Abstract
Riparian forest (CP22) buffers are implemented in the Chesapeake Bay Watershed to trap pollutants in surface runoff thus minimizing the amount of pollutants entering the stream network. For these buffers to function effectively, overland flow must enter the riparian zones as dispersed sheet flow to facilitate slowing, filtering, and infiltrating of surface runoff. The occurrence of concentrated flowpaths, however, is prevalent across the watershed. Concentrated flowpaths limit buffer filtration capacity by channeling overland flow through or around buffers. In this study, two topographic metrics (topographic openness and flow accumulation) were used to evaluate the occurrence of concentrated flowpaths and to derive effective CP22 contributing areas in four Long-Term Agroecosystem Research (LTAR) watersheds within the Chesapeake Bay Watershed. The study watersheds include the Tuckahoe Creek watershed (TCW) located in Maryland, and the Spring Creek (SCW), Conewago Creek (CCW) and Mahantango Creek (MCW) watersheds located in Pennsylvania. Topographic openness identified detailed topographic variation and critical source areas in the lower relief areas while flow accumulation was better at identifying concentrated flowpaths in higher relief areas. Results also indicated that concentrated flowpaths are prevalent across all four watersheds, reducing CP22 effective contributing areas by 78% in the TCW, 54% in the SCW, 38% in the CCW and 22% in the MCW. Thus, to improve surface water quality within the Chesapeake Bay Watershed, the implementation of riparian forest buffers should be done in such a way as to mitigate the effects of concentrated flowpaths that continue to short-circuit these buffers.
Highlights
According to the United States Environmental Protection Agency (EPA) “dirty waters” list, Chesapeake Bay is one of the most polluted water bodies in the United States
Though beyond the scope of this study, it should be noted that vertical exaggeration of the digital elevation models (DEMs) improved the ability of topographic openness to display hydrologic features in low relief areas, but the opposite effect was true for the high relief areas
The results presented in this study demonstrate the ability of two topographic metrics to analyze and visualize overland flow routing patterns, which is important for good environmental conservation planning
Summary
According to the United States Environmental Protection Agency (EPA) “dirty waters” list, Chesapeake Bay is one of the most polluted water bodies in the United States. In 2010, the EPA established a Total Maximum Daily Load (TMDL) for the Chesapeake Bay Watershed to ensure that all pollution control measures needed to fully restore the Bay’s water quality are in place by 2025, with practices in place by 2017 to meet 60 percent of the overall sediment, nitrogen and phosphorus reductions. CP22 buffers are a relatively established and accepted conservation practice used to protect water quality and enhance aquatic and wildlife habitats. These buffers typically comprise trees, shrubs, grasses and forbs planted along a stream or river. They are intended to intercept surface runoff, trap sediment, and subsequently reduce nitrogen and phosphorus loadings in the stream [8,9,10]. Riparian zones often consist of organic-rich soils that promote biological activity, resulting in macropores that act as preferential flowpaths through the soil, which increase infiltration and exfiltration [13,14]
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