................................................................... 145
Table 36 - Annual phytoplankton nutrient uptake for Humboldt Bay and sub-bays (and
standard deviations)*; note that silicon uptake assumes all phytoplankton are diatoms and
represents an upper estimation. ....................................................................................... 147
Table 37 - Upwelling season phytoplankton nutrient uptake for Humboldt Bay and sub-
bays (and standard deviations)*. ..................................................................................... 148
Table 38 - Runoff season phytoplankton nutrient uptake for Humboldt Bay and sub-bays
(and standard deviations)*. ............................................................................................. 148
Table 39 - Annual macroalgae nutrient uptake for Humboldt Bay and sub-bays (and
standard deviations)*. ..................................................................................................... 149
Table 40 - Upwelling season macroalgae nutrient uptake for Humboldt Bay and sub-bays
(and standard deviations)*. ............................................................................................. 150
Table 41 - Runoff season macroalgae nutrient uptake for Humboldt Bay and sub-bays
(and standard deviations)*. ............................................................................................. 150
xv
Table 42 - Annual eelgrass nutrient uptake for Humboldt Bay and sub-bays (and standard
deviations)*; note that reported eelgrass production only takes place during the upwelling
season (April-September) therefore the annual uptake is the upwelling season uptake. 151
Table 43 - Annual sediment nutrient flux for Humboldt Bay and sub-bays (and standard
deviations)*; negative flux values indicate uptake by sediments. .................................. 155
Table 44 - Upwelling season sediment nutrient flux for Humboldt Bay and sub-bays (and
standard deviations)*; negative flux values indicate uptake by sediments. .................... 156
Table 45 - Runoff season sediment nutrient flux for Humboldt Bay and sub-bays (and
standard deviations)*; negative flux values indicate uptake by sediments. .................... 156
Table 46 - Annual denitrification in Humboldt Bay and sub-bays (and standard
deviations). ...................................................................................................................... 157
Table 47 - Annual water budget for Humboldt Bay (Mm3/yr); the Entrance Bay may be
influenced by Eel River water in the winter when nearshore currents flow northward
though it does not receive any direct river inputs. .......................................................... 159
Table 48 - Upwelling season water budget for Humboldt Bay (Mm3). .......................... 160
Table 49 - Runoff season water budget for Humboldt Bay (Mm3). ............................... 160
Table 50 - Annual DIN budget including loading and uptake for Humboldt Bay and sub-
bays (Mg N/yr); negative values denote uptake or removal from the system. ............... 165
Table 51 - Bay entrance DIN export for 12 monthly samples illustrates the potential for
advective export of nutrients from Humboldt Bay as an additional sink to account for the
large net surplus of nutrients in the budget (total net export in this example is 16,550 Mg
N/yr). ............................................................................................................................... 166
Table 52 - Annual volumetric DIN loading and uptake rates for Humboldt Bay and sub-
bays. ................................................................................................................................ 166
Table 53 - Upwelling season DIN loading and uptake for Humboldt Bay and sub-bays
(Mg N). ........................................................................................................................... 168
Table 54 - Runoff season DIN loading and uptake for Humboldt Bay and sub-bays (Mg
N). ................................................................................................................................... 169
Table 55 - Annual phosphate-P loading and uptake for Humboldt Bay and sub-bays (Mg
P/yr)................................................................................................................................. 171
xvi
Table 56 - Upwelling season phosphate-P loading and uptake for Humboldt Bay and sub-
bays (Mg P). .................................................................................................................... 173
Table 57 - Runoff season phosphate-P loading and uptake for Humboldt Bay and sub-
bays (Mg P). .................................................................................................................... 174
Table 58 - Annual silicate loading and uptake in Humboldt Bay and sub-bays (Mg Si/yr);
phytoplankton uptake assumes all phytoplankton in Humboldt Bay are diatoms, making
this an upper estimate of possible phytoplankton silicate uptake. .................................. 175
Table 59 - Upwelling season silicate-Si loading and uptake for Humboldt Bay and sub-
bays (Mg Si); phytoplankton uptake assumes all phytoplankton in Humboldt Bay are
diatoms, making this an upper estimate of possible phytoplankton silicate-Si uptake. .. 176
Table 60 - Runoff season silicate-Si loading and uptake for Humboldt Bay and sub-bays
(Mg Si); phytoplankton uptake assumes all phytoplankton in Humboldt Bay are diatoms,
making this an upper estimate of possible phytoplankton silicate-Si uptake. ................ 177
Table 61 - Comparison of physical properties and biological uptake in Humboldt Bay and
Tomales Bay. .................................................................................................................. 183
Table 62 - Comparison of nitrate and ammonium concentrations in Humboldt Bay and
Tomales Bay; outer bay refers to areas near the bay entrance more highly influenced by
nearshore conditions, and inner bay refers to areas more isolated from nearshore
influences. ....................................................................................................................... 184
Table 63 - Comparison of nitrate and ammonium concentrations in Humboldt Bay and
eutrophic Upper Newport Bay in Southern California; note that creek nitrate and
ammonium concentrations in Humboldt Bay are the same for both seasons due to
insufficient data; tidal channel refers to areas inside the bay, and creek refers to
watershed and creek runoff. ............................................................................................ 185
Table 64 - Comparison of historic nutrient concentrations measured in Humboldt Bay
between 1962-2015; IB = Inner Bay (i.e. Arcata Bay or South Bay), OB = Outer Bay (i.e.
near Bay Entrance), US = Upwelling Season, RS = Runoff Season, ND = no data....... 187
xvii
LIST OF FIGURES
Figure 1 - Humboldt Bay (40.8° N, 124.2° W) is located in northern California
approximately 80 miles south of the California-Oregon Border (Google Earth (1), 2013).
............................................................................................................................................. 3
Figure 2 - Humboldt Bay consists of four distinctive compartments, and is adjoined by
two cities, Arcata and Eureka; note: image depicts Humboldt Bay at low tide (NAIP,
2014). .................................................................................................................................. 4
Figure 3 - Humboldt Bay watershed delineation (WBD, 2015); note, alterations have
been made to the Watershed Boundary Database polygons to more precisely represent the
contributing watersheds of Humboldt Bay based on the location of tide gates and sample
points. .................................................................................................................................. 9
Figure 4 - Aerial imagery of Arcata Bay indicating major circulation channels and
freshwater input locations (ortho-imagery: NAIP 2014). ................................................. 10
Figure 5 - Aerial imagery of the Main Channel indicating the location of major flow
channels and freshwater inputs (ortho-imagery: NAIP 2014). ......................................... 14
Figure 6 - Aerial imagery of Entrance Bay indicating the locations of major landmarks,
flow channels, and freshwater inputs (ortho-imagery: NAIP, 2014). ............................... 16
Figure 7 - Aerial imagery of South Bay indicating the locations of major flow channels,
landmarks, and freshwater inputs (ortho-imagery: NAIP 2014). ..................................... 17
Figure 8 - Average monthly upwelling indices for two locations off the northern
California coast (PFEL, 2015); note: Humboldt Bay is located at approximately 40.8
degrees north latitude. ....................................................................................................... 20
Figure 9 - Location of three calculated upwelling indices; 42N is near the California-
Oregon border, 39N is approximately west of Ukiah, California, and 33N is near San
Diego, California (Google Earth (2), 2013). ..................................................................... 22
Figure 10 - Average monthly precipitation and upwelling represent the two distinctive
seasons in Humboldt Bay, October-March and April-September (upwelling data: PFEL
2015, precipitation data: WRCC 2015). ........................................................................... 24
xviii
Figure 11 - Major nutrient sources, types of biological uptake, and sinks for Humboldt
Bay. ................................................................................................................................... 27
Figure 12 - Major processes of the nitrogen cycle in estuaries and coastal waters: (i)
nitrogen fixation, (ii) ammonium assimilation, (iii) nitrification, (iv) assimilatory nitrate
reduction, (v) ammonification or mineralization, (vi) ammonium oxidation, (vii)
denitrification, and (viii) dissolved organic nitrogen assimilation (Bianchi, 2013). ........ 30
Figure 13 - Three short-term tracer dye studies conducted in Arcata Bay to determine the
extent of potential treated wastewater contamination of oyster beds (adapted from Klamt,
1979). ................................................................................................................................ 51
Figure 14 - Sample site map and distances from the mouth of Humboldt Bay. ............... 68
Figure 15 - Professor Hurst's sample site map and distances from the mouth of Humboldt
Bay. ................................................................................................................................... 69
Figure 16 - Wiyot Tribe's sample site map and distances from the mouth of Humboldt
Bay. ................................................................................................................................... 70
Figure 17 - Wastewater treatment facility outfall map and distances from the mouth of the
Bay. ................................................................................................................................... 71
Figure 18 - Sub-bay boundary map. ................................................................................. 78
Figure 19 - Humboldt Bay EFDC model outline and sub-bay flux line map (Anderson,
2015). ................................................................................................................................ 80
Figure 20 - Example intra-bay flow rates for one tide cycle on January 1, 2012 from
EFDC hydrodynamic model (Anderson, 2015); positive values denote flood tide and
negative values denote ebb tide. ....................................................................................... 81
Figure 21 - Average upwelling season nutrient concentrations in each sub-bay between
2007 and 2015 (Hurst, 2009; Wiyot Tribe Natural Resources Department, 2015; this
study)................................................................................................................................. 97
Figure 22 - Average monthly high tide nitrate concentrations at the Bay entrance and
upwelling indices for water years 2008, 2009, 2013, and 2014 (Wiyot Tribe Natural
Resources Department, 2015; this study; PFEL, 2015). ................................................... 98
Figure 23 - Average monthly high tide silicate concentrations at the Bay entrance and
upwelling indices for water years 2008, 2009, 2013, and 2014 (Wiyot Tribe Natural
Resources Department, 2015; this study; PFEL, 2015). ................................................... 98
xix
Figure 24 - Average monthly high tide ammonium concentrations at the Bay entrance and
upwelling indices for water years 2013, and 2014 (Wiyot Tribe Natural Resources
Department, 2015; this study; PFEL, 2015). .................................................................... 99
Figure 25 - Average monthly high tide phosphate concentrations at the Bay entrance and
Bakun upwelling indices (Wiyot Tribe Natural Resources Department, 2015; this study;
PFEL, 2015). ..................................................................................................................... 99
Figure 26 - Average seasonal nitrate concentrations in Humboldt Bay measured between
2007 and 2015 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources Department,
2015; this study). ............................................................................................................. 101
Figure 27 - Average monthly nitrate concentrations at Mad River Slough and total
monthly precipitation at Woodley Island (WRCC, 2015) and for water years 2008, 2009,
2013, and 2014 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study). ........................................................................................ 101
Figure 28 - Average seasonal ammonium concentrations in Humboldt Bay measured
between 2007 and 2015 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study). ........................................................................................ 103
Figure 29 - Average monthly ammonium concentrations at Mad River Slough and total
monthly precipitation at Woodley Island (WRCC, 2015) for water years 2008, 2009,
2013, and 2014 (Hurst, 2015 b.; Wiyot Tribe Natural Resources Department, 2015; this
study)............................................................................................................................... 103
Figure 30 - Average seasonal silicate concentrations in Humboldt Bay measured between
2007 and 2015 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources Department,
2015; this study). ............................................................................................................. 105
Figure 31 - Average monthly silicate concentrations at Mad River Slough and total
monthly precipitation at Woodley Island (WRCC, 2015) for water years 2008, 2013, and
2014 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources Department, 2015;
this study). ....................................................................................................................... 105
Figure 32 - Average seasonal phosphate concentrations in Humboldt Bay measured
between 2007 and 2015 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study). ........................................................................................ 107
Figure 33 - Average monthly phosphate concentrations at Mad River Slough and total
monthly precipitation at Woodley Island (WRCC, 2015) for water years 2008, 2009,
2013, and 2014 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study). ........................................................................................ 107
xx
Figure 34 - Stoichiometric nitrogen to phosphorus (N:P) ratios in Arcata Bay and
Entrance Bay during calendar year 2014; the "Redfield ratio" of 16:1 represents the
stoichiometric N:P ratio in phytoplankton biomass. ....................................................... 109
Figure 35 - Nitrate was typically the major dissolved inorganic nitrogen species in coastal
waters entering the Bay between October 2012 and February 2015 (Wiyot Tribe Natural
Resources Department, 2015; this study). ...................................................................... 109
Figure 36 - Average maximum annual upwelling and runoff season chlorophyll-a
concentrations in Humboldt Bay measured during WY 2013 and WY 2014 (Hurst 2015
b.; Wiyot Tribe Natural Resources Department, 2015; this study). ................................ 111
Figure 37 - Minimum dissolved oxygen concentrations in Humboldt Bay measured
during WY 2013 and WY 2014 (Hurst 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study). ........................................................................................ 112
Figure 38 - Total monthly direct normal solar insolation for water years 2008, 2009,
2013, and 2014 (SoRMS, 2015). .................................................................................... 114
Figure 39 - Longitudinal and intertidal temperature gradients are greatest during the
summer as water is heated over the shallow intertidal mud flats at low tide. ................. 116
Figure 40 - Longitudinal and intertidal salinity gradients are greatest during the runoff
season as freshwater runoff dilutes Arcata Bay. ............................................................. 116
Figure 41 - Chlorophyll-a concentrations at Indian Island peak at high tide indicating
phytoplankton populations inside the Bay may originate from closer to the ocean or that
predation inside the Bay reduces concentrations (Wiyot Tribe Natural Resources
Department, 2015). ......................................................................................................... 118
Figure 42 - High and low tide chlorophyll-a concentrations along a longitudinal transect
from the Bay entrance to Arcata Bay. ............................................................................. 119
Figure 43 - High and low tide nitrate concentrations along a longitudinal transect from
the Bay entrance to Arcata Bay. ..................................................................................... 123
Figure 44 - High and low tide silicate concentrations along a longitudinal transect from
the Bay entrance to Arcata Bay. ..................................................................................... 126
Figure 45 - High and low tide ammonium concentrations along a longitudinal transect
from the Bay entrance to Arcata Bay. ............................................................................. 129
Figure 46 - High and low tide phosphate concentrations along a longitudinal transect
from the Bay entrance to Arcata Bay. ............................................................................. 131
xxi
Figure 47 - AWTF effluent ammonium, nitrate, and phosphate concentrations between
April 2011 and April 2015 (City of Arcata, 2015); note wastewater concentrations are
typically reported as mg/L. ............................................................................................. 134
Figure 48 - AWTF daily discharge flow rates between April 2011 and April 2015 indicate
significant seasonal fluctuation of discharge flow rates with peaks occurring in the winter
time due to increased inflow and direct precipitation on the 90 acre facility (City of
Arcata, 2015); note wastewater flow rates are typically reported as million gallons per
day (MGD). ..................................................................................................................... 135
Figure 49 - AWTF effluent ammonium, nitrate, and phosphate mass loads between April
2011 and April 2015 (City of Arcata, 2015); note Mg refers to million grams, equivalent
to one metric ton. ............................................................................................................ 135
Figure 50 - EWTF ammonium discharge concentration and mass load indicate seasonal
peaks may occur during the summer, and that there is little effect of dilution (City of
Eureka, 2015); note wastewater flow rates are typically reported as million gallons per
day (MGD). ..................................................................................................................... 136
Figure 51 - Average monthly intertidal sediment nutrient fluxes using flux rates from Sin
et al. (2007) and the intertidal surface area of Humboldt Bay. ....................................... 155
xxii
LIST OF ABBREVIATIONS
AWTF - Arcata wastewater treatment facility
BOD - Biochemical oxygen demand
C - Carbon
Chl-a - Chlorophyll-a
DIN - Dissolved inorganic nitrogen
DIP - Dissolved inorganic phosphorus
DO - Dissolved oxygen
DOC - Dissolved organic carbon
DON - Dissolved organic nitrogen
DSi - Dissolved inorganic silicon
EWTF - Eureka wastewater treatment facility
max - maximum
MHW - Mean high water elevation
MHHW - Mean higher high water elevation
min - minimum
MLW - Mean low water elevation
MLLW - Mean lower low water elevation
mo - month
MSL - Mean sea level elevation
N - Nitrogen
NA - Not applicable
NAVD88 - National vertical datum of 1988
ND - No data
NEP - Net ecosystem production
P - Phosphorus
xxiii
Si - Silicon
TSS - Total suspended solids
UTM10 - Universal transverse mercator: zone 10 (geospatial projection)
WWTF - Wastewater treatment facility
xxiv
LIST OF UNITS
ac - acre
°C - degrees Celsius
°F - degrees Fahrenheit
ft - feet
g - grams
hr - hours
in - inches
kg - kilograms
kWh - kilowatt-hours
L - liters
m - meters
m3 - cubic meters
Mg - megagrams
MGD - million gallons per day
mg/L - milligrams per liter
mi - miles
mi2 - square miles
mM - milimolar
Mm2 - million square meters
Mm3 - million cubic meters
n - number of samples
NTU - nephelometric turbidity units
ppt - parts per thousand
s - seconds
µg/L - micrograms per liter
xxv
µm - micrometer
µM - micromolar
1
INTRODUCTION
Humboldt Bay is a highly productive ecosystem supporting some of the largest
eelgrass beds on the Pacific Coast (CDFG, 2010), and is the most productive oyster
mariculture site in California (H.T. Harvey & Associates, 2015). Every aspect of
biological activity in the Bay relies on the supply of nutrients to support a productive
food web; however, an excess of nutrients can result in overproduction, or eutrophication.
Eutrophication can result in a loss of submerged aquatic vegetation, reduced wildlife
habitat, poor water quality, and potentially toxic algae blooms (Bricker et al., 2007). The
objective of this study is to provide a basis for comparison between wastewater nutrient
discharges and other major sources and biological uptake in Humboldt Bay to aide
decision makers in establishing management practices that support and protect all of the
beneficial uses of the Bay.
North Humboldt Bay (Arcata Bay) is of particular interest because it contains
nearly all of the oyster culture in the Bay (H.T. Harvey & Associates, 2015),
approximately 60% of the eelgrass beds (Schlosser and Eicher, 2012), receives effluent
from the Arcata wastewater treatment facility (AWTF), and experiences limited tidal
flushing due to the morphology of the Bay (Anderson, 2010; Pequegnat and Butler, 1982;
Costa, 1982). All of these factors exhibit seasonal variation creating a highly complex
and dynamic system. There are currently two proposals to increase oyster mariculture in
Arcata Bay by up to six times current levels of production (H.T. Harvey & Associates,
2
2015; Coast Seafoods Company, 2015), and the AWTF is undergoing retrofits to improve
treatment and effluent quality.
Few studies have assessed nutrient levels in Humboldt Bay and none have
characterized the relative magnitudes of sources and types of biological uptake. This
nutrient budget combines multiple datasets spanning multiple years to quantify major
dissolved inorganic nutrient sources and uptake, characterize seasonal shifts in nutrient
uptake and supply to the Bay, and estimate the contribution of major processes involved
in nutrient uptake to the overall budget.
Geographic Setting
Humboldt Bay is located approximately 80 miles south of the California-Oregon
border (Figure 1) and is the second largest coastal embayment in California next to San
Francisco Bay. Humboldt Bay is adjoined by two cities, Arcata and Eureka (Figure 2).
Arcata borders Humboldt Bay to the North with a population of approximately 17,700,
and Eureka borders Humboldt Bay to the East with a population of approximately 27,000
(US Census Bureau, 2014).
Humboldt Bay is made up of two large shallow bays, Arcata Bay and South Bay,
a deeper Entrance Bay, and a deep Main Channel connecting Arcata Bay to the Entrance
Bay (Figure 2). Entrance Bay and the Main Channel are dredged and maintained for
navigation of large industrial ships, while Arcata Bay and South Bay contain extensive
intertidal mud flats and subtidal eelgrass beds providing important habitat and creating
unique hydrodynamic characteristics.
3
Figure 1 - Humboldt Bay (40.8° N, 124.2° W) is located in northern California
approximately 80 miles south of the California-Oregon Border (Google Earth (1), 2013).
4
Figure 2 - Humboldt Bay consists of four distinctive compartments, and is adjoined by
two cities, Arcata and Eureka; note: image depicts Humboldt Bay at low tide (NAIP,
2014).
5
Hydrographic Setting
Humboldt Bay can change in volume by up to 54% during one tide cycle, creating
a tidal prism of approximately 114 Mm3 (Table 1). The surface area of the Bay between
mean higher high water (MHHW) and mean lower low water (MLLW) tide elevations
can change by up to 56% exposing up to 15 mi2 of intertidal mud flats (Anderson, 2015).
Table 1 - Surface area and volume for Humboldt Bay at various tidal data; note these data
are from a hydrodynamic model that includes portions of Mad River Slough, Freshwater
Slough, and Martin's Slough, so high tide values are slightly greater than listed
elsewhere.
Tidal Datum
Surface Area1
(mi2)
Volume1
(Mm3)
MLLW 11.8 97.7
MLW 15.8 111.0
MSL 23.6 148.1
MHW 26.5 199.3
MHHW 26.7 211.6 1Anderson (2015)
Humboldt Bay has been characterized as a protected embayment dominated by
subtidal and deep water habitat where the mouth remains open to tidal exchange
continuously (Sutula et al., 2007). Estuaries, on the other hand, are typically river-
dominated with strong mixing, significant salinity gradients due to freshwater inputs, and
stronger ebb tides (Sutula et al., 2007). Measureable dilution can occur in Arcata Bay
and South Bay during and after rainfall events, however, this behavior is episodic and
temporary (Gast and Skeesick, 1964). During the wet winter season, horizontal
stratification occurs with respect to salinity resulting from increased freshwater runoff,
6
and during the dry summer season, horizontal stratification occurs with respect to
temperature resulting from warming of water in South Bay and Arcata Bay (Gast and
Skeesick, 1964).
Humboldt Bay lies in a temperate zone receiving approximately 40 inches of rain
per year with an average annual air temperature of 53°F (Table 2). Two wastewater
treatment facilities discharge into Humboldt Bay contributing an average combined daily
flow of approximately 0.030 Mm3/d (7.8 MGD) (Table 3). The public water supply for
the region is taken from the Mad River, adjacent to the Humboldt Bay watershed to the
North (the Mad River does not flow into Humboldt Bay).
Table 2 - Average monthly precipitation for the period of record (12/1/1886-1/20/2015)
at Woodley Island in Eureka.
Month
Average
Precipitation1 (in.)
Average
Temperature1 (°F)
January 6.72 48
February 5.31 49
March 5.45 49
April 3.09 50
May 1.67 53
June 0.68 56
July 0.15 57
August 0.32 58
September 0.73 57
October 2.67 55
November 5.61 51
December 7.03 48
Annual 39.45 53 1WRCC (2015)
7
Table 3 - Average daily flow rates for the two major wastewater treatment facilities
discharging to Humboldt Bay.
Month AWTF1 (MGD) EWTF2 (MGD) Total (MGD)
January 2.61 5.36 7.97
February 2.82 4.41 7.23
March 3.21 4.53 7.74
April 2.73 4.26 6.99
May 1.74 3.52 5.26
June 1.32 3.42 4.74
July 1.12 3.28 4.40
August 1.21 3.24 4.45
September 1.37 3.32 4.69
October 1.91 3.19 5.10
November 2.24 3.11 5.35
December 2.97 3.35 6.32
Average 2.10 3.75 5.85 1City of Arcata (2015); 2City of Eureka (2015)
Watershed Characteristics
The total surface area of the Humboldt Bay watershed including the Bay is
approximately 217 mi2, of which the Bay comprises approximately 27 mi2 (Table 4). The
four largest surface water inputs to the Bay that make up approximately 90% of the
watershed surface area include Freshwater Creek that enters the Bay north of Eureka, the
Elk River that enters the Bay south of Eureka near the Bay entrance, Jacoby Creek that
enters the east side of Arcata Bay, and Little Salmon Creek that enters the southeast side
of South Bay (Figure 3). The other four minor freshwater inputs to the Bay all enter
Arcata Bay. Humboldt Bay has a relatively small contributing watershed with no major
8
river inputs compared to other bays and estuaries on the Pacific coast (Table 5). The Bay
is also adjoined by approximately 1.41 mi2 of intertidal salt marsh, though this is only
approximately 10% of the historic salt marshes that once existed due to diking for
agricultural use (Schlosser and Eicher, 2012).
Table 4 - Humboldt Bay sub-watershed surface areas.
Sub-watershed Surface Area1 (mi2)
Mad River Slough 8.36
Janes Creek/McDaniel's Slough 4.79
Jolly Giant Creek/Butcher's Slough 1.80
Washington/Rocky Gulches 2.90
Jacoby Creek/Gannon Slough 20.18
Freshwater Creek/ Freshwater Slough and Fay Slough 56.72
Elk River/Martin Slough 55.96
Little Salmon Creek/Hookton Slough 18.47
Rural and urban landscapes 20.08
Salt marshes (Schlosser and Eicher 2012) 1.41
Humboldt Bay (MHHW, Anderson 2015) 26.74 1WBD (2015)
Table 5 - Water to watershed surface areas ratios for Pacific coast bays.
Bay
Bay Surface
Area (mi2)
Watershed Surface
Area (mi2)
Bay : Watershed
Surface Area Ratio (%)
Humboldt 26 235 11%
San Francisco1 1,600 73,400 2%
San Diego2 16.5 415 4%
Coos3 17.1 605 3% 1USEPA (2015); 2City of San Diego (2013); 3NAC (2004)
9
Figure 3 - Humboldt Bay watershed delineation (WBD, 2015); note, alterations have
been made to the Watershed Boundary Database polygons to more precisely represent the
contributing watersheds of Humboldt Bay based on the location of tide gates and sample
points.
10
Arcata Bay
Arcata Bay is the northern-most unit of Humboldt Bay, and is isolated from the
ocean by the Main Channel and the Entrance Bay. Mad River Slough adjoins the Bay to
the northwest (Figure 4) draining an area of salt marshes and agricultural lands known as
the Arcata Bottoms. The Mad River Slough Channel drains the western one-third of
Arcata Bay along with all of Mad River Slough. The volume of Arcata Bay can change
by up to 57.3 Mm3 during a single tide cycle, 78% of the MHHW volume (Table 6), and
the surface area of Arcata Bay can decrease by up to 67% in a single tide cycle exposing
up to 9.6 mi2 of intertidal mud flats (Anderson, 2015).
Figure 4 - Aerial imagery of Arcata Bay indicating major circulation channels and
freshwater input locations (ortho-imagery: NAIP 2014).
11
Table 6 - Surface area and volume of Arcata Bay at different tidal datums.
Tidal Datum Surface Area1 (mi2) Volume1 (Mm3)
MLLW 4.79 16.36
MLW 6.65 21.70
MSL 12.06 38.53
MHW 14.28 66.94
MHHW 14.42 73.61 1Anderson (2015)
McDaniel's Slough adjoins the Bay to the north and is where Jane's Creek empties
into the Bay (Figure 4). Jane's Creek drains a small watershed including low forested
hills to the north of Arcata, agricultural land adjoining the City including part of the
Arcata Bottoms, and part of the City of Arcata. McDaniel's Slough is the site of current
salt marsh restoration efforts and the future site of the AWTF discharge.
Butcher's Slough is a small salt marsh located near the current outfall of the
AWTF (Figure 4) and receives freshwater from Jolly Giant Creek. Jolly Giant Creek
drains a small watershed including low forested hills above Arcata and part of the City as
well.
Gannon Slough is the site where Jacoby Creek enters Arcata Bay and includes
interspersed tidal salt marshes and stock grazing lands (Figure 4). Jacoby Creek is the
largest watershed emptying directly into Arcata Bay and includes forested hills, rural
landscapes, and agricultural lands. Freshwater Creek to the south is larger but does not
empty directly into Arcata Bay.
12
Rocky Gulch and Washington Gulch combine freshwater streams from small rural
and forested hills in a small salt marsh on the west side of Arcata Bay (Figure 4). The
small salt marsh is surrounded by diked agricultural land and enters the Bay near the
Bayside cutoff on US Highway 101.
Freshwater Slough is located on the southeast side of Arcata Bay and is where
Freshwater Creek empties into the Bay (Figure 4). The Freshwater Creek watershed
(including Freshwater Slough, Fay Slough, and Ryan Creek), is the largest sub-watershed
of Humboldt Bay draining a large area of low-lying agricultural lands, rural landscapes,
and surrounding forested hills. At low and ebbing tides Freshwater Slough drains into
the Eureka Channel that joins with the Indian/Woodley Channel before reaching the Main
Channel without mixing with the main flow from Arcata Bay in the Samoa Channel,
being separated by Woodley Island and Indian Island (Figure 4). During high and flood
tides, the tidal prism may penetrate far into Freshwater Slough preventing discharge into
the Bay; only waters that have previously drained into Eureka Channel during the ebb
tide may potentially be pushed into the eastern side of Arcata Bay. The amount of
mixing between Freshwater Slough waters, the Main Channel, and Arcata Bay may be
dependent on the elevations of each tide cycle, discharge flow rate from Freshwater
Slough, and wind speed and direction. These factors combine to reduce the direct
influence of Freshwater Slough discharge on Arcata Bay (Klamt, 1979).
13
Main Channel
The Main Channel of Humboldt Bay connects Arcata Bay to the Entrance Bay
and is isolated from the ocean by the Entrance Bay. Elk River is the second largest sub-
watershed of Humboldt Bay (WBD, 2015) and empties into the Main Channel south of
Eureka near the EWTF outfall (Figure 5). The Samoa Channel, Indian/Woodley
Channel, and Eureka Channel all converge at the north end of the Main Channel to drain
Arcata Bay and Freshwater Slough. The Main Channel is deeper than Arcata Bay and
South Bay due to dredging for ship navigation to industrial ports on either side of the
Channel (HBHRCD, 2007). Between MHHW and MLLW the tidal prism for the Main
Channel is approximately 11.2 Mm3 (Table 7). Enough volume exists in the Main
Channel at MLLW to contain over half of the maximum tidal prism from Arcata Bay, and
enough volume at MHHW to contain more than twice the maximum tidal prism from
Entrance Bay (Anderson, 2015). The surface area of the Main Channel does not change
significantly during tidal flux due to the steep side of the channel.
14
Figure 5 - Aerial imagery of the Main Channel indicating the location of major flow
channels and freshwater inputs (ortho-imagery: NAIP 2014).
Table 7 - Surface area and volume of the Main Channel at different tidal data.
Tidal Datum Surface Area1 (mi2) Volume1 (Mm3)
MLLW 1.84 30.08
MLW 1.88 32.11
MSL 2.10 35.92
MHW 2.22 40.01
MHHW 2.29 41.24 1Anderson (2015)
15
Entrance Bay
Entrance Bay is the point of convergence for the ocean, South Bay, and Main
Channel (Figure 6). There are no freshwater inputs flow into Entrance Bay, though the
EWTF outfall is near the northern end of the Bay. The Entrance Bay has enough volume
at MLLW to hold 100% of the maximum tidal prisms from South Bay and the Main
Channel combined. The surface area of the Bay varies by approximately 5% between
MLLW and MHHW due to relatively steep sides (Table 8). The entrance channel to the
Bay is deeply dredged to allow industrial ship navigation (HBHRCD, 2007).
Waters of the Entrance Bay are highly transient, acting as a mixing zone for
coastal water, Arcata Bay water, and South Bay water (Pequegnat and Butler, 1981).
Entrance Bay water assumes characteristics of North and South Bay waters at ebb tides
and of coastal waters at high tides. Nearshore currents flowing northward during the
winter runoff season bring fresh water from the Eel River eight miles to the south into the
Bay during flood tides (Barnhart et al., 1992). Nearshore currents flowing southward
during the summer may bring water from the Mad River 15 miles to the north into
Humboldt Bay during flood tides.
16
Figure 6 - Aerial imagery of Entrance Bay indicating the locations of major landmarks,
flow channels, and freshwater inputs (ortho-imagery: NAIP, 2014).
Table 8 - Surface area and volume of Entrance Bay at different tidal data.
Tidal Datum Surface Area1 (mi2) Volume1 (Mm3)
MLLW 2.96 40.36
MLW 2.97 42.95
MSL 3.10 49.15
MHW 3.11 54.56
MHHW 3.12 56.37 1Anderson (2015)
17
South Bay
South Bay is isolated from the ocean by the Entrance Bay (Figure 7) and is
volumetrically the smallest unit in Humboldt Bay (Anderson, 2015). The surface area of
South Bay can change by up to 68% between MHHW and MLLW exposing up to 4.7 mi2
of intertidal mud flats (Table 9). Little Salmon Creek empties into Hookton Slough on
the southeast side of South Bay and is the fourth largest sub-watershed of Humboldt Bay.
Two main channels drain South Bay; Southport Channel drains the western half and
Hookton Channel empties the eastern half.
Figure 7 - Aerial imagery of South Bay indicating the locations of major flow channels,
landmarks, and freshwater inputs (ortho-imagery: NAIP 2014).
18
Table 9 - Surface area and volume of South Bay at different tidal data.
Tidal Datum Surface Area1 (mi2) Volume1 (Mm3)
MLLW 2.25 10.91
MLW 4.34 14.24
MSL 6.38 24.52
MHW 6.91 37.74
MHHW 6.91 40.42 1Anderson (2015)
Oceanographic Setting
The tidal prism of Humboldt Bay can be up to 54% of the MHHW volume;
however this volume of water may not be completely replaced by new ocean water due to
limited mixing in the nearshore environment (Barnhart et al., 1992). Ebb tide water from
Humboldt Bay may differ from nearshore waters with respect to temperature and salinity
creating stratification due to differences in water density that limit mixing in the
nearshore environment (Gast and Skeesick, 1964). Speed and direction of nearshore
currents also play a role in the exchange of Bay and ocean waters; ebb tide water from
the Bay may simply flow back into the Bay if nearshore currents are not sufficient to
advect the volume away from the mouth of the Bay before the flood tide begins.
Humboldt Bay waters also differ in composition from nearshore water with respect to
trace metals and nutrients due to upwelling of deep ocean waters (Martin and Hurst,
2008). Each compartment in Humboldt Bay (Entrance Bay, Arcata Bay, Main Channel,
and South Bay) may also experience limited mixing with adjacent compartments during
tidal exchange due to differences in the physical makeup of each water body.
19
The mean tidal range at the entrance to Humboldt Bay is 4.89 ft, with a great
diurnal range (MHHW to MLLW) of 6.85 ft (Table 10). Tides in Arcata Bay generally
exhibit an increase in amplitude and a lag in phase from those observed at the mouth of
the Bay (Costa, 1982) indicating that there is some restriction to tidal flow between the
two. Tides at Humboldt Bay typically exhibit diurnal inequality with a high-high, high-
low, low-high, and low-low tide occurring daily (Barnhart et al., 1992).
Table 10 - Tidal data from the NOAA North Spit, Humboldt Bay station.
Tidal Datum
Water Surface Elevation1
(ft, NAVD88)
MLLW -0.33
MLW 0.92
MSL 3.37
MHW 5.81
MHHW 6.52 1NGS (2015)
One of the main driving factors in northern California coastal food web
productivity is upwelling of deep, nutrient-rich ocean waters. This process occurs when
sustained along-shore winds blow southward for one to two weeks, creating currents that
transport nutrient-rich subsurface waters to the photic zone (Peterson et al., 2012). This
typically occurs during the spring and summer in northern California, creating a season of
high productivity in coastal waters (Figure 8). Nitrate, phosphate, and silicate
concentrations of 34 µM (Sigleo et al., 2005), 2 µM (van Geen et al., 2000), and 42 µM
(van Geen et al., 2000), respectively, have been measured in upwelled waters off of the
20
Oregon coast. Lower nutrient concentrations (5-20 µM nitrate, 0.1-1.8 µM phosphate,
and 1-33 µM silicate) were measured in warmer surface waters attributed to non-
upwelled ocean water.
Figure 8 - Average monthly upwelling indices for two locations off the northern
California coast (PFEL, 2015); note: Humboldt Bay is located at approximately 40.8
degrees north latitude.
The Bakun upwelling index describes the volumetric transport of surface water
offshore based upon the Ekman theory of mass transport due to wind stress (Schwing et
al., 1996). The Bakun index assumes that the amount of surface water transported
offshore is directly replaced by deeper upwelled water. The Ekman theory states that in
the northern Hemisphere, transport will occur 90 degrees to the right of the direction of
wind stress, i.e. southward winds will result in transport of surface waters in the offshore
direction (Sverdrup et al., 1942). The opposite phenomenon is termed downwelling and
21
results in transport of surface waters into the deeper ocean. Downwelling can act as a
significant sink for nutrients leaving the Bay during the runoff season.
Humboldt Bay lies at approximately 40.8 degrees north latitude (40.8N), in
between the two locations where upwelling is calculated by PFEL, 39N and 42N (Figure
9). The highest upwelling on the west coast occurs at approximately 33 degrees north
latitude and decreases going north (Schwing et al., 1996). As continental shelf currents
that influence coastal conditions reverse direction throughout the year due to changes in
wind patterns (Schwartzlose and Reid, 1972), the latitude-specific upwelling index
representing conditions at Humboldt Bay may change. As the California Current flows
southward during the spring and summer, the upwelling index at 42N may produce a
more accurate depiction of upwelling events offshore from Humboldt Bay. During the
winter when the Davidson current flows northward along the coast, the upwelling index
at 39N may be more reliable for predicting upwelling events near Humboldt Bay. For
simplification, the upwelling index at 42N is used in this analysis because this location is
more representative of conditions near Humboldt Bay during the upwelling season.
22
Figure 9 - Location of three calculated upwelling indices; 42N is near the California-
Oregon border, 39N is approximately west of Ukiah, California, and 33N is near San
Diego, California (Google Earth (2), 2013).
Ecologic Setting
Humboldt Bay is made up of four morphologically distinct water bodies that
experience a limited amount of mixing between tide cycles, periodically resulting in
distinct water quality and habitat characteristics (Pequegnat and Butler, 1982). The
limited exchange between each unit with nearshore waters has been the focus of multiple
23
oceanographic studies attempting to determine the extent to which nutrients and
phytoplankton influence water quality inside the Bay.
Arcata Bay is isolated from nearshore waters by the Main Channel and the
Entrance Bay, and has been of particular concern with respect to water quality due to the
amount of oyster farming conducted there and potential threats to human health from
consumption of contaminated shellfish (Shellfish Protection Act of 1993, 1993).
Isolation from nearshore waters contributes to distinct water quality characteristics
particularly during the summer when surface water inflows are low and water
temperatures in the Bay increase above nearshore water temperatures (Gast and Skeesick,
1964). During initial precipitation events in the fall and winter, surface water runoff
introduces pathogenic bacteria to Arcata Bay often resulting in a temporary halt to oyster
harvesting (Geist, 2003). Human health issues surrounding oyster production in Arcata
Bay is one reason leading to the requirement that the AWTF disinfect its treated effluent
prior to discharge into the Bay.
In general, upwelling and runoff events can occur at any time throughout the year
and the transition from one season to another may vary (Garcia-Reyes and Largier,
2012). However, two distinct seasons can be observed in Humboldt Bay with respect to
nutrient supply, the upwelling-influenced season of April through September, and the
runoff-influenced season of October through March (Figure 10). During the upwelling
season, nutrients are introduced into Humboldt Bay from ocean upwelling, while during
the runoff season, upwelling influences decrease and runoff from the surrounding
watershed increases (Gast and Skeesick, 1964).
24
Figure 10 - Average monthly precipitation and upwelling represent the two distinctive
seasons in Humboldt Bay, October-March and April-September (upwelling data: PFEL
2015, precipitation data: WRCC 2015).
Wastewater
Currently two wastewater treatment facilities discharge into Humboldt Bay, the
Arcata wastewater treatment facility (AWTF) and the Eureka wastewater treatment
facility (EWTF), also known as the Elk River wastewater treatment facility. The AWTF
continuously discharges into the northern end of Arcata Bay and the EWTF discharges
near the entrance to Humboldt Bay on outgoing tides such that they are currently
permitted as an ocean discharge. While nutrients are not currently regulated for
wastewater discharged to Humboldt Bay, the AWTF has been monitoring nutrients since
2009 to better understand the behavior of their system with respect to nutrient dynamics
(Swanson, 2013).
25
Wastewater nutrient discharges may be a significant source of nitrogen and
phosphorus to Humboldt Bay (Pequegnat and Butler, 1981; Barnhart et al., 1992).
Barnhart et al. (1992) refer to work conducted by Pequegnat and Butler (1981) indicating
that 20-50% of the fixed nitrogen in Arcata Bay during the low runoff summer season in
1979 may have been from Eureka's treated wastewater. Many improvements have been
made to Eureka's wastewater treatment system as well as Arcata's system between then
and now; Pequegnat and Butler (1981) indicate that reduction of wastewater nitrogen
may have a significant impact on the ecology of Bay by reducing its overall productivity
due to nitrogen limited production.
Wastewater treatment typically emphasizes the removal of biochemical oxygen
demand (BOD) and total suspended solids (TSS). BOD and TSS are broad water quality
characteristics that encompass a number of physical and biological processes directly
influenced by nutrient dynamics. The AWTF uses a constructed wetland treatment
system that exhibits natural seasonal variability in nutrient discharge levels due to
changes in biological activity. The EWTF uses a more conventional system that may not
vary as much seasonally with respect to nutrient removal. Both systems experience
increased flow rates following rainfall events due to infiltration and inflow to their
systems; increased flow rates can result in increased discharge loads to the Bay.
26
REVIEW OF LITERATURE
There are many nutrient sources and types of biological uptake in estuarine
environments governed by physical, chemical, and biological transport and cycling
(Figure 11). Physical processes include advection of water containing dissolved and
particulate matter from stream runoff and ocean tides, and anthropogenic point source
discharges of treated wastewater. Chemical processes include diffusion, adsorption of
dissolved ions onto particles, and oxidation and reduction reactions influenced by
temperature, pH, and relative concentration of chemical species in equilibrium. Major
biological processes in an estuarine ecosystem can generally be broken down into
autotrophic and heterotrophic (Hagy and Kemp, 2013). Autotrophic organisms utilize
inorganic nutrients to synthesize organic matter; this includes photosynthesis by plants
and algae and bacterial nitrification of ammonium. Heterotrophic organisms consume
organic matter generated by autotrophs and include a wide variety of organisms from
bacteria to large invertebrates. This review of literature focuses on major processes that
influence nutrient supply and demand in Humboldt Bay. This provides the basis for
estimation of the annual and seasonal nutrient mass contribution of each. Previous works
conducted in Humboldt are reviewed where available; where no information in Humboldt
Bay is available, literature for nearby estuaries and bays are reviewed.
27
Figure 11 - Major nutrient sources, types of biological uptake, and sinks for Humboldt
Bay.
Nutrient Cycling
At a typical seawater pH of approximately 8, base elemental nutrients carbon,
nitrogen, phosphorus, and silicon are present in the water column as various dissolved
inorganic compounds including carbonate (CO32-), bicarbonate (HCO3
-), ammonium
(NH4+), nitrate (NO3
-), nitrite (NO2-), orthophosphate species including dihydrogen
phosphate (H2PO4-) and hydrogen phosphate (HPO4
2-), and silicic acid (H4SiO4), as well
as numerous dissolved and particulate organic compounds (Millero, 2013). Species of
orthophosphate with hereafter be referred to as phosphate and silicic acid will be referred
to as silicate. Dissolved inorganic and organic nutrients are of particular interest as they
28
form the foundation of ecosystem food webs that can lead to either healthy or eutrophic
systems (Testa et al., 2013). Particulate matter transport is a significant mechanism as
both source and uptake for nutrients in systems similar to Humboldt Bay through
watershed runoff and ocean exchange (Smith et al., 1996). A brief explanation of the
major processes in estuarine nutrient cycling involving key constituents is discussed in
the following sections.
Nitrogen Cycle
Nitrogen is an essential component of amino acids and proteins, making it an
essential nutrient for biological production (Bianchi, 2013). Nitrogen gas (N2) is the
most abundant atmospheric gas, although it is not bioavailable to organisms until it is
converted into a form such as ammonium (NH4+) or nitrate (NO3
-).
Biological fixation of atmospheric nitrogen (Figure 12, i) in marine environments
is typically insignificant unless cyanobacteria make up a significant percentage of
planktonic biomass (Howarth et al., 1988). Ammonium assimilation (Figure 12, ii) is the
process whereby organisms such as plants and phytoplankton uptake inorganic
ammonium, incorporating the already reduced form of nitrogen into organic matter
(Bianchi, 2013). Nitrification (Figure 12, iii) is the multistep process of nitrogen
oxidation from ammonium to nitrate, requiring the presence of oxygen and carbon.
Nitrification in marine sediments is an important source of nitrate for denitrification
(Seitzinger, 1988). Assimilatory nitrate reduction (Figure 12, iv) may occur when
reduced forms of nitrogen such as ammonium are low and oxygen levels are high. As
29
autotrophic plants and algae preferentially uptake ammonium first, producing oxygen in
the process, nitrate may then become an important fraction of bio-available nitrogen
(Bianchi, 2013). Ammonification, or mineralization (Figure 12, v), is the process of
organic decomposition by heterotrophic bacteria converting organic nitrogen to
ammonium. This process plays an important role in the internal nitrogen cycling of
productive marine systems as dissolved and particulate organic matter in the water
column and sediments is converted back into inorganic ammonium that becomes re-
available for autotrophic assimilation. Ammonium oxidation (Figure 12, vi), or
anammox, is the direct oxidation of ammonium with nitrate to form nitrogen gas
(Bianchi, 2013). Limited knowledge currently exists of the mechanisms of this process
and the significance of flux rates due to anammox, although one study suggests that
anammox was insignificant with respect to denitrification in a eutrophic bay (Thamdrup
and Dalsgaard, 2002). Dissolved organic nitrogen (DON) assimilation (Figure 12, viii) is
an important component of the nitrogen cycle in marine systems as a source of nitrogen
for many heterotrophic organisms and often exceeds the concentration dissolved
inorganic nitrogen (DIN), including ammonium, nitrate, and nitrite (Berman and Bronk,
2003).
