Organic matter (OM) fate and transport in watershedsudel.edu/~inamdar/BREG667/OM_2016.pdf · 2016....
Transcript of 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
• 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 – 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
OM – environmental significance?
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?
OM – environmental significance?
• 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
OM – environmental significance?
Important for ecosystem processes!
• OC – energy source in terrestrial and aquatic ecosystems
• Driver of numerous microbial processes, e.g., denitrification
OM – environmental significance?
• Provides protection for aquatic species – through absorbance of UV light
• Starting point of the aquatic food chain
• Carbon cycle and gaseous C fluxes
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 - 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
• 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 - 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
• 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 – 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
DOM – Key Processes/Mechanisms
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
DOM – Key Processes/Mechanisms
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
Key results from our studies -• DOM in watershed sources• DOM export in runoff• POC mass exports• POC patterns
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
• Definition of organic carbon (OC)• Environmental Significance of OC• Measurements and characterization• Sources of OC• Processes and mechanisms• Environmental factors
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
• 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
DOM – baseflow vs. storms
Inamdar et al., 2011, Journal of Geophysical Research
DOM – baseflow vs. storms
Inamdar et al., 2011, Journal of Geophysical Research
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
• 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
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
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
• 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
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
Dhillon & Inamdar 2014
Seasonal
%POC of SSC was greater for summer versus winter events
Seasonal pattern in POM!
Dhillon & Inamdar 2014
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?