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Under the influence of perennial dynamics of soil thawing depth, the upper layer of permafrost periodically thaws and becomes a part of the soil profile in the permafrost zone. In this case, the horizon, which is either frozen or thawed and has a thickness of several tens of centimeters, displays an elevated ice content (moisture). This horizon between the lower boundary of the active layer and the permafrost is named a protective layer or a transient permafrost layer and functions as a buffer that hinders thawing of the ice complex with its high ice content. The study of moisture using soil-regime methods and budget calculations showed that the protective layer of permafrost in sandy and loamy soils (at the depth of 1.5–5 m) contains from 25 to 60 mm (on average, 30 mm) of water in each 10-cm-thick layer of frozen soils under different types of forests in Central Yakutia. An increase in the seasonal thawing depth of permafrost-affected soils under conditions of global climate warming and anthropogenic impacts (forest fires, destruction of forest cover, etc.) causes degradation of the protective layer. The purpose of this article is to show the effect of increasing seasonal thawing depth of permafrost-affected soils on changes in the water content and water budget in permafrost areas because of the release of moisture stored in the protective layer in the context of global climate change. It was found that with an increase in the seasonal thawing depth, the protective layer should release a significant amount of water preserved in permafrost, which may change the water budget of permafrost territories. As calculations show, with an increase in the soil seasonal thawing depth by 20–30 cm on the interfluve areas, the volume of water entering the basins of nearby thermokarst depressions (alases) and rivers from frozen soils may reach 60 000–90 000 m3/km2. The obtained results can be used in modeling and predicting the dynamics of permafrost environments under the global climate change.

The characteristics of temperature dynamics in a solonetzic meadow-chernozemic soil of alas depression in Central Yakutia are described on the basis of long-term (2005–2014) stationary studies. Quick changes in weather conditions accompanied by changes in the soil temperature regime were observed during that period. Thus, the beginning of soil thawing in the spring shifted to earlier dates, and the beginning of soil freezing in the fall shifted to later dates. Temperature trends demonstrate an increase in the mean annual soil temperatures at all the depths. In total, the period of the frozen state of the soil became considerably shorter: in the middle-profile horizons, by 30–39 days. The obtained results attest to the high dynamism in temperature parameters of meadow soils in alas depressions of Central Yakutia under conditions of global climate changes.

This study was conducted to evaluate the change in total soil carbon [TSC = litter carbon (LIC) + soil organic carbon (SOC) + soil carbonate carbon (SCC)] associated with recent thermokarst activity and forest disturbance induced by the climate change and land use change in the permafrost-affected soils of Eastern Siberia. TSC stock from 80 sites in three types of the ecosystem: forests, arable land, and thermokarst were analyzed. The SOC content was positively correlated with root C density in all ecosystems. In the forest and arable land ecosystems, soil texture strongly affected SOC content, but water content was the main factor in SOC accumulation in the thermokarst ecosystem. Although the composition ratio of TSC stock significantly differed among the ecosystem, SOC was the main component of the TSC in all ecosystems. SOC and TSC stocks in thermokarst ecosystem (137.1 +/- 125.5 Mg SOC ha(-1)30 cm(-1) and 150.5 +/- 123.9 Mg TSC ha(-1 )30cm(-1)) were significantly higher than those in the forest (283 +/- 13.5 Mg SOC ha(-1) 30 cm(-l) and 51.4 +/- 20.9 Mg TSC ha(-1 )30 cm(-1)) and arable land ecosystem (41.9 +/- 16.9 Mg SOC ha(-1) 30 cm(-l) and 54.6 +/- 23.1 Mg TSC ha(-1) 30 cm(-1)), suggesting that thermokarst formation accumulates C. In the thermokarst ecosystem, significantly higher SOC stock was observed in moderately-wet and wet grassland than dry grassland suggesting that flooding increases C by suppressing organic matter decomposition. Among the forest ecosystem, forest disturbance significantly altered the C balance. Forest fire did not change the SOC and SCC stock but significantly burned the LIC stock at an average rate of 51.7 +/- 65.0% of the LIC. Water damage to the forest significantly increased the SOC stock by increasing the water content, but 58.5 +/- 62.4% of the LIC stock was dismissed. Forest cultivation significantly reduced TSC stock at an average rate of 37.3 +/- 47.2% by mineralization of the LIC. On the other hands, abandonment of arable land significantly restored TSC stock at an average rate of 92.4 +/- 83.5% by increasing C input. This study revealed that redistribution of the C stock has been occurred under the climate change and human activity. (C) 2018 Elsevier B.V. All rights reserved.