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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.

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.

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.

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.

Colloidal (size 1 nm to 1 μm) transport of major and trace elements, notably micronutrients and low-solubility geochemical tracers, is a ubiquitous and well-established feature for all surface and soil waters in boreal and subarctic regions. However, little is known on the colloidal associations of organic carbon (OC) and major and trace elements in atmospheric precipitation such as snow. This is despite significant efforts devoted to distinguishing the soluble and particulate transport of trace metals and contaminants by atmospheric aerosols. To acquire a snap-shot of major and trace element size fractionation in the snow cover of western Siberia, we sampled snow cores integrated over the entire depth (0–50 cm until bottom) across a sizable (2800 km) south - north transect in the Ob River watershed (western Siberia). A number of trace metal pollutants (Cr, Ni, Zn, Cd) exhibited significant linkage, pronounced over the first 20 km, to sources of local pollution. Some elements (P, Mn, Zn, Ba) also demonstrated an increase in their colloidal fraction in the proximity of pollution centers, possibly reflecting input from industrial centers and gas flares. Following centrifuginal ultrafiltration, we analyzed total dissolved (< 0.22 μm), two colloidal (high molecular weight, HMW50 kDa ̶ 0.22 μm; medium molecular weight MMW3 kDa ̶ 50 kDa) and low molecular weight (LMW < 3 kDa) fractions in the melted snow for all major and trace elements. We discovered sizable (20 to 70%) proportion of some major (Ca, SO4) and many trace (Fe, Y, Zn, Sb, La, Ce, Yb, Pb) elements in the colloidal (3 kDa - 0.22 μm) form, without significant link to latitude, type of biome, or the concentration of possible colloidal carrier (DOC, Fe, Al, Ca, SO4). The origin of snow water colloids in snow can be hypothesized to stem from solute freezing on lake surfaces (Fe, OC), frost flowers of the Arсtic ice (Ca, SO4), clays dispersion (Al, Si) and sulphur dioxide oxidation particles (SO4, oxyanions). Via hydrochemical mass balance calculations, we demonstrate an overwhelming impact of snow melt on spring-time riverine export of Cd, Pb, Zn, As, Sb and Cs. These preliminary results call for further studies of atmospheric colloids including those originating from rainwater.

Lake sediments accumulate various pollutants and act as efficient natural archives suitable for reconstruction the environmental conditions of the past. In contrast to fairly good knowledge of mineral sediments in lakes of European and North America boreal lakes, Siberian lakes of the boreal zone remain quite poorly studied. In this work, two cores of lake sediments of the Ob River valley were investigated. Elemental analyses were carried out on the sediments, losses on ignition were determined, and the rate of sedimentation was measured from the activity of Pb-210 and Cs-137. According to the content of organic matter, bottom sediments belong to different types: clastic (Lake Inkino, located in the Ob River floodplain) and organogenic (Lake Shchuchie on the second terrace). The rate of sedimentation in Lake Shchuchie is several times higher than that in Lake Inkino. The sediments of Lake Inkino are similar in composition (including the pattern of rare earth elements) to the suspended particulate matter of the Ob River as well as to average detrital matter of the upper continental crust. Sediments of Lake Shchuchie (sapropels) are enriched in a number of heavy metals. Based on the elemental composition, signs of diagenetic processes and authigenic mineral formation were determined, such as accumulation of carbonates and the formation of manganese oxides and hydroxides. There is an enhanced recent input of Cr, Co, Cu, Zn, Cd, Sb, Pb, and Bi in the upper layers of sediments as a result of atmospheric anthropogenic pollutant deposition.

