Initial response of CH4 fluxes and vegetation to restoration in a forestry-drained peatland

While peatlands in their natural state act as long-term carbon sinks, drainage can turn them into net carbon sources, enhancing the current climate warming. In addition, drainage threatens peatland biodiversity, water quality and the local hydrology. In Finland, restoration began already at 1980's. Restoration areas have increased with the understanding of the negative impacts of drainage and, recently, further promoted by the EU nature restoration law. Restoration of forestry drained peatlands is known to positively impact peatland biodiversity, to efficiently reduce soil carbon dioxide (CO2) emissions and to increase methane (CH4) emissions. However, several knowledge gaps related to GHG dynamics following restoration still exist. In this study we focus on one of the knowledge gaps, i.e., how different ditch blocking methods affect CH4 emissions following restoration. We conducted gas flux measurements and vegetation inventories in a nutrient-poor peatland in Ilomantsi, Eastern Finland, one and two years after the restoration (growing seasons of 2023 and 2024). The site was composed of three different ditch-blocking treatments: (a) blocking the ditches with dams (dammed), (b) filling the ditches with peat (filled), and (c) tightly filling the ditches with peat and digging pools in strips between the ditches (blocked). In the first year, the average CH4 flux (in mg m-2 h-1) at the dammed, filled and blocked treatment were 1.0, 0.9, and 0.9, respectively, while during the second year the rates at the dammed, filled and blocked treatment were 13.2, 7.6, and 1.2, respectively. The average CH4 flux at the undrained control site was 2.3 and 6.5 in years 2023 and 2024 respectively, and at the drained control site 0.3 and 0.6 in years 2023 and 2024 respectively. Our results indicate that the ditch blocking method may have an impact on post-restoration CH4 emissions. At the restored site the fluxes were higher and closer to undrained site fluxes during the second year, despite clearly lower water table depth in 2024. This highlights the role of developing vascular plant vegetation for controlling CH4 fluxes.