Page 104 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 5. Early Holocene carbon storage and microbial activity in North Sea peats
(Saunois et al. 2019) or 8–65 Tg CH4 (Reeburgh 2007). In other words, 50-90% of CH4 produced belowground is estimated to have been oxidised before reaching the atmosphere (Frenzel and Karofeld 2000). Numerous studies have measured CH4 fluxes from present-day peatlands (e.g. Hendriks et al. 2007; Tiemeyer et al. 2016). Microbial CH4 production is performed by methanogens that carry out the final steps in the anaerobic degradation of organic matter. Methanogenesis is countered by the activity of methanotrophic microorganisms that oxidize CH4 to carbon dioxide (CO2) using a variety of electron acceptors (in ‘t Zandt et al. 2018). The relative activity of methanotrophic versus methanogenic microorganisms plays a determining role in CH4 emissions to Earth’s atmosphere (Frenzel and Karofeld 2000).
Microbial surveys of phylogenetic or functional gene markers have shown that bacterial community composition is generally distinct between different types of ecosystems, e.g. peatlands (Cadillo-Quiroz et al.), estuarine and marine sediments (Purdy et al. 2002), tundra and permafrost (Ganzert et al. 2007). Marine microbial communities are highly diverse and include many uncultured phylotypes (Fry et al. 2008). Community composition is often similar between ecosystems with common environmental parameters (Kim et al. 2018), but there is a lack of knowledge of the microbial processes contributing to the production of CH4 in submerged peat deposits globally and in the North Sea in particular.
To provide a better understanding of the in situ ecosystem, particularly its role in the CH4 cycle, here we present the in situ CH4 concentrations and sediment organic matter content of submerged basal-peat deposits in the North Sea basin. Plant macrofossil analysis was performed to determine plant community composition and describe the habitat available to micro-organisms now and since peat submersion. 16S rRNA gene amplicon sequencing was performed to determine microbial diversity, and batch incubations were conducted to investigate actual and potential microbial CH4 cycle activity in the submerged peat deposits.
Materials and methods
Study area
The study region spans 150 km east to west, bordering the United Kingdom (3°) and the coastal barrier system of the Netherlands (5°), and 371 km north to south, extending from the latitude
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