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.
A three-dimensional sampling grid using passive collectors
was used to characterize the downwind gas-phase
ammonia plumes originating from a commercial chicken
house on the Delmarva Peninsula in the Chesapeake Bay
watershed. Inverse Gaussian plume modeling was used
to determine the source strength of the chicken house and
the corresponding chicken emission factors. A total of
seven field deployments were performed during two different
flocks with a sampling duration ranging from 6 to 12.6 h.
The deployments occurred during weeks 3, 4, and 5 of the
6-week chicken grow-out period in the months of May−July 2002. The ammonia emission factors ranged from 0.27
to 2.17 g of NH3-N bird-1 day-1 with a mean of 1.18 g of
NH3-N bird-1 day-1. Weighted emissions factors that
accounted for the nonlinear increase in ammonia emissions
over the 6-week grow-out period were also calculated
and ranged from 0.14 to 1.65 g of NH3-N bird-1 day-1 with
a mean of 0.74 g of NH3-N bird-1 day-1. These weighted
emission values would correspond to an annual release of
approximately 18 × 106 kg of NH3-N to the atmosphere
from broiler production on the Delmarva Peninsula. This
assumes that the emission factors in this study are
representative for the entire year with varying meteorological
conditions and are representative of all chicken husbandry
practices. The Delmarva Peninsula could represent a
significant source of nutrient nitrogen to the Chesapeake
Bay and Delaware Bay watersheds through atmospheric
deposition when considering the size of this annual release
rate, the relative short atmospheric lifetime of ammonia
due to deposition, and the proximity of the Delmarva Peninsula
to the Chesapeake and Delaware Bays.
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