Interdecadal Changes in CO 2 and CH 4 Fluxes of a Subarctic Mire: Stordalen Revisited after 20 Years

The first subarctic wetland CO₂ and CH₄ flux measurements were made at Stordalen in the beginning of the 1970s in connection with the IBP study. A return to this area in 1994-95 offered a unique opportunity to study possible interdecadal changes in northern wetland CO₂ and CH₄ emissions. Measurements of CO₂ and CH₄ fluxes were carried out in similar habitats as those investigated in 1974. The mire distribution of wet minerotrophic areas relative to the elevated ombrotrophic areas had changed dramatically over the twenty years. There were no significant differences between the CH₄-flux in 1974, 1994, and 1995. However, the CO₂ fluxes were significantly higher in 1995 than in 1974. Since differences in climatic conditions gave no cause for such a change it suggests a possible increase in decomposition rate to be due to other factors. We suggest changes in vegetation composition, altered mineralization pathways and disintegration of permafrost as causes for the interdecadal increase in decomposition rates.