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Under global warming, invasive cyanobacteria, can migrate northward and colonize lakes in permafrost-affected territories. This study tests the potential growth of M. aeruginosa onto various organic-rich solutions of those regions.

Introduction. Iron is a widespread element in groundwater, which is used for domestic and drinking water supply. When using waters from non-centralized sources, deironing of waters, as a rule, is not carried out. When such waters are used for drinking purposes, there is a likely risk of negative effects for public health. Materials and methods. Forty six sources of non-centralized water supply (private wells, water wells, springs) were studied It considered assessing the health risk with oral administration of the components through drinking water into the body. Results. For single samples in the chemical composition of waters there were determined high contents of total hardness, SO42-, Cl-, NO3-. Waters with Fe and Mn concentrations many times higher than the normative values are widespread. The main non-carcinogenic risk is iron and nitrates, which have been identified as warning and high risk levels. For other components, the values of the hazard coefficient are within the range of the minimum and acceptable levels of risk. The probability of occurrence of negative effects for the children’s age group is possible with an iron content of 5 mg/l and more, for an adult - 11 mg/l and more. Limitations. The limitation related to the incomplete route of exposure to chemical components, since only one medium (drinking water) and only one route of exposure (oral exposure) was considered on the risk assessment. This study is also limited by the number of water samples. Conclusion. The health risk associated with high iron content in water has been set for children and adults. For the children’s group (up to 6 years), the risk of developing diseases of non-infectious etiology is significantly higher, than for the adult group, as shown by the results. When iron-containing waters are used for drinking purposes, there is a risk of non-infectious pathologies.

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 (

International audience; The biomineralization of CO2, in the form of carbonate minerals, is considered as one of the efficient solutions of atmospheric CO2 removal, allowing stable and sustainable storage of this greenhouse gas. Cyanobacteria are among the most powerful microorganisms capable of precipitating carbonate minerals, both in the present and in the past. In the modern environments, high Si concentration during geoengineering biomineralization could occur due to dissolution of Mg-bearing primary silicates such as olivine. However, most of experimental studies aimed to understand the formation of these carbonates were performed in Si-poor solutions. Thus, experimental characterizations of the nature, rate, and stoichiometry of precipitated minerals in Si-rich solutions in the presence of bacteria are lacking. The present study attempted to reproduce, in controlled laboratory experiments, the processes of biomineralization in a carbonate- and Mg-bearing medium having high Si concentrations (2–4 mM, which is below the saturation with respect to amorphous silica). These experiments have been carried out in the presence of three contrasting cyanobacteria: Synechococcus sp., Chroococcidiopsis sp. and Aphanothece clathrata in order to characterize the rate of formation, stoichiometry and mineralogical nature of precipitates. The results demonstrated significant role of cyanobacteria in the precipitation of carbonate and silicate minerals by increasing the pH of the medium during photosynthesis. Magnesium precipitation rates measured between 50 and 150 h of reaction time ranged from 0.05 to 0.5 mmol h−1 gdry1 and decreased (Synechococcus sp. and Chroococcidiopsis sp.) or increased (A. clathrata) with an increase in the Si:Mg ratio in solution. The abiotic instantaneous rates of Mg and Si removal from alkaline solutions were similar to those in the presence of cyanobacteria at the same pH value suggesting that photosynthetically induced pH rise was the main factor of mineral formation. The transmission electron microscopy (TEM) and spectroscopic observations and associated analyses identified an amorphous magnesium silicate together with hydrous Mg carbonates (hydromagnesite). The formation of carbonate solid phase at high Mg: Si ratios indicated the potential for the removal of inorganic carbon at pH > 10. The difference in the degree of C removal between different species was primarily linked to different degree of pH rise during photosynthesis. Taken together, the results obtained in this study allowed an efficient reproduction of combined magnesium hydroxo-carbonates and hydrous silicates precipitation under cyanobacterial activity, suitable for geoengineering of biologically controlled CO2 sequestration in Si-Mg-carbonate-bearing solutions.

Environmental physical and chemical factors controlling the abundance and biodiversity of zooplankton in permafrost-affected lakes are poorly known yet they determine the response of aquatic ecosystems to on-going climate change and water warming. Here, we assess the current status of zooplankton communities in lakes of the Bolshezemelskaya Tundra (permafrost peatlands of NE Europe), and provide new information about the composition and structure of zooplankton. The results demonstrate that the structure of zooplankton communities is influenced by the morphometric features of lakes and the degree of lake overgrowth by macrophytes. According to the level of quantitative development of zooplankton, most tundra lakes were of the oligotrophic type with an average wet biomass of up to 1 g/m3. The largest number of species was observed in zooplankton communities of small thaw ponds with an area of up to 0.02 km2 and overgrown with macrophytes. The analysis of factors that influence the formation of the lake zoocenosis demonstrated that the species composition and quantitative characteristics of zooplankton are chiefly controlled by pH and water mineralization. A comparison of the results obtained with the literature data on the lakes of this region collected 60 years ago suggests that the ecosystems of these lakes are in a stable state. Overall, these new insights will improve our knowledge of factors controlling the zooplankton spatial dynamics in unique but quite abundant thermokarst lakes of NE European Tundra, subjected to on-going climate warming.

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.

Despite the importance of small and medium size rivers of Siberian boreal zone in greenhouse gases (GHG) emission, major knowledge gaps exist regarding its temporal variability and controlling mechanisms. Here we sampled 11 pristine rivers of the southern taiga biome (western Siberia Lowland, WSL), ranging in watershed area from 0.8 to 119,000 km

We studied two medium size pristine rivers (Taz and Ket) of boreal and subarctic zone, western Siberia, for a better understanding of the environmental factors controlling major and trace element transport in riverine systems. Our main objective was to test the impact of climate and land cover parameters (permafrost, vegetation, water coverage, soil organic carbon, and lithology) on carbon, major and trace element concentration in the main stem and tributaries of each river separately and when considering them together, across contrasting climate/permafrost zones. In the permafrost-bearing Taz River (main stem and 17 tributaries), sizable control of vegetation on element concentration was revealed. In particular, light coniferous and broadleaf mixed forest controlled DOC, and some nutrients (NO2, NO3, Mn, Fe, Mo, Cd, Ba), deciduous needle-leaf forest positively correlated with macronutrients (PO4, Ptot, Si, Mg, P, Ca) and Sr, and dark needle-leaf forest impacted Ntot, Al, and Rb. Organic C stock in the upper 30–100 cm soil positively correlated with Be, Mn, Co, Mo, Cd, Sb, and Bi. In the Ket River basin (large right tributary of the Ob River) and its 26 tributaries, we revealed a correlation between the phytomass stock at the watershed and alkaline-earth metals and U concentration in the river water. This control was weakly pronounced during high-water period (spring flood) and mostly occurred during summer low water period. Pairwise correlations between elements in both river systems demonstrated two group of solutes—(1) positively correlated with DIC (Si, alkalis (Li, Na), alkaline-earth metals (Mg, Ca, Sr, Ba), and U), this link originated from groundwater feeding of the river when the labile elements were leached from soluble minerals such as carbonates; and (2) elements positively correlated with DOC (trivalent, tetravalent, and other hydrolysates, Se and Cs). This group reflected mobilization from upper silicate mineral soil profile and plant litter, which was strongly facilitated by element colloidal status, notably for low-mobile geochemical tracers. The observed DOC vs DIC control on riverine transport of low-soluble and highly mobile elements, respectively, is also consistent with former observations in both river and lake waters of the WSL as well as in soil waters and permafrost ice. A principal component analysis demonstrated three main factors potentially controlling the major and TE concentrations. The first factor, responsible for 26% of overall variation, included aluminum and other low mobile trivalent and tetravalent hydrolysates, Be, Cr, Nb, and elements strongly complexed with DOM such as Cu and Se. This factor presumably reflected the presence of organo-mineral colloids, and it was positively affected by the proportion of forest and organic C in soils of the watershed. The second factor (14% variation) likely represented a combined effect of productive litter in larch forest growing on carbonate-rich rocks and groundwater feeding of the rivers and acted on labile Na, Mg, Si, Ca, P, and Fe(II), but also DOC, micronutrients (Zn, Rb, Ba), and phytomass at the watershed. Via applying a substituting space for time approach for south-north gradient of studied river basins, we predict that climate warming in northern rivers may double or triple the concentration of DIC, Ca, Sr, U, but also increase the concentration of DOC, POC, and nutrients.

Due to its insulating and draining role, assessing ground vegetation cover properties is important for high-resolution hydrological modeling of permafrost regions. In this study, morphological and effective hydraulic properties of Western Siberian Lowland ground vegetation samples (lichens, Sphagnum mosses, peat) are numerically studied based on tomography scans. Porosity is estimated through a void voxels counting algorithm, showing the existence of representative elementary volumes (REVs) of porosity for most samples. Then, two methods are used to estimate hydraulic conductivity depending on the sample's homogeneity. For homogeneous samples, direct numerical simulations of a single-phase flow are performed, leading to a definition of hydraulic conductivity related to a REV, which is larger than those obtained for porosity. For heterogeneous samples, no adequate REV may be defined. To bypass this issue, a pore network representation is created from computerized scans. Morphological and hydraulic properties are then estimated through this simplified representation. Both methods converged on similar results for porosity. Some discrepancies are observed for a specific surface area. Hydraulic conductivity fluctuates by 2 orders of magnitude, depending on the method used. Porosity values are in line with previous values found in the literature, showing that arctic cryptogamic cover can be considered an open and well-connected porous medium (over 99 % of overall porosity is open porosity). Meanwhile, digitally estimated hydraulic conductivity is higher compared to previously obtained results based on field and laboratory experiments. However, the uncertainty is less than in experimental studies available in the literature. Therefore, biological and sampling artifacts are predominant over numerical biases. This could be related to compressibility effects occurring during field or laboratory measurements. These numerical methods lay a solid foundation for interpreting the homogeneity of any type of sample and processing some quantitative properties' assessment, either with image processing or with a pore network model. The main observed limitation is the input data quality (e.g., the tomographic scans' resolution) and its pre-processing scheme. Thus, some supplementary studies are compulsory for assessing syn-sampling and syn-measurement perturbations in experimentally estimated, effective hydraulic properties of such a biological porous medium.

Despite recent progress in the understanding of the carbon (C) cycle of Siberian permafrost-affected rivers, spatial and seasonal dynamics of C export and emission from medium-sized rivers (50 000–300 000 km2 watershed area) remain poorly known. Here we studied one of the largest tributaries of the Ob River, the Ket River (watershed = 94 000 km2), which drains through pristine taiga forest of the boreal zone in the West Siberian Lowland (WSL). We combined continuous and discrete measurements of carbon dioxide (CO2) concentration using submersible CO2 sensor and floating chamber flux (FCO2), with methane (CH4), dissolved organic and inorganic C (DOC and DIC, respectively), particulate organic C and total bacterial concentrations over an 800 km transect of the Ket River main stem and its 26 tributaries during spring flood (May 2019) and 12 tributaries during summer baseflow (end of August–beginning of September 2019). The partial pressure of CO2 (pCO2) was lower and less variable in the main stem (2000 to 2500 µatm) compared to that in the tributaries (2000 to 5000 µatm). In the tributaries, the pCO2 was 40 % higher during baseflow compared to spring flood, whereas in the main stem, it did not vary significantly across the seasons. The methane concentration in the main stem and tributaries was a factor of 300 to 1900 (flood period) and 100 to 150 times lower than that of CO2 and ranged from 0.05 to 2.0 µmol L−1. The FCO2 ranged from 0.4 to 2.4 g C m−2 d−1 in the main channel and from 0.5 to 5.0 g C m−2 d−1 in the tributaries, being highest during August in the tributaries and weakly dependent on the season in the main channel. During summer baseflow, the DOC aromaticity, bacterial number, and needleleaf forest coverage of the watershed positively affected CO2 concentrations and fluxes. We hypothesize that relatively low spatial and seasonal variability in FCO2 of the Ket River is due to a flat homogeneous landscape (bogs and taiga forest) that results in long water residence times and stable input of allochthonous dissolved organic matter (DOM), which dominate the FCO2. The open water period (May to October) C emission from the fluvial network (main stem and tributaries) of the Ket River was estimated to 127 ± 11 Gg C yr−1, which is lower than the downstream dissolved and particulate C export during the same period. The estimated fluvial C emissions are highly conservative and contain uncertainties linked to ignoring hotspots and hot moments of emissions, notably in the floodplain zone. This stresses the need to improve the temporal resolution of FCO2 and water coverage across seasons and emphasizes the important role of WSL rivers in the release of CO2 into the atmosphere.

