Carbon gas biogeochemistry of a northern peatland - in a dynamic permafrost landscape

Abstract: This thesis is about biogeochemical processes of a northern peatland and their importance as a link between the climate and the terrestrial system. Increased temperatures on a global level, and particularly in the Arctic, have led to melting permafrost and changes in hydrology. In turn, this affect the natural exchange of radiatively important trace gases between land and atmosphere that may reinforce climate change. The aim of this thesis is to increase the understanding about the exchange of carbon dioxide (CO2), methane (CH4) and non-methane volatile organic compounds (NMVOCs) occurring in northern peatlands, to decrease uncertainty about their future carbon (C) balance. In order to pursue this aim, we designed a study that allowed measuring the C exchange at a subarctic peatland, accounting for spatial and temporal analysis at several levels. The field site was the Stordalen mire, northern Sweden. Exchange rates of CO2, and total hydrocarbons (THCs; CH4 and NMVOCs) were measured using an automatic chamber system for up to six years, at three different types of vegetation communities and permafrost regimes. The gas exchange was found to relate to different environmental and biological variables at different vegetation communities and at different temporal scales. Differences in flux rates and controls between sites could be explained with biological and environmental variables in a better way than the seasonal and interannual variability within a site.Snow season flux measurements were determined to be of high importance regarding the annual C budget. By excluding the snow season, the potential C source strength of a peatland is likely to be underestimated. The importance of combining the THCs with the CO2 to estimate the annual C balance was demonstrated as THC could be sufficient to shift the mire from a sink to a source of C to the atmosphere. Again, the C source strength may be significantly underestimated if only focusing on CO2 fluxes in wet peatland environments.