Landscape microzones within thermokarst depressions of central Yakutia under present climatic conditions

Abstract

Thermokarst (alas) of Central Yakutia is an intrazonal dynamic landscape in the form of rounded depressions with peculiar soils and meadow vegetation, microclimate, and fauna that are very different from the surrounding typical taiga landscapes. During the formation of alas depression, complete processing of thawed ground with the formation of new soils occurs and entirely changes the biogeochemical cycle. Because this system is closed, all water-soluble substances, such as N/C and soluble salts, etc., accumulate inside the depression. Using standard methods and instruments, we measured the main properties of alas soils. Depending on the hydrothermal and physicochemical regimes, thawing depth, and greenhouse gas (GHG) flux, three main belts of soils and vegetation were distinguished within the alas: (1) steppe meadow, located on most elevated places, not sufficiently moistened, with alas steppe soils and steppe vegetation; (2) middle meadow, located lower than stepped meadow in elevation, normally moist, with alas sod-meadow soils and highest productivity vegetation; and (3) wet meadow, located around the lake, excessively moistened, with alas marshy sod-meadow soils and marsh vegetation. Therefore, the soils of wet and real meadows, due to the abundance of organic matter, are significant sources of CO2 and CH4, especially in humid years. Under the climate warming observed over recent decades in this territory, the alas ecosystem has undergone considerable change. Thus, the classification and mapping of belts within the alas can have both applied and fundamental importance.