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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Hyporheic Processes
NITRIFICATION-DENITRIFICATION COUPLING IN THE HYPORHEIC ZONE OF THE SHINGOBEE RIVER, MN: ESTIMATING KINETIC PARAMETERS AND TEMPERATURE DEPENDENCE USING PERFUSION CORES.
R.W. Sheibley1, A.P. Jackman1, J.H. Duff2, and F.J. Triska2. 1Department of Chemical Engineering, One Shields Ave., University of California Davis, Davis, CA 95616, 2U.S. Geological Survey, 345 Middlefield Road, Mail Stop 439, Menlo Park, CA 94025
Nitrification and denitrification kinetics were modeled using sediment perfusion cores designed to incorporate groundwater discharge and streamwater penetration into bed sediments. Experimental results from January and September 1998 showed that the upper regions of the sediment cores were capable of supporting coupled nitrification-denitrification where groundwater-derived NH4+ was converted to NO3- and then subsequently reduced via denitrification. Process results were modeled using a Crank Nicolson finite difference approximation to a 1-dimensional advection-dispersion equation that allowed estimation of kinetic parameters for nitrification and denitrification. Both processes were modeled using 1st order reaction kinetics and kinetic parameters were estimated by trial-and-error. Rate coefficients for nitrification (k1) and denitrification (k2) ranged from 0.2 to 15.8 hr-1 and 0.2 to 8.0 hr-1, respectively. Rate constants varied with temperature and appeared to follow an Arrhenius relationship at the temperature range of this study (7.5 to 22oC). Activation energies for nitrification and denitrification were calculated to be 162 and 81.5 kJ/mol, respectively. The temperature dependence of nitrification and denitrification helped explain seasonal variation of NH4+ and NO3- observed in the surface water at the site. These results demonstrate the important effect of temperature on the release of nutrients from hyporheic sediments into sand-bottomed headwater streams.
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