Small lakes of the boreal zone are highly sensitive indicators of both global environmental change and local anthropogenic pressure. This work presents the results of multidisciplinary study of three small, seasonally stratified lakes of NW Russia, conducted since 2002 to the present time. These lakes were subjected to various degree of impact by rural population and agricultural activity since the beginning of twentieth century but the population and anthropogenic pressure have decreased since 1990s. To monitor the recovering of these lakes from human impact and to relate the evolution of their hydrochemical parameters to short-term weather events and global climatic trend, we measured the lake water temperature and chemical composition (carbon, macro- and micronutrients, trace elements) in summer and winter over full depth of the water column. The pH and concentration of DIC, SO4 and H2S decreased over past decade. Concentrations of Si and nitrite increased over past 15 years, probably linked to progressive replacement of diatoms by cyanobacteria. We also recorded an increase in concentration of Cl and major cations in all lakes, likely linked to increasing connection to groundwater reservoirs. Some trace elements (Fe, Mn, Al, Zn, As, Pb) can serve as suitable indicators of on-going natural processes controlling lake response to external factors. Unlike widely reported global trend of DOC and Fe concentration increase in boreal surface waters of Europe and Northern America, such trend was not discernable in studied Fe-rich humic lakes. We conclude on the necessity of complex, multidisciplinary studies of small humic lakes in the boreal zone, because these “model” lakes can serve as important proxies of on-going environmental changes in highly abundant aquatic ecosystems of poorly characterized regions of NW Russia.

Olivine is an important mineral that controls the sequestration of atmospheric CO2 in the form of secondary carbonate minerals during chemical and biological weathering of mafic rocks on Earth. Despite significant efforts in characterization of olivine reactivity and coupled secondary mineral precipitation both in abiotic and biotic systems, little is known on olivine behavior in the presence of bacterial consortia, which are the dominant forms of microbial life impacting mineral reactivity in natural settings. To address this gap, we studied the interaction of olivine with a bacterial consortium composed of typical freshwater cyanobacterium Synechococcus sp. and heterotrophic aerobic Pseudomonas reactans, isolated from a CO2 storage site in Icelandic basalts. We quantified the impact of this consortium on the dissolution rate of olivine and we characterized the precipitation of secondary mineral phases while monitoring various biological (number of cells, bacterial biomass) and physicochemical (pH, Si, Mg, Ca, alkalinity, dissolved organic and inorganic carbon) parameters of the medium over a period of ∼21 days. Heterotrophic bacteria and their organic exometabolites enhanced the release of Mg and Si and produced leaching features (etch pits) at the olivine surface whereas cyanobacterial photosynthesis raised the pH and favored precipitation of hydrous Mg carbonates and silicates in the vicinity of the cells. During microbially-induced transformation of aquatic carbon, the latter was sequestered in the form of cyanobacterial biomass (about 66%) and their soluble organic exometabolites (11%), and stored as secondary Mg carbonates (23%). Overall, the impact of bacterial consortium is higher than that of individual species and may represent important and understudied biotically-controlled mechanism of CO2 sequestration in natural waters.

Sphagnum moss, lichen and peat are widely present in arctic regions, covering millions of km² in permafrost-dominated regions. This multi-component low vegetation strata plays a key role in surfaces fluxes in these areas, as they are the most widespread interface between the atmosphere and the geosphere. Therefore, characterizing their transfer properties such as hydraulic and thermal conductivities is crucial for climate change impacts forecasting in arctic regions. In this work, 12 samples were collected in a discontinuous permafrost arctic area (Khanymey Research Station, Russian Federation) and dried to ensure their conservation. Collected samples have been digitally reconstructed by X-ray scanning. After having assessed morphological and hydraulic properties using numerical analysis of the obtained 3D digital tomographies (Cazaurang et al, submitted), we aim here at developing and using both experimental and numerical methodologies to characterize thermal properties of these samples of Sphagnum, lichen and peat. This new study consist in comparisons of numerically and experimentally estimated thermal properties for contributing to the existing knowledge on Sphagnum, lichen and peat transfer properties. Experiments consist of a steady-state thermal conductivity estimation using a hot plate source on real arctic vegetation cover samples. For this purpose, samples are placed in a confined thermal atmosphere and a constant heat flux is applied at sample base. Thermal conductivity is then retrieved with the resolution of Fourier’s heat conduction law. Similarly, numerical computations are conducted on the same digital reconstructions than those used for hydraulic properties determination. Simulations consist of a numerical reproduction of previously described experiments, allowing to strengthen the analysis of the experimental data. Additionally, the definition of representative elementary volumes of the studied samples is also undertaken using the numerical results.Compiling these assessments of transfer properties will represent essential information to simulate the dynamics of the permafrost underneath the arctic bryophytic layers with a devoted catchment-scale permafrost models. For instance in the framework of the HiPerBorea project (hiperborea.omp.eu), this approach will be used to forecast the impacts of climate warming on boreal permafrost-dominated catchments.

The fate of organic carbon (OC), nutrients and metals accumulated in thawing permafrost ice is at the forefront of environmental studies in the Arctic. In contrast to a fairly good understanding of the chemical nature of dissolved OC (DOC) and metals in surface Arctic waters, the speciation and colloidal status of solutes accommodated in the dispersed ground ice remain virtually unknown. Here we used a size fractionation procedure (centrifugal ultrafiltration) to quantify the proportion of colloidal (3 kDa to 0.45 μm) and conventionally dissolved low molecular weight (LMW

To better understand freezing - thawing cycles operating in peat soils of permafrost landscapes, we experimentally modelled bi-directional freezing and thawing of the three sections of 90-cm long peat core collected from a discontinuous permafrost zone in western Siberia. We measured translocation of microorganisms and changes in porewater chemistry (pH, UV absorbance, dissolved organic carbon (DOC), and major and trace element concentrations) after thawing and two-way freezing of peat cores. We demonstrate that bi-directional freezing and thawing of a peat core is capable of strongly modifying the vertical pattern of bacteria, DOC, nutrients, and trace element concentrations. Sizeable enrichment (a factor of 2 to 5) of DOC, macro- (P, K, Ca) and micro-nutrients (Ni, Mn, Co, Rb, B) and some low-mobile trace elements in several horizons of ice and peat porewater after freeze/thaw experiment may stem from physical disintegration of peat particles, leaching of peat constituents and opening of isolated (non-connected) pores during freezing front migration. However, due to the appearance of multiple maxima of element concentration after a freeze-thaw event, the use of peat ice chemical composition as environmental archive for paleo-reconstructions is unwarranted.

