Initial Response of Methane Emissions to Restoration Methods in a Forestry-Drained Peatland

Abstract While peatlands in their natural state act as long-term carbon sinks, drainage can turn them into net carbon sources, accelerating climate warming. Restoration of forestry-drained peatlands improves many ecosystem services, including biodiversity and reductions in soil carbon dioxide (CO 2 ) emissions, but typically increases methane (CH 4 ) emissions. However, the dynamics of CH₄ emissions after rewetting and the influence of different restoration methods remain poorly understood, especially at the early stages after restoration. We examined the initial response of CH 4 emissions to rewetting in nutrient-poor peatlands in Eastern Finland, focusing on how environmental conditions shaped by different ditch-blocking methods (damming, filling with peat, tightly filling with peat) impact CH 4 fluxes. We measured CH4 gas fluxes one and two years after restoration and compared with undrained and drained reference sites. Restoration increased CH 4 emissions relative to the drained reference site emissions and emissions remained lower than at the undrained site. CH 4 emissions increased from the first to the second year since restoration, coinciding with vegetation development, especially the rising Leaf Area Index (LAI). The ditch blocking methods resulted in a distinct pattern, with the tightly filled treatment having lower emissions than the dammed and filled treatment. Across the sites, CH 4 emissions were significantly controlled by LAI, temperature, and water table depth and experienced strong interannual variation. Our results imply that methane emissions resulting from peatland restoration can be mitigated by effective ditch filling that is associated with lower LAI and deeper water table in the ditches, at least during the first years after restoration.