Sediment Sources and Transport in the Chesapeake Bay Watershed

Science Center Objects

Prepared by Allen C. Gellis and John W. Brakebill, U.S. Geological Survey (March 2013)

Impact of Sediment on Chesapeake Bay and its Watershed

As the largest and most productive estuary in North America, Chesapeake Bay is a vital ecological and economic resource. In recent decades, however, the bay and its tributaries have been degraded by excessive inputs of nutrients (nitrogen and phosphorus) and sediment from contributing watersheds, and in 1998, the bay was classified as “impaired” according to guidelines set forth in the Clean Water Act. Consequently, a Total Maximum Daily Load (TMDL) was established to reduce inputs of nutrients and sediment to meet water-quality standards in the bay (U.S. Environmental Protection Agency, 2010). The TMDL requires that all practices designed to reduce nutrients and sediment be implemented by 2025 to achieve progress toward meeting standards for dissolved oxygen, water clarity, and chlorophyll in the bay. The six states in the watershed and the District of Columbia have each prepared a Watershed Implementation Plan (WIP) to provide details about the types of management practices that will be used to meet the TMDL requirements. Additional information on the TMDL and WIPs can be found at http://www.epa.gov/chesapeakebaytmdl/.

Sediment is a major contributor to ecological degradation in Chesapeake Bay. Excessive sediment has an adverse effect on the health of streams in the bay watershed, on submerged aquatic vegetation, and on living resources in the estuary; it results in degraded water quality, loss of habitat, and population declines in biological communities. Sediment also is associated with and transports other contaminants, such as phosphorus.

Sediment sources in the Chesapeake Bay watershed include agricultural areas, forests, roads, urban areas, construction sites, gullies and ditches, mines, and streambeds and banks. Management strategies to reduce sediment inputs differ depending on whether the sediment is eroded from upland areas or from streambeds and banks. Therefore, it is important to identify the location of the sediment source in the watershed as a first step in designing management strategies. Sediment “fingerprinting” studies, particularly in small watersheds, help to identify these sources and determine the types of management practices that will most effectively reduce sediment erosion and transport in these watersheds (Gellis and Walling, 2011).

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