Methane, Methanogens and Permafrost

Permafrost_thaw_ponds_in_Hudson_Bay_Canada_near_Greenland

10th November 2014.

It has been known for some time that permafrost stores a significant proportion of global soil carbon, and that thawing permafrost acts as an atmospheric source of methane and carbon dioxide, thereby creating a positive feedback to climate change.  Earlier in 2014, an international team of researchers discovered a new methanogen in the class Methanomicrobia.  They named the new species Methanoflorens stordalenmirensis and proposed a new family for it: Methanoflorentaceae.

New research by the same team, at the same Swedish field site, has shed more light on the activities of M. stordalenmirensis.  The team used a natural gradient of permafrost thaw to determine how thaw-induced changes in vegetation and hydrology affect methane dynamics.  They found that average methane fluxes were zero at an intact permafrost site, but increased to 1.46 mg CH4 m−2 h−1 at a thawing Sphagnum site, and increased further to 8.75 mg CH4 m−2 h−1 at a fully thawed site dominated by Eriophorum.  There was also a significant difference in the isotopic signature of the produced methane: average δ13C of emitted methane was −79.6 ‰ at the Sphagnum site and −66.3 ‰ at the Eriophorum site.  A similar pattern was observed for porewater CH4 isotopes between the Sphagnum and Eriophorum site.

These changes in methane dynamics were accompanied by changes in the microbial communities of the sites.  For the intact site there was a low abundance of methanogens, whilst the communities at the Eriophorum site and the deeper (anaerobic) layers of the Sphagnum site contained 20-30 % methanogens.  The Sphagnum site was dominated by hydrogenotrophic methanogens, including species similar to M. stordalenmirensis, whilst the Eriophorum site featured a high abundance of acetoclastic methanogens in the genus Methanosaeta.

Further analysis suggested that M. stordalenmirensis was the best single-variable predictor of isotopic patterns, although a multi-variable model also highlighted the importance of organic matter chemistry.  Altogether, these results show how ecosystem-scale methane dynamics are driven by changes in the composition of microbial communities.  Such research can be incorporated into future models of permafrost thaw and climate change methane feedbacks.

Lead author Carmody McCalley at the University of New Hampshire said: “By taking microbial ecology into account, we can accurately set up climate models to identify how much methane comes from thawing permafrost versus other sources such as fossil-fuel burning.”

References:

Discovery of a novel methanogen prevalent in thawing permafrost. 2014. Mondav, R., Woodcroft, B.J., Kim, E-H., et al. Nature Communications, 5, doi:10.1038/ncomms4212.

Methane dynamics regulated by microbial community response to permafrost thaw. 2014. McCalley, C.K., Woodcroft, B.J., Hodgkins, S.B., et al. Nature, 514, doi:10.1038/nature13798.

Photo: Permafrost thaw ponds, Hudson Bay, by Steve Jurvetson. CC BY 2.0

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