2012 report potter lake campus, douglas county, kansas water quality evaluation 2011 january 13,...
TRANSCRIPT
Potter Lake University of Kansas
Lawrence Campus, Douglas County, Kansas
Water Quality Evaluation
2011
January 13, 2012
Prepared by the Department of Environment, Health & Safety
University of Kansas, Lawrence Campus
Cover Photograph
A view of Potter Lake (looking north) taken in 1911, the year it was constructed.
Modified From: KU Oread web page April 11, 2011.
i
TableofContents
1. Introduction ....................................................................................................................... 1
2. Description of the Potter Lake and its Watershed ............................................................. 1
3. Remediation Measures Taken to Improve the Water Quality of Potter Lake .................... 6
4. Water Quality Monitoring Program for Potter Lake .......................................................... 7
5. Results of the Monitoring Program .................................................................................... 7
A. Water Temperature ....................................................................................................... 7
B. Secchi Disc Transparency ............................................................................................. 11
C. Turbidity ....................................................................................................................... 11
D. Chlorophyll a ................................................................................................................ 12
E. Phosphorus ................................................................................................................... 12
F. Nitrogen ........................................................................................................................ 18
G. pH ................................................................................................................................. 18
H. Alkalinity ...................................................................................................................... 22
I. Dissolved Oxygen .......................................................................................................... 22
6. Trophic State Index ........................................................................................................... 25
7. Conclusions ....................................................................................................................... 28
8. References ....................................................................................................................... 30
Appendix A. Complete Data Set Collected During the 2011 Water Quality Monitoring Program
of Potter Lake. ......................................................................................................... 31
A.1. Temperature ..................................................................................................................... 32
A.2. Secchi disc transparency ................................................................................................... 32
A.3. Turbidity ............................................................................................................................ 32
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A.4. Water Chemistry ............................................................................................................... 33
A.5. pH ...................................................................................................................................... 33
A.6. Dissolved Oxygen ............................................................................................................... 34
A.7. Trophic State Indices .......................................................................................................... 34
ListofTables
Table 1. Possible outcome predicted based on R. E. Carlson’s Trophic State Indices (from
Carlson and Simpson, 1996). .......................................................................................... 26
Table 2. Potter Lake Trophic State Indices based on samples collected at 0.5 m during March
through October, 2011. The summer period includes data collected during June, July,
August and September. .................................................................................................. 28
ListofFigures
Figure 1. Bathymetric map of Potter Lake, Douglas County, Lawrence, Kansas (38.96° N
Latitude; 95.24° W Longitude). This map was created by the Kansas Biological Survey
(2010). ............................................................................................................................ 2
Figure 2. Watershed area (ca. 0.029 square mile or 19 acres) for Potter Lake (black‐outlined
area). .............................................................................................................................. 3
Figure 3. Aerial view of the Potter Lake watershed (from Google Earth) ..................................... 4
Figure 4. Stormwater conveyance system that provides the majority of the water input to
Potter Lake. .................................................................................................................... 5
Figure 5. Water temperature profiles from Potter Lake during March through October, 2011. . 8
Figure 6. Regression analysis between the weekly mean air temperature and the surface water
(0.5 m) temperature of Potter Lake during March through October, 2011. ................. 9
iii
Figure 7. Water density profiles for Potter Lake during March through October, 2011. ............ 10
Figure 8. Secchi disc depth (centimeters) from Potter Lake during March trhrough October,
2011. ............................................................................................................................. 13
Figure 9. Seasonal water column profiles of turbidity in Potter Lake during March through
October, 2011. ............................................................................................................. 14
Figure 10. Non‐algal turbidity values for Potter Lake collected during March through October,
2011. Note that the zero (0) values for the June, July and August 3.0 m samples
were calculated as negative numbers and given zero values. .................................. 15
Figure 11. Linear regression relationship between the chlorophyll a concentration (0.5 m) and
the Secchi disc depth (i.e., transparency).................................................................. 16
Figure 12. Concentrations of chlorophyll a in Potter Lake at 0.5 m during March through
October, 2011. ........................................................................................................... 17
Figure 13. Concentrations of Total Nitrogen in Potter Lake at 0.5 m and 3.0 m during March
trhough October, 2011. ............................................................................................. 19
Figure 14. Mean pH (± 1 Standard Deviation) for Potter Lake during the monitoring program
during March, June through October, 2011. ............................................................. 20
Figure 15. Summertime pH (Mean ± 1 Standard Deviation) in Potter Lake, during June through
September, 2011. ...................................................................................................... 21
Figure 16. Dissolved oxygen profiles for Potter Lake during March through October 2011. ..... 23
Figure 17. Oxygen saturation profiles for Potter Lake during March through October 2011. .... 24
Figure 18. Seasonal variations in the Trophic State Indices for Potter Lake, March – October,
2011. .......................................................................................................................... 27
1
1. Introduction Potter Lake [referred to as “Potter’s Lake” by the Kansas Department of Health and
Environment (KDHE) and the U.S. Environmental Protection Agency (EPA); U.S. Geological
Survey Hydrologic Unit Code (HUC) 8: 10270104, HUC 11: 020; Station: LM073401] is located in
northwestern Kansas in Lawrence, Kansas, and lies within the Lower Kansas River Basin. The 1‐
acre lake was constructed in 1911 on the campus of the University of Kansas (KU), Lawrence
Campus, in Douglas County, to provide fire protection for the campus. KDHE added the lake to
the state’s Clean Water Act, Section 303(d) list in 1996 because of aquatic life use impairment.
