Page 118 - 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
Local vegetation succession in the mid North Sea at Doggerbank
In the lower part of the Fredricksborg NE core (Fig. 4B), from 191 cm onward, a change from nearly purely minerogenic substrate (LOI550 is ca. 1%) to slightly higher LOI550 values, varying around 6% (Fig. S1), points to the presence of a sparse pioneer vegetation. In the three lower samples, megaspores of Selaginella selaginoides were found. S. selaginoides is a heliophilous (needing/tolerating a high level of direct sunlight) circumpolar Boreal-montane species growing in damp neutral to alkaline conditions, including dune-slacks, fens, flushes, mires and short upland grassland (Tobolski and Ammann 2000). In Northern Scandinavia it occurs in mires, at lake margins and damp heath meadows (Bjune, Birks and Seppä 2004). Peat formation through paludification started at 183 cm depth, evidenced by a sudden increase (to 75%) of organic material burnt at 550°C.
The plant macrofossil content of the peat deposits in Fredricksborg NE (Fig. 4B) is dominated by bryophytes, Sphagnum as well asbrown mosses. Peat accumulation began with Sphagnum papillosum, quickly followed by the brown moss Tomentypnum nitens and subsequently by the brown mosses Warnstorfia sp. and Drepanocladus sp. Sphagnum papillosum is a typical moss of acid raised bog but in the Netherlands it also occurs in fenland areas as well as sand regions, including dune-slacks i.e. on the Wadden Islands (Bryologische en Lichenologische Werkgroep 2015).
Local vegetation succession is analogous across sites
It is striking that the same three-step bryophyte dominated sequence of Sphagnum- Tomentypnum nitens-Warnstorfia/Drepanocladus occurs in both geographically as well as temporally different sites. However, in contrast to the sequence of the Max Gundelach site, where Sphagnum magellanicum is present only at the start of the sequence, Sphagnum papillosum is present throughout the peat deposits at the Fredricksborg NE site. In general, plant remains are better preserved in the layers dominated by Sphagnum spp. than in those dominated by brown mosses.
Estimating CH4 storage, organic matter and CO2 equivalents
The study area (116 km by 372 km, Fig. 1B and 1C) spans a surface area of 43,158 km2, an area larger than the land surface of the Netherlands (41,865 km2). Based on the average peat
116