Denitrification (Figure 12, vii) is the multistep enzymatic process of reducing
nitrate-nitrogen to form gaseous constituents including nitrous oxide (N2O) and nitrogen
gas (N2) (Bianchi, 2013). Denitrification can be a significant pathway for nitrogen
removal from marine systems (Seitzinger, 1988). Denitrification of nitrate to nitrogen
gas has been attributed to removal of as much as 40-50% of dissolved inorganic nitrogen
30
input from marine systems. Nitrate may be supplied from nitrifying bacteria in oxic
surface layers or diffusion from the water column, though studies have shown that
nitrification in sediments is the primary source of nitrate for denitrification in marine
sediments. Nitrification can increase during daylight from autotrophic organisms
producing oxygen in surface sediments. Denitrification rates are typically greater than
nitrate fluxes into sediments indicating nitrate produced in surface layers does not have a
net flux into the water column. Overall denitrification rates decrease during daylight due
to the increased thickness of oxic surface layers resulting from photosynthesis (Risgaard-
Petersen et al., 1994).
Figure 12 - Major processes of the nitrogen cycle in estuaries and coastal waters: (i)
nitrogen fixation, (ii) ammonium assimilation, (iii) nitrification, (iv) assimilatory nitrate
reduction, (v) ammonification or mineralization, (vi) ammonium oxidation, (vii)
denitrification, and (viii) dissolved organic nitrogen assimilation (Bianchi, 2013).
Phosphorus Cycle
The marine phosphorus cycle includes dissolved inorganic phosphorus, organic
phosphorus, phosphorus adsorbed to particles, and phosphorus-metal oxide complexes
(Bianchi, 2013). Dissolved inorganic phosphorus in the form of orthophosphate (H2PO4-
31
or HPO42-) has a higher turnover rate compared to dissolved organic phosphorus,
increasing its potential availability as a nutrient source in coastal waters (Benitez-Nelson
and Buesseler, 1999). Organic phosphorus can be particulate or dissolved and includes
DNA, cellular membranes, and ATP used by organisms for energy transfer (Bianchi,
2013). Phosphorus-metal oxide complexes, the most common of which is ferric
oxyhydroxide, can also be a significant source or uptake for phosphorus dependent upon
salinity, temperature, and oxidation-reduction conditions; reducing conditions as a result
of anoxia in sediments, can increase phosphorus release (Conley et al., 1995).
Phosphorus concentrations can increase or decrease with suspension of particles as
phosphorus adsorbs to, or desorbs from, particle surfaces distributed throughout the water
column.
Silicon Cycle
The marine silicon cycle is primarily a function of dissolved silicic acid (H4SiO4)
utilized by marine diatoms to synthesize biomass (Paerl and Justic, 2013). Diatoms
produce at a very high rate (up to two doublings per day or more) and assimilate silicon
in a 1:1 ratio with nitrogen, increasing the importance of this organism in the nitrogen
cycle (Brzezinski, 1985). Silicon can come from upwelled ocean waters as well as
watershed runoff from weathered geological formations, and the major form of storage is
through sedimentation (Bianchi, 2013).
32
Nutrient Sources and Uptake
Humboldt Bay is a highly productive system in the summer that can become
limited by nitrogen and experiences low productivity in the winter due to reduced ocean
upwelling, decreased sunlight, and lower temperatures (Pequegnat and Butler, 1981).
Upwelled ocean waters rich in nutrients promote phytoplankton production in nearshore
waters during the spring and summer that enter the Bay through tidal interaction.
Phytoplankton from nearshore waters, subtidal eelgrass beds, algae growing on intertidal
mud flats, and salt marsh grasses are all primary producers that utilize nutrients and solar
energy during the productive upwelling season. Tidal flushing transports nutrients and
phytoplankton from nearshore waters into the Bay during the upwelling season, whereas
eelgrass, mudflat algae, and salt marsh grasses are all endogenous nutrient consumers
originating and growing only inside the Bay (Schlosser and Eicher, 2012).
Nutrient sources to Humboldt Bay may include oceanic exchange, watershed
runoff, wastewater inflow, decomposition of organic matter in sediments, and
atmospheric fixation. Nutrient uptake and sinks may include oceanic exchange, primary
productivity, oyster and fish harvesting, denitrification, and volatilization of gases.
Humboldt Bay is an important habitat for seasonally migrating birds and fish (Barnhart et
al., 1992) that may be a significant source of nutrient import or form of uptake and
export; however, estimation of the complex migration patterns and behaviors of the
numerous species with respect to nutrient cycling is beyond the scope of this project.
33
Atmospheric Fixation
Carbon and nitrogen are fixed from the atmosphere as carbon dioxide and
nitrogen gas, respectively, although nitrogen fixation is likely a minor contributor to
overall loadings in nitrogen-limited estuaries (Howarth et al., 1988). Atmospheric
nitrogen gas (N2) is fixed by some species of bacteria and algae, although no information
is available on the presence or distribution of these species in Humboldt Bay. Fixation
rates in oceans and estuaries vary from 0.002-1.8 g N/m2/yr, with estuarine fixation rates
typically being higher than those in oceans (Howarth et al., 1988). Carbon dioxide from
the atmosphere diffuses into the water column and is consumed by autotrophic organisms
during photosynthesis, producing organic carbon. This process is likely the main source
of carbon to a highly productive estuarine system such as Humboldt Bay (Bianchi, 2013).
Phytoplankton Production
Phytoplankton production may account for more than half of the total ecosystem
primary productivity in coastal systems (Paerl and Justic, 2013), and can be determined
by measuring chlorophyll-a concentrations and light penetration into the water column
(Ryther and Yentsch, 1957). High rates of phytoplankton production, determined as
chlorophyll-a concentrations, and excessive nutrient availability in estuaries is an
indicator of eutrophication (Bricker et al., 2003). Estimates for phytoplankton nutrient
assimilation rates vary widely because they have been found to be dependent primarily
on nutrient availability and secondarily on light availability (Ryther and Yentsch, 1957;
Curl and Small, 1965). An accurate model for estimating dynamic assimilation rates in
34
Humboldt Bay has not been established, however, Harding (1973) collected samples at
18 locations throughout the Humboldt Bay system measuring chlorophyll-a and light
penetration, and estimated primary production rates for phytoplankton using the methods
of Ryther and Yentsch (1957). Primary productivity for phytoplankton was estimated by
correlating carbon uptake with chlorophyll-a concentrations, resulting in a mean
assimilation ratio of 10.9 g C/hr/g Chl-a, with a range of 1.3-46.8 g C/hr/g Chl-a. Ryther
and Yentsch (1957) measured an average phytoplankton uptake rate of 1.7 g C/hr/g Chl-a
in the Puget Sound of Washington state, with a range of 0.3 - 5.1 g C/hr/g Chl-a.
Studying waters off the coast of Newport Oregon, Curl and Small (1965) measured
assimilation ratios between 6 - 21 g C/hr/g Chl-a, with a mean of 8.1 g C/hr/g Chl-a.
Significant differences in uptake rates are associated with variations in water column
nutrient concentrations; values of 0-3 g C/hr/g Chl-a indicate nutrient depletion, 3-5 g
C/hr/g Chl-a indicate borderline nutrient deficiency, and 5-10 g C/hr/g Chl-a indicate
nutrient rich waters (Curl and Small, 1965).
Using the widely accepted Redfield ratio of carbon, nitrogen, and phosphorus
contained in planktonic biomass of 106:16:1 (C:N:P; Fleming 1940), nitrogen and
phosphorus assimilation ratios can also be estimated from chlorophyll-a concentrations
(Table 11). Diatoms are some of the most abundant and fast growing phytoplankton
utilizing silicon at a stoichiometric ratio of 1:1 with nitrogen (Brzezinski, 1985). There
are no data available on the relative abundance of diatoms and other species of
phytoplankton in Humboldt Bay; to account for the likelihood that diatom blooms do
occur, silicon uptake is included in phytoplankton assimilation ratios.
35
Table 11 - Phytoplankton assimilation ratios from three independent studies (g/hr/g Chl-
a); it should be noted that these values vary significantly, likely due to variations in
ambient nutrient concentrations that can influence phytoplankton uptake rates.
Source Location Carbon Silicon Nitrogen Phosphorus
Ryther and
Yentsch (1957)
Puget Sound,
WA 1.7 0.6 0.3 0.04
Curl and Small
(1965)
Newport,
OR 8.1 2.9 1.4 0.2
Harding
(1973)
Humboldt Bay,
CA 10.9 3.8 1.9 0.3
Eelgrass Production
Pequegnat and Butler (1982) estimated that eelgrass production could make up
approximately 18% of the total plant production in Humboldt Bay, and eelgrass beds may
cover approximately 32% of the surface area of the Bay (Schlosser and Eicher, 2012).
Harding (1973) measured eelgrass biomass in South and North Humboldt Bay between
April and August 1973 estimating a total net production for Humboldt Bay of nearly 22
million kg. The area covered by eelgrass in the Bay at that time was approximately 12.2
Mm2, indicating an annual areal production rate of approximately 565 g/m2/yr. A more
recent study conducted found that the eelgrass distribution in the Bay was approximately
22.8 Mm2 (Schlosser and Eicher, 2012), indicating that the eelgrass beds have expanded
and a greater amount of eelgrass productivity may be expected.
Macroalgae Production
Pequegnat and Butler (1982) estimated that microalgae and macroalgae growing
on the subtidal and intertidal mudflats may account for approximately 37% of the total
36
plant production in Humboldt Bay (8,200 Mg/yr). Schlosser and Eicher (2012) estimated
that in late summer and fall of 2007 and 2008, macroalgae covered approximately 12% of
the total surface area of Humboldt Bay (8.7 Mm2), or approximately 23% of the intertidal
mud flats. The most abundant species were filamentous forms including Chaetomorpha
aerea, tubular forms including Ulva intestinalis, and sheet forms including Ulva spp.
Pregnall and Rudy (1985) estimated the production rate of the macroalgal species
Enteromorpha spp. in the Coos Bay estuary in Oregon State of approximately 1,100 g
C/m2/yr. Coos Bay is approximately 150 miles north of Humboldt Bay and likely
experiences similar growing seasons. Pregnall and Rudy (1985) observed initial algal
growth beginning in April, peaking in August, and ceasing in November; a similar
pattern of macroalgal growth has been observed in the Entrance Bay of Humboldt Bay
(Schlosser and Eicher, 2012). Significant inter-annual variability in temporal and spatial
distribution of macroalgal mats may occur in Humboldt Bay; though very little
information exists on this topic. Schlosser and Eicher (2012) noted a general trend of
macroalgal mats persisting for longer periods of time at one site in Humboldt Bay
between 2002 and 2008, and noted observations that mats were increasingly noticeable
on the intertidal mud flats of Arcata Bay.
Salt Marsh Production
Pequegnat and Butler (1982) estimated that the salt marshes around Humboldt
Bay may contribute 22% of the total plant production and Schlosser and Eicher (2012)
estimated that salt marshes make up 5% of the surface area of the Bay (1.41 mi2). Salt
37
marshes lie in the upper intertidal boundaries of the Bay and likely only receive periodic
interaction with tidal Bay waters during higher high tides, although rainfall and surface
water flow may increase the effects of nutrient export by salt marshes. Salt marshes may
provide seasonal storage for dissolved nutrients as plant uptake removes nutrients from
tidal and surface waters (Valiela et al., 1978). Marshes can also act as storage for
particulate matter when flows are low, and a source for particulate matter when flows are
higher, during precipitation and runoff events or high tides. Marshes may import
nutrients and particulate matter during the summer growing season when flows are
generally lower, and export nutrients during the fall and winter when plants senesce and
flows increase.
Mariculture
There are currently approximately 10.42 metric tons (dry weight) of shellfish
stock being cultured in Arcata Bay, half of which are harvested each year (H.T. Harvey &
Associates, 2015). This represents a potentially significant sink for nutrients as the
oysters filter phytoplankton from the water converting it to biomass that is harvested and
exported from the system. Jansen et al. (2012) measured annual nutrient accumulation
rates in blue mussels of 560 mg C/g tissue/yr, 168 mg N/g tissue/yr, and 12 mg P/g
tissue/yr (a stoichiometric ratio of 47:14:1). If one-half of the oysters are harvested each
year (Wagschal, 2015), this would result in a net annual export of 2.918 Mg C/yr, 0.875
Mg N/yr, and 0.063 Mg P/yr.
38
There are currently two major proposals to expand oyster farming in Arcata Bay
by up to six times its current level of production, significantly increasing the amount of
nutrients exported from the system through this pathway. Oysters filter particles from the
water column to feed. Applying the filtration rate used by H.T. Harvey & Associates
(2015) of 2.54 L/g/hr (Cranford et al., 2011), the current standing stock of oysters in
Arcata Bay (10.42 x 106 g) may be capable of filtering 6.35 x 105 m3 of water each day,
or approximately 1% of the MHW volume of Arcata Bay.
Sediment Flux
Sediments can act as source and storage for nutrients with significant seasonal and
diurnal variation due to changes in wind patterns, sediment loads, production rates,
vegetative cover, temperature, sunlight, oxygen availability, pH, tidal immersion and
emersion, and microorganisms living in the sediments (Thompson, 1971; Mackin and
Aller, 1984; Smith et al., 1985; Smith et al., 1996; Sin et al., 2007). Nutrients in
suspended sediment loads from creeks and ocean tides can settle over parts of the mud
flats in Humboldt Bay with significant seasonal variation due to wind patterns
(Thompson, 1971). Erosion of the mud flats of northern Arcata Bay was witnessed by
Thompson (1971) between November and April due to southerly winds that increase
wave erosion across the long fetch of the Bay. Between spring and fall, Thompson
(1971) observed winds prevailing from the north that resulted in less wave erosion in
northern Arcata Bay and increased accretion. This behavior was also observed at other
locations in the Bay indicating that erosion will occur on the side of the Bay where the
39
prevailing wind direction is over the longest open water fetch, and accretion will occur in
locations more shielded from the prevailing wind fetch. These patterns may have
significant effects on particulate and dissolved nutrients in the water column as well as
sediment nutrient fluxes.
Marine sediments may act as a storage for organic matter as algae and other
organisms die and settle out of the water column, while the sediments may act as a source
for dissolved inorganic and organic nitrogen as this material is re-mineralized through
heterotrophic decomposition. Denitrification in anoxic sediments may be a sink for
dissolved inorganic nitrogen, although Sin et al. (2007) indicate that algae covered
sediments reduce the sediment-water interface by assimilating nitrate and ammonium
from the water column and reducing the ability for these nutrients to reach sediments.
The mud flats of Humboldt Bay experience significant seasonal coverage by macroalgal
mats (Schlosser and Eicher, 2012). Areas without macroalgae may be influenced by
benthic microalgae (Sin et al., 2007).
North and South Humboldt Bay contain extensive intertidal mud flats that may
provide a significant medium for potential nutrient cycling via particle settling and burial,
remineralization of nutrients via heterotrophic bacteria, pore water exchange of dissolved
nutrients, microalgal photosynthesis at the surface, and microfauna that both consume
organic material and burrow through sediments increasing the pore water exchange rates
(Sin et al., 2007). There are no data available on the spatial or temporal distribution of
any of these processes in Humboldt Bay, and the wide seasonal distribution of eelgrass
and macroalgae over the intertidal mudflats of the Bay further complicate any estimation
40
of sediment nutrient flux due to photosynthetic uptake of sediment nutrient sources
(Larned, 2003). Additional complicating factors include intertidal variation due to
immersion and emersion resulting in varying amounts of exposure to sunlight and
atmospheric oxygen, diel variation due to sunlight that drives photosynthesis and oxygen
production at the sediment-water interface, diel and seasonal gradients in water
temperature and salinity due to runoff, upwelling, and evaporation, and nutrient gradients
between the sediment and water column due to all of the aforementioned processes
(Garber et al., 1992).
Sin et al. (2007) documented nitrate, ammonium, phosphate, and silicate flux
rates in microalgal covered intertidal silt and clay sediments in Yaquina Bay, Oregon,
approximately 220 miles to the north of Humboldt Bay (Table 12). Sediment type likely
influences sediment nutrient flux as well as vegetative cover such as microalgae,
macroalgae, eelgrass, and marsh grasses (Sin et al., 2007). Thompson (1971) described
the sediment material of Humboldt Bay's intertidal mud flats as clayey silt with no
specification as to organic content, whereas the sediments examined by Sin et al. (2007)
were predominantly sand (approximately 70-80%) with 10-20% silt, 7-9% clay, and 0.6-
0.9% total organic carbon content (another site was also included in this study that is
omitted from this review because it contained more sand than the other two sites which is
less comparable to sediments of the Humboldt Bay mud flats).
Sin et al. (2007) estimated that net nitrate fluxes were always into the sediments
from the water column regardless of light exposure (Table 12). During light exposure,
algae may uptake nitrate for production, while during dark periods, coupled nitrification-
41
denitrification may be responsible for nitrate removal. Nitrate production via nitrification
of ammonium was estimated to be less than the demand for nitrate due to uptake and
denitrification resulting in a net negative flux rate during all periods. Sediment
ammonium fluxes indicated sediments were a source of ammonium during both light and
dark periods, though dark flux rates were generally higher due to reduced algal uptake
during photosynthesis. Ammonium efflux from sediments was possibly the result of re-
mineralization of ammonium from decomposing organic matter (Kemp et al., 1990).
Phosphate fluxes into sediments were measured during light periods, possibly due to
photosynthetic uptake and/or chemical adsorption to oxidized iron (II) present in oxic
sediments (Bray et al., 1973). Phosphate fluxes out of sediments were measured during
dark periods, possibly due to anoxia resulting from cessation of photosynthesis by
overlying algae and plants (Taft and Taylor, 1976). Silicate fluxes varied with light and
dark phases, being uptaken by sediments during light phases and released to the water
column during dark phases. Silicate uptake was attributed to algal production and release
may be attributed to biogenic recycling (Barelson et al., 1987).
Table 12 - Nutrient flux rates for microalgae-covered intertidal sediments in Yaquina
Bay, Oregon (mg/m2/hr); negative values denote sediment uptake.
Photoperiod Nitrate-N1 Ammonium-N1 Phosphate-P1 Silicate-Si1
light -1.40 to -0.15
(-0.39)
-0.73 to 0.60
(-0.06)
-0.23 to 0.03
(-0.08)
-2.61 to 0.00
(-1.29)
dark -1.71 to -0.13
(-0.45)
-0.05 to 1.41
(0.43)
-0.06 to 0.37
(0.11)
-0.81 to 7.95
(2.39) 1Sin et al. (2007)
42
Denitrification
In a survey of six estuaries, Seitzinger (1988) estimated that denitrification may
be responsible for 20-50% removal of all nitrogen inputs. Few studies have directly
measured denitrification rates in estuaries of the eastern Pacific coast; although many
different analytical techniques have been developed to measure denitrification with
varying accuracy. Denitrification rates between 0.70-3.50 mg N/m2/hr have been
measured in other estuaries and bays around the world (Seitzinger, 1988), although most
of these systems are on the Atlantic Ocean and may have limited applicability to systems
on the northeastern Pacific coast. The highest rates of denitrification occur in eutrophic
waters with high nutrient loads and low oxygen. Of the systems presented by Seitzinger,
Oremland et al. (1984) measured denitrification rates in intertidal sediments of San
Francisco Bay between 0.02-0.05 mg N/m2/hr in San Francisco Bay following the
acetylene inhibition methodology described below.
Denitrification in intertidal sediments covered by marine vegetation such as
eelgrass and algae is complicated by the ammonium uptake and oxygen generation by the
plants during photosynthesis (Risgaard-Petersen et al., 1994). During the summer and
fall in Humboldt Bay, algae may cover approximately 23% and eelgrass another 59% of
the mud flats (Schlosser and Eicher, 2012); this does not include the rest of the mud flats
that may be covered in microalgae including benthic diatoms. Oxygen generation by
macroalgae during photosynthesis has been found to reduce denitrification of nitrate from
the water column by approximately 60% (Risgaard-Petersen et al., 1994); however,
43
during both light and dark periods, nitrate from the water column made up 73% and 92%
of nitrate used for denitrification, respectively.
Multiple methods have been used to determine denitrification rates in marine
systems including a system-wide mass balance approach, inference from nitrate removal
in overlying waters, laboratory measurements of gas production, and inference from
stoichiometric nitrogen-phosphorus ratios in sediment pore water (Seitzinger, 1988). The
mass balance approach infers the amount of nitrogen lost due to denitrification from a
mass balance of inputs and outputs; any nitrogen that is not accounted for in the mass
balance is attributed to denitrification. This method may only be as accurate as the
estimates for other sources and sinks in the mass balance and does not account for spatial
variability or identify specific processes involved in denitrification (Seitzinger, 1988).
Denitrification rates are also inferred from decreases in nitrate or nitrite
concentrations in the overlying water column assuming nitrate loss is due to
denitrification. This method may overestimate denitrification rates because it does not
account for other processes that are involved in nitrate production and removal such as
nitrate reduction to ammonium, or plant uptake, and nitrification in oxic layers of
sediments respectively (Seitzinger, 1988).
Analytical laboratory techniques have also been developed to directly measure the
products of denitrification including nitrous oxide and nitrogen gas. One method
measures nitrous oxide production as an indicator of denitrification (the precursor to
nitrogen gas in the denitrification process) by inhibiting the final stage of nitrogen gas
production using acetylene (Balderston et al., 1976; Yoshinari and Knowles, 1976). This
44
method has been found to be problematic as acetylene incompletely inhibits reduction of
nitrous oxide under certain conditions and also inhibits nitrification (Hynes and Knowles,
1978). Denitrification in sediments can be directly linked to nitrification in which case
this method would underestimate denitrification (Seitzinger, 1988). Direct measurement
of nitrogen gas produced from sediments is complicated by the fact that nitrogen is the
most abundant gas in our atmosphere, creating the potential for contamination; however,
Seitzinger (1980) has established a method for this technique that eliminates
contamination.
Other researchers have estimated denitrification for a whole estuary from non-
conservative dissolved inorganic nitrogen fluxes (Smith et al., 1987). A detailed nitrogen
budget is constructed where DIN import is compared with storage and export of organic
and inorganic nitrogen, and any unaccounted-for DIN is assumed to be lost to
denitrification. Using this method Smith et al. (1991) estimated denitrification rates in
Tomales Bay, California (approximately 200 miles south of Humboldt Bay) of 1.81
mg/m2/hr. An accurate nitrogen budget requires a wide variety of data including
dissolved and particulate organic nitrogen, dissolved inorganic nitrogen, sediment-
nitrogen flux rates, suspended sediment nitrogen content, benthic plant nitrogen content,
atmospheric nitrogen fixation, and a water budget including an estimation of tidal
flushing.
In a parallel study in Tomales Bay following the work of Smith et al. (1991),
Dollar et al. (1991) directly measured sediment nutrient fluxes. Applying stoichiometric
principles of carbon, nitrogen, and phosphorus content of planktonic material (106:16:1,
45
C:N:P) Dollar et al. determined a sediment denitrification rate of between 0.70-0.76 mg
N/m2/hr.
Humboldt Bay Flushing Times
Various estimates of flushing times in Humboldt Bay between 1 and 30 days have
been derived using multiple approaches. Gast and Skeesick (1964) estimated a flushing
rate for Humboldt Bay of approximately 8 days ±50% (15 tide cycles, or 0.07
replacement per tide cycle). This approach estimates the freshwater volume in the Bay
using the difference between an average salinity and a maximum salinity, and then
divides this by the total freshwater inflow during a single tide cycle (Equation 1) to
determine how many tide cycles are required for full replacement of the freshwater
fraction in the Bay. Gast and Skeesick cite Ayers (1956) as their source for this approach
although Ayers cites the work of Ketchum (1951) as the originator of this approach. This
approach may be more applicable for estuaries where high rates of freshwater inflow are
the dominant source of water, whereas in Humboldt Bay this is not the case.
Gast and Skeesick (1964) noted that higher salinity occurred inside Arcata Bay
during the summer and fall due to evaporation, and lower salinities occurred inside
Arcata and South Bays during the winter and spring due to precipitation and runoff.
After significant dilution during the wet season in Arcata and South Bays, salinities
returned to values measured at the Bay entrance approximately four months and two
months later, respectively indicating that Arcata Bay has a much lower flushing rate than
South Bay, though the flushing rates of both bays are quite low.
46
𝑡 =(
𝑆𝑚𝑎𝑥 − 𝑆𝑎𝑣
𝑆𝑚𝑎𝑥) ∗ 𝑉ℎ𝑖𝑔ℎ
𝑄𝑖𝑛
(1)
Where,
t = tidal flushing time (number of tide cycles)
Smax = maximum salinity (ppt)
Sav = average salinity (ppt)
Vhigh = high tide volume (106ft3)
Qin = total freshwater inflow per tide cycle (106ft3/cycle)
Casebier and Toimil (1973) estimated flushing times for Arcata Bay using three
different methods. During the low flow summer season, a flushing time of approximately
one day (2.1 tide cycles, or 0.48 replacement per tide cycle) was calculated (Equation 2).
This approach assumes complete mixing of the tidal prism, likely resulting in a very low
estimate of the exchange rate. It is unclear what volumes were used for the Bay and tidal
prism in their calculations; the volume used (V) should have been the high tide volume
and not the low tide volume (Ketchum, 1951); this would result in a significant
underestimate of the flushing time. During the winter runoff season, a flushing time of
approximately 0.4 days (0.8 tide cycles, or 1.25 replacement per tide cycle) was
calculated using the same approach applied by Gast and Skeesick (1964) above in
Equation 1 from Ketchum (1951). A third approach was applied that models salinity
gradients along a longitudinal pathway incorporating a dispersion term that may increase
the flushing time depending upon the value used (which was not specified). Model
results with F=0.08 (0.08 replacement per tide cycle, 12.5 tide cycles, or approximately 6
47
days) indicated the best fit to observed measurements. Their calculations are reportedly
within an order of magnitude meaning their estimates for exchange rates range from 2.4
hours to 10 days during the summer and from one hour to 60 days during the winter.
𝑡 =𝑉 − 𝑃
𝑃 (2)
Where,
t = tidal flushing time (number of tide cycles)
V = high tide volume (103ac ∙ ft)
P = tidal prism (103ac ∙ ft)
Costa (1982) estimated a flushing time for Mad River Slough of approximately 43
days (85 tidal cycles, or 0.01 replacement per tide cycle), and indicated that Arcata Bay
would likely have a flushing time much less. No details were provided for the method
employed to calculate the Mad River Slough flushing time.
ANATEC Laboratories (1982) conducted a tracer dye study in Arcata Bay
estimating 99% replacement in 16.4 days (approximately 33 tide cycles, or 0.03
replacement per tide cycle). During this study, wind and rain from a February storm may
have interrupted the normal flow patterns in the Bay as well as causing vertical
stratification due to salinity differences between increased freshwater runoff and the Bay
water. The results were not used in any type of advanced mathematical or computational
model due to budget and time restrictions, although the longer replacement times found
48
during a winter storm indicate previous estimates of flushing times are likely significantly
low.
Using a three-dimensional hydrodynamic model, Anderson (2010) estimates 90%
flushing times for Arcata Bay to be over 30 days (0.02 per tide cycle), for Entrance Bay
to be 1.6 days (0.31 per tide cycle), and South Bay to be 14 days (0.04 per tide cycle).
The simulation runs that resulted in these estimates ran for one month from June to July
2009, and may represent a lower estimate due to low streamflow to the Bay during this
summer period. The model package consists of an open source numerical model called
Environmental Fluid Dynamics Code (EFDC) built for the US EPA and run by a
proprietary interface program called EFDC Explorer by Dynamic Solutions International
that allows advanced input and output processing (Craig, 2013). The three-dimensional
finite difference hydrodynamic model is a formulation of the three-dimensional navier-
stokes equations of fluid motion and incorporates many fluid properties including
temperature, salinity, viscosity, eddy diffusivity, and bottom roughness to increase the
accuracy of simulated fluid motion (Hamrick, 1992). The hydrodynamic model contains
1,475 horizontal segments with an average size of 210 m by 230 m, and each cell is
divided into three vertical layers. The relatively small resolution of the spatial cells
(previous approaches treat the entire Bay as one cell), addition of realistic physical
properties of fluid motion, and use of a dynamic finite difference numerical solution
approach makes estimates from this model much more robust than previous approaches
to estimating flushing times. The model has been calibrated using continuously
monitored data from the NOAA North Spit station, South Bay, and Mad River Slough
49
(Anderson, 2010). The model also incorporates forcing functions including tidal
elevation and temperature at the Bay entrance, tributary streamflow from creeks
emptying into Humboldt Bay, and atmospheric data including air temperature, relative
humidity, wind speed and direction, atmospheric pressure, solar radiation, and cloud
coverage. It should be noted that the model has only been roughly calibrated at a few
locations in the Bay and may undergo further calibration and verification.
Humboldt Bay Circulation Studies
Horizontal and vertical circulation patterns in Humboldt Bay have been
documented using naturally occurring water quality parameters such as salinity,
temperature, dissolved oxygen, and dissolved nutrients. Additional horizontal circulation
patterns have been documented using tracer dyes and drift poles that provide information
about velocity and distribution of water currents that are more difficult to determine using
constituents that exist everywhere naturally such as salinity. Gast and Skeesick (1964)
documented the seasonal patterns of horizontal and vertical stratification that occur with
respect to salinity due to increased freshwater inflow during the winter runoff season and
with respect to temperature in the summer due to sunlight heating water over the shallow
mud flats and reduced runoff. Vertical stratification tends to be very weak in Humboldt
Bay during the winter due to the shallow inner bays and high rate of mixing that occurs in
the channels due to the large tidal prisms and wind driven mixing. Due to the weak
stratification of the Bay during storms and the vertical homogeneity that exists during the
rest of the year, the Bay is assumed to be vertically homogeneous for the purposes of this
50
project. Gast and Skeesick (1964) also conducted a tracer study sometime between 1961
and 1964, documenting bulk circulation patterns using drift poles and tracer dye. Drift
poles were tracked from the shore and used to indicate flow direction while the tracer dye
was used to document bulk circulation patterns and current velocity. Results of these
studies were not presented with any advanced numerical analysis with respect to flushing
times or mixing rates.
Klamt (1979) documented the potential for wastewater discharged from Arcata
and Eureka to reach oyster beds in Arcata Bay within a single tide cycle using a
fluorescent tracer dye during April 1979. While streamflow conditions were not
documented, streamflow into the Bay may have been elevated due to the study occurring
during the spring after winter rainfall in the watershed increases stream flows. No
appreciable rainfall occurred during the study indicating there may have also been an
absence of wind-driven mixing from storm conditions. One study injected dye at the
decommissioned Hill Street wastewater treatment facility (WWTF) at high tide and
measureable amounts of dye were detected near the Murray Street WWTF (also
decommissioned) at the slack tide (Figure 13). This dye study documented the relative
isolation of Freshwater Creek/Slough effluent from Arcata Bay. A second dye study
injected dye into the old AWTF effluent near high tide (near the south end of what is now
Oxidation Pond 1) and measureable amounts were detected approximately 2.5 miles
downstream near the center of Arcata Bay at slack tide (Figure 13). This study illustrates
the relative isolation of Arcata Bay such that discharge from the AWTF will not exit
Arcata Bay on a single tide cycle. A third dye study injected dye into the effluent of the
51
decommissioned Murray Street WWTF in Eureka near low tide and measureable
amounts were detected far into Arcata Bay in both the Jacoby Creek branch of the Arcata
Channel and the Mad River Slough Channel (Figure 13). This study illustrates the
potential for water in the Main Channel to reach far into Arcata Bay on flood tides.
Figure 13 - Three short-term tracer dye studies conducted in Arcata Bay to determine the
extent of potential treated wastewater contamination of oyster beds (adapted from Klamt,
1979).
52
ANATEC Laboratories Inc. et al (1982) conducted a fluorescent tracer dye study
in Arcata Bay during February and March of 1982. The dye was injected at the
confluence of the Arcata Channel and Jacoby Creek Channel in the northwestern part of
Arcata Bay. Dye was injected continuously for five days attempting to reach a steady
state concentration in the Bay after which a die-off could be monitored that would
indicate a flushing rate for the Bay. Due to tidal exchange, surface runoff, and
subsequent storm events, a steady state dye concentration was not reached and the team
resigned to monitoring the die-off of the dye that had been injected in the first five days
of the study. Samples were collected from the surface and at 3 m depth from 50 locations
at high and low tides during daylight hours. During this period multiple storm events
occurred, introducing moderate winds and heavy rainfall, complicating sampling, diluting
Bay waters, increasing runoff, and altering mixing patterns due to wind-driven mixing.
Findings of the ANATEC Laboratories et al. (1982) tracer study indicate that
rainfall and increased runoff during the storm events were sufficient enough to dilute the
salinity in Arcata Bay to approximately 25 ppt, although vertical stratification was also
observed, whereby bottom salinities were closer to 29 ppt. This vertical stratification
marked a difference between landward freshwater inputs and seaward saltwater flows
that were tracked as the saltwater front moved into Mad River Slough Channel and
Arcata Channel over the following three days. This finding is significant with respect to
tidal flushing as increased streamflow and rainfall might theoretically decrease the
residence time in Arcata Bay, when in reality the difference in water density caused by
rainfall might actually act to further isolate waters within the Bay. However, wind events
53
blowing from the east resulted in transport of dye from its origins in the east side of
Arcata Bay to the western side faster than expected. Dye concentrations in the Arcata
Channel and Mad River Slough Channel were very similar likely due to the confluence of
these two channels in the Samoa Channel during each ebb tide cycle which results in near
complete mixing. Waters in the southeastern portion of the Bay including
Indian/Woodley Island Channel and Eureka Channel were isolated from dyes in the rest
of the Bay, showing up one and two days after the other two, respectively, indicating that
these channels are relatively isolated from the main channels of the western portion of the
Bay that converge into the Samoa Channel.
In March 2004 the California Department of Health Services conducted a
fluorescent tracer dye study in Arcata Bay during low streamflow conditions at Gannon
Slough, Eureka Slough, and Butcher's Slough (CDHS, 2006). Conditions and results
from this study closely follow those of Klamt (1979). Dye injected at Butcher's and
Gannon Sloughs during ebb tides indicate that limited transport occurs across the mud
flats separating Arcata Channel and Mad River Slough Channel, and that dye was not
transported far enough out of the Bay to reach the confluence of the two channels where
direct mixing could occur. Dye was injected at the railroad bridge in Eureka Slough on
an ebb tide and reached the mouth of the Bay during a single ebb tide cycle. This is a
much greater distance than observed by Klamt (1979) during the dye study conducted
from the former Hill Street WWTF located near the railroad bridge in Eureka Slough.
While it is not clear what the change in tidal elevation was during March 2004 study, the
tidal range during the April 1979 study was only 2.8 feet following the lower high tide.
54
This may indicate that during a larger tidal ebb, water may flow from Eureka Slough all
the way to the mouth of the Bay, whereas during a minor tidal ebb, water may not reach
much past the confluence of the Samoa Channel and Eureka Channel (Figure 13). This
finding is significant with respect to the degree to which water from Freshwater Slough
interacts with the rest of Arcata Bay. CDHS (2006) measured the dye plume from the
Eureka Slough injection in the Mad River Slough Channel and Arcata Channel during the
subsequent flood tide indicating that during larger tidal cycles constituents from different
reaches of the Bay may be interacting. The tidal characteristics of Humboldt Bay are
characterized by semidiurnal inequality (Barnhart et al., 1992); generally containing a
higher high, higher low, lower high, and lower low tide each day. This results in one
tidal elevation change being greater or less than the following one. This characteristic
significantly complicates mixing and tidal flushing characteristics of the Bay.
Humboldt Bay Nutrient Studies
Gast (1962) collected an extensive set of nutrient data for Humboldt Bay
including depth, temperature, chlorinity, salinity, density, dissolved oxygen, phosphate-P,
and silicate-Si. Monthly samples were collected at 12 sites throughout the Humboldt Bay
system and one site outside the mouth of the Bay from September, 1961 to September,
1962 (n = 503). This study did not measure nitrogenous constituents (ammonium,
nitrate, and nitrite) which have subsequently been determined to be the primary limiting
nutrient in Humboldt Bay (Pequegnat and Butler, 1981). Samples were also collected at
multiple depths supporting the conclusion that vertical homogeneity exists throughout the
55
Bay due to the large tidal prism and strong mixing on flood and ebb tides (Gast and
Skeesick, 1964). The ranges of silicate and phosphate measured by Gast (1962) are listed
in (Table 13). Concentrations of silicate and phosphate near the Bay entrance were
higher than those inside the Bay during September and October of 1961 and again
between March and May of 1962 which were attributed to ocean upwelling events.
Table 13 - Phosphate and silicate concentration ranges measured near the Bay entrance,
in Arcata Bay, and in South Bay.
Location Units Phosphate-P1 Silicate-Si1
Bay Entrance µM
(µg/L)
1.1 - 3.0
(35.3 - 93.9)
8.6 - 40.2
(242 - 1,129)
Arcata Bay µM
(µg/L)
1.4 - 2.8
(44.6 - 87.7)
13.9 - 40.1
(390 - 1,126)
South Bay µM
(µg/L)
1.3 - 3.2
(41.2 - 98.2)
15.5 - 39.6
(435 - 1,112) 1Gast (1962)
Janeway (1981) sampled seven locations around the perimeter of Arcata Bay, one
location along the Main Channel, and near the Entrance Bay, and two locations along the
shore of the Samoa Peninsula 17 times between July 1979 and March 1980 (n = 187).
Samples were collected at the lowest tides twice per month to measure water flowing into
the Bay from tributaries and the AWTF as well as measuring water leaving the Bay, and
flowing into the ocean. Samples were analyzed for ammonium-N, nitrate-N, phosphate-
P, dissolved oxygen, water temperature, conductivity, and pH. This study was conducted
to help the City of Arcata establish its natural wastewater treatment system rationale for
56
discharging into Arcata Bay. The ranges of nutrients measured in the Bay by Janeway
(1981) are listed in Table 14.
Data collected by Janeway (1981) indicate that no upwelling conditions were
experienced during the study; there were no decreases in water temperature and
corresponding increases in salinity and nutrients near the Bay entrance. The typical
upwelling season is March or April through September, with maximum upwelling
typically occurring in June or July according to average monthly upwelling indices
(PFEL, 2015); this may indicate that upwelling occurred prior to July 1979 or after
March 1980. Because of this, nutrient concentrations were consistently higher near the
sloughs of the Bay than inside the Bay or near the Bay entrance. Data collected at six
locations near the sloughs surrounding Arcata Bay are in good agreement indicating
nitrate concentrations were higher during the fall and winter runoff season;
approximately 0.5 mg/L as N (36 µM) compared to approximately 0.1 mg/L as N (7 µM)
during the rest of the study period. Janeway attributed the higher levels of nitrate during
the runoff season to oxidation of fecal material from pasturelands and septic systems as
well as urban runoff. Phosphate concentration data from the six slough stations around
Arcata Bay were in generally good agreement with the exception of data from Gannon
Slough that were significantly higher than all other stations during three sample periods
in August, September, and October 1979. Omitting that exception, phosphate
concentrations were higher during July and August only; approximately 0.25 mg/L as P
(8 µM) compared to approximately 0.1 mg/L as P (3 µM) during the rest of the study
period. High values measured near Gannon Slough were closer to 0.7 mg/L as P (23
57
µM); the higher values near Gannon Slough may be due to the large size of the Jacoby
Creek watershed. Janeway attributed the depressed concentrations of phosphate during
the runoff season to dilution from rainfall. Ammonium concentration data were also in
generally good agreement with the exception of Gannon Slough and Freshwater Slough.
Ammonium concentrations at the stations that were in agreement were generally higher
during July and August, approximately 0.1 mg/L as N (7 µM), falling to approximately
0.05 mg/L as N (4 µM). Ammonium concentrations near Gannon Slough and Freshwater
Slough were significantly higher than other stations during the late summer and fall;
approximately 0.7 mg/L as N (50 µM) and 0.4 mg/L as N (29 µM), respectively.
Janeway attributed the lower levels of ammonium during the winter runoff season to
dilution from rainfall.
Janeway (1981) measured three sample locations near the Bay entrance showing
relatively good agreement with respect to phosphate and nitrate, although ammonium
concentrations show questionable variability and magnitude, being far greater than have
been reported by any other source. Phosphate does not show much variation near the Bay
entrance remaining approximately 0.07 mg/L as P (2 µM) throughout the study period.
Nitrate rose from approximately 0.04 mg/L as N (3 µM) to approximately 0.08 mg/L as
N (6 µM) from October through January. Upwelled nitrate concentrations in nearshore
waters of this region of the Pacific Ocean can reach 0.5 mg/L as N (34 µM) indicating
these levels are not the result of strong upwelling (Sigleo et al., 2005). Ammonium
concentrations near the Bay entrance were higher during August and September reaching
58
0.3 mg/L as N (24 µM) but remaining much lower during the rest of the study period, less
than 0.05 mg/L as N (4 µM).
Table 14 - Phosphate, nitrate, and ammonium concentration ranges (and medians)
measured near the Bay entrance and inside Arcata Bay between July 1979 and March
1980.
Location Units Phosphate-P1 Nitrate-N1 Ammonium-N1
Bay Entrance µM 1.3 - 4.8
(2.3)
0.7 - 8.6
(3.6)
0.7 - 24.3
(2.9)
Bay Entrance µg/L 40 - 150
(70)
10 - 120
(50)
10 - 340
(40)
Arcata Bay µM 1.3 - 25.2
(2.6)
0.7 - 47.8
(6.4)
0.7 - 85.7
(3.6)
Arcata Bay µg/L 40 - 780
(80)
10 - 670
(90)
10 - 1,200
(50) 1Janeway (1981)
Pequegnat and Butler (1981) sampled six locations throughout Humboldt Bay
twice in 1980 (n = 12); once during an upwelling period, and once during a non-
upwelling period. Samples were analyzed for nitrate, nitrite, ammonium, phosphate, and
silicate. They determined that nitrogen can become the limiting nutrient during periods
of high productivity in Humboldt Bay, indicating that an increase in nitrogen supplied to
the system may result in increased biological production. They also estimated that the
AWTF and EWTF were discharging enough nitrogen to Arcata Bay and the Main
Channel to increase the concentration in that part of the system by 0.5 µM (7 µg/L);
though there is no indication as to where data came from for this calculation. This
implies a wastewater discharge nitrogen load of between 0.336-0.596 Mg N/d, assuming
a MLLW volume of 48 Mm3 and a MHW volume of 85.1 Mm3, respectively (Shapiro
59
and Associates, Inc., 1980). Ranges of nutrient concentrations measured by Pequegnat
and Butler (1981) are listed in Table 15.
Table 15 - Phosphate, nitrate, ammonium, and silicate concentration ranges (and means)
measured near the Bay entrance, in Arcata Bay, and in South Bay.
Location Units Phosphate-P1 Nitrate-N1 Ammonium-N1 Silicate-Si1
Arcata Bay µM 1.87 - 2.23
(2.09)
0.5 - 2.6
(1.4)
1.1 - 1.5
(1.3)
22.9 - 26.9
(24.9)
Arcata Bay µg/L 57.92 - 69.07
(64.66)
7.0 - 36.4
(19.6)
15.4 - 21.0
(17.9)
643.2 - 755.5
(698.6)
Main Channel µM 1.27 - 1.90
(1.59)
0.5 - 4.0
(2.3)
0.8 - 2.3
(1.6)
13.5 - 21.9
(17.7)
Main Channel µg/L 39.34 - 58.85
(49.09)
7.0 - 56.0
(31.5)
13.5 - 21.9
(17.7)
379.2 - 615.1
(497.1)
Bay Entrance µM 0.03 - 1.44
(0.74)
0.3 - 12.6
(6.5)
0.0 - 1.9
(0.95)
2.1 - 19.2
(10.7)
Bay Entrance µg/L 0.93 - 44.6
(22.8)
4.2 - 176.5
(90.3)
0.0 - 26.6
(13.3)
59.0 - 539.2
(299.1)
South Bay µM 0.73 - 1.44
(1.08)
0.0 - 2.1
(1.4)
0.2 - 1.5
(0.8)
7.7 - 16.5
(12.0)
South Bay µg/L 22.61 - 44.60
(33.45)
0.0 - 29.4
(19.6)
2.8 - 21.0
(10.9)
216.3 - 463.4
(337.0) 1Pequegnat and Butler (1981)
Pequegnat and Butler (1982) estimated plant production in Arcata Bay for a 150
day period between early spring and early fall indicating that 22% (5 million kg), 23%
(5.2 million kg), 18% (4 million kg), and 37% (8.2 million kg) are attributable to salt
marsh, phytoplankton, eelgrass, and mudflat algae, respectively; the methods used to
determine these values is not indicated. Chlorophyll and nutrient concentrations were
greater in nearshore waters during upwelling events indicating this as the source of
nutrients and phytoplankton. Compared with values in nearshore waters, chlorophyll
60
concentrations inside the Bay were lower during the spring and summer; this was
attributed to nutrient-limitation. During the winter, productivity in and out of the Bay
was lower than in the spring and summer upwelling season. However, in the late winter,
chlorophyll production inside the Bay began before production outside the Bay; this was
attributed to shallow water over the mud flats of the Bay where phytoplankton could be
exposed to sunlight whereas in the deeper nearshore waters, phytoplankton may be
transported below the photic zone decreasing production.