In 2000, KDHE developed a Total Maximum Daily Loads (TMDL) to address the phosphorus
loading and associated eutrophication, high pH, and secondary contact recreation impairments.
The eutrophication impairment of Potter Lake was believed to be associated with
fertilizer usage within the watershed (KDHE TMDL, 2000). Background inputs of phosphorus
were suspected to come from nutrient recycling from the sediments, geological sources and
wildlife waste. There were no identified point sources of phosphorus input within the
watershed. The lake has a small watershed (ratio of watershed area: lake surface area ≈ 19)
and the lake has no natural stream inflow; rather, most of the inflow waters are derived from
the stormwater conveyance system in the areas to the south and west of the lake.
Ongoing efforts by the University of Kansas have been undertaken to improve the water
quality of Potter Lake. These efforts have significantly improved the lake’s water quality and
the results of an eight‐month monitoring program are presented in this report. Based on the
findings of the water quality monitoring program, it is believed that Potter Lake should be
delisted from the Kansas list of impaired waters 303(d) list.
2. DescriptionofthePotterLakeanditsWatershed Situated on the campus of the University of Kansas, Lawrence Campus, Potter Lake has a
surface area of approximately (ca.) 1.0 acre, a maximum depth of 12.0 feet (3.66 meters) and a
mean depth of 5.4 feet (1.65 m) (Figure 1). The lake holds ca. 1,783,690 gallons of water (6,752
m3 or 5.4 acre feet). The land use within the ca. 0.029 square mile (ca. 19 acre) watershed has
been described as “100% urban (campus)” (KDHE TMDL, 2000); however, over 50% of the
drainage area directly surrounding the lake is covered with grass and trees (Figure 2, 3). There
are no natural stream inflows to the lake. The primary source of water to Potter Lake is from
stormwater runoff via its conveyance system in the area (Figure 4). There is a small amount of
water input from direct precipitation onto the lake surface, sheet runoff and there may be a
2
Figure 1. Bathymetric map of Potter Lake, Douglas County, Lawrence, Kansas (38.96° N Latitude; 95.24° W Longitude). This map
was created by the Kansas Biological Survey (2010).
3
Figure 2. Watershed area (ca. 0.029 square mile or 19 acres) for Potter Lake (black‐outlined area).
4
Figure 3. Aerial view of the Potter Lake watershed (from Google Earth).
5
Figure 4. Stormwater conveyance system that provides the majority of the water input to
Potter Lake.
6
small amount of groundwater inflow. Surface water outflow from the lake is not continuous.
Two water outflow pathways are present, both of which flow into the regional stormwater
drainage system which eventually flows into the Kansas River. One outflow pathway is via an
overflow standpipe within the lake. The second is an overflow spillway located on the
northwestern end of the lake.
The soils of the Potter Lake watershed have been mapped as Martin‐Sogn‐Vinland
association, although the Vinland‐Martin complex makes up the major part of the drainage area
(7 – 15% slopes) (U.S. Department of Agriculture, Soil Conservation Service, 1977). This
complex is on the slide slopes below limestone and sandstone formations. The presence of
limestone within the watershed has an influence on the chemical characteristics (e.g., pH and
alkalinity) of Potter Lake.
3. Remediation Measures Taken to Improve the Water Quality ofPotterLake
The watershed area directly surrounding Potter Lake is totally covered with sod grass
and trees (see Figure 3). Since at least 2000, that area has received limited fertilizer
application, an activity which was identified in the TMDL as a potential source of phosphorus to
the lake. In the spring of 2008, the Potter Lake Project, a student lead effort, was established to
coordinate with efforts being made by the KU Departments of Design and Construction
Management and Facilities and Operations, Landscaping Division, to improve and enhance the
lake’s water quality. In March 2009, Asian Grass Carp were added to the lake to help control
the growth of aquatic weeds. Also in 2009, student volunteers were organized by the Potter
Lake Project to manually remove some of the aquatic vegetation from the lake. In September,
2010, a $125,000 dredging project was completed to remove approximately 5,000 cubic yards
(3,823 cubic meters) of sediments containing decaying vegetation from the lake bottom.