Bacterially-induced sequestration of atmospheric CO2 is at the forefront of geomicrobiological research due to high potential of this process in the mitigation of climate warming. Cyanobacteria have been known to form stromatolites since the Precambrian and could be used to enhance this process by sequestering carbon via the biomineralization of Mg and Ca carbonates. Currently, olivine (MgSiO4) is considered as one of the most efficient silicate minerals suitable for CO2 capture in the form of secondary Mg carbonates. However, the role of dissolved Si on the efficiency of biomineralization is not sufficiently well understood. The present study intended to reproduce in the laboratory the processes of biomineralization by Synechococcus sp. cyanobacteria extracted from modern stromatolites in a carbonate- and Mg-bearing medium containing various Si concentrations, in order to characterize the rates and stoichiometry of reactions as well as mineralogical nature of precipitates. The results demonstrated the dominant role of cyanobacterial metabolism in the precipitation of carbonate minerals by increasing the pH of the medium via photosynthesis and providing a template in the form of cell walls and their EPS for mineral nucleation. Transmission electron microscopy and other microscopic and spectroscopic observations and analyses identified magnesium carbonates and silicates, such as nesquehonite (MgCO3·3H2O) and/or hydromagnesite (Mg5(CO3)4(OH)2·4(H2O) together with amorphous analogue of sepiolite (Mg4Si6O15(OH)2·6H2O) as dominant precipitated minerals. Apparent inorganic C precipitation rates were not affected by the concentration of Mg and Si in the initial solution. However, the carbon sequestration potential was 20–40% higher in the presence of Si. Overall, the experimental approach developed in this study allows efficient reproduction of combined Mg hydroxy‑carbonate and hydrous silicate precipitation under cyanobacterial activity and helps to constrain optimal conditions of cyanobacteria-induced CO2 sequestration.

To better understand freezing - thawing cycles operating in peat soils of permafrost landscapes, we experimentally modelled bi-directional freezing and thawing of peat collected from a discontinuous permafrost zone in western Siberia. We measured translocation of microorganisms and changes in porewater chemistry (pH, UV absorbance, dissolved organic carbon (DOC), and major and trace element concentrations) after thawing and two-way freezing of the three sections of 90-cm-long peat core. We demonstrate that bi-directional freezing and thawing of a peat core is capable of strongly modifying the vertical pattern of bacteria, DOC, nutrients, and trace element concentrations. Sizeable enrichment (a factor of 2 to 5) of DOC, macro- (P, K, Ca) and micro-nutrients (Ni, Mn, Co, Rb, B), and some low-mobile trace elements in several horizons of ice and peat porewater after freeze/thaw experiment may stem from physical disintegration of peat particles, leaching of peat constituents, and opening of isolated (non-connected) pores during freezing front migration. However, due to the appearance of multiple maxima of element concentration after a freeze-thaw event, the use of peat ice chemical composition as environmental archive for paleo-reconstructions is unwarranted.

Shallow thaw (thermokarst) lakes abundant in regions of permafrost-affected peatlands represent important sources of carbon dioxide and methane emission to the atmosphere, however the quantitative parameters of phytoplankton communities which control the C cycle in these lakes remain poorly known. This is especially true considering the roles of permafrost, hydrochemical composition of lakes, lake sizes and season as major governing factors on phytoplankton abundance and biodiversity. In this work, we quantified phytoplankton characteristics of 27 thermokarst lakes (sizes ranging from 115 m2 to 1.24 km2) sampled in spring, summer and autumn across a permafrost gradient (isolated, sporadic, discontinuous and continuous zone) in the Western Siberia Lowland (WSL). The biodiversity indices were highest during all seasons in lakes of the continuous permafrost zone and rather similar in lakes of isolated, sporadic and discontinuous permafrost zone. Considering all seasons and permafrost zones, the biomass and cell number of phytoplankton correlated with Dissolved Organic Carbon (DOC), phosphate, and some metal micro-nutrients (Ni, Zn). The strongest correlations were observed for Cyanophycea during summer, with pH, Ni, Cu, Zn, Sr, Ba (cell number) and Cu, Zn, Ba (biomass), and during autumn, with DOC, K, Cr, Cu, Zn, Ba, Cd, Pb (biomass). Using a substituting space for time approach for climate warming and permafrost thaw and suggesting a shift in permafrost boundaries northward, we foresee an increase in cell number and biomass in continuous permafrost zone in spring and summer, and a decrease in phytoplankton abundance in the discontinuous and sporadic permafrost zones. The biodiversity of phytoplankton in the continuous permafrost zone might decrease whereas in other zones, it may not exhibit any sizably change. However, in case of strong deepening of the active layer down to underlaying mineral horizons, and the release of some limiting nutrients (Si, P) due to enhanced connectivity of the lake with groundwater, the share of cyanobacteria and diatoms may increase.

In contrast to fairly good knowledge of dissolved ( 0.45 µm) fluxes of carbon, nutrients and metals from the land to the ocean, colloidal (1 kDa−0.45 µm) forms of solutes are rarely quantified. This is especially true for Siberian rivers draining into the Arctic Ocean: because of organic-rich soils, colloidal fractions of elements are high and may sizably impact coastal biological processes. However, the main environmental parameters such as seasons, river size, climate, permafrost distribution and landscape parameters of the watershed controlling colloidal distribution of organic carbon (OC) and metals remain totally unknown. Here we used on-site centrifugation combined with ultrafiltration via 3, 30 and 100 kDa pore size membranes and 1 kDa dialysis to characterize colloidal size fractionation of OC and metals in 32 western Siberian rivers, ranging in size from 10 to 150,000 km2 watershed area, across a climate and permafrost gradient (from absent to continuous permafrost). The dominant forms of OC and metals was low molecular weight LMW

Detailed knowledge of the flood period of Arctic rivers remains one of the few factors impeding rigorous prediction of the effect of climate change on carbon and related element fluxes from the lan ...

Organic carbon (OC), iron (Fe), metal, and phosphorus (P) are key aquatic components that largely determine the biotic and abiotic functioning of freshwater systems, including groundwater, soil water, lakes, rivers, and their estuaries [...]

