Greenhouse gas emissions and phosphorus release as a response to water table dynamics in different land uses of boreal peatlands

Drainage of peatlands increases greenhouse gas emissions and leaching of phosphorus. Greenhouse gas emissions can be mitigated by rewetting, but it may increase leaching of phosphorus from decayed peat. This work studied the ways in which water table depth dynamics affect nitrous oxide and methane fluxes, carbon dioxide emissions, and the risk of phosphorus leaching in a cultivated peatland, an abandoned cultivated peatland, a peatland forest, and a pristine peatland. The potential for phosphorus leaching was studied using soil extractions. Seasonal greenhouse gas fluxes and the effects of different environmental variables on the fluxes were studied using a dataset from field conditions. The effects of water table dynamics on soil greenhouse gas fluxes and dissolution of phosphorus were studied in the laboratory. The results showed that remaining phosphorus retention capacity was commonly low in decayed topsoil peat and better, for example, in the mineral subsoil of the cultivated peatland. The drained peatlands were remarkable sources of nitrous oxide and carbon dioxide emissions compared to the pristine peatland in field conditions. Water table depth and temperature considerably affected greenhouse gas fluxes. Full rewetting minimized net greenhouse gas emissions from soil but caused the dissolution of phosphorus. Lowering of the water table increased carbon dioxide emissions, caused peaks in nitrous oxide emissions in nitrogen-rich peatlands, and phosphorus release occurred also during the lowering in thicker peat profiles. In conclusion, full rewetting effectively mitigates soil-borne greenhouse gas emissions, but it can cause phosphorus release. If full rewetting is not feasible, the high soil-borne carbon dioxide emissions should be mitigated by partial rewetting. In that case, varying water conditions in surface peat cause a risk of nitrous oxide emissions in nitrogen-rich sites, and wet conditions increase the risk of phosphorus release. Therefore, the excess availability of nitrogen and phosphorus should be avoided.