HR: 14:55h
AN: H53F-06 INVITED     [Abstracts]
TI: Nitrogen removal in floodplains through denitrification: results from an isotope field experiment
AU: * Scott, D T
EM: dtscott@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20192 United States
AU: Harvey, J W
EM: jwharvey@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20192 United States
AU: Noe, G
EM: gnoe@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20192 United States
AU: Bohlke, J
EM: jkbohlke@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20192 United States
AB: Biogeochemical transformations of nitrogen within lotic systems influence the speciation and nitrogen load to downstream water bodies. Within a stream network, redox gradients at the interface between surface and subsurface water result in regions of potential denitrification. During periods of high-flow, water and nutrients from the main channel of a stream are routed onto the adjacent floodplain resulting in greater solute interactions with particle and microbial surfaces. We have found that over 80% of the nitrogen load going onto a floodplain in Northeastern Louisiana is removed from the water column. A $^{15}$N-enriched nitrate tracer experiment within the floodplain demonstrated that a large portion of the nitrate is denitrified between the surface water and the top 3cm of soil. The overall nitrate removal within a given floodplain is dependent on the hydrologic residence time, and the field results highlight that for low to medium flood events the residence time is great enough for denitrification to remove the majority of the nitrate pool. Our results demonstrate that active floodplains are biogeochemical hotspots within stream networks, and suggest that floodplains within the Southeastern USA reduce the nitrate load to the coastal seas.
DE: 1821 Floods
DE: 1829 Groundwater hydrology
DE: 1845 Limnology
DE: 1871 Surface water quality
DE: 1890 Wetlands
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting