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The thawing and subsequent decomposition of large stocks of soil organic carbon (SOC) currently stored in the northern circumpolar permafrost region are projected to result in a ‘positive’ feedback on global warming. The magnitude of this feedback can only be assessed with improved knowledge about the total size and geographic distribution of the permafrost SOC pool. This study investigates SOC storage in an under-sampled mountain permafrost area in the Russian High Altai. SOC stocks from 39 soil pits are upscaled using a GIS-based land cover classification. We found that the top 100 cm of soils in Aktru Valley and the adjacent Kuray Basin only holds on average 2.6 ± 0.6 kg C m−2 (95% confidence interval), of which only c. 1% is stored in permafrost. Global warming will result in an upward shift of alpine life zones, with new plant cover and soil development at higher elevations. As a result, this type of mountain permafrost area might act as a net C sink in the future, representing a ‘negative’ feedback on global warming. Electronic supplementary material The online version of this article (10.1007/s13280-020-01433-6) contains supplementary material, which is available to authorized users.

The majority of organic carbon (OC), nutrients, and dissolved trace elements in soil porewaters are present in the form of colloids which determine element transport, bioavailability, and overall impact on ecosystems. Climate warming and permafrost thaw in high latitudes will primarily affect the soil liquid phase thereby modifying delivery of colloids to the hydrological network and their role in C transport and emission. Here we studied colloids in peat porewaters across a natural gradient of sporadic, isolated, discontinuous and continuous permafrost zone in the Western Siberian Lowland (WSL), the largest peatland in the world. The depth of sampling and the microrelief (mounds and hollows) had a generally weak impact on the proportion of colloidal forms (3kDa 0.45 μm) of OC, major (Fe, Al, P, alkali and alkaline-earth metals) and trace elements (TE) including micronutrients (Zn, Mn, Ni, Co, Cu), toxicants (Sb, As, Cd, Pb) and geochemical tracers (trivalent and tetravalent cations). Considering all micro-landscapes together, there was no sizable change in the proportion of colloidal fraction of OC, Fe, Al, P, micronutrients and toxicants across the permafrost zones. The majority of colloidal forms of all elements of these groups were represented by a size fraction between 3 and 30 kDa and were essentially Fe-Al-organic compounds with an average Fe:Al:OC molar ratio of 1.9:1:308. Overall, the degree of impact from environmental factors on OC and metal distribution among various colloidal fractions can be classified as depth ≤ permafrost type < microlandscape. Applying a substitution “space for time scenario” for the climate warming and permafrost thaw in Western Siberia, we do not expect sizable changes in C and element colloidal status during active layer thickness increase and permafrost boundary shift northward. Future studies of colloids in peat ice (below the active layer) are needed to assess possible changes in delivery of C and metals from soil to rivers and onward into the Arctic Ocean under massive permafrost thawing in the WSL.

Soil pore waters are a vital component of the ecosystem as they are efficient tracers of mineral weathering, plant litter leaching, and nutrient uptake by vegetation. In the permafrost environment, maximal hydraulic connectivity and element transport from soils to rivers and lakes occurs via supra-permafrost flow (i.e. water, gases, suspended matter, and solutes migration over the permafrost table). To assess possible consequences of permafrost thaw and climate warming on carbon and Green House gases (GHG) dynamics we used a "substituting space for time" approach in the largest frozen peatland of the world. We sampled stagnant supra-permafrost (active layer) waters in peat columns of western Siberia Lowland (WSL) across substantial gradients of climate (-4.0 to -9.1°C mean annual temperature, 360 to 600mm annual precipitation), active layer thickness (ALT) (>300 to 40cm), and permafrost coverage (sporadic, discontinuous and continuous). We analyzed CO2, CH4, dissolved carbon, and major and trace elements (TE) in 93 soil pit samples corresponding to several typical micro landscapes constituting the WSL territory (peat mounds, hollows, and permafrost subsidences and depressions). We expected a decrease in intensity of DOC and TE mobilization from soil and vegetation litter to the supra-permafrost water with increasing permafrost coverage, decreasing annual temperature and ALT along a latitudinal transect from 62.3°N to 67.4°N. However, a number of solutes (DOC, CO2, alkaline earth metals, Si, trivalent and tetravalent hydrolysates, and micronutrients (Mn, Co, Ni, Cu, V, Mo) exhibited a northward increasing trend with highest concentrations within the continuous permafrost zone. Within the "substituting space for time" climate change scenario and northward shift of the permafrost boundary, our results suggest that CO2, DOC, and many major and trace elements will decrease their concentration in soil supra-permafrost waters at the boundary between thaw and frozen layers. As a result, export of DOC and elements from peat soil to lakes and rivers of the WSL (and further to the Arctic Ocean) may decrease.

