HR: 10:40h
AN: B42A-02 INVITED    [Abstracts]
TI: Linking Nitrate Uptake and Water Storage in an Antarctic Stream
AU: * Koch, J C
EM: kochjc@colorad.edu
AF: INSTAAR University of Colorado, Boulder, 1560 30th St, Boulder, CO 80309,
AU: McKnight, D M
EM: diane.mcknight@colorado.edu
AF: INSTAAR University of Colorado, Boulder, 1560 30th St, Boulder, CO 80309,
AU: Baeseman, J
EM: jbaesema@kent.edu
AF: Kent State University Department of Biological Sciences, 27 Cunningham Hall, Kent, OH 44242,
AB: A nitrate enrichment experiment was performed in Huey Creek, a glacial meltwater stream in the McMurdo Dry Valleys of Antarctica, to determine processes responsible for nitrate loss in a polar desert stream with no visible vegetation. Streamflow in Huey follows a diel cycle, resulting in temporal and spatial variability in two separate storage areas – a near-stream and far-lateral hyporheic zone. Near-stream hyporheic exchange occurred in only one of four monitored stream reaches, with a mean uptake rate of 0.042 umol N/m2/hr. Uptake rates could not be balanced by nitrite, ammonium, and nitrous oxide production, suggesting the importance of biomass as a source and sink of nitrogen. During high flows, nitrate loss is accompanied by a pulse of ammonium that accounts for an average of 42% of the total nitrate loss. Ammonium production is 4.4 times greater than nitrate loss during one hour of the flood, providing further evidence that nitrogen has been stored in the subsurface biomass, and is mineralized as a result of the fresh water penetrating the hyporheic zone. Properties of the far-lateral hyporheic zone were also flow-dependent. Exchange from stream to subsurface occurred during floods, when anabranches moved water laterally across the channel banks. Exchange back to the stream occurred with the recession of flood stage. Pulses of nitrate species downstream of this storage zone suggest significant denitrification in this far-lateral hyporheic zone. The first flood recession plume consisted mainly of nitrite, while the second was dominated by ammonium, suggesting a greater amount of denitrification in the second pulse. Both pulses were accompanied by high quantities of DOC (121 and 287% of mean background mass, respectively) – an unexpected result in this carbon-limited system. These results highlight the linkage between water and desert ecosystems, and challenge researchers to understand both spatial and temporal variability in potential ecological hotspots and stream flow in order to correctly interpret biogeochemically important solute data.
DE: 0469 Nitrogen cycling
DE: 1820 Floodplain dynamics
DE: 1860 Streamflow
DE: 4227 Diurnal, seasonal, and annual cycles (0438)
DE: 4804 Benthic processes, benthos (0408)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting