Aquatic Sciences Meeting, Albuquerque 2001

SS08 Processes at the Benthic Interface (Environmental Connections)

Date: Monday, February 12, 2001, Time: 2:15:00 PM

Location: Ruidoso/Pecos

Duff, J, H, U.S. Geological Survey, Menlo Park, USA, jhduff@usgs.gov

Sheibley, R, W, University of California, Davis, USA, rwsheibley@ucdavis.edu

Jackman, A, P, University of California, Davis, USA, apjackman@ucdavis.edu

Triska, F, J, U.S. Geologicalo Survey, Menlo Park, USA, fjtriska@usgs.gov

A COMPARISON OF FOUR APPROACHES FOR ESTIMATING NITRIFICATION AND DENITRIFICATION IN SEDIMENTS FROM THE SHINGOBEE RIVER, NORTH CENTRAL MINNESOTA.

Four approaches were used to identify and quantify inorganic nitrogen cycling in sediments of the Shingobee River; 1) whole stream mass balance, 2) in situ porewater gradients, 3) sediment perfusion cores, and 4) sediment enzyme assays. Overall, we calculated similar nitrification and denitrification rates using all four approaches. Nitrification rates ranged from 190-850 umol m-2 h-1 and denitrification rates ranged from 320-3200 umol m-2 h-1. In summer, inorganic N dissolved in groundwater discharge and stream water consists predominantly of ammonium. Thus, rate estimates for denitrification using whole stream mass balances and in situ porewater gradients were inferred from ammonium losses due to nitrification. Denitrification rates measured directly from sediment enzyme assays in perfusion cores and slurries were higher than nitrification rates, suggesting that the rate of denitrification in the stream is controlled by nitrification, and that nitrification is an important source of nitrate for denitrifyers in this system.

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Aquatic Sciences Meeting, Albuquerque 2001

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