Nutrients from these sediments and decaying vegetation were being recycled back into the lake
water feeding the growth of a green surface “scum.” That green material, which covered the
lake surface in 2010, was actually made up of a very small (ca. 1 millimeter across), rootless,
seed‐bearing flowing plant called watermeal (Wolffia sp.). The growth of this plant is usually
indicative of an abundant availability of nutrients (e.g., phosphorus and nitrogen) in the lake
water. Also in the fall of 2010, a $200,000 stormwater runoff project was undertaken to reduce
the amount of runoff from Jayhawk Boulevard.
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4. WaterQualityMonitoringProgramforPotterLake The water quality monitoring program was begun in March, 2011, and continued
through October, 2011. Sampling time was usually midday (between 1100 and 1300 hours).
Sampling was conducted over the deepest part of the lake (Latitude: 38.96 N; Longitude: 95.25
W). The monitoring program involved monthly sampling of physical and chemical
characteristics of the water quality. The following parameters were measured: Secchi disc
transparency, depth profiles of temperature, pH, turbidity and dissolved oxygen concentration
using an Horiba U‐10 Water Quality Meter, and water chemical analyses for concentrations of
total phosphorus, total nitrogen, Kjeldahl nitrogen, nitrate, nitrite (conducted by Pace Analytical
Services, Inc., Lenexa, Kansas) and chlorophyll a (conducted by the Kansas Department of
Health & Environment, Bureau of Environmental Field Services, Topeka, Kansas). On one
occasion (June, 2011), water samples were analyzed for alkalinity (as CaC03 mg/liter; by Pace
Analytical Services, Inc.). Water samples for chemical analyses were collected from two depths,
one near the lake surface (0.5 meters or 1.64 feet) and one near the lake bottom (3.0 meters or
9.84 feet). These water samples were kept cold and in the dark and delivered to the analytical
laboratories within 24 hours of collection. (Complete data set in Appendix A.)
5. ResultsoftheMonitoringProgram
A. WaterTemperature The depth and seasonal changes in water temperature observed in the water column of
Potter Lake was similar to other aquatic water bodies in the Midwest. Following ice cover
during the winter months, the surface water temperatures began to warm up (Figure 5) as the
air temperatures began to increase the week of February 13, 2011, when the mean average air
temperature first remained above freezing (mean average air temperature that week was 47° F;
maximum air temperature 75° F ) (weather station KLWC data from Lawrence Municipal
Airport; Weather Underground web page). At the beginning of this monitoring program on
March 16, 2011, the surface waters (0 – 0.5 meters) were already above 50° F (10° C) and the
bottom waters (1.5 – 3 meters) ranged from 44 – 46 ° F (6.7 – 7.7 ° C). The lake waters
continued to increase in temperature through the spring and summer, reaching a maximum
surface water temperature in July (86° F, 30.3 ° C). After that time, the lake water temperature
began to first gradually decline and then more rapidly declined between August and October
when the rate of the lake water temperature decline greatly increased in sync with the rapidly
decreasing air temperatures. There was a strong positive dependent relationship (r2 = 0.8794)
8
Figure 5. Water temperature profiles from Potter Lake during March through October, 2011.
9
Figure 6. Regression analysis between the weekly mean air temperature and the surface water (0.5 m) temperature of Potter
Lake during March through October, 2011.
10
Figure 7. Water density profiles for Potter Lake during March through October, 2011.
11
between the weekly mean air temperature and the surface water (0.5 m) temperature (Figure
6).
Another characteristic of lakes in relation to the solar heating of their waters is thermal
stratification. As the water temperature increases, the density of water decreases. Depending
on a lake’s morphology (e.g., depth and surface area), orientation to prevailing winds and the
direction and velocity of the prevailing winds, a lake can become thermally stratified into a
warm surface layer (epilimnion) and a colder bottom layer (hypolimnion) with a transition zone
(metalimnion) where the water temperature changes very rapidly (at least 1° C per meter).
Converting the temperature profiles from Potter Lake into water density profiles (based on
water temperature only) revealed that the lake was thermally stratified in June and July, 2011
(Figure 7). Therefore, Potter Lake appears to be a dimictic aquatic system, that is, the lake
waters mix completely from top to bottom twice a year (in the spring and late summer/fall).
B. SecchiDiscTransparency The Secchi disc depth is a measure of the transparency of the lake water. In Potter Lake,
the Secchi depth ranged from 95 ‐ 237 cm during March through October 2011 (Figure 8). The
mean (x)̄ Secchi disc depth for this eight‐month period was 179±46 cm. During the summer
months (June – September), the range was 114 – 195 cm (x ̄ summer = 180 ±39 cm). Except for
March and August, the Secchi disc depth was fairly stable, averaging 204 ±17 cm.
C. Turbidity The waters of Potter Lake were fairly clear throughout the sampling period, especially
from the surface to 2.0 m (Figure 9). The overall average turbidity for the 0.0 – 2.0 m portion of
the lake’s water column was 4±2 NTU. Some of the turbidity readings from water deeper than
2.0 m were very high possibly due to disturbance of epiphytic periphyton (attached algae)
growing on benthic macrophytes.