Henderson (2004) conducted a survey of water quality parameters in the Salmon
Creek watershed of South Humboldt Bay to determine impacts from forestry and dairy
activities. Ammonia-nitrogen remained below detection (0.5 mg N/L, 35.7 µM) in all
samples from the headwaters to the NWR. Henderson notes that the detection limit of
0.5 mg N/L was too high for this type of study though this indicates ammonia-nitrogen
levels were not excessively high in Salmon Creek. Henderson also notes that the dairy
operations adjacent to and upstream of sample locations ceased prior to the study such
that this study was unable to determine potential water quality impacts from dairy
operations. The extent of agricultural impacts to nutrients in creeks around Humboldt
Bay is not well documented.
Tennant (2006) sampled 21 locations around the perimeter of Humboldt Bay and
4 locations outside the Bay on the shorelines north and south of the Bay entrance.
Measurements of ammonium, nitrate, and phosphate were collected in the water column
over a period of one year (n = 300) and the data were segregated into a wet season
(November through May) and a dry season (June through October). An unknown
61
number of sediment pore samples were also collected from various sites throughout the
Bay during this study and analyzed for nitrogen and phosphorus content. This work
addressed how ammonium, nitrate, and phosphate levels in the water and sediment affect
eel grass density in Humboldt Bay. Tennant concluded that nitrogen and phosphorus
supplied to eelgrass through the sediments were sufficient to meet saturation levels for
eelgrass growth and that concentrations in the water column were not likely the direct
cause of eelgrass density variation. The greatest concentrations of nitrate were observed
near the Bay entrance during the dry season which may indicate upwelling was a
dominant source of nitrate to the Bay during this study (Table 16 and Table 17). Nitrate
concentrations inside the Bay were higher during the runoff season than during the dry
season possibly due to low productivity. Phosphate concentrations remained relatively
low and steady throughout the Bay and during each season. Ammonium concentrations
were also relatively low and steady through the Bay for the duration of the study with the
exception of March and April when concentrations seemed to increase at some locations
in the Bay and not others; the reason for the sporadically high ammonium data is unclear.
Hurst (2009) measured nitrate, nitrite, phosphate, silicate, temperature, salinity,
pH, turbidity, and dissolved oxygen at three locations in Humboldt Bay between October
2007 and July 2009. Data collected between October 2007 and October 2008 were
published in a poster presentation (Martin and Hurst, 2008) while the rest of the data
remain unpublished. Martin and Hurst (2008) measured higher concentrations of nitrate
and silicate near Mad River Slough during the runoff season indicating that land-based
sources may be significant in Humboldt Bay. These data also support the previous
62
conclusion by Pequegnat and Butler (1981) that nitrate-nitrogen is the limiting nutrient to
productivity in Humboldt Bay. Ranges of nutrients measured in Humboldt Bay by Hurst
(2009) are listed in Table 18.
Previous studies in Humboldt Bay have documented seasonal patterns of
upwelling and the influences of runoff with respect to nutrients, salinity, and temperature.
However none of these previous studies have included information on wastewater
discharges or the flow rates of various sources so that a comparison of relative masses
associated with the sources could be evaluated. Many of these studies were conducted
over thirty years ago such that any conclusions drawn may not be relevant to present
conditions. Previous studies have also failed to quantify in detail, estimations of nutrient
uptake to allow a relative comparison to nutrient sources to provide a basis for
establishing potential biological and water quality impacts of sources.
This study will combine recent nutrient data from Humboldt Bay and WWTFs
with hydrodynamic simulation model flow rates and stream flow estimations to calculate
current nutrient loading to Humboldt Bay. This study will also estimate nutrient uptake
by major biological processes using recent measurements of chlorophyll-a, eelgrass, and
macroalgae distribution in the Bay for comparison to major inputs. Data will be gathered
from intertidal samples (adjoining high and low tide samples) collected along a transect
between the Bay entrance and Arcata Bay to investigate internal nutrient and
phytoplankton dynamics. These samples will provide evidence of internal nutrient
dynamics in the Bay to support conclusions about sources and uptake that boundary
values collected at one tide stage weeks apart may not suffice to explain.
63
Table 16 - Dry Season phosphate, nitrate, and ammonium concentration ranges (and
means) measured throughout Humboldt Bay; note that low and high range values were
estimated from plots, whereas means were gathered from tabulated data.
Location Units Phosphate-P1 Nitrate-N1 Ammonium-N1
Arcata Bay µM 0 - 11
(3.8)
0 - 5
(1.7)
0 - 20
(2.7)
Arcata Bay µg/L 0 - 341
(116)
0 - 70
(24)
0 - 280
(38)
Central Bay µM 1 - 6
(3.3)
1 - 18
(9.7)
1 - 6
(2.4)
Central Bay µg/L 31 - 186
(102)
14 - 252
(137)
14 - 84
(33)
Bay Entrance µM 1 - 7
(3.5)
11 - 28
(18.0)
1 - 18
(3.1)
Bay Entrance µg/L 31 - 217
(109)
154 - 392
(252)
14 - 252
(44)
South Bay µM 0 - 25
(3.6)
0 - 13
(2.7)
0 - 13
(2.0)
South Bay µg/L 0 - 774
(113)
0 - 182
(38)
0 - 182
(28) 1Tennant (2006)
64
Table 17 - Wet season phosphate, nitrate, and ammonium concentration ranges (and
means) measured throughout Humboldt Bay; note that low and high range values were
estimated from plots, whereas means were gathered from tabulated data.
Location Units Phosphate-P1 Nitrate-N1 Ammonium-N1
Arcata Bay µM 1 - 10
(3.2)
0 - 25
(7.6)
0 - 33
(6.5)
Arcata Bay µg/L 31 - 310
(99)
0 - 350
(107)
0 - 462
(91)
Central Bay µM 1 - 12
(2.5)
0 - 15
(8.9)
0 - 29
(5.8)
Central Bay µg/L 31 - 372
(78)
0 - 210
(125)
0 - 406
(82)
Bay Entrance µM 1 - 3
(2.0)
3 - 16
(8.9)
0 - 42
(6.4)
Bay Entrance µg/L 31 - 93
(63)
42 - 224
(125)
0 - 588
(89)
South Bay µM 1 - 12
(3.2)
0 - 19
(8.0)
0 - 44
(8.1)
South Bay µg/L 31 - 372
(898)
0 - 266
(113)
0 - 616
(113) 1Tennant (2006)
Table 18 - Ranges (and medians) of phosphate, nitrate, nitrite, and silicate measured in
Humboldt Bay.
Location Units Phosphate-P1 Nitrate-N1 Nitrite-N1 Silicate-Si1
Bay Entrance µM 0.4 - 2.1
(1.2)
2.2 - 24.3
(12.3)
0.1 - 0.5
(0.3)
5.4 - 43.4
(16.0)
Bay Entrance µg/L 12.4 - 245
(37.2)
30.8 - 556
(172)
1.4 - 7.0
(4.2)
152 - 1,219
(449)
Indian Island µM 0.5 - 2.6
(1.3)
0.0 - 20.8
(6.7)
0.1 - 0.4
(0.3)
3.8 - 37.1
(18.1)
Indian Island µg/L 15.5 - 80.5
(40.3)
0.0 - 291
(93.8)
1.4 - 5.6
(4.2)
107 - 1,042
(508)
Mad River Slough µM 0.8 - 2.9
(1.5)
0.0 - 20.9
(2.7)
0.1 - 0.5
(0.2)
2.8 - 66.3
(16.8)
Mad River Slough µg/L 24.8 - 89.8
(46.5)
0.0 - 293
(37.8)
1.4 - 7.0
(2.8)
79 - 1,862
(472) 1Hurst (2009)
65
METHOD
Sample Collection
Six water quality data sets contributed to this work:
1. Grab samples collected at ten locations inside of Humboldt Bay (Figure 14) by
boat between January 2014 and February 2015. On each sample day, one sample
was collected within one hour of high tide and another sample was collected at the
same location within one hour of low tide for a total of 20 samples on each day
(n=238). Adjacent high and low tides were sampled each day with the exception
of one low tide sample collected on the afternoon of 12/30/2014 and one high tide
sample collected on the morning of 12/31/2014 with one full tide cycle in
between. Temperature, dissolved oxygen (DO), and salinity of these samples
were determined in the field. Determination of pH, total suspended solids (TSS),
turbidity, chlorophyll-a, dissolved organic carbon (DOC), silicate, nitrate, nitrite,
ammonium, and phosphate for the samples was performed in the laboratory.
2. Grab samples collected by Humboldt State University Professor of Chemistry
Matthew Hurst's student research team every two weeks at up to seven freshwater
creek inlets around the perimeter of the Bay (Figure 15) between October 2012
and December 2014 (n=250). Temperature, DO, and salinity of these samples
were determined in the field. Determination of pH, TSS, turbidity, chlorophyll-a,
DOC, silicate, nitrate, nitrite, ammonium, and phosphate for the samples was
performed in the laboratory.
66
3. Grab samples collected by the Wiyot Tribe's Natural Resources Department every
two weeks at up to five locations in and around Humboldt Bay near high tide
(Figure 16). Three of the locations were collected by boat inside of the Bay (Bay
Entrance, Samoa Channel, and Indian Island), the Mad River Slough sample was
collected from the railroad bridge crossing on Highway 255, and Hookton Slough
was collected at a dock in South Bay the day prior to the other samples, also near
high tide. This dataset includes two separate time periods, October 2007 to July
2009 (three locations inside the Bay, n=138), and October 2012 to February 2015
(five locations, n=285). Temperature, DO, and salinity of these samples were
determined in the field, and determination of pH, silicate, nitrate, and phosphate
was performed in the laboratory. For October 2012 to February 2015,
determination of TSS, turbidity, chlorophyll-a, DOC, nitrite, and ammonium was
performed in the laboratory.
4. In-situ measurements from a multi-instrument data sonde deployed by the Wiyot
Tribe's Natural Resources Department on a fixed pier on the eastern shore of
Indian Island (Figure 14 and Figure 16), taking readings every 15 minutes since
December 2004. Readings include temperature, salinity, DO, pH, turbidity,
depth, and chlorophyll-a. Laboratory determination of chlorophyll-a and field
determination of temperature, salinity, and DO from grab samples in the other
data sets were used to calibrate the data sonde.
67
5. AWTF effluent (Figure 17) monitoring on a weekly basis since April 2011 for
ammonium and nitrate (n=121), and weekly measurements of phosphate from
October 2010 to August 2013 (n=107).
6. EWTF effluent (Figure 17) monitoring on a monthly basis since January 2010 for
ammonium (n=65).
Grab samples were collected from eight feet below the water surface near the
center of the channel using a peristaltic pump and drill driver; if the water depth did not
permit sampling at this depth, samples were collected from four feet below the water
surface. Sampling depth was held constant at eight feet below the surface regardless of
total water depth because the Bay has been characterized as vertically homogeneous
(Gast and Skeesick, 1964; Casebier and Toimil, 1973). Three liters of sample were
collected at each site, pumped directly into clean HDPE or polycarbonate bottles, and
placed into an insulated cooler out of sunlight until analysis. Analyses generally took
place within 12 hours of sample collection. Chlorophyll-a, DOC, and nutrient samples
were frozen between the time of preparation and the time of analysis.
68
Figure 14 - Sample site map and distances from the mouth of Humboldt Bay.
69
Figure 15 - Professor Hurst's sample site map and distances from the mouth of Humboldt
Bay.
70
Figure 16 - Wiyot Tribe's sample site map and distances from the mouth of Humboldt
Bay.
71
Figure 17 - Wastewater treatment facility outfall map and distances from the mouth of the
Bay.
72
Sample Analyses
All Bay grab samples were collected, handled, and analyzed using the same
methods and equipment. Methodology from Standard Methods for the Examination of
Water and Wastewater were followed for all analyses and instrument calibrations
(APHA, AWWA, WEF, 2012). The same hand held multi-parameter instrument (YSI
556 MPS) was used for field determination of all samples for dissolved oxygen (DO),
water temperature, and salinity were determined. Samples were brought back to a
laboratory at Humboldt State University where turbidity, pH, and total suspended solids
(TSS) were determined. Turbidity was determined using the Hach 2100Q turbidimeter,
pH was measured using an ion-selective probe, and TSS was determined using Whatman
934-AH glass fiber filters. Chlorophyll-a samples were prepared by filtering sample
water through 0.7 µm glass fiber filters and then freezing the filters in small plastic vials
until the time of analysis. Chlorophyll-a was extracted using acetone and then measured
at Humboldt State University's Telonicher Marine Laboratory in Trinidad, California
using a Turner Designs Trilogy fluorometer. Nutrient samples and dissolved organic
carbon (DOC) samples were prepared by filtering sample water through 0.45 µm
polycarbonate track-etched membrane filters. Filtrate was then frozen until analyses
were carried out. Nutrient analyses were carried out at Humboldt State University's
Telonicher Marine Laboratory in Trinidad using a Bran+Luebbe Autoanalyzer 3. DOC
analyses were carried out at Humboldt State University's BioCore laboratory using a
Shimadzu TOC-L Total Organic Carbon / Nitrogen Analyzer; samples run in the TOC
73
analyzer were filtered prior to analysis, the resulting concentrations thus represented the
dissolved component of TOC.
Nutrient samples remained frozen until analyses were conducted, approximately
every few months. Frozen samples from each run were saved and re-run during the
following analysis to ensure no degradation of nutrients had occurred while frozen.
Standards were also analyzed before and after freezing to ensure freezing had no effects
on concentrations. Both of these quality assurance tests indicated no depletion or loss of
any nutrient took place during the freezing and storage of samples.
Ammonium-nitrogen was analyzed following the automated phenate method
(Standard Methods: 4500-NH3 G). Nitrite-nitrogen and nitrate-nitrogen were analyzed
following the automated cadmium reduction method (Standard Methods: 4500-NO3- F).
Orthophosphate-phosphorus was analyzed following the automated ascorbic acid
reduction method (Standard Methods: 4500-P F). Silicate-silicon was analyzed following
the automated method for molybdate-reactive silica (Standard Methods: 4500-SiO2 E).
Dissolved organic carbon was analyzed following the high-temperature combustion
method for total organic carbon (Standard Methods: 5310 B) following filtration of
samples with 0.45 µm polycarbonate track-etched membrane filters to remove the
particulate component of total organic carbon.
The data sonde deployed on the Indian Island pier collects measurements every 15
minutes using a YSI 6600 EDS multi-instrument sonde. The sonde contains instruments
for reading water temperature, water depth, turbidity, salinity, pH, dissolved oxygen, and
chlorophyll-a. Chlorophyll-a readings from the sonde are adjusted based upon a
74
correction factor derived from lab measurements of chlorophyll-a in grab samples
collected at the same time and location of the sonde. The sonde is also removed and
calibrated every two weeks by the Wiyot Tribe Natural Resources Department.
Data Analyses
Two main components make up the nutrient budget, loading from sources, and
uptake or storage. Due to the variety of sources for nutrient loading data to Humboldt
Bay, many of the datasets do not overlap in time. Where this is the case, daily, monthly,
seasonal, and annual statistics may be used for calculations. Little or no data are
available for nutrient removal mechanisms in Humboldt Bay such as phytoplankton
production, macroalgae production, eelgrass production, and denitrification, so reference
values are used in conjunction with available water quality data and local atmospheric
data to estimate this portion of the budget as closely as possible. In order to compile a
budget for the whole system, no single nutrient cycling process was explored
exhaustively.
For each source or type of uptake, a statistic for sample standard deviation is
presented and varies in derivation depending upon the available data. Where multiple
years of data are available, the sample standard deviation represents the inter-annual
variability in the data. Where data from another system are applied to Humboldt Bay, or
literature values are used, the sample standard deviation may represent the sample or
measurement variation. Standard deviation statistics are described in more detail in the
following sections for each source and type of uptake. Standard deviation statistics are
75
not presented for hydraulic fluxes because the statistics presented for each nutrient source
or type of uptake includes variation in the hydraulic flux used to calculate them.
All annual statistics are presented in terms of water years (October through
September). Water years are defined by the calendar year that they end in. For example,
water year 2012 (WY 2012) is October 1, 2011 through September 30, 2012. All
concentrations are listed in molar and mass concentrations when convenient, different
agencies and disciplines may require different concentration units; note that wastewater
concentration units are typically reported as mass concentration (e.g. mg/L) whereas
typical oceanographic and ecologic concentration units are reported as molar
concentration (e.g. mM). Volume is reported in million cubic meters (Mm3), and mass is
reported in million grams (Mg), equivalent to a metric ton. The term loading is used to
describe the mass input from various sources, and the terms uptake or production are
used to denote removal or storage. Geospatial analyses were carried out using ESRI
ArcMap 10.1 and QGIS 2.6.1 in the Universal Transverse Mercator zone 10 (UTM10)
coordinate projection. All elevation data are with respect to the North American Vertical
Datum of 1988 (NAVD88).
In order to compare the relative magnitudes of each source and type of uptake,
mass loads are calculated using concentration and flow data due to the large difference in
flow rates between sources such as wastewater discharge, streamflow, and ocean tides.
This project includes the compilation of flow rate estimations as well as nutrient
concentrations for the three major hydraulic components, wastewater, streamflow, and
ocean tides, such that mass loading rates (mass per time) can be calculated for direct
76
comparison to one another and allow formation of a mass budget for the system.
Precipitation volumes have also been calculated for comparison of the magnitude of
hydraulic inputs to the Bay though precipitation is assumed to have no impact on nutrient
loading.
A nutrient mass balance relies on principles of conservation of mass (Equation 3)
to account for all sources, sinks, and types of storage. Tracking influx and efflux is much
simpler for conservative constituents such as water and salt than it is for nonconservative
constituents such as nitrogen, carbon, and phosphorus that are involved in many
chemical, physical, and biological transformations (Smith and Hollibaugh, 2006).
Limitations in data availability and computational modeling make a comprehensive
nutrient mass balance infeasible, therefore major constituents and processes are estimated
using available data to account for significant sources and uptake in the nutrient budget.
A computational model that can simulate water, salt, and temperature fluxes has been
constructed for Humboldt Bay (Anderson, 2010) though nutrient cycling has yet to be
included.
∑ 𝑀𝑎𝑠𝑠𝑖𝑛 − ∑ 𝑀𝑎𝑠𝑠𝑜𝑢𝑡 + ∑ 𝑀𝑎𝑠𝑠𝑠𝑡𝑜𝑟𝑎𝑔𝑒 = 0 (3)
The first step in constructing a mass-based nutrient budget from concentration
data requires a water budget quantifying volumes and flow rates. To calculate the mass
of any constituent, concentration (mass per volume) is multiplied by flow rate (volume
per time) resulting in a mass loading rate (mass per time) that allows comparison of the
77
magnitudes of different sources and uptake. For flow rates entering and leaving
Humboldt Bay, the boundary was set to be the approximate boundary of the water surface
at MHHW, and the boundary to the ocean was set as a line crossing the Bay entrance at
the outermost points of the north and south jetties.
Humboldt Bay is made up of four morphologically distinct compartments (Arcata
Bay, Main Channel, Entrance Bay, and South Bay) that have been defined here using the
approximate MHHW boundary in order to estimate the amount of water and nutrients
exchanged between each (Figure 18). Surface areas for each sub-compartment of the Bay
were estimated using polygons derived from the USGS WBD vector files that were
augmented to fit the water boundary of the active Bay (Table 19). The WBD polygons
included salt marshes and wetlands adjoining the Bay that are not considered active parts
of the normal tidally influenced surface area.
78
Figure 18 - Sub-bay boundary map.
79
Table 19 - Sub-bay and associated watershed surface areas.
Sub-Bay Compartment
Surface Area1
(Mm2)
Contributing Watershed
Area2 (Mm2)
Arcata Bay 37 245
Main Channel 6 145
Entrance Bay 8 0
South Bay 18 48 1Anderson (2015); 2WBD (2015)
Tidal Volumes
Flow rates between the ocean and the Bay, and between sub-bays of Humboldt
Bay were generated using a calibrated hydrodynamic circulation model (Anderson,
2015). The model of Humboldt Bay was constructed using the Environmental Fluid
Dynamics Code Explorer (EFDC Explorer) software and calibrated for water surface
elevation, salinity, and temperature (Anderson, 2010). Sub-compartment polygons were
used to delineate flux boundaries in the model (Figure 19), and flow rates were generated
on a 15 minute timestep for the period of 1/1/2012 to 3/31/2015 (example: Figure 20).
80
Figure 19 - Humboldt Bay EFDC model outline and sub-bay flux line map (Anderson,
2015).
81
Figure 20 - Example intra-bay flow rates for one tide cycle on January 1, 2012 from
EFDC hydrodynamic model (Anderson, 2015); positive values denote flood tide and
negative values denote ebb tide.
Watershed Runoff Volumes
Sub-watershed areas were estimated using the USGS National Hydrography
Dataset (NHD) and Watershed Boundary Dataset (WBD) vector file polygons for the
Humboldt Bay watershed. In the cases of Mad River Slough/Liscom Slough, Jacoby
Creek/McDaniel's Slough, and Jolly Giant Creek/Butcher's Slough, the Humboldt Bay
WBD polygon had to be subdivided further to delineate these sub-watersheds as they are
not detailed in the original WBD polygon set. These additional sub-watersheds were
delineated in order to specify a watershed area for grab samples that were collected at the
point of discharge into Humboldt Bay. It should be noted that Mad River Slough is not a
typical watershed, it is more of a brackish slough with minimal streamflow and is mostly
influenced by tidal flows; however, due to the amount of agricultural lands draining into
the slough, it is treated as a typical stream flow for the purposes of this nutrient budget.
82
Due to lack of direct flow measurements for many freshwater creeks entering
Humboldt Bay, an estimation of runoff flows was made using data from the nearby
USGS streamflow gaging station on Little River (Table 20). The station provides
average daily streamflow data (USGS, 2015) that were applied to each sub-watershed of
Humboldt Bay. The Little River watershed is similar in size and location (approximately
6 Nmi north) to the Humboldt Bay sub-watersheds, and should have similar geologic,
runoff, and precipitation characteristics. Average daily streamflow for Little River was
divided by the area of the watershed to get a flow rate per unit surface area; this value
was then multiplied by the surface area of each sub-watershed of Humboldt Bay to get an
average daily flow rate for each freshwater stream entering the Bay.
Table 20 - Surface area and streamflow characteristics for each stream entering Humboldt
Bay and nearby Little River.
Name
Surface Area1
(Mm2)
Minimum2
(m3/s)
Average2
(m3/s)
Maximum2
(m3/s)
Little River 116 0.074 2.726 68.244
Mad River Slough 22 0.014 0.509 12.743
Jane's Creek 12 0.008 0.292 7.304
Jolly Giant Creek 5 0.003 0.110 2.750
Jacoby Creek 52 0.033 1.229 30.756
Rocky/Washington Gulches 8 0.005 0.176 4.418
Freshwater Creek 147 0.093 3.453 86.438
Elk River 145 0.092 3.406 85.271
Little Salmon Creek 48 0.030 1.124 28.139 1WBD (2015); 2USGS (2015)
83
Precipitation Volumes
Average monthly precipitation for the period of record (1886 to 2015) collected
by the National Weather Service at Woodley Island in Eureka was applied to the surface
area of each sub-bay to estimate hydraulic loads to the Bay from direct precipitation.
While this hydraulic load does not carry any significant nutrient loads, it is included to
serve as a point of relative comparison for other hydraulic loads. It should be noted that
monthly precipitation during the period of study varied greatly from the historic averages
(0% to 388%); therefore the historic average was used as a point of relative comparison
instead of the anomalous (lower) recent values.
Ocean Nutrient Loads
Nutrient measurements collected inside the Entrance Bay within one hour of high
tide are considered representative of nearshore waters as the large volume of water
entering the Bay during each tide cycle likely replaces much of the volume of the
Entrance Bay. Mass loading to Humboldt Bay and individual compartments from
nearshore waters were calculated using the sum of the flood tide volumes (Anderson,
2015), tidal flushing rates for each sub-bay (Anderson, 2010), and nutrient concentrations
near the Bay entrance from various datasets (Wiyot Tribe Natural Resources Department,
2015; this study). Flushing rates from Anderson (2010) were provided for Arcata Bay,
Entrance Bay, and South Bay; a flushing rate for the Main Channel was calculated as the
volume-weighted average of the Entrance Bay (0.31/tide cycle) and Arcata Bay (0.02/tide
cycle) flushing rates since it connects the two (0.14/tide cycle); and a flushing rate for
84
Humboldt Bay was calculated as a volume-weighted average of all sub-bay flushing rates
(0.12/tide cycle). The sample standard deviation reported for ocean nutrient loading
represents inter-annual variability in annual and seasonal loading from two years of
nutrient data collected (n = 2).
Wastewater Nutrient Loads
Wastewater loading for the AWTF was calculated from daily flow rate data and
weekly nutrient concentration data. Daily nutrient concentrations were linearly
interpolated and multiplied by daily flow rates to estimate daily discharge loads for
ammonium-nitrogen, nitrate-nitrogen, and orthophosphate-phosphorus. The results of the
linear interpolation were then summed on a monthly basis for the period of record
(approximately four years of weekly ammonium and nitrate data collected between April
2011 and May 2015, and nearly three years of weekly phosphate data collected between
October 2010 and August 2013) and used to calculate average monthly and annual
loadings to Arcata Bay (City of Arcata, 2015).
Wastewater loading for the EWTF was calculated from monthly ammonium-
nitrogen and flow rate data (collected between January 2010 and June 2015), and a single
measurement for nitrate-nitrogen and orthophosphate-phosphorus collected on August
31, 2015 (City of Eureka, 2015). This single measurement may not represent the average
effluent nitrate or phosphate concentrations of the EWTF, possibly resulting in a
significant over or under-estimation. Daily nutrient concentrations and flow rates were
linearly interpolated and multiplied to estimate daily discharge loads for ammonium-
85
nitrogen, nitrate-nitrogen, and orthophosphate-phosphorus. The standard deviation
reported for wastewater nutrient loading represents inter-annual variability between
approximately three years of data (n = 3).
Watershed Nutrient Loads
Watershed loading was calculated using estimated daily inflow rates for each
stream based on individual watershed size, scaled by the flow rate at the nearby USGS
Little River stream gaging station (USGS, 2015), and average nutrient concentrations
taken from available data (Hurst, 2015 b.). Due to the lack of nutrient data from the
surrounding watershed, average nutrient concentrations were applied to the entire
watershed and were not varied with time. However, the hydraulic loads do vary with
time, increasing and decreasing nutrient loads to the Bay from the watershed in direct
proportion to the calculated flow rates. It remains unclear whether nutrient loads vary
between sub-watersheds due to differences in land use.
Sixteen samples collected at Freshwater Slough had low enough salinity (below
5.3 ppt) to indicate sufficient freshwater runoff without significant interference from Bay
water. These samples were collected between December 2012 and November 2014
(Hurst, 2015 b.). Typical Bay salinity is closer to that of the ocean, approximately 34
ppt, such that selecting for low salinity samples at watershed discharge locations would
more accurately indicate the freshwater runoff from the watershed. The standard
deviation reported for watershed nutrient loading represents inter-annual variability
between approximately two and a half years of data (annual, n = 2; upwelling and runoff
86
seasons, n = 3); data collection began during the upwelling season of 2012 and ended
during the runoff season of 2015 such that there are two annual means and three seasonal
means.
Phytoplankton Uptake
Phytoplankton carbon uptake rates were calculated using an average between high
(10.9 g C/hr/g Chl-a) and low (1.7 g C/hr/g Chl-a) nutrient assimilation ratios for
chlorophyll-a measured by Harding (1973) and Ryther and Yentsch (1957), respectively.
Assimilation rates for nitrogen and phosphorus were determined using the Redfield ratio
of 106:16:1 (C:N:P) from Fleming (1940), and silicon uptake rates were determined
using a 1:1 (N:Si) uptake ratio for diatoms suggested by Brzezinski (1985). Silicon is
included in the phytoplankton uptake estimations to account for any diatom blooms that
may occur. Diatoms are only one species of phytoplankton and may not be the dominant
species at all times, therefore the application of silicon uptake by diatoms to all
phytoplankton uptake calculations likely results in an overestimation of silicon uptake.
Average monthly chlorophyll-a concentrations were calculated for Arcata Bay,
Entrance Bay, South Bay, and the Main Channel using multiple datasets at various
locations over a period of many years in some cases. Arcata Bay data include all samples
collected from the Mad River Slough, Indian Island, McDaniel's Slough, Indian/Woodley
Island Channel, Arcata Channel, Bird Island, and Mad River Slough Channel sample
sites between October 2007 and February 2015 (n = 302). Entrance Bay samples include
all data collected at the Bay entrance sample site between October 2007 and February
87
2015 (n = 76). South Bay data include all samples collected from the Hookton Slough
and South Bay sample sites between October 2012 and February 2015 (n = 42). Main
Channel data include all samples collected from the Eureka Channel, Samoa Channel,
and Main Channel sample sites between October 2012 and February 2015 (n = 101). All
water quality data are listed in Appendix B.
Sample frequency varied from 1-4 times monthly. Average chlorophyll-a
concentrations and uptake rates were applied to average monthly volumes of each sub-
bay using output from a hydrodynamic model for Humboldt Bay (Anderson, 2015);
average monthly volumes approximate the MSL volume of each bay. Note that this
assumes complete mixing and homogeneous uptake by chlorophyll-a throughout the
water column. This condition is not likely the case since light attenuation in the deeper
channels and bays may limit phytoplankton uptake and production, however, a more
precise spatial and temporal model of the vertical and horizontal distribution of spectral
qualities that occurred is beyond the scope of this project. This assumption may result in
an over-estimation of phytoplankton production in the Bay.
The standard deviation reported in phytoplankton production was calculated using
the percent relative sample standard deviation from the mean of the two uptake rates
proposed by Ryther and Yentsch (1957) and Harding (1973) of 73%. Sample standard
deviations were also calculated for the inter-annual variation between the two years of
data and ranged from 17-70%; these values were all less than the relative sample standard
deviation due to the range in uptake rates, so the latter was used as the more conservative
estimate of uncertainty.
88
Macroalgae Uptake
Macroalgae nutrient uptake in Humboldt Bay was calculated using the areal
distribution of macroalgal mats in Humboldt Bay estimated by Schlosser and Eicher
(2012), monthly production rates measured by Pregnall and Rudy (1985), and the
stoichiometric ratio of nutrients in macroalgae of 640:42:1 (C:N:P) estimated by Duarte
(1992). Schlosser and Eicher (2012) estimated an areal distribution of macroalgae in
Arcata Bay, Entrance Bay, and South Bay to be 4.18 Mm2, 0.58 Mm2, and 3.96 Mm2,
respectively. Pregnall and Rudy (1985) indicated monthly macroalgae production for the
months of May through November resulting in a growing season production distribution
(Table 21). Standard deviation reported in macroalgae production was calculated using
the percent relative sample standard deviation (% RSD) from the mean reported by
Pregnall and Rudy (1985).
Table 21 - Monthly macroalgae production rates measured in Coos Bay, Oregon; % RSD
is the percent of the standard deviation relative to the mean.
Month
Macroalgae Production1
(g C/m2)
Standard Deviation1
(g C/m2) % RSD
May 24.9 20.6 83%
June 135.5 81.3 60%
July 285.2 131.1 46%
August 369.2 193.8 52%
September 224.8 70.9 32%
October 80.4 33.7 42%
November 8.5 3.5 41% 1Pregnall and Rudy (1985)
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Eelgrass Uptake
Average monthly eelgrass biomass accumulation measured in Humboldt Bay
(Table 22) by Harding (1973) have been applied to more recent surveys of eelgrass bed
distribution in Arcata Bay, South Bay, and Entrance Bay of approximately 14.48 Mm2,
7.88 Mm2, and 0.50 Mm2 respectively, made by Schlosser and Eicher (2012) to calculate
current potential eelgrass production in each bay. Using elemental ratios of carbon,
nitrogen, and phosphorus of 246:14:1 (C:N:P) measured by Fourqurean et al. (1997) in
eelgrasses of Tomales Bay (approximately 200 miles south of Humboldt Bay), monthly
and annual eelgrass uptake was calculated for Humboldt Bay. Standard deviation
reported in eelgrass production was calculated using the percent relative sample standard
deviation from the mean elemental composition by percent of dry weight reported by
Fourqurean et al. (1997) for carbon, nitrogen, and phosphorus (0.6%, 0.07%, and 0.02%
respectively). The standard deviation associated with inter-annual variation in spatial
distribution and density of eelgrass beds is likely much greater than the standard
deviation reported here, though no data on these phenomena could be located for
Humboldt Bay.
Harding (1973) only measured biomass between April and August, representing
the majority of the growing season in northern California for eelgrass of April through
September (NMFS, 2014), though Harding's data indicate eelgrass biomass was
decreasing during August so biomass accumulation for April through July is assumed to
be the total annual biomass increase. Fourqurean et al. (1997) found that elemental ratios
in eelgrass varied temporally and spatially, and eelgrass beds can expand and contract
90
significantly in one year such that the estimates of production listed in Table 22 may vary
significantly from year to year.
Table 22 - Average monthly eelgrass production rates measured in Arcata Bay and South
Bay.
Month
Eelgrass Production1
(g C/m2)
April 116
May 109
June 209
July 131
August 0 1Harding (1973)
Sediment Flux
Areal sediment flux rates of nitrate, ammonium, phosphate, and silicate measured
by Sin et al. (2007) for microalgae covered intertidal mud flats in Yaquina Bay Oregon
were applied to the approximate surface area of intertidal mud flats in Humboldt Bay to
estimate sediment fluxes. Sin et al. (2007) measured flux rates approximately every other
month for one year under both light and dark conditions such that diurnal and seasonal
variation in sediment fluxes could be calculated for Humboldt Bay. Months that were not
measured by Sin et al. (2007) were linearly interpolated between measurements to
generate a monthly set of sediment flux rates for both light and dark periods (Table 23
and Table 24). Values measured by Sin et al. (2007) were multiplied by the average
number of light and dark hours per day for each month, and the number of days per
month to estimate monthly sediment fluxes for nitrate, ammonium, phosphate, and
91
silicate. Intertidal mud flat surface area in Humboldt Bay was calculated as the
difference between MLLW and MHHW surface area of each sub-bay from a
hydrodynamic model for Humboldt Bay (Anderson, 2015). Standard deviation reported
for seasonal and annual sediment fluxes are with respect to the mean of monthly values
reported by Sin et al. (2007).
Table 23 - Monthly light and dark period intertidal sediment flux rates for nitrate and
ammonium; values in bold are actual measurements, values in italics are linearly
interpolated between measured values (bold).
Nitrate
(µmol/m2/hr)
Nitrate
(µmol/m2/hr)
Ammonium
(µmol/m2/hr)
Ammonium
(µmol/m2/hr)
Month Light Dark Light Dark
October -20.5 -21.5 -2.5 22.5
November1 -11.0 -22.0 -10.0 45.0
December -10.5 -21.0 -31.0 32.5
January1 -10.0 -20.0 -52.0 20.0
February -15.0 -10.0 -35.2 -52.0
March -20.0 -15.5 -18.4 -27.5
April1 -25.0 -9.0 -1.7 24.6
May -30.5 -26.5 7.5 21.5
June1 -36.0 -44.0 16.7 18.3
July -45.3 -59.0 16.3 49.3
August1 -54.7 -74.0 16.0 80.3
September1 -30.0 -21.0 5.0 0.0 1Sin et al. (2007)
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Table 24 - Monthly light and dark period intertidal sediment flux rates for phosphate and
silicate; values in bold are actual measurements, values in italics are linearly interpolated
between measured values (bold).
Phosphate
(µmol/m2/hr)
Phosphate
(µmol/m2/hr)
Silicate
(µmol/m2/hr)
Silicate
(µmol/m2/hr)
Month Light Dark Light Dark
October 0.0 -0.5 -32.5 -14.5
November1 0.0 1.0 -40.0 0.0
December -3.7 6.5 -20.0 141.5
January1 -7.4 12.0 0.0 283.0
February -4.6 -7.4 -8.3 0.0
March -1.8 -6.6 -16.7 -4.1
April1 1.0 -5.8 -25.0 -8.3
May -0.5 -5.0 -59.0 -12.4
June1 -2.0 -4.3 -93.0 -16.6
July -1.3 -3.5 -70.3 -20.7
August1 -0.7 -2.7 -47.7 -24.9
September1 0.0 -1.9 -25.0 -29.0
1Sin et al. (2007)
Denitrification
Denitrification in Humboldt Bay was calculated using an average of the three
estimates for Tomales Bay presented by Dollar et al. (1991) and Smith et al. (1991).
Dollar et al. (1991) estimated denitrification in Tomales Bay of between 1.2-1.3
mmol/m2/d (average 1.25 mmol/m2/d) by applying stoichiometric principles of plankton
uptake of carbon, nitrogen, and phosphorus through direct measurement of sediment
nutrient fluxes. Smith et al. (1991) estimated a denitrification rate of 3.1 mmol/m2/d for
93
the same system at the same time using a whole system nutrient budget technique. Direct
measurement of sediment fluxes may result in high or low estimates of whole-system
denitrification due to local anomalies (Dollar et al., 1991); the whole-system nutrient
budget approach may also contain significant uncertainty due to a lack of direct
measurement of fluxes. Therefore an average of the two estimates (1.25 mmol/m2/d and
3.1 mmol/m2/d) is used to estimate denitrification in Humboldt Bay (2.2 mmol/m2/d)
using a sample standard deviation of 1.3 mmol/m2/d. The average denitrification rate is
applied to the MHHW surface area of Humboldt Bay. Applying both denitrification and
sediment nitrate flux may overlap with respect to nitrate uptake by the sediments, though
there remains uncertainty as to the source of nitrate for denitrification. The linkage
between the two processes of sediment nitrate uptake for algae production and
denitrification is organic matter which is not assessed during this analysis; therefore, both
processes are included to account for this uncertainty. If nitrate uptake by sediments
includes nitrate flux for denitrification, then there will be a partial overlap since sediment
flux includes algae uptake. However if denitrification is linked to nitrification of
ammonium in sediments and not from the water column, then the two processes are de-
coupled via organic matter generation and breakdown such that for the purposes of
estimating DIN uptake they are at least partially independent forms of uptake.
94
RESULTS
The general progression of data presented in the following sections begins with a
classification of the two main seasons with respect to dissolved inorganic nutrient
concentrations. This is followed by evidence supporting previous conclusions that
dissolved inorganic nitrogen (DIN) is the limiting nutrient in Humboldt Bay. Followed
by a description of the level of eutrophication in Humboldt Bay with respect to
chlorophyll-a and dissolved oxygen concentrations established by the National Estuarine
Eutrophication Assessment (Bricker et al., 1999; Bricker et al., 2003; Bricker et al.,
2007). Then a characterization of processes regulating dissolved inorganic nutrients is
examined using data collected at adjacent low and high tides along a longitudinal transect
from the Bay entrance to upper Arcata Bay providing evidence for nutrient cycling in
Humboldt Bay. This is followed by a mass quantification of major nutrient sources and
uptake, using nutrient concentrations and hydraulic fluxes that are described in detail
previously. Finally, the mass budgets of DIN and DIP are presented.
Atmospheric nitrogen fixation and oyster production calculations indicate these
are minor contributors to the nutrient budgets so they have been omitted for
simplification, although a discussion of potential oyster impacts on phytoplankton
populations is included. Nitrite is typically a minor dissolved inorganic nitrogen
constituent in marine waters as an intermediate between ammonium and nitrate
conversion during nitrification and denitrification (Bianchi, 2013). Nitrite was a minor
constituent in most samples (typically less than 10% of nitrate) with the exception of
95
samples where nitrate was depleted. However, nitrite did not exceed 0.6 µM (8.4 µg
N/L) in all Bay entrance samples (n = 111) or 2.1 µM (29.4 µg N/L) in all samples inside
the Bay (n = 444). Therefore nitrite is reported as a part of the sum of nitrate and nitrite.
Upwelling Season Response
The upwelling season (April-September) has been previously defined previously
with respect to seasonal properties of the Bakun upwelling index near Humboldt Bay, and
supported by findings of previous studies discussed in the Review of Literature. The
following results support the characterization of the upwelling season in Humboldt Bay
with respect to dissolved inorganic nutrient concentrations near the Bay entrance and
Bakun upwelling indices. Average seasonal nutrient concentrations in each sub-bay are
also presented to provide a relative characterization of each within the Bay.
Nitrate concentrations as high as 34 µM (0.48 mg N/L) have been measured in
upwelled waters off of the Oregon coast (Sigleo et al., 2005) and the highest nitrate
concentration measured near the entrance to Humboldt Bay was 26 µM (0.36 mg N/L) on
February 21, 2013 (Wiyot Tribe Natural Resources Department, 2015). Average
upwelling season nitrate concentrations were significantly higher near the Bay entrance
than inside the Bay as a result of upwelled nutrients in nearshore waters and significant
uptake of nutrients inside Humboldt Bay (Figure 21 and Figure 22).
Silicate concentrations were significantly higher in Arcata Bay and South Bay
than near the Bay entrance with the highest average silicate concentrations occurring in
South Bay (Figure 21). Since there are no wastewater inputs in South Bay, higher silicate
96
concentrations may be attributable to natural variation in watershed geology and not to
wastewater discharge. Greater silicate concentrations inside Humboldt Bay compared
with nearshore concentrations indicates there is a significant internal source of silicate in
the system. This source may be mineralization of silicate in sediments from accumulated
watershed runoff particulate matter or diatoms from nearshore production, although the
actual source of this silicate is not clear from data presented in this study. Silicate
concentrations decreased near the Bay entrance during the upwelling season due to
diatom production in nearshore waters (Figure 23). However, early season upwelling
events indicate that upwelling is a significant source of silicate to the Bay when
production is low. Silicate and nitrate show a similar seasonal pattern of decreasing
significantly during the upwelling season near the Bay entrance as diatoms uptake nitrate
and silicate in a 1:1 stoichiometric ratio (Figure 22 and Figure 23). This indicates that
diatoms are a major phytoplankton species influencing nutrient uptake in nearshore
waters and Humboldt Bay.
Ammonium concentrations are much lower than silicate and nitrate
concentrations in nearshore waters and increase less during upwelling events (Figure 24).
Ammonium uptake by phytoplankton during the upwelling season is also significantly
less than nitrate and silicate, though this may be complicated by re-mineralization of
ammonium from phytoplankton biomass following uptake of nitrate from upwelling.
Ammonium concentrations were also greater inside Arcata Bay compared with South
Bay and nearshore waters (Figure 21) indicating a significant source of ammonium exists
97
in Arcata Bay. This source is likely from re-mineralization of accumulated material in
Arcata Bay as opposed to freshwater sources as will be discussed later.
Phosphate concentrations are lower than silicate, nitrate, and ammonium in
nearshore waters, although phosphate also shows signs of increasing during non-
productive season upwelling events and being assimilated by phytoplankton during the
productive part of the upwelling season (Figure 25). Phosphate is assimilated by
phytoplankton at a much lower ratio with nitrogen, which explains the relatively low
decrease in phosphate concentrations during the productive upwelling season compared
with nitrate. Greater concentrations of phosphate were also measured in Arcata Bay than
in South Bay or nearshore waters (Figure 21), although as mentioned previously with
respect to ammonium, this source is likely from re-mineralization of accumulated
material in the Bay and not from freshwater sources as will be discussed later.
Figure 21 - Average upwelling season nutrient concentrations in each sub-bay between
2007 and 2015 (Hurst, 2009; Wiyot Tribe Natural Resources Department, 2015; this
study).
98
Figure 22 - Average monthly high tide nitrate concentrations at the Bay entrance and
upwelling indices for water years 2008, 2009, 2013, and 2014 (Wiyot Tribe Natural
Resources Department, 2015; this study; PFEL, 2015).
Figure 23 - Average monthly high tide silicate concentrations at the Bay entrance and
upwelling indices for water years 2008, 2009, 2013, and 2014 (Wiyot Tribe Natural
Resources Department, 2015; this study; PFEL, 2015).
99
Figure 24 - Average monthly high tide ammonium concentrations at the Bay entrance and
upwelling indices for water years 2013, and 2014 (Wiyot Tribe Natural Resources
Department, 2015; this study; PFEL, 2015).
Figure 25 - Average monthly high tide phosphate concentrations at the Bay entrance and
Bakun upwelling indices (Wiyot Tribe Natural Resources Department, 2015; this study;
PFEL, 2015).
100
Runoff Season Response
The runoff season (October-March) has been previously defined with respect to
seasonal properties of precipitation in Humboldt Bay. The following results support the
characterization of the runoff season in Humboldt Bay with respect to dissolved inorganic
nutrient concentrations at Mad River Slough and total monthly precipitation at Woodley
Island. Average seasonal nutrient concentrations in each sub-bay are also presented to
provide a relative characterization of each within the Bay.
