Page 115 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

The highest concentration of CH4 was observed at the Vittorio site, at the latitude of Vlieland. The Vittorio site had the second thickest peat layer in this study, but the thickness of the peat layer does not appear to play a determining role in CH4 concentrations, as both thick and thin peat layers harboured both high and low CH4 concentrations.
Four sites (Fig. 2a-d) representing both high and low CH4 concentrations were chosen for 16S rRNA gene-based sequencing to unravel the microbial community structure. A second cluster of four sites (Fig. 2e-f) was chosen from the Doggerbank area to investigate the role and potential of in situ microbial communities in CH4 cycling.
Peat developed due to rising groundwater during climate warming
Radiocarbon dating (Table S2) indicated that peat formation began 13,680 calibrated years before present (cal yr BP) at the Fredricksborg NE site (Doggerbank region) and 11,760 cal yr BP at the Max Gundelach site (nearby Vlieland). Peat formation ceased 12,880 cal yr BP at the Fredricksborg NE site and 8,290 cal yr BP at the Max Gundelach site.
Radiocarbon-dating revealed that active peat formation at the Max Gundelach site within the Vlieland region prevailed for approximately 2,000-3,000 years longer than the Fredricksborg NE site at the Doggerbank region (Table S2). The period of active peat formation depended on the ability of peat formation to keep up with the rising groundwater table and on hydrological conditions; e.g., peat formation commenced earlier in areas with a less permeable substrate than in areas with a sandy substrate. For plant macrofossil analysis, one of the most southern sites, Max Gundelach, and one of the most northern sites, Fredricksborg NE, were chosen as representative of the local onset and termination of North Sea peat development, respectively.
Plant macrofossil analysis and local vegetation history
The peat layer of the Max Gundelach site is approximately 85 cm thick, and radiocarbon dating revealed that an active peatland persisted for 3,470 years between 11,760 and 8,290 cal yr BP. This is a far longer period than what occurred at the Fredricksborg NE site, where the peat layer is only 10 cm thick and radiocarbon dating indicated that a peatland was active during an earlier and shorter 800-year period between 13,680 and 12,880 cal yr BP. Plant macrofossil analysis denoted that peat accumulation occurred through paludification due to a rising water table at both the older northern and younger southern sites.
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