The turbidity observed in Potter Lake appeared to be due to algal material based on an
evaluation of the Non‐Algal Turbidity (NAT) (Walker 1987). That analysis estimates if the
turbidity, as it affects the water clarity (i.e., Secchi disc depth), is due to algal material (i.e.,
chlorophyll a) or is due to non‐algal material (e.g., suspended clay or other inorganic material).
The relationship is as follows:
NAT = 1/Secchi (m) – 0.025*Chl‐a (ug/L) (resulting units of m‐1).
The 0.025 term associated with the chlorophyll concentration is a default value of the slope of
the chlorophyll versus Secchi relationship (units of m2/mg) calibrated from 65 Corps of Engineer
impoundments data set (Walker 1983). If the NAT value is less than 0.4, the turbidity is all due
12
to algal cells. Values above 1.0 indicate increasing importance of clay or other inorganic (i.e.,
non‐algal) material. Values that calculate to negative numbers should be given zero values as
there is little guidance on that result.
In Potter Lake, the NAT values for 0.5 m samples ranged from 0.24 – 0.57 (x ̄ =
0.40±0.10). For 3.0 m samples, the NAT ranged from 0.00 – 0.87 (x ̄ = 0.24±0.28) (the zero
values were actually calculated to negative numbers) (Figure 10). These NAT values indicate
that the turbidity of Potter Lake is primarily due to algal material.
A similar way to look at the cause of the observed turbidity is to evaluate the
relationship between measured chlorophyll a concentrations and Secchi disc transparency. A
regression analysis of these data from Potter Lake clearly illustrates that there is a strong
inverse relationship between the amount of chlorophyll a (0.5 m) and the Secchi disc
transparency (r2 = 0.74) (Figure 11). Therefore, as the amount of chlorophyll increased, the
Secchi disc transparency decreased. This analysis supports the NAT data that the observed
turbidity in Potter Lake is primarily due to algal material.
D. Chlorophylla The distribution of chlorophyll a in lake water is an indicator of the distribution of
phytoplankton (i.e., algal) biomass in aquatic systems. During this monitoring program, water
samples from two depths (0.5 and 3.0 m) were collected during March through October, 2011.
All samples collected from 3.0 m in April, May, June, July and August were contaminated with
material believed to be periphyton, not free floating algae (i.e., phytoplankton). Chlorophyll a
concentrations in the 0.5 m samples collected during the 8 month monitoring period ranged
from 1.99 – 18.83 µg/liter with a mean of 8.51±5.83 µg/liter (analytical method: AWWA, APHA,
WEF 10200‐H) (Figure 12). During the summer period (June – September), the mean
chlorophyll a concentration in the 0.5 m samples was 10.23±3.69 µg/liter. The relatively high
concentration of chlorophyll a in August (16.34 µg/liter) was believed to be the result of the
lake destratifying thermally (see Figure 7) and the lake water mixing from top to bottom. KDHE
has set a 12 µg/liter target as the limit for primary contact recreation and a 20 µg/liter target
for secondary contact. Potter Lake only exceeded the primary target limit twice (March and
August, 2011) and never exceeded the secondary contact target limit.
E. Phosphorus Phosphorus concentrations in lake water were measured as Total Phosphorus, that is,
the combination of both organic and inorganic forms of phosphorus. Samples were collected
from two depths, 0.5 and 3.0 meters. The analytical method used to analyze for total
phosphorus (EPA 365.4: Total Phosphorous, Colorimetric, Automated, Block Digester AA II) has
13
Figure 8. Secchi disc depth (centimeters) from Potter Lake during March through October, 2011.
14
Figure 9. Seasonal water column profiles of turbidity in Potter Lake during March through October, 2011.
15
Figure 10. Non‐algal turbidity values for Potter Lake collected during March through October, 2011. Note that the zero (0) values
for the June, July and August 3.0 m samples were calculated as negative numbers and given zero values.
16
Figure 11. Linear regression relationship between the chlorophyll a concentration (0.5 m) and the Secchi disc depth (i.e.,
transparency).
17
Figure 12. Concentrations of chlorophyll a in Potter Lake at 0.5 m during March through October, 2011.
18
a detection limit of 5 µg/liter. The total phosphorus concentrations in water samples collected
at 0.5 m in Potter Lake were all below the level of detection (< 5 µg/liter) throughout the eight‐
month monitoring program. The total phosphorus concentrations in water samples collected at
3.0 m were also all below the level of detection except during June and July, 2011, when total
phosphorus concentrations were 110 and 90 µg/liter respectively. During these two months,
the lake was thermally stratified and the dissolved oxygen at 3.0 m was extremely low in June
and July, 0.06 and 0.04 mg/liter respectively (see Section 5.I.).
