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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 19 Jul 2019

Submitted as: research article | 19 Jul 2019

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

Isotopic evidence for alteration of nitrous oxide emissions and producing pathways contribution under nitrifying conditions

Guillaume Humbert1,2, Mathieu Sébilo1,3, Justine Fiat4, Longqi Lang5, Ahlem Filali4, Véronique Vaury1, Mathieu Spérandio5, and Anniet M. Laverman2 Guillaume Humbert et al.
  • 1Sorbonne Université, CNRS, INRA, IRD, UPD, UPEC, Institute of Ecology and Environmental Sciences – Paris, iEES, F-75005 Paris, France
  • 2Centre National de la Recherche Scientifique (CNRS), ECOBIO – UMR 6553, Université de Rennes, 35042 Rennes, France
  • 3CNRS/Univ. Pau & Pays Adour/E2S UPPA, Institut des Sciences Analytiques et de Physico-Chimie pour l’Environnement et les Matériaux, UMR 5254, 64000, Pau, France
  • 4Irstea, UR PROSE, CS 10030, F-92761, Antony Cedex, France
  • 5LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France

Abstract. Nitrous oxide (N2O) emissions by a nitrifying biofilm reactor were investigated with N2O isotopocules. The site preference of N2O (15N-SP) indicated the contribution of producing and consuming pathways in response to changes in oxygenation level (from 0 to 21 % O2 in the gas mix), temperature (from 13.5 to 22.3 °C), and ammonium concentrations (from 6.2 to 62.1 mg N L−1). Nitrite reduction, either nitrifier-denitrification or heterotrophic denitrification, was the main N2O producing pathway under the tested conditions. Nitrite oxidation rates decreased as compared to ammonium oxidation rates at temperatures above 20 °C and sub-optimal oxygen levels, increasing N2O production by the nitrite reduction pathway. Below 20 °C, a difference in temperature sensitivity between hydroxylamine and ammonium oxidation rates is most likely responsible for an increase in the N2O production via the hydroxylamine oxidation pathway (nitrification). A negative correlation between the reaction kinetics and the apparent isotope fractionation was additionally shown from the variations of δ15N and δ18O values of N2O produced from ammonium.

Guillaume Humbert et al.
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Status: final response (author comments only)
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Guillaume Humbert et al.
Guillaume Humbert et al.
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Short summary
Mitigating emissions of the greenhouse gas N2O requires understanding of the relative contribution of its producing processes in response to environmental variables. We show, using isotopic analysis, that N2O emissions from a nitrifying system were sensitive to oxygenation, temperature, and NH4+ concentrations with nitrite reduction being the main N2O source. Temperature appears to be the main control on N2O production, due to its dissimilar effects on ammonium and nitrite oxidizing activities.
Mitigating emissions of the greenhouse gas N2O requires understanding of the relative...