The Effects of Urbanization and Retention‐Based Stormwater Management on Coastal Plain Stream Nutrient Export

Abstract

Abstract Stormwater nutrient pollution can be more effectively managed if there is a predictable link between urbanization and pollutant export. The goal of this study was to determine the effects of increased watershed impervious surface cover (ISC) and retention‐based stormwater management on stream discharge and nutrient export from coastal plain streams in the southeastern United States. To quantify coastal plain stream nutrient export, measurements of stream discharge and concentrations of dissolved nutrients, particulate nitrogen, and algal biomass (as chlorophyll a ) were collected during baseflow and stormflow for four years from five streams on Marine Corps Base Camp Lejeune near Jacksonville, North Carolina. The study streams had watersheds that spanned a range of ISC (1–38%) and included an urban watershed drained extensively by stormwater ponds. Urban streams had higher rates of annual discharge than less impacted streams due to elevated discharge at all rates of flow, more cumulative discharge at high flows, and dampened seasonal patterns. Streams with higher watershed ISC had higher rates of annual export of all measured nutrients due to increased stream discharge and concentrations of inorganic and particulate nitrogen. The relative importance of dissolved organic nitrogen decreased with watershed ISC, but it was still the dominant form of nitrogen export in every study stream except the stream that was dominated by particulate nitrogen export from stormwater pond algal production. Based on these findings, this study suggests that stormwater management emphasizing stormwater harvesting and evapotranspiration, increased wetland area, and decreased anthropogenic nutrient sources could reduce nutrient export from urban coastal plain streams.