Towards more sustainable hydrological management and land use of drained coastal peatlands--A biogeochemical balancing act

Worldwide, drainage-based water management is applied to facilitate agricultural use of coastal peatland areas, leading to large-scale peat oxidation and land subsidence. Meanwhile, there is a strong call for a more sustainable use and management of drained peatlands. Drainage severely enhances greenhouse gas emission and land subsidence, which can be counteracted by rewetting. However, this advocated alternative may also induce unwanted processes affecting ecosystem functioning. In this overview we discuss the complex biogeochemical responses related to drainage and rewetting in peatlands and compare the biogeochemical effects of deep drainage to those of rewetting in order to identify the most sustainable management strategy for drained coastal peatlands. Due to drainage, oxidation of the iron sulphide pool leads to a highly underestimated source of sulphate for adjacent surface waters, indirectly enhancing eutrophication. Although rewetting also enhances eutrophication by mobilisation and discharge of phosphorus to surface waters, we propose this effect may be mitigated by co-discharged iron, binding phosphorus. As rewetting is expected to reduce societal costs and maximises ecosystem services of peatlands, we suggest to rewet drained agricultural peatlands wherever feasible. We discuss several promising, more sustainable, land use alternatives for rewetted coastal peatlands. KEY WORDS: drainage, eutrophication, restoration, review, rewetting, paludiculture