The content and the profile distribution of the element composition of the 1 meter high peat deposits in flat frost mound bogs are investigated. The botanical composition of peat is described. The results of the botanical composition analysis of peat showed that deposits consist mainly of sphagnum mosses, lichens, shrubs, green mosses, pine wood, as well as pine and birch bark. A good correlation between the degree of peat decomposition and the brightness of dry peat measured by the CIE L*a*b* color model is revealed. As a result of the study of peat samples’ color, it has been found that this parameter can be used as an express method for the rapid assessment of peat degree decomposition. The highest concentration of the organic carbon occurs at the base of the peat deposit (64.4±0.2%). The nitrogen concentration in permafrost peat is higher than in thawed (1.0 ± 0.2% and 0.7 ± 0.1%, respectively, the difference is significant at p = 0.001). The C / N ratio decreases from 72 ± 16 in 0-40 cm in the thawed layer to 50 ± 10 in the frozen part (40-100 cm). Within the bottom low boundary of the seasonally thawed layer, a local increase in the N concentration was detected, as well as an almost 2-fold decrease in the C/N ratio. It is most likely related to the high increase in the rate of microbial activity on the border between the thawed layer and the permafrost peat. It was revealed that most of the elements are concentrated in the upper (thawed) part of the peat deposit. Among them, only Na, Mg, Ca, Zn, Ba, As and Sb have a significant difference. Despite the fact that significant differences according to non-parametric U-criterion Mann-Whitney test were identified only for 7 elements, the distribution of the rest along elements the frozen and thawed peat layer is similar in nature. So for Na, Mg, Al, P, K, Ca, Ti, Fe, Zn, Ba, Li, B, V, Cr, Mn, Co, Ni, Cu, Ga, As, Rb, Sr, Y, Zr, Nb, Mo, Cd, Sb, Cs, the upper quartiles of concentrations in the seasonally thawed layer are 1.2 - 6.9 times higher than in the permafrost peat, and for C, N, Al, Ba, B, V, Co, Cu , Zr, Nb, Mo it is 1,0 - 0,6 times lower, respectively. Generally, according to the element composition, it is safe to say that the differences stem from the botanical composition. In general, according to the elemental composition it can be said that the differences are primarily due to the botanical composition. The active layer comprises mainly sphagnum mosses and lichens, the woody peat already appears in the lower permafrost part of the deposit. A correlation between the brightness of peat and the total content of ash elements (R2 = 0.65, excluding 1 sample) was revealed within the active layer. Taking into account the fact that the brightness correlates with the degree of decomposition, it may be concluded that higher upper quartile of the concentrations of elements in the active layer relates to the slower peat accumulation rate for the last 3 thousand years and, correspondingly, a large accumulation of dust components from the atmosphere by the peat layers.

The study of suspended solids in the West Siberian rivers is of great importance from the point of view of biogeochemistry, since in the rivers there are the formation and transformation of abrasion products of banks and bottom, suspended and dissolved organic matter and solid river flow, which are carried out from the land to the Kara Sea and further to the North Arctic Ocean. Studies of river suspension are necessary to understand the processes of modern sedimentation, as well as for the ecological assessment of the water area state. Mechanisms of sedimentation are largely associated with the processes of physical and biological weathering, generation, transformation and transport of suspended matter from the catchment to floodplain landscapes. In this regard, the role of studying the connection of the qualitative composition of river suspended matter with landscape parameters (level of the catchment area swappiness, nature of the soil cover, composition of soil-forming rocks, presence (absence) of permafrost, etc. is high. For example, the river of the north-taiga subzone, the catchment area of which is heavily swamped, and the river of the tundra zone with a slightly swampy watershed are represented. The influence of flood waters on the concentration of some elements in rivers with contrasting watersheds is considered. The contribution of groundwater and the effect of soil solutions on the overall migration flow are estimated.

