Modelling Dissolved Organic Carbon and Nitrogen in Streams and Rivers Across Atlantic Canada Marie France Jutras, Mina Nasr, Thomas Clair, Paul Arp Presented by: Marie France Jutras
Introduction OBJECTIVES: i) Introduce DOC 3 model to generate daily to annual stream water DOC and DON fluxes based on local hydrological and topographic controls ii) Introduce relationship between DOC and DON iii) Show how DOC 3 works for small, medium and large forest catchments in Atlantic Canada iv) And in connection with the forest hydrology model ForHyM (Balland et al., 2006)
DOC & DON DOC Dissolved Organic Carbon Used to describe the thousands of dissolved compounds found in water that derive from organic materials (such as decomposed plant matter). Effects water chemistry and also forms complexes with trace metals (like Hg) and helps the transport of these metals through a watershed. DON Dissolved Organic Nitrogen Used to describe the dissolved organic level of nitrogen present in stream water. It differentiates from dissolved mineral nitrogen as DON focuses on the nitrogen such as amino acids, humic acids that flow with the water. Highest DOC concentrations typically occur summer to fall; lowest levels occur during winter and spring.
DOC 3 Approach Theoretical and empirical background observations (uplands): Net DOC production is proportional to rate of net primary production (NPP) and organic matter decay: both increase with increasing soil moisture and temperature DOC fluxes from forest litter increase with increasing DOC pool size within the forest floor Net DOC flux decreases drastically down the soil profile DOC concentrations in soil leachates are not strongly related to changing soil moisture conditions
DOC 3 Approach Theoretical and empirical background (wetland literature): Water flowing surficially through wet areas and wetlands provides most of the stream entering DOC Incoming water generally stays within the acrotelm Wetland flooding dilutes surface accumulated DOC
DOC3 Model used to: predict in stream colour, measure DOC & DON concentrations based on daily soil temperature and moisture changes as well as discharge.
DOC 3 Approach Dominant upland DOC flow (DOC U ): fairly quick trickle down towards groundwater pools and flow channels (flowpath 1) Within the soil, much of DOC U is lost or retained through (i) biological degradation (A layers), (ii)adsorption within the Al and Fe enriched B and BC layers. DOC U flow along the fractured bedrock surface is subject to pooling and delays Wetlands transfer DOC W directly into streams Overall basin to stream transfers depend on wet area (A W ) to basin area (A B ) ratios, as follows:
DOC 3 Approach DOC net flux (production & transfers) is sensitive to flow rates, substrate type and temperature Converting net transfer fluxes into concentrations yields
DOC 3 Approach DOC DOC concentrations: uplands wetlands (surface water based) DOC concentrations: uplands (ground water based) where represents the delay times k DOC the production coefficients and MC and T the soil moisture and temperature conditions Ea is the activation energy of the DOC production process
DOC 3 Approach DOC 3 model calibrations refer to adjusting k DOC (a basin specific DOC release parameter) and τ (lag time) for the upland and wetland flow paths Available for calibration: DOC concentration data, derived from weekly to biweekly grab sampling The calibration results were generalized by relating k DOC and τ to the area percentages of open water (lakes, ponds; A S ), wet areas per basin (A W ), and basin size (A B )
DOC 3 Approach Generalized DOC 3 Model formulation: all streams, all records R 2 = 0.48,and RMSE=3.8mgL 1 A S : open water surface per basin
DON Fluxes DON is directly related to stream exported dissolved organic carbon. DOC 3 modeling used for model export of organic nitrogen. Calculating DOC on a daily level Calculating DOC/DON fraction on a daily level / convert to DON Given the relationship between DOC and DOC, we can find direct DON exports on a yearly basis (kg/ha/yr) by using: Qstream = rate of stream discharge
ForHyM: to determine soil moisture, temeprature and flow rates Forest Hydrology Modelling (ForHyM) Input: daily rain, snow and air temperature Output run off interflow Base flow substrate moisture substrate temperature Depends on latitude, altitude, watershed area, slope, aspect, vegetation cover, soil profile. slope
Wet Areas Mapping through digital elevation modelling Cartographic depth to water determination <0.5 m pink (0 m) to red 0.5m Used to determine the wet area ratios used in DOC 3
Study Areas New Brunswick 4 sites Nova Scotia 13 sites PEI 2 sites Newfoundland 7 sites 2 sites in Kejimkujik National Park used to calibrate the site (Moosepit Brook and Mersey River) Watershed areas ranged from 70 to 9.5 million ha Wet area % within basins varied from 3 to 10% (DTW<10 cm) to 7 to 30% (DTW<75cm)
Results Stream discharge and groundwater fluctuations Weather, soil and stream discharge conditions are regionally highly synchronized across the basins
DOC results: good conformance between actual and best fitted results across basins
Results but note: DOC within small streams (Basin areas < 200 ha or so) lagged stream discharge by about a 1 2 day (this would need to be confirmed by way of daily DOC sampling) For the larger basin (Moosepit Brook, about 2000 ha) there was an additional lag of 9 days For the largest basin (Mersey River at KNP, about 20,000 ha), there was another delay of about 70 days.
Results For the large Mersey River basin, year by year variations in soil moisture deficits also varied according to seasonal soil moisture deficits: small deficits would produce the small streambased mid summer peaks, while large deficits would not. DOC concentrations were highly synchronized across small basins, esp. after accounting for basin sized DOC lags
Determining DOC fluxes: Modelled Actual
Determining DOC fluxes (KNP basins): actual versus projected flux summary, monthly, annual
Results Note : Dissolved organic carbon (DOC, left) and N (DON, right) increase with increasing wet area coverage per basin, as formulated
DON & DOC Taking care of basin wide N inputs and outputs, including DON Note: most of atmospherically deposited N is either taken up by vegetation, and some of the incoming nitrate N is lost through denitirification. This particular loss increases across basins with increasing A W /A B ratios. Murphy et al. 2009 Forest Ecology and Management.
Conclusion The DOC 3 model, + Forest Hydrology Model, + the digital derivation of open water and wet area percentages per watershed sets up a GIS framework for: modelling DOC and DON concentrations and fluxes from small to large watersheds main DOC and DON concentration and flux predictors: daily weather records (precipitation, air temperature) watershed area wet area per watershed (DTW.5m): DOC & DON, Nitrate N lake water area per watershed: DOC & DON Nitrate N open area per watershed: DOC & DON Nitrate N Note: Wet areas per watershed (DTW.5m) > wetland areas
Thank You Pockwock-Bowater Watershed Project