Average runoff season nitrate concentrations are significantly higher in Arcata
Bay, the Main Channel, and South Bay compared with the upwelling season as biological
productivity decreases (Figure 26). Nitrate concentrations are higher near the Bay
entrance during the runoff season indicating nearshore waters still contain significant
amounts of nitrate compared with waters inside the Bay. Waters in Mad River Slough
increase in nitrate concentration following precipitation events indicating that watershed
runoff may contribute significantly more nitrate during the runoff season than during the
upwelling season (Figure 27).
101
Figure 26 - Average seasonal nitrate concentrations in Humboldt Bay measured between
2007 and 2015 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources Department,
2015; this study).
Figure 27 - Average monthly nitrate concentrations at Mad River Slough and total
monthly precipitation at Woodley Island (WRCC, 2015) and for water years 2008, 2009,
2013, and 2014 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study).
102
Average runoff season ammonium concentrations are greater in Arcata Bay and
South Bay compared with upwelling season concentrations due to decreased biological
productivity (Figure 28). Higher ammonium concentrations in Arcata Bay, South Bay,
and the Main Channel are due to re-mineralization of accumulated organic matter and not
necessarily the direct result of freshwater discharge as will be discussed later.
Ammonium concentrations show an opposite trend with distance from the Bay entrance
compared with nitrate (Figure 26 and Figure 28, respectively). This is due to nitrate
being the major DIN constituent in nearshore waters and ammonium increasing in
significance inside the Bay due to uptake of nitrate and re-mineralization of accumulated
organic matter producing ammonium. Waters near Mad River Slough also indicate that
ammonium concentrations increase following precipitation and runoff events indicating
ammonium discharge from watershed runoff may increase significantly during the runoff
season (Figure 29).
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Figure 28 - Average seasonal ammonium concentrations in Humboldt Bay measured
between 2007 and 2015 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study).
Figure 29 - Average monthly ammonium concentrations at Mad River Slough and total
monthly precipitation at Woodley Island (WRCC, 2015) for water years 2008, 2009,
2013, and 2014 (Hurst, 2015 b.; Wiyot Tribe Natural Resources Department, 2015; this
study).
104
Average seasonal silicate concentrations in Humboldt Bay increase with distance
from the Bay entrance, with the greatest concentrations occurring during the runoff
season and in South Bay (Figure 30). During the upwelling season, lower silicate
concentrations in nearshore waters compared with those inside the Bay are due to diatom
production. During the runoff season, higher silicate concentrations inside the Bay are
due to mineralization of particulate matter. Sediment loads from the watershed may
contain significant amounts of siliceous particulate matter, although the relative
contribution of this source compared to diatomaceous material accumulated during the
productive upwelling season is not clear from data collected during this study. Silicate
concentrations in Mad River Slough generally increase following precipitation events
(Figure 31), indicating that watershed contributions of dissolved silicate may be
significant; although as mentioned previously, there may be significant amounts of
siliceous material contained in watershed sediment loads as well.
2014 was an exceptional year with below average precipitation and high silicate
concentrations at Mad River Slough during the upwelling season (Figure 31). This is in
contrast to the two other years of data that indicate a clear relationship of increased runoff
and silicate exists. Mad River Slough does not necessarily represent a typical watershed
input to Humboldt Bay as it is largely tidally influenced and collects drainage from a
large flat area of agricultural pastureland. However, this site has one of the longest and
most continuous nutrient datasets for a watershed runoff site in Humboldt Bay.
Insufficient data exist to determine seasonal patterns of DIN, phosphate, and silicate from
freshwater runoff sources to Humboldt Bay as all of the samples from Mad River Slough
105
had salinity greater than or equal to 20 ppt. The cause of the increased silicate
concentrations in Mad River Slough during the upwelling season of 2014 is not clear.
Figure 30 - Average seasonal silicate concentrations in Humboldt Bay measured between
2007 and 2015 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources Department,
2015; this study).
Figure 31 - Average monthly silicate concentrations at Mad River Slough and total
monthly precipitation at Woodley Island (WRCC, 2015) for water years 2008, 2013, and
2014 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources Department, 2015;
this study).
106
Average seasonal phosphate concentrations increased with distance from the Bay
entrance into Arcata Bay and were similar in South Bay and the Bay entrance, indicating
that there is a source of phosphate in Arcata Bay (Figure 32). Phosphate concentrations
were lower throughout the Bay during the runoff season indicating that an increased
supply from upwelling in nearshore waters and higher re-mineralization as temperatures
increase play an important role in generating phosphate in the system. As will be
discussed later, phosphate loads from freshwater sources decrease significantly during the
upwelling season. Mad River Slough phosphate concentrations decreased significantly
during the runoff season indicating that watershed runoff is a minor contributor of
phosphate to the system (Figure 33). Increasing phosphate concentrations in Mad River
Slough during the upwelling season indicates decomposition and re-mineralization of
organic matter may significantly increase watershed phosphate contributions during the
upwelling season. However, this does not take into account lower watershed runoff flow
rates during the upwelling season that may counteract increasing concentrations to
moderate the seasonal changes in mass discharge.
107
Figure 32 - Average seasonal phosphate concentrations in Humboldt Bay measured
between 2007 and 2015 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study).
Figure 33 - Average monthly phosphate concentrations at Mad River Slough and total
monthly precipitation at Woodley Island (WRCC, 2015) for water years 2008, 2009,
2013, and 2014 (Hurst, 2009; Hurst, 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study).
108
Nitrogen Limitation
Seasonal nitrogen limitation in Humboldt Bay has been determined by Pequegnat
and Butler (1981) using bioassay tests, and is supported by more recent observations by
Martin and Hurst (2008). Nitrogen is typically the limiting nutrient in healthy estuarine
and coastal waters (Bricker et al., 2007). Stoichiometric nitrogen to phosphorus ratios
(N:P) in Humboldt Bay provide additional support for the limiting role of nitrogen
(Figure 34). The N:P ratio in upwelled ocean water is approximately 15:1, similar to the
stoichiometric ratio found in phytoplankton biomass of 16:1 (Fleming, 1940). This
famous ratio is called the "Redfield Ratio" after Redfield (1934) who first proposed the
stoichiometric relationship of nitrogen to phosphorus in phytoplankton, although he
initially proposed a ratio of 20:1. Fleming (1940) later modified this relationship using a
wider collection of measurements. Due to the similarity between the natural N:P ratio in
upwelled seawater and the stoichiometric composition of phytoplankton, as
phytoplankton assimilate DIN and phosphate, the relative concentration in the water
should remain the same. An N:P ratio below 16:1 indicates DIN will be limiting to
phytoplankton production (Ryther and Yentsch, 1957). While phytoplankton will
assimilate ammonium before nitrate (Dortch et al., 1982), ammonium is generally a
minor constituent in nearshore waters compared with nitrate (Figure 35).
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Figure 34 - Stoichiometric nitrogen to phosphorus (N:P) ratios in Arcata Bay and
Entrance Bay during calendar year 2014; the "Redfield ratio" of 16:1 represents the
stoichiometric N:P ratio in phytoplankton biomass.
Figure 35 - Nitrate was typically the major dissolved inorganic nitrogen species in coastal
waters entering the Bay between October 2012 and February 2015 (Wiyot Tribe Natural
Resources Department, 2015; this study).
110
Eutrophication Level
Data from estuaries throughout the United States used for the National Estuarine
Eutrophication Assessment by the National Oceanic and Atmospheric Administration
classify systems with typical chlorophyll-a concentrations between 0-5 µg/L and 5-20
µg/L as low and medium eutrophication respectively (Bricker et al. 1999; Bricker et al.,
2003; Bricker et al. 2007). An average of maximum annual chlorophyll-a concentrations
in Humboldt Bay measured during WY 2013 and WY 2014 (Figure 36) indicate the
system is in the medium range of eutrophication during the upwelling season (Table 25).
The Entrance bay, Main Channel, and South Bay remain in the low eutrophication range
during the runoff season, while Arcata Bay is in the medium eutrophication range year-
round. Maximum chlorophyll-a concentrations were measured in the Main Channel
indicating phytoplankton blooms from nearshore waters increase productivity inside the
Bay at times. Lower concentrations in Arcata Bay than the Main Channel indicate that
nutrient limitation and grazing may play significant roles in reducing phytoplankton
populations in Arcata Bay. The highest chlorophyll-a concentrations measured in
Humboldt Bay of 20 µg/L occurred in the Main Channel on April 26, 2013 and June 21,
2013.
111
Figure 36 - Average maximum annual upwelling and runoff season chlorophyll-a
concentrations in Humboldt Bay measured during WY 2013 and WY 2014 (Hurst 2015
b.; Wiyot Tribe Natural Resources Department, 2015; this study).
Table 25 - Eutrophication classification system based upon maximum annual
chlorophyll-a concentrations in an estuary developed by the National Estuarine
Eutrophication Assessment (Bricker et al., 2003).
Eutrophication Status Maximum Chlorophyll-a
Low 0-5 µg/L
Medium 5-20 µg/L
High 20-60 µg/L
Hyper-eutrophic > 60 µg/L
A second eutrophication classification developed by the National Estuarine
Eutrophication Assessment uses bottom water dissolved oxygen (Bricker et al. 1999;
Bricker et al., 2003; Bricker et al. 2007). This classification indicates that Humboldt Bay
exhibits biologically stressful concentrations of dissolved oxygen in the Main Channel
112
during the upwelling season, although the rest of the Bay remains healthy with respect to
this classification (Figure 37). Note that this classification system uses bottom water
dissolved oxygen as the indicator (Table 26) whereas dissolved oxygen concentrations
measured in Humboldt Bay represent water column measurements and may not be
directly comparable. Bottom water and water column values may vary significantly due
to sunlight availability, water depth, vegetative cover, and biological activity occurring at
the sediment water interface. The relationship between bottom water and water column
dissolved oxygen in Humboldt Bay has not been documented.
Figure 37 - Minimum dissolved oxygen concentrations in Humboldt Bay measured
during WY 2013 and WY 2014 (Hurst 2015 b.; Wiyot Tribe Natural Resources
Department, 2015; this study).
113
Table 26 - Eutrophication classification system based upon minimum annual dissolved
oxygen concentrations in an estuary developed by the National Estuarine Eutrophication
Assessment (Bricker et al., 2003).
Eutrophication Status Minimum Bottom Water
Dissolved Oxygen
Anoxic 0 mg/L
Hypoxic 0-2 mg/L
Biologically Stressful 2-5 mg/L
Climatic Anomalies
Upwelling and runoff seasons are typical, based on decades of atmospheric data,
and can vary significantly from year to year. Extreme variations in climatic conditions
can result in abnormal environmental conditions of nutrient loading and biological
production. Annual precipitation was below normal for all four of the water years when
nutrient data were collected in Humboldt Bay (Table 27). Low precipitation translates to
reduced runoff and potentially fewer nutrients entering Humboldt Bay from the
surrounding watershed.
Solar insolation is another important environmental factor influencing
productivity in Humboldt Bay. As a coastal region in northern California, Humboldt Bay
can experience cool foggy summers and cool wet winters. While solar insolation data for
the Humboldt Bay region only dates back to May 2007 (SoRMS, 2015), WY 2014 was
approximately 140% of the annual average insolation with significantly higher insolation
occurring during the winter of 2013-2014 (Figure 38). Increased solar insolation during
WY 2014 may have resulted in increased biological nutrient uptake.
114
Table 27 - Total annual precipitation at Woodley Island during the sampling period was
between 50-84% of the average for the period of record.
Water Year
(Oct-Sept)
Total Annual
Precipitation1 (in)
Percent of Average
for Period of Record
1886-2014 39.5 (average) 100%
2008 33.1 84%
2009 30.3 77%
2013 32.0 81%
2014 19.8 50%
2015 (Oct-Feb) 24.8 91% 1WRCC (2015)
Figure 38 - Total monthly direct normal solar insolation for water years 2008, 2009,
2013, and 2014 (SoRMS, 2015).
Intertidal Properties
Samples collected along a longitudinal transect from the Bay entrance to Arcata
Bay during adjoining high and low tides provides evidence for temporal and spatial
115
distribution of nutrient sources and uptake. Temperature and salinity affect water density
that may change the mixing properties of the Bay with nearshore currents. The extent to
which Bay waters mix with nearshore currents is not well understood and likely varies
seasonally as nearshore and inner Bay conditions change. Spatial and intertidal
temperature gradients in the Bay are greatest during the summer as sunlight and warm air
temperatures heat water flowing over the shallow intertidal mud flats (Figure 39). Note
that Figure 39 shows the location of samples collected along the longitudinal transect
analyzed throughout the following section. Salinity gradients between the Bay entrance
and Arcata Bay are greatest during the winter when increased precipitation and runoff
results in increased dilution (Figure 40). Nearshore waters near the Bay entrance are also
lower in salinity during the runoff season due to dilution of nearshore currents flowing
northward from the Eel River approximately eight miles to the south of the mouth of
Humboldt Bay. The mouth of the Mad River 15 miles to the north may also influence
conditions at the Bay entrance when nearshore currents flow southward in the summer.
116
Figure 39 - Longitudinal and intertidal temperature gradients are greatest during the
summer as water is heated over the shallow intertidal mud flats at low tide.
Figure 40 - Longitudinal and intertidal salinity gradients are greatest during the runoff
season as freshwater runoff dilutes Arcata Bay.
117
Chlorophyll-a
Chlorophyll-a concentrations measured using an in-situ data sonde at Indian
Island typically peak at high tides and reach minima at low tides (Figure 41). Continuous
measurements at Indian Island represent the water that moves between Arcata Bay and
the Main Channel as these two bodies may not be completely mixed. During ebbing
tides, water from Arcata Bay is moving into the Main Channel. Decreasing chlorophyll-a
concentrations during these periods indicates lower phytoplankton populations exist
inside the Bay. Grazing of phytoplankton by filter-feeding shellfish and zooplankton
(Cloern, 1991), and reduced production due to nutrient limitation may significantly
reduce phytoplankton populations in Arcata Bay, although the relative extent to which
these processes contribute to reducing phytoplankton populations is not clear.
A carrying capacity analysis was completed for the recent proposed expansion of
shellfish mariculture in Arcata Bay and concluded that even with a twelve-fold increase
in shellfish production, phytoplankton food sources would not be significantly affected
(H.T. Harvey & Associates, 2015). This study suggested that while farmed shellfish may
filter large volumes of water and remove a significant amount of phytoplankton, the high
turnover rate of phytoplankton (doubling more than two times per day) would more than
account for removal by farmed filter feeders. This study did not account for grazing by
native shellfish populations and zooplankton such that the extent to which grazing
actually occurs in Arcata Bay is not clear. The dynamics of phytoplankton reproduction
and consumption by filter feeders is not directly addressed in this analysis, however the
export of oysters from Arcata Bay has been estimated to be minor compared with other
118
types of uptake (approximately 0.05% of DIN uptake, and 0.04% of phosphate uptake
annually in Arcata Bay).
Figure 41 - Chlorophyll-a concentrations at Indian Island peak at high tide indicating
phytoplankton populations inside the Bay may originate from closer to the ocean or that
predation inside the Bay reduces concentrations (Wiyot Tribe Natural Resources
Department, 2015).
During the upwelling season of 2014, phytoplankton production increased in
nearshore waters with higher chlorophyll-a concentrations occurring near the Bay
entrance during high tide, and significantly lower production occurring inside the Bay at
low tide (Figure 42). This is a strong indication that phytoplankton production begins in
nearshore waters and decreases once inside the Bay. The combination of upwelled
nutrients and increased sunlight during the upwelling season resulted in increased
phytoplankton production, though concentrations inside the Bay remained low (less than
5 µg/L) with respect to eutrophication metrics established by Bricker et al. (2003).
During the non-upwelling/runoff season of October through March, phytoplankton
production remained low throughout the Bay and in nearshore waters due to reduced
nutrient and sunlight availability.
119
Figure 42 - High and low tide chlorophyll-a concentrations along a longitudinal transect
from the Bay entrance to Arcata Bay.
120
Nitrate
Increased phytoplankton production in June 2014 (Figure 42) followed an early
season upwelling event in March 2014, indicated by increased nitrate concentrations near
the Bay entrance at high tide (Figure 43). As phytoplankton production increased in June
2014 (Figure 42), nitrate concentrations near the Bay entrance decreased due to
assimilation by phytoplankton (Figure 43). Upwelling conditions were observed again on
June 16, 2014, indicated by elevated nitrate concentrations near the Bay entrance and into
the Main Channel (Figure 43). Elevated levels of nitrate in the Entrance Bay and Main
Channel coincide with high chlorophyll-a concentrations (Figure 42) indicating nitrate
was in excess of phytoplankton demand in nearshore waters. High productivity of
phytoplankton, eelgrass, macroalgae, and denitrification inside Arcata Bay during this
time resulted in low nitrate concentrations at low tide. Limited exchange between the
Entrance Bay, Main Channel, and Arcata Bay increase residence times in each
compartment and may play a significant role in lower nitrate concentrations as more time
is allowed for uptake and removal. Low nitrate concentrations in Arcata Bay at low tide
are also a strong indicator that freshwater sources have little or no impact on ambient
nitrate concentrations in the Bay.
During the low runoff season of January 2014, low nitrate concentrations inside
Arcata Bay compared with the Bay entrance may be attributed to denitrification, as
production and assimilation would have been minimal at this time. This study did not
determine nitrate-specific uptake by various processes as no data are available for
denitrification or uptake of nitrate in Humboldt Bay. However, the mass of nitrate-
121
nitrogen removed annually and seasonally via denitrification is estimated using literature
values from a similar system and is reported in later sections.
The runoff season including January 2014 resulted in below-average precipitation,
while the following runoff season including February 2015 saw above-normal
precipitation. These phenomena may explain why nitrate concentrations decreased with
distance from the Bay entrance in January 2014, while in February 2015 nitrate
concentrations increased with distance from the Bay entrance (Figure 43). Lower runoff
in January 2014 may have reduced the watershed runoff nitrate load to the Bay, resulting
in lower nitrate concentrations compared with normal runoff conditions the following
year. On October 12, 2014 nitrate concentrations increased with distance from the Bay
entrance following 2.5 inches of rainfall on September 24, 2014. This evidence indicates
that freshwater sources may have a significant impact on nitrate concentrations in Arcata
Bay during the runoff season.
The Average AWTF nitrate discharge during the runoff season is approximately
1.6 Mg nitrate-N whereas watershed runoff contributes approximately 34 Mg nitrate-N
indicating that watershed runoff is the major freshwater contributor of nitrate to Arcata
Bay during the runoff season and not the AWTF. An average runoff season watershed
discharge to Arcata Bay is approximately 0.766 Mm3/d and the average watershed nitrate
concentration used in this analysis is 17.7 µM (248 µg N/L). Applying these values to
the MSL volume of Arcata Bay results in a potential nitrate concentration increase of
0.35 µM (4.9 µg N/L) during a typical runoff season day. The average runoff season
ambient nitrate concentration in Arcata Bay is 9.1 µM (127 µg N/L) indicating watershed
122
runoff may account for less than 4% of the nitrate in Arcata Bay on a single day. Arcata
Bay does not completely flush during a single day so nutrients may accumulate in the
Bay over a longer period. This is also complicated by the fact that uptake of nutrients in
the Bay may provide temporary storage and periodic release. These calculations are
intended to serve as a comparison of the relative magnitude of nutrient inputs to the Bay
with respect to the volume and ambient concentrations in the Bay.
123
Figure 43 - High and low tide nitrate concentrations along a longitudinal transect from
the Bay entrance to Arcata Bay.
124
Silicate
In July and August 2014, silicate concentrations at the Bay entrance fell to below
limiting concentrations for diatom production of 2 µM (28 µg N/L; Fisher et al., 1992;
Figure 44), indicating the phytoplankton bloom in nearshore waters (indicated by an
increase in chlorophyll-a, Figure 42) may have been predominantly diatomaceous.
During this period nitrate was similarly low (below the 2 µM limiting concentration) at
high tide indicating that both could have been limiting factors to nearshore phytoplankton
production. However, inside Arcata Bay only silicate was elevated while nitrate
remained low throughout, indicating nitrate was the limiting nutrient inside the Bay.
Nitrate may be assimilated by various types of aquatic vegetation inside the Bay and is
also removed via denitrification, whereas silicate is not significantly impacted by either
of these processes. This is likely the reason why nitrate concentrations decrease in the
Bay while silicate concentrations remain elevated.
During the low runoff season experienced in January 2014, silicate concentrations
were approximately equal throughout Bay and during both tides, whereas during the
following normal runoff season of 2014-2015, silicate concentrations increased with
distance from the Bay entrance and at low tide. This indicates that during the runoff
season silicate concentrations in the Bay increase due to watershed runoff. Applying the
average watershed runoff silicate concentration used in this analysis of 127 µM (1.78 mg
Si/L) and the average runoff season daily watershed inflow to Arcata Bay of 0.766
Mm3/d to the MSL volume of the Bay results in a potential increase in silicate
concentration of 2.5 µM (71 µg Si/L). The ambient water column silicate concentration
125
in Arcata Bay during the runoff season is 29.3 µM (256 µg Si/L) indicating that
watershed runoff may account for 9% of the daily silicate in in the Bay. Note that this
calculation does not account for reduced tidal exchange and biological cycling that may
significantly increase or decrease the actual impact of inputs on ambient concentrations in
the Bay.
126
Figure 44 - High and low tide silicate concentrations along a longitudinal transect from
the Bay entrance to Arcata Bay.
127
Ammonium
Ammonium concentrations generally increased with distance from the Bay
entrance and were higher at low tides indicating a significant internal source exists
(Figure 45). Ammonium discharge from the AWTF decreases significantly during the
summer due to plant uptake in the natural treatment system (average ammonium
concentration decreases from 237 mM, 16.9 mg N/L, to 85 mM, 6.1 mg N/L,
respectively). Applying these concentrations to the average daily discharge from the
AWTF results in potential daily increases in ammonium concentration in the MSL
volume of Arcata Bay of 0.3 µM (3.7 µg N/L) during the runoff season and 0.1 µM (1.1
µg N/L) during the upwelling season. The average ammonium concentration in Arcata
Bay during the runoff season was 6.8 µM (95 µg N/L) and during the upwelling season
was 5.8 µM (80.6 µg N/L), indicating that the AWTF discharge may account for
approximately 4% and 1% of the daily ammonium in Arcata Bay during the runoff and
upwelling seasons respectively.
Ammonium concentrations throughout the Bay remained above limiting
concentrations for phytoplankton production (2 µM, 28 µg N/L; Fisher et al., 1988) all
year with the exception of February 1, 2015 at high tide. However, phytoplankton
production will decrease at concentrations up to 5 µM (Hurst, 2015 a.), while 2 µM is the
concentration where phytoplankton production essentially ceases completely. Minimum
ammonium concentrations in Arcata Bay during the upwelling and runoff seasons of
2014 were 3.4 µM and 1.1 µM, respectively (47.6 µg N/L and 15.4 µg N/L, respectively)
with averages of 6.8 µM and 7.1 µM, respectively (95.2 µg N/L and 99.5 µg N/L,
128
respectively). Marine plants typically assimilate ammonium preferentially to nitrate at
ammonium concentrations above 0.5 µM (7 µg N/L; Eppley et al., 1969; Strickland et al.,
1969) indicating that ammonium plays a significant role in limiting production in the
Bay.
129
Figure 45 - High and low tide ammonium concentrations along a longitudinal transect
from the Bay entrance to Arcata Bay.
130
Phosphate
Phosphate concentrations inside Arcata Bay remained in excess of metabolic
requirements for phytoplankton production at all times (0.2 µM, 6.2 µg P/L; Fisher et al.,
1992) with the exception of the July 2014 diatom bloom near the Bay entrance and in the
Main Channel (Figure 46). Phosphate concentrations generally increased with distance
from the Bay entrance and at low tides during the upwelling season (April-September),
indicating a high degree of uptake near the Bay entrance and contribution of internal
sources in the Bay.
Following the low runoff season including January and March 2014, phosphate
concentrations decreased slightly with distance from the Bay entrance (Figure 46),
whereas during the normal runoff season of 2014-2015, concentrations increased with
distance from the Bay entrance. This indicates freshwater sources may increase
phosphate concentrations in the Bay during the runoff season. However, as mentioned
previously, phosphate concentrations decreased at Mad River Slough and Freshwater
Slough with increasing precipitation suggesting wastewater from the AWTF may
influence phosphate concentrations in Arcata Bay during the runoff season. On
December 30, 2014 concentrations were higher at high tide than at low tide between the
Bay entrance and Arcata Bay, although it should be noted that this is the only sample
where there was a single tide cycle between low tide and high tide samples. The low tide
sample was collected on December 30th in the afternoon, and the high tide sample was
collected on December 31st in the morning, although it is unclear whether this caused the
difference in phosphate concentrations.
131
Figure 46 - High and low tide phosphate concentrations along a longitudinal transect
from the Bay entrance to Arcata Bay.
132
Nutrient Sources
Major dissolved inorganic nutrient inputs to Humboldt Bay include ocean influx,
wastewater discharge, watershed runoff, and sediment flux. It should be noted that other
major sources of nutrient inputs to bays and estuaries not considered here include
particulate organic and inorganic matter, and dissolved organic matter. These nutrient
forms can be a source of dissolved inorganic nutrients as material decays and dissolved
inorganic nutrients are mineralized. Also note that sediment flux estimates use values
from another similar estuarine system on the Oregon coast applied to Humboldt Bay.
Ocean Influx
Average seasonal dissolved inorganic nutrient loading to Humboldt Bay increases
by between 4-40% during the upwelling season compared to the runoff season due to
nutrient rich upwelled ocean water (Table 28). Chlorophyll-a production increases by
approximately 290% on average during the upwelling season as nearshore phytoplankton
production is stimulated by the upwelled nutrients and increased sunlight availability.
During the upwelling season, DIN loading increases by approximately 20% (ammonium
by 40% and nitrate + nitrite by 15%), phosphate increases by approximately 12%, and
silicate-Si increases by approximately 4%.
133
Table 28 - Average annual and seasonal chlorophyll-a and nutrient loading to Humboldt
Bay (and standard deviations).
Constituent
Upwelling Season
(Apr-Sep)
Runoff Season
(Oct-Mar) Annual
Chlorophyll-a1 (Mg) 188
(± 28)
48
(± 8)
237
(± 36)
Nitrate + Nitrite1 (Mg N) 6,151
(± 1,298)
5,329
(± 1,008)
11,480
(± 291)
Ammonium1 (Mg N) 1,682
(± 152)
1,202
(± 217)
2,883
(± 369)
Phosphate1 (Mg P) 1,404
(± 440)
1,250
(± 249)
2,653
(± 191)
Silicate1 (Mg Si) 16,860
(± 3,964)
16,138
(± 776)
32,998
(± 3,188) 1This study, Wiyot Tribe Natural Resources Department (2015)
Wastewater Discharge
Nutrient data from the AWTF have been made available by the City of Arcata for
the purposes of this study (City of Arcata, 2015). Ammonium and nitrate measurements
have been collected on a weekly basis since April 2011, and phosphate concentrations
were collected on a weekly basis between October 2010 and August 2013. Ammonium
is the most significant source of DIN from the AWTF during the high discharge runoff
season (Figure 47). Seasonal fluctuations in ammonium, nitrate, and phosphate
concentrations from the AWTF are due, in part, to fluctuations in flow rates resulting
from increased influent to the facility, and direct rainfall on the approximately 90 acres of
ponds and wetlands (Figure 48). Multiplying the nutrient concentration by the flow rate
to get a mass discharge rate significantly alters the apparent discharge of nutrients from
the treatment facility, especially with respect to phosphate (Figure 49). Phosphate
concentrations increase during the summer when flow rates are lower (Figure 47),
134
however, the mass discharge of phosphate from the facility increases during the winter as
biological activity slows and decomposition of organic matter releases phosphate into the
water column (Figure 49). Since ammonium and nitrate concentrations increase during
the winter due to reduced biological uptake and storage, the seasonal pattern of higher
discharge concentration and mass remains the same for these constituents.
Figure 47 - AWTF effluent ammonium, nitrate, and phosphate concentrations between
April 2011 and April 2015 (City of Arcata, 2015); note wastewater concentrations are
typically reported as mg/L.
135
Figure 48 - AWTF daily discharge flow rates between April 2011 and April 2015 indicate
significant seasonal fluctuation of discharge flow rates with peaks occurring in the winter
time due to increased inflow and direct precipitation on the 90 acre facility (City of
Arcata, 2015); note wastewater flow rates are typically reported as million gallons per
day (MGD).
Figure 49 - AWTF effluent ammonium, nitrate, and phosphate mass loads between April
2011 and April 2015 (City of Arcata, 2015); note Mg refers to million grams, equivalent
to one metric ton.
136
Monthly ammonium concentrations and flow rates were made available for the
EWTF by the City of Eureka dating back to January 2010, and a single measurement of
nitrate and orthophosphate was collected on August 31, 2015 (City of Eureka, 2015).
The EWTF utilizes a more conventional treatment system resulting in less seasonal
variation than the AWTF (Figure 50). Eureka's system includes a nitrifying trickling
filter that converts ammonium to nitrate, which explains why the EWTF effluent
ammonium is lower and nitrate is higher than the AWTF, even though the AWTF has a
lower average inflow rate (Table 29). Seasonal fluctuation in effluent flow from the
EWTF is also much less than the AWTF due to much less open surface wetland and pond
area for collecting precipitation. Less variation in the effluent flow rate also results in the
same pattern of discharge concentration and mass load (Figure 50).
Figure 50 - EWTF ammonium discharge concentration and mass load indicate seasonal
peaks may occur during the summer, and that there is little effect of dilution (City of
Eureka, 2015); note wastewater flow rates are typically reported as million gallons per
day (MGD).
137
Table 29 - Nutrient concentration and loading ranges (and means) for the AWTF and
EWTF; only one value for nitrate and phosphate were collected for EWTF effluent on
August 31, 2015.
Wastewater
Treatment Facility Units Phosphate-P Nitrate-N Ammonium-N
AWTF1 mM 0.07 - 0.25
(0.15)
0.01 - 0.31
(0.06)
0.01 - 2.68
(0.75)
AWTF1 mg/L 2.1 - 7.8
(4.6)
0.2 - 4.3
(0.9)
0.2 - 37.5
(10.5)
AWTF1 Mg/d 0 - 0.12
(0.03)
0 - 0.06
(0.01)
0 - 0.62
(0.09)
EWTF2 mM 0.31 1.06 0.01 - 0.93
(0.12)
EWTF2 mg/L 9.7 14.9 0.1 - 13.0
(2.5)
EWTF2 Mg/d 0.10 - 0.36
(0.17)
0.15 - 0.55
(0.26)
0 - 0.21
(0.04) 1City of Arcata, 2015; 2City of Eureka, 2015
The potential increase in nitrogen concentration of Arcata Bay due to wastewater
discharge from the AWTF and EWTF estimated by Pequegnat and Butler (1981) of 0.5
µM (7.0 µg N/L), is an order of magnitude greater than what is now the case given
current conditions. Wastewater loading implied by Pequegnat and Butler (1981) was
between 0.34-0.60 Mg N/d and is comparable to the current combined average annual
DIN discharge of 0.403 Mg N/d load from the AWTF and EWTF. However, since the
EWTF does not discharge to Arcata Bay, a more accurate estimation of this calculation
using the average DIN discharge load from the AWTF of 0.09 Mg N/d (City of Arcata,
2015) and a MHW volume of approximately 66.9 Mm3 (Anderson, 2015), results in a
0.10 µM (1.35 µg N/L) potential increase in the concentration of Arcata Bay. This
calculation was strictly done for comparison to previous methods. This assumes the Bay
138
is completely mixed, does not account for any of the numerous processes involved in
nitrogen cycling in the Bay. Discussion of the comparative magnitude of the wastewater
DIN load to Arcata Bay with other sources and types of uptake will be discussed in a
later section.
The EWTF discharges directly into the Main Channel near the Bay entrance on
outgoing tides only such that their nutrient load may have a minimal impact on Arcata
Bay and South Bay. The MHHW-MLLW tidal prism in the Main Channel is
approximately 11 Mm3 whereas the MLLW volume of the Entrance Bay is approximately
40 Mm3 indicating the EWTF discharge may not completely exit the Bay before the tide
reverses direction. DIN loading from the EWTF is primarily in the form of nitrate-N as
their system utilizes a nitrifying trickling filter that converts much of the ammonium to
nitrate. The EWTF only discharges on outgoing tides such that any measureable effects
of their discharge on waters near the Coast Guard sample station and Bay entrance
sample station would be detectable near low tide. Of the 12 low tide samples collected at
these locations, there is no discernable pattern of elevated nitrate levels from the EWTF
discharge. The maximum discharge from the EWTF is approximately 0.04 Mm3/d (9.8
MGD), nitrate-N measured in their effluent was approximately 1.1 mM (15 mg N/L), the
average flow rate from the Main Channel to the Entrance Bay is 242 Mm3/d (63,930
MGD) resulting in a possible increase in concentration of the main channel flow of
approximately 0.16 µM (2.3 µg N/L) assuming complete mixing. An increase in nitrate
concentration of this magnitude would be virtually impossible to attribute to the EWTF
discharge apart from other possible causes.
139
Annual ammonium and nitrate mass discharges from the AWTF and EWTF
indicate that the AWTF is a much more significant source of ammonium while the EWTF
is potentially a more significant source of nitrate (Table 30 and Table 31). It should be
noted that the calculation of nitrate-N discharged from the EWTF is based upon a single
measurement of nitrate-N concentration and the actual annual average may vary
significantly from the measured value (Table 31). The AWTF utilizes a natural
constructed wetland treatment system that exhibits significant seasonal variability of
ammonium discharge increasing approximately 335% during the runoff season as the
vegetation in the system senesces, decreasing DIN uptake and releasing nitrogen stored in
decaying biomass through re-mineralization (Table 30). The average annual hydraulic
discharge from the EWTF is over two times the average annual hydraulic discharge from
the AWTF, and the estimated phosphate discharge from the EWTF (based on a single
phosphate sample) is over four times that of the AWTF.
Table 30 - AWTF annual and seasonal hydraulic and nutrient loading to Humboldt Bay
(and standard deviations).
Constituent
Upwelling Season
(Apr-Sep)
Runoff Season
(Oct-Mar) Annual
Discharge1 (Mm3) 0.98 (± 0.25) 1.61 (± 0.34) 2.58 (± 0.62)
Nitrate1 (Mg N) 0.81 (± 0.07) 1.64 (± 0.56) 2.44 (± 0.59)
Ammonium1 (Mg N) 6.98 (± 5.17) 30.39 (± 8.59) 37.38 (± 14.91)
Phosphate1 (Mg P) 4.65 (± 0.55) 8.55 (± 1.76) 13.19 (± 2.21) 1City of Arcata, 2015
140
Table 31 - EWTF annual and seasonal hydraulic and nutrient loading to Humboldt Bay
(and standard deviations); note that only one measurement of nitrate and phosphate were
available so the uncertainty reported for these values is attributed completely to the
variation in flow rate used to calculate the mass discharge.
Constituent
Upwelling Season
(Apr-Sep)
Runoff Season
(Oct-Mar) Annual
Discharge1 (Mm3) 2.94 (± 0.49) 3.36 (± 0.54) 6.30 (± 0.66)
Nitrate1 (Mg N) 43.80 (± 7.31) 50.15 (± 8.04) 93.95 (± 9.84)
Ammonium1 (Mg N) 8.80 (± 3.46) 6.04 (± 4.12) 14.85 (± 4.19)
Phosphate1 (Mg P) 28.42 (± 4.74) 32.54 (± 5.22) 60.96 (± 6.39) 1City of Eureka, 2015
Watershed Runoff
Freshwater runoff nutrient concentration data from the watersheds surrounding
Humboldt Bay are sparse and limited to unpublished reports that differ in location,
frequency, time of year, and sampling method. Data from Hurst (2015 b.) only includes
16 samples from one location over the course of two years when salinity was below 5.3
ppt. During the runoff season, the average salinity in Arcata Bay is approximately 30 ppt
(Hurst, 2015 b.; Wiyot Tribe Natural Resources Department, 2015; this study) such that
any sample from the surrounding sloughs with salinities of 5.3 ppt would theoretically
contain approximately 80% runoff and 20% Bay water. An average of the 16 low salinity
samples is used for all mass calculations such that mass discharge is directly proportional
to the flow rates applied to each daily discharge calculation. Watershed hydraulic loads
were calculated using average daily flow rates from the nearby Little River stream gaging
station scaled by the size of individual watersheds.
141
Nutrient concentrations in Freshwater Slough samples collected by Hurst (2015
b.) follow similar seasonal patterns with respect to precipitation and runoff discussed
previously for samples collected at Mad River Slough. Data collected at Mad River
Slough contained approximately four years of samples providing better insight into inter-
annual variability in watershed runoff, although none of those samples contained
sufficiently low salinity to be used to represent freshwater runoff. Data collected at
Freshwater Slough contain only approximately two years of data (n = 55) with an average
salinity of 17.3 ppt indicating significant influence by freshwater runoff occurs at this
site.
Average annual ammonium and phosphate inputs to Humboldt Bay from
watershed runoff are similar (13.8 Mg N/yr and 11.1 Mg P/yr, respectively) while nitrate
inputs are approximately five times greater (77.1 Mg N/yr; Table 32). Nitrate in
watershed runoff may be from oxidized organic nitrogen and ammonium coming from
urban runoff, septic tank leachate, agricultural fertilization, agricultural livestock manure,
and naturally occurring organic matter (Castro et al., 2003). Phosphate in freshwater
runoff may come from decomposition and re-mineralization of naturally occurring and
anthropogenic organic matter, or weathering of geologic formations that may be
increased by anthropogenic behaviors such as deforestation (Froelich et al., 1982;
Nedwell et al., 1999). Dissolved silicate is the most abundant dissolved inorganic
nutrient supplied by the watershed of Humboldt Bay, although particulate silicon in
sediment loads from the watershed may provide a more significant source of silicon to
the Bay. Particulate silicon may mineralize once inside the Bay to release dissolved
142
silicate, however particulate silicon contributions from the watershed have not been
determined during this study. Silicon is the second most abundant element in the Earth's
crust being transported from the land to the sea by weathering of natural geologic
formations and watershed runoff (Bianchi, 2013).
Average seasonal watershed runoff to Humboldt Bay may increase by nearly four
times during the runoff season, significantly increasing the nutrient loads associated with
this source (Table 33 and Table 34). Due to the method of calculating these loads, i.e.,
using the same flow rate series and a single nutrient concentration value, all percent
seasonal changes in loading are equal. Hydraulic and nutrient discharges may increase
by nearly 300% during the runoff season in comparison with the low runoff upwelling
season.
Table 32 - Annual watershed hydraulic and nutrient loading to Humboldt Bay (and
standard deviations).
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Main
Channel
Discharge1 (Mm3/yr) 307.3
(± 49.6)
172.1
(± 27.4)
33.5
(± 5.5)
101.6
(± 16.7)
Nitrate + Nitrite2 (Mg N/yr) 77.1
(± 62.1)
43.2
(± 34.8)
8.4
(± 6.8)
25.5
(± 20.5)
Ammonium2 (Mg N/yr) 13.8
(± 7.8)
7.7
(± 4.4)
1.5
(± 0.8)
4.5
(± 2.6)
Phosphate2 (Mg P/yr) 11.1
(± 9.3)
6.2
(± 5.2)
1.2
(± 1.0)
3.7
(± 3.1)
Silicate2 (Mg Si/yr) 1,093.4
(± 377.5)
612.4
(± 211.4)
119.3
(± 41.2)
361.6
(± 124.8) 1USGS (2015); 2Hurst (2015 b.)
143
Table 33 - Upwelling season (April-September) watershed hydraulic and nutrient loading
to Humboldt Bay (and standard deviations).
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Main
Channel
Discharge1 (Mm3) 63.7
(± 36.7)
35.7
(± 20.3)
7.0
(± 4.1)
21.1
(± 12.4)
Nitrate + Nitrite2 (Mg N) 16.0
(± 12.9)
9.0
(± 7.2)
1.7
(± 1.4)
5.3
(± 4.3)
Ammonium2 (Mg N) 2.9
(± 1.6)
1.6
(± 0.9)
0.3
(± 0.2)
0.9
(± 0.5)
Phosphate2 (Mg P) 2.3
(± 1.9)
1.3
(± 1.1)
0.3
(± 0.2)
0.8
(± 0.6)
Silicate2 (Mg Si) 226.7
(± 78.3)
127.0
(± 43.8)
24.7
(± 8.5)
75.0
(± 25.9) 1USGS (2015); 2Hurst (2015 b.)
Table 34 - Runoff season (October-March) watershed hydraulic and nutrient loading to
Humboldt Bay (and standard deviations)
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Main
Channel
Discharge1 (Mm3) 243.6
(± 36.7)
136.5
(± 20.3)
26.6
(± 4.1)
80.6
(± 12.4)
Nitrate + Nitrite2 (Mg N) 61.1
(± 12.9)
34.2
(± 7.2)
6.7
(± 1.4)
20.2
(± 4.3)
Ammonium2 (Mg N) 10.9
(± 1.6)
6.1
(± 0.9)
1.2
(± 0.2)
3.6
(± 0.5)
Phosphate2 (Mg P) 8.8
(± 1.9)
4.9
(± 1.1)
1.0
(± 0.2)
2.9
(± 0.6)
Silicate2 (Mg Si) 866.7
(± 78.3)
485.5
(± 43.8)
94.6
(± 8.5)
286.7
(± 25.9) 1USGS (2015); 2Hurst (2015 b.)
Sediment Flux
Intertidal sediments can uptake and release nutrients. Data published by Sin et al.
(2007) indicate that on an annual basis, sediments are a net source of ammonium only,
144
and provide net uptake for nitrate, phosphate, and silicate. For simplicity these data are
presented together in a later section for nutrient uptake.
Nutrient Uptake
Major types of dissolved inorganic nutrient uptake in Humboldt Bay have been
quantified including phytoplankton production, macroalgae production, eelgrass
production, sediment flux, and denitrification. These processes do not necessarily
represent permanent sinks as nutrient cycling is a highly dynamic and complex set of
processes. Assimilation by phytoplankton, macroalgae, and eelgrass may only act as a
temporary storage for nutrients; once the organisms die, their biomass will decay and part
of it will re-mineralize, releasing dissolved inorganic nutrients to the water column.
Denitrification is the only sink for DIN included in the mass budgets that results in
removal of DIN from the system. Export to the ocean is the only other significant
nutrient sink, however this has not been quantified due to complications of determining
mixing between nearshore waters and those of the Bay.
Phytoplankton Uptake
Phytoplankton nutrient mass uptake in each bay was calculated using the average
monthly volume of each bay (approximately the MSL volume) and average monthly
chlorophyll-a concentrations of each bay (Table 35). The Entrance Bay has the largest
volume (approximately 32% of the Humboldt Bay volume on average) and experiences
the highest average chlorophyll-a concentrations due to the high rate of exchange with
nearshore waters (Table 35). Arcata Bay and South Bay experience lower average
145
chlorophyll-a concentrations during the productive upwelling season compared with the
other sub-bays due to nutrient limitation, limited exchange with nearshore waters, and
zooplankton and shellfish grazing. Arcata Bay contains nearly all of the mariculture
shellfish in the Bay so it should be noted that the similarity between South Bay and
Arcata Bay indicates that mariculture has little impact on phytoplankton populations in
the Bay.
Table 35 - Average annual and seasonal chlorophyll-a concentrations for sub-bay and
average volume of each bay.
Constituent
Entrance
Bay
Arcata
Bay
Main
Channel
South
Bay
Average Volume1 (Mm3) 49 44 36 26
Average Annual
Chlorophyll-a Concentration (µg/L)2 3.3 2.3 3.2 2.3
Average Upwelling Season
Chlorophyll-a Concentration (µg/L)2 5.6 3.5 5.4 3.5
Average Runoff Season
Chlorophyll-a Concentration (µg/L)2 1.3 1.4 1.4 1.0
1Anderson (2015); 2 this study, Harding (1973), Hurst (2009), Hurst (2015 b.), Ryther and
Yentsch (1957), Wiyot Tribe Natural Resources Department (2015)
Uncertainty in phytoplankton nutrient uptake is approximately 73% of the mean
due to the wide range of uptake rates in the literature used in the calculations. Average
annual nitrogen, phosphorus, and silicon uptake by phytoplankton in the Entrance Bay is
approximately 51% greater than in Arcata Bay while the volume of the Entrance Bay is
only approximately 13% larger (Table 36). This indicates that phytoplankton production
in the Entrance Bay is higher than in Arcata Bay per unit volume which may be due to
nutrient limitation and phytoplankton grazing in Arcata Bay. Entrance Bay is highly
146
influenced by nearshore waters where phytoplankton production typically begins during
the upwelling season. While some of the organic phytoplankton biomass used to
calculate nutrient uptake is imported from nearshore waters, phytoplankton reproduction
rates of more than two times per day (H.T. Harvey & Associates, 2015) indicate that a
significant amount of biomass will be generated inside the Bay due to limited exchange
rates that result in residence times of up to 30 days (Anderson, 2010). As phytoplankton
populations enter the Bay, chlorophyll-a concentrations decrease moving through each
compartment from the Main Channel to Arcata Bay and South Bay due to grazing and
nutrient limitation (Table 35). Some of the phytoplankton biomass will re-mineralize and
some will either be stored in the biomass of grazers or in sediments as phytoplankton
settle out of the water column. The amount of re-mineralization relative to the amount of
phytoplankton biomass imported to the system is not clear. However, the high
reproduction rates suggest that the net effect of phytoplankton production in the Bay will
be a decrease in dissolved inorganic nutrient concentrations in the water column.
