Hydrologic and Biogeochemical Storm Response in Choptank Basin Headwaters

Abstract

This study quantified the effect of hydric soils on the hydrology and biogeochemistry of sub-watersheds across the Delmarva Peninsula. For hydrology, long-term data were compiled for 13 United States Geological Survey sites and evaluated for hydric soil effects. Results show that hydric soils reduce baseflow by increasing ponding and subsurface water storage, resulting in greater evapotranspiration. In contrast, hydric soils were unrelated to stormflow, which was instead driven by topography. During hourly sampling of 18 storms in the Choptank Basin, most forms of nitrogen and phosphorus increased in concentration due to erosion and re-suspension of sediments. Nitrate, however, decreased during storms due to dilution of nitrate-rich groundwater by runoff. Baseflow nitrate concentrations decreased with forested hydric soils, likely due to greater denitrification in forested hydric areas. Annually, much of the total nitrogen and phosphorus export occurred during storms, emphasizing the need to sample a wide range of flows to improve estimates of nutrient losses.