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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-250
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-250
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 02 Jul 2019

Submitted as: research article | 02 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Direct O2 control on the partitioning between denitrification and dissimilatory nitrate reduction to ammonium in lake sediments

Adeline N. Y. Cojean1, Jakob Zopfi1, Alan Gerster1, Claudia Frey1, Fabio Lepori2, and Moritz F. Lehmann1 Adeline N. Y. Cojean et al.
  • 1Department of Aquatic and Stable Isotope Biogeochemistry, University of Basel, Bernoullistrasse 30, CH-4056 Basel, Switzerland
  • 2Institute of Earth Science, Scuola Universitaria Professionale della Svizzera Italiana (SUPSI), Trevano, CH-6952 Canobbio, Switzerland

Abstract. Lacustrine sediments are important sites of fixed nitrogen (N) elimination through the reduction of nitrate to N2 by denitrifying bacteria, and are thus critical for the mitigation of anthropogenic loading of fixed N in lakes. In contrast, dissimilatory nitrate reduction to ammonium (DNRA) retains bioavailable N within the system, promoting internal eutrophication. Both processes are thought to occur under oxygen-depleted conditions, but the exact O2 thresholds particularly of DNRA inhibition are uncertain. In O2-manipulation laboratory experiments with dilute sediment slurries and 15NO3 additions at low- to sub-micromolar O2 levels, we investigated how, and to what extent, oxygen controls the balance between DNRA and denitrification in lake sediments. In all O2-amended treatments, oxygen significantly inhibited both denitrification and DNRA compared to anoxic controls, but even at relatively high O2 concentrations (≥ 70 µmol L−1), nitrate reduction by both denitrification and DNRA was observed, suggesting a relatively high O2 tolerance. Nevertheless, differential O2 control and inhibition effects were observed for denitrification versus DNRA in the sediment slurries. Below 1 µmol L−1 O2, denitrification was favored over DNRA, while DNRA was systematically more important than denitrification at higher O2 levels. Our results thus demonstrate that O2 is an important regulator of the partitioning between N-loss and N-recycling in sediments. In natural environments, where O2 concentrations change in near bottom waters on an annual scale (e.g., overturning lakes with seasonal anoxia), a marked seasonality with regards to internal N eutrophication versus efficient benthic fixed N elimination can be expected.

Adeline N. Y. Cojean et al.
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Adeline N. Y. Cojean et al.
Adeline N. Y. Cojean et al.
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Short summary
Our results demonstrate the importance of oxygen (O2) in regulating the fate of N in the sediments of Lake Lugano South Basin, Switzerland. Therefore our study suggests that, by changing O2 concentration in bottom waters, the seasonal water column turnover may significantly regulate the partitioning between N-removal and N-recycling in surface sediments, and it is likely that a similar pattern can be expected in a wide range of environments.
Our results demonstrate the importance of oxygen (O2) in regulating the fate of N in the...
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