in the Neversink River Basin, New York The relationship of dissolved organic carbon concentration to catchment characteristics in the Neversink River Basin, New York Kyongho Son1,2 and Karen Moore1, 1New York City Department of Environmental Protection, 2Hunter College, City University of New York(kson@dep.nyc.gov) 4. DOC concentration across watersheds and years 1.Research Background and Objective The relationship between watershed characteristics from 12 watersheds and annual median DOC concentration Recent studies of long-term trends have shown an increase in dissolved organic carbon (DOC) concentrations in streams and lakes across northern Europe and North America. This increase in DOC may be problematic for drinking water supplies due to the potential for a corresponding increase in disinfection by products (DBPs), following chlorination. In this study, a variety of alternative hypotheses are proposed and tested to explore the mechanisms for observed DOC increases in order to understand sources of variability and change in this important water quality parameter. This analysis is based on DOC data from 12 USGS stream gauging stations within the Neversink River Basin, located in the Catskill Mountains, New York and included an analysis of the changes in DOC concentration at the event, seasonal, and annual scales. We examined the relationships between DOC concentrations observed at these 12 sites and catchment characteristics. The catchment characteristics include topography (slope, wetness index), vegetation density(leaf area index), and climate influences (precipitation and temperature). W5(Biscuit Brook) WY 1992 WY 1992 to WY 2014 WY 1993 WY 1994 had higher DOC concentrations than the other two years. Higher DOC concentrations in WY 1994 are related to higher precipitation. Correlation coefficient (r2 ) value between annual precipitation and annual median DOC concentration at W5 is 0. 22. WY 1994 2. Key Controls on DOC processes DOC = F(T,V,S,H,A,P,W,…) We calculated the watershed averaged slope, wetness index (TWI), leaf area index (LAI) and base flow flow ratio for the 12 watersheds. Base flow is calculated based on Nathan and McMahon (1990). Slope and TWI have high correlation with LAI. W-7 has the highest slope, the lowest TWI and the lowest LAI. Base flow ratio (base flow/ total flow) has a consistent pattern among years. WY 1992 has the highest base flow ratios. WY 1993 has lower base flow ratio than WY 1994, while WY 1994 has higher annual precipitation than WY 1993. Among the watersheds, W-3 has the lowest base flow ratio, and W-6 has the highest ratio. We explored the relationship between watershed characteristics and annual median DOC concentrations in the WY 1992, 1993 and 1994. Only slope and base flow ratio (base flow/total flow) were found to have negative correlations with DOC concentrations. In the WY 1992, base flow ratio explained 30% of DOC variation among 10 watersheds (W10 andW12 are excluded). In the WY 1993, slope explained 29% of DOC variation among 12 watersheds. Topographic features Vegetation species and vegetation density Soil properties (hydraulic parameters, soil carbon and clay contents) Hydrologic flow partition (storm flow vs base flow) Atmospheric chemistry deposition (NOX, and SO2) Precipitation and Temperature. Wetland soil 6. Ongoing Project: Process-based DOC modeling 3. Study sites 5. DOC concentration vs daily mean Flow across watersheds The study site is located in the Neversink River basin, part of New York City water supply watershed. Mean annual precipitation at Slide mountain is 1590 mm, and 20-35% of total precipitation fell as snow. Peak discharge occurs in the April. Major land use is forest (>98%), consisting of American beech, red maple, sugar maple and yellow birch. Steep slopes, quick-draining shallow till, and slowly weathering bedrock. W7 W5 W6 W9 W11 W10 W8 W4 W3 W2 WI Seasonal variation of daily precipitation, air temperature and streamflow in the WY 1992, WY1993 and WY 1994. We have utilized process-based ecohydrologic model (RHESSys) to simulate the DOC concentration at the 12 gauged watersheds. Remote sensed data are used to derive vegetation data for improving the model input parameterization. RHESSys will be calibrated and validated with measured streamflow, nitrate and DOC fluxes. RHESSys will be used to test the impact of climate change and forest disturbance on ecohydrologic processes, including streamflow, ET, nitrate and carbon fluxes. Most watersheds have positive correlations between DOC concentration and mean daily flow, but Its correlation values vary across years and watersheds. At W7 (Winnisook), daily flow explained 56% and 68% of DOC concentration in the WY 1993 and WY 1994 , respectively. At W11 (SC20), daily flow explained 81% of DOC concentration in WY 1993, but the values decreased to 5% in the WY 1994. 12 USGS gauged stations in the Neversink River Basin were used to analyze the stream DOC variation. 7. Summary ID Watershed name W1 Main Branch(MB) W2 West Branch(WB) W3 East Branch(EB) W4 New Hill(NH) W5 Biscuit Brook(BB) W6 Wildcat(WC) W7 Winnisook(WS) W8 Otter Pool(OP) W9 High Falls (HF) W10 Tisons(TS) W11 Shelter Creek(SC20) W12 Clear Creek(CL25) The difference of DOC concentration among years can be explained by annual precipitation. For one of the three water years, slope and base flow ratio explained DOC variation among the watersheds. DOC concentrations had positive correlations with daily streamflow. Storm flow explained the variation of DOC concentration better than base flow. WY 1993 and WY 1994 have similar base flow ratio (0.25 ~ 0.26). For the two years, storm flow explained higher variation of DOC concentration, compared to baseflow. For WY 1994, storm flow has slightly higher correlation values (0.33) with DOC concentration than total flow(0.30). Storm flow (mm/day) Reference Nathan, R. J. and T. A. McMahon (1990). "Evaluation of automated techniques for base flow and recession analysis." Water Resources Research 26(7): 1465-1473. Base flow (mm/day)