A comprehensive, distributed parameter, annual, watershed nonpoint source management system (WATNPS) was developed for land management planning. WATNPS simulates annual sediment, nitrogen (chemical and livestock organic), and phosphorus (chemical and livestock organic) yields from nonpoint sources. The system is linked to a GIS platform to reduce the input required by personnel during analysis. WATNPS predicts potential impacts of land management practices on surface water quality. Data were compiled for the Middle Fork Holston River (MFHR) drainage basin, Owl Run and Nomini Creek watersheds in Virginia. WATNPS utilizes annual screening models for the prediction of pollutant yields. Overland delivery ratio, phosphorus yield, and animal waste models were modified for use in the system. In-stream delivery ratio, and pollutant routing procedures were developed as a part of the overall system functionality. Development and calibration of individual in-stream delivery ratio parameters was performed based on single year data from Nomini Creek and Owl Run. A procedure was developed to rank individual watersheds and sites based on predicted pollutant yields during screening. Simulation results and individual watershed characteristics were used during the development of a drainage quality index (DQI). The DQI was developed using statistical analysis to link a water quality indicator to predicted yields and watershed characteristics. The DQI was developed to assess the impact of management within individual watersheds and among watersheds within a drainage basin. WATNPS was validated using observed data. During simulations WATNPS predicted sediment yields within 50% of observed values. Nutrient yields were predicted within a order of magnitude. Simulation of alternative livestock management practices in Owl Run reflected the same trends identified in the observed data. The Hutton Creek simulation was also consistent with water quality observations. A watershed ranking based on the DQI assessment was compared to one provided by local personnel to compare predicted trends to observed watershed conditions. A demonstration of WATNPS selected a single watershed based on watershed rankings. Critical sites were identified during WATNPS site assessment and BMPs were developed. Following BMP implementation the watershed was simulated to determine the impact on sediment, nitrogen, and phosphorus yields. / Ph. D.

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