F. Nitrogen The amount of nitrogen was measure as dissolved inorganic nitrogen (nitrate and
nitrite), Kjeldahl Nitrogen and Total Nitrogen. Forms of dissolved inorganic nitrogen are related
to nutrient availability for algal growth. Kjeldahl nitrogen is a measure of the organic nitrogen
plus ammonium present in the water (it does not measure the amount of nitrate or nitrite
present). Total nitrogen is a measure of all forms of nitrogen present in the water column, both
inorganic and organic.
For samples collected from 0.5 m in Potter Lake, concentration of nitrite was never
above the level of detection (0.10 mg/liter) throughout the study period. Nitrate at 0.5 m was
only above the level of detection (0.015 mg/liter) in March and April (0.33 and 0.22 mg/liter,
respectively). Samples from 3.0 m followed a similar pattern throughout the study period with
nitrite below the level of detection throughout the study period and nitrate only detectable in
March, April and August (0.45, 0.20, 0.10 mg/liter, respectively).
The trend in Kjeldahl nitrogen and total nitrogen were nearly identical at both depths
throughout the study period. The amount of total nitrogen was almost always equal to or
slightly greater than the amount of Kjeldahl nitrogen. For samples collected from 0.5 m, the
total nitrogen concentration ranged from 0.32 – 1.30 mg/liter (x ̄=0.67±0.34 mg/liter) (Figure
13). During the summer months (June through September), the total nitrogen concentration
ranged from 0.30 – 1.00 mg/liter (x ̄=0.61±0.26). For those samples collected from 3.0 m, the
total nitrogen concentration was slightly higher than at 0.5 m ranging from 0.46 – 1.70 mg/liter
(x ̄ =1.07±0.44 mg/liter). During the summer months, the concentrations of total nitrogen
ranged from 0.46 – 1.70 mg/liter (x ̄=1.27±0.49 mg/liter).
G. pH
The relative acidity (low pH) or basicity (high pH) of lake waters is a function of the
buffering capacity or acid neutralizing capacity (alkalinity) of the water, the rate of
photosynthesis by algae and macrophytes, and the rate of respiration by plants and bacteria.
19
Figure 13. Concentrations of Total Nitrogen in Potter Lake at 0.5 m and 3.0 m during March through October, 2011.
20
Figure 14. Mean pH (± 1 Standard Deviation) for Potter Lake during the monitoring program during March, June through October,
2011.
21
Figure 15. Summertime pH (Mean ± 1 Standard Deviation) in Potter Lake during June through September, 2011.
22
The range in pH in Potter Lake (0 – 3.2 m) during the study period for all depths (March, June –
October, 2011) was 6.51 – 8.26 (x ̄= 7.52±0.39). During April and May, the pH probe on the
Horiba U‐10 was not functioning properly. Taking each sample depth individually, the mean pH
during the monitoring program (Figure 14) ranged from 7.80±0.28 at surface (0.0 m) and
decreased to 6.64±0.15 at 3.2 m. The pH of the waters 2.5 m and above had an overall mean
pH of 7.66±0.25. The mean pH of water 3.0 m and deeper was 6.89±0.38. During the summer
months (June – September), the mean pH from 0.0 – 3.2 m ranged from 6.64 – 7.75 (overall x ̄=
7.35±0.37) (Figure 15). KDHE has set an optimal pH range of 6.5 – 8.5 for aquatic water bodies;
therefore, Potter Lake is within that range.
H. Alkalinity The buffering capacity or acid neutralizing capacity of lake water is referred to as
alkalinity. This parameter is a measure of the inorganic carbon equilibrium within a system
imparted by the presence and concentrations of carbon dioxide, bicarbonate and carbonate in
the water. In Kansas and within the watershed of Potter Lake, there is a significant amount of
limestone (i.e., carbonate) present that directly influences the alkalinity of Potter Lake.
Water samples from 0.5 and 3.0 m were analyzed for alkalinity in June, 2011. The
alkalinity at both depths was the same, 110 mg/liter as calcium carbonate (2,196 µeq/liter as
calcium carbonate). At this value, Potter Lake is very well buffered and a non‐sensitive aquatic
system. EPA has set a value of <25 mg/liter as calcium carbonate as the level below which a
lake would be sensitive to acidic inputs.
I. DissolvedOxygen The amount of dissolved oxygen in lakes reflects the balance between the rates of
supply of oxygen from the atmosphere and photosynthesis versus the consumption of oxygen
by organism (e.g., respiration) and nonbiotic chemical reactions. During the spring months in
Potter Lake, the supply of oxygen to the surface waters was very high in contrast to
consumptive uses of oxygen (Figure 16). The percent oxygen saturation in the surface waters
during April, 2011, was over 100% at 0.0 m and there was an oxygen peak between 2.0 – 2.5 m
indicating high photosynthetic activity as the water clarity was very high (Secchi disc depth was
187 cm) (Figure 17). In May, 2011, the oxygen saturation was exceptionally high between 0.0 –
2.0 m, ranging from 99 – 112% when, again, the water transparency was very high (Secchi disc
depth was 197 cm). During June and July, 2011, the lake had become thermally stratified and
the bottom waters (below 2.0 m) had become anoxic (the percent saturation of these waters
ranged from 0.0 – 5.8 %). The lake appeared to have turned over (i.e., mixed from top to
bottom) just before our August sampling and, although the lake was no longer thermally
23
Figure 16. Dissolved oxygen profiles for Potter Lake during March through October 2011.