SF and the Si isotope measurements at STAiG were supported by NERC grant NE/R002134/1 to PS; PS would also like to cite the support of a Carnegie Trust Research Incentive Grant, which helped the setup of various isotope techniques in the St Andrews Isotope Geochemistry (STAiG) laboratories. C.D. Coath is thanked for laboratory support and the European Research Council is acknowledged for funding (ICY-LAB, grant agreement 678371). The use of silicon (Si) isotopes has led to major advances in our understanding of Si cycling in modern and past environments. This inter‐laboratory comparison exercise provides the community with the first set of soil and plant reference materials with an analytically challenging matrix containing organic material that is known to induce isotopic bias, for use as secondary reference materials in Si isotope measurement. Seven laboratories analysed four soil reference materials (GBW‐07401, GBW‐07404, GBW‐07407, TILL‐1) and one plant reference material (ERM‐CD281). Participating laboratories employed a range of chemical preparation methods and analytical setups but all analyses were performed by MC‐ICP‐MS. Irrespective of the chemical preparation method or analytical conditions, the results show excellent agreement among laboratories within 2s for at least three replicates. Data were combined together to calculate δ29Si and δ30Si mean values (relative to NBS 28) and their expanded uncertainties (U, coverage factor k = 2). The δ30Si values are as follow: GBW‐07401: ‐0.27 ± 0.06 ‰, GBW‐07404: ‐0.76 ± 0.12 ‰, GBW‐07407: ‐1.82 ± 0.17 ‰, TILL‐1: ‐0.16 ± 0.06 ‰ and ERM‐CD281: ‐0.28 ± 0.11 ‰. Also, a compilation of published data provides an up‐to‐date mean δ30Si for BHVO‐2 of ‐0.28 ± 0.08 ‰. Postprint

Several rivers of Chile from the latitude 30 degrees-38 degrees have been sampled during a stable anticyclonic period (October 2008). Firstly, our aim was to evaluate the dissolved chemical composition (major and trace elements) of poorly known central Chilean rivers. Secondly, we used a co-inertia analysis (see Doledec and Chessel in Freshw Biol 31:277-294, 1994) to explore the possible relationships between the concentrations of elements and the environmental parameters [surface of the basin (km(2))/mining activity (%)/average height (m)/watershed mean slope (%)/% of the surface covered by vegetation, sedimentary rocks, volcano-sedimentary rocks, volcanic rocks, granitoid rocks/erosion rate (mm/year)]. Globally, the major elements concentration could be explained by a strong control of mixed silicate and carbonate and evaporate lithology. The statistical treatment reveals that the highest metal and metalloids loads of Tinguiririca, Cachapoal, Aconcagua, Choapa, Illapel and Limari could be explained by the contribution of the mining activities in the uppermost part of these watersheds and/or by the higher geochemical background. Indeed, it remains difficult to decipher between a real mining impact and a higher geochemical background. Even if these rivers could be impacted by AMD process, the size of these watersheds is capable of diluting AMD waters by the alkaline character of tributaries that induce acid neutralization and decrease the level of metals and metalloids.

Greenhouse gas (GHG) emission from inland waters of permafrost-affected regions is one of the key factors of circumpolar aquatic ecosystem response to climate warming and permafrost thaw. Riverine systems of central and eastern Siberia contribute a significant part of the water and carbon (C) export to the Arctic Ocean, yet their C exchange with the atmosphere remains poorly known due to lack of in situ GHG concentration and emission estimates. Here we present the results of continuous in situ pCO2 measurements over a 2600 km transect of the Lena River main stem and lower reaches of 20 major tributaries (together representing a watershed area of 1 661 000 km2, 66 % of the Lena's basin), conducted at the peak of the spring flood. The pCO2 in the Lena (range 400–1400 µatm) and tributaries (range 400–1600 µatm) remained generally stable (within ca. 20 %) over the night–day period and across the river channels. The pCO2 in tributaries increased northward with mean annual temperature decrease and permafrost increase; this change was positively correlated with C stock in soil, the proportion of deciduous needleleaf forest, and the riparian vegetation. Based on gas transfer coefficients obtained from rivers of the Siberian permafrost zone (k=4.46 m d−1), we calculated CO2 emission for the main stem and tributaries. Typical fluxes ranged from 1 to 2 gCm-2d-1 (>99 % CO2, % CH4), which is comparable with CO2 emission measured in the Kolyma, Yukon, and Mackenzie rivers and permafrost-affected rivers in western Siberia. The areal C emissions from lotic waters of the Lena watershed were quantified by taking into account the total area of permanent and seasonal water of the Lena basin (28 000 km2 ). Assuming 6 months of the year to be an open water period with no emission under ice, the annual C emission from the whole Lena basin is estimated as 8.3±2.5 Tg C yr−1, which is comparable to the DOC and dissolved inorganic carbon (DIC) lateral export to the Arctic Ocean.

