SS2.02 Biogeochemical Process at the Sediment-Water Interfaces
Date: Tuesday, June 11, 2002
Time: 2:45:00 PM
Location: Carson B
 
SmithLK, University of Colorado, Boulder, USA, smithlk@cires.colorado.edu
Voytek, M, A, U.S. Geological Survey, Reston, USA, mavoytek@usgs.gov
Bohlke, J, K, U.S. Geological Survey, Reston, USA, jkbohlke@usgs.gov
Mroczkowsi, S, , U.S. Geological Survey, Reston, USA, smroczko@usgs.gov
Kirshtein, J, , U.S. Geological Survey, Reston, USA, jkirshte@usgs.gov
 
MEASUREMENT OF DENITRIFICATION IN TWO AGRICULTURALLY-IMPACTED STREAMS USING MEMBRANE MASS SPECTROMETRY
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Membrane inlet mass spectrometry (MIMS) is being used to quantify denitrification rates in two agriculturally-impacted streams. Sediment cores consisting of different substrates - grain size, organic C and N, periphyton - were collected, incubated in a flow-through system, and dissolved N2 concentrations were measured every 24-hours. The highest denitrification rates were measured in cores with a lush growth of submerged aquatic vegetation and ranged from 350 - 800 umoles N2 m-2 h-2 at three such sites. The lowest rates were measured in cores collected from areas with coarse sediment and little organic material or plant life. Rates from these sites ranged from 100 - 200 umoles N2 m-2 h-2. A pilot study was conducted to investigate the effect of nitrate and DOC (acetate) additions on the denitrification rates. In both manipulations, denitrification rates of the controls decreased over the time-course. Rates for the nitrate additions were variable, and those for the DOC additions remained constant. The data suggest that nitrate and DOC limitation can occur in these impacted streams. We suspect that sediment geomorphology may influence penetration of the substrate required for denitrification.