The study of suspended solids in the West Siberian rivers is of great importance from the point of view of biogeochemistry, since in the rivers there are the formation and transformation of abrasion products of banks and bottom, suspended and dissolved organic matter and solid river flow, which are carried out from the land to the Kara Sea and further to the North Arctic Ocean. Studies of river suspension are necessary to understand the processes of modern sedimentation, as well as for the ecological assessment of the water area state. Mechanisms of sedimentation are largely associated with the processes of physical and biological weathering, generation, transformation and transport of suspended matter from the catchment to floodplain landscapes. In this regard, the role of studying the connection of the qualitative composition of river suspended matter with landscape parameters (level of the catchment area swappiness, nature of the soil cover, composition of soil-forming rocks, presence (absence) of permafrost, etc. is high. For example, the river of the north-taiga subzone, the catchment area of which is heavily swamped, and the river of the tundra zone with a slightly swampy watershed are represented. The influence of flood waters on the concentration of some elements in rivers with contrasting watersheds is considered. The contribution of groundwater and the effect of soil solutions on the overall migration flow are estimated.

Thawing of frozen peat in discontinuous permafrost zones may significantly modify the environment at local (slumps and engineering damages) and global (greenhouse gases regime) scales. We studied the aquatic geochemistry of CO2, CH4, dissolved organic carbon (DOC), P, Si, and colloidal trace metal from hollows, depressions, permafrost subsidences and soil waters in the actively thawing discontinuous permafrost zone of Western Siberia Lowland (WSL). This site of abrupt permafrost collapse is dominated by minerotrophic fens located within the flat mound peat bog. The CO2, DOC, major and trace metal concentrations decreased with the increase of the surface area of the water body, along the hydrological continuum (soil water → hollows → depressions and permafrost subsidences → thaw ponds → thermokarst lakes). Aqueous concentrations of CO2, CH4, Ca, Si, P, Al, Fe, Nd, and U were a factor of 4 to 10 higher in the site of catastrophic thaw compared to the steady thawing of a palsa peat bog that was previously studied in the same region. The colloids (1 kDa–0.45 μm) formed in hot spots were strongly enriched in Fe, Al, and trivalent and tetravalent hydrolysates relative to organic carbon. Because the increase in the thickness of the thawing depth intensifies the input of inorganic components from deep mineral horizons, abrupt permafrost thaw enriches the surface waters in Al-rich colloids and low molecular weight organic complexes. As a result, the WSL's surface water colloidal composition may shift from DOM-rich and DOM-Fe-rich to DOM-Al-rich, and the release of low-soluble trivalent and tetravalent hydrolysates from the soil to the river will increase. We hypothesize that in sites of abrupt permafrost thaw, there is direct mobilization of soil waters to a hydrological network (rivers and lakes) and there is minimal transformation by autochthonous processes, which is unlike the case of steady permafrost thawing. Therefore, the change in physical factors, such as water pathways and the water residence time, within a given elementary landscape will likely control the overall impact of on-going permafrost thaw on both the surface water chemistry and dissolved greenhouse gas pattern of the territory. For this, high-resolution (

The West Siberian Plain stands out among other boreal plains by phenomenal bogging, which has both global and regional significance. The polygonal bogs, frozen raised-mound bogs, and ombrotrophic ridge-hollow raised bogs are the most extensive bog types in the study area. These bogs commonly show highly diverse surface patterns consisting of mounds, polygons, ridges, hollows, and fens that correspond to the microtopes. Here we investigated how the microtopographic features of the landscape affect the thermal and hydrologic conditions of the soil as well as the nutrient availability and consequently, the dynamics of carbon and related elements. The effect of the surface heterogeneity on the temperature regimes and depths of permafrost is most significant. All of these factors together are reflected, through the feedback system, by a number of hydrochemical parameters of bog waters, such as dissolved organic and inorganic carbon (DOC, DIC), specific conductivity (Cond), SO42&ndash, Cl&ndash, P, Sr, Al, Ti, Cu, V, B, Cs, Cd, Rb, As, U, and rare earth elements (REEs). Among the studied parameters, DOC, SO42, Al, V, and Mn differ most significantly between the convex and concave microforms. The DOC content in bog water is significantly affected by the water residence time, which is significantly longer in soils of mound/polygons than fens. Plants biomass is higher on the mounds which also have some effect that, due to leaching, should lead to more carbon entering into the water of the mounds. It is also shown that atmospheric-dust particles have a noticeable effect on the hydrochemical parameters of bog waters, especially on mounds. The ongoing climate warming will lead to an increase in the fens area and to a decrease in the content of DOC and many elements in bog waters.