International audience; Quantifying the link between cyanobacterial activity and the carbon isotope signature of precipitated carbonate minerals is crucial for reconstructing the environmental conditions present at the time of carbonate mineral formation. In this study, calcite was precipitated in the presence and absence of Synechococcus sp. cyanobacteria in batch reactors. The temporal evolution of the carbon isotope composition of calcite (δ13CCalcite) and dissolved inorganic carbon (δ13CDIC) was monitored to evaluate the rate and degree to which the carbon isotope compositions in calcite are modified during and after its precipitation. The presence of cyanobacteria promoted calcium carbonate formation by increasing fluid pH and the CaCO3 saturation state. It also changed significantly the carbon isotope composition of dissolved inorganic carbon due to the preferential incorporation of 12C into the biomass. This generated an isotope disequilibrium between the calcite and the aqueous fluid phase over time after the calcite precipitated. The carbon isotope composition of the calcite evolved continuously towards mineral-fluid isotope equilibrium after its precipitation, at geometric surface area normalized rates ranging from 1.75 × 10−14 to 1.71 × 10−13 mol 13C/m2/s. These rates are sufficiently fast such that the δ13CDIC value of aqueous fluids in calcite-rich rocks would be buffered by the δ13CCalcite value of the co-existing calcite. Mass balance calculations suggest that the carbon isotope composition of calcite could change noticeably when the calcite is in isotope disequilibrium with its co-existing fluid, for example through the presence of a local 12C sink such as photosynthetic microorganisms or 12C source such as decomposition of organic material.

International audience; Bioerosion is a process with a high socioeconomic impact that contributes to coastal retreat, and likely to increase with climate change. Whereas limestone bioerosion is well explained by a combination of mechanical and chemical pathways, the bioerosion mechanisms of silicates, which are harder and chemically more resistant, remain elusive. Here we investigated the interface between siltstone and freshwater rock-boring bivalves Lignopholas fluminalis (Bivalvia: pholadidae). Remains of a microbial biofilm were observed only in the poorly consolidated part of the rock within the macroborings created by bivalves. Secondary Mn-bearing minerals identified in the biofilm suggest that microbes promoted silicate rock weathering by dissolving Mn-rich chlorites. Moreover, hard mineral debris found in a biofilm attached to the shells likely contributed to the abrasion of the rock substrate. thus, beyond the classical view of chemical and/or mechanical action(s) of macroborers, silicate bioerosion may also be facilitated by an unexpected synergistic association between macro-and microorganisms. Bioerosion is a commonplace strategy developed by living organisms, which consists in boring hard substrates of various origins, including biological materials (e.g., wood, shells, and bones) 1 , mud 2 , rocks 3 and even synthetic materials. Depending on the nature of the substrate and the borer, bioerosion ensures a wide range of metabolic activities and ecosystem services, ranging from nutrition 4 to the creation of microhabitats protected from predators for themselves as well as for secondary dwellers 5. Gaining knowledge into the occurrence, rates and mechanisms of boring is of fundamental importance for a series of reasons. First and historically, mankind has been confronted with macroborers through the damages caused by shipworms on vessels, wooden wharfs and docks 5,6. More broadly, bioerosion has socioeconomic impacts whenever manufactured materials are damaged, including plastic, metals and concrete materials such as levees or coastal defences 3,6. Second, bioerosion contributes to element recycling, shaping landscapes through the weakening of rocky shorelines and participating to coastal retreat 5 , for which the current rates are likely to be modified drastically as a result of climate change 6. Third, the creation of microhabitats by macroborers such as bivalves is correlated with a significant increase of the abundance of species assemblages, thus partly contributing to local faunal biodiversity 7. Finally, fossil records of macro-bioerosion may be used as a biological proxy to estimate the paleo-location of intertidal and shallow subtidal marine environments, marking ancient shorelines 8. The mechanisms of rock bioerosion associated to macroborers and especially bivalves have been a source of lively debate for decades, and can be schematically divided into two main pathways. First, rock boring can open

