Annual carbon gas budget for a subarctic peatland, Northern Sweden

Abstract. Temperatures in the Arctic regions are rising, thawing permafrost and exposing previously stable soil organic carbon (OC) to decomposition. This can result in northern latitude soils, which have accumulated large amounts of OC potentially shifting from atmospheric C sinks to C sources with positive feedback on climate warming. In this paper, we estimate the annual net C gas balance (NCB) of the subarctic mire Stordalen, based on automatic chamber measurements of CO₂ and total hydrocarbon (THC; CH₄ and NMVOCs) exchange. We studied the dominant vegetation communities with different moisture and permafrost characteristics; a dry Palsa underlain by permafrost, an intermediate thaw site with Sphagnum spp. and a wet site with Eriophorum spp. where the soil thaws completely. Whole year accumulated fluxes of CO₂ were estimated to 29.7, −35.3 and −34.9 gC m⁻² respectively for the Palsa, Sphagnum and Eriophorum sites (positive flux indicates an addition of C to the atmospheric pool). The corresponding annual THC emissions were 0.5, 6.2 and 31.8 gC m⁻² for the same sites. Therefore, the NCB for each of the sites was 30.2, −29.1 and −3.1 gC m⁻² respectively for the Palsa, Sphagnum and Eriophorum site. On average, the whole mire was a CO₂ sink of 2.6 gC m⁻² and a THC source of 6.4 gC m⁻² over a year. Consequently, the mire was a net source of C to the atmosphere by 3.9 gC m⁻² (based on area weighted estimates for each of the three plant communities). Early and late snow season efflux of CO₂ and THC emphasize the importance of winter measurements for complete annual C budgets. Decadal vegetation changes at Stordalen indicate that both the productivity and the THC emissions increased between 1970 and 2000. Considering the GWP₁₀₀ of CH₄, the net radiative forcing on climate increased 21% over the same time. In conclusion, reduced C compounds in these environments have high importance for both the annual C balance and climate.