Permafrost thaw in continental lowlands produces large number of thermokarst (thaw) lakes, which act as a major regulator of carbon (C) storage in sediments and C emission in the atmosphere. Here we studied thaw lakes of the NE European permafrost peatlands - shallow water bodies located within frozen peat bogs and receiving the majority of their water input from lateral (surface) runoff. We also conducted mesocosm experiments via interacting lake waters with frozen peat and dominant ground vegetation - lichen and moss. There was a systematic decrease in concentrations of dissolved C, CO2, nutrients and metals with an increase in lake size, corresponding to temporal evolution of the water body and thermokarst development. We hypothesized that ground vegetation and frozen peat provide the majority of C, nutrients and inorganic solutes in the water column of these lakes, and that microbial processing of terrestrial organic matter controls the pattern of CO2 and nutrient concentrations in thermokarst lakes. Substrate mass-normalized C, nutrient (N, P, K), major and trace metal release was maximal in moss mesocosms. After first 16 h of reaction, the pCO2 increased ten-fold in mesocosms with moss and lichen; this increase was much less pronounced in experiments with permafrost peat. Overall, moss and lichen were the dominant factors controlling the enrichment of the lake water in organic C, nutrients, and trace metals and rising the CO2 concentration. The global significance of obtained results is that the changes in ground vegetation, rather than mere frozen peat thawing, may exert the primary control on C, major and trace element balance in aquatic ecosystems of tundra peatlands under climate warming scenario.

In order to foresee possible changes in the elementary composition of Arctic river waters, complex studies with extensive spatial coverage, including gradients in climate and landscape parameters, are needed. Here, we used the unique position of the Ob River, draining through the vast partially frozen peatlands of the western Siberia Lowland and encompassing a sizable gradient of climate, permafrost, vegetation, soils and Quaternary deposits, to assess a snap-shot (8–23 July 2016) concentration of all major and trace elements in the main stem (~3000 km transect from the Tom River confluence in the south to Salekhard in the north) and its 11 tributaries. During the studied period, corresponding to the end of the spring flood-summer baseflow, there was a systematic decrease, from the south to the north, of Dissolved Inorganic Carbon (DIC), Specific Conductivity, Ca and some labile trace elements (Mo, W and U). In contrast, Dissolved Organic Carbon (DOC), Fe, P, divalent metals (Mn, Ni, Cu, Co and Pb) and low mobile trace elements (Y, Nb, REEs, Ti, Zr, Hf and Th) sizably increased their concentration northward. The observed latitudinal pattern in element concentrations can be explained by progressive disconnection of groundwaters from the main river and its tributaries due to a northward increase in the permafrost coverage. A northward increase in bog versus forest coverage and an increase in DOC and Fe export enhanced the mobilization of insoluble, low mobile elements which were present in organo-ferric colloids (1 kDa—0.45 µm), as confirmed by an in-situ dialysis size fractionation procedure. The chemical composition of the sampled mainstream and tributaries demonstrated significant (p &lt, 0.01) control of latitude of the sampling point, permafrost coverage, proportion of bogs, lakes and floodplain coverage and lacustrine and fluvio-glacial Quaternary deposits of the watershed. This impact was mostly pronounced on DOC, Fe, P, divalent metals (Mn, Co, Ni, Cu and Pb), Rb and low mobile lithogenic trace elements (Al, Ti, Cr, Y, Zr, Nb, REEs, Hf and Th). The pH and concentrations of soluble, highly mobile elements (DIC, SO4, Ca, Sr, Ba, Mo, Sb, W and U) positively correlated with the proportion of forest, loesses, eluvial, eolian, and fluvial Quaternary deposits on the watershed. Consistent with these correlations, a Principal Component Analysis demonstrated two main factors explaining the variability of major and trace element concentration in the Ob River main stem and tributaries. The DOC, Fe, divalent metals and trivalent and tetravalent trace elements were presumably controlled by a northward increase in permafrost, floodplain, bogs, lakes and lacustrine deposits on the watersheds. The DIC and labile alkaline-earth metals, oxyanions (Mo, Sb and W) and U were impacted by southward-dominating forest coverage, loesses and eluvial and fertile soils. Assuming that climate warming in the WSL will lead to a northward shift of the forest and permafrost boundaries, a “substituting space for time” approach predicts a future increase in the concentration of DIC and labile major and trace elements and a decrease of the transport of DOC and low soluble trace metals in the form of colloids in the main stem of the Ob River. Overall, seasonally-resolved transect studies of large riverine systems of western Siberia are needed to assess the hydrochemical response of this environmentally-important territory to on-going climate change.

International audience; Despite the importance of soil and surface waters freezing in permafrost landscapes, the behaviour of dissolved organic carbon (DOC), nutrients and metals during periodic freezethaw cycles (FTC) remains poorly known. The ongoing climate warming is likely to increase the frequency of FTC in continental aquatic settings, which could modify the chemical composition of waters. In this study, we conducted 9 repetitive cycles of overnight freezing (-20 °C) and 5 hours thawing (4°C) in the laboratory using representative 0.22 µm-filtered waters from NE European permafrost peatland: leachates of vegetation and soil, and natural surface waters (depression, thermokarst lake and river). Only minor (< 5%-15%) changes of DOC concentrations, SUVA254 and molecular weight were observed in all leachates and the depression water. In contrast, several trace elements (Fe, Al, P, Mn, As, and REE) exhibited sizable variations during FTC (> 10%). The leachates and the depression water were enriched in trace elements, whereas the thermokarst lake and the river demonstrated a decrease in concentration of Fe (-39 and-94 %, respectively), Al (-9 and-85 %), and Mn (-10 and-79 %) during FTC. Overall, the observations demonstrated an increase in aliphatic low molecular weight organic matter (OM), and the precipitation of Fe, Al hydroxides and organo-mineral particles. Therefore, enhanced of frequency of FTC can favour the release of metals and toxicants from acidic OM-rich surface waters and maintain stable OM-metals-colloids in large lakes and rivers, thus regulating aquatic transport of DOC and metals from soils to the Arctic Ocean.

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.

Emission of greenhouse gases (GHGs) from inland waters is recognized as highly important and an understudied part of the terrestrial carbon (C) biogeochemical cycle. These emissions are still poorly quantified in subarctic regions that contain vast amounts of surface C in permafrost peatlands. This is especially true in NE European peatlands, located within sporadic to discontinuous permafrost zones which are highly vulnerable to thaw. Initial measurements of C emissions from lentic waters of the Bolshezemelskaya Tundra (BZT; 200,000 km2) demonstrated sizable CO2 and CH4 concentrations and fluxes to the atmosphere in 98 depressions, thaw ponds, and thermokarst lakes ranging from 0.5 × 106 to 5 × 106 m2 in size. CO2 fluxes decreased by an order of magnitude as waterbody size increased by > 3 orders of magnitude while CH4 fluxes showed large variability unrelated to lake size. By using a combination of Landsat‐8 and GeoEye‐1 images, we determined lakes cover 4% of BZT and thus calculated overall C emissions from lentic waters to be 3.8 ± 0.65 Tg C yr−1 (99% C‐CO2, 1% C‐CH4), which is two times higher than the lateral riverine export. Large lakes dominated GHG emissions whereas small thaw ponds had a minor contribution to overall water surface area and GHG emissions. These data suggest that, if permafrost thaw in NE Europe results in disappearance of large thermokarst lakes and formation of new small thaw ponds and depressions, GHG emissions from lentic waters in this region may decrease.