Constraining the mechanisms controlling the riverine flux of major cations and their isotopes including that of Mg to the World Ocean is one of the challenges in Earth surface isotope geochemistry. In an attempt to identify the main factors affecting the Mg isotopic composition of large rivers including vegetation, climate and lithology of the watershed, we studied the largest, in terms of discharge, Siberian river, Yenisey, and 20 of its main tributaries, during spring flood, summer flow and winter. The working hypothesis was that the influence of bedrock composition is most pronounced in winter, when the soils are frozen and the rivers are fed by deep underground waters. Thus, we anticipated that the presence of permafrost will help to distinguish the impact of surface processes, linked to biological uptake and release, and deep soil/underground transport of Mg from mineral sources. In contrast to these expectations, no sizable differences in the Mg isotope composition of the river water (±0.1‰) for both the Yenisey tributaries and its main channel has been observed between the spring flood (May) and the winter (March) period. Those two periods are characterized by the differences of discharge and degree of lithological impact on element source in the river water. Regardless of the season, there was no straightforward control of lithology (relative abundance of carbonates, basalts, granites and sedimentary rocks) on δ26Mg in the main tributaries of the Yenisey river. Our findings suggest that the use of riverine Mg isotope signature for tracing weathering mechanisms and dominant lithological impact is not straightforward at the scale of large rivers whose watersheds present multiple lithologies, variable climatic conditions and vegetation types.

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.

Towards a better understanding of photosynthetic algae interaction with less common trace elements, we performed adsorption experiments of Al, Ga, Ge, Cr (VI), Mo, and W onto four diatom species typical for marine, estuarine, and freshwater aquatic systems. Using a surface complexation approach, we tentatively identified the nature of functional groups involved in the complexation of trace elements with diatom surface moieties and we quantified the stability of surface complexes formed at the diatom – solution interface. The differences in binding properties between freshwater and marine species are linked to variable proportion of three main binding groups at the diatom surfaces, namely amine, carboxylate and silanol. Under acidic conditions, the oxyanion (MoO42−, WO42−, CrO42−) sorption occurred electrostatically with a 1:1 ratio to the protonated amino groups. Trivalent cations (Ga3+ and Al3+) were complexed by deprotonated carboxyl groups, while the anionic hydroxylated forms of these metals (Ga(OH)4− and Al(OH)4−) formed mononuclear monodentate complex with positively charged amino groups at higher pH. Finally, Ge(IV) sorption was controlled by interaction with neutral carboxylic, silanol and amino groups. Taken together, the surface complexation model developed in this study allows rigorous description of anions and trivalent hydrolysates adsorption onto diatom surfaces and demonstrates potential importance of diatoms for the control of trace element transfer in aquatic settings.

The spatial and temporal variations in concentrations of dissolved organic carbon in the Yenisei River and its major tributaries are analyzed. The results obtained suggest that the maximal contribution to the flows of dissolved organic carbon in the Yenisei River is made by cryohydromorphic forest landscapes of the Central Siberian Plateau.

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 (

Rivers are significant contributors of Fe to theocean. However, the characteristics of chemically reactive Fe remain poorly constrained, especially in large Arctic rivers, which drain landscapes highly susceptible to climate change and carbon cycle alteration. The aim of this study was a detailed characterisation (size, mineralogy, and speciation) of riverine Fe-bearing particles (> 0.22 µm) and colloids (1 kDa – 0.22 µm) and their association with organic carbon (OC), in the Lena River and tributaries, which drain a catchment almost entirely underlain by permafrost. Samples fromthe main channel and tributaries representing watersheds that span a wide rangein topography and lithology were taken after the spring flood in June 2013 and summer baseflow in July 2012. Fe-bearing particles were identified, usingTransmission Electron Microscopy, as large (200 nm – 1 µm) aggregates of smaller (20 nm - 30 nm) spherical colloids of chemically-reactive ferrihydrite.In contrast, there were also large (500 nm – 1 µm) aggregates of clay (illite) particles and smaller (100 - 200 nm) iron oxide particles (dominantly hematite) that contain poorly reactive Fe. TEM imaging and Scanning Transmission X-raymicroscopy (STXM) indicated that the ferrihydrite is present as discrete particles within networks of amorphous particulate organic carbon (POC) and attached to the surface of primary produced organic matter and clay particles.Together, these larger particles act as the main carriers of nanoscale ferrihydrite in the Lena River basin. The chemically reactive ferrihydrite accounts for on average 70 ± 15 % of the total suspended Fe in the Lena River and tributaries. These observations place important constraints on Fe and OC cycling in the Lena River catchment area and Fe-bearing particle transport to the Arctic Ocean. The Lena River Study

