Understanding the role of scale in assessing sediment and nutrient loads from Coastal Plain watersheds delivered to the Chesapeake Bay

Urban and agricultural runoff is the principal contributor to non-point source (NPS) pollution and subsequent impairments of streams, rivers, lakes, and estuaries. Urban and agricultural runoff is a major source of sediment, nitrogen (N) and phosphorus (P) loading to receiving waters. Coastal waters in the southeastern U.S. are vulnerable to human impacts due to the proximity to urban an agricultural land uses, and hydrologic connection of the Coastal Plain to receiving waters. To mitigate the impacts of urban and agricultural runoff, a variety of stormwater control measures (SCMs) are implemented. Despite the importance of the Coastal Plain on water quality and quantity, few studies are available that focus on prediction of nutrient and sediment runoff loads from Coastal Plain watersheds. The overall goals of my dissertation are to assess the effect of urban and agricultural watershed on coastal waters through monitoring and modeling, and to characterize treatment performance of SCMs. These goals are addressed in four independent studies. First, we developed the Storm Water Management Model (SWMM) and the Hydrologic Simulation Program-Fortran (HSPF) models for an urbanized watershed to compared the ability of these two models at simulating streamflow, peak flow, and baseflow. Three separate monitoring and modeling programs were conducted on: 1) six urban land uses (i.e. commercial, industrial, low density residential, high density residential, transportation, and open space); 2) container nursey; and 3) a Coastal Plain retention pond. This study provides methods for estimating watershed pollutant loads. This is a key missing link in implementing watershed improvement strategies and selecting the most appropriate urban BMPs at the local scale. Results of these projects will help urban planners, urban decision makers and ecological experts for long-term sustainable management of urbanized and agricultural watersheds.