Base flow nutrient discharges from lower delmarva peninsula watersheds of Virginia, USA
Received for publication August 11, 2008. Proper management of shallow coastal systems, which are vulnerable to nutrient enrichment, requires knowledge of land use impacts on nutrient discharges. This study quantified base flow nutrient concentrations and yields for 1 yr (May 2001–April 2002) from 14 first-order streams on the Virginia Eastern Shore (VaES) on the Delmarva Peninsula and assessed their relationships with land cover and soil drainage class in their watersheds. Base flow water discharge rates (1.4–31.5 cm yr–1) were likely lower than the long-term average due to a severe drought. Seasonal mean nitrate concentrations were higher in winter, while mean dissolved organic carbon and ammonium concentrations were higher in summer. Annual base flow-weighted mean total dissolved nitrogen (TDN) concentrations were positively related to percent (%) agricultural land cover (r2 = 0.43; p = 0.02) and % very poorly drained soils (r2 = 0.51; p = 0.009) and negatively related to % forested land cover (r2 = 0.54; p = 0.005). Patterns of base flow TDN yields were similar to those of concentrations but were also positively related to % developed land cover (r2 = 0.40; p = 0.03). Agricultural and developed land covers, together with very poorly drained soil, accounted for 91% of the variability of TDN yields (p = 0.0001). Using a multiple regression model, the base flow TDN loading rate to a coastal lagoon on the VaES, a system vulnerable to nutrient enrichment, was estimated to be 28,170 kg N yr–1.