Sheibley, R. W. University of California, Davis, rwsheibley@ucdavis.edu
Jackman, A. P. University of California, Davis, apjackman@ucdavis.edu
Duff, J. H. U S Geological Survey, WRD, jhduff@usgs.gov
Triska, F. J. U S Geological Survey, WRD, fjtriska@usgs.gov

 
INORGANIC N FLUX IN SEDIMENT PERFUSION CORES FROM THE HYPORHEIC ZONE OF THE SHINGOBEE RIVER, MINNESOTA.
 
Naturally-occurring low oxygen, ammonium-rich groundwater (325 ug N/L) was perfused through 20-cm long cores of sand/silt sediment for 6 days (0.145 cm s-1). Artificially-oxygenated outlet water was recirculated back into the cores at -5 cm to simulate groundwater-stream water mixing. Nitrate, nitrite, ammonium, and nitrous oxide were measured during various experiments in the inlet, outlet and porewater of the columns. Nearly all of the ammonium disappeared as groundwater was advected through the sediment. Increase of nitrate or nitrite in porewater or the surface reservoir was not observed at any time. Phospholipid assays (biomass estimates) and KCl extractions (ammonium desorption) with core sediments suggested that most of the ammonium loss was due to microbially-mediated inorganic N transformation. We hypothesize that nitrate does not build up in porewater because it is denitrified as fast as it is formed. Adding acetylene to nitrate-enriched groundwater (500 ug N/L) perfused through the sediment cores (acetylene block technique) resulted in nitrous oxide formation along the entire column, indicating that denitrification was occurring throughout. Inorganic N profiles in the sediment perfusion cores closely resembled inorganic N profiles observed in hyporheic sediment in situ.
 
Day: Wednesday, Feb. 3
Time: 02:15 - 02:30pm
Location: Eldorado Hotel
 
Code: CS64WE0215E