Therefore phytoplankton production inside Humboldt Bay is represented as a form of
dissolved inorganic nutrient uptake and not a source.
Average upwelling season phytoplankton production increases by over 330% in
Humboldt Bay over runoff season production (Table 37 and Table 38). Seasonal
production increases the most in the Main Channel and Entrance Bay (approximately
419% and 383%, respectively) with less seasonal fluctuation in Arcata Bay and South
Bay (244% and 291%, respectively), indicating the Entrance Bay and Main Channel are
more productive than Arcata Bay and South Bay during the upwelling season. Higher
147
relative seasonal productivity in the Main Channel than in South Bay may indicate a
higher degree of influence from nearshore waters. Further development of a model to
estimate phytoplankton nutrient uptake in Humboldt Bay could significantly decrease the
range of uncertainty associated with these estimations.
Estimating phytoplankton nutrient uptake and cycling in Humboldt Bay poses one
of the largest challenges due to their highly transient nature, high reproduction rate, and
soft tissue that readily re-mineralizes to form dissolved inorganic phosphorus and
nitrogen for re-uptake. Since phytoplankton production is much higher in nearshore
waters (as indicated by higher phytoplankton production rates near the Bay entrance), and
decreases significantly inside Humboldt Bay, it can be assumed that phytoplankton
import is a significant source of organic matter in the Bay. In the short-term,
phytoplankton can uptake significant amounts of inorganic nutrients, though in the long-
term they may be a significant source of nutrients.
Table 36 - Annual phytoplankton nutrient uptake for Humboldt Bay and sub-bays (and
standard deviations)*; note that silicon uptake assumes all phytoplankton are diatoms and
represents an upper estimation.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Nitrogen (Mg N/yr) 2,537
(± 1,851)
607
(± 443)
296
(± 216)
928
(± 677)
707
(± 516)
Phosphorus (Mg P/yr) 351
(± 256)
84
(± 61)
41
(± 30)
128
(± 94)
98
(± 71)
Silicon (Mg Si/yr) 5,088
(± 3,712)
1,216
(± 887)
593
(± 433)
1,860
(± 1,357)
1,418
(± 1,034) *this study, Harding (1973), Hurst (2009), Hurst (2015 b.), Ryther and Yentsch (1957), Wiyot
Tribe Natural Resources Department (2015)
148
Table 37 - Upwelling season phytoplankton nutrient uptake for Humboldt Bay and sub-
bays (and standard deviations)*.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Nitrogen (Mg N) 2,076
(± 1,514)
490
(± 358)
329
(± 240)
790
(± 576)
467
(± 341)
Phosphorus (Mg P) 287
(± 209)
68
(± 49)
45
(± 33)
109
(± 80)
65
(± 47)
Silicon (Mg Si) 4,163
(± 3,037)
983
(± 717)
659
(± 481)
1,583
(± 1,155)
937
(± 684) *this study, Harding (1973), Hurst (2009), Hurst (2015 b.), Ryther and Yentsch (1957), Wiyot
Tribe Natural Resources Department (2015)
Table 38 - Runoff season phytoplankton nutrient uptake for Humboldt Bay and sub-bays
(and standard deviations)*.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Nitrogen (Mg N) 492
(± 359)
150
(± 109)
60
(± 44)
164
(± 120)
118
(± 86)
Phosphorus (Mg P) 66
(± 48)
21
(± 15)
8
(± 6)
23
(± 17)
16
(± 12)
Silicon (Mg Si) 986
(± 720)
300
(± 219)
121
(± 88)
329
(± 240)
237
(± 173) *this study, Harding (1973), Hurst (2009), Hurst (2015 b.), Ryther and Yentsch (1957), Wiyot
Tribe Natural Resources Department (2015)
Macroalgae Uptake
Macroalgae uptake is calculated using monthly carbon uptake proposed by
Pregnall and Rudy (1985), the elemental ratio of carbon, nitrogen, and phosphorus in
macroalgae presented by Duarte (1992), and the approximate size of the algal mats
estimated by Schlosser and Eicher (2012). The uncertainty reported for calculations of
macroalgae production are a product of the standard error reported by Duarte (1992) for
the elemental composition of macroalgae by percent of dry weight.
149
Arcata Bay and South Bay account for approximately 94% of the total nutrient
uptake by macroalgal mats in Humboldt Bay, with the Entrance Bay accounting for only
6% (Table 39). Annual nutrient uptake in Arcata Bay and South Bay differs by only 5%
though the surface area of the intertidal mud flats in Arcata Bay is approximately twice
that of South Bay, indicating algal mat production may have a significantly larger impact
on nutrient uptake in South Bay with respect to the size of the Bay. Pregnall and Rudy
(1985) indicate that macroalgal mats growing in Coos Bay Oregon (approximately 150
miles north of Humboldt Bay) have a growing season between May and November such
that production in the runoff season (October-March) accounts for only approximately
8% of the total annual production (Table 40 and Table 41).
Macroalgal mats in Humboldt Bay are washed out of the Bay during late fall
storms that introduce high winds and rough waters to the Bay (Schlosser and Eicher,
2012). While a portion of the mats may remain in the Bay being re-mineralized to form
dissolved inorganic nutrients, much of the biomass is exported from the system.
However, the amount of macroalgal biomass exported from Humboldt Bay, and the
amount that remains a part of the food web inside the Bay is not documented.
Table 39 - Annual macroalgae nutrient uptake for Humboldt Bay and sub-bays (and
standard deviations)*.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Nitrogen (Mg N/yr) 755
(± 358)
362
(± 160)
343
(± 162)
50
(± 24)
Phosphorus (Mg P/yr) 40
(± 19)
19
(± 9)
18
(± 9)
2.7
(± 1.3) *Duarte (1992), Pregnall and Rudy (1985), Schlosser and Eicher (2012)
150
Table 40 - Upwelling season macroalgae nutrient uptake for Humboldt Bay and sub-bays
(and standard deviations)*.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Nitrogen (Mg N) 695
(± 333)
333
(± 160)
316
(± 151)
46
(± 22)
Phosphorus (Mg P) 37
(± 18)
18
(± 8)
17
(± 8)
2.4
(± 1.2) *Duarte (1992), Pregnall and Rudy (1985), Schlosser and Eicher (2012)
Table 41 - Runoff season macroalgae nutrient uptake for Humboldt Bay and sub-bays
(and standard deviations)*.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Nitrogen (Mg N) 59
(± 25)
29
(± 12)
27
(± 11)
4.0
(± 1.7)
Phosphorus (Mg P) 3.1
(± 1.3)
1.5
(± 0.6)
1.4
(± 0.6)
0.2
(± 0.1) *Duarte (1992), Pregnall and Rudy (1985), Schlosser and Eicher (2012)
Eelgrass Uptake
Average monthly eelgrass production was estimated using monthly biomass
production measured by Harding (1973), eelgrass bed areal estimates from Schlosser and
Eicher (2012), and the elemental composition of the dominant species of eelgrass in
Humboldt Bay (Zostera marina) reported by Fourqurean et al. (1997). Eelgrass is only
seasonally productive with no net production reported during the fall and winter between
August and March (Harding, 1973); therefore all of the annual eelgrass production occurs
during the upwelling season. Approximately 63% of all eelgrass production in Humboldt
Bay occurs in Arcata Bay, with 34% occurring in South Bay and only 2% estimated in
the Entrance Bay (Table 42). Production in Arcata Bay is approximately 85% higher
151
than in South Bay due to the larger size of the eelgrass beds reported by Schlosser and
Eicher (2012). Note that the small uncertainty reported in eelgrass production is due to
use of the standard error in measurements of eelgrass elemental composition (Fourqurean
et al., 1997) as this was the only estimate of uncertainty available for this calculation. No
information on inter-annual variability of eelgrass bed distribution in Humboldt Bay
could be located.
Eelgrass is similar to macroalgae in terms of potential export of nutrients from the
Bay. During the storms of late fall and winter, eelgrass beds are dislodged and
significant amounts of eelgrass are flushed out of the Bay on ebbing tides. Some of this
biomass may remain in the Bay being re-cycled as part of the benthic food web, though
the fraction of total eelgrass production exported and the fraction that remains is not
documented.
Table 42 - Annual eelgrass nutrient uptake for Humboldt Bay and sub-bays (and standard
deviations)*; note that reported eelgrass production only takes place during the upwelling
season (April-September) therefore the annual uptake is the upwelling season uptake.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Nitrogen (Mg N/yr) 301
(± 9)
191
(± 6)
104
(± 3)
6.5
(± 0.2)
Phosphorus (Mg P/yr) 49
(± 3)
31
(± 2)
17
(± 1)
1.1
(± 0.1) *Fourqurean et al. (1997), Schlosser and Eicher (2012)
Sediment Flux
Sediment flux may account for uptake and release of various nutrients; however,
for simplicity sediment flux data are presented here together. Sediment flux rates
152
measured by Sin et al. (2007) in Lower Yaquina Estuary, Oregon indicate sediments
uptake nitrate, phosphate, and silicate, and release ammonium during the upwelling
season (Figure 51). These data also indicate that sediments may be a periodic source of
phosphate and silicate, and uptake ammonium during the runoff season. Sediment flux
may account for a variety of processes such as denitrification, mineralization of organic
matter, algal uptake, adsorption, and desorption. For simplicity all of these processes
have been grouped into the general process of sediment flux, therefore estimates of
sediment flux in Humboldt Bay using values from a different system contain a high
degree of uncertainty. Sediment fluxes have been applied to the approximate surface area
of the intertidal mud flats between MHHW and MLLW in Humboldt Bay such that the
resulting fluxes are directly proportional to the amount of intertidal mud flats in each sub-
bay. These estimates do not include fluxes that may occur in sub-tidal sediments and do
not account for spatial variation due to differences in sediment type and cover.
On an annual basis, net nitrate flux is into the sediments (uptake) and is nearly
three times greater than ammonium flux from the sediments (release) indicating
Humboldt Bay's intertidal mud flats may provide significant storage for dissolved
inorganic nitrogen (Table 43). During the upwelling season, nitrate uptake is nearly
twice as great as ammonium release, resulting in significant sediment DIN uptake.
However, during the runoff season, higher net DIN uptake occurs due to ammonium
uptake. It should be noted that during the study conducted by Sin et al. (2007), used to
estimate sediment fluxes in Humboldt Bay, nitrate concentrations in the water column
increased during this period due to ocean upwelling, whereas nitrate concentrations in
153
Arcata Bay decrease during the upwelling season due to high productivity and limited
tidal exchange. Sediment nitrate uptake has been found to be proportional to water
column nitrate concentrations such that lower nitrate concentrations may result in lower
sediment flux rates (Boynton and Kemp, 1985). Therefore, estimates of sediment nitrate
uptake from Sin et al. (2007) may represent a high estimate.
Seasonal sediment ammonium fluxes change by approximately 460%, from
uptake (negative flux) during the runoff season, to release (positive flux) during the
upwelling season. Ammonium released from sediments may indicate that higher
temperatures during the upwelling season result in increased re-mineralization of
ammonium from decomposing organic matter. During this time, algal production is at a
maximum such that any increase in ammonium efflux from sediments would be in excess
of metabolic demand by benthic organisms.
Phosphate uptake by sediments may increase by approximately 330% during the
upwelling season (Table 44 and Table 45), due to either uptake by benthic algae or
increased chemical adsorption to ferric oxyhydrides that occurs in the presence of oxygen
(Conley et al., 1995). Average dissolved oxygen concentrations in the water column of
Humboldt Bay are higher during the runoff season. However, photosynthesizing algae on
the intertidal mud flats during the upwelling season produce oxygen that may increase
adsorption of phosphate. The difference between benthic dissolved oxygen and water
column dissolved oxygen has not been documented in Humboldt Bay therefore the
potential for phosphate adsorption has not been determined.
154
Silicate sediment flux changes from release (positive flux) during the runoff
season to uptake (negative flux) during the upwelling season (Figure 51). Silicate release
from sediments during the runoff season may be an indicator of mineralization of
particulate matter from watershed sediment loads or re-mineralization of diatomaceous
material accumulated during the upwelling season. Sediment loads from watershed
runoff may be a significant source of particulate silicon to the system that have not been
accounted for during this study. High silicate uptake during the upwelling season may be
due to benthic diatom production, although this form of uptake has also not been
determined in Humboldt Bay. Silicate release during the runoff season occurred during
December and January according to data gathered by Sin et al. (2007). The magnitude of
the release was equal to approximately 87% of the total uptake during the rest of the year,
and occurred following precipitation events between September and December. This
indicates that significant silicate release from sediments may be due to recently deposited
siliceous material from watershed runoff.
155
Figure 51 - Average monthly intertidal sediment nutrient fluxes using flux rates from Sin
et al. (2007) and the intertidal surface area of Humboldt Bay.
Table 43 - Annual sediment nutrient flux for Humboldt Bay and sub-bays (and standard
deviations)*; negative flux values indicate uptake by sediments.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Nitrate (Mg N/yr) -129
(± 52)
-83
(± 33)
-40
(± 16)
-1.4
(± 0.6)
-3.9
(± 1.6)
Ammonium (Mg N/yr) 33
(± 214)
21
(± 138)
10
(± 67)
0.4
(± 2.4)
1
(± 6)
Phosphate (Mg P/yr) -13
(± 37)
-8
(± 24)
-4
(± 12)
-0.1
(± 0.4)
-0.4
(± 1.1)
Silicate (Mg Si/yr) -34
(± 38)
-22
(± 24)
-11
(± 12)
-0.4
(± 0.4)
-1
(± 1) *Anderson (2015), Sin et al. (2007)
156
Table 44 - Upwelling season sediment nutrient flux for Humboldt Bay and sub-bays (and
standard deviations)*; negative flux values indicate uptake by sediments.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Nitrate (Mg N) -89
(± 66)
-58
(± 42)
-28
(± 20)
-1
(± 1)
-3
(± 2)
Ammonium (Mg N) 46
(± 559)
30
(± 361)
14
(± 175)
0.5
(± 6.1)
1
(± 17)
Phosphate (Mg P) -10
(± 46)
-6.6
(± 30)
-3
(± 15)
-0.1
(± 0.5)
-0.3
(± 1.4)
Silicate (Mg Si) -208
(± 171)
-134
(± 111)
-65
(± 54)
-2.3
(± 1.9)
-6
(± 5) *Anderson (2015), Sin et al. (2007)
Table 45 - Runoff season sediment nutrient flux for Humboldt Bay and sub-bays (and
standard deviations)*; negative flux values indicate uptake by sediments.
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Nitrate (Mg N) -40
(± 3)
-26
(± 2)
-13
(± 1)
-0.4
(± 0.03)
-1.2
(± 0.1)
Ammonium (Mg N) -15
(± 10)
-8
(± 6)
-4
(± 3)
-0.1
(± 0.1)
-0.4
(± 0.3)
Phosphate (Mg P) -2
(± 3)
-2
(± 2)
-1
(± 1)
-0.03
(± 0.03)
-0.1
(± 0.1)
Silicate (Mg Si) 174
(± 246)
112
(± 159)
54
(± 77)
2
(± 3)
5
(± 7) *Anderson (2015), Sin et al. (2007)
Denitrification
Annual denitrification in Humboldt Bay may account for approximately 768 Mg
N removal from the system (Table 46). No data were provided by Dollar et al. (1991) for
seasonal variation in denitrification determined for Tomales Bay, so upwelling and runoff
season denitrification are equal to one-half the annual estimate. Since the same areal
denitrification rate was applied to each sub-bay of Humboldt Bay, the relative
157
magnitudes of denitrification are proportional to the relative surface area of each bay.
Denitrification is assumed to be a benthic process that occurs due to various species of
bacteria in the sediments, thus denitrification rates are relative to the surface area of each
bay and not volume. Given the relative size of each sub-bay, Arcata Bay makes up
approximately 54% of the total estimated denitrification in Humboldt Bay, and South
Bay, Entrance Bay, and the Main Channel make up approximately 26%, 12%, and 9%
respectively.
The bacterial cycle of denitrification involves multiple steps and species of
bacteria, each of which is governed by different factors such as labile carbon availability,
alkalinity, temperature, and inorganic nitrogen availability. The method used here to
estimate denitrification in Humboldt Bay simplifies all of these processes into a single
empirical rate estimate from a similar system that does not account for any of these
factors.
Table 46 - Annual denitrification in Humboldt Bay and sub-bays (and standard
deviations).
Constituent
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
DIN* (Mg N/yr) 768
(± 462)
414
(± 249)
198
(± 119)
90
(± 54)
66
(± 40) *Anderson (2015), Dollar et al. (1991), Smith et al. (1991)
Water Budget
Average annual inflows to Humboldt Bay (Table 47) indicate that total tidal
inflow is over two orders of magnitude greater than all other inflows combined, with
158
wastewater being the smallest contributor. Tidal exchange volume for the whole Bay,
approximately 14% of the total tidal inflow for Humboldt Bay, is over one order of
magnitude greater than all other sources combined. The tidal exchange volume is a
product of the total tidal influx and the individual exchange rates for each sub-bay. This
indicates that even with limited tidal exchange, the ocean end member is still the most
substantial hydraulic input to Humboldt Bay.
Watershed flows contain were calculated using flow rates from nearby Little
River scaled by the size of each individual watershed and do not represent actual
streamflows from each source to the Bay. Watershed inflows estimated for Humboldt
Bay are equal to approximately 4% of the tidal exchange volumes, and are over 34 times
greater than wastewater inflows (Table 47).
Average annual wastewater inflows to Humboldt Bay are the smallest hydraulic
input compared with tidal exchange, watershed runoff, and precipitation (Table 47).
Wastewater is equal to approximately 0.1% of the estimated tidal exchange volumes, 3%
of watershed runoff, and 13% of precipitation falling directly on the Bay annually. In
Arcata Bay, the AWTF discharge is equal to approximately 0.4% of the estimated annual
tidal exchange volume, 1.5% of watershed runoff volumes, and 6.9% of direct
precipitation falling on Arcata Bay.
159
Table 47 - Annual water budget for Humboldt Bay (Mm3/yr); the Entrance Bay may be
influenced by Eel River water in the winter when nearshore currents flow northward
though it does not receive any direct river inputs.
Water Source
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Total Tidal Inflow1 66,874 35,653 17,272 67,558 42,293
Tidal Flushing2 8,299 594 617 21,112 6,131
Watershed Runoff3 307 172 34 NA* 102
Direct Precipitation4 69.3 37.4 17.9 8.1 5.9
WWTF5 8.88 2.58 NA NA 6.30
1Anderson (2015); 2Anderson (2010) and Anderson (2015); 3USGS (2015) and WBD (2015); 4WRCC (2015); 5City of Arcata (2015) and City of Eureka (2015)
Wastewater hydraulic loads increase by approximately 280% during the runoff
season due to infiltration in collection systems and direct precipitation on oxidation ponds
and constructed wetlands. Watershed runoff increases by nearly 300% during the runoff
season due to precipitation on the watershed, and precipitation directly falling on the Bay
increases by nearly 400% during the runoff season (Table 48 and Table 49). Lower
watershed runoff with respect to precipitation may be due to water that becomes
entrained in sediments and groundwater, terrestrial evaporation, or due to the indirect
method of using Little River flow data to calculate stream flows for Humboldt Bay.
Precipitation data, on the other hand, are from a weather station inside Humboldt Bay.
Discharge from the AWTF increases by approximately 65% during the runoff season due
to the large open water surface area of the pond and wetland treatment system
(approximately 90 acres, or 0.36 Mm2), and inflow and infiltration into the municipal
wastewater collection system. Discharge from the EWTF only increases by
160
approximately 15%, due to inflow and infiltration into their municipal wastewater
collection system. Tidal volumes change little between seasons due to the large
magnitude of the flow rates. Small seasonal variation in tidal flux is the result of varying
tidal elevations between seasons, and other environmental factors that may be included in
the hydrodynamic model from which they were derived.
Table 48 - Upwelling season water budget for Humboldt Bay (Mm3).
Water Source
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Total Tidal Inflow1 33,543 17,756 8,580 33,631 21,062
Tidal Flushing2 4,163 296 306 10,510 3,053
Watershed Runoff3 63.7 35.7 7.0 NA 21.1
Direct Precipitation4 11.7 6.3 3.0 1.4 1.0
WWTF5 3.91 0.98 NA NA 2.94
1Anderson (2015); 2Anderson (2010) and Anderson (2015); 3USGS (2015) and WBD (2015); 4WRCC (2015); 5City of Arcata (2015) and City of Eureka (2015)
Table 49 - Runoff season water budget for Humboldt Bay (Mm3).
Water Source
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Total Tidal Inflow1 33,331 17,897 8,692 33,927 21,232
Tidal Flushing2 4,136 298 310 10,602 3,078
Watershed Runoff3 244 136 27 NA 81
Direct Precipitation4 57.7 31.1 14.9 6.7 4.9
WWTF5 4.97 1.61 NA NA 3.36
1Anderson (2015); 2Anderson (2010) and Anderson (2015); 3USGS (2015) and WBD (2015); 4WRCC (2015); 5City of Arcata (2015) and City of Eureka (2015)
161
Nutrient Budgets
Annual and seasonal dissolved inorganic nitrogen, phosphorus, and silicon
budgets are included in the following sections containing sources and uptake estimations
for Humboldt Bay as a whole, and each sub-bay individually. Dissolved inorganic
nutrient loading to Arcata Bay, South Bay, and the Main Channel from the ocean were
calculated using flushing rate estimations from Anderson (2010). Dissolved inorganic
nutrients entering the Bay from the ocean are entrained in the Entrance Bay and the Main
Channel before entering Arcata Bay, allowing time for biological processes to influence
actual influent nutrient loads. These processes are complex and vary with time and space
making an accurate estimation of uptake and release in each compartment difficult and
beyond the scope of this project. Dissolved inorganic nutrients may be taken up as they
enter the Bay and then re-cycled as the plant material lyses nutrients upon expiration.
Therefore dissolved inorganic nutrients that are consumed and incorporated into organic
material may be re-introduced to another part of the Bay as dissolved inorganic nutrients
multiple times during the residence time of the Bay.
Annual DIN Budget
DIN uptake estimates for phytoplankton, macroalgae, and eelgrass do not include
individual speciation for nitrate, nitrite, and ammonium because these estimates were
calculated using elemental biomass content of nitrogen. Therefore, budgets are presented
with respect to DIN only. Standard deviations reported for types of uptake
(phytoplankton uptake, macroalgae uptake, eelgrass uptake, sediment flux, and
162
denitrification) are products of standard deviations reported by the literature sources used
to calculate these forms of uptake and do not represent inter-annual variability. Standard
deviations reported for wastewater loading are the product of multiple years of sampling,
and do represent inter-annual variability in these sources. Uncertainty in watershed
loading represents inter-annual variability in flows from Little River stream gage station
as a single average nutrient concentration was used in all calculations of watershed
discharge. It should be noted that inter-annual standard deviations were calculated for
phytoplankton uptake based on variations in average chlorophyll-a concentrations,
although the larger and more conservative estimate of uncertainty from the wide range of
uptake rates in the literature was used instead.
Average annual DIN loading to Humboldt Bay is dominated by ocean exchange
with watershed runoff and wastewater contributing only 0.6% and 1.0%, respectively
(Table 50). Average annual DIN uptake accounts for only 31% of sources, indicating a
significant sink is unaccounted for in this budget. Advective transport of DIN out of the
Bay with the ebbing tides may account for this as the exchange rates in the Entrance Bay
and Main Channel (0.31 and 0.14 respectively) are much higher than for Arcata Bay and
South Bay (0.02 and 0.04 respectively) as indicated by Anderson (2010). To illustrate
this point, multiplying the low tide Bay entrance sample DIN concentrations by the ebb
tide volume at the time of the sample indicates annual export could account for over
16,000 Mg N/yr (Table 51) which is greater than the estimated average annual DIN
import from the ocean (14,363 Mg N/yr). The difference in estimations of import and
export are due to the differences between datasets used for each calculation; only one
163
year of low tide data are available at the Bay entrance whereas there are multiple years of
data for high tide samples. This example is only to illustrate that the potential magnitude
of advective export from the Bay may be on a similar scale as advective import. This
suggests that export of dissolved nutrients through tidal exchange may be the largest
pathway for nutrient removal from Humboldt Bay. Advective export of dissolved
inorganic nutrients from Humboldt Bay also includes internal mineralization from
organic matter such that export of dissolved inorganic nutrients may be greater than
import.
Phytoplankton uptake is the largest potential type of DIN uptake in Humboldt Bay
(Table 50) accounting for approximately 57% of all DIN uptake. This is followed by
macroalgae (17%), denitrification (17%), eelgrass (7%), and sediment flux (2%).
Wastewater DIN loading (149 Mg N/yr) is less than estimates of uptake, with the
exception of sediment flux (96 Mg N/yr). This indicates that wastewater DIN discharge
to Humboldt Bay is minor in comparison with estimations of uptake and may play a
minor role in stimulating biological production in the Bay annually.
Arcata Bay and South Bay indicate net-negative average annual DIN balances
may exist, suggesting high productivity relative to DIN inputs (Table 50). Comparing
total annual DIN uptake in South Bay and Arcata Bay based upon MSL volume of each
indicates a similar rate of DIN uptake occurs in each bay (Table 52). DIN loading is
significantly higher in South Bay due to the proximity to the ocean and higher tidal
flushing rate (Table 52). The AWTF and watershed runoff make up approximately 12%
and 15% of the annual DIN load to Arcata Bay, respectively, indicating freshwater
164
sources of DIN are minor contributors to DIN-stimulated production in Arcata Bay. The
combined average annual wastewater DIN load to Humboldt Bay is approximately 64%
larger than the total watershed DIN load due to potential discharges from the EWTF.
Whereas in Arcata Bay, the AWTF DIN load is only approximately 78% of the
watershed load on average. Note that 86% of the estimated EWTF DIN load is made up
of nitrate which is based upon a single effluent nitrate measurement and may not
represent the true average effluent concentration resulting in significant over or under-
estimation.
In South Bay, watershed runoff makes up approximately 2% of the average
annual DIN load with the ocean accounting for the other 98% (Table 50). Average
annual DIN uptake in South Bay includes macroalgae (35%), phytoplankton (30%),
denitrification (20%), and eelgrass production (11%) with sediment flux accounting for
only approximately 3% of the total uptake. In Arcata Bay, DIN uptake consists of
phytoplankton uptake (37%), denitrification (25%), macroalgae uptake (22%), eelgrass
uptake (12%), and sediment flux (4%). Denitrification and eelgrass production in Arcata
Bay are 109% and 84% greater than in South Bay, respectively, due to the relative size of
each.
165
Table 50 - Annual DIN budget including loading and uptake for Humboldt Bay and sub-
bays (Mg N/yr); negative values denote uptake or removal from the system.
Source/Uptake Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Ocean1,2,3 14,363
(± 705)
239
(± 12)
513
(± 25)
4,488
(± 220)
2,082
(± 102)
WWTF4 149
(± 25)
40
(± 15) NA NA
109
(± 14)
Watershed3,5 91
(± 70)
51
(± 39)
10
(± 8) NA
30
(± 23)
Phytoplankton2,3,5,6 -2,537
(± 1,851)
-607
(± 443)
-296
(± 216)
-928
(± 677)
-707
(± 516)
Macroalgae7,8 -755
(± 358)
-362
(± 171)
-343
(± 162)
-50
(± 24) NA
Denitrification1,9 -768
(± 462)
-414
(± 249)
-198
(± 119)
-90
(± 54)
-66
(± 40)
Eelgrass8,10 -301
(± 6)
-191
(± 6)
-104
(± 3)
-7
(± 0.2) NA
Sediment Flux1,11 -96
(± 233)
-62
(± 151)
-30
(± 73)
-1
(± 3)
-2.9
(± 7)
Net 10,146
(± 3,710)
-1,305
(± 1,086)
-447
(± 606)
3,413
(± 978)
1,445
(± 702) 1Anderson (2015); 2This study; 3Wiyot Tribe Natural Resources Department (2015); 4City of
Arcata (2015) and City of Eureka (2015); 5Hurst (2009) and Hurst (2015 b.); 6Harding (1973) and
Ryther and Yentsch (1957); 7Duarte (1992), Pregnall and Rudy (1985); 8Schlosser and Eicher
(2012); 9Dollar et al. (1991) and Smith et al. (1991); 10Fourqurean et al. (1997); 11Sin et al. (2007)
166
Table 51 - Bay entrance DIN export for 12 monthly samples illustrates the potential for
advective export of nutrients from Humboldt Bay as an additional sink to account for the
large net surplus of nutrients in the budget (total net export in this example is 16,550 Mg
N/yr).
Date
DIN
(µM)
Ebb Flow*
(Mm3/tide)
Export
(Mg N/tide)
Export
(Mg N/mo)
1/20/2014 14.5 79 16 995
3/22/2014 22.5 110 35 2,162
6/3/2014 15.1 93 20 1,173
6/16/2014 17.6 139 34 2,053
7/17/2014 17.7 107 26 1,641
8/13/2014 8.0 130 15 906
9/12/2014 19.2 106 28 1,706
10/12/2014 9.6 70 9 586
11/2/2014 20.3 101 29 1,718
12/30/2014 9.0 117 15 913
2/1/2015 9.6 124 17 1,034
2/10/2015 22.0 87 27 1,662
*Anderson (2015)
Table 52 - Annual volumetric DIN loading and uptake rates for Humboldt Bay and sub-
bays.
Loading/Uptake Rate
Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Loading Rate1,2 (g N/m3/yr) 150 9 21 91 62
Uptake Rate1,3 (g N/m3/yr) -60 -42 -40 -22 -22 1Anderson (2015), Hurst (2009), Hurst (2015 b.), this study, Wiyot Tribe Natural Resources
Department (2015); 2City of Arcata (2015), City of Eureka (2015); 3Dollar et al. (1991), Duarte
(1992), Fourqurean et al. (1997), Harding (1973), Pregnall and Rudy (1985), Ryther and Yentsch
(1957), Schlosser and Eicher (2012), Sin et al. (2007), Smith et al. (1991),
167
Seasonal DIN Budgets
Average DIN loading to Humboldt Bay is dominated by nearshore influences
during the runoff and upwelling seasons making up approximately 98% and 99% of the
loads respectively (Table 54 and Table 55). Although ocean upwelling significantly
increases DIN loading to the Bay during the upwelling season compared with the runoff
season (20% increase), this source far outweighs all other inputs combined throughout
the year. Total DIN uptake in Humboldt Bay increases by approximately 250% during
the upwelling season due to phytoplankton production (increases by over 300%),
macroalgae production (nearly all macroalgae production occurs during the upwelling
season), and eelgrass production (100% of the annual eelgrass production is assumed to
occur during the upwelling season). Sediment DIN uptake decreases during the
upwelling season by nearly 20% compared with the runoff season due to algal and
bacterial assimilation of nutrients mineralized in sediments.
Wastewater and watershed DIN loading decrease by 28 Mg N and 53 Mg N, 68%
and 26%, respectively, during the upwelling season indicating that these sources have a
natural pattern of reducing DIN output during the productive season in Humboldt Bay.
The majority of the decrease in DIN loading to the Bay from wastewater sources during
the upwelling season is due to the AWTF, the AWTF DIN load decreases by 24 Mg N
while the EWTF load decreases by 4 Mg N. The natural relationship between patterns of
increased productivity in Humboldt Bay and decreased DIN discharge from the AWTF
reduces the potential impact of the AWTF discharge on stimulating production in the
168
Bay. However, there is no indication that DIN discharges from either WWTF are
significant enough to contribute to over-production in the Bay.
Table 53 - Upwelling season DIN loading and uptake for Humboldt Bay and sub-bays
(Mg N).
Source/Uptake Humboldt
Bay Arcata Bay
South
Bay
Entrance
Bay
Main
Channel
Ocean1,2,3 7,832
(± 705)
131
(± 12)
280
(± 25)
2,448
(± 220)
1,135
(± 102)
WWTF4 60
(± 21)
8
(± 5) NA NA
53
(± 11)
Watershed3,5 19
(± 14)
11
(± 8)
2
(± 2) NA
6
(± 5)
Phytoplankton2,3,5,6 -2,045
(± 1,492)
-457
(± 333)
-235
(± 172)
-764
(± 557)
-589
(± 430)
Macroalgae7,8 -695
(± 333)
-333
(± 160)
-316
(± 151)
-46
(± 22) NA
Denitrification1,9 -384
(± 231)
-207
(± 125)
-99
(± 60)
-45
(± 27)
-33
(± 20)
Eelgrass8,10 -301
(± 9)
-191
(± 6)
-104
(± 3)
-7
(± 0.2) NA
Sediment Flux1,11 -43
(± 624)
-28
(± 403)
-13
(± 195)
-1
(± 7)
-1
(± 19)
Net 4,443
(± 3,430)
-1,067
(± 1,051)
-486
(± 608)
1,585
(± 834)
571
(± 586) 1Anderson (2015); 2This study; 3Wiyot Tribe Natural Resources Department (2015); 4City of
Arcata (2015) and City of Eureka (2015); 5Hurst (2009) and Hurst (2015 b.); 6Harding (1973) and
Ryther and Yentsch (1957); 7Duarte (1992), Pregnall and Rudy (1985); 8Schlosser and Eicher
(2012); 9Dollar et al. (1991) and Smith et al. (1991); 10Fourqurean et al. (1997); 11Sin et al. (2007)
169
Table 54 - Runoff season DIN loading and uptake for Humboldt Bay and sub-bays (Mg
N).
Source/Uptake Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Ocean1,2,3 6,531
(± 1,225)
109
(± 20)
233
(± 44)
2,041
(± 383)
947
(± 178)
WWTF4 88
(± 9)
32
(± 9) NA NA
56
(± 12)
Watershed3,5 72
(± 55)
40
(± 8)
8
(± 6) NA
24
(± 18)
Phytoplankton2,3,5,6 -492
(± 359)
-150
(± 109)
-60
(± 44)
-164
(± 120)
-118
(± 86)
Macroalgae7,8 -59
(± 25)
-29
(± 12)
-27
(± 11)
-4
(± 2) NA
Denitrification1,9 -384
(± 231)
-207
(± 125)
-99
(± 60)
-45
(± 27)
-33
(± 20)
Eelgrass8,10 0.0 0.0 0.0 0.0 NA
Sediment Flux1,11 -53
(± 12)
-34
(± 8)
-17
(± 4)
-1
(± 0.1)
-2
(± 0.4)
Net 5,703
(± 1,917)
-238
(± 291)
38
(± 169)
1,827
(± 531)
874
(± 314) 1Anderson (2015); 2This study; 3Wiyot Tribe Natural Resources Department (2015); 4City of
Arcata (2015) and City of Eureka (2015); 5Hurst (2009) and Hurst (2015 b.); 6Harding (1973) and
Ryther and Yentsch (1957); 7Duarte (1992), Pregnall and Rudy (1985); 8Schlosser and Eicher
(2012); 9Dollar et al. (1991) and Smith et al. (1991); 10Fourqurean et al. (1997); 11Sin et al. (2007)
Annual Phosphate-P Budget
Annual phosphate-P loading and removal is dominated by ocean loading and
phytoplankton uptake (97% and 78%, respectively). Wastewater accounts for
approximately 3% of the total phosphate-P load to Humboldt Bay and the AWTF
contributes approximately 21% of the total load to Arcata Bay (Table 55). Annual
wastewater phosphate-P loads to Humboldt Bay are equal to 16% of the total uptake,
with phytoplankton uptake being nearly 375% greater than wastewater loads. Combined
170
wastewater and watershed loading of phosphate-P is equal to approximately 44% of the
tidal influx from nearshore waters. This indicates that freshwater phosphate-P loads to
Arcata Bay may have significant impacts on phosphate concentrations in the Bay. As
mentioned previously, phosphate is not a limiting nutrient in Humboldt Bay such that an
excess of phosphate in the Bay is not expected to stimulate biological production. The
EWTF phosphate-P discharge may be over four times as great as AWTF annually, though
only one measurement of phosphate-P from the EWTF was available. The annual net
balance in phosphate-P loading and uptake in Humboldt Bay is net-positive, whereby
uptake only accounts for approximately 17% of loading to the Bay. This indicates a
significant amount of phosphate-P may be returned to the ocean through advection of
ebbing tides.
171
Table 55 - Annual phosphate-P loading and uptake for Humboldt Bay and sub-bays (Mg
P/yr).
Source/Uptake Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Ocean1,2,3 2,653
(± 191)
44
(± 3)
95
(± 7)
829
(± 60)
385
(± 28)
WWTF4 74
(± 4)
13
(± 2) NA NA
61
(± 6)
Watershed3,5 11
(± 2)
6
(± 1)
1
(± 0.2) NA
4
(± 1)
Phytoplankton2,3,5,6 -351
(± 256)
-84
(± 61)
-41
(± 30)
-128
(± 94)
-98
(± 71)
Macroalgae7,8 -40
(± 19)
-19
(± 9)
-18
(± 9)
-18
(± 1) NA
Eelgrass8,9 -49
(± 3)
-31
(± 2)
-17
(± 1)
-1
(± 0.1) NA
Sediment Flux1,10 13
(± 25)
-8
(± 16)
-4
(± 8)
-0.1
(± 0.3)
17
(± 1)
Net 2,286
(± 499)
-79
(± 94)
16
(± 54)
682
(± 155)
351
(± 107) 1Anderson (2015); 2This study; 3Wiyot Tribe Natural Resources Department (2015); 4City of
Arcata (2015) and City of Eureka (2015); 5Hurst (2009) and Hurst (2015 b.); 6Harding (1973) and
Ryther and Yentsch (1957); 7Duarte (1992), Pregnall and Rudy (1985); 8Schlosser and Eicher
(2012); 9Fourqurean et al. (1997); 10Sin et al. (2007)
Seasonal Phosphate-P Budgets
Seasonal phosphate-P loading to Humboldt Bay is dominated by nearshore
influences during upwelling and runoff seasons contributing approximately 98% and 96%
of the total phosphate-P loads, respectively. Total phosphate-P loading to Humboldt Bay
increases by approximately 12% during the upwelling season due to ocean upwelling
whereas wastewater and watershed phosphate-P contributions decrease by 20% and 74%,
respectively. AWTF phosphate-P loading nearly doubles during the runoff season
compared to the upwelling season as vegetation in the natural treatment system senesces,
172
releasing phosphate-P into the water column and flow rates increase due to rainfall. The
net seasonal phosphate-P balance between loading and uptake in Humboldt Bay remains
positive during both seasons indicating an excess of phosphate-P is available to the
system. The net phosphate-P balances in Arcata Bay and South Bay are net-negative
during the upwelling season, indicating a high level of uptake with respect to loading.
During the upwelling season, phosphate-P uptake in Arcata Bay and South Bay is
approximately 300% and 40% greater than loading, respectively. Since phosphate-P is
not a limiting nutrient in Arcata Bay, the net deficit during the upwelling season in Arcata
Bay and South Bay indicates estimations of phosphate-P uptake may be high or
phosphate-P loading may be low.
173
Table 56 - Upwelling season phosphate-P loading and uptake for Humboldt Bay and sub-
bays (Mg P).
Source/Uptake Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Ocean1,2,3 1,404
(± 440)
23
(± 7)
50
(± 16)
439
(± 137)
203
(± 64)
WWTF4 33
(± 4)
5
(± 0.5) NA NA
28
(± 5)
Watershed3,5 2
(± 1)
1
(± 1)
0.3
(± 0.1) NA
1
(± 0.4)
Phytoplankton2,3,5,6 -283
(± 206)
-63
(± 46)
-33
(± 24)
-106
(± 77)
-81
(± 59)
Macroalgae7,8 -37
(± 18)
-18
(± 8)
-17
(± 8)
-17
(± 1) 0
Eelgrass8,9 -49
(± 3)
-31
(± 2)
-17
(± 1)
-1
(± 0.1) 0
Sediment Flux1,10 -10
(± 46)
-7
(± 30)
-3
(± 15)
-0.1
(± 0.5)
-0.3
(± 1)
Net 1,061
(± 718)
-89
(± 95)
-19
(± 63)
315
(± 216)
151
(± 130) 1Anderson (2015); 2This study; 3Wiyot Tribe Natural Resources Department (2015); 4City of
Arcata (2015) and City of Eureka (2015); 5Hurst (2009) and Hurst (2015 b.); 6Harding (1973) and
Ryther and Yentsch (1957); 7Duarte (1992), Pregnall and Rudy (1985); 8Schlosser and Eicher
(2012); 9Fourqurean et al. (1997); 10Sin et al. (2007)
174
Table 57 - Runoff season phosphate-P loading and uptake for Humboldt Bay and sub-
bays (Mg P).
Source/Uptake Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Ocean1,2,3 1,250
(± 249)
21
(± 4)
45
(± 9)
390
(± 78)
181
(± 36)
WWTF4 41
(± 7)
9
(± 2) NA NA
33
(± 5)
Watershed3,5 9
(± 2)
5
(± 1)
1
(± 0.2) NA
3
(± 1)
Phytoplankton2,3,5,6 -68
(± 50)
-21
(± 15)
-8
(± 6)
-23
(± 17)
-16
(± 12)
Macroalgae7,8 -3
(± 1)
-2
(± 1)
-1
(± 1)
-1
(± 0.1) 0
Eelgrass8,9 0 0 0 0 0
Sediment Flux1,10 -2
(± 3)
-2
(± 2)
-1
(± 1)
-0.03
(± 0.03)
-0.1
(± 0.1)
Net 1,226
(± 312)
11
(± 25)
35
(± 17)
366
(± 94)
200
(± 54) 1Anderson (2015); 2This study; 3Wiyot Tribe Natural Resources Department (2015); 4City of
Arcata (2015) and City of Eureka (2015); 5Hurst (2009) and Hurst (2015 b.); 6Harding (1973) and
Ryther and Yentsch (1957); 7Duarte (1992), Pregnall and Rudy (1985); 8Schlosser and Eicher
(2012); 9Fourqurean et al. (1997); 10Sin et al. (2007)
Annual Silicate-Si Budget
Tidal influx is the major source of silicate-Si to Humboldt Bay comprising 97%
of the total annual inputs, with the remaining 3% of the load coming from the watershed
(Table 58). The silicate-Si content of wastewater has not been determined, although it is
unlikely that it is significantly greater than watershed runoff as silicate is typically
derived from weathering of geologic formations. Phytoplankton uptake calculations
assume 100% of the phytoplankton populations are diatoms which may not be the case,
making this an upper estimate of possible phytoplankton silicate-Si uptake. Watershed
175
silicate-Si loading in Arcata Bay contributes approximately 53% of the total input
annually indicating that watershed runoff is a significant source of silicate-Si in Arcata
Bay. The net-negative annual silicate balance in Arcata Bay indicates that estimations of
uptake are high as silicate is not a limiting nutrient in the Bay. This is likely due to the
high estimation of phytoplankton uptake based upon the assumption that all
phytoplankton are diatoms.
Table 58 - Annual silicate loading and uptake in Humboldt Bay and sub-bays (Mg Si/yr);
phytoplankton uptake assumes all phytoplankton in Humboldt Bay are diatoms, making
this an upper estimate of possible phytoplankton silicate uptake.
Source/Uptake Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Ocean1,2,3 32,998
(± 3,188)
550
(± 53)
1,179
(± 114)
10,312
(± 996)
4,784
(± 462)
Watershed3,4 1,093
(± 177)
612
(± 98)
119
(± 20) NA
362
(± 59)
Phytoplankton2,3,4,5 -5,088
(± 3,712)
-1,216
(± 887)
-593
(± 433)
-1,860
(± 1,357)
-1,418
(± 1,034)
Sediment Flux1,6 -34
(± 50)
-22
(± 33)
-11
(± 16)
-0.4
(± 1)
-1
(± 2)
Net 28,970
(± 7,126)
-76
(± 1,071)
694
(± 582)
8,451
(± 2,354)
3,726
(± 1,557) 1Anderson (2015); 2This study; 3Wiyot Tribe Natural Resources Department (2015); 4Hurst
(2009) and Hurst (2015 b.); 5Harding (1973) and Ryther and Yentsch (1957); 6Sin et al. (2007)
Seasonal Silicate-Si Budgets
Seasonal silicate-Si loading to Humboldt Bay is dominated by nearshore
influences during the runoff and upwelling seasons contributing 94% and 99% of the
total loads respectively (Table 59 and Table 60). Phytoplankton silicate-Si uptake may
be approximately 200-400% higher during the upwelling season in the various sub-bays
176
of Humboldt Bay. Sediment silicate-Si flux changes from uptake (negative flux) to
release (positive flux) between the upwelling and runoff seasons. This indicates benthic
diatoms may be a significant form of uptake for silicate-Si during the upwelling season
and mineralization may be a significant source during the runoff season. Estimated
sediment release of silicate-Si during the runoff season may equal 33% and 81% of the
watershed load in Arcata Bay and South Bay respectively. Watershed silicate-Si loading
to Humboldt Bay increases by approximately 280% during the runoff season due to
increased runoff.
Table 59 - Upwelling season silicate-Si loading and uptake for Humboldt Bay and sub-
bays (Mg Si); phytoplankton uptake assumes all phytoplankton in Humboldt Bay are
diatoms, making this an upper estimate of possible phytoplankton silicate-Si uptake.
