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.

Water-Quality Parameters and Total Aerobic Bacterial and Vibrionaceae Loads in Eastern Oysters (Crassostrea virginica) From Oyster-Gardening Sites

“…2c). Low topographic relief and highly permeable soils along the Delaware Inland Bays commonly cause nutrients from the surrounding watershed to be deposited in the estuarine waters (Volk et al 2006). Subsequently, eutrophic conditions caused by increased nutrient inputs occur when organic matter decomposes.…”

Temporal and Spatial Dynamics of Diel-Cycling Hypoxia in Estuarine Tributaries

“…Volk et al (2006) estimated that the mean annual total nitrogen loading (1999)(2000)(2001) for Rehoboth Bay alone was 358,000 kg N year −1 . Phytoplankton density, based on chlorophyll a (Chl a) measurements, increases along a seaward to landward gradient and is highest within the tidal tributaries (Chaillou et al 1996;Entrix and JEEAI 2004;Tyler 2004).…”

Agroforestry and grass buffer effects on water quality in grazed pastures

“…For example, in the unglaciated plains of Ohio, 20-75% of the loss occurs in base flow (Owens et al 1991) while on highly permeable soils in the mid-Atlantic coastal Plains, 43-75% of the loss occurs in subsurface or groundwater flow (Volk et al 2006). These changes can be partially attributed to decreased infiltration, porosity, pasture growth and increased bulk density due to cattle management (McDowell et al 2003;Drewry et al 2000).…”