Soil-ecological conditions of the north taiga flat-mound bog, Western Siberia

Of particular interest in the north of Western Siberia are frozen flat-mound bogs. Being formed in a transitional climatic zone, on the southern front of the permafrost zone, these frozen peatlands may turn out to be highly reactive upon thawing and deliver high amounts of solutes to the hydrologi-cal network. A detailed study of a flat-mound bog was carried out in a key area of about 3 hectares (Purovsky district, Yamalo-Nenets Autonomous Okrug). The soil-ecological conditions of the site are described, as well as the effect of spatial heterogeneity on the composition and properties of soils. Us-ing topographic mapping and photogrammetry, it was identified that the bog surface is characterized by distinct microtopography (mounds-hollows-thermokarst subsidence with a percentage areas ratio of 49:30:21, respectively). Small-scale variations in ecohydrological settings, microtopography, and vegetation affect the distribution of nutrients, organic carbon in soils, and DOC (dissolved organic carbon) in bog waters. The main soil types are Dystric Hemic Cryic Histosols and Dystric Hemic His-tosols (Gelic) found on mounds and in subsidence, respectively. If the peat thickness decreases to 40–60 cm, then Spodic Histic Turbic Cryosols (Albic, Arenic) and Histic Turbic Cryosols (Albic, Arenic) form. In hollows and fens, Dystric Epifibric Histosols, Spodic Histic Turbic Cryosols (Arenic), and Gleyic Histic Entic Podzols (Turbic) are the most common. The proportion of soils with frozen peat is no more than 20% of the area of the key site and permafrost lies deeper, in the underlying rocks. It was found that carbon stocks within the key area vary from 31.1 to 91.3 kg/m2. The maximum values are observed in transit subsidences/hollows between mounds, where water is discharged. Concentrations of macro-microelements in bog waters vary depending on microform types. For some elements (e.g., DOC, Fe, Al, B, Si, Ti, V, Rb, Sb, Cs, REEs (rare earth elements), Pb, Th, U), they are approximately equal or 1.5–2 higher on the mounds. The export of DOC and other elements in permafrost areas is primarily controlled by the residence time of water and movement ways along the profile. In addition to this, the physicochemical properties of peat and biomass, which are also higher on mounds, influ-ence the distribution and accumulation of nutrients

Spatial heterogeneity of soil acidity properties in peatlands of Western Siberia

The formation of significant amounts of low molecular weight (LMW) water-soluble organic compounds, which are highly reactive compounds of a non-specific nature, is a feature of the biogeocenoses of the North. Soil acidity, which in turn depends on LMW organic acids content, regulates the migration ability of compounds in landscapes and the bioavailability of nutrients. With an increase in the active layer thickness of peat soils in Western Siberia in the course of climate warming, new portions of LMW water-soluble organic compounds will enter, which will be quickly processed by microorganisms into CH4 and CO2. Five key sites were considered, located within thawed oligotrophic, frozen mound and polygonal bogs. The analysis of zonal patterns of acidity changes in the waters of peat soils indicates an increase in the pH in the series: northern taiga<forest tundra<southern tundra. A feature of the most acidic soils of the northern taiga is the high content of low molecular weight organic acids, the accumulation of which is determined by the species diversity of the vegetation cover and high humidity. The decrease in the content of acids in the soils of the southern tundra is due to changes in climatic conditions and, accordingly, the quality and quantity of organic material involved in the processes of mineralization and humification. Relationships between the pH of the soil solution and such parameters as the specific conductivity, the content of dissolved organic carbon, and the specific UV-absorbency (SUVA245) were revealed. Comparison of the acidity indices of peat soils of the zonal series of the European Northeast with similar ones obtained for the study area of Western Siberia showed that, at the same values of actual acidity, the exchangeable acidity values of peat soils of Western Siberia are slightly lower

PHOTOCHEMICAL TRANSFORMATION OF DISSOLVED ORGANIC MATTER AND BEHAVIOR OF METALS IN THE WATERS OF THE SOUTHERN TAIGA BOG COMPLEX, WESTERN SIBERIA

