organic matter (om) fate and transport in watershedsudel.edu/~inamdar/breg667/om_2016.pdf · 2016....

Organic matter (OM) fate and transport in watersheds

Outline

• Definition of organic carbon (OC)• Environmental Significance of OC• Measurements and characterization• Sources of OC• Processes and mechanisms• Environmental factors

Key results from our studies -• DOM in watershed sources• DOM export in runoff• POC mass exports• POC patterns

OM - definitionDissolved Organic matter - DOM < 0.2 - 0.7 micronParticulate Organic matter - POM ≥ 0.2 - 0.7 micronColloidal - 0.001 to 1 micron

Gives color to runoff waters.

OM - definition

OM - composition

Includes mixture of numerous organic compounds

Carbohydrates, proteins, amino acids, humic acids, fulvic acids, etc.

And Elements -

N, P, S….. Molecules with these elements

• C makes up about 67% of OM

Outline



OM – environmental significance?

Human health implications -

• DOC – drinking water supplies – can generate disinfection byproducts (DBPs) – when water is chlorinated

• DBPs –

• Trihalomethanes (THM) – MCL 80 ppb• Haloacetic acid (HAA) – MCL 60ppb


Human health implications -

• Big Elk Creek – (Fair Hill) – drinking water source for the Town of Elkton in MD

• White Clay Creek – drinking water for Newark, DE• Brandywine, Hoopes Reservoir – Wilmington, DE

• DBP compliance monitoring – TOC, THM, HAA?


• DOM – primary vehicle for organic contaminants, e.g., pesticides

• Organic acids in DOM – act as chelating agents –transport of toxic heavy metals – e.g., Mercury

OM - significance

C, N, and P components of organic matter can be bioavailable and can contribute to eutrophication!

DOC, DON, DOP


Important for ecosystem processes!

• OC – energy source in terrestrial and aquatic ecosystems

• Driver of numerous microbial processes, e.g., denitrification


• Provides protection for aquatic species – through absorbance of UV light

• Starting point of the aquatic food chain

• Carbon cycle and gaseous C fluxes

Outline



OM - measurements

Organic Carbon

Determined by –

• Absorption of light by spectrophotometer

• Wet oxidation of OM and measurement of CO2 released or the consumption of oxidant – dichromates or permanganates

• Dry oxidation of OM in presence of O2 and the CO2 released is measured – LECO and TOC analyzer

OM - measurements

UV and fluorescence techniques

• C proportional to UV absorbed – Beer-Lambert Law: Absorbance directly proportional to concentration & path length.

• UV absorbance at 254 nm – measure of DOC• Provide some estimates on the aromatic, humic, or

non-humic components• Specific UV absorbance (SUVA), Sr (spectral slope

ratio)

OM - measurements

Absorbance measured by spectrophotometer = A (unitless)

Decadal absorbance =A / path length in meters

Naperian absorbance =2.303*A/ path length

OM - measurements

Fluorescence Excitation Emission Matrices (EEMs)

Fluorescence indices characterize the C composition - HIX, FI, %humic-like, % protein-like, etc.

OM - measurements

New In-situ/field instruments – measure UV or fluorescence and convert to OC using a regression relationship

e.g., Spectrolyser

OM - measurements

Spectrolyser estimated versus lab measured data for DOC and Nitrate

Outline



OM - Sources

Where does it come from?• Plant and animal organic matter – primary source• Photosynthesis – primary origin

Terrestrial ecosystems – leaf litter, root exudates, soil organic matter, humus, C sorbed on minerals

- Allochthonous sources

OM - Sources

Aquatic ecosystems – production by algae, bacteria, ….Autochthonous sources

OM - Sources

Human-impacted watersheds – animal and human waste (manure, sewage, etc.)

DOM – Sources and fate

Figure from Bolan et al., 2011 -

1 – throughfall and stemflow;2 – root exudates;3 – microbial lysis;4 – humification;5 – litter/crop residue decomposition; 6 – organic amendments; 7 – microbial degradation; 8 – microbial assimilation; 9 – lateral flow; 10 – sorption; 11 – leaching.

Outline



OM – Key Processes/Mechanisms

Key processes affecting OM -

Sorption/complexation

• Sorption – retention of DOM on mineral surfaces -affects mobility and degradation – most important mechanism in terrestrial ecosystems

• Complexation – formation of soluble or insoluble DOM-metal complexes

DOM – Key Processes/Mechanisms

Sorption -

Fe and Al oxides. Critical factors –

• Surface area of the oxides

• DOM quality – hydrophobic or hydrophilic constituents; hydrophobic, aromatic, HMW DOM are preferentially sorbed and decrease with soil depth

• Redox conditions; reduced conditions – lead to reductive dissolution of oxides – loss of sorption surfaces

