Page 119 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

thickness of 0.29 m (minimum: 0.07 m, maximum: 0.88 m), the estimated volume of peat is 12.4 km3 (min: 3.0, max: 38.0, km3). Multiplying this estimated volume by the average observed CH4 concentration (2.14 μmol L-1), we estimate that 0.411 Tg CH4 (min: 0.100, max: 1.256, Tg CH4) is present in the study area.
Carbon storage and its CO2 equivalent were calculated using the estimated peat volume of 12.4 km3 and 103 kg m-3, the average organic matter density of compressed peat in the Netherlands (Erkens, Van Der Meulen and Middelkoop 2016). This volume of peat is estimated to hold 740.8 Tg C (min: 180.4, max: 2,270.1), assuming the convention that dry peat biomass has carbon concentration 0.5 g C g-1 (Gorham 1991; Heijmans et al. 2008). This is equivalent to 2,716.2 Tg CO2 (minimum: 661.5, maximum: 8,323.8), if released into the atmosphere, assuming a conversion of soil C to CO2 of 1.00:3.67 (van den Bos 2003).
Variations in organic matter between local environments
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Sediment OM content was highest in the peat-containing layer at all sites (Fig. S1. The percentage of OM burnt at 550°C (LOI550) was greater than the percentage of OM burnt at 330°C (LOI330) in all cores. Whilst, OM burnt at 330°C and 550°C follow comparable trends (Fig. S1), OM burnt at 330°C showed greater variation with depth than when burnt at 550°C at all sites. However, in general, there was a ceiling of not more than 50% OM burnt when exposed to temperatures of 330°C.
The maximum OM burnt (80%) at 550°C occurred at all sites except the Theodor site. The thickness of the peat layer at the Theodor site is thin, 8 cm, which is thinner than the mean peat- layer thickness of all sites (0.29 m). The LOI results for the Fredricksborg NE site were distinctive because LOI330 and LOI550 were substantially more alike than at other sites. Proportions of OM burnt at 330°C was highest for the Vittorio and Fredricksborg NE sites.
Methanogenic archaea actively perform methylotrophic methanogenesis
To investigate the potential of the in situ microbial community for CH4 cycling (schematic of process, Fig. 1A), batch incubations were prepared with an anoxic slurry of artificial seawater and freshly collected peat sediment and amended with a range of methanogenic substrates. Pore water analysis indicated that the peat layers were converted into a marine ecosystem. The peat deposits at Dorthea Shallow SW, Doothea SSW, Dorthea NW, and Fredricksborg NE (showed
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