Organic matter (OM) fate and transport in watersheds

Transcription

1 Organic matter (OM) fate and transport in watersheds

2 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

3 OM - definition Dissolved Organic matter - DOM < micron Particulate Organic matter - POM micron Colloidal to 1 micron Gives color to runoff waters.

4 OM - definition

5 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

6 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

7 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

8 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?

9 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

10 OM - significance C, N, and P components of organic matter can be bioavailable and can contribute to eutrophication! DOC, DON, DOP

11 OM environmental significance? Important for ecosystem processes! OC energy source in terrestrial and aquatic ecosystems Driver of numerous microbial processes, e.g., denitrification

12 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

13 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

14 OM - measurements Organic Carbon Determined by Absorption of light by spectrophotometer Wet oxidation of OM and measurement of CO 2 released or the consumption of oxidant dichromates or permanganates Dry oxidation of OM in presence of O 2 and the CO 2 released is measured LECO and TOC analyzer

15 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)

16 OM - measurements Absorbance measured by spectrophotometer = A (unitless) Decadal absorbance = A / path length in meters Naperian absorbance = 2.303*A/ path length

17 OM - measurements Fluorescence Excitation Emission Matrices (EEMs) Fluorescence indices characterize the C composition - HIX, FI, %humic-like, % protein-like, etc.

18 OM - measurements New In-situ/field instruments measure UV or fluorescence and convert to OC using a regression relationship e.g., Spectrolyser

19 OM - measurements Spectrolyser estimated versus lab measured data for DOC and Nitrate

20 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

21 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

22 OM - Sources Aquatic ecosystems production by algae, bacteria,. Autochthonous sources

23 OM - Sources Human-impacted watersheds animal and human waste (manure, sewage, etc.)

24 DOM Sources and fate Figure from Bolan et al., 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.

25 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

26 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 DOMmetal complexes

27 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

28 OM Key Processes/Mechanisms Kaiser and Kalbitz, Soil Biology and Biochemistry. DOC concentrations decrease with depth Aromatic, humic, HMW DOM decrease; microbial products increase with depth

29 DOM Key Processes/Mechanisms Microbial process - Microbial breakdown of OM into lower molecular weight constituents and the release of CO 2 10 to 44% of DOM in soil solution degradable Microbial decomposition can also breakdown POM and thus enhance the leaching of DOM

30 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

31 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

32 OM Key Factors Key factors affecting OM Environmental factors Landuse and management

33 DOM Key Factors Environmental factors ph Temperature Soil moisture Precipitation/water flux Freeze-thaw

34 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)

35 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

36 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

37 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/humic DOM

38 OM Key Factors Freeze-thaw effects - Breakdown of OM increased amounts of DOM

39 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

40 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

41 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

42 DOM sources Intensive study catchment - 12 ha Big Elk Creek subcatchment Hillshade view (2 m LIDAR) Wetness index (2 m LIDAR)

43 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 sources

44 DOM watershed sources TF LTU WSW HY SGW RGW Seep DGW DOC [mg L -1 ] DON [mg L -1 ] Inamdar et al., 2012, Biogeochemistry

45 DOM watershed sources TF LTU a b c WSW HY SGW RGW Seep DGW SUVA [L mgc -1 m -1 ] a 254 [m -1 ] HIX TF LTU d e f WSW HY SGW RGW Seep DGW % protein-like fluorescence S R FI Inamdar et al., 2012, Biogeochemistry

46 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 S R ) decreased with soil depth

47 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

48 DOM baseflow vs. storms Inamdar et al., 2011, Journal of Geophysical Research

49 DOM baseflow vs. storms Inamdar et al., 2011, Journal of Geophysical Research

50 DOM baseflow vs. storms Inamdar et al., 2011, Journal of Geophysical Research

51 DOM key points DOC concentrations are higher during storms versus baseflow same is true for a254 and HIX % proteins lower during storms

52 Typical DOM response DOC Runoff flowpaths and sources responsible for DOM Inamdar et al., 2011, 2012, 2013 Forest floor / litter layer % humiclike DOM Rainfall /throughfall groundwater seeps Soil water groundwater % proteinlike DOM Throughfall, litter layer & soil water - key sources of DOM during storms/high flow

53 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

54 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

55 POM POC & DOC exports vary considerably with catchment scale and storm magnitude Location & Reference Watershed size (km 2 ) 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) Bear Brook, N.H. (Fisher & Likens, 1973) Moisie River, Quebec (Naiman, 1982) 0.1 Temperate forest Temperate forest Boreal forest Haean Basin, S. Korea (Jeong et al., 2012) 0.38 Mountainous, deciduous forest MacKenzie River, Oregon (Naiman & Sedell, 1979) South Pennies, UK (Pawson et al., 2008) NE Scotland (Hope et al., 1997a) Gwangneung catchment (Kim et al., 2010) Jyozankei, Japan (Sakamoto et al., 1998) 1287 Temperate forest Peatland Range of catchments Deciduous forest N/A Temperate forest

56 POM 14 storm events were sampled Sep Dec Nicole (2010) 151 mm; Qt mm Irene (2011) 155 mm; Qt mm Sandy (2012) 119 mm; Qt mm Stream water concentrations DOC: mgl -1 POC: mgl -1. Dhillon and Inamdar, 2013, Geophysical Research Letters

57 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

58 POM Runoff OC flux versus event precipitation amount The rate of increase of POC versus DOC for large events was Threshold, mm? 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.

59 POM

60 POM Mass exports of OC and the contribution of large storms In just 59 hours, Irene contributed 44% of the total OC flux for 2011! 87% of Irene OC was POC Irene POC - 56% of 2011 POC flux Irene DOC - 19% of 2011 DOC flux DOC flux contribution is large, but POC larger! Dhillon & Inamdar 2014

61 POM Impact extends to N - Without the large storms, the dissolved fractions compose the majority of annual flux DON = 40% of TDN 2011 N = 6.43 kg/ha Thus, extreme storms produce a shift in the type of C and N forms in runoff implications for receiving aquatic systems. Irene N = 2.04 kg/ha Inamdar et al., 2015

62 POM Sadro & Melack, 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 ( mm) flipped lake status from net autotrophic to net heterotrophic.

63 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

64 POM Hurricane Nicole storm Large storm of Aug 14, 2011 Dhillon & Inamdar 2014 POC peak concentrations precedes DOC. DOC dilution at peak flow for large events; no such response for POC

65 Seasonal Seasonal pattern in POM! %POC of SSC was greater for summer versus winter events Dhillon & Inamdar 2014

66 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

67 Questions & Comments?