OM – Key Processes/Mechanisms

Kaiser and Kalbitz, 2012. Soil Biology and Biochemistry.DOC concentrations decrease with depthAromatic, humic, HMW DOM decrease; microbial products increase with depth


Microbial process -

• Microbial breakdown of OM into lower molecular weight constituents and the release of CO2

• 10 to 44% of DOM in soil solution – degradable

• Microbial decomposition can also breakdown POM –and thus enhance the leaching of DOM


Photo-oxidation/degradation

• More dominant in aquatic systems – streams, lakes, water bodies

• Can result in photo-cleavage of HMW DOM – to produce lower MW DOM species

• Can change DOM as water travels through the aquatic system

Outline

• Definition of organic carbon (OC)• Environmental Significance of OC• Measurements and characterization• Sources of OC• Processes and mechanisms• Factors


OM – Key Factors

Key factors affecting OM –

• Environmental factors• Landuse and management

DOM – Key Factors

Environmental factors

• pH

• Temperature

• Soil moisture

• Precipitation/water flux

• Freeze-thaw

OM – Key Factors

pH effects -

• Contradictory and difficult to predict

• Dissolution of C can be influenced by pH

• Some watershed scale studies suggest DOC increase in stream waters because of decrease in acidic deposition (e.g., Monteith et al., 2007)

OM – Key Factors

Temperature effects -

• Result in increased production of POM and DOM because of mineralization of soil OM

• Increased degradation of DOM• Warmer temps – greater plant production and therefore

OM (moisture is key)• Seasonal variability – greater DOM conc. in summer

than in winter

OM – Key Factors

Moisture effects -

• Rewetting after dry periods – enhance DOM leaching • Breakdown of OM over the dry period• Cell lysis• Disruption of soil structure• Especially – production of labile, LMW DOM

• Wet conditions – favor greater amounts of DOM

• Case of – wetlands - reduced conditions – impede oxidation of DOM, release of OM from sorption surfaces

• Larger extents of wetlands – more DOM

OM – Key Factors

Water flux and flow paths

• In forested watersheds –

• Greater amounts of water flux from near surface flow paths – increased POM and DOM exports; more aromatic, humic DOM

• Deeper flow paths – low DOC; less aromatic/humicDOM

OM – Key Factors

Freeze-thaw effects -

• Breakdown of OM – increased amounts of DOM

OM – Key Factors

Landuse and management effects -

• OM decreases – due to cultivation, forest clearing• Tillage will oxidize OM and thus reduce the OM

pools in soils

• POM and DOM may increase for landscapes receiving organic manure inputs – poultry litter, etc. -- DOM from such systems is especially labile

• OM from urban systems – more labile DOM; high pulses

• OM – Forest > grasslands > cropland

OM – Key Factors

Landuse effects -

• Forested versus wetland watersheds

Forested – low DOM in baseflow; sharp increases with storms and hydrologic flow paths

Wetlands – high DOM in baseflow; dilution of DOC with storms and surficial flows

Outline


Key results from our Fair Hill studies -• DOM in watershed sources• DOM export in runoff• POC mass exports• POC patterns

DOM sources

Intensive study catchment -

12 ha Big Elk Creek subcatchment

Wetness index(2 m LIDAR)Hillshade view

(2 m LIDAR)

DOM sources

DOM for source waters (multiple locations, spatially distributed): • Rainfall• Throughfall• Stemflow • Litter leachate• Soil water (zero & tension)• Shallow & deep groundwater• GW Seeps• Hyporheic zone• Stream water

DOM – watershed sources

DON [mg L-1]

0.01 0.1 1 10

DOC [mg L-1]

1 10 100

TFLTU

WSWHY

SGWRGWSeepDGW

Inamdar et al., 2012, Biogeochemistry

DOM – watershed sources

SUVA [L mgC-1 m-1]

0 2 4 6 8 10

TFLTU

WSWHY

SGWRGWSeepDGW

a254 [m-1]

1 10 100

HIX

0.2 0.4 0.6 0.8 1.0

% protein-like fluorescence0 5 10 15 20 25 30

TFLTU

WSWHY

SGWRGWSeepDGW

FI1.2 1.4 1.6 1.8

SR

0 2 4 6 8

a b c

e fd

Inamdar et al., 2012, Biogeochemistry

DOM – key points

• DOC, DON concentrations were highest for surficial watershed sources (e.g., LT, TF, WSW)

• Surficial sources were also more aromatic and humic

• DOM concentrations and aromatic/humic content decrease for deeper sources - removal of DOM through sorption processes

• % protein-like content – was highest in groundwater sources – more bioavailable?

