Assessing the effectiveness of riparian buffers for reducing organic nitrogen loads in the Coastal Plain of the Chesapeake Bay watershed using a watershed model

Authors: LEE, S. - University Of Maryland; McCarty, Gregory; Moglen, Glenn; LI, X. - US Department Of Agriculture (USDA); WALLACE, C.W - Interstate Commission On The Potomac River Basin

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2020
Publication Date: 3/5/2020
Citation: Lee, S., McCarty, G.W., Moglen, G.E., Li, X., Wallace, C. 2020. Assessing the effectiveness of riparian buffers for reducing organic nitrogen loads in the Coastal Plain of the Chesapeake Bay watershed using a watershed model. Journal of Hydrology. https://doi.org/10.1016/j.jhydrol.2020.124779.
DOI: https://doi.org/10.1016/j.jhydrol.2020.124779

Interpretive Summary: Riparian buffers are an important conservation practice to mitigate agricultural pollution of surface water in the Chesapeake Bay watershed. Although forested and grassed riparian buffers have been implemented in this region through government programs, the impacts of riparian buffers on water quality have not been fully examined. The objective of this study was to assess the long-term effects of riparian buffers to improve water quality in the Bay watershed using the SWAT model. Various riparian buffer implementation scenarios were analyzed to assess the extent that buffers reduce organic nitrogen loading. Findings showed that the effectiveness of riparian buffers increased from 17% to 45% with an increase in the extent of riparian buffer implementation. This study supports ongoing riparian buffer programs in the Bay watershed by demonstrating the effectiveness of riparian buffers and informing implementation guidelines.

Technical Abstract: Riparian buffers are an important conservation practice to mitigate water quality degradation in the Coastal Plain of the Chesapeake Bay watershed (CBW). Although forested and grassed riparian buffers have been implemented in this region through government programs, the impacts of riparian buffers on water quality have been rarely examined. The objective of this study was to assess the long-term effects of riparian buffers to improve water quality in the Coastal Plain of the CBW. A watershed model, Soil and Water Assessment Tool (SWAT), was employed for this study. The model has been commonly used to quantify the effectiveness of conservation practices for reducing pollutant loads. Considering impacts of model uncertainty (i.e., equifinality) on the effectiveness of riparian buffers, we adopted all parameter sets that produced acceptable simulation results. Multiple riparian buffer implementation scenarios were developed to generate the baseline condition on organic nitrogen (ON) loads without riparian buffers and examine variation of ON loads with areal coverage of riparian buffers. Through the calibration processes, a total of 235 acceptable parameter sets were identified and used to simulate ON loads. The simulation results indicated that riparian buffers significantly reduce ON loads. Without riparian buffers, annual ON loads from the 220 km2 study watershed were 18 to 34 metric tons, but declined to 8 to 21 metric tons with riparian buffers. The effectiveness of riparian buffers increased from 17% to 45% with an increase in the extent of riparian buffer implementation. The effectiveness of riparian buffers tended to be higher during early spring than other seasons as high soil water conditions promote occurrence of surface water flow and thus ON loads. Riparian buffers were more efficient on croplands than other land use types due to high soil nutrient levels caused by fertilizer applications. The effectiveness of riparian buffers differed considerably by parameter set. Thus, efforts to consider model uncertainty are important to provide better insight into the impacts of conservation practices. This study supports ongoing riparian buffer programs for the Mid-Atlantic Coastal Plain by demonstrating the effectiveness of riparian buffers and informing implementation guidelines.