This session is devoted to the latest results on soil characteristics and biogeochemistry of seasonally snow covered areas, where the combination of dormant vegetation, cold temperatures, and extensive snow cover suggests little or no soil biological activity occurs outside of the summer growing season. However several authors observed a surprising amount of soil biological activity beneath deep snow packs, which was attributed primarily to relatively warm soil conditions below the insulating snow cover. Consistent CO2 and N2O emissions have been recorded from subnivean soils. In general, microbial activity can continue as long as free water is available, typically down to -5 °C, although microbial activity has been reported at temperatures as low as -6.5 °C. The overall impact of snow cover on the soil thermal regime depends mainly on the timing, duration, accumulation, and melting processes of seasonal snow cover. In particular in the continuous permafrost regions, the presence of seasonal snow cover can result in an increase of the mean annual soil temperature by several degrees centigrade, whereas in discontinuous and sporadic permafrost regions the absence of seasonal snow cover may be a key factor for permafrost development.
Moreover, the snow cover stores water in the hydrological cycle and it represents a storage compartment for nutrients that are deposited with precipitation or by dry deposition. When snow melts, the concentration of solutes in the melt-water is not constant but changes with time and the initial 30% of melt-water can contain as much as 50-80% of the total solutes in the original snow, with some ions removed sooner than others. A major factor regulating the effect of snowmelt chemistry is the degree to which melt-water enters the soil. Forest soils have a major effect on the snowmelt chemistry, but even poorly developed soils and talus can modify melt-water chemistry before it enters the stream.