Soil-atmosphere CO2 and CH4 fluxes in a nutrient-poor drained peatland forest in boreal Sweden

In countries such as Sweden, where between 1.5 and 2.0 million hectares of natural peatlands have been drained for forestry purposes, knowledge on soil-atmosphere greenhouse gas (GHG) fluxes from these areas is required for national GHG accounting as well as for identifying suitable management strategies (e.g. forestry vs rewetting) to reduce GHG emissions. In this study, we applied the manual chamber method (incl. clear and dark chambers) to investigate the soil-atmosphere carbon dioxide (CO₂) and methane (CH₄) exchanges in a nutrient-poor drained peatland forest in boreal Sweden over two growing seasons (2018-2019). Combined with an array of vegetated and vegetation-removal plots we further partitioned the soil-atmosphere CO₂ exchange into its individual component fluxes of heterotrophic and autotrophic respiration as well as gross and net primary production. In addition, we collected soil environmental, vegetation and meteorological data to determine the key biotic and abiotic controls of these fluxes. All measurements were carried out along multiple transects at 5, 25 and 50 m distances from the main drainage ditch to explore their spatial variability. For comparison, we used similar GHG flux data from an automated chamber system at the nearby natural Degerö mire. We found divergent magnitudes and patterns in the soil-atmosphere CO₂ exchange and its component fluxes between the drained peatland forest and the natural mire, altogether resulting in a close-to-zero soil-atmosphere CO₂ balance at the drained site compared to a net CO₂ uptake at the mire. The CH₄ emissions from the drained peatland forest were significantly reduced compared to the natural mire; however, due to a relatively high mean water table level the drained site continued to act as a persistent CH₄ source. Overall, these detailed data will serve as a baseline for evaluating the impact of future rewetting activities (planned for 2020 at the site) on the GHG balance and will provide the various forest stakeholders valuable decision-support for developing sustainable and climate-responsible forest management strategies.