Source/Uptake Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Ocean1,2,3 16,860
(± 3,964)
281
(± 66)
602
(± 142)
5,269
(± 1,239)
2,444
(± 575)
Watershed3,4 227
(± 131)
127
(± 72)
25
(± 15) NA
75
(± 44)
Phytoplankton2,3,4,5 -4,101
(± 2,992)
-916
(± 668)
-472
(± 344)
-1,532
(± 1,117)
-1,181
(± 862)
Sediment Flux1,6 -208
(± 171)
-134
(± 111)
-65
(± 54)
-2
(± 2)
-6
(± 5)
Net 12,777
(± 7,257)
-643
(± 917)
90
(± 554)
3,735
(± 2,358)
1,332
(± 1,485) 1Anderson (2015); 2This study; 3Wiyot Tribe Natural Resources Department (2015); 4Hurst
(2009) and Hurst (2015 b.); 5Harding (1973) and Ryther and Yentsch (1957); 6Sin et al. (2007)
177
Table 60 - Runoff season silicate-Si loading and uptake for Humboldt Bay and sub-bays
(Mg Si); phytoplankton uptake assumes all phytoplankton in Humboldt Bay are diatoms,
making this an upper estimate of possible phytoplankton silicate-Si uptake.
Source/Uptake Humboldt
Bay
Arcata
Bay
South
Bay
Entrance
Bay
Main
Channel
Ocean1,2,3 16,138
(± 776)
269
(± 13)
576
(± 28)
5,043
(± 242)
2,339
(± 112)
Watershed3,4 867
(± 166)
485
(± 92)
95
(± 18) NA
287
(± 56)
Phytoplankton2,3,4,5 -986
(± 720)
-300
(± 219)
-121
(± 88)
-329
(± 240)
-237
(± 173)
Sediment Flux1,6 174
(± 246)
112
(± 159)
54
(± 77)
2
(± 3)
5
(± 7)
Net 16,193
(± 1,907)
567
(± 482)
605
(± 211)
4,716
(± 485)
2,395
(± 348) 1Anderson (2015); 2This study; 3Wiyot Tribe Natural Resources Department (2015); 4Hurst
(2009) and Hurst (2015 b.); 5Harding (1973) and Ryther and Yentsch (1957); 6Sin et al. (2007)
178
DISCUSSION
Seasonal Responses
Ocean upwelling increases DIN, phosphate-P, and silicate-Si loads to Humboldt
Bay by approximately 20%, 12%, and 4%, respectively, while uptake increases by
approximately 248%, 406%, and 418%, respectively, indicating other environmental
factors such as sunlight and temperature play significant roles in increased biological
production. During the productive upwelling season, combined wastewater and
watershed DIN and phosphate-P loads decrease by approximately 50% and 30%,
respectively, indicating dissolved inorganic nutrient loading from freshwater sources is
naturally offset from patterns of biological productivity in Humboldt Bay. The AWTF
DIN load decreases by approximately 75% (24 Mg N) on average during the upwelling
season compared to the runoff season. The upwelling season AWTF DIN load (8 Mg N)
is also minor with respect to increases in uptake by phytoplankton (307 Mg N),
macroalgae (305 Mg N), eelgrass (191 Mg N), and sediments (28 Mg N).
Phosphate-P concentrations increase throughout the Bay during the upwelling
season as ocean upwelling increases the load from the ocean to the Bay and internal
sources increase supply. Concentrations of phosphate-P in Arcata Bay are higher than at
the Bay entrance due to either freshwater sources, re-mineralization of organic matter, or
desorption from sediments. While freshwater phosphate-P loads are lower during the
upwelling season, the AWTF discharge contributes approximately 16% of the total load
to Arcata Bay. Applying the average upwelling season phosphate-P discharge from the
179
AWTF (0.025 Mg P/d) to the MSL volume of Arcata Bay (38.5 Mm3) results in a
potential increase in concentration of the whole Bay of approximately 0.05 µM (0.66 µg
P/L). The average upwelling season phosphate-P concentration in Arcata Bay is 1.8 µM
(25.2 µg P/L) indicating that the daily AWTF phosphate-P discharge may only account
for approximately 2.8% of the daily amount of phosphate-P in Arcata Bay. This indicates
that the AWTF phosphate-P discharge may not be the cause of elevated concentrations in
Arcata Bay during the upwelling season. This also indicates that mineralization and
desorption may be significant sources of phosphate-P in Arcata Bay during the upwelling
season. However, the relative contribution of these two mechanisms has not been
determined.
Freshwater contributions of phosphate-P to Arcata Bay are more significant with
respect to ocean loading than freshwater DIN contributions. During the upwelling
season, wastewater phosphate-P contributions to Arcata Bay make up 16% of the total
load, while watershed runoff only accounts for approximately 4% of the total load.
During the runoff season, wastewater phosphate-P contributions to Arcata Bay make up
25% of the total load, and watershed runoff accounts for 14%. It should be noted that
biological production in Humboldt Bay shows no indication of being phosphorus-limited
such that phosphate-P discharges from freshwater sources should not stimulate over-
production in the Bay.
Silicate-Si concentrations are significantly higher in Arcata Bay and South Bay
throughout the year indicating significant internal sources exist. Silicate-Si in wastewater
discharge has not been determined, however, silicate-Si concentrations are significantly
180
higher in South Bay than in Arcata Bay indicating wastewater discharges do not have a
significant impact on silicate-Si concentrations in the Bay since there is no WWTF in
South Bay. Silicate-Si concentrations are also greater during the runoff season than
during the upwelling season, indicating high uptake during the upwelling season and
increased mineralization during the runoff season which may contribute to significant
changes in water column silicate-Si concentrations in the Bay throughout the year.
Budget Surpluses
Approximately 70-85% of the total annual dissolved inorganic nutrient loading to
Humboldt Bay from all sources is unaccounted for by production and uptake, indicating
advection of water from the system on ebb tides is the major mechanism of nutrient
removal from Humboldt Bay. Evidence in support of nutrient export on ebbing tides
includes nutrient concentrations measured at the Bay entrance near low tide that indicate
outgoing tidal flows often contain higher nutrient concentrations than incoming tides.
Increased nutrient concentrations in ebb tide water may be due to mineralization of
organic matter in the system and nutrient loading from freshwater sources inside the Bay
It should be noted that freshwater sources are minor in comparison to tidal influx
indicating that mineralization is a significant source of nutrients in Humboldt Bay. It
should also be noted that the scope of this study did not include an estimation of
advective nutrient export from the Bay due to the complexity of determining the internal
nutrient dynamics that contribute to increased export. Quantifying mineralization of
organic matter in the water column was also omitted from the scope of this project for the
181
same reasons, although some consideration of mineralization in sediments is included in
sediment flux estimations.
Budget Deficits
Net deficits in the dissolved inorganic nutrient balances indicate uptake is greater
than supply and suggest nutrient-limited production inside the Bay. Net deficits occurred
for the average annual and upwelling season budget estimates of DIN, phosphate, and
silicate in Arcata Bay indicating a high level of productivity with respect to nutrient
supply, and the potential for nutrient limitation as opposed to over-production. South
Bay similarly indicates nutrient limitation may contribute to limited production during
the upwelling season as net nutrient deficits occur for DIN and phosphate. The greatest
deficits occurred with respect to DIN in Arcata Bay during the upwelling season where
uptake was approximately 700% greater than supply. This is also an indicator that
estimations of uptake may be high and that estimations of loading may be low.
Phytoplankton production represents the largest pool for nutrient uptake in
Humboldt Bay annually, accounting for approximately 57% of all DIN uptake (2,569 Mg
N/yr) and 78% of all phosphate-P uptake (355 Mg P/yr). While estimates of
phytoplankton production are greater than all other types of uptake combined for DIN
and phosphate-P, it is unclear what the magnitude of the net uptake is with respect to re-
mineralization of organic biomass imported from nearshore waters. Therefore,
estimations of phytoplankton uptake represent an upper limit of dissolved inorganic
nutrient removal from the water column inside the Bay.
182
Denitrification represents the second largest potential pathway for annual DIN
uptake in Humboldt Bay, accounting for 17% of all DIN uptake estimated (768 Mg N/yr).
Denitrification represents actual removal from the system making it an important
mechanism for nitrogen cycling in the Bay since it will not result in re-mineralized DIN.
Lower N:P ratios in Arcata Bay compared with the Bay entrance indicate denitrification
represents a significant DIN removal mechanism in the Bay, supporting estimates of high
removal in the budget.
Comparison with Other Systems
Humboldt Bay is a non-eutrophic, upwelling-influenced, nitrogen-limited estuary.
The following is a comparison with two systems; the first is similar to Humboldt Bay and
is also considered a healthy non-eutrophic estuary. The second is a highly eutrophic
estuary in Southern California impacted by agricultural nutrient runoff and experiencing
overproduction of macroalgae.
Comparison of annual biological uptake rates and average ammonium and nitrate
concentrations in Humboldt Bay and Tomales Bay (Smith et al., 1991) indicate Humboldt
Bay may be less productive with respect to phytoplankton and macroalgae uptake, though
more productive with respect to eelgrass production (Table 61). Denitrification estimates
for Humboldt Bay were calculated using findings from Smith et al. (1991) and Dollar et
al. (1991); therefore the areal denitrification for both systems are identical and there is no
other basis for comparison of this process between the two systems. However,
comparisons can be made with respect to nutrient concentrations. Nutrient
183
concentrations in Humboldt Bay appear to be greater during the upwelling season and
lower during the runoff season (Table 62). Tomales Bay has a significantly larger
watershed that may contribute significantly to higher nutrient concentrations during the
runoff season, though limited data are available for Humboldt Bay. Higher nutrient
concentrations in Humboldt Bay during the upwelling season may be due to greater
influence from upwelling or lower productivity.
Table 61 - Comparison of physical properties and biological uptake in Humboldt Bay and
Tomales Bay.
Parameter
Humboldt
Bay
Tomales
Bay
Bay Area (Mm2) 691 288
Watershed Area (Mm2) 2352 5608
Creek Inputs (Mm3/yr) 3072,3 908
Phytoplankton Uptake (mg N/m2/d) 1004 1278
Macroalgae Uptake (mg N/m2/d) 305,6 638
Eelgrass Uptake (mg N/m2/d) 125,7 68
Denitrification (mg N/m2/d) 301,8,9 468, 259
Total DIN uptake (mg N/m2/d) 144 222-243 1Anderson (2015); 2WBD (2015); 3USGS (2015); 4This study, Harding (1973), Hurst (2009),
Hurst (2015), Ryther and Yentsch (1957), Wiyot Tribe Natural Resources Department (2015); 5Schlosser and Eicher (2012); 6Duarte (1992), Pregnall and Rudy (1985); 7Fourqurean et al.
(1997); 8Smith et al. (1991); 9Dollar et al. (1991)
184
Table 62 - Comparison of nitrate and ammonium concentrations in Humboldt Bay and
Tomales Bay; outer bay refers to areas near the bay entrance more highly influenced by
nearshore conditions, and inner bay refers to areas more isolated from nearshore
influences.
Location and
Constituent
Summer -
Humboldt
Bay1
Summer -
Tomales
Bay2
Winter -
Humboldt
Bay1
Winter -
Tomales
Bay2
Outer Bay NO3 (µM) 13 4 11 15
Inner Bay NO3 (µM) 3 1 9 15
Watershed NO3 (µM) 18 1 18 75
Outer Bay NH4 (µM) 4 1 3 3
Inner Bay NH4 (µM) 6 0.5 7 4
Watershed NH4 (µM) 3 0.1 3 1 1Hurst (2009), Hurst (2015), Wiyot Tribe Natural Resources Department (2015); 2Smith et al.
(1991)
Upper Newport Bay in Southern California is a eutrophic estuary receiving high
nutrient loads from the creek runoff as well as experiencing high nutrient concentrations
inside the estuary (Table 63). Comparison of ambient ammonium and nitrate
concentrations in the two systems indicates that Humboldt Bay has significantly lower
nitrate concentrations during both the upwelling and runoff seasons. Ammonium
concentrations are also higher in Upper Newport Bay though not as significant as nitrate,
possibly due to the high rate of uptake by macroalgae and phytoplankton. The analysis
from Boyle et al. (2004) indicates that tidal channels in Upper Newport Bay may
experience greater than 75% cover by macroalgae in the summer and fall.
185
Table 63 - Comparison of nitrate and ammonium concentrations in Humboldt Bay and
eutrophic Upper Newport Bay in Southern California; note that creek nitrate and
ammonium concentrations in Humboldt Bay are the same for both seasons due to
insufficient data; tidal channel refers to areas inside the bay, and creek refers to
watershed and creek runoff.
Location and Constituent
Summer -
Humboldt
Bay1
Summer -
Newport
Bay2
Winter -
Humboldt
Bay1
Winter -
Newport
Bay2
Tidal Channel NO3 (µM) 13 290 9 140
Creek NO3 (µM) 18 45 18 43
Tidal Channel NH4 (µM) 6 8 7 11
Creek NH4 (µM) 3 9 3 14 1Hurst (2009), Hurst (2015), Wiyot Tribe Natural Resources Department (2015); 2Boyle et al.
(2004)
Historical Changes
Humboldt Bay has been the subject of at least five significant nutrient studies
since 1962 (other studies have been conducted but remain unpublished). Methods of
measuring nutrients have varied, as have sampling locations and time of day with respect
to tidal interaction. A series of average nutrient concentrations from various studies
conducted since 1962 are presented below (Table 64). Runoff season nitrate and
ammonium concentrations inside the Bay and at the Bay entrance have increased since
1980. This may indicate that land use has changed around Humboldt Bay and in the Eel
River watershed. Eel River waters flow northward during the winter runoff season and
may influence waters near the Bay entrance. Phosphate and silicate show no indication
of increasing at either location or season indicating any land use changes that have
resulted in ammonium and nitrate increases have not affected phosphate and silicate. It
186
should be noted that upgrades in wastewater treatment technology in the AWTF and
EWTF may have reduced nutrient loads from these sources such that increases in nutrient
concentrations may not be attributable to these sources. It should also be noted that none
of these concentrations represents extremely high concentrations and that nutrient levels
in Humboldt Bay have remained relatively low during these studies. Recall the Newport
Bay tidal channel nitrate concentration of 290 µM (Table 63).
187
Table 64 - Comparison of historic nutrient concentrations measured in Humboldt Bay
between 1962-2015; IB = Inner Bay (i.e. Arcata Bay or South Bay), OB = Outer Bay (i.e.
near Bay Entrance), US = Upwelling Season, RS = Runoff Season, ND = no data.
Year Location, Season
Nitrate
(µM)
Ammonium
(µM)
Phosphate
(µM)
Silicate
(µM)
19621 IB, US ND ND 2.2 27.3
19802 IB, US 2.4 1.5 1.8 21.4
19813 IB, US 5.2 15.5 5.7 ND
20064 IB, US 4.7 2.4 3.6 ND
2009-20155 IB, US 3.4 5.8 1.8 23.7
19621 IB, RS ND ND 2.2 27.3
19802 IB, RS 0.8 0.8 1.3 15.2
19813 IB, RS 18.2 5.0 2.9 ND
20064 IB, RS 8.2 6.8 3.0 ND
2009-20155 IB, RS 9.1 6.7 1.5 29.3
19621 OB, US ND ND 2.1 24.4
19802 OB, US 12.6 1.9 1.4 19.2
19813 OB, US 2.6 9.3 2.5 ND
20064 OB, US 18.0 3.1 3.5 ND
2009-20155 OB, US 12.6 3.9 1.4 16.8
19621 OB, RS ND ND 2.1 24.4
19802 OB, RS 0.3 0.0 0.0 2.1
19813 OB, RS 4.3 2.5 2.2 ND
20064 OB, RS 8.9 6.4 2.0 ND
2009-20155 OB, RS 11.1 3.0 1.2 18.1 1Gast (1962); 2Pequegnat and Butler (1981); 3Janeway (1981); 4Tennant (2006); 5Hurst (2009),
Hurst (2015), Wiyot Tribe Natural Resources Department (2015), this study
188
FUTURE RESEARCH
Estimations of nutrient uptake by phytoplankton, denitrification, and sediment
flux used in this study were gathered from literature studies of similar systems that
resulted in significant uncertainty. Uncertainty in these estimates can be reduced using
more detailed conceptual and numerical models, and site-specific studies of these
processes in Humboldt Bay. Estimations of nutrient loading from watershed sources to
Humboldt Bay relied on average nutrient concentrations from a single location and
streamflow rates from nearby Little River. These estimates could be significantly
improved with additional water quality sampling of the watershed surrounding Humboldt
Bay, and measurement of streamflow rates from creeks emptying directly into Humboldt
Bay. Estimations of nutrient loading to Humboldt Bay from nearshore waters is highly
complex and involves the mixing of internal compartments in the Bay, mixing between
the Humboldt Bay tidal prism and nearshore waters, various environmental conditions,
and various biological processes of uptake and re-mineralization. A combination of
hydrodynamic and biodynamic modeling may greatly improve estimation of nutrient
contributions to Humboldt Bay from nearshore waters.
189
CONCLUSION
Humboldt Bay is a healthy nitrogen-limited estuary where dissolved inorganic
nutrients and phytoplankton from nearshore waters are the major influences on
productive upwelling season nutrient cycling in the Bay. Limited exchange rates
between Arcata Bay and the ocean may reduce ocean nutrient loading by up to 98%,
however, nearshore DIN and DIP loading remain more than twice as great as wastewater
and watershed runoff sources combined on an annual basis. During the upwelling
season, DIN discharge from the AWTF decreases by 75%, significantly reducing
potential impacts to the Bay during this period of high productivity. All estimations of
individual biological DIN and DIP uptake processes in Arcata Bay are greater than the
AWTF DIN and DIP discharge further supporting the conclusion that wastewater nutrient
discharge has little or no significant impact on biological productivity in Arcata Bay
compared with other nutrient sources.
190
REFERENCES
ANATEC Laboratories Inc., RAMLIT Associates, & Hugo B. Fischer Inc. (1982).
Humboldt Bay Nonpoint Source Study Project: Planning Study of Nonpoint
Source Bacterial Contamination, and Circulation and Flushing of Humboldt Bay.
Santa Rosa, CA: California Water Quality Control Board.
Anderson, J. (2010). A Three-Dimensional Hydrodynamic and Transport Model of
Humboldt Bay. Poster Presentation. Eureka, CA.
Anderson, J. (2015, June). Unpublished Data. McKinleyville, CA.
APHA, AWWA, WEF. (2012). Standard Methods for the Examination of Water and
Wastewater (22nd ed.). (E. W. Rice, R. B. Baird, A. D. Eaton, & L. S. Clesceri,
Eds.) American Public Health Association, American Water Works Association,
Water Environment Federation.
Ayers, J. C. (1956). Population Dynamics of the Marine Clam. Limnology and
Oceanography, 1(1), 26-34.
Balderston, W. L., Sherr, B., & Payne, W. J. (1976). Blockage by acetylene of nitrous
oxide reduction in Pseudomonas perfectomarinus. Applied and Environmental
Microbiology, 31, 504-508.
Barelson, W. M., Hammond, D. E., & Johnson, K. S. (1987). Benthic fluxes and the
cycling of biogenci silica and carbon in two southern California borderland
basins. Geochimica et Cosmochimica Acta, 51(6), 1345-1363.
Barnhart, R. A., Boyd, M. J., & Pequegnat, J. E. (1992). The Ecology of Humboldt Bay
California: An Estuarine Profile. U.S. Fish and Wildlife Service.
Benitez-Nelson, C. R., & Buesseler, K. O. (1999). Variability of inorganic and organic
phosphorus turnover rates in the coastal ocean. Nature, 398, 502-505.
Berman, T., & Bronk, D. A. (2003). Dissolved organic nitrogen: a dynamic participant in
aquatic ecosystems. Aquatic Microbial Ecology, 31, 279-305.
Bianchi, T. S. (2013). Estuarine Chemistry. In J. W. Day Jr., B. C. Crump, W. M. Kemp,
& A. Yanez-Arancibia, Estuarine Ecology (2nd ed., pp. 39-83). Hoboken, NJ:
John Wiley & Sons, Inc.
191
Boyle, K. A., Kamer, K., & Fong, P. (2004). Spatial and Temporal Patterns in Sediment
and Water Column Nutrients in a Eutrophic Southern California Estuary.
Estuaries, 27(3), 378-388.
Boynton, W. R., & Kemp, W. M. (1985). Nutrient regeneration and oxygen consumption
by sediments along an estuarine salinity gradient. Marine Ecology Progress
Series, 23, 45-55.
Bray, J. T., Bricker, O. P., & Troup, B. N. (1973). Phosphate in Interstitial Waters of
Anoxic Sediments: Oxidation Effects during Sampling Procedure. Science,
180(4093), 1362-1364.
Bricker, S. B., Clement, C. G., Pirhalla, D. E., Orlando, S. P., & Farrow, D. R. (1999).
National Estuarine Eutrophication Assessment: Effects of Nutrient Enrichment in
the Nation's Estuaries. Silver Spring, MD: NOAA.
Bricker, S. B., Ferreira, J. G., & Simas, T. (2003). An integrated methodology for
assessment of estuarine trophic status. Ecological Modelling, 169(1), 39-60.
Bricker, S., Longstaff, B., Dennison, W., Jones, A., Boicourt, K., Wicks, C., & Woerner,
J. (2007). Effects of Nutrient Enrichment in the Nation's Estuaries: A Decade of
Change. National Estuarine Eutrophication Assessment. Silver Spring, MD:
NOAA.
Brzezinski, M. A. (1985). The Si:C:N Ratio of Marine Diatoms: Interspecific Variability
and the Effect of Some Environmental Variables. Journal of Phycology, 21, 347-
357.
Casebier, T. A., & Toimil, L. J. (1973). Physical Dynamics of Arcata Bay. Arcata, CA:
Humboldt State College.
Castro, M. S., Driscoll, C. T., Jordan, T. E., Reay, W. G., & Boynton, W. R. (2003).
Sources of Nitrogen to Estuaries in the United States. Estuaries, 26(3), 803-814.
CDFG. (2010). Status of the Fisheries Report: an Update Through 2008. Marine Region
7. Monterey, CA: California Department of Fish and Wildlife.
CDHS. (2006). Twelve-Year Sanitary Survey Report: Shellfish Growing Area
Classification for Humboldt Bay. California Department of Health Services,
Division of Drinking Water and Environmental Management, Environmental
Management Branch, Environmental Health Services Section, Preharvest
Shellfish Unit.
City of Arcata. (2015). Wastewater Treatment Facility Unpublished Data.
192
City of Eureka. (2015). Wastewater Treatment Facility Unpublished Data.
City of San Diego. (2013). Watershed Asset Management plan, Appendix A: San Diego
Bay Watershed. Storm Water Division, Transportation and Storm water
Department. San Diego, CA: City of San Diego.
Cloern, J. E. (1991). Tidal stirring and phytoplankton bloom dynamics in an estuary.
Journal of Marine Research, 49, 203-221.
Coast Seafoods Company. (2015). Humboldt Bay Shellfish Culture Permit Renewal and
Expansion Project: Initial Study. Eureka, CA: Humboldt Bay Harbor, Recreation,
and Conservation District.
Conley, D. J., Smith, W. M., Cornwell, J. C., & Fisher, T. R. (1995). Transformation of
Particle-bound Phosphorus at the Land-Sea Interface. Estuarine, Coastal and
Shelf Science, 40, 161-176.
Conway, H. L. (1977). Interactions of Inorganic Nitrogen in the Uptake and Assimilation
by Marine Phytoplankton. Marine Biology, 39, 221-232.
Costa, S. L. (1982). The Physical Oceanography of Humboldt Bay. Proceedings of the
Humboldt Bay Symposium (pp. 2-31). Eureka, CA: The Humboldt Bay
Symposium Committee.
Craig, P. M. (2013, June). User's Manual for EFDC_Explorer7.1: A Pre/Post Processor
for the Environmental Fluid Dynamics Code. Edmonds, WA: Dynamic Solutions-
International, LLC.
Cranford, P. J., Ward, J. E., & Shumway, S. E. (2011). Bivalve filter feeding: variability
and limits of the aquaculture biofilter. In Shellfish aquaculture and the
environment (pp. 81-124).
Curl, Jr., H., & Small, L. F. (1965, April). Variations in Photosynthetic Assimilation
Ratios in Natural, Marine Phytoplankton Communities. Limnology and
Oceanography, 10, R67-R73.
Dollar, S. J., Smith, S. V., Vink, S. M., Obrebski, S., & Hollibaugh, J. T. (1991). Annual
cycle of benthic nutrient fluxes in Tomales Bay, California, and contribution of
the benthos to total ecosystem metabolism. Marine Ecology Progress Series, 79,
115-125.
Dortch, Q., Clayton, Jr., J. R., Thoreson, S. S., Bressler, S. L., & Ahmed, S. I. (1982).
Response of Marine Phytoplankton to Nitrogen Deficiency: Decreased Nitrate
Uptake vs Enhanced Ammonium Uptake. Marine Biology, 70, 13-19.
193
Duarte, C. M. (1992). Nutrient concentration of aquatic plants: Patterns across species.
Limnology and Oceanography, 37(4), 882-889.
Dudley, B. J., Gahnstrom, A. M., & Walker, D. L. (2001). The role of benthic vegetation
as a sink for elevated inputs of ammonium and nitrate in a mesotrophic estuary.
Marine Ecology Progress Series, 219, 99-107.
Egge, J. K., & Aksnes, D. L. (1992). Silicate as regulating nutrient in phytoplankton
competition. Marine Ecology Progress Series, 83, 281-289.
Eppley, R. W., Coatsworth, J. L., & Solorzano, L. (1969). Studies of Nitrate Reductase in
Marine Phytoplankton. Limnology and Oceanography, 14(2), 194-205.
Fisher, T. R., Harding, L. W., Stanley, D. W., & Ward, L. G. (1988). Phytoplankton,
nutrients, and turbidity in the Chesapeake, Delaware, and Hudson estuaries.
Estuarine, Coastal and Shelf Science, 27(1), 61-93.
Fisher, T. R., Peele, E. R., Ammerman, J. W., & Harding, Jr., L. W. (1992). Nutrient
limitation of phytoplankton in Chesapeake Bay. Marine Ecology Progress Series,
82, 51-63.
Fleming, R. H. (1940). The composition of plankton and units for reporting population
and production. Proceedings of the Sixth Pacific Science Congress of California
(pp. 535-540). Berkley, CA: UC Berkeley press.
Fourqurean, J. W., Moore, T. O., Fry, B., & Hollibaugh, J. T. (1997). Spatial and
temporal variation in C:N:P ratios, d15N, and d13C of eelgrass Zostera marina as
indicators of ecosystem processes, Tomales Bay, California, USA. Marine
Ecology Progress Series, 157, 147-157.
Froelich, P. N. (1988). Kinetic control of dissolved phosphate in natural rivers and
estuaries: A primer on the phosphate buffer mechanism. Limnology and
Oceanography, 33(4 part 2), 649-668.
Froelich, P. N., Bender, M. L., & Luedtke, N. A. (1982). The Marine Phosphorus Cycle.
American Journal of Science, 282, 474-511.
Garber, J. H., Collins, Jr., J. L., & Davis, M. W. (1992). Impact of Estuarine Benthic
Algal Production on Dissolved Nutrients and Water Quality in the Yaquina River
Estuary, Oregon. Reston, VA: USGS.
Garcia-Reyes, M., & Largier, J. L. (2012). Seasonality of coastal upwelling off central
and northern California: New insights, including temporal and spatial variability.
Journal of Geophysical Research, 117, 1-17.
194
Gast, J. A. (1962). An Oceanographic Survey of the Humboldt Bay System: Physical and
Chemical Data. Arcata, CA: Humboldt State College.
Gast, J. A., & Skeesick, D. G. (1964). The Circulation, Water Quality, and Sedimentation
of Humboldt Bay, California. Oceanography. Arcata, CA: Humboldt State
College.
Geist, J. K. (2003). Humboldt Bay and Watershed Fecal Coliform Study. Arcata, CA:
North Coast Regional Water Quality Control Board and Department of Health
Services-Preharvest Shellfish Sanitation Unit.
Google Earth (1). (2013, April 9). Humboldt Bay. Retrieved July 9, 2015, from Google
Earth: 643547.97 m E 4405666.82 m N
Google Earth (2). (2013, April 9). California. Retrieved October 21, 2015, from Google
Earth: 11 S 349402.44 m E 3966453.05 m N
H.T. Harvey & Associates. (2015). Draft Environmental Impact Report for the Humboldt
Bay Mariculture Pre-Permitting Project. Eureka, CA: Humboldt Bay Harbor,
Recreation and Conservation District.
Hagy, I. J., & Kemp, W. M. (2013). Estuarine Food Webs. In J. W. Day, Jr., B. C.
Crump, W. M. Kemp, & A. Yanez-Arancibia, Estuarine Ecology (2nd ed., pp.
417-441). Hoboken, NJ: John Wiley & Sons, Inc.
Hamrick, J. M. (1992). Three-Dimensional Environmental Fluid Dynamics Computer
Code: Theoretical And Computational Aspects. Gloucester Point, VA: Virginia
Institute of Marine Science.
Harding, Jr., L. W. (1973). Primary Production in Humboldt Bay. Arcata, CA: Humboldt
State University.
HBHRCD. (2007). Humboldt Bay Management Plan. Eureka, CA: Humboldt Bay
Harbor, Recreation, and Conservation District.
Hemminga, M. A., Koutstaal, B. P., van Soelen, J., & Merks, A. G. (1994). The nitrgoen
supply to intertidal eelgrass (Zostera marina). Marine Biology, 118, 223-227.
Henderson, J. (2004). Impacts to Humboldt Bay NWR From Forestry and Dairy Activities
in the Salmon Creek Watershed. Portland, OR: U.S. Fish and Wildlife Service,
Region 1.
195
Howarth, R. W., Marino, R., Lane, J., & Cole, J. J. (1988). Nitrogen fixation in
freshwater, estuarine, and marine ecosystems. 1. Rates and importance.
Limnology and Oceanography, 33(4-2), 669-687.
Humboldt Baykeeper. (2015). Unpublished data.
Hurst, M. (2009). Unpublished Data. Arcata, CA.
Hurst, M. (2015 a., 12 1). Limiting Nitrogen Concentrations for Phytoplankton
Production. (C. R. Swanson, Interviewer)
Hurst, M. (2015 b.). Unpublished Data. Arcata, CA: Humboldt State University and the
City of Arcata.
Hynes, R. K., & Knowles, R. (1978). Inhibition by Acetylene of Ammonia Oxidation in
Nitrosomonas Europaea. FEMS Microbiology Letters, 4, 319-321.
Janeway, W. D. (1981). A Comparison of the Water Quality from Point and Non-Point
Source Discharges into Northern Humboldt Bay, Humboldt County, California.
Arcata, CA: Humboldt State University.
Jansen, H. M., Strand, O., Verdegem, M., & Smaal, A. (2012). Accumulation, release and
turnover of nutrients (C-N-P-Si) by the blue mussel Mytilus edulis under
oligotrophic conditions. Journal of Experimental Marine Biology and Ecology,
416-417, 185-195.
Kemp, W. M., Sampou, J. C., Mayer, M., Henriksen, K., & Boynton, W. R. (1990).
Ammonium recycling versus denitrification in Chesapeake Bay sediments.
Limnology and Oceanography, 35(7), 1545-1563.
Ketchum, B. H. (1951). The exchanges of fresh and salt water in tidal estuaries. Journal
of Marine Research, 10, 18-38.
Kjerfve, B., & Magill, K. E. (1989). Geographic and Hydrodynamic Characteristics of
Shallow Coastal Lagoons. Marine Geology, 88, 187-199.
Klamt, R. R. (1979). Humboldt Bay Wastewater Circulation Studies. Santa Rosa, CA:
California Water Quality Control Board.
Larned, S. T. (2003). Effects of the invasive, nonindigenous seagrass Zostera japonica on
nutrient fluxes between the water column and benthos in a NE Pacific estuary.
Marine Ecology Progress Series, 254, 69-80.
196
Lomas, M. W., & Glibert, P. M. (1999). Temperature regulation of nitrate uptake: A
novel hypothesis about nitrate uptake and reduction in cool-water diatoms.
Limnology and Oceanography, 44(3), 556-572.
Mackin, J. E., & Aller, R. C. (1984). Ammonium adsorption in marine sediments.
Limnology and Oceanography, 29(2), 250-257.
Martin, J., & Hurst, M. (2008). Temporal Variation and Cycling of Trace Elements in the
Humboldt Bay Estuary. Presentation Poster. Arcata, CA.
Millero, F. J. (2013). Chemical Oceanography (4th ed.). Boca Raton, FL: CRC Press.
NAC. (2004). Coos Bay, Oregon Geographic Response Plan. Coos Bay, OR: Northwest
Area Committee (NAC).
NAIP. (2014, September 23). National Agricultural Imagery Program: 1 m resolution
orthoimagery. Salt Lake City, UT: USDA FSA Aerial Photography Field Office.
Nedwell, D. B., Jickells, T. D., Trimmer, M., & Sanders, R. (1999). Nutrients in
Estuaries. Estuaries, 29, 43-92.
NGS. (2015, July 1). Tidal Elevation. Retrieved July 10, 2015, from National Geodetic
Survey:
http://www.ngs.noaa.gov/Tidal_Elevation/diagram.jsp?PID=LV0361&EPOCH=1
983-2001
NMFS. (2014). California Eelgrass Mitigation Policy and Implementing Guidelines.
NOAA Fisheries, West Coast Region.
Oremland, R. S., Umberger, C., Culbertson, C. W., & Smith, R. L. (1984). Denitrification
in San Francisco Bay Intertidal Sediments. Applied and Environmental
Microbiology, 47(5), 1106-1112.
Paerl, H. W., & Justic, D. (2013). Estuarine Phytoplankton. In J. W. Day Jr., B. C.
Crump, W. M. Kemp, & A. Yanez-Arancibia, Estuarine Ecology (2nd ed., pp. 84-
110). Hoboken, New Jersey: John Wiley & Sons, Inc.
Pequegnat, J. E., & Butler, J. H. (1981). The Role of Nutrients in Supporting
Phytoplankton Productivity in Humboldt Bay. La Jolla, CA: California Sea Grant
College Program.
Pequegnat, J. E., & Butler, J. H. (1982). The Biological Oceanography of Humboldt Bay.
Humboldt Bay Symposium Proceedings (pp. 39-51). Eureka, CA: Humboldt Bay
Symposium Committee.
197
Peterson, B., Butzerin, J., Fresh, K., Burke, B., Peterson, J., Morgan, C., & Fisher, J.
(2012). Ocean Ecosystem Indicators of Salmon Marine Survival in the Northern
California Current. Silver Spring, MD: NOAA Fisheries. Retrieved from
Northwest Fisheries Science Center.
PFEL. (2015, July 22). Upwelling Indices. Retrieved July 22, 2015, from Pacific
Fisheries Environmental Laboratory:
http://www.pfeg.noaa.gov/products/PFEL/modeled/indices/upwelling/NA/data_d
ownload.html
Pregnall, A. M., & Rudy, P. P. (1985). Contribution of green macroalgal mats
(Enteromorpha spp.) to seasonal production in an estuary. Marine Ecology -
Progress Series, 24, 167-176.
Redfield, A. C. (1934). On the Proportions of Organic Derivatives in Sea Water and their
Relation to the Composition of Plankton. University Press of Liverpool, 176-192.
Risgaard-Petersen, N., Rysgaard, S., Nielsen, L. P., & Revsbech, N. P. (1994, May).
Diurnal Variation of Denitrification and Nitrification in Sediments Colonized by
Benthic Microphytes. Limnology and Oceanography, 39(3), 573-579.
Rosenfeld, J. K. (1979). Ammonium adsorption in nearshore anoxic sediments.
Limnology and Oceanography, 24(2), 356-364.
Ryther, J. H., & Dunstan, W. M. (1971). Nitrogen, Phosphorus, and Eutrophication in the
Coastal Marine Environment. Science, 171(3975), 1008-1013.
Ryther, J. H., & Yentsch, C. S. (1957). The Estimation of Phytoplankton Production in
the Ocean from Chlorophyll and Light Data. Limnology and Oceanography, 2(3),
281-286.
Schlosser, S., & Eicher, A. (2012). Humboldt Bay and Eel River Estuary Benthic Habitat
Project. University of California San Diego, Scripps Institution of Oceanography.
California Sea Grant College Program.
Schwartzlose, R. A., & Reid, J. L. (1972). Near-Shore Circulation in the California
Current. Calif. Mar. Res. Comm., CalCOFI Rept., 16, 57-65.
Schwing, F. B., O'Farrell, M., Steger, J. M., & Baltz, K. (1996). Coastal Upwelling
Indices, West Coast of North America, 1946-95. Pacific Grove, CA: Pacific
Fisheries Environmental Laboratory.
198
Seitzinger, S. P. (1988). Denitrification in freshwater and coastal marine ecostystems:
Ecological and geochemical significance. American Society of Limnology and
Oceanography, 33(4-2), 702-724.
Seitzinger, S. P., & Sanders, R. W. (1997). Contribution of dissolved organic nitrogen
from rivers to estuarine eutrophication. Marine Ecology Progress Series, 159, 1-
12.
Seitzinger, S., Nixon, S., Pilson, M. E., & Burke, S. (1980). Denitrification and N2O
production in near-shore marine sediments. Geochimica et Cosmochimica Acta,
44(11), 1853-1855.
Shapiro and Associates, Inc. (1980). Humboldt Bay Wetlands Review and Baylands
Analysis. San Francisco, CA: U.S. Army Corps of Engineers.
Shellfish Protection Act of 1993, Cal. Water Code § 14950 (January 1, 1993).
Sigleo, A. C., Mordy, C. W., Stabeno, P., & Frick, W. E. (2005). Nitrate variability along
the Oregon coast: Estuarine-coastal exchange. Estuarine, Coastal and Shelf
Science, 64, 211-222.
Sin, Y., Sigleo, A. C., & Song, E. (2007). Nutrient Fluxes in the Microalgal-dominated
Intertidal Regions of the Lower Yaquina Estuary, Oregon (USA). Northwest
Science, 81(1), 50-61.
Skeesick, D. G. (1963). A Study of Some Physical-Chemical Characteristics of Humboldt
Bay. Arcata, CA: Humboldt Sate College.
Smith, C. J., DeLaune, R. D., & Patrick Jr., W. H. (1985). Fate of Riverine Nitrate
Entering and Estuary: I. Denitrification and Nitrogen burial. Estuaries, 8(1), 15-
21.
Smith, S. V., & Hollibaugh, J. T. (1997). Annual Cycle and Interannual Variability of
Ecosystem Metabolism in a Temperate Climate Embayment. Ecological
Monographs, 67(4), 509-533.
Smith, S. V., & Hollibaugh, J. T. (2006). Water, salt, and nutrient exchanges in San
Francisco Bay. Limnology and Oceanography, 504-517.
Smith, S. V., Chambers, R. M., & Hollibaugh, J. T. (1996). Dissolved and particulate
nutrient transport through a coastal watershed-estuary system. Journal of
Hydrology, 176, 181-203.
199
Smith, S. V., Hollibaugh, J. T., Dollar, S. J., & Vink, S. (1991). Tomales Bay
Metabolism: C-N-P Stoichiometry and Ecosystem Heterotrophy at the Land-Sea
Interface. Estuarine, Coastal and Shelf Science, 33, 223-257.
Smith, S. V., Wiebe, W. J., Hollibaugh, J. T., Dollar, S. J., Hager, S. W., Cole, B. E., . . .
Wheeler, P. A. (1987). Stoichiometry of C, N, P, and Si fluxes in a temperate-
climate embayment. Journal of Marine Research, 45, 427-460.
SoRMS. (2015, July). Humboldt State University Solar Radiation Monitoring Station.
Arcata, CA.
Strickland, J. D., Holm-Hansen, O., Eppley, R. W., & Linn, R. J. (1969). The Use of a
Deep Tank in Plankton Ecology. I. Studies of the Growth and Composition of
Phytoplankton Crops at Low Nutrient Levels. Limnology and Oceanography,
14(1), 23-34.
Sutula, M., Creager, C., & Wortham, G. (2007). Technical Approach to Develop Nutrient
Numeric Endpoints for California Esutaries. Sacramento, CA: California State
Water Resources Control Board.
Sverdrup, H. U., Johnson, M. W., & Fleming, R. H. (1942). The Oceans Their Physics,
Chemistry, and General Biology. New York, NY: Prentice-Hall, Inc.
Swanson, C. R. (2013). Nitrogen Mass Assessment for Treatment Options in the Arcata
Wastewater Treatment Facility. Arcata, CA: Arcata Marsh Research Institute.
Taft, J. L., & Taylor, R. (1976). Phosphorus Distribution in the Chesapeake Bay.
Chesapeake Science, 17(2), 67-73.
Testa, J. M., Kemp, W. M., Hopkinson Jr., C. S., & Smith, S. V. (2013). Ecosystem
Metabolism. In J. W. Day Jr., B. C. Crump, W. M. Kemp, & A. Yanez-
Aranciabia, Estuarine Ecology (2nd ed., pp. 381-416). Hoboken, NJ: John Wiley
& Sons, Inc.
Thamdrup, B., & Dalsgaard, T. (2002). Production of N2 through Anaerobic Ammonium
Oxidation Coupled to Nitrate Reduction in Marine Sediments. Applied and
Environmental Microbiology, 68(3), 1312-1318.
Thompson, R. W. (1971). Recent Sediments of Humboldt Bay, Eureka, California.
Arcata, CA: Humboldt State College.
US Census Bureau. (2014, May). Arcata (city), California. Retrieved July 10, 2015, from
State & County QuickFacts:
200
http://factfinder.census.gov/faces/tableservices/jsf/pages/productview.xhtml?src=
bkmk
USEPA. (2008). Indicator Development for Estuaries. Washington, DC: USEPA.
USEPA. (2015, March 17). San Francisco Bay Delta: About the Watershed. Retrieved
July 10, 2015, from USEPA: http://www2.epa.gov/sfbay-delta/about-watershed
USGS. (2015, July 20). National Water Information System: Web Interface. Retrieved
July 20, 2015, from USGS 11481200 Little R NR Trinidad CA:
http://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site_no=1148120
0
Valiela, I., Teal, J. M., Volkmann, S., Shafer, D., & Carpenter, E. J. (1978). Nutrient and
particulate fluxdes in a salt marsh ecosystem: Tidal exchanges and inputs by
precipitation and groundwater. Limnology and Oceanography, 23(4), 798-812.
van Geen, A., Takesue, R. K., Goddard, J., Takahashi, T., Barth, J. A., & Smith, R. L.
(2000). Carbon and nutrie nt dynamics during coastal upwelling off Cape Blanco,
Oregon. Deep-Sea Research II, 47, 975-1002.
Wagschal, A. (2015, March 4). Annual Oyster Harvest Rate. (C. R. Swanson,
Interviewer)
WBD. (2015). Watershed Boundary Database. USGS, National Geospatial Program.
Retrieved July 10, 2015, from
http://viewer.nationalmap.gov/viewer/nhd.html?p=nhd
Wiyot Tribe Natural Resources Department. (2015). Unpublished Data.
WRCC. (2015, January 20). Period of Record Monthly Climate Summary. Eureka, CA:
Western Regional Climate Center.
Yoshinari, T., & Knowles, R. (1976). Acetylene inhibition of nitrous oxide reduction by
denitrifiying bacteria. Biochemical and Biophysical Research Communications,
69, 705-710.
201
APPENDIX A - SAMPLE SITE COORDINATES
Sample site coordinates in UTM zone 10 projection.
