Preprints
https://doi.org/10.5194/bg-2021-337
https://doi.org/10.5194/bg-2021-337

  11 Jan 2022

11 Jan 2022

Review status: this preprint is currently under review for the journal BG.

High peatland methane emissions following permafrost thaw: enhanced acetoclastic methanogenesis during early successional stages

Liam Heffernan1,2,, Maria A. Cavaco3,, Maya P. Bhatia3, Cristian Estop-Aragonés4, Klaus-Holger Knorr4, and David Olefeldt1 Liam Heffernan et al.
  • 1Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2H1, Canada
  • 2Evolutionary Biology Centre, Department of Ecology and Genetics/Limnology, Uppsala University, Norbyvägen 18D, 752 36, Uppsala, Sweden
  • 3Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2H1, Canada
  • 4Institute of Landscape Ecology, Ecohydrology and Biogeochemistry Group, University of Münster, Münster, Germany
  • These authors contributed equally to this work.

Abstract. Permafrost thaw in northern peatlands often leads to increased methane (CH4) emissions, but gaps remain in our understanding of the underlying controls responsible for increased emissions and the duration for which they persist. We assessed how shifting ecological conditions affect microbial communities, and the magnitude and stable isotopic signature (δ13C) of CH4 emissions along a thermokarst bog transect in boreal western Canada. Thermokarst bogs develop following permafrost thaw when dry, elevated peat plateaus collapse and become saturated and dominated by Sphagnum mosses. We differentiated between a young and a mature thermokarst bog stage (~30 and years ~200 since thaw, respectively). The young bog located along the thermokarst edge, was wetter, warmer and dominated by hydrophilic vegetation compared to the mature bog. Using 16S rRNA gene high throughput sequencing, we show that microbial communities were distinct near the surface and converged with depth, but lesser differences remained down to the lowest depth (160 cm). Microbial community analysis and δ13C data from CH4 surface emissions and dissolved gas depth profiles show that hydrogenotrophic methanogenesis was the dominant pathway at both sites. However, the young bog was found to have isotopically heavier δ13C-CH4 in both dissolved gases profiles and surface CH4 emissions, suggesting that acetoclastic methanogenesis was relatively more enhanced throughout the young bog peat profile. Furthermore, young bog CH4 emissions were three times greater than the mature bog. Our study suggests that interactions between ecological conditions and methanogenic communities enhance CH4 emissions in young thermokarst bogs, but these favorable conditions only persist for the initial decades after permafrost thaw.

Liam Heffernan et al.

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Liam Heffernan et al.

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High peatland methane emissions following permafrost thaw: enhanced acetoclastic methanogenesis during early successional stages Liam Heffernan, Maria A, Cavaco, Maya P. Bhatia, Cristian Estop-Aragonés, Klaus-Holger Knorr, David Olefeldt https://dataverse.scholarsportal.info/dataset.xhtml?persistentId=doi:10.5683/SP3/5TSH9V

Liam Heffernan et al.

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Short summary
Permafrost thaw in peatlands leads to waterlogged conditions, a favourable environment for methane (CH4) producing microbes and high CH4 emissions. High CH4 emission in the initial decades following thaw are due to a vegetation community that produces suitable organic matter to fuel CH4 producing microbes, along with warm and wet conditions. High CH4 emissions after thaw persist for up to 100 years, after which environmental conditions are less favourable for microbes and high CH4 emissions.
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