Measurement of the 13C isotopic signature of methane emissions from Northern European wetlands

Rebecca E. Fisher, James L. France, David Lowry, Mathias Lanoisellé, Rebecca Brownlow, John A. Pyle, Michelle Cain, Nicola Warwick, Ute M. Skiba, Julia Drewer, Kerry J. Dinsmore, Sarah R. Leeson, Stéphane J.-B. Bauguitte, Axel Wellpott, Sebastian J. O'Shea, Grant Allen, Martin W. Gallagher, Joseph Pitt, Carl J. Percival, Keith BowerCharles George, Garry D. Hayman, Tuula Aalto, Annalea Lohila, Mika Aurela, Tuomas Laurila, Patrick M. Crill, Carmody K. McCalley, Euan G. Nisbet

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Abstract

Isotopic data provide powerful constraints on regional and global methane emissions and their source profiles. However, inverse modeling of spatially-resolved methane flux is currently constrained by a lack of information on the variability of source isotopic signatures. In this study, isotopic signatures of emissions in the Fennoscandian Arctic have been determined in chambers over wetland, in the air 0.3 to 3 m above the wetland surface and by aircraft sampling from 100 m above wetlands up to the stratosphere. Overall the methane flux to atmosphere has a coherent δ13C isotopic signature of -71 ± 1‰, measured in situ on the ground in wetlands. This is in close agreement with δ13C isotopic signatures of local and regional methane increments measured by aircraft campaigns flying through air masses containing elevated methane mole fractions. In contrast results from wetlands in Canadian boreal forest further south gave isotopic signatures of -67 ± 1 ‰. 
Wetland emissions dominate the local methane source measured over the European Arctic in summer. Chamber measurements demonstrate a highly variably methane flux and isotopic signature, but the results from air sampling within wetland areas show that emissions mix rapidly immediately above the wetland surface and methane emissions reaching the wider atmosphere do indeed have strongly coherent C isotope signatures. The study suggests that for boreal wetlands (>60°N) global and regional modeling can use an isotopic signature of -71‰ to apportion sources more accurately, but there is much need for further measurements over other wetlands regions to verify this.
Original languageEnglish
Pages (from-to)605–623
JournalGlobal Biogeochemical Cycles
Volume31
Issue number3
Early online date31 Mar 2017
DOIs
Publication statusPublished - Mar 2017

Keywords

  • methane
  • wetland
  • isotopes

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