Soil pore waters are a vital component of the ecosystem as they are efficient tracers of mineral weathering, plant litter leaching, and nutrient uptake by vegetation. In the permafrost environment, maximal hydraulic connectivity and element transport from soils to rivers and lakes occurs via supra-permafrost flow (i.e. water, gases, suspended matter, and solutes migration over the permafrost table). To assess possible consequences of permafrost thaw and climate warming on carbon and Green House gases (GHG) dynamics we used a "substituting space for time" approach in the largest frozen peatland of the world. We sampled stagnant supra-permafrost (active layer) waters in peat columns of western Siberia Lowland (WSL) across substantial gradients of climate (-4.0 to -9.1°C mean annual temperature, 360 to 600mm annual precipitation), active layer thickness (ALT) (300 to 40cm), and permafrost coverage (sporadic, discontinuous and continuous). We analyzed CO

The microbial activity in the soils of the permafrost-affected zones is assumed to be one of the major factors that modify the organic carbon and nitrogen cycle under current climate change. In contrast to the extensive research centered on bacterial abundance, diversity, and metabolic activity in permanently and seasonally frozen mineral soils from high latitudes, frozen peat (organic) environments remain poorly characterized in terms of the physiological diversity and metabolic potential of bacteria. The evolution of soil heterotroph microbial number and metabolic activity across the “seasonally thawed (active)—permanently frozen layer” boundary was studied on 100-cm-thick cores from frozen peat mounds located in the discontinuous permafrost zone in western Siberia. There was a systematic decrease of metabolic activity in the upper 40 cm of the peat core from the surface layers of the mosses and lichens towards the beginning of the frozen horizon, followed by an abrupt increase in bacterial metabolism exactly at the border between the thawed layer and the permafrost table. The aerobic viable cell count and total bacterial number from the active layer were similar to those from the permafrost peat layer. The highest metabolic activity was observed at the beginning of the frozen peat layer and might correspond to the highest availability of amino substrates, which were depleted in the active layer but preserved in the deeper frozen horizons. The enhanced microbial activity at the frozen peat-active layer boundary in western Siberia may persist for another 50–100 years based on the current rate of increase in active layer thickness.

Mobilization of dissolved organic carbon (DOC) and related trace elements (TEs) from the frozen peat to surface waters in the permafrost zone is expected to enhance under ongoing permafrost thaw and active layer thickness (ALT) deepening in high-latitude regions. The interstitial soil solutions are efficient tracers of ongoing bio-geochemical processes in the critical zone and can help to decipher the intensity of carbon and metals migration from the soil to the rivers and further to the ocean. To this end, we collected, across a 640 km latitudinal transect of the sporadic to continuous permafrost zone of western Siberia peatlands, soil porewaters from 30 cm depth using suction cups and we analyzed DOC, dissolved inorganic carbon (DIC), and 40 major elements and TEs in 0.45 µm filtered fraction of 80 soil porewaters. Despite an expected decrease in the intensity of DOC and TE mobilization from the soil and vegetation litter to the interstitial fluids with the increase in the permafrost coverage and a decrease in the annual temperature and ALT, the DOC and many major and trace elements did not exhibit any distinct decrease in concentration along the latitudinal transect from 62.2 to 67.4° N. The DOC demonstrated a maximum of concentration at 66° N, on the border of the discontinuous/continuous permafrost zone, whereas the DOC concentration in peat soil solutions from the continuous permafrost zone was equal to or higher than that in the sporadic/discontinuous permafrost zone. Moreover, a number of major (Ca, Mg) and trace (Al, Ti, Sr, Ga, rare earth elements (REEs), Zr, Hf, Th) elements exhibited an increasing, not decreasing, northward concentration trend. We hypothesize that the effects of temperature and thickness of the ALT are of secondary importance relative to the leaching capacity of peat, which is in turn controlled by the water saturation of the peat core. The water residence time in peat pores also plays a role in enriching the fluids in some elements: the DOC, V, Cu, Pb, REEs, and Th were a factor of 1.5 to 2.0 higher in mounds relative to hollows. As such, it is possible that the time of reaction between the peat and downward infiltrating waters essentially controls the degree of peat porewater enrichments in DOC and other solutes. A 2° northward shift in the position of the permafrost boundaries may bring about a factor of 1.3 ± 0.2 decrease in Ca, Mg, Sr, Al, Fe, Ti, Mn, Ni, Co, V, Zr, Hf, Th, and REE porewater concentration in continuous and discontinuous permafrost zones, and a possible decrease in DOC, specific ultraviolet absorbency (SUVA), Ca, Mg, Fe, and Sr will not exceed 20 % of their current values. The projected increase in ALT and vegetation density, northward migration of the permafrost boundary, or the change of hydrological regime is unlikely to modify chemical composition of peat porewater fluids larger than their natural variations within different micro-landscapes, i.e., within a factor of 2. The decrease in DOC and metal delivery to small rivers and lakes by peat soil leachate may also decrease the overall export of dissolved components from the continuous permafrost zone to the Arctic Ocean. This challenges the current paradigm on the increase in DOC export from the land to the ocean under climate warming in high latitudes.

