Watershed scale modeling of dissolved organic carbon export from variable source areas

Authors: MUKUNDAN, RAJITH - New York City Department Of Environmental Protection; GELDA, RAKESH - New York City Department Of Environmental Protection; MOKNATION, MAHROKH - Hunter College; Zhang, Xuesong; STEENHUIS, TAMMO - Cornell University

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2023
Publication Date: 8/31/2023
Citation: Mukundan, R., Gelda, R., Moknation, M., Zhang, X., Steenhuis, T. 2023. Watershed scale modeling of dissolved organic carbon export from variable source areas. Journal of Hydrology. 625(S1). Article e130052. https://doi.org/10.1016/j.jhydrol.2023.130052.
DOI: https://doi.org/10.1016/j.jhydrol.2023.130052

Interpretive Summary: Dissolved organic carbon (DOC) in New York City's water supply watersheds is a concern for drinking water safety. There is a need for a process-based approach to inform effective watershed management. This study incorporated algorithms to represent saturation excess runoff from variable source areas in the Soil and Water Assessment Tool – Carbon (SWAT-C) to simulate DOC in the forested Neversink Reservoir watershed in northeastern United States. The model was successfully tested for simulating streamflow and DOC flux at six sites within the watershed. By conducting sensitivity analysis using the model, we found that projected future increases in precipitation could noticeably increase DOC flux from the watershed. Overall, we anticipate that the modified SWAT-C model will be a useful tool for understanding influence of climate and watershed management on DOC to develop mitigation strategies.

Technical Abstract: Dissolved organic carbon (DOC) in surface water impacts global carbon cycle, ecosystem productivity, and water quality in drinking water supply systems. Few physically based watershed models have the capability to simulate carbon cycling and predict DOC in surface waters under the influence of natural and anthropogenic drivers. In this work we transform the SWAT-Carbon (C) model to predict DOC from variable source runoff areas in a humid forested watershed in northeastern United States. Remotely sensed data were used to parameterize and simulate forest growth and evapotranspiration. The calibrated model was able to simulate streamflow and DOC flux at six sites across the watershed with good accuracy when compared to measured data. The DOC predictions across sites showed model sensitivity to soil properties particularly soil depth and available water capacity. Spatial distribution of DOC export across the watershed followed the pattern of surface runoff from variable source areas. Model sensitivity of DOC flux to changes in climate shows greater sensitivity to precipitation changes compared to temperature changes. The overall good performance of the model and wider use of SWAT makes it a valuable tool for watershed scale modeling of DOC to understand the influence of climate, watershed management and to develop mitigation strategies. The methods presented in this study can be used in forested watersheds in regions where runoff from variable source areas is important for water quality predictions.