Characterization of lowland permafrost mires in subarctic Sweden

25% of the Northern hemisphere is underlain by permafrost, and this area has decreased during recent decades because of climate change. The effects of climate change are especially pronounced in subarctic regions such as the Abisko region in Sweden. Abisko is located along the southern boundary of permafrost occurrence in Eurasia. The existence of permafrost is also observed at low altitudes due to the combined effect of peatlands and low precipitation. Seasonal thawing of permafrost results in the development of the active layer. The active layer depth is one of the climate change indicators which influences the ecological, hydrological, and biogeochemical processes in permafrost regions. Prior studies show that the active layer thickness in subarctic Sweden is increasing at 0.7 - 1.3 cm/year.
The main purpose of the study is to establish a methodology to collect input and calibration datasets for cryohydrogeological models. The following experiments were conducted at the Storflaket mire in Abisko to determine the (i) thermal properties by the installation of temperature loggers, estimation of thermal conductivity, and heat capacity, (ii) hydrological properties by the installation of soil moisture sensors, determination of soil moisture retention properties, and hydraulic conductivity, and (iii) geological properties by estimating porosity, bulk density, organic matter content, and visual soil parameters (color, distance to permafrost table from surface, and rooting depth). Results of the experiments demonstrated that the permafrost mire is a highly porous, organic matter-rich soil with variable rooting depth. The van Genuchten Mualem model was found to adequately represent the variably saturated properties of the soil. The soil moisture and temperature sensors showed spatial variability affected by surface type, soil type, and vegetation depth. The measured mean thermal conductivity and specific heat capacity of 0.409 W/(mK) and 3.15 MJ/(m³K) are within the range of literature values for highly organic peatland soils. The measured parameters provide the database for cryohydrogeological models to estimate active layer depth due to climate change.