Ecohydrology and biogeochemistry of peatlands – processes and their implications for restoration efforts and greenhouse gas mitigation

Peatlands store about a third of the global soil carbon stocks, despite covering only 3 % of the land surface. The formation of peatlands needs an excess of water in the landscape, as e.g. through high precipitation, low evapotranspiration, or high groundwater table levels. Water saturation and anoxic conditions are essential for preservation of peat and carbon storage, as under anoxic conditions thermodynamic and enzymatic constraints slow the degradation of organic matter. However, under anoxic conditions, the strong greenhouse gas methane (CH₄) is formed. In (near) natural peatlands, CH₄ emissions are outweighed by C uptake, i.e., carbon storage and net negative radiative forcing. Both factors are yet sensitive to modification of the hydrology. Drained peatlands are therefore currently a large source of greenhouse gases to the atmosphere.

Within the saturated peat, the availability of terminal electron acceptors (TEAs), both inorganic and organic, largely determines the ratio of CO₂ to CH₄ formation. The importance of electron accepting capacities (EAC) of organic matter is thereby increasingly acknowledged, representing eventually >95 % of total EAC in peat soils. We incubated 60 peat samples from four different depths of 15 sites located in five major peatland regions around the globe covering both bog and fen samples and characterized their EAC for anaerobic CO₂ formation. To assess effects in long term incubations, another incubation of >700 days was conducted in which we also determined the nominal oxidation state of carbon (NOSC) in POM and DOM prior to and after incubation with and without oxygen. In a third incubation experiment using inoculates from contrasting peatland sites, we elucidate the role of microbial potentials versus thermodynamics for CH₄ formation.

For peatland restoration, this implies that detailed investigations of the peatland hydrology, its dynamics, and corresponding controls on CO₂ and CH₄ formation are necessary, along with an assessment of potential redistribution and fluxes of nutrients and elements, and concomitant succession of vegetation, exerting further control on CO₂ and CH₄ turnover and emission.