International audience; In a Siberian river, the concentrations of chemical species vary with the hydrological regime. Dissolved Organic Matter (DOM) and aluminum ions show a parallel trend in the course of the hydrological year. However, the speciation of aluminum in this natural environment remains an open question. We propose here a combination of spectroscopic techniques to investigate the proximity between the aluminum atoms and DOM. First, one-dimensional (1D) solid-state Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR) and 1D and 2D solution NMR spectra were acquired, providing a clear overview of the DOM composition. Second, the sensitivity enhancement yielded by Dynamic Nuclear Polarization enabled the NMR detection of proximities between the 27Al and 13C nuclei. Hence, we show that 8.3 ± 1.3% of the carboxylate groups observed by NMR are connected to the Al3+ ions in the DOM sample. We here demonstrate for the first time how advanced solid-state NMR methods can provide key information about the localization of aluminum in such complex natural materials.

Particulate material plays a major role in the transport of sparingly soluble nutrients such as P and Fe in natural surface waters. Microbes might gain access to these nutrients either indirectly through particulate dissolution or directly through microbial attack. As such, it seems reasonable to expect a link between the particulate material concentration and bacterial growth in natural surface waters. To explore this link, a series of microcosm growth experiments were performed in the presence of a typical freshwater cyanobacteria, Synechococcus sp., grown in dilute BG-11 culture media in the presence and absence of basaltic and continental riverine particulate material. Results demonstrate that riverine particulates can increase bacterial biomass by 1) triggering bacterial growth in otherwise unfavourable conditions, 2) increasing total maximum biomass concentration, and 3) inducing bacteria growth during the post-exponential phase. These effects are found to be enhanced by increasing particulate concentration. Results also indicate a positive feedback between the nutrient release from the particulates and growing bacteria, where dissolving particulates enhance bacterial growth, which further promotes particulate dissolution by altering fluid pH. Microscopic analysis showed direct physical contact between particulates and cyanobacteria, suggesting that bacteria attach directly on mineral surfaces to gain required nutrients. Furthermore, frequent bacteria clusters were observed associated with particulates, indicating an increasing aggregation of bacteria in the presence of particulate material, which may facilitate a higher burial efficiency of organic carbon.

The metal excretion and metal sorption are two important microbial processes in the regulation of intracellular metal concentration. However, the contribution of freshwater phototrophic biofilm to metal efflux in the environment and its related isotopic fractionation remain poorly known. In this study, Cu efflux from a mature phototrophic biofilm and related Cu isotopic fractionation between the biofilm and aqueous solution were studied over 4 days in closed batch and open drip-flow reactors (BR and DFR, respectively). The impact of a 48-h drying event on Cu efflux from the biofilm and its isotopic signature was quantified in the BR. Cu excretion from the biofilm depended on Cu concentration in the biomass and did not show a latent phase. For the wet biofilm, in DFR, the Cu efflux rate decreased over time whereas in BR, Cu efflux exhibited fluctuations with a net re-sorption phase. During short-term early excretion over the first 4 h (BR) and 24 h (DFR), the enrichment of solution in heavy isotopes with a Δ65Cu(sol–biofilm) of +0.7 ± 0.2‰ could be explained by a combination of i) desorption via competition between H+ and Cu2+ for surface sites and ii) release of isotopically heavy Cu(II)-organic complexes. In addition, there was a retention of isotopically light Cu (I) within the cells which is consistent with the biofilm ability to reduce Cu. With further exposure of the wet biofilm to the solution, a progressive decrease of Δ65Cu(sol–biofilm), down to 0 and −0.36‰ respectively in BR and DFR after 96 h, could be explained by an active efflux of Cu(I) and by a passive diffusion of Cu2+, both of these processes favoring light isotopes. The re-hydrated and wet biofilms showed distinctly different behavior during excretion, in terms of magnitude of the flux and direction of the fractionation for long term exposure. Indeed, the efflux from the re-hydrated biofilm was ten times higher than the one from the wet biofilm and the re-hydrated biofilm did not exhibit a decrease of Δ65Cu(sol–biofilm) after 24 h of reaction. This could be related to partial devitalization of the biofilm during drying, producing a release of isotopically heavy Cu and decreasing the intensity of Cu(I) active efflux of light isotopes. Taken together, the Cu isotopic signature in natural aquatic environments containing phototrophic biofilms varies up to 1‰ on a daily scale.

