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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.

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 (

A land cover map of two arctic catchments, nearby the Abisko Scientific Research Station, was obtained from a classification of a Sentinel-2 satellite image and a ground survey performed in July 2022. The two contiguous catchments, Miellajokka and Stordalen, are covered by various ecotypes, from boreal forest to alpine tundra and peatland. The Random Forest algorithm correctly identified 83% of polygon pixels reserved for testing. The developed workflow relied solely on open source software and acquired ground observations. Space organization was directed by the altitude as shown by the intersection of the land cover with the topography. Comparison between this new land cover map and previous ones based on data acquired between 2008 and 2011 demonstrates some trends of vegetation cover evolution in response to climate change in the considered area. The potential applications in terms of permafrost modeling (hiperborea.omp.eu) are finally discussed.

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.

Despite the importance of river suspended matter (RSM) for carbon, nutrient, and trace metal transfer from the land to the ocean, the mineralogical control on major and trace element speciation in the RSM remains poorly constrained. To gain a better understanding of environmental and seasonal factors controlling the mineral and chemical composition of riverine suspended load, we studied, over several hydrological seasons, including winter baseflow, the RSM of a large boreal river in Western Siberia (Ob in its middle course) and its two small tributaries. The concentration of RSM increased from 2–18 mg/L in winter to 15–105 mg L−1 during the spring flood. Among the dominant mineral phases of the RSM in the Ob River, quartz (20–40%), albite (4–18%), smectite (2–14%), and chlorite (6–16%) increased their relative proportions with an increase in discharge in the order “winter ≤ summer < spring flood”; illite (5–15%) was not affected by seasons or discharge, whereas the abundance of calcite (0–30%) decreased with discharge, from winter to summer and spring. Seasonal variation of elemental composition of the Ob River’s RSM allowed distinguishing three main groups of elements. Sodium, K, Si, Al, trivalent, and tetravalent hydrolysates increased their concentrations in the RSM with an increase in discharge, reflecting enhanced contribution of lithogenic material during high flow, whereas the concentration of alkaline-earth metals (Ca, Sr, Ba), P, Mn, and As decreased with discharge, reflecting accumulation of these elements in the suspended matter under ice. At the same time, a number of nutrients and trace elements demonstrated progressive accumulation in the RSM during winter (Ca, P, Cu, Zn, Mo, As, Cd, Sb). Micronutrients (V, Co), Fe, and Cr exhibited a minimum during summer, which could reflect both the uptake of these elements by the biota during baseflow (micronutrients) and their enhanced export during winter and spring compared to summer (Fe). The RSM of small tributaries demonstrated quite a different pattern compared to the Ob River main stem. Maximal concentration of suspended matter was observed at low discharges during the winter. During this period, the RSM was dominated by amorphous Fe hydroxides. Overall, the obtained results confirm the overwhelming impact of peatlands on element export in suspended form in small rivers of Western Siberia, and strong seasonal variations of both mineralogy and chemistry of the RSM in the Ob River main stem. Elemental yields (watershed-normalized export), assessed for the first time for the middle course of the Ob River and tributaries, were shifted towards the more important role of particulate vs. dissolved export for a number of trace elements, compared to that of the small and medium-sized rivers of Western Siberia, draining the taiga forest and peatlands of the boreal zone. The contrasting pattern of RSM chemical composition across the year demonstrated the importance of seasonal approach for sampling river suspended matter and calls a need for addressing strongly understudied RSM sources during winter baseflow, under ice.

Riverine particulates dominate the transport of vital nutrients such as Si, Fe or P to the ocean margins, where they may increase primary production by acting as slow-release fertilizer. Furthermore, the supply of particulate surface area to the ocean is considered to be a major control of organic carbon burial. Taken together, these observations suggest a close link between the supply of riverine particulate material and the organic carbon cycle. To explore this link, we conducted microcosm experiments to measure the growth of the marine diatom Thalassiosira weissflogii in the presence and absence of different types and concentrations of riverine particulate material. Results demonstrate a strong positive effect of riverine particulate material on diatom growth with increased total diatom concentrations and slowed post-exponential death rates with increasing particulate concentration. Moreover, SEM and optical microscope investigations confirm that riverine particulates facilitate organic carbon burial through their role in the aggregation and sedimentation of phytoplankton. The supply of riverine particulate material has been shown to be markedly climate sensitive with their fluxes increasing dramatically with increasing global temperature and runoff. This pronounced climate sensitivity implies that riverine particulates contribute substantially in regulating atmospheric CO2 concentrations through their role in the organic carbon cycle.

—: Experiments on modeling the phase fractionation of trace elements (Mn, Co, Ni, Cu, Zn, Cd, Pb, Tl, Ga, Y, REE, V, As, Sb, and U) at interaction between acidic volcanic waters with seawater, accompanied by the sequential precipitation of Fe and Al hydroxides, show that the coprecipitation efficiency of various trace elements with Fe and Al hydroxides differs. The most dramatic differences were found for Ga and REE: Ga is predominantly accommodated by Fe hydroxide, whereas REE are bound mostly to Al hydroxide. It was established that, in addition to pH value, the degree of coprecipitation of trace elements also depends on the relative volume fraction of seawater, with its increase likely leading a shift in the adsorption equilibrium and, as a consequence, to a change in the coprecipitation efficiency of trace elements.

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.

The bivalve genus Galatea Bruguière, 1797 (Venerida: Donacidae) was thought to contain exclusively brackish-water clams, the ranges of which are confined to estuaries and lower tidal parts of large rivers in West Africa. This genus was therefore included to the global freshwater bivalve checklists (Bogan 2013; Graf 2013) as a largely estuarine group. Conversely, a review of published data alongside our field surveys indicate that at least three populations of Galatea spp. largely occur in freshwater environment, i.e. those from the Sanaga (Cameroon), Niger (Nigeria), and Volta (Ghana) rivers. The systematic placement of these populations is unclear, as are the taxonomic status and validity of numerous nominal taxa described in this genus from a variety of localities throughout the Atlantic Coast of Africa (Angola to Senegal). We tentatively assign the populations from Niger and Volta to Galatea paradoxa (Born, 1778), while the Sanaga’s population is considered here as Galatea schwabi (Clench, 1929). However, these taxa do not share clear morphological differences and may belong to a single widespread species. In this study, we present the first DNA sequence data for a Galatea member, i.e. G. schwabi. Our COI phylogeny supports its placement within the family Donacidae suggesting sister relationships between Galatea and Donax Linnaeus, 1758. Most Galatea populations play a vital role for local riparian communities in West Africa as an intensively exploited food source. Furthermore, the clams are heavily threaten by anthropogenic impacts such as dam construction, riverbed substrate mining, and river pollution. The fishing loads and habitat degradation altogether lead to the rapid decreasing of Galatea populations in several water bodies, e.g. the Volta River in Ghana. It is impossible to develop conservation and management plans for these clams due to the lack of reliable species-level taxonomic concept of the genus. It is clear that the Galatea taxonomy and ecology need a thorough revision in the future based on DNA sequences of newly collected samples from all West African rivers, in which these remarkable clams occur.

The distribution of dissolved major- and trace elements in the mixing zone of the Ural River and the North Caspian waters was studied based on the natural observations data from 2016–2017. Conservative behavior was established for most of major ions (Na, K, Mg, SO4) and some trace elements (Li, Rb, Cs, Sr, Co, Ni, Cu, Zn, Sb, Ga, Y, U, B, F, Cr, Ge, Mo, W) with common parameters of relationships between their concentrations and chloride content for different years. The distribution of components of the carbonate system is controlled by chemogenic precipitation of calcium carbonate at the mouth beach. This process leads to the removal from solution up to 11–17% calcium and 6–8% hydrocarbonates carried by river runoff, and a simultaneous decrease in the pH value. Nutrients are involved in the processes of biological assimilation and regeneration. The mixing zone of the Ural River and Caspian waters is characterized by: (a) phytoplankton consumption of large amounts of silicon and nitrates (up to 58–88 and 61–67%, respectively, of their content in riverine waters), (b) removal of significant part (up to 18–25%) of nitrites, and (c) additional input of phosphates into solution, presumably from pore waters of the surface layer of bottom sediments in amounts 1.5–3 times greater than those removed with river runoff. A distinctive feature of barium migration is an additional input into solution (up to 20%) at the initial stage of salinization owing to the desorption from terrigenous material. The coagulation and flocculation of organic and organo-mineral colloids lead to the removal of significant part (up to 25–100%) of dissolved manganese, iron, aluminum, and rare-earth elements runoff, as well as to the removal of lead, titanium, zirconium, and hafnium from solution in amounts 1.1–6 times greater than their contents in the river water mass.

The concentrations of macrocomponents (Na, K, Mg, Ca, and P) and trace elements (Rb, Cs, Be, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Pb, Cd, Ag, Sn, Sb, Al, Ga, rare earth elements, Ti, Zr, Hf, Th, U, Nb, Ta, B, V, Cr, Ge, As, Mo, and W) were measured in 12 macrophyte species selected in the freshwater part of the Volga mouth area. Close correlations between the average specific contents were established: (a) most of the studied trace elements, which confirms the phenomenon of group concentration found earlier for heavy metals and chromium; (b) magnesium, calcium, and trace elements capable of their isomorphic substitution; (c) the typically biogenic elements potassium and phosphorus. A regular increase in the concentrations of trace elements and, to a lesser extent, of magnesium and calcium was found in the series “helophytes → large-leaved hydrophytes → variegate-leaved hydrophytes → small-leaved hydrophytes, including hydrophytes completely immersed in water,” which corresponds to an increase in the effective surface area of plants in the aquatic environment.

According to experimental modeling data, the quantitative characteristics of macro and trace elements phase fractionation in the process of ice formation from fresh surface waters were obtained. Significant variations in the values of the integral distribution coefficient were established, apparently due to processes not associated with the entering of elements into the ice crystal lattice. It was suggested that such processes may include ice adhesive uptake of suspended and colloidal particles, sorption of organic and inorganic components on the surface of growing ice, formation of chemogenic solid phases at the water–ice boundary, and flocculation and coagulation of colloids near the boundary between the liquid and solid phases.

—The contents of ions of basic salt composition (Na+, K+, Mg2+, Ca2+, $${\text{C}}{{{\text{l}}}^{ - }}{\text{,}}$$$${\text{SO}}_{{\text{4}}}^{{{\text{2}} - }}{\text{,}}$$$${\text{HCO}}_{{\text{3}}}^{ - }$$), dissolved nutrients (Si, P), and trace elements (Li, Rb, Cs, Sr, Ba, B, V, Ge, As, Mo, Mn, Fe, Co, Cu, Zn, Cd, Sb, Tl, Pb, Al, Ga, Ti, Zr, Hf, U, Y, REE) were determined for the first time in the surface and ground waters of Matua Island (Central Kuriles). It was concluded that the chemical composition of the waters was controlled by three main sources: cyclic sea salts, dissolved weathering products of volcanic rocks, and volcanic exhalations. Biological processes played an insignificant role.

Published data and research results from the authors on the concentrations of dissolved trace elements (P, Si, Li, Rb, Cs, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Cd, Tl, Pb, Al, Ga, Y, Ti, Zr, Hf, Th, U, rare earth elements, B, F, V, Cr, Ge, As, Mo, W, and Sb) in the rivers discharging into the catchment areas of the White and Kara seas have been synthesized. The mean concentrations of the vast majority of trace elements are found to be not much different from the values of the global runoff, and only some of them (P, Fe, Zn, Cd, Y, Zr, B, and W for the rivers of the White Sea catchment area and Cs, Fe, Zn, and Cd for the rivers of the Kara Sea catchment area) differ threefold in concentrations. The lack of significant differences in the mean concentrations could be a result of their spatial variability smoothed out over the extent of large catchment areas.

Data on the levels of major ions (Na+, K+, Mg2+, Ca2+, $${\text{C}}{{{\text{l}}}^{ - }}{\text{,}}$$$${\text{SO}}_{{\text{4}}}^{{{\text{2}} - }}{\text{,}}$$$${\text{HCO}}_{{\text{3}}}^{ - }$$) and dissolved trace elements (Rb, Cs, Be, Sr, Ba, B, Si, Pmin, V, Cr, Ge, As, Mo, W, Sb, Te, Mn, Fe, Co, Ni, Cu, Zn, Cd, Ag, Sn, Pb, Al, Ga, Ti, Zr, and U) in the waters of 30 springs in Moscow during the winter low water period are presented. The geometric mean values and ranges of concentration of the studied components, as well as correlations between them were established. The presence of hydrochemical anomalies of dissolved iron and manganese in the northeast of Moscow with an excess of the maximum permissible concentration (MPC) for these elements was revealed, whereas in the rest of the city their concentrations corresponds to the natural background levels almost everywhere.

International audience; Background and aims Vanadium (V), niobium (Nb), and tantalum (Ta), recognized as Technology-Critical Element (TCE), are highly growing in demand for industrial development. Despite their economic relevance, little is known about their environmental concentrations, especially in marine ecosystems like mangroves. This paper describes concentrations and distribution patterns of Group Va elements (V, Nb and Ta) in plant organs and sediments from diverse mangroves of the Indian Sundarbans. Method Sediment cores and plant organs of eight dominant mangrove species were sampled and analyzed for V, Nb and Ta by ICP-MS. Stable carbon isotope (delta C-13) in mangrove leaves were analyzed by EA-IRMS. Result Mean concentrations (mg kg(-1)) of V, Nb and Ta decreased in the order V (84.7 +/- 12.5) > Nb (37.5 +/- 4) > Ta (3 +/- 0.8) in the sediment and V (0.6 +/- 0.6) > Nb (0.02) > Ta (0.002) in the mangrove plants. Species-specific variability in bioaccumulation factor (V: 0.012-0.035; Nb: 0.001-0.003; Ta: 0.001-0.005), translocation factor (V: 0.5-5.1; Nb: 0.26-7.06; Ta: 0.22-2.56) and enrichment factor (V: 0.008-0.027; Nb: 0.0002-0.001; Ta: 1.0 x 10(-5)-3.0 x 10(-6)) indicated different partitioning of Group Va elements within the plant organs and varying degree of mangrove uptake efficiency. Conclusion Results showed a general decrease in V, Nb and Ta concentrations with their increasing atomic weight. Their total concentrations in plants were related to the degree of enrichment of substrate sediments. The phytoextraction capacity varied amongst mangrove species depending on their CO2 uptake efficiency. Given increased demand for TCEs, results may have important implications for bioremediation processes.

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.