24
Figure 17. Oxygen saturation profiles for Potter Lake during March through October 2011.
25
stratified, the entire water column (0.0 – 3.2 m) had depressed oxygen levels (ranged from 0.0
– 51.6%) with the waters between 1.5 – 2.5 m ranging from 6.1 – 10.9% saturation and the
waters 3.0 m and below were completely anoxic (0.0% saturation). During September and
October, 2011, anoxic conditions never returned. In September, the oxygen levels were
moderate throughout the water column (ranged from 43.2 – 73.6%). In October, the percent
oxygen saturation trended downwards with increasing depth ranging from 43.8% at 0.5 m to
14.1% at 3.0 m. The extensive macrophyte growth along the shoreline appeared to be
senescing which would account for the observed lower levels of oxygen in the lake waters.
6. TrophicStateIndex The natural aging process of lakes is called eutrophication. Generally, as inputs of
nutrients (e.g., nitrogen and phosphorus) increase in lake water, the more plants and animals
can be sustained by the lake. Using the Secchi disc transparency, chlorophyll a, total
phosphorus and total nitrogen, the degree of eutrophication, or trophic status, of a lake can be
defined. Based on three of these parameters, R. E. Carlson (Carlson1977, 1981, 1983; Carlson
and Simpson 1996) developed the following Trophic Status Indices (TSI) and C. R. Kratzer and P.
L. Brezonik (1981) developed a TSI based on the total nitrogen data from lake water.
TSISD = 60 ‐ 14.41 [ln Secchi disk (meters)]
TSITP = 14.42 [ln Total phosphorus (µg/L)] + 4.15
TSICHL = 9.81 [ln Chlorophyll a (µg/L)] + 30.6
TSITN = 14.43 [ ln Total Nitrogen (mg/L)] + 54.45
If the TSI value is above 70 the water body is considered Hypereutrophic; between 50 and 70,
Eutrophic; between 40 and 50, Mesotrophic; less than 40, Oligotrophic (Table 1).
Using the data collected from 0.5 m in Potter Lake during March through October, 2011,
the Trophic State Indices for Secchi disc depth, Chlorophyll and Total Nitrogen were in the high
Mesotrophic to slightly Eutrophic range (47 – 52) while the TSITP was in the slightly Oligotrophic
range (37) (Figure 18; Table 2). The summer average indices (time period of June – September)
were similar to the overall averages from the eight‐month monitoring period.
It should be noted that a value of total phosphorus = 10 µg/liter was used to calculate
the TSITP because the 0.5 m concentrations of total phosphorus were all below the level of
detection (5 µg/liter) throughout the sampling period. A value of 10 µg/liter for total
26
Table 1. Possible outcome predicted based on R. E. Carlson’s Trophic State Indices (from Carlson and Simpson, 1996).
Chl SD TP(µ/L) (m) (µg/L)
<30 <0.95 >8 <6Oligotrophy: Clear water, oxygen throughout the year in the hypolimnion
Water may be suitable for an unfiltered water supply.
Salmonid fisheries dominate
30-40 0.95-2.6 8 - 4 6 - 12 Hypolimnia of shallower lakes may become anoxic
Salmonid fisheries in deep lakes only
40-50 2.6-7.3 4 - 2 12 - 24
Mesotrophy: Water moderately clear; increasing probability of hypolimnetic anoxia during summer
Iron, manganese, taste, and odor problems worsen. Raw water turbidity requires filtration.
Hypolimnetic anoxia results in loss of salmonids. Walleye may predominate
50-60 7.3-20 2 - 1 24-48Eutrophy: Anoxic hypolimnia, macrophyte problems possible
Warm-water fisheries only. Bass may dominate.
60-70 20-56 0.5-1 48-96Blue-green algae dominate, algal scums and macrophyte problems
Episodes of severe taste and odor possible.
Nuisance macrophytes, algal scums, and low transparency may discourage swimming and boating.
>80 >155 <0.25 192-384 Algal scums, few macrophytes Rough fish dominate; summer fish kills possible
TSI Attributes Water Supply Fisheries & Recreation
70-80 56-155 0.25- 0.5 96-192Hypereutrophy: (light limited productivity). Dense algae and macrophytes
27
20
30
40
50
60
70
1‐Mar 1‐Apr 2‐May 2‐Jun 3‐Jul 3‐Aug 3‐Sep 4‐Oct 4‐Nov
TSI
Potter Lake Trophic State IndexMarch ‐ October 2011
Secchi TSI
Chl a TSI
TP TSI
TN TSI
Eutrophic
Mesotrophic
Oligotrophic
Figure 18. Seasonal variations in the Trophic State Indices for Potter Lake during March through October, 2011.
