Growth Season Dynamics Of CO2 Exchange In A Subarctic Mire: A Comparison Of Automated Chamber Measurements During Three Years

Peatlands are well-known to be a long-term sink for atmospheric carbon dioxide (CO₂). However the carbon balance and, hence, CO₂ flux can be significantly changed and peatlands may even become a significant atmospheric carbon source in a changing climate. Here we present results of CO2 flux measurements obtained by an automatic chamber method in a subarctic mire (Stordalen, 68° 22'N, 19° 03'E) during 3 seasons, 2002 to 2004. The study years had quite different climate (temperature, precipitation), causing different seasonal CO₂ flux patterns. In this presentation a detailed analysis of the causes for interannual differences in the carbon balance will be presented. Three different ecotypes (dry ombrotrophic, mesotrophic and wet minerotrophic) are studied and significant differences between their functional responses to different climate conditions were found. All three were atmospheric sinks in terms of accumulated CO₂ fluxes during the growing season (90 days). The dry ombrotrophic system accumulated 20-30 g C/m\², the mesotrophic between 37 and 43 g C/m\² and the wet minerotrophic system between 70 and 115 g C/m\². The interannual variability was mainly controlled by variations in snow-melt and precipitation patterns and the subsequent effects these have on the soil moisture regime. The CO₂ flux measurements presented provide a useful compliment to landscape scale micrometeorological (eddy correlation) measurements of CO₂ exchange over the mire conducted at the same site. Extrapolating the automated chamber fluxes to the mire as a whole gives mean growing season uptake rates that compare well with the corresponding numbers obtained with the eddy correlation method.