HR: 17:15h
AN: H14D-05    [Abstracts]
TI: Control of groundwater recharge-discharge on coupled N-processing across the sediment- water interface of floodplain sediments
AU: * Scott, D
EM: dtscott@unl.edu
AF: University of Nebraska - Lincoln, 214 Bessey Hall, Lincoln, NE 68588-0340, United States
AU: Harvey, J W
EM: jwharvey@usgs.gov
AF: U.S. Geological Survey, 1221 Sunrise Valley Drive Mailstop 430, Reston, VA 20191, United States
AU: Noe, G B
EM: gnoe@usgs.gov
AF: U.S. Geological Survey, 1221 Sunrise Valley Drive Mailstop 430, Reston, VA 20191, United States
AU: Böhlke, J
EM: jkbohlke@usgs.gov
AF: U.S. Geological Survey, 1221 Sunrise Valley Drive Mailstop 430, Reston, VA 20191, United States
AB: From headwater agricultural streams to floodplain sloughs, denitrification is a common and environmentally important redox mediated reaction that occurs as dissolved NO₃^- is transported across the sediment- water interface within these systems. Factors influencing denitrification rates include carbon quality, NO₃^- availability, and the presence of O₂. Here we present findings illustrating the influence of net groundwater recharge-discharge on nitrogen fate within two floodplain sloughs. Using a combination of slough-scale flood measurements (within 2 floodplain sloughs) and labeled ¹⁵NO₃^- additions, we show that coupled nitrogen removal is 4 times higher in the recharging slough. Our results suggest that O₂ delivery to the sediment-water interface of the recharging slough resulted in measurable nitrification, relative to the discharging slough where nitrification was not detected. The redox profiles (e.g. Fe) and hydrologic gradients are consistent with the deeper penetration of O₂ into the sediments within the recharging slough. Although the recharge/discharge N-flux was small relative to the overall N-balance within each slough, the subtle changes in recharge/discharge altered O₂ availability and redox conditions near the sediment-water interface enhancing coupled N-removal within the recharging slough. These results suggest that O₂ delivery across the sediment-water interface (e.g. hyporheic environments) may enhance net N-removal, especially if NO₃^- is limiting.
DE: 0469 Nitrogen cycling
DE: 0471 Oxidation/reduction reactions (4851)
DE: 1871 Surface water quality
DE: 1890 Wetlands (0497)
SC: Hydrology [H]
MN: 2007 Fall Meeting