Link for citation: Raudina T.V., Smirnov S.V., Istigechev G.I., Pokrovsky O.S. Photochemical transformation of dissolved organic matter and behavior of metals in the waters of the southern taiga bog complex, Western Siberia. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 182-193. In Rus. The relevance. Dissolved organic matter is one of the largest biologically available sources of carbon in terrestrial and aquatic ecosystems, and its dynamics are critical to local and global carbon cycles. Destruction of organic matter during migration determines the biological cycle of elements and their stability. Important processes that lead to the transformation or removal of the dissolved organic matter are bio- and photodegradation. To date, enough research has been carried out to study the composition of humic substances, forms of metals, and the processes of migration of organo-mineral compounds in natural waters of the taiga zone, Western Siberia. Work is underway to study the dissolved organic carbon bioavailability, but the mechanisms of its photochemical transformations in different seasons of the year have not been studied. At the same time, photochemical mineralization of dissolved organic compounds largely regulates the biogeochemical cycles of elements by changing their bioavailability, the intensity of carbon dioxide emission from surface waters into the atmosphere, and the removal of dissolved trace elements through precipitation and coagulation. The main aim is to assess changes in the chemical composition and the rate of the dissolved organic matter and dissolved metals removal in the waters of the southern taiga bog complex (Western Siberia) under the sunlight exposure on a spatio-temporal scale. Objects: soil waters within different bog landscapes (open sedge-sphagnum fen, tall ryam (pine-shrub-sphagnum phytocenosis with high pine trees), and waterlogged mixed forest) of the Bakchar bog complex located in the southeastern part of the Ob-Irtysh interfluves, the Vasyugan plain. The waters were taken at a depth by digging a pit (40´40 cm area, 40 cm depth), which allowed the surrounding gravitational water to fill it up to the depth of 10–20 cm. The sampling took place during two field period in 2020 (June and October). Methods. pH, water temperature, specific conductivity (Cond) and dissolved oxygen were measured using a multiparameter instrument (WTW MULTI 3430 SET). The dissolved organic carbon was measured by a high-temperature thermic oxidation method using a Shimadzu TOC-LCPN analyzer, with an uncertainty of 2 %. The absorbance was measured at wavelengths up to 800 nm, 1 nm step using quartz 10 mm cuvette on a Cary-50 spectrophotometer. Major cations (Ca, Mg, Na, K), Si, and trace metals were determined with an ICP-MS Agilent CE 7500 with In and Re as internal standards and three various external ones. In the photodegradation experimental design, we followed the methodology which is sunlight exposure of sterile filtered (0,2 μm) samples in quartz reactors in the outdoor pool. Results. The authors revealed the influence of photodegradation on the qualitative and quantitative composition of dissolved organic substances and the behavior of metals in water samples of bog landscapes of the taiga zone of Western Siberia on spatiotemporal scales. It was established that from 3 to 30 % of the dissolved organic carbon can be removed from soil water under the influence of sunlight with maximum values in early June. At the same time, in autumn, despite the decrease in the amount of solar radiation, the photodegradable DOC can also reach 10–12 %. In general, there is a decrease in the percentage of the dissolved organic carbon loss in the waters in the row fen>ryam>forest. The dissolved organic carbon removal can be associated both with the transition of a part into an inorganic form, and with the destruction of high-molecular organic substances. A significant change (p<0.05) in the optical parameters is noted, which is consistent with the behavior of the dissolved organic matter during photolysis. In addition, under the influence of insolation, the transformation of organo-mineral compounds occurs, which leads to a change in the forms of metals. The greatest losses relative to control were observed for rare earth elements (Y, La, Ce, Pr, Nd), as well as Ti, V, which in some cases reach 70 % (more significant in fen waters). These trace elements show behavior similar to dissolved organic carbon,  Al and Fe, which confirms the importance of organic and organo-Fe-Al-colloids determining the behavior of most elements in acidic waters with a high content of organic matter

Colloidal organic carbon and trace elements in peat porewaters across a permafrost gradient in Western Siberia

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

Colloids in Thermokarst Lakes along a Permafrost and Climate Gradient of Permafrost Peatlands in Western Siberia Using In Situ Dialysis Procedure

Thermokarst lakes in the Western Siberian Lowland (WSL) are major environmental factors controlling organic carbon and trace metal storage in inland waters and greenhouse gas emissions to the atmosphere. In contrast to previously published research devoted to lake hydrochemistry, hydrobiology, sedimentary carbon, and processes controlling the lake total dissolved (<0.45 μm) solute composition, the colloidal forms of organic carbon (ОC), and related elements remain poorly known, especially across the permafrost gradient in this environmentally important region. Here we sampled 38 thermokarst lakes in the WSL, from the continuous to the permafrost-free zone, and we assessed both the total (<0.45 μm) and low-molecular-weight (<1 kDa) concentrations of 50 major and trace elements using conventional filtration and in situ dialysis. We aimed at quantifying the relationships between the colloidal content of an element and the lake surface area, permafrost coverage (absent, sporadic, isolated, discontinuous, and continuous), pH, and the concentrations of the main colloidal constituents, such as OC, Fe, and Al. There was a positive correlation between the lake area and the contents of the colloidal fractions of DOC, Ni, rare earth elements (REE), and Hf, which could be due to the enhanced mobilization of OC, trace metals, and lithogenic elements from silicate minerals in the soil porewater within the lake watershed and peat abrasion at the lake border. In all permafrost zones, the colloidal fractions of alkalis and alkaline-earth metals decreased with an increase in lake size, probably due to a decrease in the DOC concentration in large lakes. There was an increase in the colloidal fractions of DOC, Fe, Al, trivalent and tetravalent trace cations, Mn, Co, Ni, As, V, and U from the southern, permafrost-free zone to the northern, permafrost-bearing zones. This observation could be explained by an enhanced feeding of thermokarst lakes by suprapermafrost flow and the thawing of dispersed peat ice in the northern regions. Considering the large permafrost gradient of thermokarst lakes sampled in the present study, and applying a space-for-time substitution approach, we do not anticipate sizable changes in the colloidal status of DOC or major or trace elements upon climate warming and the permafrost boundary shifting northwards. For incorporating the obtained results into global biogeochemical models of OC, metal micronutrients, and toxicant migration in the permafrost regions, one has to consider the connectivity among lakes, soil waters, and rivers. For this, measurements of lake colloids across the main hydrological seasons, notably the winter period, are necessary

Seasonal and Spatial Variations of Dissolved Organic Matter Biodegradation along the Aquatic Continuum in the Southern Taiga Bog Complex, Western Siberia

The inland aquatic ecosystems play a significant role in the global carbon cycle, owing to the metabolism of terrestrially derived organic matter as it moves through fluvial networks along the water continuum. During this transport, dissolved organic matter (DOM) is microbial processed and released into the atmosphere, but the degree and intensity of this processing vary greatly both spatially and temporally. The Western Siberian Lowlands is of particular interest for a quantitative assessment of DOM biodegradation potential because the global areal-scale effects of DOM biodegradation in abundant surface organic-rich waters might be the highest in this region. To this end, we collected water samples along a typical aquatic continuum of the Bakchar Bog (the north-eastern part of the Great Vasyugan Mire) and, following standardized protocol, conducted an experimental study aimed at characterizing the seasonal and spatial variability of dissolved organic carbon (DOC) biodegradability. The biodegradable DOC fraction (BDOC) over the exposure incubation period ranged from 2% to 25%. The natural aquatic continuum “mire–forest–stream–river” demonstrated the systematic evolution of biodegradable DOC among the sites and across the seasons. The highest biodegradation rates were measured during spring flood in May and decreased along the continuum. The maximum possible CO2 production from DOM yielded the maximum possible flux in the range of 0.1 and 0.2 g C-CO2 m−2 day−1 d, which is an order of magnitude lower than the actual net CO2 emissions from the inland waters of the WSL. This study suggests that although the biodegradation of the humic waters of the WSL can sizably modify the concentration and nature of the DOM along the aquatic continuum, it plays only a subordinary role in overall C emissions from the lakes and rivers of the region

Dissolved organic carbon and major and trace elements in peat porewater of sporadic, discontinuous, and continuous permafrost zones of western Siberia

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

Permafrost thaw and climate warming may decrease the CO2, carbon, and metal concentration in peat soil waters of the Western Siberia Lowland

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 600 mm annual precipitation), active layer thickness (ALT) (>300 to 40 cm), 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)

Permafrost thaw and climate warming may decrease the CO2, carbon, and metal concentration in peat soil waters of the Western Siberia Lowland

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 600 mm annual precipitation), active layer thickness (ALT) (>300 to 40 cm), 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)

Bacteria primarily metabolize at the active layer/permafrost border in the peat core from a permafrost region in western Siberia

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