HR: 1330h
AN: NB33F-07    [Abstracts]
TI: Hydrologic Controls on Slough-scale Nitrogen Processing Within Southeastern U.S. Floodplains
AU: * Scott, D T
EM: dtscott@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20191 United States
AU: Harvey, J W
EM: jwharvey@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20191 United States
AU: Noe, G B
EM: gnoe@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20191 United States
AU: Böhlke, J
EM: jkbohlke@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20191 United States
AB: Floodplains are biogeochemically active ecosystems where riverine nitrogen undergoes a series of transformations during flooding, including uptake, mineralization, nitrification, and denitrification. The extent of coupled N-transformations and ultimate denitrification of riverine nitrogen within floodplains imparts a positive impact to downstream water bodies by reducing riverine nitrogen loads. We measured N-fluxes of nitrate, ammonia, and dissolved & particulate organic nitrogen into and out of 2 adjacent floodplain sloughs during 2 flood events along the Tangipahoa River in Northeastern Louisiana. Isotope and slough mass-balance measurements demonstrate that the incoming nitrate was removed from each slough at the sediment-water interface, mostly through denitrification. Net organic nitrogen fluxes were zero between the incoming/outgoing flood water. Although the monitored sloughs are less than 100m apart, NH₃ export from each slough was distinct. The directional component of vertical exchange within each slough controlled NH₃ by (1) replenishing O₂ required for nitrification to the sediment-water interface and/or (2) transporting NH₃ rich subsurface water into the slough. Isotopic measurements from the ¹⁵NO₃ tracer experiment within floodplain mesocosms suggest limited nitrification under upwelling conditions, consistent with the slough mass-fluxes. These results suggest that when surface-subsurface exchange promotes nitrification, overall floodplain N-removal is enhanced by coupled nitrification-denitrification. In conclusion, N-dynamics within this Southeastern floodplain are largely influenced by both hydrology and geomorphology, which control both the incoming N mass-flux and coupling of N-reactions.
DE: 1806 Chemistry of fresh water
DE: 1821 Floods
DE: 1871 Surface water quality
DE: 1890 Wetlands
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly