The annual balance of biogenic greenhouse gases (GHGs; carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)) in the atmosphere is well studied. However, the contributions of specific natural land sources and sinks remain unclear, and the effect of different human land use activities is understudied. A simple way to do this is to evaluate GHG soil emissions. For CO2, it usually comprises 60-75% of gross respiration in natural terrestrial ecosystems, while local human impact can increase this share to almost 100%. Permafrost-affected soils occupying 15% of the land surface mostly in the Eurasia and North America contain approximately 25% of the total terrestrial carbon. The biogenic GHG soil emissions from permafrost are 5% of the global total, which makes these soils extremely important in the warming world. Measurements of CO2, methane, and nitrous oxide, from eighteen locations in the Arctic and Siberian permafrost, across tundra, steppe, and north taiga domains of Russia and Svalbard, were conducted from August to September during 2014-2017 in 37 biotopes representing natural conditions and different types of human impact. We demonstrate that land use caused significant alteration in soil emission and net fluxes of GHGs compared to natural rates, regardless of the type and duration of human impact and the ecosystem type. The cumulative effect of land use factors very likely supported an additional net-source of CO2 into the atmosphere because of residual microbial respiration in soil after the destruction of vegetation and primary production under anthropogenic influence. Local drainage effects were more significant for methane emission. In general, land use factors enforced soil emission and net-sources of CO2 and N2O and weakened methane sources. Despite the extended heat supply, high aridity caused significantly lower emissions of methane and nitrous oxide in ultra-continental Siberian permafrost soils. However, these climatic features support higher soil CO2 emission rates, in spite of dryness, owing to the larger phytomass storage, presence of tree canopies, thicker active layer, and greater expressed soil fissuring. Furthermore, the Birch effect was much less expressed in ultra-continental permafrost soils than in permafrost-free European soils. Models and field observations demonstrated that the areal human footprint on soil CO2 fluxes could be comparable to the effect of climate change within a similar timeframe. Settlements and industrial areas in the tundra function as year-round net CO2 sources, mostly owing to the lack of vegetation cover. As a result, they could compensate for the natural C-balance on significantly larger areas of surrounding tundra. (C) 2020 Elsevier B.V. All rights reserved.

In permafrost regions, the thaw depth strongly controls shallow subsurface hydrologic processes that in turn dominate catchment runoff. In seasonally freezing soils, the maximum expected frost depth is an important geotechnical engineering design parameter. Thus, accurately calculating the depth of soil freezing or thawing is an important challenge in cold regions engineering and hydrology. The Stefan equation is a common approach for predicting the frost or thaw depth, but this equation assumes negligible soil heat capacity and thus exaggerates the rate of freezing or thawing. The Neumann equation, which accommodates sensible heat, is an alternative implicit equation for calculating freeze-thaw penetration. This study details the development of correction factors to improve the Stefan equation by accounting for the influence of the soil heat capacity and non-zero initial temperatures. The correction factors are first derived analytically via comparison to the Neumann solution, but the resultant equations are complex and implicit. Explicit equations are obtained by fitting polynomial functions to the analytical results. These simple correction factors are shown to significantly improve the performance of the Stefan equation for several hypothetical soil freezing and thawing scenarios. Copyright (c) 2015 John Wiley & Sons, Ltd.

Soil temperature regimes were studied in three ecosystems of the north of Western Siberia in the zone of isolated permafrost: the forest ecosystem with gleyic loamy sandy podzol (Stagnic Albic Podzol), the flat-topped peat mound ecosystem with humus-impregnated loamy sandy to light loamy peat cryozem (Histic Oxyaquic Turbic Cryosol (Arenic)), and the peat mound (palsa) ecosystem with oligotrophic destructive permafrost-affected peat soil (Cryic Histosol). Annual temperature measurements in the soil profiles demonstrated that these soils function under different temperature regimes: very cold permafrost regime and cold nonpermafrost regime. The following annual temperature characteristics proved to be informative for the studied soils: sums of above-zero temperatures at the depths of 10 and 20 cm, the maximum depth of penetration of temperatures above 10A degrees C, and the number of days with daily soil temperatures above (or below) 0A degrees C at the depth of 20 cm. On the studied territory, the insulating effect of the snow cover in winter was at least two times more pronounced than the insulating effect of the vegetation cover in summer. Cryogenic soils of the studied region are characterized by the high buffering towards changing climatic parameters. This is explained by the presence of the litter and peat horizons with a very low thermal diffusivity and by the presence of permafrost at a relatively shallow depth with temperature gradients preventing penetration of heat to the permafrost table.