Management strategies for dissolved organic carbon reduction from forested watersheds using the SWAT-C model

Authors: LEE, D - Auburn University; KARKI, R - University Of Maryland; KALIN, L - Auburn University; SRIVASTAVA, P - University Of Maryland; Zhang, Xuesong

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2025
Publication Date: 2/20/2025
Citation: Lee, D., Karki, R., Kalin, L., Srivastava, P.K., Zhang, X. 2025. Management strategies for dissolved organic carbon reduction from forested watersheds using the SWAT-C model. Environmental Management. 75:1181–1200. https://doi.org/10.1007/s00267-025-02128-y.
DOI: https://doi.org/10.1007/s00267-025-02128-y

Interpretive Summary: In water supply watersheds, dissolved organic carbon (DOC) from forests can form harmful disinfection byproducts (DBPs) in drinking water. Here, we tested the Soil and Water Assessment Tool – Carbon (SWAT-C) for simulating DOC in the Big Creek watershed, which is a major tributary of the Big Creek Lake that supplies drinking water for the City of Mobile, Alabama. Our results show that SWAT-C can satisfactorily represent the transport of DOC from different land use types, such as forests, wetlands, and hay. We also showed that land management (e.g., forest conversion and raking) can effectively reduce DOC from the watershed. This study demonstrates the applicability of SWAT-C for evaluating strategies aimed at reducing risks associated with high DOC loading in drinking water supply watersheds.

Technical Abstract: Forests globally serve as crucial carbon sinks, yet accurately quantifying carbon cycle processes within forested watersheds is challenging due to their complexity. In addition, dissolved organic carbon (DOC) transport from forest ecosystems significantly impacts drinking water quality through disinfection byproducts (DBPs) formations. Although the Soil and Water Assessment Tool-Carbon (SWAT-C) has been widely used to understand carbon fluxes at watershed scales, the model was primarily evaluated in non-forested watersheds or for TOC/DOC loading in aquatic systems, omitting terrestrial carbon flux simulations. This study assessed the applicability of the Soil and Water Assessment Tool-Carbon (SWAT-C) model in simulating carbon fluxes in terrestrial and aquatic systems in the forested Big Creek watershed in Alabama, which serves as a drinking water source of the City of Mobile, AL, and quantitatively analyzed dominant pathways of DOC transport across the landscape. In addition, three management strategy scenarios (i.e., conversion and raking scenarios in forests and adjusting biomass harvest in agricultural lands) aimed at reducing DOC transport were evaluated. With calibration efforts using the remotely sensed dataset, SWAT-C demonstrated proficiency in simulating terrestrial carbon fluxes in forest dominated regions as well as TOC loading from streams in the forested watershed (R2>0.6 and PBIAS < 4.0%). Results emphasize the importance of initializing and calibrating the parameters of dominant land use/cover (LULC) types to enhance model performance in carbon flux simulations. All three management scenarios could reduce DOC transport into streams, with the conversion of loblolly pine forests to restored longleaf pine forests notably achieving a 40% reduction in forest-derived DOC yields. These findings offer valuable insights for watershed-scale carbon cycling modeling as well as help inform forest-dominant watershed management strategies to mitigate DOC yields.