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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2018. This work is distributed under
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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 22 Oct 2018

Research article | 22 Oct 2018

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

Attribution of N2O sources in a grassland soil with laser spectroscopy based isotopocule analysis

Erkan Ibraim1,3, Benjamin Wolf2, Eliza Harris4, Rainer Gasche2, Jing Wei1, Longfei Yu1, Ralf Kiese2, Sarah Eggleston1, Klaus Butterbach-Bahl2, Matthias Zeeman2, Béla Tuzson1, Lukas Emmenegger1, Johan Six3, Stephan Henne1, and Joachim Mohn1 Erkan Ibraim et al.
  • 1Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Air Pollution & Environmental Technology, CH-8600 Dübendorf, Switzerland
  • 2Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research (IMK-IFU), D-82467 Garmisch-Partenkirchen, Germany
  • 3ETH-Zürich, Swiss Federal Institute of Technology, Department of Environmental Systems Science, CH-8092 Zürich, Switzerland
  • 4University of Innsbruck, Institute of Ecology, Sternwartestrasse 15, A-6020 Innsbruck, Austria

Abstract. Nitrous oxide (N2O) is the primary atmospheric constituent involved in stratospheric ozone depletion and contributes strongly to changes in the climate system through a positive radiative forcing mechanism. The atmospheric abundance of N2O has increased from 270 ppb during the pre-industrial era to approx. 330 ppb in 2018. Even though it is well known that microbial processes in agricultural and natural soils are the major N2O source, the contribution of specific soil processes is still uncertain. The relative abundance of N2O isotopocules (14N14N16N, 14N15N16O, 15N14N16O and 14N14N18O) carries process-specific in-formation and thus can be used to trace production and consumption pathways. While isotope ratio mass spectroscopy (IRMS) was traditionally used for high-precision measurement of the isotopic composition of N2O, quantum cascade laser absorption spectroscopy (QCLAS) has been put forward as a complementary technique with the potential for on-site analysis. In recent years, preconcentration combined with QCLAS has been presented as a technique to resolve subtle changes in ambient N2O isotopic composition.

From the end of May until the beginning of August 2016, we investigated N2O emissions from an intensively managed grassland at the study site Fendt in Southern Germany. In total, 612 measurements of ambient N2O were taken by combining preconcentration with QCLAS analyses, yielding δ15Nα, δ15Nβ, δ18O and N2O concentration with a temporal resolution of approximately one hour and precisions of 0.46 ‰, 0.36 ‰, 0.59 ‰ and 1.24 ppb, respectively. Soil δ15N-NO3 values and concentrations of NO3 and NH4+ were measured to further constrain possible N2O-emitting source processes. Furthermore, the concentration footprint area of measured N2O was determined with a Lagrangian particle dispersion model (FLEXPART-COSMO) using local wind and turbulence observations. These simulations indicated that night-time concentration observations were largely sensitive to local fluxes. While bacterial denitrification and nitrifier denitrification were identified as the primary N2O-emitting processes, N2O reduction to N2 largely dictated the isotopic composition of measured N2O. Fungal denitrification and nitrification-derived N2O accounted for 34–42 % of total N2O emissions and had a clear effect on the measured isotopic source signatures. This study presents the suitability of on-site N2O isotopocule analysis for disentangling source and sink processes in-situ and found that at the Fendt site bacterial denitrification/nitrifier denitrification is the major source for N2O, while N2O reduction acted as a major sink.

Erkan Ibraim et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Erkan Ibraim et al.
Erkan Ibraim et al.
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Short summary
Nitrous oxide (N2O) is an important greenhouse gas and the major stratospheric ozone depleting substance, therefore, mitigation of anthropogenic N2O emissions is needed. To trace N2O emitting source processes, in this study, we observed N2O isotopocules above an intensively managed grassland research site with a recently developed laser spectroscopy method. Our results indicate that the domain of denitrification/nitrifier denitrification was the major N2O source.
Nitrous oxide (N2O) is an important greenhouse gas and the major stratospheric ozone depleting...