28
Table 2. Potter Lake Trophic State Indices based on samples collected at 0.5 m during March
through October, 2011. The summer period includes data collected during June,
July, August and September.
March - October Average
Std. Dev.
Summer Average
Std. Dev.
TSISD 52 5 52 4
TSITP 37 0 37 0
TSICHL 49 8 53 4
TSITN 47 8 46 7
phosphorus, two times the detection limit, was deemed the best estimate to use to calculate
the TSITP. The TSICHL data are believed to best reflect the trophic status of Potter Lake.
7. Conclusions In the 2000, the TMDL for Potter Lake identified two parameters that were associated
with the lake’s impairment: pH and eutrophication. The pH levels cited in the TMDL for
samples collected during the summer of 1994 ranged from 8.82 – 9.01 (x ̄= 8.92). Also cited as
an impairment in the TMDL was the TSICHL greater than 70, a value that put the lake’s trophic
status in the Hypereutrophic category.
During the 8‐month monitoring (March – October) in 2011, the highest pH measured
was 8.26 in one surface water sample (0.0 m) collected in October. During the summer months
(June – September), the highest pH measured was 7.95 in a surface water sample (0.0 m)
during June. The overall six‐month mean pH for all depths in Potter Lake was 7.52 (± 0.39)
while the summertime overall mean for all depths was 7.35 (± 0.37). KDHE has set an optimal
pH range of 6.5 – 8.5 for aquatic water bodies; therefore, Potter Lake is well within that range.
The TSICHL over the eight month monitoring program ranged from 37 – 59 (x ̄= 49±8).
During the summer months, the TSICHL ranged from 49 – 58 (x ̄ = 53±4). These data would
characterize the lake as either Mesotrophic or slightly Eutrophic. At no time was the TSICHL near
the Hypereutrophic category referred to in the 2000 TMDL.
29
Those efforts that have been undertaken by the University of Kansas since 2000 appear
to have remediated the water quality problems referred to in the 2000 TMDL. Ongoing efforts
to maintain and improve Potter Lake should further enhance the water quality of this lake.
Therefore, based on the data collected during this eight‐month monitoring program (2011),
Potter Lake does not appear to have any impairment. These findings would support the
position that Potter Lake be delisted from the Kansas 303(d) list of impaired water bodies.
30
8. References
Carlson, R.E. 1977. A trophic state index for lakes. Limnology and Oceanography. 22:361‐369.
Carlson, R.E. 1980. More complications in the chlorophyll‐Secchi disk relationship. Limnology
and Oceanography. 25:378‐382.
Carlson, R.E. 1981. Using trophic state indices to examine the dynamics of eutrophication.
p. 218‐221. In: Proceedings of the International Symposium on Inland Waters and Lake
Restoration. U.S. Environmental Protection Agency. EPA 440/5‐81‐010.
Carlson, R.E. 1983. Discussion on “Using differences among Carlson’s trophic state index values
in regional water quality assessment”, by Richard A. Osgood. Water Resources Bulletin.
19:307‐309.
Carlson, R.E. and J. Simpson. 1996. A Coordinator’s Guide to Volunteer Lake Monitoring
Methods. North American Lake Management Society. 96 pp.
Kratzer, C.R. and P.L. Brezonik. 1981. A Carlson‑type trophic state index for nitrogen in Florida
lakes. Water Res. Bull. 17: 713‐715.
U.S. Department of Agriculture, Soil Conservation Service, 1977. Soil survey of Douglas County,
Kansas. 73pp.
Walker, W. W., Jr. 1984. Trophic Indices for Reservoirs. Lake and Reservoir Management, North
American Lake Management Society. U.S. Environmental Protection Agency. EPA
440/5/84‐001. pp. 435 – 440.
Walker, W. W., Jr. , 1985. Empirical methods for predicting eutrophication in impoundments;
Report 3, Phase II: Model refinements, Technical Report E‐81‐9, U.S. Army Engineer
Waterways Experiment Station, Vicksburg, MS., NTIS No. AD A155 483.
31
AppendixA.CompleteDataSetCollectedDuringthe2011WaterQualityMonitoringProgramofPotterLake.
