Page 143 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

et al. 2012). In lakes formed within low-centered polygons on Samoylov Island in the Lena Delta, a symbiotic association between submerged brown mosses and aerobic methanotrophs was shown to reduce CH4 emissions by at least 5% (Liebner et al. 2011). In a thermokarst pond near Igarka, northern Siberia, methanotrophic activity was found mainly in floating mats consisting of Sphagnum peat moss and sedges in the top 20 cm of the water body (Blodau et al. 2008). This CH4 filter can be more efficient at lower temperatures due to an increasing imbalance between methanogenesis and methanotrophy at higher temperatures (van Winden et al. 2012). The development of peat vegetation during thermokarst lake development could thus have pronounced effects on net CH4 fluxes. This is, however, beyond the scope of this review.
Role of nitrogen- and metal-dependent anaerobic oxidation of methane in thermokarst lakes
Under anoxic conditions, anaerobic methanotrophic prokaryotes can oxidize CH4 using a suite
of alternative electron acceptors. The methane that passes this anoxic filter can be oxidized by 6 aerobic methanotrophs. In a study on thermokarst lakes Winkel et al. observed a high abundance of potentially cold-adapted “Candidatus Methanoperedenaceae” ANME-2d sequences in 16S rRNA gene data (Winkel et al. 2019). “Candidatus Methanoperedens”
archaea can perform nitrate-, manganese-, or iron-driven anaerobic oxidation of methane
(AOM) (Haroon et al. 2013; Ettwig et al. 2016; Cai et al. 2018; Leu et al. 2020). They are of terrestrial origin and occur in, amongst others, wetland and permafrost habitats (Winkel et al.
2019).
Stable δ 13C–CH4 isotope calculations on pore water samples of Vault Lake, Alaska, indicated that 41-83% of the dissolved CH4 is oxidized by AOM, but relative contributions of AOM activities with specific electron acceptors remain elusive (Heslop et al. 2019). “Candidatus Methanoperedens” archaea were also detected (0.3-2.1% of archaeal 16S rRNA gene reads) in a study by de Jong et al. in thermokarst lake sediments in Utqiagvik, Alaska, despite very low nitrate concentrations ranging from 0.8 to 2.4 uM (de Jong et al. 2018). Iron and manganese concentrations were not measured in this study. A study by Winkel et al. on deep sea permafrost found “Candidatus Methanoperedens” archaea sequences in deep layers, with nitrate concentrations in the millimolar range (Winkel et al. 2018). However, there is
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