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Journal of Environmental Quality Abstract -

Denitrification as a Sink for Dissolved Nitrous Oxide in a Freshwater Riparian Fen


This article in JEQ

  1. Vol. 28 No. 1, p. 257-262
    Received: Mar 30, 1998

    * Corresponding author(s): gbm@dmu.dk
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  1. Gitte Blicher-Mathiesen * and
  2. Carl Chr. Hoffmann
  1. National Environmental Res. Inst., Dep. of Streams and Riparian Areas, Vejlsøvej 25, DK-8600 Silkeborg, Denmark.



Denitrification as a sink of dissolved nitrous oxide (N2O) was investigated in a freshwater riparian fen. In a 15-m transect extending from the hillslope and into the fen the groundwater concentrations of nitrate (NO3) declined from 1.8 mM NO3 (25 mg L−1) to less than 0.01 mM NO3, dissolved oxygen (O2) and nitrous oxide (N2O) declined from approximately 110 µM O2 (3.5 mg O2 L−1) and 4.0 µM N2O-N (56 µg N L−1), respectively, to zero and the dissolved N2 concentration increased by 589 µM N2-N (8.2 mg N L−1). The NO3 reduction was 0.42 µM cm−3 d−1 or 7.71 µM cm−2 d−1 in sediment columns with continuous upward groundwater flow through the sediment. Concomitant with NO3 reduction, N2O was produced at a rate of 54.4 nM N2O-N cm−2 d−1 in this same 18-cm narrow sediment zone. However, the N2O produced was subsequently reduced at the same rate closer to the sediment surface. In 15NO3 experiments on chloramphenicol-treated anaerobic sediment slurries, the denitrifying enzyme activity (DEA) was estimated to be 118 ± 16.7 nmol N (N2-N + N2O-N) g fresh weight 1−1 d−1, of which 36% accumulated as N2O. Thus, in this permanently water-covered riparian fen, denitrification served as a sink for both the dissolved N2O in groundwater recharging the fen and the N2O produced within the riparian sediment.

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