Response of greenhouse gas fluxes to simulated water level management under contrasting climate scenarios in a peatland mesocosm study.

Boreal peatlands strongly affect the global climate system by providing an important store for carbon (C) cycle and a natural source of methane. Over the past century, however, vast areas of natural peatlands have been drained to gain productive land, turning them into large potential C sources. Currently, there is a scientific debate on how to best manage historically drained boreal peatlands to improve their function in climate change mitigation. To investigate this, we conducted a climate chamber mesocosm experiment to assess the effects of climate change and water level (WL) management on GHG emissions. Three WL managements: low, medium, and high WL (rewetting) were simulated under both present (2022 growing season) and a moderate future climate scenario, RCP 4.5. The observed biweekly GHG fluxes from the mesocosm experiment were used as inputs into a radiative forcing (RF) model to assess the cooling/warming effect of different strategies. The results revealed that WL management had a significant effect on peatland CH4 emissions, while climate change had not. High WL management increased CO2 sink capacity through Sphagnum moss restoration, while low and medium WL managements decreased it. RF modelling suggested that high WL management under both present and future climates, and medium WL under future climate, have the potential to result in a long-term shift from a C source to a sink under favourable conditions. These strategies are suggested for their greater climate benefit potential. Our study highlights the need to consider WL-climate interactions for better predicting peatland GHG mitigation potential.