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Numerical modeling of coupled nitrification-denitrification in
sediment perfusion cores from the hyporheic zone of the Shingobee
River, MN
Sheibley, RW | Jackman, AP | Duff, JH | Triska, FJ
Advances in Water Resources [Adv. Water Resour.]. Vol. 26, no. 9,
pp. 977-987. Sep 2003.
Nitrification and denitrification kinetics in sediment perfusion
cores were numerically modeled and compared to experiments on
cores from the Shingobee River MN, USA. The experimental design
incorporated mixing groundwater discharge with stream water
penetration into the cores, which provided a well-defined,
one-dimensional simulation of in situ hydrologic conditions.
Ammonium (NH sub(4) super(+)) and nitrate (NO sub(3) super(-))
concentration gradients suggested the upper region of the cores
supported coupled nitrification-denitrification, where
groundwater-derived NH sub(4) super(+) was first oxidized to NO
sub(3) super(-) then subsequently reduced via denitrification to N
sub(2). Nitrification and denitrification were modeled using a
Crank-Nicolson finite difference approximation to a
one-dimensional advection-dispersion equation. Both processes were
modeled using first-order reaction kinetics because substrate
concentrations (NH sub(4) super(+) and NO sub(3) super(-)) were
much smaller than published Michaelis constants. Rate coefficients
for nitrification and denitrification ranged from 0.2 to 15.8 h
super(-1) and 0.02 to 8.0 h super(-1), respectively. The rate
constants followed an Arrhenius relationship between 7.5 and 22
degree C. Activation energies for nitrification and
denitrification were 162 and 97.3 kJ/mol, respectively. Seasonal
NH sub(4) super(+) concentration patterns in the Shingobee River
were accurately simulated from the relationship between perfusion
core temperature and NH sub(4) super(+) flux to the overlying
water. The simulations suggest that NH sub(4) super(+) in
groundwater discharge is controlled by sediment nitrification
that, consistent with its activation energy, is strongly
temperature dependent.
 Descriptors: Article Subject Terms Biogeochemistry | Cores | Denitrification | Experimental
Data | Groundwater/surface water relationship | Kinetics | Model
Studies | Nitrification | Seasonal Variations | Seasons | Surface-groundwater Relations | Article Geographic Terms USA, Minnesota,
Shingobee R.
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