Browsing by Author "Granqvist, Anna-Liisa"

Pristine mires are an important carbon storage, but after drainage, the carbon is released from the peat through aerobic decomposition. In Finland, half of the original mire area has been drained, mainly for forestry purposes. Majority (83 %) of the drained area is suitable for forestry. Out of the forestry-suited drained peatlands, the nutrient-rich forestry drained peatlands emit high amounts of CO2 due to high aerobic decomposition as nutrient-rich conditions are favourable for decomposing bacteria. Rewetting of these nutrient-rich peatlands could offer a solution for halting the CO2 emission, but the CH4 emission increases after rewetting. The studies show differing results of CH4 emission from nutrient-rich rewetted peatlands. There are studies reporting both high and low emission of CH4 from nutrient-rich peatlands, and differing studies on how the emission evolves in time. This thesis focused on three variables that could affect the CH4 emission: time from rewetting, water level and site type. There were 27 different study sites at 8 locations. These sites were rewetted 3 to 28 years prior to measurements and represented nutrient-rich tree-covered peatlands (Rhtkg, Mtkg, Ptkg). Ptkg was the least nutrient-rich site type in the study. The CH4 flux was measured with a chamber method from July to November of 2021. Water level was monitored with loggers and manual measurements. The data was analysed with linear regression and analysis of variance, depending on the independent variable. Mean CH4 fluxes were used to compare sites with each other. The results show that water level affects the CH4 emission at statistically significant level. When water level is deeper than 10cm below ground level, the CH4 emission is low. One site differed from this trend and despite the high water level, the CH4 emission was close to zero. Time from rewetting did not affect CH4 emission at statistically significant level, but there was a visible trend of older rewetted peatlands emitting less than more recently rewetted ones. This finding was contradicting to the literature as it was supposed that the more recently rewetted peatlands emit less CH4. Out of site types, the Mtkg2 and Rhtkg site types emitted most, but there was no statistical significance. When analysed with using both the water level and site type, there were statistical differences between site types. When comparing mean CH4 emissions from nutrient-rich (Rhtkg+Mtkg) and least nutrient-rich (Ptkg) peatlands at the same water level, the Ptkg sites emitted less, but not at a statistically significant level. The findings indicate that, when rewetting a nutrient-rich tree-covered peatland, it should be done so that the water-level does not rise above 10cm, but this is very difficult or impossible to regulate. Restoration process and how it develops is difficult to foresee and the end-result might differ. Research on CH4 emissions from rewetted nutrient-rich peatlands and what affects it is increasingly important as CH4 affects the climate change in the near future.