International audience; In order to quantify the impact of evapotranspiration phenomena on active layer dynamics in a permafrost-dominated forested watershed in Central Siberia, we performed a numerical cryohydrological study of water and energy transfer using a new open source cryohydrogeology simulator, with two innovative features: the spatially distributed, mechanistic handling of evapotranspiration and the inclusion of the developed numerical tool in the high performance computing tool box for numerical simulation of fluid dynamics OpenFOAM®. In this region, the heterogeneity of solar exposure leads to strong contrasts in vegetation cover, which constitute the main source of variability of hydrological conditions at the landscape scale. The uncalibrated numerical results reasonably reproduce the measured soil temperature profiles and the dynamics of infiltrated waters revealed by previous biogeochemical studies. The impacts of the thermo-hydrological processes on the water fluxes from the soils to the stream are discussed through comparison between numerical results and field data. The impact of evapotranspiration on water fluxes is studied numerically, which highlights a strong sensitivity to the variability of rooting depth and corresponding evapotranspiration at the slopes of different aspects in the catchment.

Chemical weathering of mafic rocks represents substantial sink of atmospheric CO2 yet the mechanismes of this process in high-latitude regions are poorly understood. This work addresses geochemical migration and partitioning of major and trace elements between rock, soil and surface waters during chemical weathering of mafic rocks and soil formation under the influence of a glacial moraine in the northwestern Russian subarctic. We used multidisciplinary approach which included major and trace element chemical analysis, Sr isotopic measurements, and mineralogical structural and microscopic investigations. Quaternary (Pleistocene) deposits were observed even in the deepest horizons of soil profiles and confirm a strong moraine influence as most soils showed podzolic features. Chemical and Sr isotopic analyses revealed a strong impact of the moraine on soil chemistry and mineralogy. Mineralogical studies showed the presence of non-aeolian quartz and zircon in soils which were not linked to the nature of the parental rocks (i.e. mafic and felsic). At the same time, we observed the presence of etch pit corrosion on the surface of zircons and feldspars, and a newly-formed matter adjacent to the surface of primary phases. The chemical index of alteration (CIA) showed weak or no weathering of rocks within the soil profile and the weathering intensity scale confirmed the “felsic” chemical composition of soils developed over mafic and ultramafic rocks. Analysis of Sr radiogenic isotopes demonstrated preferential removal of easily weatherable and less radiogenic minerals over the full depth of soil profile and a more radiogenic signature of the granitic moraine compared to mafic and felsic bedrocks. The composition of most surface waters reflected the weathering of silicate rocks but did not allow for distinguishing purely mafic source. The chemical weathering rates of ultramafic rocks were calculated to be higher than those for the granitic till, but the moraine depositions which dominate this region hide evidence of the real weathering process. This could be due to retention of Mg and Ca in soil due to precipitation of secondary phases such as Mg-vermiculite or divalent cation adsorption on mineral, organic or organo-mineral phases. As a result, weathering rates estimated for the olivinite rock appear to be lower than the weathering rates of mafic rocks reported in other boreal and subarctic regions. Overall, the felsic moraine deposits are capable to sizably decrease the weathering intensity of mafic rocks which should be taken into account for chemical weathering modelling of high-latitude regions subjected to glaciation in the past.

The formation of Mg-rich carbonates in continental lakes throughout the world is highly relevant to irreversible CO2 sequestration and the reconstruction of paleo-sedimentary environments. Here, preliminary results on Mg-rich carbonate formation at the coastal zone of Lake Vtoroe Zasechnoe, representing the Setovskiye group of water bodies located in the forest-steppe zone of Southwest Western Siberia, are reported. The Setovskiye lakes are Cl&minus, &ndash, Na+&ndash, (SO42&minus, ) type, alkaline, and medium or highly saline. The results of microscopic and mineralogical studies of microbialites from shallow coastal waters of Lake Vtoroe Zasechnoe demonstrated that Mg in the studied lake was precipitated in the form of hydrous Mg carbonates, which occur as radially divergent crystals that form clusters in a dumbbell or star shape. It is possible that hydrous Mg carbonate forms due to the mineralization of exopolymeric substances (EPS) around bacterial cells within the algal mats. Therefore, the Vtoroe Zasechnoe Lake represents a rare case of Mg-carbonates formation under contemporary lacustrine conditions. Further research on this, as well as other lakes of Setovskiye group, is needed for a better understanding of the possible role of biomineralization and abiotic mechanisms, such as winter freezing and solute concentration, in the formation of authigenic Mg carbonate in modern aquatic environments.

