Soil Organic Carbon Inventory and Permafrost Mapping in Tarfala Valley, Northern Sweden : A first estimation of the belowground soil organic carbon storage in a sub-arctic high alpine permafrost environment

Abstract:

Permafrost regions in the Northern Hemisphere store large amounts of organic carbon and are vulnerable to climate change. Due to a sustained warming of the climate, strongest in the northern high latitudes, permafrost thaws and organic carbon could be released in significant amounts which should not be neglected. This study investigates the soil organic carbon (SOC) storage in the Tarfala Valley (600 – 2’100 m a.s.l.), Northern Sweden, and aims to give a first estimation of the total  carbon stock in a sub-arctic high alpine permafrost environment. Further the study describes the actual extent of permafrost in the Tarfala Valley. To achieve these aims, two field studies were carried out, one in summer to collect soil samples and one in winter to measure the bottom temperature of snow (BTS). In addition, the soil samples were analysed in the laboratory for bulk density, loss on ignition and elemental analyses. The estimated total SOC in the Tarfala catchment area of 31.2 km² is 23.0 kt C for 0 – 30 cm and 28.2 kt C for 0 – 100 cm, which is on average 0.9 kg C m^-2 for the upper meter of soil in the study area. Even though the soil organic carbon values are relatively low, these results  contribute to the on-going soil organic carbon inventories in the circum-arctic. In Tarfala Valley, permafrost can be considered as continuous at an altitude above 1’561 m a.s.l., discontinuous above 1’218 m a.s.l. and sporadic above 875 m a.s.l. based on a logistic regression model with the altitude as single independent variable. This implies that most of the permafrost affected ground is at an altitude where only sparse or no vegetation is present and only low amounts of organic carbon is stored. In brief, Tarfala Valley cannot be considered as a permafrost carbon hotspot, because this sub-arctic alpine environment does not have the potential to release large amounts of carbon as a result of climate warming and permafrost thawing.