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Nitrogen Loads through Baseflow, Stormflow, and Underflow to Rehoboth Bay, Delaware
Author(s) -
Volk J. A.,
Savidge K. B.,
Scudlark J. R.,
Andres A. S.,
Ullman W. J.
Publication year - 2006
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2005.0373
Subject(s) - baseflow , hydrology (agriculture) , bay , environmental science , watershed , arithmetic underflow , storm , wetland , nitrate , streamflow , oceanography , drainage basin , ecology , geology , geography , cartography , geotechnical engineering , machine learning , computer science , biology , programming language
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 (NH 4 + ), nitrate + nitrite (NO 3 − + NO 2 − ), 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 (25500–33800 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 (259 000–316000 kg/yr). These N loads from the watershed were much greater than those from direct atmospheric deposition (49000–64 500 kg/yr) and from a local wastewater treatment plant (9700–13700 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.