Arctic regions contain large amounts of organic carbon (OC) trapped in soil and wetland permafrost. With climate warming, part of this OC is released to aquatic systems and degraded by microorganisms, thus resulting in positive feedback due to carbon (C) emission. In wetland areas, water bodies are spatially heterogenic and separated by landscape position and water residence time. This represents a hydrological continuum, from depressions, smaller water bodies and lakes to the receiving streams and rivers. Yet, the effect of this heterogeneity on the OC release from the soil and its processing in waters is largely unknown and not accounted for in C cycle models of Arctic regions. Here we investigated the dissolved OC (DOC) biodegradation of aquatic systems along a hydrological continuum located in two discontinuous permafrost sites: in western Siberia and northern Sweden. The biodegradable dissolved OC (BDOC15; % DOC lost relative to the initial DOC concentration after 15 days incubation at 20 °C) ranged from 0 to 20% for small water bodies located at the beginning of the continuum (soil solutions, small ponds, fen and lakes) and from 10 to 20% for streams and rivers. While the BDOC15 increased, the removal rate of DOC decreased along the hydrological continuum. The potential maximum CO2 production from DOC biodegradation was estimated to account for only a small part of in-situ CO2 emissions measured in peatland aquatic systems of northern Sweden and western Siberia. This suggests that other sources, such as sediment respiration and soil input, largely contribute to CO2 emissions from small surface waters of permafrost peatlands. Our results highlight the need to account for large heterogeneity of dissolved OC concentration and biodegradability in order to quantify C cycling in arctic water bodies susceptible to permafrost thaw.

The physical and chemical consequences of massive ground ice (wedges) melt upon permafrost thaw is one of the central issues of environmental research linked to climate warming in the Arctic. Little is known about the chemical properties of dispersed ground ice abundant throughout permafrost peatlands that can easily melt with increasing active layer thickness (ALT). This is especially pertinent in continental lowlands, that account for sizeable areas of the Arctic, and contain high amount of organic carbon in both solid (peat) and liquid (porewater) phases. Here we studied 8 peat cores (0–130 cm depth)—comprised of porewater from the active layer (0–45 cm) as well as ice dispersed in frozen peat (40–130 cm)—across a latitudinal profile of Western Siberia Lowland (WSL) extending from discontinuous into continuous permafrost zones. Dissolved Organic Carbon (DOC), alkali and alkaline-earth metals (Ca, Mg, Sr, Ba, Li, Rb, Cs), sulfate, phosphorus, some trace elements (Al, Fe, Mn, Zn, Ni, Co, V, As, Y, REE, Zr, Hf, U) were sizably [more than 3 times] enriched in peat ice compared to peat porewaters from the active layer. In most sampled cores, there was a local maximum of strong enrichment (up to factors between 14 and 58) in DOC, P, Ca, Mg, Mn, Fe, Sr, As located 30–50 cm below the active layer. This maximum likely occurred due to solute concentration during full freezing of the soil column during winter. There was a sizable correlation between DOC, Al, Fe and other major and trace element concentrations that suggests strong control of organic complexes and organo-mineral (Al, Fe) colloids on element migration throughout the peat profile. The pool of C, major cations and trace metals in peat ice (40–130 cm) was approximately 3–55 times higher than the pool of these elements in porewaters from the active layer (0–40 cm). A 1-m increase of the ALT over the next 100 years is capable of mobilizing 58 ± 38 Tg of DOC from soil ice into the rivers and lakes of the WSL latitudinal belt (63–67 °N). This fast lateral export of C (3.7 ± 2.7 t C km−2 y−1) may double current C yields in WSL rivers (3.4 ± 1.3 t C km−2 y−1). A strong increase (150–200%) in riverine export of Zn, P and Cs may also occur while other micronutrients (Fe, Ni, Co, Ba, Mo, Rb) and toxicants (Cd, As, Al) may be affected to a lesser degree (20–30% increase). We propose a global peat ice inventory in permafrost regions is essential for assessing the consequences of permafrost thaw on surface aquatic systems.

Thermokarst lakes and ponds formed due to thawing of frozen peat in high-latitude lowlands are very dynamic and environmentally important aquatic systems that play a key role in controlling C emission to atmosphere and organic carbon (OC), nutrient, and metal lateral export to rivers and streams. However, despite the importance of thermokarst lakes in assessing biogeochemical functioning of permafrost peatlands in response to climate warming and permafrost thaw, spatial (lake size, permafrost zone) and temporal (seasonal) variations in thermokarst lake hydrochemistry remain very poorly studied. Here, we used unprecedented spatial coverage (isolated, sporadic, discontinuous, and continuous permafrost zone of the western Siberia Lowland) of 67 lakes ranging in size from 102 to 105 m&sup2, for sampling during three main hydrological periods of the year: spring flood, summer baseflow, and autumn time before ice-on. We demonstrate a systematic, all-season decrease in the concentration of dissolved OC (DOC) and an increase in SO4, N-NO3, and some metal (Mn, Co, Cu, Mo, Sr, U, Sb) concentration with an increase in lake surface area, depending on the type of the permafrost zone. These features are interpreted as a combination of (i) OC and organically bound metal leaching from peat at the lake shore, via abrasion and delivery of these compounds by suprapermafrost flow, and (ii) deep groundwater feeding of large lakes (especially visible in the continuous permafrost zone). Analyses of lake water chemical composition across the permafrost gradient allowed a first-order empirical prediction of lake hydrochemical changes in the case of climate warming and permafrost thaw, employing a substituting space for time scenario. The permafrost boundary shift northward may decrease the concentrations and pools of dissolved inorganic carbon (DIC), Li, B, Mg, K, Ca, Sr, Ba, Ni, Cu, As, Rb, Mo, Sr, Y, Zr, rare Earth elements (REEs), Th, and U by a factor of 2&ndash, 5 in the continuous permafrost zone, but increase the concentrations of CH4, DOC, NH4, Cd, Sb, and Pb by a factor of 2&ndash, 3. In contrast, the shift of the sporadic to isolated zone may produce a 2&ndash, 5-fold decrease in CH4, DOC, NH4, Al, P, Ti, Cr, Ni, Ga, Zr, Nb, Cs, REEs, Hf, Th, and U. The exact magnitude of this response will, however, be strongly seasonally dependent, with the largest effects observable during baseflow seasons.

