Specifics of boglands freezing in the north and northwest of the European part of Russia under climate change

Long-term complex observations covering the period of 1949-2018 made possible to determine the average annual characteristics of the depth of freezing of wetlands in the North and Northwest of the European territory of Russia together with main factors of its formation, and spatial and temporal variability. The main factors that determine the depth of freezing of wetlands are ambient temperature, snow cover thickness, and a degree of watering of the micro landscape (water reserves of the micro landscape). At the initial stage of freezing, the major factor is the ambient temperature, when intensity of the freezing reaches 0.5-0.8 cm/day. As snow falls, the freezing rate becomes smaller, and when the snow cover thickness reaches 25-30 cm the depth amounts to 0.2-0.3 cm/day and smaller. It was found that the spatial variability of the freezing depth decreases from large values of the coefficient of variation (0.3-0.4) at the depth of 20-30 cm to less than 0.1 when the depth exceeds 60 cm. The largest values of the depth are recorded in the North of the Kola Peninsula, where sometimes they reach from 84 to 97 cm with the average values of 48-66. In large hummocky bogs, when the seasonal freezing comes down to 63-65 cm it links with the permafrost layer. On average, swamps of these bogs freeze down to a depth of 68 cm. The average climatic depth of freezing of oligotrophic bogs of the North-West is 21-24 cm; in some years, freezing of them reaches 32-40 cm. It has been shown that the relative warming of the climate resulted in decreasing in the depth of freezing of wetlands in the North and North-West of the European territory of Russia. Relative to the previous climatic period, the depth of frost penetration in the northern Ilasskoye bog decreased by 32%, and in north-western Lammin-Suo bog - by 31%.