Page 34 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 1. General introduction
of North America and Europe started to melt and global sea levels rose rapidly (Törnqvist and Hijma 2012). Currently, the continental margins in which these peatlands are found are responsible for approximately 40 percent of oceanic carbon sequestration, and their contribution is expected to further increase (Muller-Karger et al. 2005). With ongoing sea level rise, it is important to better understand the role and fate of marine peat sediments on the global carbon cycle.
Drained peatlands provide habitats for methane-cycling microbial communities
Peatlands are amongst the most important man-modified ecosystems worldwide. Due to human-induced land-use changes, many peatlands are drained, which generally leads to a shift from GHG sink to source (Joosten 2009). As a clear example of the impacts, 2,500 years ago the Netherlands was largely covered with peat (Joosten, Tanneberger and Moen 2017). Nowadays, however, peatlands only cover roughly 10 percent of the Dutch land surface (Wong, Batjes and de Jager 2007). Landscape changes in the Netherlands have induced losses of 19.8 km3 peat through excavation and combustion (34%), drainage consolidation (18%) and associated peat oxidation (48%) (Erkens, van der Meulen and Middelkoop 2016).
Besides surface loss and GHG release, peatland drainage has also led to landscape destabilization. Therefore, the construction of drainage ditches, canals, and pumping stations has been crucial to keep the lowlands safe and dry for agriculture and habitation. In most of these landscape reinforcement structures, iron sheet piles are used to prevent land erosion and slumping. Interestingly, several studies have indicated an interaction of the in situ microbial community with these iron structures. Under normal circumstances, the corrosion of sheet piles leads to gradual deterioration and often makes replacement necessary. However, natural deposit layers on these sheet piles can prevent degradation and significantly increase their life span. Studies on these protective layers have shown that methanogenic archaea are abundantly present (Kip and van Veen 2015; Kip et al. 2017; in ’t Zandt et al. 2019).
The interaction between boreal peatlands and permafrost intensifies in a warming world
On a global scale, the largest peatland area is found in boreal climates. Boreal peatlands cover about 70% of the global peatland area, or 3.5 million km2 (Kivinen and Pakarinen 1981; Charman 2002; Joosten and Clarke 2002). Lower average temperatures in boreal peatlands
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