Sample Site Longitude Latitude
Wiyot Tribe Sample Sites
Hookton Slough (HS) 396750 4503670
Bay Entrance (BE) 397065 4512670
Samoa Channel (SC) 400915 4519100
Mad River Slough (MRS) 403110 4524445
Indian Island (II) 402390 4518855
Professor Hurst's Sample Sites
Mad River Slough (MRS) 403110 4524445
McDaniel's Slough (MDS) 407260 4523880
Butcher's Slough (BS) 408080 4523385
Freshwater Slough (FWS) 406418 4515718
Eureka Channel (EC) 402040 4517895
Jacoby Creek (JC) 409790 4521300
Elk River (ER) 399158 4512386
Author's Sample Sites
South Bay (SB) 396570 4510875
Bay Entrance (BE) 397065 4512670
Coast Guard Station (CG) 397500 4513390
Main Channel (MC) 399925 4517475
Samoa Channel (SC) 400915 4519100
Mad River Slough Channel (MRC) 403355 4521930
Bird Island (BI) 403195 4519970
Arcata Channel (AC) 405510 4521285
Indian/Woodley Channel (I/W) 403935 4519685
Indian Island (II) 402390 4518855
202
APPENDIX B - WATER QUALITY DATA
203
South Bay (SB) entrance station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/03/22 10:40 Low 10.39 33.12 8.84 0.38 31.75 15.60 1.43 8.29 0.29
2014/03/22 16:54 High 9.34 33.87 7.36 0.04 29.21 24.04 1.93 4.43 0.20
2014/06/03 09:38 Low 13.50 34.05 7.74 0.57 21.83 3.32 1.33 7.05 0.19
2014/06/03 16:38 High 10.48 33.92 11.12 4.52 14.47 4.87 0.37 1.75 0.16
2014/06/16 08:05 Low 13.12 34.31 7.44 2.07 26.68 8.48 1.43 5.10 0.31
2014/06/16 14:49 High 9.86 34.21 8.52 10.79 26.23 13.54 1.07 2.77 0.48
2014/07/17 09:30 Low 13.56 33.89 8.05 1.70 16.23 4.26 1.20 7.19 0.24
2014/07/17 15:45 High 11.08 33.79 9.42 8.29 10.12 8.54 0.92 2.88 0.21
2014/08/13 07:11 Low 14.00 34.04 7.62 1.90 10.12 8.54 0.92 2.88 0.21
2014/08/13 13:45 High 12.51 33.99 11.54 6.54 11.22 3.36 1.09 7.51 0.19
2014/09/12 07:35 Low 13.94 34.01 7.48 2.10 24.91 14.25 1.37 7.01 0.35
2014/09/12 15:37 High 13.10 33.90 9.19 4.00 18.68 17.03 1.47 4.40 0.23
2014/10/12 08:08 Low 12.68 33.67 0.83 19.86 5.59 1.00 7.24 0.43
2014/10/12 13:49 High 12.12 33.69 1.76 19.14 7.47 1.24 4.48 0.39
2014/11/02 13:00 Low 13.64 33.48 8.32 0.91 8.42 17.97 1.41 4.96 0.33
2014/11/02 07:51 High 13.99 33.30 8.75 1.05 15.23 12.70 1.26 7.06 0.41
2014/12/30 12:41 Low 10.13 31.15 9.24 0.78 27.80 2.09 0.72 7.09 0.52
2014/12/31 06:58 High 0.25 17.02 8.79 1.32 3.50 0.20
2015/02/01 15:26 Low 10.80 31.10 6.96 0.70 18.52 8.00 0.86 0.82 0.23
2015/02/01 08:31 High 10.80 31.10 6.96 0.70 18.52 8.00 0.86 0.82 0.23
2015/02/10 09:08 Low 12.70 26.90 7.38 0.43 32.60 7.50 0.81 5.10 0.20
2015/02/10 14:50 High 12.80 27.70 8.78 0.20 25.37 3.38 0.67 1.46 0.09
204
Bay Entrance (BE) station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/01/20 08:00 Low 9.91 33.30 10.00 0.66 13.74 9.66 1.23 4.88 0.24
2014/01/20 12:55 High 9.92 33.46 10.50 0.32 15.00 13.71 1.42 4.22 0.27
2014/03/22 10:50 Low 10.39 32.37 8.90 0.26 29.01 16.57 1.61 5.98 0.31
2014/03/22 17:01 High 9.58 33.86 7.80 0.26 28.84 23.53 1.95 3.22 0.19
2014/06/03 09:50 Low 13.27 33.97 7.86 5.22 25.15 8.65 1.58 6.41 0.29
2014/06/03 16:47 High 10.49 33.94 10.58 7.71 23.28 7.27 0.55 2.69 0.22
2014/06/16 08:20 Low 13.02 34.33 7.38 6.62 32.90 13.21 1.74 4.35 0.39
2014/06/16 14:57 High 9.62 34.20 8.10 10.52 21.95 13.34 1.19 2.73 0.49
2014/07/17 09:40 Low 14.40 33.95 8.01 4.16 22.23 8.30 2.13 9.37 0.33
2014/07/17 15:55 High 12.29 33.76 12.16 7.71 0.74 0.17 0.21 2.17 0.01
2014/08/13 07:24 Low 14.70 34.16 7.99 4.37 12.84 3.18 1.07 4.83 0.19
2014/08/13 13:55 High 12.35 33.92 11.41 6.32 1.83 2.91 0.48 3.06 0.11
2014/09/12 07:50 Low 14.20 34.06 8.59 3.02 22.33 14.66 1.45 4.51 0.28
2014/09/12 15:47 High 13.51 33.86 10.80 7.79 14.40 16.22 1.42 3.51 0.09
2014/10/12 08:19 Low 12.36 33.68 1.88 18.96 4.73 0.90 4.90 0.41
2014/10/12 13:57 High 11.81 33.70 1.45 18.14 4.49 1.22 4.16 0.37
2014/11/02 13:07 Low 13.94 33.36 8.80 1.14 7.89 15.80 1.31 4.54 0.31
2014/11/02 08:00 High 14.28 33.04 8.79 1.36 14.66 13.71 1.29 5.12 0.38
2014/12/30 12:49 Low 10.79 30.37 8.91 0.65 29.67 3.02 0.80 5.97 0.55
2014/12/31 07:12 High 11.10 0.00 0.16 15.67 10.20 1.57 2.48 0.24
2015/02/01 15:35 Low 12.10 30.20 8.10 1.62 17.97 8.20 1.06 1.38 0.21
2015/02/01 08:45 High 11.30 30.60 7.93 0.95 17.16 10.62 0.99 0.90 0.23
2015/02/10 09:17 Low 12.90 25.10 7.47 0.49 43.78 14.05 1.40 7.96 0.34
2015/02/10 15:24 High 12.80 27.70 8.39 0.28 26.60 6.71 0.83 3.76 0.18
205
Coast Guard (CG) station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/01/20 08:10 Low 9.89 33.25 10.76 0.55 13.59 9.22 1.19 6.72 0.23
2014/01/20 13:02 High 9.94 33.46 10.30 0.66 14.37 13.00 1.31 3.60 0.25
2014/03/22 11:00 Low 11.06 31.74 8.90 0.16 30.34 15.60 1.53 8.79 0.32
2014/03/22 17:10 High 9.30 33.92 7.44 0.30 29.89 24.79 1.98 3.92 0.20
2014/06/03 09:57 Low 14.23 34.02 7.40 1.28 27.23 6.82 1.50 7.37 0.28
2014/06/03 16:55 High 10.30 33.95 10.31 8.14 18.76 8.04 0.56 2.45 0.21
2014/06/16 12:49 Low 14.50 34.43 7.01 3.98 34.97 10.03 1.71 5.36 0.34
2014/06/16 15:02 High 9.45 34.21 7.55 11.60 28.91 17.49 1.45 4.33 0.57
2014/07/17 09:45 Low 15.00 34.14 7.62 2.98 23.90 5.57 1.52 7.56 0.26
2014/07/17 16:00 High 12.37 33.76 12.37 5.13 0.73 0.08 0.17 2.09 0.00
2014/08/13 07:30 Low 15.29 34.25 7.50 3.68 17.28 2.97 1.28 6.12 0.22
2014/08/13 14:00 High 12.13 33.95 11.10 6.73 1.16 3.70 0.53 2.77 0.11
2014/09/12 08:00 Low 14.69 34.14 7.83 3.21 25.96 14.30 1.42 6.13 0.34
2014/09/12 15:53 High 13.38 33.88 10.35 8.47 15.25 16.63 1.41 3.30 0.14
2014/10/12 08:26 Low 12.58 33.67 1.99 19.62 5.01 0.95 5.61 0.40
2014/10/12 14:02 High 11.65 33.71 1.19 18.30 7.63 1.38 5.39 0.39
2014/11/02 13:14 Low 13.85 33.39 8.59 1.18 8.29 16.57 1.35 3.57 0.29
2014/11/02 08:06 High 14.40 32.81 8.65 1.30 18.26 14.58 1.42 7.04 0.41
2014/12/30 12:56 Low 10.54 29.54 8.97 0.64 34.88 4.24 0.95 6.27 0.53
2014/12/31 07:20 High 0.19 15.91 6.14 1.90 2.20 0.22
2015/02/01 15:42 Low 11.30 30.60 7.86 0.95 17.02 10.66 1.04 1.17 0.23
2015/02/01 08:55 High 11.30 30.60 7.86 0.95 17.02 10.66 1.04 1.17 0.23
2015/02/10 09:25 Low 13.00 25.70 7.40 0.34 40.45 10.68 1.16 7.39 0.29
2015/02/10 15:38 High 12.90 28.00 8.40 0.10 19.35 3.67 0.65 1.86 0.09
206
Main Channel (MC) station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/01/20 08:25 Low 9.89 32.99 0.90 13.15 6.30 1.05 5.38 0.19
2014/01/20 13:17 High 9.95 33.39 10.20 0.69 14.16 11.11 1.24 4.54 0.25
2014/03/22 11:15 Low 11.47 30.82 8.45 0.46 27.69 10.08 1.28 7.44 0.36
2014/03/22 17:25 High 10.88 32.67 8.94 0.21 30.19 19.54 1.73 6.30 0.31
2014/06/03 10:09 Low 16.18 34.10 6.42 0.67 31.97 4.06 1.67 8.66 0.26
2014/06/03 17:10 High 11.43 33.96 9.79 8.22 27.39 7.85 0.77 3.21 0.30
2014/06/16 08:41 Low 16.32 34.64 6.38 1.34 40.00 5.52 1.83 6.35 0.27
2014/06/16 15:16 High 10.07 34.23 7.50 9.93 29.85 18.29 1.42 2.98 0.52
2014/07/17 10:00 Low 16.69 34.39 6.66 1.58 32.41 3.14 1.87 8.41 0.26
2014/07/17 16:10 High 12.50 33.78 11.61 7.63 1.03 0.07 0.22 2.24 0.00
2014/08/13 07:43 Low 16.86 34.49 6.36 1.89 28.59 3.04 1.76 8.26 0.26
2014/08/13 14:15 High 12.54 33.92 12.10 6.41 0.26 1.25 0.32 2.39 0.06
2014/09/12 08:15 Low 16.27 34.32 7.06 3.31 33.40 14.81 1.75 6.29 0.34
2014/09/12 16:06 High 13.83 33.95 9.17 4.54 17.18 22.54 1.43 4.32 0.22
2014/10/12 08:39 Low 14.58 33.55 1.39 24.72 9.73 1.70 7.52 0.43
2014/10/12 14:14 High 11.85 33.69 1.48 18.80 7.20 1.39 5.27 0.40
2014/11/02 13:28 Low 14.13 33.24 8.65 1.09 9.24 10.51 0.96 5.03 0.29
2014/11/02 08:18 High 14.82 32.16 8.28 1.26 27.46 15.04 1.51 8.15 0.46
2014/12/30 13:09 Low 10.00 27.70 9.17 0.73 46.11 10.00 1.03 7.70 0.50
2014/12/31 07:32 High 0.26 17.01 8.55 1.98 2.08 0.24
2015/02/01 15:56 Low 11.30 30.90 7.88 0.99 15.31 10.75 1.04 0.55 0.25
2015/02/01 09:10 High 11.30 30.90 7.88 0.99 15.31 10.75 1.04 0.55 0.25
2015/02/10 09:38 Low 13.00 24.10 6.96 0.45 52.65 13.56 1.36 10.24 0.36
2015/02/10 15:53 High 13.00 26.40 8.14 0.50 36.60 9.33 1.04 5.86 0.22
207
Samoa Channel (SC) station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/01/20 08:33 Low 9.92 32.97 11.15 0.23 13.54 6.35 1.08 6.16 0.19
2014/01/20 13:25 High 9.97 33.32 10.31 0.66 13.69 10.10 1.20 5.17 0.24
2014/03/22 11:30 Low 11.52 30.70 8.39 0.81 28.44 10.97 1.31 7.17 0.36
2014/03/22 17:37 High 11.54 31.93 8.89 0.16 30.35 15.52 1.58 6.71 0.34
2014/06/03 10:18 Low 16.66 34.15 6.40 0.61 37.65 3.17 1.68 8.80 0.33
2014/06/03 17:18 High 12.88 33.96 8.89 8.02 21.15 6.29 0.91 5.15 0.27
2014/06/16 08:47 Low 16.91 34.71 6.07 1.19 41.24 4.16 1.87 6.12 0.24
2014/06/16 15:24 High 10.81 34.26 7.41 9.23 36.60 17.88 1.88 4.39 0.54
2014/07/17 10:05 Low 17.10 34.46 6.45 1.33 33.93 2.79 1.84 8.41 0.24
2014/07/17 16:18 High 12.88 33.81 11.10 7.75 2.30 0.30 0.35 2.51 0.03
2014/08/13 07:51 Low 17.51 34.59 6.06 1.90 32.63 2.79 1.95 7.95 0.26
2014/08/13 14:20 High 13.26 33.99 11.40 6.43 1.69 1.41 0.44 3.07 0.08
2014/09/12 08:25 Low 16.92 34.41 7.00 2.47 34.97 15.06 1.82 5.59 0.29
2014/09/12 16:14 High 13.77 33.95 9.32 4.31 17.78 15.68 1.49 3.18 0.18
2014/10/12 08:46 Low 15.10 33.52 1.28 26.84 10.30 1.13 7.12 0.41
2014/10/12 14:22 High 11.98 33.71 2.24 19.42 8.09 1.90 6.17 0.36
2014/11/02 13:35 Low 14.34 32.99 8.43 0.57 12.31 17.62 1.33 5.37 0.32
2014/11/02 08:27 High 14.96 31.87 8.43 1.41 31.81 15.63 1.62 8.60 0.48
2014/12/30 13:17 Low 10.03 27.81 9.10 0.77 45.63 8.74 1.39 9.06 0.57
2014/12/31 07:41 High 0.40 21.38 5.85 2.33 4.05 0.34
2015/02/01 16:05 Low 11.50 30.90 7.72 1.27 15.17 10.26 1.07 1.28 0.25
2015/02/01 09:20 High 11.50 30.90 7.72 1.27 15.17 10.26 1.07 1.28 0.25
2015/02/10 09:45 Low 13.20 24.60 6.73 0.55 49.91 13.87 1.47 10.51
2015/02/10 16:03 High 13.00 26.40 7.91 0.48 39.31 10.20 1.14 7.11
208
Mad River Slough Channel (MRC) station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/01/20 09:15 Low 8.98 32.64 11.18 0.30 8.36 1.20 0.74 4.76 0.06
2014/01/20 14:00 High 10.08 32.98 10.51 0.71 13.32 6.10 1.08 5.79 0.19
2014/03/22 11:45 Low 11.66 29.94 8.70 0.13 26.43 6.73 1.22 7.11 0.34
2014/03/22 17:29 High 11.69 31.14 8.65 0.46 29.91 12.58 1.42 7.18 0.37
2014/06/03 10:30 Low 17.57 34.31 5.66 0.39 39.05 1.37 1.83 8.47 0.24
2014/06/03 17:31 High 17.56 34.20 6.78 3.37 35.76 3.23 1.74 8.76 0.31
2014/06/16 08:57 Low 17.38 34.90 5.65 1.08 45.30 2.43 2.24 6.07 0.20
2014/06/16 15:36 High 15.28 34.50 6.95 3.30 29.71 6.62 1.22 7.36 0.54
2014/07/17 10:20 Low 18.30 34.81 5.81 1.53 45.75 2.60 2.33 7.67 0.27
2014/07/17 16:33 High 14.95 34.11 7.78 10.56 22.23 5.00 1.44 6.87 0.26
2014/08/13 08:01 Low 18.44 34.89 5.53 2.09 43.27 2.71 2.45 7.93 0.26
2014/08/13 14:30 High 15.00 34.17 8.63 4.30 15.30 3.12 1.18 5.94 0.21
2014/09/12 08:38 Low 17.67 34.66 5.95 1.02 40.07 10.11 2.18 5.42 0.25
2014/09/12 16:24 High 15.32 34.13 8.68 4.97 24.51 13.82 1.66 4.31 0.24
2014/10/12 08:58 Low 15.72 33.45 0.81 32.60 11.02 1.62 6.93 0.39
2014/10/12 14:32 High 13.80 33.61 1.03 22.72 14.46 2.12 6.04 0.38
2014/11/02 13:48 Low 15.03 32.11 8.12 1.17 23.71 18.83 1.44 7.93 0.43
2014/11/02 08:38 High 15.10 31.60 9.21 1.74 36.02 18.32 2.09 7.50 0.43
2014/12/30 13:34 Low 9.34 25.11 9.44 0.91 62.35 7.50 1.21 11.43 0.73
2014/12/31 07:53 High 0.55 32.36 6.30 2.18 4.19 0.47
2015/02/01 16:17 Low 13.20 28.70 8.76 1.42 29.17 4.93 1.27 1.76 0.09
2015/02/01 09:36 High 12.00 30.20 7.11 1.32 19.04 7.87 1.02 1.21 0.20
2015/02/10 09:57 Low 12.90 22.90 6.72 0.95 60.33 18.80 1.90 13.35 0.61
2015/02/10 16:14 High 13.30 24.60 7.74 0.71 50.39 13.76 1.49 10.86 0.40
209
Bird Island (BI) station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/01/20 09:43 Low 9.34 32.79 11.13 0.49 13.10 4.37 1.02 7.23 0.17
2014/01/20 14:10 High 10.05 33.07 10.20 0.77 13.66 7.14 1.12 6.23 0.20
2014/03/22 12:05 Low 11.52 30.34 8.35 1.09 27.51 7.79 1.19 7.83 0.34
2014/03/22 18:12 High 11.71 31.35 8.76 0.61 31.51 13.21 1.45 7.09 0.35
2014/06/03 10:45 Low 17.30 34.26 5.50 0.63 34.89 1.53 1.69 7.80 0.20
2014/06/03 17:48 High 14.83 34.02 7.36 1.96 28.27 6.49 1.52 8.33 0.29
2014/06/16 09:10 Low 16.93 34.80 5.93 1.56 44.77 3.19 2.01 10.71 0.32
2014/06/16 15:53 High 12.55 34.32 7.55 5.62 30.42 12.52 1.41 6.08 0.56
2014/07/17 10:30 Low 17.71 34.61 5.83 1.47 38.96 2.06 2.05 7.13 0.22
2014/07/17 16:37 High 13.69 33.92 9.15 6.08 13.58 3.90 0.93 4.87 0.20
2014/08/13 08:12 Low 18.08 34.71 5.78 1.80 37.26 2.79 2.17 8.80 0.27
2014/08/13 14:40 High 13.53 33.99 10.81 5.72 2.28 1.41 0.53 3.38 0.10
2014/09/12 08:50 Low 17.40 34.52 6.32 1.80 39.62 11.25 2.03 6.44 0.29
2014/09/12 16:35 High 14.86 34.05 9.27 6.33 22.04 14.68 1.52 4.47 0.18
2014/10/12 09:13 Low 15.63 33.47 1.13 30.76 9.62 1.38 8.56 0.37
2014/10/12 14:43 High 12.89 33.67 1.09 20.40 14.46 2.04 6.22 0.35
2014/11/02 13:59 Low 14.73 32.56 8.53 1.41 18.29 16.31 1.38 7.24 0.37
2014/11/02 08:49 High 15.03 31.50 8.56 1.04 35.98 16.55 1.66 9.25 0.48
2014/12/30 13:46 Low 9.89 26.88 9.09 0.57 49.80 10.09 1.42 10.11 0.53
2014/12/31 08:06 High 0.49 25.63 7.44 2.25 5.12 0.39
2015/02/01 16:27 Low 13.00 29.00 8.25 1.76 26.00 4.86 1.09 2.95 0.16
2015/02/01 09:48 High 11.80 30.60 7.38 1.35 16.84 8.72 0.97 1.09 0.22
2015/02/10 10:09 Low 12.90 24.20 6.88 0.70 53.91 15.28 1.54 5.75 0.46
2015/02/10 16:23 High 13.20 25.00 7.91 0.81 47.47 12.83 1.37 9.29 0.39
210
Arcata Channel (AC) station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/01/20 09:53 Low 8.85 32.45 10.31 0.62 10.80 3.75 0.90 5.20 0.13
2014/01/20 14:30 High 10.24 32.84 11.18 0.85 12.72 4.62 1.01 5.87 0.16
2014/03/22 12:15 Low 10.67 29.61 8.05 0.82 26.67 5.50 1.18 8.60 0.30
2014/03/22 18:29 High 11.73 30.88 8.54 0.36 29.77 11.30 1.35 7.93 0.38
2014/06/03 10:56 Low 17.03 34.27 5.21 0.60 36.76 0.85 1.79 10.09 0.18
2014/06/03 18:00 High 16.20 34.09 6.58 1.59 40.29 4.34 1.99 14.66 0.35
2014/06/16 09:18 Low 16.85 35.07 5.05 1.42 43.95 0.75 1.97 4.81 0.09
2014/06/16 16:04 High 14.99 34.47 7.12 3.42 35.85 9.32 1.73 6.51 0.40
2014/07/17 10:40 Low 18.06 34.80 5.11 2.47 46.69 1.49 2.24 6.37 0.19
2014/07/17 16:50 High 15.32 34.15 7.54 3.20 23.78 4.93 1.51 7.52 0.27
2014/08/13 08:25 Low 18.05 34.89 5.06 2.29 44.85 3.23 2.22 8.38 0.31
2014/08/13 14:48 High 14.81 34.14 8.85 5.06 12.90 3.01 1.03 5.96 0.21
2014/09/12 09:02 Low 17.34 34.59 5.88 1.63 41.66 11.84 2.12 6.96 0.28
2014/09/12 16:46 High 14.87 34.08 8.71 3.22 24.52 9.93 1.73 5.31 0.23
2014/10/12 09:23 Low 15.50 33.44 1.60 36.46 13.76 1.68 8.52 0.38
2014/10/12 14:50 High 14.31 33.59 1.10 24.21 14.40 2.06 7.32 0.41
2014/11/02 14:11 Low 15.07 31.91 8.02 0.72 26.27 14.42 1.44 9.42 0.43
2014/11/02 08:59 High 15.27 30.94 8.72 1.60 42.94 18.34 1.69 9.60 0.49
2014/12/30 14:00 Low 9.52 25.96 9.27 0.64 56.60 9.01 1.60 11.35 0.57
2014/12/31 08:18 High 0.57 34.06 3.84 2.04 6.89 0.49
2015/02/01 16:37 Low 13.50 28.40 7.71 2.17 32.07 7.44 1.36 8.80 0.24
2015/02/01 10:00 High 12.10 29.90 6.95 1.51 20.91 7.32 1.09 1.92 0.23
2015/02/10 10:21 Low 12.50 23.10 6.88 0.74 60.08 17.25 1.56 11.42 0.45
2015/02/10 16:32 High 13.20 24.50 7.36 1.06 52.14 14.52 1.57 12.21 0.48
211
Indian/Woodley Channel (I/W) station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/01/20 10:15 Low 9.37 32.69 10.77 0.38 14.02 4.14 1.14 11.10 0.24
2014/01/20 14:47 High 10.13 33.06 10.84 1.96 14.18 7.28 1.15 6.30 0.20
2014/03/22 12:30 Low 11.80 29.98 8.35 0.66 29.00 7.83 1.17 8.20 0.39
2014/03/22 18:41 High 12.39 30.90 9.01 0.55 30.39 11.64 1.37 7.49 0.37
2014/06/03 11:06 Low 17.52 34.30 6.19 0.74 32.95 1.90 1.55 6.47 0.21
2014/06/03 18:13 High 16.08 34.07 7.23 1.55 30.56 4.62 1.66 9.03 0.27
2014/06/16 09:27 Low 17.70 35.06 5.89 1.52 43.49 1.98 1.83 5.82 0.18
2014/06/16 16:17 High 14.05 34.39 7.65 5.68 31.73 10.52 1.52 5.53 0.40
2014/07/17 10:52 Low 18.38 34.75 6.36 1.00 36.01 1.30 1.98 5.40 0.16
2014/07/17 17:00 High 34.01 8.61 5.03 17.66 4.72 1.21 5.84 0.26
2014/08/13 08:33 Low 18.46 34.92 5.28 1.66 31.20 0.55 2.06 4.03 0.10
2014/08/13 15:00 High 14.75 34.16 9.46 5.38 11.58 2.69 1.01 5.40 0.20
2014/09/12 09:30 Low 17.59 34.57 6.57 1.10 34.85 8.64 2.03 5.32 0.17
2014/09/12 16:55 High 15.68 34.15 8.32 3.33 27.14 11.59 1.62 5.80 0.28
2014/10/12 09:34 Low 15.65 33.45 1.69 27.55 8.24 1.45 6.59 0.34
2014/10/12 14:59 High 13.78 33.62 0.60 22.29 11.09 1.82 6.53 0.35
2014/11/02 14:21 Low 14.82 32.32 8.25 0.64 20.51 14.01 1.41 7.89 0.40
2014/11/02 09:10 High 14.99 31.18 10.43 1.40 29.56 13.97 1.67 5.55 0.39
2014/12/30 14:11 Low 9.79 26.15 9.38 0.90 52.80 8.09 1.42 9.29 0.48
2014/12/31 08:29 High 0.57 31.29 6.00 1.93 4.60 0.47
2015/02/01 16:47 Low 13.20 28.90 8.01 2.37 22.44 1.82 0.92 1.37 0.08
2015/02/01 10:15 High 11.90 30.30 7.42 1.74 18.34 8.22 1.03 1.91 0.26
2015/02/10 10:28 Low 13.00 24.20 6.93 1.10 54.62 13.84 1.49 10.30 0.40
2015/02/10 16:40 High 13.20 24.40 7.80 0.85 51.49 14.42 1.40 10.26 0.42
212
Indian Island (II) station water quality data.
Date/Time (LST) Tide
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/01/20 10:37 Low 9.56 32.89 10.70 0.50 13.12 5.14 1.05 5.92 0.18
2014/01/20 14:58 High 10.62 33.02 11.38 0.61 13.03 6.36 1.08 5.72 0.19
2014/03/22 12:40 Low 11.66 29.98 8.26 0.64 29.98 9.14 1.21 8.29 0.41
2014/03/22 18:51 High 11.74 31.42 8.70 0.48 34.45 13.55 1.46 7.18 0.36
2014/06/03 11:17 Low 17.14 34.21 6.29 0.63 32.09 2.41 1.63 7.71 0.23
2014/06/03 18:24 High 14.80 33.99 7.75 3.12 31.92 6.42 1.51 11.95 0.33
2014/06/16 09:36 Low 16.74 34.70 5.98 1.58 40.66 4.50 1.88 7.58 0.27
2014/06/16 16:28 High 12.54 34.33 7.45 6.78 33.05 11.13 1.59 5.23 0.38
2014/07/17 11:05 Low 17.52 34.54 6.16 1.32 33.67 2.10 1.93 7.82 0.21
2014/07/17 17:10 High 14.77 34.06 8.77 1.23 17.60 3.70 1.13 6.03 0.24
2014/08/13 08:40 Low 17.10 34.55 6.09 6.10 30.26 2.27 1.90 7.32 0.22
2014/08/13 15:10 High 14.30 34.08 10.15 7.09 8.60 1.91 0.77 4.66 0.16
2014/09/12 09:42 Low 17.24 34.48 7.26 2.83 32.92 12.67 2.01 5.21 0.20
2014/09/12 17:04 High 15.27 34.13 8.78 3.89 24.46 20.04 1.59 5.22 0.25
2014/10/12 09:44 Low 15.51 33.48 9.79 0.96 28.02 11.11 1.31 5.10 0.41
2014/10/12 15:07 High 13.29 33.65 11.51 1.28 20.98 14.45 1.80 7.50 0.39
2014/11/02 14:28 Low 14.60 32.54 8.33 1.14 17.76 20.22 1.45 6.29 0.39
2014/11/02 09:19 High 15.32 31.80 9.37 1.68 28.88 23.76 1.58 7.71 0.44
2014/12/30 14:23 Low 10.21 26.73 9.33 1.10 50.12 6.40 1.45 8.27 0.51
2014/12/31 08:40 High 8.50 0.51 33.44 15.86 1.31 5.62 0.47
2015/02/01 17:04 Low 13.00 29.10 8.20 1.87 23.06 3.40 1.01 2.03 0.14
2015/02/01 10:30 High 11.70 30.70 7.55 1.31 16.36 9.46 1.05 1.62 0.29
2015/02/10 10:38 Low 13.00 24.00 7.10 0.75 54.75 14.27 1.46 10.23 0.44
2015/02/10 16:49 High 14.10 24.30 8.74 1.22 52.63 13.63 1.49 10.23 0.46
213
Mad River Slough (MRS) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2012/10/13 11:44 15.90 33.30 28.00 4.00 2.20 7.20 0.10
2012/10/20 11:07 15.70 32.70 1.60 24.60 4.20 2.10 5.90 0.10
2012/10/27 16:10 14.41 31.65 2.21 25.90 5.80 2.60 4.70 0.10
2012/11/03 12:03 14.86 32.22 2.12 23.00 4.50 1.90 7.60 0.20
2012/11/17 12:12 12.84 31.95 1.70 23.40 5.10 1.80 7.40 0.20
2012/12/01 11:56 12.71 27.64 1.90 40.40 11.20 1.80 11.50 0.40
2012/12/15 10:58 8.91 28.11 1.57 43.20 9.80 1.60 10.70 0.40
2012/12/29 10:10 8.21 22.58 1.28 62.50 15.90 1.90 13.00 0.50
2013/01/14 12:18 7.39 28.09 2.04 46.10 12.70 1.60 6.70 0.30
2013/01/26 14:05 9.84 28.47 9.34 1.98 39.00 9.50 1.50 5.30 0.20
2013/02/09 13:32 8.86 29.55 9.49 3.47 24.80 3.80 1.20 4.20 0.10
2013/02/23 11:40 9.46 30.75 9.41 3.77 16.10 1.20 0.90 3.40 0.00
2013/03/10
2013/04/13 14:00 13.90 30.37 2.49 29.60 2.90 1.80 6.60 0.10
2013/04/27 12:30 14.00 33.20 4.20 27.50 3.20 1.90 7.50 0.10
2013/05/11 10:45 16.04 33.40 8.85 8.61 14.60 0.00 1.50 6.00 0.00
2013/05/26 13:55 18.63 34.10 9.36 6.15 22.10 0.80 1.90 5.00 0.00
2013/06/08 11:43 17.94 32.88 7.46 8.14 2.00 1.50 2.00 0.00
2013/06/22 14:40 19.74 34.01 8.01 9.35 6.20 0.20 3.70 2.70 0.00
2013/07/06 13:00 20.20 34.30 7.35 5.93 3.80 0.00 2.80 2.60 0.00
2013/07/20 11:57 17.33 34.78 7.92 6.33 1.90 0.00 2.70 2.40 0.00
2013/08/16 13:00 22.29 34.82 8.00 2.93 4.80 0.40 3.00 2.80 0.00
214
Mad River Slough (MRS) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2013/08/24 18:10 18.58 34.55 7.42 3.90 24.30 0.70 2.80 3.30 0.00
2013/09/07 15:34 20.70 34.35 7.23 3.83 24.60 0.20 2.80 2.70 0.00
2013/09/20 18:05 18.33 34.16 7.66 1.38 25.20 0.80 3.10 2.70 0.00
2013/10/05 15:25 16.00 32.36 8.73 1.86 24.80 0.80 2.10 3.10 0.00
2013/10/19 16:35 13.92 33.10 8.36 1.09 21.60 1.70 1.90 3.70 0.00
2013/11/08 15:15 12.80 32.60 10.16 0.90 17.50 2.70 1.50 3.60 0.00
2013/11/23 17:10 10.36 33.04 10.10 1.15 19.30 2.00 1.30 5.40 0.10
2013/12/07 13:05 6.48 32.85 10.54 1.07 16.90 2.50 1.20 4.20 0.00
2013/12/21 16:50 7.27 32.91 10.76 1.38 14.80 3.20 1.10 3.80 0.00
2014/01/15 14:10 9.04 32.44 10.24 0.59 15.90 3.20 1.10 5.50 0.10
2014/02/02 12:45 9.67 32.76 10.04 1.12 15.90 3.00 1.10 4.40 0.10
2014/02/15 12:20 12.32 31.67 9.49 1.74 26.00 5.80 1.30 13.50 0.40
2014/03/02 17:48 13.23 27.79 1.42 36.10 8.60 1.80 8.50 0.60
2014/03/15 13:26 14.15 26.96 8.91 1.55 33.20 6.80 1.40 9.70 0.50
2014/03/29 12:00 12.85 29.51 8.85 0.87 25.90 5.00 1.30 5.80 0.20
2014/04/12 11:00 15.08 30.21 8.53 1.32 21.40 2.30 1.20 4.70 0.10
2014/04/26 11:00 15.45 31.55 7.95 1.64 19.40 3.10 1.60 4.10 0.20
2014/05/10 13:36 17.90 32.57 6.72 1.33 29.40 2.30 2.20 5.00 0.20
2014/05/26 12:45 18.54 33.80 7.35 0.49 30.20 1.90 1.80 4.80 0.20
2014/06/14 14:31 18.44 34.72 7.93 0.44 44.80 3.29 2.09 8.27 0.24
2014/06/28 14:43 19.35 34.75 6.96 2.10 40.50 2.12 2.10 9.45 0.26
2014/07/26 10:49 19.66 34.90 6.36 2.50 46.10 1.55 2.41 6.39 0.22
215
Mad River Slough (MRS) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/08/05 19:39 19.43 34.81 7.50 3.70 53.70 2.20 2.25 6.75 0.28
2014/08/26 12:36 18.94 33.71 6.63 0.91 42.32 2.16 2.38 7.62 0.34
2014/09/02 13:31 20.14 34.84 6.19 2.10 44.15 2.25 2.80 6.18 0.33
2014/09/16 13:20 18.48 34.60 6.20 3.25 22.38 2.50 1.66 3.13 0.20
2014/09/30 13:00 18.91 32.79 6.04 0.96 56.57 9.26 2.25 7.37 0.51
2014/10/14 12:54 16.16 33.47 4.48 1.49 32.85 7.59 2.19 6.74 0.35
2014/10/28 13:34 15.35 31.62 9.90 1.16 38.61 8.17 2.22 10.83 0.53
2014/11/11 16:02 14.95 32.22 8.69 1.43 29.97 7.91 1.97 6.25 0.47
2014/11/29 13:17 12.75 28.98 8.33 1.52 40.46 15.69 2.24 8.12 0.47
2014/12/09 13:30 13.67 28.97 8.75 1.37 41.81 13.85 1.92 11.30 0.49
216
McDaniel's Slough (MDS) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2012/10/13 11:14 16.40 32.80 36.36 4.74 3.32 7.50 0.20
2012/10/20 10:30 16.50 31.70 3.43 41.32 7.08 3.77 10.39 0.34
2012/11/03 11:15 15.69 30.70 3.49 41.88 10.12 3.24 10.12 0.36
2012/11/17 16:26 13.28 30.10 3.42 31.81 5.80 2.12 5.90 0.17
2012/12/01 10:19 12.77 14.10 2.28 69.23 30.94 3.34 22.03 0.83
2012/12/15 12:15 7.94 24.70 1.77 60.58 15.88 1.41 12.12 0.42
2012/12/29 13:10 8.00 21.50 0.45 78.68 61.80 1.49 11.81 0.60
2013/01/14 13:53 6.53 24.20 2.10 68.42 19.96 1.48 9.46 0.33
2013/01/26 13:09 10.13 26.20 9.16 0.94 50.10 12.73 1.30 7.28 0.19
2013/02/09 12:22 8.56 25.60 1.92 43.06 7.84 1.10 5.85 0.09
2013/02/23 11:10 9.64 27.90 4.19 33.36 4.88 0.92 5.05 0.08
2013/03/10 2.83 70.40 4.98 1.44 5.88 0.08
2013/04/13 16:00 15.51 27.00 5.21 24.53 2.38 1.59 6.09 0.05
2013/04/27 14:41 14.93 29.80 3.68 31.53 4.38 1.84 10.48 0.20
2013/05/11 11:49 15.73 25.40 5.01 4.81 27.86 9.75 2.15 12.59 0.36
2013/05/26 15:20 20.20 33.70 7.88 6.35 21.52 0.64 2.03 4.05 0.00
2013/06/08 13:07 20.40 32.00 6.23 6.48 22.40 1.10 0.99 3.24 0.00
2013/06/22 15:40 21.83 33.00 5.56 5.04 13.50 0.43 6.81 4.50 0.00
2013/07/06 14:40 23.10 29.70 6.56 3.50 21.20 0.11 2.70 3.15 0.00
2013/07/20 14:26 19.23 34.60 5.49 3.76 18.10 0.71 2.04 4.52 0.00
2013/08/16 10:12 22.63 34.60 4.29 3.68 28.60 0.68 1.92 5.07 0.00
2013/08/24 16:05 20.24 34.40 6.36 2.20 29.50 0.55 2.23 3.76 0.00
2013/09/07 15:10 21.99 34.50 5.13 3.31 46.90 0.41 3.17 4.39 0.00
2013/09/20 16:00 17.73 32.40 7.29 1.59 37.00 1.34 1.63 3.37 0.00
217
Freshwater Slough (FWS) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2012/10/13 13:37 16.20 25.20 52.64 8.84 1.27 3.31 0.12
2012/10/20 11:51 15.50 19.10 2.55 111.56 11.79 1.49 5.17 0.16
2012/10/27 14:58 13.38 13.13 2.33 131.64 14.14 1.22 3.25 0.10
2012/11/03 13:55 14.63 23.34 5.51 114.45 8.60 1.50 4.48 0.15
2012/11/17 11:00 11.90 20.05 2.32 105.59 8.60 1.16 5.23 0.11
2012/12/01 13:23 11.56 0.05 0.62 108.79 24.56 0.44 1.68 0.14
2012/12/15 10:05 6.78 2.69 1.08 176.00 11.63 0.62 3.25 0.06
2012/12/29 09:21 7.76 0.08 0.12 177.00 11.78 0.59 1.69 0.05
2013/01/14 10:53 4.33 0.21 0.14 163.00 14.67 0.81 2.47 0.05
2013/01/26 15:10 8.61 1.30 10.73 0.43 188.00 10.53 0.70 2.47 0.09
2013/02/09 14:42 6.41 0.14 12.42 0.45 166.00 9.46 0.92 5.06 0.06
2013/02/23 12:40 7.92 1.70 11.29 1.74 140.00 7.12 1.62 6.02 0.06
2013/03/10 0.29
2013/04/13 15:00 13.97 3.21 1.97 52.36 9.63 3.67 4.02 0.06
2013/04/27 11:45 14.91 16.70 132.06 1.84 2.90 5.39 0.02
2013/05/11 04:45 14.55 4.90 9.72 4.17 104.36 2.49 3.41 4.96 0.04
2013/05/26 14:45 18.38 25.60 6.79 7.40 32.21 0.50 2.02 3.84 0.00
2013/06/08 12:08 20.21 21.80 6.06 6.33 33.40 0.71 1.57 2.48 0.00
2013/06/22 13:30 21.80 23.10 4.68 6.94 27.60 0.06 1.98 1.95 0.00
2013/07/06 13:50 22.87 26.30 5.64 3.89 44.20 0.31 2.08 2.14 0.00
2013/07/20 13:16 19.31 27.00 4.85 4.75 62.40 1.47 2.09 2.91 0.07
2013/08/16 11:39 23.01 23.36 4.95 4.87 92.80 4.01 1.57 2.39 0.19
2013/08/24 17:10 19.96 26.06 5.62 6.46 64.40 3.30 2.21 4.26 0.16
218
Freshwater Slough (FWS) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2013/09/07 16:45 20.21 27.92 6.57 7.16 89.60 0.16 1.97 2.66 0.00
2013/09/20 16:45 17.85 25.62 5.98 2.94 100.80 6.96 2.52 3.89 0.15
2013/10/05 14:30 15.17 20.51 9.09 4.59 80.40 7.52 1.46 3.74 0.00
2013/10/19 15:37 13.42 24.66 8.22 1.26 66.40 3.60 1.18 2.55 0.00
2013/11/08 13:50 12.78 28.09 10.07 2.15 47.80 2.64 1.15 3.48 0.00
2013/11/23 18:10 7.94 10.02 10.55 1.14 154.80 5.24 0.96 3.99 0.00
2013/12/07 11:00 4.48 17.66 11.18 0.82 126.60 6.88 0.85 5.43 0.00
2013/12/21 16:00 6.18 19.89 11.32 0.84 99.80 5.42 0.74 4.51 0.00
2014/01/15 13:15 7.72 23.33 10.29 1.95 66.48 5.65 0.75 6.49 0.13
2014/02/02 13:24 8.86 25.61 9.65 3.41 54.35 5.64 0.83 5.85 0.14
2014/02/15 11:39 10.75 0.13 12.01 1.43 93.54 38.58 0.67 2.75 0.29
2014/03/02 18:50 10.95 1.53 10.19 0.29 142.18 13.67 0.65 2.35 0.17
2014/03/15 12:33 13.27 5.34 8.01 1.11 142.77 22.29 0.86 7.27 0.38
2014/03/29 19:54 10.67 0.11 12.12 0.34 98.37 15.24 0.55 1.13 0.31
2014/04/12 10:06 16.07 16.34 7.67 6.67 91.91 0.52 0.48 1.93 0.00
2014/04/26 10:56 15.45 18.56 8.12 6.08 75.53 0.43 0.62 2.21 0.04
2014/05/10 12:55 14.87 5.06 9.23 1.71 93.46 5.74 0.67 1.44 0.11
2014/05/26 12:04 20.40 23.93 6.48 1.54 12.70 0.59 0.75 2.00 0.03
2014/06/14 13:41 20.74 28.75 5.86 1.00 29.60 0.64 1.26 6.82 0.15
2014/06/28 13:29 21.29 28.47 4.62 2.10 63.20 3.07 1.49 6.70 0.35
2014/07/26 10:08 20.28 34.51 6.06 5.00 68.75 2.70 1.40 5.84 0.23
2014/08/05 18:55 21.79 32.17 6.76 5.60 39.85 0.46 1.43 3.91 0.15
2014/08/26 13:23 20.15 33.00 6.32 1.19 12.45 0.25 1.42 4.25 0.09
219
Freshwater Slough (FWS) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/09/02 14:23 22.05 29.13 7.00 2.78 11.55 0.07 0.98 3.95 0.07
2014/09/16 14:22 19.15 30.88 7.94 3.98 18.59 1.43 0.94 3.21 0.18
2014/09/25 16:41 17.71 9.97 31.80 38.40 1.67 7.88 0.61
2014/09/30 13:43 19.67 30.92 5.43 5.08 79.43 13.95 1.28 4.11 0.43
2014/10/14 14:51 16.22 29.86 3.62 1.64 53.10 10.35 1.78 5.83 0.40
2014/10/24 19:14 0.80 9.48 0.77 43.30 43.60 1.40 3.15 0.42
2014/10/28 14:33 14.04 29.62 7.94 1.55 95.42 24.71 1.67 6.50 0.42
2014/11/11 16:02 14.47 25.34 7.16 3.16 71.79 15.36 1.60 5.11 0.36
2014/11/29 14:53 11.67 0.25 11.15 2.96 137.70 42.72 1.05 1.40 0.48
2014/12/09 14:25 13.21 23.14 8.73 0.58 75.62 12.27 1.96 14.32 0.46
2014/12/12 0.94 27.60 27.20 0.59 1.72 0.25
220
Eureka Channel (EC) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2012/10/13 13:05 13.90 33.30 21.15 5.71 1.86 0.15
2012/10/20 11:38 15.00 32.60 1.20 24.37 5.28 2.27 9.50 0.22
2012/10/27 15:34 13.91 31.44 2.20 25.48 4.41 1.67 10.90 0.26
2012/11/03 12:42 13.60 32.66 1.05 16.45 6.26 1.43 6.58 0.23
2012/11/17 11:49 11.93 32.74 1.73 14.65 5.89 1.24 4.98 0.14
2012/12/01 12:17 13.19 29.34 0.95 20.36 6.20 0.88 5.72 0.16
2012/12/15 10:32 10.88 31.80 2.51 20.01 8.93 1.08 4.95 0.29
2012/12/29 09:45 10.10 28.09 0.89 33.87 11.37 1.00 5.16 1.71
2013/01/14 11:35 8.70 31.01 2.95 29.80 13.22 1.32 4.51 0.18
2013/01/26 14:35 9.90 28.35 9.32 1.24 39.55 11.09 1.27 4.19 0.13
2013/02/09 14:04 9.49 29.49 9.94 6.44 25.63 7.86 1.11 3.18 0.09
2013/02/23 12:10 10.01 29.89 9.55 3.17 29.80 6.47 1.09 3.71 0.11
2013/03/10 2.53 41.71 5.09 1.93 8.86 0.12
2013/04/13 14:30 12.64 31.14 1.72 29.68 6.33 1.91 6.71 0.15
2013/04/27 13:00 12.70 33.20 3.83 25.61 12.43 2.21 6.67 0.16
2013/05/11 10:15 14.98 33.50 9.03 14.68 21.32 0.42 1.03 6.45 0.00
2013/05/26 14:25 12.06 34.10 8.66 6.04 39.71 14.02 2.04 5.51 0.27