The assessment of riverine fluxes of carbon, nutrients, and metals in surface waters of permafrost-affected regions is crucially important for constraining adequate models of ecosystem functioning under various climate change scenarios. In this regard, the largest permafrost peatland territory on the Earth, the Western Siberian Lowland (WSL) presents a unique opportunity of studying possible future changes in biogeochemical cycles because it lies within a south&ndash, north gradient of climate, vegetation, and permafrost that ranges from the permafrost-free boreal to the Arctic tundra with continuous permafrost at otherwise similar relief and bedrocks. By applying a &ldquo, substituting space for time&rdquo, scenario, the WSL south-north gradient may serve as a model for future changes due to permafrost boundary shift and climate warming. Here we measured export fluxes (yields) of dissolved organic carbon (DOC), major cations, macro- and micro- nutrients, and trace elements in 32 rivers, draining the WSL across a latitudinal transect from the permafrost-free to the continuous permafrost zone. We aimed at quantifying the impact of climate warming (water temperature rise and permafrost boundary shift) on DOC, nutrient and metal in rivers using a &ldquo, approach. We demonstrate that, contrary to common expectations, the climate warming and permafrost thaw in the WSL will likely decrease the riverine export of organic C and many elements. Based on the latitudinal pattern of riverine export, in the case of a northward shift in the permafrost zones, the DOC, P, N, Si, Fe, divalent heavy metals, trivalent and tetravalent hydrolysates are likely to decrease the yields by a factor of 2&ndash, 5. The DIC, Ca, SO4, Sr, Ba, Mo, and U are likely to increase their yields by a factor of 2&ndash, 3. Moreover, B, Li, K, Rb, Cs, N-NO3, Mg, Zn, As, Sb, Rb, and Cs may be weakly affected by the permafrost boundary migration (change of yield by a factor of 1.5 to 2.0). We conclude that modeling of C and element cycle in the Arctic and subarctic should be region-specific and that neglecting huge areas of permafrost peatlands might produce sizeable bias in our predictions of climate change impact.

Understanding the conditions of dissolved organic matter (DOM) release from thawing peat in the Arctic regions and identifying the pathways of processing DOM by soil and aquatic heterotrophic bacteria are critical in the context of rapid climate change. Until now, experimental approaches did not allow quantitative predictions of temperature and biota effects on carbon release from peat in permafrost-affected aquatic environments. In this study, we incubated frozen peat and its aqueous leachate at various temperatures (4, 25 or 45 degrees C), with and without culturable heterotrophic bacteria Iodobacter sp., extracted from thermokarst lakes, to quantify the release and the removal rate of organic carbon (OC) with time. The metabolic diversity of the native microbial community associated with the substrates involved in OC processing was also characterized. Transmission electron microscopy revealed that, after degradation, the associated bacteria are mostly located in the inner parts of plant cells, and that the degradation of organic matter around bacteria is more pronounced at 4 and 25 degrees C compared to 45 degrees C. The metabolic diversity of heterotrophic bacteria was equally high at 4 and 25 degrees C, but lower at 45 degrees C. Regardless of the microbial consortium (native community alone or with added culturable heterotrophs), both the OC release from peat and the OC removal from peat leachate by bacteria were similar at 4 and 25 degrees C. Very low apparent activation energies of DOM biodegradation between 4 and 25 degrees C (- 4.23 +/- 12.3 kJ mol(-1)) suggest that the short-period of surface water warming in summer would have an insignificant effect on DOM microbial processing. Such duration (1-3 weeks) is comparable with the water residence time in peat depressions and permafrost subsidences, where peat degradation and DOM microbial processing occur. This questions the current paradigm of a drastic effect of temperature rise on organic carbon release from frozen peatlands, and should be considered for modelling short-term climate impacts in these regions.

The fate of the vast stocks of organic carbon stored in permafrost of the Western Siberian Lowland, the world's largest peat-land, is uncertain. Specifically, the amount of greenhouse gas emissions ...

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.

Photo-induced degradation of dissolved organic matter (DOM) and organo-mineral colloids is one of the major factor responsible for transformation of DOM and dissolved metals in boreal and subarctic waters. In contrast to fairly good understanding of this process in inland waters of high latitude zone, the transformation of riverine DOM and associated trace element (TE) colloids in the Arctic estuaries remains virtually unknown. We incubated, under sunlight in outdoor pools, quartz reactors filled with mixtures of sterile filtered riverine and estuarine water. The water samples were collected in the estuarine zone of the largest European Arctic river, Severnaya Dvina. After 1 month of exposure to sunlight, ≤ 5% change of dissolved organic carbon (DOC) concentration and specific ultraviolet (254 nm) absorption occurred. This decrease was within the experimental uncertainty and it implies quite high resistance of river dissolved organic matter to photo-degradation in this estuary. Moreover, very low photodegradability of DOM in the freshwater point of the Severnaya Dvina River may require revisiting the current paradigm of the importance of DOC photolysis in large Arctic rivers. A novel finding was that the percentages of overall removal of Fe and some insoluble elements were quite similar across the full range of studied salinities, whereas the apparent rate of metal removal decreased with the increase of salinity. Overall, the salinity weakly impacted the removal of riverine DOC and metals in the estuarine water via photolysis and coagulation under sunlight. As a result, photoreactivity of DOM and dissolved metals in riverine end members corrected for estuarine dilution can be used to approximate the photolytic transformation of riverine material in the Arctic coastal zone.

The heterotrophic mineralization of dissolved organic matter (DOM) controls the CO2 flux from the inland waters to the atmosphere, especially in the boreal waters, although the mechanisms of this process and the fate of trace metals associated with DOM remain poorly understood. We studied the interaction of culturable aquatic (Pseudomonas saponiphila) and soil (Pseudomonas aureofaciens) Gammaproteobacteria with seven different organic substrates collected in subarctic settings. These included peat leachate, pine crown throughfall, fen, humic lake, stream, river, and oligotrophic lake with variable dissolved organic carbon (DOC) concentrations (from 4 to 60mgL-1). The highest removal of DOC over 4days of reaction was observed in the presence of P. aureofaciens (33±5%, 43±3% and 53±7% of the initial amount in fen water, humic lake and stream, respectively). P. saponiphila degraded only 5% of DOC in fen water but did not affect all other substrates. Trace elements (TE) were essentially controlled by short-term (0-1h) adsorption on the surface of cells. Regardless of the nature of organic substrate and the identity of bacteria, the degree of adsorption ranged from 20 to 60% for iron (Fe3+), 15 to 55% for aluminum (Al), 10 to 60% for manganese (Mn), 10 to 70% for nickel (Ni), 20 to 70% for copper (Cu), 10 to 60% for yttrium (Y), 30 to 80% for rare earth elements (REE), and 15 to 50% for uranium (UVI). Rapid adsorption of organic and organo-mineral colloids on bacterial cell surfaces is novel and potentially important process, which deserves special investigation. The long-term removal of dissolved Fe and Al was generally consistent with solution supersaturation degree with respect to Fe and Al hydroxides, calculated by visual Minteq model. Overall, the biomass-normalized biodegradability of various allochthonous substrates by culturable bacteria is much lower than that of boreal DOM by natural microbial consortia.

