The aim of the study was to investigate the effects of climate change on soil hydrology and carbon (C) fluxes in boreal peatland ecosystems, with implications for the feasibility of cultivating reed canary grass (Phalaris arundinacea, L; RCG) as a way to restore the C sink in cutaway peatlands under Finnish conditions. First, hydrological models were developed for pristine peatland ecosystems and the cutaway peatlands under RCG cultivation. Concurrently, the hydrological responses to varying climatic forcing and mire types were investigated for these ecosystems. Thereafter, process-based models for estimating the seasonal and annual C exchanges were developed for the pristine mires and cutaway peatlands. The C models incorporated the hydrological models for corresponding ecosystems. Model simulations based on the climate scenarios (ACCLIM, developed by the Finnish Meteorological Institute, FMI) were further carried out to study the impacts of climate change on the C exchanges in the peatland ecosystems during the 21st century.
The simulation showed that the water table (WT) in the pristine Finnish mires would draw down slightly during the 21st century. Such a change in WT would be related to a decrease in the CO2 sink but an increase in the CH4 source at the country scale, as driven mainly by the rising temperature (Ta) and increasing precipitation (P). These changes in CO2 / CH4 fluxes would decrease the total C-greenhouse gas (GHG) sink (CO2 equilibrium) by 68% at the country scale, and the changes would be more pronounced toward the end of the century. The majority of pristine fens in southern and western Finland and the pristine bogs near the coastal areas would become centurial CO2 sources under the changing climate. On the other hand, the major distribution of fens in northern Finland would act to increase the CH4 source at the country scale, whereas the CH4 emission would tend to decrease with WT in the southern and western areas of Finland. Peat extraction and RCG cultivation tends to limit the influence of WT on the root-zone moisture content in a peatland ecosystem, resulting in a high sensitivity of soil moisture content to the regularity of summer rainfall. However, the phenological cycle of RCG may represent an adaptive feature of photosynthesis to the stochasticity of summer precipitation. By the end of the 21st century, climate change will decrease the CO2 sequestration by 63% - 87% in a cutaway RCG peatland during a main rotation period of 12 years. Nevertheless, the site could sustain a net CO2 sink, which is comparable to the pristine peatlands in the same region.