Subarctic peatlands in a changing climate : greenhouse gas response to experimentally increased snow cover

Abstract: The rate of change of our climate has been amplified since the industrial revolution and is expected to change even further by the end of this century. Global temperature and precipitation are expected to increase considerably over the next century. These increases are expected to be magnified in the Arctic regions. In a high latitude peatland like Storflaket, near Abisko (Northern Sweden), at the fringe of the 0°C isotherm, the environment is quite sensitive to changes in climate. Precipitation here is mainly in the form of snow. Increases in snow cover will most likely affect permafrost and active layer thickness (the layer on top of permafrost that thaws and refreezes annually), since snow insulates the ground from the low winter temperatures, resulting in relatively warm ground temperatures. With the vast stocks of carbon stored as peat in frozen mires, the thawing of this landscape will possibly make it available for decomposition and subsequent emissions as Greenhouse gases. A snow manipulation experiment that simulates future scenarios of increased winter precipitation initiated in 2005 was further investigated to understand the impacts of increased snow cover on the active layer thickness and the implications of this on carbon dioxide and methane emissions. A 1m high snow fence has been installed on Storflaket perpendicular to the prevailing wind direction every winter since 2005. The snow fences result in about doubled the snow depth on treatment plots compared to control plots. Active layer thickness has increased significantly on treatment plots after the doubling of snow cover, which has in turn increased the emission of CO2 from treated plots through ecosystem respiration. Also, there has been more carbon uptake on the treatment plots than on the control plots. Thus, the cycling of carbon has simply been enhanced. Significant differences were recorded between control and treatment plots in terms of the CO2 exchange, soil moisture content and the reflected PAR. Surprisingly, CH4 emission was almost inexistent for both sites. This means that Storflaket continues to be a very lucrative carbon sink. This thesis presents these results in detail and discusses the possible reasons for the findings.