Page 147 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

a significant CH4 filter in marine and brackish environments, its role in coastal thermokarst landscapes should be further investigated. In addition, with the expected sea level rise, these transition ecosystems become increasingly relevant in the near future.
Furthermore, the effects of warming on methanogenic substrate production in the field remain understudied. Q10 values can be used to describe rate changes of GHG production and consumption in response to temperature increase. Q10 values are both substrate- and process- specific (Davidson and Janssens 2006; de Jong et al. 2018). Published Q10 values from field studies in Alaska, Québec, and the Lena Delta, Siberia, range between 1.7 and 16, which furthermore stresses the heterogeneity of these ecosystems (Walter and Heimann 2000). Besides spatial heterogeneity, seasonality also affects measured GHG fluxes and microbial community structure and potential (Martinez-Cruz et al. 2015). This stresses the need for multiseason field data.
Few studies additionally measured nitrous oxide (N2O) production in thermokarst lakes. Nitrous oxide is a potent greenhouse gas with an almost 300 times higher GWP than CO2 (Myhre et al. 2013). Several studies indicated that subarctic tundra and thawed Arctic peatlands, ponds, and lakes are sources of N2O (Abnizova et al. 2012; Voigt et al. 2017b, 2017a). Data on N2O emissions from the Arctic are, however, scarce.
Future research on microbial GHG drivers is therefore needed to fill current knowledge gaps and to more accurately predict the fate and climate feedback of thermokarst lakes in a warmer world (see “Outstanding questions”).
Glossary
16S rRNA gene - A molecular biological proxy with which the identity and phylogeny of a microorganism can be determined. Its gene product is part of the small subunit of the prokaryotic ribosome.
Active layer - The top layer of permafrost soil that is exposed to thaw during summer and freezes over during the autumn and winter seasons.
ANME - Anaerobic methanotrophic archaea. These microorganisms oxidize methane either syntrophically with a sulfate-reducing partner, or independently of a syntrophic partner with nitrate, iron, or manganese as terminal electron acceptor.
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