• DOM molecular size (inversely related to SR) decreased with soil depth

Outline



DOM – baseflow vs. storms

Inamdar et al., 2011, Journal of Geophysical Research

DOM – key points

• DOC concentrations are higher during storms versus baseflow – same is true for a254 and HIX

• % proteins lower during storms

“Typical” DOM response

groundwater seeps

Rainfall/throughfall

Forest floor / litter layer

Soil water

groundwater

Runoff flowpaths and sources responsible for DOMInamdar et al., 2011, 2012, 2013

Throughfall, litter layer & soil water - key sources of DOM during storms/high flow

DOC

% humic-

likeDOM

% protein-

likeDOM

DOM – Key Points

• DOM concentrations and aromatic/humic contents increased with rise in hydrograph level --contributions from surficial sources such as TF, LT, SW

• % protein-like DOM followed a dilution trajectory –however mass still increased – bioavailable DOM mass exports increase during events

Outline



POM

Location & ReferenceWatershed size (km2) Ecosystem type DOC export

(kg C ha-1 yr-1)POC export (kg C ha-1 yr-1)

DOC/POC

Hubbard Brook,N.H. (Hobbie & Likens, 1973) 0.1 Temperate forest 11.8 3.4 3.5

Bear Brook, N.H. (Fisher & Likens, 1973) 1.0 Temperate forest 17.8 1.7 10.2

Moisie River, Quebec (Naiman, 1982) 19871 Boreal forest 42.6 4.8 8.9

Haean Basin, S. Korea (Jeong et al., 2012) 0.38 Mountainous,

deciduous forest 6.7 4.34 1.6

MacKenzie River, Oregon (Naiman & Sedell, 1979) 1287 Temperate forest 11.4 6.4 1.8

South Pennies, UK (Pawson et al., 2008) 0.38 Peatland 153.9 739.7 0.2

NE Scotland (Hope et al., 1997a) 1320-2100 Range of catchments 13.4-115 1-85.3

Gwangneung catchment (Kim et al., 2010) 0.22 Deciduous forest 40 50 0.8

Jyozankei, Japan (Sakamoto et al., 1998) N/A Temperate forest 33 21 1.6

POC & DOC exports vary considerably with catchment scale and storm magnitude

POM

14 storm events were sampled Sep. 2010 – Dec. 2011

• Nicole (2010) – 151 mm; Qt -13.5 mm• Irene (2011) – 155 mm; Qt - 32.7 mm

• Sandy (2012) – 119 mm; Qt -18.5 mm

Stream water concentrations

DOC: 0.7-18.3 mgL-1

POC: 0.05 –252 mgL-1.

Dhillon and Inamdar, 2013, Geophysical Research Letters

POM

TS Nicole, Sep 30, 2010 (151 mm) TS Irene, Aug 27, 2011 (155 mm)

• DOC dilution at peak flow for large events; no such response for POC. • Water input outpaces DOC supply at peak flows – supply limitation.

Dhillon and Inamdar, 2014 Biogeochemistry

POM

The rate of increase of POC versus DOC for large events was dramatically different.

Once a precipitation threshold (erosive energy associated with precipitation amount?) was exceeded POC exports increased exponentially while DOC supply was constrained to a linear increase.

Dhillon & Inamdar, 2013, Geophysical Research Letters.

Runoff OC flux versus event precipitation amount

Threshold, 75-100mm?

POM

Mass exports of OC and the contribution of large stormsIn just 59 hours, Irene contributed 44% of the total OC flux for 2011!

87% of Irene OC was POCIrene POC - 56% of 2011 POC fluxIrene DOC - 19% of 2011 DOC flux

DOC flux contribution is large, but POC larger!

Dhillon & Inamdar 2014

POM

Irene N = 2.04 kg/ha

DON = 40% of TDN

2011 N = 6.43 kg/ha

Impact extends to N -

Without the large storms, the dissolved fractions compose the majority of annual flux

Thus, extreme storms produce a shift in the type of C and N forms in runoff………implications for receiving aquatic systems.

Inamdar et al., 2015

POM

Sadro & Melack, 2012 - Large allochthonous inputs of C from extreme storm events could flip receiving lentic ecosystems from net autotrophy to net heterotrophy status

Emerald Lake, CA (2.7 ha) - one autumn event (150-200 mm) flipped lake status from net autotrophic to net heterotrophic.

Outline



POMHurricane Nicole storm Large storm of Aug 14, 2011

POC peak concentrations precedes DOC. DOC dilution at peak flow for large events; no such response for POC


Seasonal

%POC of SSC was greater for summer versus winter events

Seasonal pattern in POM!


Seasonal

Seasonal differences in storm-event DOM (Singh et al., 2014)

• For the same discharge value, DOC concentrations in storm runoff were higher for summer & fall events

• % protein like DOM was lower for summer events, but, early autumn events showed a spike

• Important seasonal controls – both hydrologic and biogeochemical processing

Questions & Comments?

organic matter (om) fate and transport in watershedsudel.edu/~inamdar/breg667/om_2016.pdf · 2016....

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