In the boreal and subarctic zone, the moss and peat interactions with rainwater and snowmelt water in shallow surface ponds control the delivery of dissolved organic matter (DOM) and metal to the rivers and further to the Arctic Ocean. The transformation of peat and moss leachate by common aquatic microorganisms and the effect of temperature on DOM mineralization by heterotrophs remain poorly known that does not allow predicting the response of boreal aquatic system to ongoing climate change. We used experimental approach to quantify the impact of boreal aquatic bacteria P. reactans, and two culturable bacteria extracted from a thaw lake of the permafrost zone (Bolshezemelskaya tundra, NE Europe): Iodobacter sp. and cyanobacterial associate dominated by order Chroococcales (Synechococcus sp). The interaction of these bacterial cultures with nutrient-free peat and moss leachate was performed in order to (1) quantify the impact of temperature (4, 25 and 45 °C) on peat leachate processing by heterotrophs; (2) compare the effect of heterotrophic bacteria and cyanobacterial associate on moss and peat leachate chemical composition, and (3) quantify the DOC and metal concentration change during cyanobacterial growth on leachate from frozen and thawed peat horizon and moss biomass. The efficiency of peat DOM processing by two heterotrophs was not modified by temperature rise from 4 to 45 °C. The DOC concentration decreased by a factor of 1.6 during 3 days of moss leachate reaction with Iodobacters sp. or cyanobacterial associate at 25 °C. The SUVA245 increased twofold suggesting an uptake of non-aromatic DOM by both microorganisms. The growth of cyanobacteria was absent on peat leachate but highly pronounced on moss leachate. This growth produced tenfold decrease in P concentration, a factor of 1.5–2.0 decrease in DOC, a factor of 4 and 100 decrease in Fe and Mn concentration, respectively. Adsorption of organic and organo-mineral colloids on bacterial cell surface was more important factor of element removal from organic leachates compared to intracellular assimilation and/or Fe oxyhydroxide precipitation. Overall, we demonstrate highly conservative behavior of peat leachate compared to moss leachate in the presence of culturable aquatic bacteria, a lack of any impact of heterotrophs on peat leachate and their weak impact on moss leachate. A very weak temperature impact on DOM processing by heterotrophs and lack of difference in the biodegradability of DOM from thawed and frozen peat horizons contradict the current paradigm that the warming of frozen OM and its leaching to inland waters will greatly affect microbial production and C cycle. Strong decrease in concentration of P, Fe and Mn in the moss leachate in the presence of cyanobacterial associate has straightforward application for understanding the development of thermokarst lakes and suggests that, in addition to P, Fe and Mn may become limiting micronutrients for phytoplankton bloom in thermokarst lakes.

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 relationship between dissolved organic matter (DOM) and heterotrophic bacterioplankton controls the ecological status of freshwater ecosystems and the fate of metals in aquatic environments. To improve our understanding of physicochemical and biological processes controlling the DOC and related trace elements in the Arctic estuary, we conducted experiments of the biodegradation and physicochemical coagulation of DOM and associated trace elements. For the experiments, water from the estuarine zone of the Severnaya Dvina River in Russia, the largest pristine European Arctic river, was mixed with sterile river water from the freshwater zone, sampled during spring flood in June and summer base flow in August. We revealed a lack of transformation of allochthonous organic matter in spring and measurable degradation of more autochthonous DOM in summer. According to their behavior during incubation experiments, several groups of trace metals were distinguished, comprising (1) nonconservative Fe, Mn, A...

Bacterial mineralization of allochthonous (soil) dissolved organic matter (DOM) in boreal waters governs the CO 2 flux from the lakes and rivers to the atmosphere, which is one of the main factor of carbon balance in high latitudes. However, the fate of colloidal trace element (TE) during bacterial processing of DOM remains poorly constrained. We separated monoculture of Pseudomonas saponiphila from a boreal creek and allowed it to react with boreal Fe-rich peat leachate of approximate colloidal (3 kDa–0.45 µm) composition C 1000 Fe 12 Al 3.3 Mg 2 Ca 3.7 P 1.2 Mn 0.1 Ba 0.5 in nutrient-free media. The total net decrease of Dissolved Organic Carbon (DOC) concentration over 4 day of exposure was within 5% of the initial value, whereas the low molecular weight fraction of C org (LMW kDa ) yielded a 16%-decrease due to long-term bio-uptake or coagulation. There was a relative depletion in Fe over C org of 0.45 µm, colloidal and LMW fraction in the course of peat leachate interaction with P. saponiphila . Al, Mn, Ni, Cu, Ga, REEs, Y, U were mostly affected by bacterial presence and exhibited essentially the adsorption at the cell surface over first hours of reaction, in contrast to Fe, Ti, Zr, and Nb that showed both short-term adsorption and long-term removal by physical coagulation/coprecipitation with Fe hydroxide. The low molecular weight fraction (LMW kDa ) of most TE was a factor of 2–5 less affected by microbial presence via adsorption or removal than the high molecular weight (HMW) colloidal fractions (

In Arctic regions, water bodies are hot spots of dissolved organic carbon (DOC) biodegradation, and their well-known large heterogeneity in the permafrost affected area could lead to a misrepresentation of their importance in the carbon (C) cycle. In this study, the biodegradation potential of various water bodies from two hydrological continuums has been assessed via 15 days aerobic incubation of waters. Results show that biodegradability of waters increases along the continuum while the removal rate of DOC decreases as the consequence of a preferential biodegradation of low molecular weight organic acids (LMWOA). This preferential uptake leads to a relative accumulation of aromatic compounds in the end-members of the continuum. This suggests a shift in the dominantly used pools of DOC along the continuum: a rapidly consumed DOC pool at the beginning of the continuum and a more slowly consumed one at the end of the continuum.