Denitrification as a Sink for Dissolved Nitrous Oxide in a Freshwater Riparian Fen
- Gitte Blicher-Mathiesen * and
- Carl Chr. Hoffmann
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 (NO−3) declined from 1.8 mM NO−3 (25 mg L−1) to less than 0.01 mM NO−3, 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 NO−3 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 NO−3 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 15NO−3 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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