Soil moisture and temperature variation under different types of tundra vegetation during the growing season: A case study from the Fuglebekken catchment, SW Spitsbergen

• Seasonal changes of moisture and temperature of Arctic soils were studied.
• Temperature of Arctic soils is connected with influence of cold thawing water.
• Cryosols covered by wet moss tundra vegetation are the wettest and coldest.
• Cryosols covered by lichen-herb-heath tundra vegetation are the driest and warmest.

The main objective of this paper is to discuss the range of temperature and moisture differences and variability in tundra vegetation and Arctic soils in the context of weather changes during the growing season. Research was carried out in Wedel Jarlsberg Land (SW Spitsbergen) in a small non-glaciated catchment in the vicinity of the Polish Polar Station in Hornsund. Measurements of air and soil temperature and changes in volumetric soil water content were carried out between June 24 and September 9 of 2008. The studied sites represented: (1) Turbic Cryosol, poorly covered by vegetation and exhibiting evidences of strong cryogenic processes; (2) Hyperskeletic Cryosol covered by a community of wet moss tundra vegetation with variable moisture which evolves under the influence of water flowing from the adjacent mountain slopes occupied by Little Auk colonies; and (3) Haplic Cryosol covered by lichen–herb–heath tundra vegetation, located on a raised marine terrace. Hyperskeletic Cryosol is the wettest of all the soil profiles studied. This profile shows the largest fluctuations in water content, related to the rate of snow melting on mountain slopes and the outflow of ablation water. The volumetric soil water content in Hyperskeletic Cryosol varies from 29% to 71%, with an average value of 49%. The mean volumetric soil water content in the driest Haplic Cryosol is 6% and ranges from 3% to 10% throughout the growing season. This is related to its sandy texture and a large number of stones, which leads to fast infiltration of snowmelt water and rainfall. Turbic Cryosol shows an intermediate volumetric water content ranging from 21% to 38%, with a mean value of 30%. The thermal regimes of the soils studied are also variable. The warmest soil was the driest Haplic Cryosol, as no influence of cold thawing water was observed. During the measurement period, the mean soil temperature at a depth of 10 cm in Haplic Cryosol was 6.3 °C. Turbic Cryosol was ca. 1.2 °C–1.5 °C colder than Haplic Cryosol. Hyperskeletic Cryosol was the coldest in comparison with the other soils studied because of the moss cover having insulating capacity. The temperatures recorded in this profile at a depth of 10 cm reached a mean value of 3.2 °C. The results indicate that cold water inflow from melting snow cover greatly affects soil temperature in the first part of summer (ablation season). This is related to an increase in solar radiation and air temperature leading to more intensive snow melting. This relationship is particularly evident in the first ten days of July. The highest soil surface temperatures (> 20 °C) were recorded in the beginning of July under intense solar radiation (25–27 MJ/m2 d− 1). In the second part of August, thermal gradients were weaker and soil temperatures in all the pedons studied were almost the same, ranging between + 3 °C and + 6 °C. This was due to limited solar energy inflow and heat migration into the soil transported with rainfall.