HR: 15:10h
AN: H23J-07    [Abstracts]
TI: Spatial Distribution of Nitrate Flux from the Streambed of a Low-Relief Coastal Catchment on Virginia's Eastern Shore
AU: * Flewelling, S A
EM: saf5f@virginia.edu
AF: University of Virginia, 291 McCormick Rd PO BOX 400123, Charlottesville, VA 22904, United States
AU: Hornberger, G
EM: gmh3k@virginia.edu
AF: University of Virginia, 291 McCormick Rd PO BOX 400123, Charlottesville, VA 22904, United States
AU: Herman, J
EM: jherman@virginia.edu
AF: University of Virginia, 291 McCormick Rd PO BOX 400123, Charlottesville, VA 22904, United States
AU: Mills, A
EM: amills@virginia.edu
AF: University of Virginia, 291 McCormick Rd PO BOX 400123, Charlottesville, VA 22904, United States
AB: Nitrate is a pervasive chemical contaminant in groundwater. The fate of groundwater nitrate is not well understood. We study the fate of groundwater nitrate as it discharges through the streambed of Cobb Mill Creek. The Cobb Mill Creek catchment is located on the eastern shore of Virginia and provides an attractive setting for studying some elements of the nitrogen cycle due to large inputs of agriculturally-derived nitrogen. The catchment is 496 hectares with land uses dominated by forested and agricultural areas. Concentrations of nitrate in the groundwater of Cobb Mill Creek are often close to or exceeding the US EPA drinking water standard of 10 ppm nitrate-N. Concentrations of nitrate in stream water are almost an order of magnitude lower. Previous work has indicated that denitrification in the streambed of Cobb Mill Creek is the most likely cause for the removal of nitrate in groundwater, but removal is spatially variable. We installed dense grids of seepage meters in several reaches of Cobb Mill Creek to investigate spatial patterns of nitrate removal across the channel cross section. We measured the rates of groundwater seepage and the concentrations of nitrate and chloride in groundwater discharging from the streambed. The data indicate that certain areas of the streambed are dominated by vertical upwelling of deep groundwater where denitrification is the primary cause for nitrate removal. Other portions of the streambed receive groundwater that flows through the riparian zone where plant uptake and evapo-concentration may also be important in nitrate dynamics.
DE: 0400 BIOGEOSCIENCES
DE: 0402 Agricultural systems
DE: 0469 Nitrogen cycling
SC: Hydrology [H]
MN: 2007 Fall Meeting