American Society of Agricultural and Biological Engineers



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Agricultural BMPs, Nutrient Load Reductions, and Watershed Restoration –The Octoraro Creek Watershed and the Chesapeake Bay

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005  701P0105.(doi:10.13031/2013.18101)
Authors:   John R. Shuman

The Octoraro Creek drains 208 square miles in Lancaster and Chester counties in Pennsylvania and Cecil County in Maryland, and enters the Susquehanna River at the head of the Chesapeake Bay. Land use is 75 percent agricultural, largely with Old Order Amish and English dairy farming and swine farming. Streamflow data over the last 9 years shows no change in nitrate concentrations in either branch of Octoraro Creek, with median nitrate concentrations in the 7.4 to 8.4 mg/L range. About 95 percent of the nitrates in Octoraro Creek are estimated to originate from nonpoint sources. Streamflow nitrates are highest during baseflow periods in winter, when biological uptake and denitrification rates are reduced. Nitrate concentrations in groundwater are also elevated, with the watershed being the epicenter in Pennsylvania for high groundwater nitrates. These high nitrate concentrations pose public health, herd health, and economic issues in the watershed.

The absence of any change in nitrate concentrations in the Octoraro over the last 9 years has occurred despite the aggressive implementation of agricultural Best Management Practices (BMPs) in the watershed. Nutrient and sediment load reductions predicted when BMPs are implemented are theoretical reductions that, in some cases, may take years to be realized in a watershed. This is germane to the Chesapeake Bay watershed model, which assumes no time lag for full BMP effectiveness. The current use of Bay model predictions as data that document progress in reducing nutrient loads to the Bay is not an appropriate measure of restoration success. The definition and measures of success in restoration have direct implications for how we proceed with restoration science, policy, politics, and the reality of TMDL attainment.

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