The features of the organic matter composition of the lake waters of the Ob River floodplain in the winter low-water and the spring flood periods were investigated. It is shown that the organic matter of the studied lakes is significantly different from the organic matter of the Ob water. In the winter low-water season, floodplain lakes accumulate a large amount of organic aromatic allochotic substances, and in the flood there are changes in the composition of organic matter

The properties and elemental composition of the Histosols of polygonal frozen bog in Western Siberia are characterized. The study of peat soils allowed an evaluation of the effect of micro-landscape on main properties and major element concentrations. According to acid-base characteristics and the ash content, the studied soils can be qualified as oligotrophic. The soil profile shows a tendency to increase the TOC in the lower horizons, and especially, in the peat soils of the polygons. The highest average TOC, Ca, Mg, K, P, Fe, and Na concentrations in the peat profile are observed in the soils of polygons (1.2-2.2 times). A large number of phytomass and plant productivity contribute to the enrichment of soils with carbon and some elements on the polygons. In addition, the difference between the soils of polygons and hollows in terms of the thermal conditions and peat hydrophysical characteristics is reflected in their elemental composition and properties.

The Siberian forest is a tremendous repository of terrestrial organic carbon (C), which may increase owing to climate change, potential increases in ecosystem productivity and hence C sequestration. Phosphorus (P) availability could limit the C sequestration potential, but tree roots may mine the soil deep to increase access to mineral P. Improved understanding and quantification of the processes controlling P availability in surface and deep soil layers of Siberian forest ecosystems are thus required. The objectives of the present study were to (1) evaluate P status of surface and deep soil horizons from different forest plots in southwestern Siberia and (2) assess the effects of physicochemical soil properties, microbiological activity and decomposition processes on soil P fractions and availability. Results revealed high concentrations of total P (879–1042 mg kg−1 in the surface mineral soils) and plant-available phosphate ions. In addition, plant-available phosphate ions accumulated in the subsoil, suggesting that deeper root systems may mine sufficient available P for the trees and the potentially enhanced growth and C sequestration, may not be P-limited. Because the proportions of total organic P were large in the surface soil layers (47–56% of total P), we concluded that decomposition processes may play a significant role in P availability. However, microbiological activity and decomposition processes varied between the study plots and higher microbiological activity resulted in smaller organic P fractions and consequently larger available inorganic P fractions. In the studied Siberian soils, P availability was also controlled by the physicochemical soil properties, namely Al and Fe oxides and soil pH.

The Russian boreal forest, which mainly consists of extensive forests in Siberia, is the largest continuous forest region on Earth and represents 70 % of the world's boreal forest. Siberian forest is a tremendous repository of terrestrial organic carbon (C), which may increase owing to climate change, potential increases in ecosystem productivity and hence C sequestration. Phosphorus (P) availability could limit the C sequestration potential, but tree roots may mine the soil deeper to increase access to mineral P. Improved understanding and quantification of the processes controlling P availability in surface and deep soil layers of forest ecosystems are thus required. Relative contributions of organic and inorganic P and, consequently, P availability in forest ecosystems depend on decomposition processes, which could be strongly affected by vegetation composition, temperature, precipitation, and their changes due to a warming climate. The objectives of the present study were to (1) evaluate P status of surface and deep forest soil horizons from two contrasted biomes in Southwestern Siberia (i.e. forest steppe in the West Siberian plain and blackish ("chernevaya" in Russian) taiga in the low Salair mountains) and (2) assess the effects of vegetation (siberian fir stand, common aspen stand and herbs in a forest gap) and local climate on soil P fractions. Results revealed high contents in total P (645–1042 mg kg−1 in the surface mineral soils) and available inorganic P (diffusive phosphate ions in one week = 83–126 mg kg−1). In addition, there was an accumulation of diffusive phosphate ions in the subsoils resulting from differences between soil horizons in total inorganic P and soil properties. Consequently, deeper root systems may mine substantial amounts of available P for the trees and the potential enhanced growth and C sequestration due to climate change should thus a~priori not be P-limited. High proportions of total organic P (47–56 % of total P in the surface mineral soils) show that decomposition processes potentially play a significant role in P availability. Results show that decomposition processes are affected by vegetation (deciduous broadleaved trees, evergreen coniferous, herbs) and local climate (precipitations; snow cover with its isolating effect on soil). Results on the effects of plant species and local climate improved our understanding of the potential effects of climate change on P availability through warming and vegetation redistribution.