Initial Response of CH4 Fluxes to Restoration in a Forestry-Drained Peatland and the Effect of the Ditch Blocking Methods

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. 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 how different ditch blocking methods and environmental variables affect CH4 emissions following restoration. We conducted gas flux measurements in nutrient-poor peatlands in Ilomantsi, Eastern Finland, one and two years after the restoration. 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). Additionally, we measured undrained and drained control sites. The restored site had significantly higher CH4 flux (on average 2.10 mg m-2 h-1) compared to the drained site (0.47 mg m-2 h-1) but still lower flux than the pristine site (3.50 mg m-2 h-1). The ditch blocking methods caused differences in CH4 flux, with the blocked treatment having lower CH4 flux (1.03 mg m-2 h-1) than the two other treatments (2.47 mg m-2 h-1). CH4 flux was significantly controlled by Leaf Area Index (LAI), temperature and water table depth. At the restored site the fluxes were higher and closer to the undrained site fluxes during the second year, despite a clearly lower water table depth, which highlights the role of developing vascular plant vegetation for controlling CH4 fluxes.