2013/06/08 11:15 15.71 33.94 8.81 13.68 10.70 3.31 1.77 3.53 0.04
2013/06/22 14:03 16.83 34.28 9.59 11.70 0.16 1.33 2.11 0.00
2013/07/06 13:25 17.60 34.01 8.92 10.49 6.20 1.43 1.59 2.33 0.02
2013/07/20 12:40 15.22 34.40 8.61 6.38 3.40 1.25 1.75 2.65 0.00
2013/08/16 12:12 21.17 34.52 9.60 3.00 2.00 0.15 1.98 2.31 0.00
2013/08/24 17:35 16.06 34.13 9.54 6.88 14.20 1.62 1.48 2.69 0.00
2013/09/07 16:15 19.41 34.00 8.19 5.87 16.00 0.55 1.91 2.74 0.00
221
Eureka Channel (EC) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2013/09/20 17:33 17.19 33.52 8.39 3.45 23.60 1.64 2.05 2.63 0.00
2013/10/05 15:00 15.53 32.73 9.25 1.67 25.30 4.96 1.80 4.69 0.10
2013/10/19 16:05 13.03 33.47 9.13 1.61 24.30 6.85 1.68 4.45 0.07
2013/11/08 14:25 10.47 33.78 9.85 1.87 21.90 13.84 1.80 4.68 0.24
2013/11/23 17:40 10.57 32.90 9.94 1.10 18.30 4.77 1.28 5.17 0.09
2013/12/07 10:25 5.95 32.46 10.28 1.03 19.40 3.29 1.12 4.77 0.01
2013/12/21 16:20 7.87 33.09 11.27 1.42 16.10 6.81 1.08 4.31 0.04
2014/01/15 13:45 9.78 32.93 10.52 1.25 14.19 6.51 1.13 4.99 0.18
2014/02/02 12:58 9.95 33.44 8.83 0.90 16.29 11.87 1.36 4.01 0.24
2014/02/15 11:58 11.19 31.67 1.38 14.77 7.69 1.03 4.91 0.22
2014/03/02 18:08 13.31 27.37 9.16 2.01 33.69 5.71 0.87 4.63 0.25
2014/03/15 12:03 11.91 31.15 8.71 0.68 21.66 9.40 1.18 5.77 0.34
2014/03/29 11:40 10.79 32.61 9.56 1.09 14.86 8.03 0.99 4.68 0.15
2014/04/12 10:35 12.59 32.07 8.78 1.51 19.41 9.29 1.24 5.94 0.26
2014/04/26 11:15 11.48 33.19 9.04 2.20 16.96 12.10 1.33 4.38 0.22
2014/05/10 13:14 17.58 32.30 7.64 1.32 23.57 1.53 1.33 5.79 0.15
2014/05/26 12:26 14.96 33.74 8.28 3.68 24.39 5.45 1.36 5.59 0.24
2014/06/14 14:07 12.82 34.30 7.72 4.60 34.95 14.07 1.67 5.85 0.39
2014/06/28 14:20 15.96 34.26 9.53 4.40 18.08 1.39 1.09 7.33 0.19
2014/07/26 10:25 18.74 34.55 6.95 2.00 36.10 1.75 2.02 9.26 0.22
2014/08/05 19:21 13.96 34.06 9.27 5.60 19.70 6.71 1.31 7.41 0.35
2014/08/26 12:58 15.90 34.14 8.14 3.33 16.31 2.05 1.47 9.11 0.27
2014/09/02 13:57 19.60 34.52 7.12 4.60 35.84 1.43 2.16 7.44 0.30
2014/09/16 13:51 17.30 34.34 9.19 2.60 31.47 3.36 1.88 7.50 0.30
222
Eureka Channel (EC) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/09/30 13:20 18.39 32.88 6.01 1.20 32.95 4.49 2.20 11.02 0.48
2014/10/14 13:14 13.63 7.78 1.16 25.76 9.44 1.81 7.51 0.43
2014/10/28 13:50 14.83 32.80 9.48 0.95 14.49 4.31 1.27 8.18 0.35
2014/11/11 15:42 13.33 33.26 8.56 0.65 18.43 10.57 1.64 7.59 0.63
2014/11/29 14:30 13.08 28.81 9.50 1.75 34.30 6.22 1.38 5.55 0.34
2014/12/09 13:47 14.77 30.85 9.33 0.65 14.29 3.09 0.73 5.06 0.19
Jacoby Creek (JC) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/09/25 16:15 14.85 10.09 58.50 86.40 1.23 1.42 0.30
2014/10/24 19:51 13.99 0.08 10.60 0.24 51.70 94.00 0.93 1.75 0.18
2014/11/29 15:21 11.70 0.06 1.24 35.40 59.90 0.90 3.22 0.27
2014/12/12 1.77 36.00 68.80 0.70 1.61 0.17
Elk River (ER) station water quality data (Hurst, 2015 b.).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/09/25 17:15 17.70 22.45 25.30 43.30 3.51 14.53 1.34
2014/10/24 18:25 15.30 19.34 6.00 0.77 24.10 34.10 2.16 11.02 0.71
2014/11/29 13:59 12.87 23.54 0.87 18.80 18.60 1.74 9.37 0.45
223
Bay Entrance (BE) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Nitrite
(µM)
2007/10/12 11.10 33.27 8.82 18.29 18.06 1.12 0.29
2007/10/17 12.94 33.34 9.25 5.87 5.66 0.77 0.21
2007/10/26 10.00 33.91 7.97 27.81 18.48 1.55 0.38
2007/11/09 10.52 33.17 8.35 16.04 12.85 1.25 0.19
2007/11/21 10.19 33.28 6.89 19.95 13.24 1.31 0.24
2007/12/07 10.48 32.29 9.51 18.34 11.50 1.11 0.25
2007/12/13 8.96 33.60 7.01 26.86 17.45 1.27 0.26
2007/12/28 8.98 32.73 9.37 14.42 9.90 0.90 0.17
2008/01/11 10.06 30.35 9.42 16.76 6.94 0.84 0.25
2008/01/25 9.15 31.88 9.26 21.85 13.79 1.43 0.18
2008/02/08 9.34 32.80 8.92 21.35 15.15 1.34 0.35
2008/02/26 9.39 32.83 8.64 18.21 12.67 1.19 0.20
2008/03/07 9.22 33.25 7.75 25.14 17.62 1.39 0.28
2008/03/21 9.06 33.16 7.86 6.51 9.77 1.94 0.16
2008/04/04 8.65 33.51 6.68 9.52 39.71 7.85 0.22
2008/04/18 8.56 33.00 6.94 13.64 8.04 0.81 0.43
2008/05/02 8.52 33.70 5.70 11.03 12.07 0.90 0.27
2008/05/16 8.25 33.83 7.03 9.64 17.82 1.37 0.37
2008/05/23 8.55 33.90 8.55 14.46 13.86 1.18 0.26
2008/06/06 10.51 33.66 10.11 5.44 13.38 0.96 0.13
2008/06/20 8.34 33.97 5.25 24.16 16.91 1.17 0.50
2008/07/03 9.96 33.52 8.52 7.46 2.21 0.42 0.35
2008/07/18 10.95 33.93 8.68 9.63 24.34 2.14 0.31
2008/08/01 11.07 33.83 9.30 5.73 9.33 0.79 0.27
224
Bay Entrance (BE) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2008/08/15 9.58 33.66 6.76 14.79 11.03 0.96 0.40
2008/08/29 10.78 33.82 7.99 9.09 8.33 0.84 0.27
2008/09/12 10.88 33.97 9.25 12.90 18.37 1.65 0.29
2008/09/26 11.81 33.58 7.91 7.47 10.89 1.41 0.54
2008/10/10 10.08 33.57 7.59 9.26 16.45 1.44 0.31
2008/10/30 10.17 33.53 8.76 23.41 12.46 1.39
2008/11/14 11.24 33.07 8.48 16.26 7.39 1.02
2008/12/24 9.19 31.96 9.55 16.89 7.42 0.88
2009/01/09 9.52 32.68 8.41 17.40 9.00 1.05
2009/01/23 9.80 32.76 8.94 16.76 8.39 0.66
2009/01/30 9.06 33.59 7.41 21.99 13.50 1.20
2009/02/13 9.05 32.40 9.55 14.02 9.70 0.72
2009/02/27 10.14 30.49 9.19 15.53 5.77 0.71
2009/03/13 9.41 32.71 7.88 15.91 9.77 0.88
2009/03/27 8.34 32.59 4.99 30.29 17.84 2.17
2009/04/10 8.88 33.29 9.12 16.48 13.07 1.25
2009/04/24 8.05 32.24 6.28 36.56 20.31 2.56
2009/05/08 10.21 32.87 8.79 16.65 12.11 1.29
2009/05/22 8.76 33.61 7.83 43.36 17.50 1.82
2009/06/05 10.31 33.45 5.66 3.91 0.58
2009/06/14 10.84 33.04 9.01 6.97 3.97 0.75
2009/07/02 10.53 31.19 10.51 15.56 2.25 0.62
2012/10/04 14:06 10.24 33.66 8.03 19.29 15.88 1.56 5.00 0.23
2012/10/18 13:24 11.39 33.28 9.34 7.60 5.87 0.87 3.58 0.13
225
Bay Entrance (BE) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2012/11/02 13:02 11.99 33.14 8.92 9.09 7.31 0.86 2.40 0.14
2012/11/16 12:02 11.97 33.08 9.07 1.80 11.66 4.68 0.72 2.48 0.08
2012/12/04 13:44 13.30 30.41 8.72 0.33 18.90 3.93 0.72 3.74 0.12
2012/12/14 11:10 11.42 32.77 8.17 0.23 13.42 8.83 0.99 2.59 0.24
2012/12/28 10:33 10.73 29.15 9.25 0.51 26.02 6.21 0.81 2.51 0.29
2013/01/11 09:55 10.10 33.08 8.35 0.80 18.70 13.08 1.26 2.06 0.10
2013/01/25 09:07 9.54 32.28 9.19 1.06 24.26 15.96 1.39 2.18 0.07
2013/02/08 08:36 9.29 32.51 10.08 6.26 15.14 11.71 1.02 2.10 0.13
2013/02/21 07:55 8.28 33.73 8.13 2.09 36.96 26.41 2.15 2.80 0.16
2013/03/12 12:28 8.78 33.74 8.29 1.97 27.95 23.85 2.04 4.27 0.13
2013/03/29 13:45 9.45 32.80 10.27 7.15 7.94 7.69 0.79 4.28 0.11
2013/04/12 13:22 8.47 33.79 5.94 1.88 34.97 24.65 2.42 6.02 0.16
2013/04/26 12:39 9.19 33.78 8.34 2.26 34.37 25.08 2.22 3.67 0.19
2013/05/10 13:06 9.30 33.44 8.38 8.54 28.45 17.14 1.73 3.55 0.06
2013/05/24 12:06 9.24 33.76 8.17 5.11 32.28 22.98 2.11 4.59 0.33
2013/06/07 12:26 9.76 33.08 8.21 9.77 16.60 11.07 1.56 2.43 0.13
2013/06/21 10:50 9.43 33.89 6.04 8.82 29.70 20.47 2.06 4.18 0.23
2013/07/02 08:20 11.36 33.75 7.26 5.99 20.20 11.93 1.45 4.61 0.23
2013/07/19 09:18 11.11 33.80 9.72 9.39 4.30 6.37 0.88 2.76 0.00
2013/08/15 07:17 10.36 33.62 6.67 4.52 19.30 15.66 2.11 7.00 0.18
2013/08/23 13:30 10.58 33.36 8.60 5.66 15.70 12.36 1.33 1.67 0.03
2013/09/06 13:00 12.27 33.23 9.27 6.78 8.60 6.15 1.01 3.04 0.15
2013/09/18 11:13 10.71 34.13 6.92 6.59 22.80 13.85 1.71 2.62 0.00
2013/10/04 11:19 9.96 33.86 7.53 0.07 23.30 16.17 1.71 1.89 0.12
226
Bay Entrance (BE) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2013/10/18 11:01 9.41 31.86 6.53 2.54 28.30 20.52 1.99 2.78 0.13
2013/11/07 12:50 9.55 31.75 8.01 1.80 23.10 18.59 1.86 2.70 0.23
2013/11/22 13:14 9.79 31.74 8.47 1.22 17.90 14.21 1.58 2.83 0.13
2013/12/06 13:20 8.94 33.13 7.73 0.54 20.30 15.70 1.57 1.92 0.01
2013/12/20 12:26 8.69 33.68 6.75 0.77 24.30 19.46 1.80 1.86 0.00
2014/01/14 09:07 9.92 33.29 9.71 2.36 14.75 12.57 1.35 3.03 0.23
2014/01/31 10:38 9.92 33.29 9.11 1.07 14.21 12.77 1.30 1.51 0.24
2014/02/14 10:31 11.02 31.60 9.28 0.77 14.28 7.22 0.90 1.40 0.16
2014/02/28 09:50 11.08 32.68 9.27 1.73 9.28 4.97 0.70 1.53 0.11
2014/03/14 10:19 11.05 32.69 8.56 0.41 14.63 9.33 1.05 2.10 0.27
2014/03/28 08:38 10.27 33.06 9.72 1.73 15.75 10.01 0.98 1.62 0.11
2014/04/11 09:51 10.19 33.62 8.15 1.59 18.98 16.03 1.46 2.96 0.24
2014/04/25 08:51 9.72 33.65 8.58 3.17 23.48 20.60 1.64 1.82 0.14
2014/05/09 08:27 10.87 33.25 9.04 3.52 17.33 12.84 1.22 3.19 0.21
2014/05/23 07:45 9.26 33.81 5.57 2.10 24.93 20.62 1.81 3.59 0.32
2014/06/13 13:09 9.80 34.08 7.95 4.57 32.34 19.78 1.35 3.94 0.48
2014/06/27 13:06 11.83 33.81 13.03 9.78 0.01 0.06 0.02 4.05 0.00
2014/07/11 5.69 12.16 10.67 0.96 3.75 0.24
2014/07/25 11:38 11.56 33.95 7.81 2.54 18.53 13.56 1.40 5.44 0.30
2014/08/08 10:53 11.50 33.55 9.88 10.16 5.06 6.64 0.66 3.47 0.17
2014/08/22 10:55 12.61 34.36 9.69 5.85 4.39 5.54 0.65 3.21 0.12
2014/09/04 08:45 11.87 34.40 8.70 1.34 15.09 9.69 1.50 5.70 0.37
2014/09/19 09:40 14.15 34.27 9.92 2.66 11.65 2.02 0.39 2.16 0.00
2014/10/03 08:22 12.42 34.30 7.11 1.39 18.03 10.03 1.37 2.63 0.29
227
Bay Entrance (BE) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/10/24 11:36 14.12 32.28 8.56 1.31 2.61 3.63 0.66 2.98 0.17
2014/11/06 09:59 13.37 32.07 8.31 1.01 12.37 10.49 0.99 2.43 0.42
2014/11/20 08:41 13.98 34.86 8.48 1.66 2.59 1.80 0.50 2.14 0.09
2014/12/05 09:15 14.72 33.09 8.34 9.09 0.96 0.44 2.26 0.06
2014/12/19 08:13 14.63 30.80 8.57 0.27 12.32 1.99 0.46 1.95 0.09
2015/01/08 12:35 11.29 32.70 8.59 1.61
2015/01/23 12:43 11.82 31.93 9.02 18.52 8.00 0.86 0.82 0.23
2015/02/09 14:52 12.84 29.53 9.21 24.28 3.63 0.66 1.35 0.12
2015/02/20 11:51 12.12 32.59 7.90 10.40 6.74 0.79 0.87 0.32
228
Indian Island (II) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Nitrite
(µM)
2007/10/12 20.34 15.31 1.69 0.31
2007/10/17 17.22 5.75 1.45 0.32
2007/10/26 18.01 9.68 1.49 0.38
2007/11/09 20.40 8.41 1.47 0.32
2007/11/21 15.02 7.85 1.26 0.31
2007/12/07 23.92 13.73 1.16 0.29
2007/12/13 28.68 18.61 1.60 0.35
2007/12/28 32.06 19.38 1.57 0.33
2008/01/11 34.93 8.52 0.78 0.30
2008/01/25 28.11 17.48 1.59 0.24
2008/02/08 34.96 9.97 0.94 0.39
2008/02/26 38.08 15.33 1.47 0.26
2008/03/07 25.73 20.79 1.85 0.30
2008/03/21 6.54 10.79 1.09 0.25
2008/04/04 8.19 13.69 1.24 0.26
2008/04/18 6.16 5.31 0.67 0.12
2008/05/02 5.99 6.84 0.91 0.07
2008/05/16 5.65 0.37 0.58 0.16
2008/05/23 7.30 0.03 0.51 0.27
2008/06/06 5.80 0.55 0.45 0.17
2008/06/20 20.46 2.86 0.60 0.43
2008/07/03 8.22 0.86 0.60 0.30
2008/07/18 9.67 14.90 1.85 0.35
2008/08/01 6.20 6.02 1.21 0.28
229
Indian Island (II) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2008/08/15 11.33 5.50 1.41 0.39
2008/08/29 10.51 3.76 1.05 0.27
2008/09/12 19.37 6.56 2.00 0.38
2008/09/26 9.06 7.99 1.65 0.36
2008/10/10 9.29 11.36 2.26 0.29
2008/10/30 18.21 6.09 1.28
2008/11/14 21.51 6.30 1.46
2008/12/24 21.44 8.08 1.35
2009/01/09 22.37 9.39 1.10
2009/01/23 17.28 8.32 1.03
2009/01/30 11.16 4.71 0.73
2009/02/13 21.30 7.33 1.00
2009/02/27 31.86 5.89 1.05
2009/03/13 23.21 5.81 1.05
2009/03/27 19.06 7.15 0.94
2009/04/10 3.85 1.48 0.94
2009/04/24 25.06 2.88 1.35
2009/05/08 15.16 2.27 1.09
2009/05/22 22.55 2.08 1.33
2009/06/05 14.79 0.48 2.57
2009/06/14 19.60 0.16 1.52
2009/07/02 16.42 1.06 1.54
2012/10/04 14:46 14.24 33.78 8.59 25.74 10.52 1.85 8.78 0.22
2012/10/18 14:11 14.66 33.17 8.80 17.83 5.11 1.51 7.14 0.25
230
Indian Island (II) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2012/11/02 13:53 14.05 32.67 8.81 18.56 3.78 1.49 7.26 0.24
2012/11/16 13:03 12.09 32.79 9.05 1.38 15.37 4.50 1.25 4.93 0.20
2012/12/04 13:04 12.68 24.59 8.76 1.60 47.47 11.28 1.44 10.38 0.39
2012/12/14 12:15 11.33 31.58 8.71 0.61 20.32 7.73 1.13 5.85 0.30
2012/12/28 11:57 9.68 25.06 9.06 0.51 47.61 10.31 1.14 7.24 0.34
2013/01/11 11:21 9.80 31.42 9.24 0.40 26.03 10.99 1.27 4.73 0.24
2013/01/25 10:22 9.32 31.30 9.25 1.86 29.61 12.23 1.42 5.35 0.17
2013/02/08 09:33 9.12 32.21 9.54 3.66 19.74 12.39 1.29 4.25 0.18
2013/02/21 09:06 8.81 31.57 9.25 1.69 32.11 9.35 1.34 5.06 0.12
2013/03/12 13:21 10.62 31.62 9.76 1.15 25.34 14.40 1.69 4.99 0.16
2013/03/29 14:50 12.80 31.97 10.36 1.53 17.36 6.97 1.33 5.02 0.11
2013/04/12 14:17 12.29 31.35 8.54 1.01 22.47 10.16 1.82 8.50 0.17
2013/04/26 13:54 12.51 32.86 8.87 3.04 31.96 14.25 2.04 5.06 0.17
2013/05/10 13:41 13.74 33.04 9.36 6.64 31.64 8.20 1.61 4.81 0.14
2013/05/24 13:06 13.91 33.40 8.89 5.01 26.20 9.69 1.92 5.14 0.20
2013/06/07 13:03 15.73 33.02 9.28 8.74 11.50 4.33 1.54 2.49 0.09
2013/06/21 11:50 16.76 34.18 9.48 16.75 5.40 0.83 1.64 2.05 0.00
2013/07/02 09:11 19.26 33.89 7.44 5.65 6.80 0.49 1.97 3.05 0.00
2013/07/19 10:27 16.86 34.35 8.02 4.40 4.40 0.05 2.12 1.96 0.00
2013/08/15 09:03 18.57 33.83 8.45 4.10 3.30 0.02 2.00 2.22 0.00
2013/08/23 14:16 13.32 33.57 9.48 8.74 12.70 3.76 1.22 2.88 0.00
2013/09/06 14:04 17.31 33.38 9.01 7.48 6.80 0.25 1.22 1.86 0.00
2013/09/18 12:29 16.48 34.26 8.62 2.18 17.20 2.66 1.77 1.95 0.00
2013/10/04 12:15 14.34 33.05 8.07 1.22 20.20 5.72 1.49 3.45 0.12
231
Indian Island (II) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2013/10/18 12:18 11.92 31.59 8.96 0.81 25.70 9.93 1.69 2.71 0.09
2013/11/07 14:01 11.39 31.66 9.89 0.95 20.60 11.01 1.64 2.81 0.17
2013/11/22 14:24 11.37 31.35 10.63 0.94 16.30 4.17 1.24 3.56 0.04
2013/12/06 14:11 8.60 32.71 9.64 0.79 17.30 6.89 1.33 3.56 0.04
2013/12/20 13:33 7.19 32.82 9.13 1.37 15.70 7.86 1.19 3.00 0.02
2014/01/14 10:04 9.01 32.92 8.82 0.64 13.68 6.90 1.08 4.61 0.19
2014/01/31 11:54 10.63 33.06 9.45 1.05 14.58 8.54 1.15 3.63 0.19
2014/02/14 11:15 11.52 21.25 8.10 0.73
2014/02/28 11:01 11.67 31.42 8.98 1.14 17.68 7.53 1.03 4.18 0.25
2014/03/14 11:32 12.74 29.35 8.15 1.32 27.67 8.77 1.17 7.49 0.36
2014/03/28 09:44 11.69 31.56 8.10 0.98 27.27 11.04 1.31 4.46 0.24
2014/04/11 10:47 13.07 31.69 8.41 0.87 20.90 8.28 1.26 5.95 0.25
2014/04/25 09:58 12.88 32.61 8.05 2.00 17.91 8.66 1.37 4.84 0.29
2014/05/09 09:23 15.10 33.12 7.30 1.20 16.28 3.45 1.46 7.69 0.21
2014/05/23 09:07 16.01 33.46 6.94 0.96 21.04 3.40 1.35 5.07 0.18
2014/06/13 14:11 13.64 34.32 7.50 1.43 33.71 14.01 1.76 6.53 0.56
2014/06/27 14:28 15.28 34.50 9.10 7.77 17.76 2.33 1.09 5.61 0.23
2014/07/11 13:13 16.75 34.81 8.16 3.84 20.88 1.93 1.08 6.98 0.20
2014/07/25 12:35 16.70 34.30 8.04 5.11 21.17 2.45 1.25 5.96 0.21
2014/08/08 11:56 16.79 34.57 7.96 6.04 27.50 3.85 1.60 6.94 0.31
2014/08/22 11:42 16.49 34.72 7.03 1.22 23.73 8.58 1.86 8.32 0.31
2014/09/04 09:12 17.65 35.02 7.06 1.64 35.88 2.50 2.09 5.47 0.24
2014/09/19 11:32 17.32 34.61 7.33 0.74 27.96 2.79 1.73 8.74 0.27
2014/10/03 09:31 16.67 33.66 6.92 1.88 34.34 4.74 2.23 8.29 0.47
232
Indian Island (II) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/10/24 12:48 15.88 32.35 7.84 0.86 18.61 4.81 1.55 7.39 0.33
2014/11/06 10:36 14.49 32.11 9.23 0.77 20.70 6.87 1.52 5.06 0.40
2014/11/20 09:30 13.12 34.36 7.95 1.11 11.97 4.46 1.22 4.19 0.33
2014/12/05 10:00 14.54 31.24 8.44 0.80 11.61 3.01 0.71 3.35 0.14
2014/12/19 09:05 13.22 28.78 8.40 0.42 27.72 4.52 1.04 6.01 0.26
2015/01/08 13:11 10.94 30.51 8.27 1.61
2015/01/23 13:43 12.22 31.74 8.79 20.13 8.10 1.04 1.30 0.22
2015/02/09 15:32 13.65 26.35 8.36 46.76 12.49 1.32 8.98 0.39
2015/02/20 12:39 12.82 30.99 7.94 17.57 6.59 0.89 1.37 0.29
233
Mad River Slough (MRS) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Nitrite
(µM)
2007/10/12 14.66 33.35 7.58 18.76 1.44 1.29 0.24
2007/10/17 13.70 32.90 7.67 20.88 2.70 2.07 0.25
2007/10/26 13.77 31.03 8.14 22.60 4.06 1.87 0.41
2007/11/09 12.59 32.22 8.47 19.97 5.41 1.70 0.33
2007/11/21 11.03 31.16 7.99 21.04 5.92 1.74 0.42
2007/12/07 10.32 30.21 8.71 26.15 9.02 1.01 0.36
2007/12/13 7.99 29.63 9.17 36.56 16.21 1.35 0.41
2007/12/28 7.09 27.36 9.55 50.03 20.90 1.63 0.41
2008/01/11 9.04 21.45 9.58 66.29 18.83 1.52 0.48
2008/01/25 7.39 28.91 9.77 41.06 16.95 1.39 0.27
2008/02/08 9.68 24.13 9.77 52.09 16.20 1.38 0.36
2008/02/26 10.81 28.79 9.20 39.07 14.69 1.52 0.29
2008/03/07 10.95 29.14 9.34 28.34 9.31 1.08 0.20
2008/03/21 12.23 27.34 9.91 13.63 5.71 1.85 0.24
2008/04/04 12.23 30.05 8.90 6.96 2.83 2.01 0.11
2008/04/18 13.36 32.08 7.83 8.95 4.75 1.27 0.07
2008/05/02 14.05 31.79 8.18 8.37 1.00 1.03 0.06
2008/05/16 17.96 33.32 8.73 6.60 0.45 1.27 0.08
2008/05/23 13.33 33.68 7.68 13.57 0.15 1.18 0.24
2008/06/06 15.39 33.84 7.98 9.11 0.00 0.87 0.14
2008/06/20 17.55 34.25 8.64 15.32 3.43 1.76 0.15
2008/07/03 18.23 34.30 8.73 11.55 0.91 1.59 0.16
2008/07/18 17.42 33.69 7.34 9.12 2.60 1.85 0.10
2008/08/01 19.34 34.22 8.83 5.61 0.99 1.88 0.08
234
Mad River Slough (MRS) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2008/08/15 18.84 34.28 7.89 8.64 2.55 2.50 0.14
2008/08/29 18.71 34.00 7.38 17.28 0.18 1.79 0.22
2008/09/12 16.61 34.35 8.26 16.78 0.73 2.26 0.22
2008/09/26 16.44 33.95 8.22 13.46 1.97 2.61 0.20
2008/10/06 17.21 33.46 7.48 14.97 1.96 2.88 0.21
2008/10/30 13.02 33.62 8.90 10.85 1.66 1.36
2008/11/14 13.71 31.52 8.22 15.95 3.30 1.08
2008/12/24 7.17 29.96 9.66 21.71 6.57 2.27
2009/01/09 8.95 27.38 8.82 27.64 11.04 1.36
2009/01/23 9.75 29.93 9.39 13.23 7.06 0.79
2009/01/30 9.47 30.78 9.91 12.67 3.71 0.85
2009/02/13 6.82 28.47 9.74 16.66 5.14 1.07
2009/02/27 11.81 24.97 8.08 32.67 6.99 1.15
2009/03/13 11.92 27.14 8.42
2009/03/27 13.30 26.58 9.60 13.34 2.13 0.85
2009/04/10 12.66 29.92 9.21 2.82 0.37 0.83
2009/04/24 15.44 31.82 7.56 19.41 1.34 1.30
2009/05/08 16.45 27.66 7.40 13.15 1.35 1.85
2009/05/22 16.54 31.87 7.61 17.82 0.78
2009/06/05 15.75 33.15 25.68 0.41 1.68
2009/06/14 18.66 33.49 7.89 25.85 0.06 2.15
2009/07/02 18.26 31.41 8.55 18.85 0.03 1.75
2012/10/04 08:24 16.92 33.83 7.61 24.57 1.08 2.14 6.39 0.03
2012/10/18 09:02 15.48 33.11 7.43 31.35 4.68 2.75 6.71 0.18
235
Mad River Slough (MRS) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2012/11/02 15:05 14.72 32.38 8.11 25.98 4.49 1.86 6.84 0.20
2012/11/16 14:32 12.32 32.25 8.65 1.84 24.16 4.89 1.84 5.49 0.25
2012/12/04 14:13 12.07 19.97 9.20 3.83 68.03 25.17 2.53 16.31 0.71
2012/12/14 15:56 10.10 25.63 8.58 1.64 42.46 9.70 1.70 10.20 0.42
2012/12/28 12:44 8.76 22.67 8.94 1.31 58.84 27.01 1.64 11.16 1.83
2013/01/11 12:30 8.57 27.92 9.15 1.62 43.29 11.52 1.52 6.94 0.31
2013/01/25 11:22 9.41 29.71 9.40 3.34 35.01 9.31 1.37 4.82 0.14
2013/02/08 10:52 9.21 30.11 9.35 2.28 21.89 4.57 1.17 4.59 0.06
2013/02/21 10:19 9.14 30.82 10.05 3.23 17.40 1.30 0.90 3.76 0.06
2013/03/12 14:29 11.86 29.43 9.91 2.75 19.75 4.49 1.31 4.38 0.04
2013/03/29 15:56 14.95 31.17 9.90 2.35 18.18 1.82 1.32 4.99 0.01
2013/04/12 15:34 14.62 30.09 8.55 2.63 28.47 2.65 1.75 6.48 0.09
2013/04/26 14:43 15.00 32.57 9.17 2.41 27.18 3.18 1.81 5.78 0.04
2013/05/10 15:06 15.92 33.34 9.97 10.02 16.98 0.00 1.29 4.96 0.00
2013/05/24 14:15 16.94 34.02 8.74 4.67 20.29 0.60 1.85 4.69 0.00
2013/06/07 14:09 17.63 33.08 9.54 9.49 4.50 0.12 1.79 8.13 0.00
2013/06/21 12:40 19.08 34.37 8.49 11.10 2.70 0.11 2.27 2.46 0.00
2013/07/02 10:39 20.94 34.19 7.01 6.82 5.60 0.02 2.84 2.23 0.00
2013/07/19 11:33 17.91 34.52 7.73 4.62 0.90 0.06 2.83 2.31 0.00
2013/08/15 10:14 20.34 34.02 7.96 3.63 2.00 0.05 2.75 2.19 0.00
2013/08/23 15:38 17.87 34.06 7.66 3.56 22.50 1.24 2.44 4.52 0.00
2013/09/06 15:07 21.36 33.94 7.54 3.75 22.80 0.17 3.03 2.22 0.00
2013/09/18 13:16 18.61 34.48 7.84 2.04 21.50 0.25 2.43 2.31 0.00
2013/10/04 14:43 16.00 32.46 7.39 1.35 24.70 0.82 2.21 3.30 0.00
236
Mad River Slough (MRS) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2013/10/18 13:45 13.51 31.26 8.74 0.44 20.90 3.12 1.74 3.21 0.00
2013/11/07 15:16 12.36 31.55 9.62 0.63 15.40 2.23 1.29 2.84 0.00
2013/11/22 15:10 10.78 31.33 9.62 1.08 17.80 3.69 1.23 4.02 0.08
2013/12/06 15:12 7.51 32.50 9.71 1.54 17.00 2.41 1.22 4.20 0.02
2013/12/20 16:24 6.90 32.95 9.86 0.87 13.90 3.46 1.04 3.73 0.00
2014/01/14 11:30 8.87 32.42 8.76 0.86 14.81 3.30 1.02 5.08 0.14
2014/01/31 12:46 10.44 32.62 9.00 1.05 14.55 3.95 1.05 4.32 0.15
2014/02/14 13:40 12.09 29.92 7.75 1.11 23.33 5.12 1.28 10.80 0.31
2014/02/28 11:48 12.21 29.76 8.38 0.96 21.29 5.28 1.04 5.50 0.30
2014/03/14 12:55 13.61 26.51 7.89 1.44 34.73 7.36 1.47 10.32 0.47
2014/03/27 13:51 13.67 29.02 8.10 1.27 27.87 5.04 1.53 5.47 0.22
2014/04/11 11:54 14.82 29.90 8.24 1.15 22.85 2.96 1.25 5.24 0.18
2014/04/25 10:52 14.29 31.82 7.79 0.06 17.66 2.41 1.40 5.00 0.16
2014/05/09 10:35 16.37 32.94 6.77 0.28 21.92 1.50 1.71 5.30 0.13
2014/05/23 10:14 18.21 33.56 6.17 0.52 30.32 1.51 1.77 5.13 0.15
2014/06/13 15:15 18.71 34.59 7.50 1.03 42.57 3.22 1.95 6.84 0.22
2014/06/27 15:25 19.46 34.87 6.34 2.00 42.23 2.09 2.17 8.61 0.28
2014/07/11 14:17 19.31 35.29 6.47 2.61 51.01 1.98 2.42 7.73 0.28
2014/07/25 13:57 20.06 34.77 6.58 3.27 42.21 1.43 2.07 6.35 0.24
2014/08/08 13:04 19.68 35.04 6.73 3.35 53.74 2.56 2.51 7.06 0.31
2014/08/22 13:16 2.03 35.13 6.69 0.61 42.09 2.07 2.35 5.68 0.34
2014/09/04 22:47 18.51 35.31 6.72 0.40 44.08 2.34 2.55 6.10 0.32
2014/09/19 12:16 19.08 34.87 6.36 0.92 42.76 3.02 2.39 7.75 0.36
2014/10/03 10:46 18.15 33.57 7.05 1.66 41.13 4.90 2.60 7.87 0.54
237
Mad River Slough (MRS) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/10/24 13:59 16.31 31.06 7.13 0.68 33.81 8.76 2.14 9.00 0.50
2014/11/06 10:57 15.13 30.65 7.83 1.32 30.13 9.82 1.94 8.55 0.49
2014/11/20 10:58 12.92 33.35 7.63 0.90 27.70 7.91 2.15 5.98 0.51
2014/12/05 11:42 13.78 31.83 7.73 0.75 28.89 8.01 1.61 7.50 0.43
2014/12/19 11:07 11.49 24.54 8.98 0.77 65.22 13.88 2.26 14.59 0.73
2015/01/08 14:41 10.27 30.03 8.83 1.56
2015/01/23 15:09 12.27 30.16 8.79 33.05 8.28 1.31 2.44 0.23
2015/02/09 17:09 14.06 22.07 8.40 68.62 21.29 2.33 5.81 0.76
2015/02/20 13:59 13.77 28.21 8.29 36.98 7.54 1.29 3.75 0.30
238
Hookton Slough (HS) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2012/10/04 09:08 14.67 33.17 7.32 20.86 1.75 1.45 9.34 0.11
2012/10/18 14:45 15.32 32.46 8.08 22.00 3.98 1.63 7.16 0.17
2012/11/01 15:20 14.64 32.18 8.63 21.23 5.71 1.43 6.70 0.20
2012/11/15 14:44 11.83 32.00 8.90 30.99 6.64 1.53 7.95 0.30
2012/12/04 09:05 11.74 20.47 8.83 68.46 19.28 1.20 9.32 0.38
2012/12/13 12:33 9.43 27.91 8.56 53.98 11.66 1.21 9.64 0.39
2013/01/10 14:17 8.72 12.29 10.28 110.19 20.43 0.92 5.09 0.21
2013/01/24 13:55 10.03 21.16 9.53 76.73 14.10 0.87 5.97 0.17
2013/02/07 14:10 9.25 13.77 11.12 109.81 15.09 0.79 4.50 0.10
2013/02/20 12:08 9.82 19.95 10.69 73.92 7.77 0.50 2.45 0.05
2013/03/11 15:11 11.89 25.77 10.82 50.55 7.00 1.99 7.73 0.05
2013/03/28 15:22 13.18 31.00 10.07 20.27 3.47 1.39 6.51 0.02
2013/04/11 15:16 14.05 23.05 10.11 55.90 4.08 2.22 8.60 0.06
2013/04/25 14:42 15.44 31.49 10.60 22.86 2.93 1.65 4.86 0.04
2013/05/09 15:04 15.55 31.45 9.77 21.84 0.92 1.35 6.96 0.05
2013/05/23 15:19 19.57 31.53 9.69 23.34 0.00 1.95 4.62 0.00
2013/06/06 14:00 17.63 31.50 9.96 4.00 1.86 1.39 1.14 2.11
2013/06/20 13:37 21.76 32.66 10.31 6.20 0.41 1.75 1.23 2.11
2013/07/02 11:28 20.78 33.48 6.41 1.50 0.02 1.41 1.38 2.11
2013/07/19 12:21 17.85 34.00 6.18 7.10 0.18 1.68 1.83 0.00
2013/08/15 11:06 21.68 33.39 7.51 22.30 0.05 1.47 1.12 2.11
2013/08/23 15:39 17.77 33.84 7.17 20.00 1.60 1.57 3.55 0.06
2013/09/05 15:11 22.16 33.82 6.41 26.30 0.83 1.94 1.86 0.02
2013/09/17 14:53 20.39 34.05 8.52 33.70 1.29 1.75 2.17 0.09
239
Hookton Slough (HS) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2013/10/03 14:30 16.89 28.73 8.96 46.20 3.03 1.35 4.73 0.21
2013/10/17 14:55 13.78 31.14 9.30 27.30 2.73 1.23 3.58 0.06
2013/11/06 14:23 12.10 31.42 8.59 26.30 5.13 1.17 8.12 0.31
2013/11/21 15:38 11.97 29.72 9.04 31.70 6.11 1.03 7.67 0.37
2013/12/05 15:20 7.02 32.23 9.30 28.40 5.17 0.87 9.00 0.35
2013/12/19 15:36 7.13 32.54 9.81 36.00 8.59 0.81 9.06 0.40
2014/03/27 09:49 11.36 31.84 8.05 0.99 31.40 13.24 1.40 5.88 0.25
2014/04/09 12:09 15.54 22.36 7.15 2.03 68.68 8.72 0.68 7.73 0.38
2014/04/25 12:57 14.38 26.26 8.11 2.40 43.04 5.66 0.44 6.34 0.25
2014/05/07 11:48 16.14 27.79 7.42 4.67 37.34 0.40 0.36 1.98 0.00
2014/05/22 10:58 18.83 31.98 7.06 1.77 21.28 0.36 0.62 2.21 0.00
2014/06/12 15:03 19.62 34.55 7.97 1.66 37.34 1.71 1.65 8.04 0.25
2014/06/26 15:00 18.93 34.42 7.17 4.27 28.59 2.03 1.09 4.61 0.27
2014/07/10 13:32 18.75 34.90 7.04 3.24 40.43 1.79 1.91 5.36 0.23
2014/07/24 14:12 20.87 34.39 7.66 3.22 37.70 0.93 1.91 3.23 0.21
2014/08/07 14:10 19.33 34.65 7.73 5.76 44.60 2.53 1.71 4.82 0.33
2014/08/21 14:27 21.49 34.88 8.50 1.68 34.66 0.50 1.51 2.67 0.12
2014/09/02 11:24 20.21 35.34 5.93 1.63 43.43 0.92 1.40 2.46 0.03
2014/09/18 01:23 19.51 34.20 6.12 1.26 36.73 6.82 1.32 6.76 0.48
2014/10/01 11:41 17.63 32.70 6.10 1.82 41.36 11.30 1.44 9.89 0.69
2014/10/22 15:00 15.65 32.47 7.32 1.93 37.76 9.19 1.49 9.36 0.63
2014/11/05 14:28 15.49 29.69 7.70 3.02 43.54 10.00 1.25 10.58 0.54
2014/11/18 10:08 11.96 33.00 7.36 0.33 36.54 12.20 1.71 7.64 0.56
2014/12/04 02:37 14.18 20.12 8.38 1.42 104.87 28.05 1.06 7.92 0.59
240
Hookton Slough (HS) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/12/18 10:07 13.11 29.20 7.92 0.33 36.87 7.12 0.98 6.60 0.32
2015/01/07 14:39 10.76 30.67 8.20 2.10
2015/01/22 14:05 11.61 29.21 8.15 46.47 10.76 0.97 4.11 0.27
2015/02/05 14:36 12.95 27.61 8.38 48.10 11.69 0.96 3.20 0.27
2015/02/19 13:04 12.91 27.53 7.42 46.57 8.27 0.98 5.98 0.33
241
Samoa Channel (SC) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2012/12/04 12.78 25.26 8.80 1.11 48.16 9.55 1.27 8.21 0.25
2012/12/14 11.42 32.65 8.28 0.51 10.58 6.42 0.81 4.17 0.17
2012/12/28 10.51 28.93 8.88 0.82 29.08 7.73 0.97 5.12 0.31
2013/01/11 10.07 32.72 8.54 0.89 19.99 11.60 1.25 3.41 0.14
2013/01/25 9.53 32.62 9.25 1.89 23.79 14.68 1.41 3.94 0.11
2013/02/08 9.31 32.69 10.01 6.44 14.23 10.85 1.02 3.36 0.15
2013/02/21 8.78 32.96 9.66 1.12 31.12 19.90 1.84 4.03 0.15
2013/03/12 9.35 33.21 8.86 6.30 21.31 19.26 1.91 4.58 0.14
2013/03/29 9.90 32.77 9.96 5.20 7.46 8.62 1.03 4.67 0.12
2013/04/12 11.01 32.48 8.10 7.60 27.12 13.78 1.93 7.06 0.18
2013/04/26 10.30 33.45 8.64 27.23 19.24 2.10 4.31 0.17
2013/05/10 10.87 33.95 8.35 5.70 28.50 14.92 1.85 5.23 0.12
2013/05/24 10.27 34.16 8.82 6.22 30.38 18.78 2.00 5.55 0.30
2013/06/07 12.07 33.02 8.30 10.57 25.00 15.04 1.97 3.38 0.25
2013/06/21 13.25 33.91 9.33 10.20 5.01 1.40 2.30 0.02
2013/07/02 17.68 33.76 7.96 7.94 6.40 1.39 1.61 3.85 0.00
2013/07/19 14.34 34.03 8.98 7.69 2.40 1.80 1.46 2.34 0.00
2013/08/15 16.06 33.64 9.20 4.81 3.30 0.65 1.29 2.30 0.00
2013/08/23 11.37 33.40 9.26 7.90 12.80 7.82 1.05 2.57 0.03
2013/09/06 14.00 33.23 9.68 6.31 6.90 2.78 0.77 1.85 0.00
2013/09/18 11.33 34.12 7.34 1.24 20.60 12.03 1.47 3.23 0.14
2013/10/04 11.75 33.57 7.96 1.02 23.20 12.71 1.62 2.75 0.14
2013/10/18 9.89 31.79 7.64 3.02 27.10 18.20 1.81 2.18 0.13
2013/11/07 9.77 31.78 8.53 1.39 24.10 18.46 1.86 2.88 0.26
242
Samoa Channel (SC) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2013/11/22 10.59 31.47 9.43 1.29 15.00 8.67 1.29 3.15 0.09
2013/12/06 8.95 33.14 7.78 0.48 20.40 16.37 1.67 2.34 0.00
2013/12/20 8.50 33.40 9.72 1.31 19.60 13.15 1.43 2.91 0.04
2014/01/14 10.09 33.25 9.43 1.30 12.10 9.66 1.11 3.05 0.19
2014/01/31 10.34 33.40 9.56 1.87 13.16 12.13 1.19 2.81 0.23
2014/02/14 11.17 31.96 8.94 0.77 14.27 7.18 0.96 3.22 0.19
2014/02/28 11.14 32.47 9.22 1.55 10.99 5.57 0.75 2.02 0.13
2014/03/14 11.97 31.16 8.56 0.57 22.22 9.31 1.13 4.44 0.30
2014/03/28 10.97 32.83 8.86 1.49 24.08 13.81 1.36 3.44 0.20
2014/04/11 11.99 32.60 8.75 1.25 17.42 10.10 1.17 1.87 0.23
2014/04/25 11.29 33.27 8.75 3.09 16.17 12.46 1.35 4.09 0.30
2014/05/09 14.41 32.23 7.63 1.35 16.02 4.78 1.52 7.33 0.23
2014/05/23 14.27 33.52 7.34 2.01 17.17 5.97 1.34 5.21 0.23
2014/06/13 11.24 34.10 8.85 5.31 33.50 17.68 1.41 4.06 0.42
2014/06/27 12.72 34.26 11.89 6.39 5.24 0.21 0.33 3.92 0.03
2014/07/11 5.27 12.89 9.53 1.08 4.42 0.21
2014/07/25 14.79 34.05 8.45 4.27 17.79 4.82 1.22 6.03 0.23
2014/08/08 13.25 34.32 8.40 7.99 14.81 8.12 1.19 4.91 0.29
2014/08/22 13.51 34.43 8.16 1.22 10.44 6.73 1.25 5.47 0.23
2014/09/04 15.36 34.57 8.14 2.62 24.97 5.21 1.71 4.86 0.30
2014/09/19 15.90 34.45 8.12 0.81 17.20 1.25 1.31 7.99 0.19
2014/10/03 14.77 34.10 7.40 2.37 22.23 11.64 1.67 4.87 0.38
2014/10/24 14.95 32.02 8.13 1.10 9.69 3.89 1.11 5.70 0.25
2014/11/06 13.53 32.26 8.10 1.10 12.69 9.79 1.08 2.61 0.33
243
Samoa Channel (SC) station water quality data (Wiyot Tribe Natural Resources Department, 2015).
Date/Time (LST)
Temp.
(°C)
Salinity
(ppt)
DO
(mg/L)
Chl-A
(µg/L)
Silicate
(µM)
Nitrate
(µM)
Phosphate
(µM)
Ammonium
(µM)
Nitrite
(µM)
2014/11/20 13.25 34.61 8.09 1.75
2014/12/05 14.65 32.99 8.26 0.64 10.84 1.79 0.60 2.56 0.09
2014/12/19 13.96 30.39 8.51 0.40 18.54 3.57 0.83 4.25 0.18
2015/01/08 11.11 32.87 8.13 1.53
2015/01/23 11.81 32.79 8.51 15.91 9.14 0.96 1.19 0.21
2015/02/09 13.49 27.31 8.47 39.18 10.85 1.12 6.39 0.30
2015/02/20 12.15 32.46 7.93 13.14 6.91 0.85 1.03 0.30