title: Nitrogen loads through baseflow, stormflow, and underflow to Rehoboth Bay, Delaware.
abstract: A detailed study of water and nitrogen (N) discharge from a small, representative subwatershed of Rehoboth Bay, Delaware, was conducted to determine total N loads to the bay. The concentrations of ammonium (NH4(+)), nitrate + nitrite (NO3(-) + NO2(-)), and dissolved and particulate organic N were determined in baseflow and storm waters discharging from Bundicks Branch from October 1998 to April 2002. A novel hydrographic separation model that accounts for significant decreases in baseflow during storm events was developed to estimate N loads during unsampled storms. Nitrogen loads based on gauged flows alone (7100-19,100 kg/yr) significantly underestimated those based on land use-land cover (LULC) and estimated N export factors from different classes of LULC (32,000-40,600 kg/yr). However, when ungauged underflow and associated N loads were included in the total loads (25,500-33,800 kg/yr), there was much better agreement with LULC export models. This suggests that in permeable coastal plain sediments, underflow contributes significantly to N fluxes to estuarine receiving waters, particularly in drier years. Based on the similarity in LULC, N loads from the Bundicks Branch subwatershed were used to estimate upland loads to the entire Rehoboth Bay Watershed (259,000-316,000 kg/yr). These N loads from the watershed were much greater than those from direct atmospheric deposition (49,000-64,500 kg/yr) and from a local wastewater treatment plant (9700-13,700 kg/yr). While the watershed was the principal source of N at all times during the year, the relative contributions from the watershed, wastewater, and direct atmospheric deposition varied predictably with season.
authors.affiliation: Watershed Assessment Section, Delaware Department of Natural Resources and Environmental Control, 820 Silver Lake Boulevard, Suite 220, Dover, DE 19904, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Volk
authors.forename: K B
authors.initials: KB
authors.lastname: Savidge
authors.forename: J R
authors.initials: JR
authors.lastname: Scudlark
authors.forename: A S
authors.initials: AS
authors.lastname: Andres
authors.forename: W J
authors.initials: WJ
authors.lastname: Ullman
mesh_terms: D003691:Delaware; D004784:Environmental Monitoring / Q000379:methods; D008962:Models, Theoretical; D009584:Nitrogen / Q000032:analysis*; D012621:Seasons; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D014873:Water Pollutants; D009584:Nitrogen