32
A.1.Temperature(°C)
Depth March April May June July August September October
0.0 10.7 15.2 18.4 27.7 29.8 28.2 20.5 18.400.5 10.5 13.8 17.3 27.5 30.3 27.9 20.5 18.301.0 9.3 13.3 16.5 27.2 30.3 27.6 20.4 18.201.5 7.7 13.0 16.1 25.3 30.2 27.5 20.4 18.202.0 6.9 11.8 15.8 22.5 29.4 27.4 20.6 18.102.5 6.7 10.2 15.5 20.5 27.4 27.3 20.4 18.103.0 6.7 9.6 15.2 17.7 23.4 26.9 20.0 18.003.2 9.5 14.8 17.0 22.6 26.4 20.4
A.2.Secchidisctransparency(cm)
Month Secchi Depth
16-Mar-11 95.56-Apr-11 1873-May-11 1977-Jun-11 19512-Jul-11 21711-Aug-11 11415-Sep-11 193.513-Oct-11 236.5
A.3.Turbidity(NTU)
Depth March April May June July August September October
0.0 6 3 2 3 3 7 4 20.5 6 3 2 3 2 10 1 41.0 6 3 3 4 2 7 1 31.5 8 3 3 9 2 6 0 32.0 9 3 3 7 8 6 3 32.5 8 3 4 25 36 6 3 23.0 13 5 7 17 38 94 2 23.2 7 10 31 89 0 141
33
A.4.WaterChemistry
0.5 meters ParameterDate Chl a Nitrate Nitrite N03 + NO2 Kjeldahl N Total N Total P TN/TP Alkalinity
µg/liter mg/liter mg/liter mg/liter mg/liter mg/liter mg/liter ** mg CaCO3/l
Method Detection Limit 0.03 0.015 0.10 0.0092 0.077 0.10 0.005 0.38
March 16, 2011 18.80 0.33 ND 0.34 1.00 1.30 ND 130
April 6, 2011 3.17 0.22 ND 0.22 0.66 0.88 ND 88
May 3, 2011 1.99 ND ND ND 0.32 0.32 ND 32
June 7, 2011 9.39 ND ND ND 0.36 0.30 ND 30 110
July 12, 2011 8.73 ND ND ND 1.00 1.00 ND 100
August 11, 2011 16.34 ND ND ND 0.64 0.64 ND 64
September 15, 2011 6.47 ND ND ND 0.48 0.48 ND 48
October 13, 2011 3.17 ND ND ND 0.43 0.43 ND 43
3.0 meters ParameterDate Chl a Nitrate Nitrite N03 + NO2 Kjeldahl N Total N Total P TN/TP Alkalinity
µg/liter mg/liter mg/liter mg/liter mg/liter mg/liter mg/liter ** mg CaCO3/l
Method Detection Limit 0.03 0.015 0.10 0.0092 0.077 0.10 0.005 0.38
March 16, 2011 7.00 0.45 ND 0.46 0.66 1.10 ND 110
April 6, 2011 14.31 0.20 ND 0.21 0.95 1.20 ND 120
May 3, 2011 14.08 ND ND ND 0.62 0.62 ND 62
June 7, 2011 127.37 ND ND ND 1.20 1.30 0.11 12 110
July 12, 2011 84.50 ND ND ND 1.60 1.60 0.09 18
August 11, 2011 46.18 0.10 ND ND 1.60 1.70 ND 170
September 15, 2011 3.84 ND ND ND 0.46 0.46 ND 46
October 13, 2011 3.26 ND ND ND 0.58 0.58 ND 58
** TN/TP values calculated using TP = 0.01 mg/liter (2xDL) when TP analyses results were “ND”.
A.5.pH
Depth March April May June July August September October
0.0 7.50 7.95 7.49 7.65 7.67 8.260.5 7.58 7.87 7.63 7.51 7.17 8.11.0 7.60 7.76 7.63 7.39 7.42 8.011.5 7.64 7.80 7.54 7.29 7.20 7.822.0 7.63 7.81 7.41 7.24 7.35 7.762.5 7.58 7.48 7.16 7.18 7.28 7.743.0 7.50 7.05 6.65 6.93 7.28 7.673.2 6.85 6.57 6.51
34
A.6.DissolvedOxygen(mg/liter)
Depth March April May June July August September October
0.0 10.24 10.62 10.8 6.29 7.10 4.02 4.1 4.020.5 9.84 10.10 10.16 6.25 7.10 2.62 3.95 4.111.0 9.67 10.25 10.5 5.33 5.90 1.67 6.74 2.771.5 9.91 10.10 11.22 8.27 3.52 0.86 5.73 2.412.0 9.70 11.75 10.1 4.89 1.02 0.48 5.45 2.052.5 9.21 11.60 8.2 0.52 0.10 0.84 4.6 1.633.0 5.65 10.20 5.33 0.06 0.04 0.01 4.66 1.333.2 10.30 1.8 0.05 0.00 0.00
A.7.TrophicStateIndices
16-Mar-11 6-Apr-11 3-May-11 7-Jun-11 12-Jul-11 11-Aug-11 15-Sep-11 13-Oct-11
SD 61 51 50 50 49 58 50 48
Chl a - 0.5 59 42 37 53 52 58 49 42
TP - 0.5 37 37 37 37 37 37 37 37
TN - 0.5 58 53 38 37 54 48 44 42