The purpose of this work is to study the variability of the isotope composition (δ18О, δD, d exc) of the snow cover on a long transect of Western Siberia from the southern taiga to the tundra. The study of the snow cover is of paleogeographic, paleogeocryological, and paleohydrological value. The snow cover of western Siberia was sampled on a broadly NS transzonal profile from the environs of Tomsk (southern taiga zone) to the eastern coast of the Gulf of Ob (tundra zone) from February 19 to March 4, 2014. Snow samples were collected at 31 sites. Most of the samples represented by fresh snow, i.e., snow that had fallen a day before the moment of sampling were collected in two areas. In the area of Yamburg, the snow specimens collected from the surface are most probably settled snow of different ages. The values of δ18О in the snow from Tomsk to Yamburg varied from–21.89 to–32.82‰, and the values of δD, from–163.3 to–261.2‰. The value of deuterium excess was in the range of 4.06–19.53‰.

This work focuses on the behavior of the stable Mg and Si isotope compositions of the largest Arctic river, the Yenisey River and 28 of its major and minor tributaries during the spring flood period. Samples were collected along a 1500 km latitudinal profile covering a wide range of permafrost, lithology, and vegetation. Despite significant contrasts in the main physico-geographical, climate, and lithological parameters of the watersheds, the isotope composition of both dissolved Mg and Si was found to be only weakly influenced by the degree of the permafrost coverage, type of vegetation (forest vs. tundra), and lithology (granites, basalts, carbonates or terrigenous rocks). This observation is generally consistent with the lack of chemical uptake of Mg and Si by soil mineral formation and vegetation during the early spring. The radiogenic Sr isotope composition of the Yenisey and its tributaries varied within a narrow range (0.708 ⩽ 87Sr/86Sr ⩽ 0.711) reflecting the dominance of Phanerozoic rock weathering and/or atmospheric deposition on these compositions. The Mg and Si isotopic compositions of riverine samples reflect two main processes with distinct isotopic signatures. First, isotopically heavier Mg (δ26Mg = −1.0 ± 0.2‰) and isotopically lighter Si (δ30Si = 1.0 ± 0.25‰) are added to the waters by river suspended matter dissolution and leaching from vegetation biomass/topsoil litter. Second, isotopically lighter Mg (δ26Mg = −1.5 to −1.75‰) and isotopically heavier Si (δ30Si = 1.75–2.0‰) are delivered to the Yenisey’s tributaries from deep underground water feeding the rivers via taliks. This lighter Mg and heavier Si isotopic composition is interpreted to originate from Precambrian dolomite dissolution and aluminosilicate dissolution coupled with authigenic mineral precipitation, respectively, in deep underground water reservoirs. Taking account of the isotopic composition evolution over the course of the year established earlier on mono-lithological watersheds of the Yenisey basin, the average annual isotopic signatures of the Yenisey river arriving to the Arctic Ocean are estimated to be δ26Mg = −1.58 ± 0.30‰ and δ30Si = +1.60 ± 0.25‰. As the Yenisey is the largest river feeding the Arctic Ocean and as it samples a large variety of environments and lithologies, these values may be reasonable estimates for the average Mg and Si isotopic composition of the dissolved riverine flux to the Arctic Ocean.

On-going permafrost thaw in discontinuous permafrost regions produces significant amounts of small permafrost subsidence and depressions, while large lakes are likely to drain into streams and rivers. The intensification of permafrost thaw may alter the size distribution and chemical composition of organo-Fe–Al colloids in lakes and rivers. We used a continuum of surface water bodies, from permafrost subsidence, small depressions and thaw ponds to large lakes and rivers that drain the Western Siberia Lowland (WSL), to assess OC, major and the trace element size distribution between the 20-μm, 5-μm, 1.2-μm, 0.45-μm, 0.22-μm, 0.025-μm and 1-kDa (∼1.4 nm) size fractions. This approach allowed us to distinguish the organic and organo-ferric colloids that were responsible for the transport of trace elements in surface waters and address their evolution during possible physico-chemical and biological processes. Both conventionally dissolved (

Assessing multi-annual riverine export fluxes of carbon, nutrients and metals from the continent to the Arctic Ocean is crucial for constraining the current status and foreseeing future changes in riverine export induced by climate change. Over 3 consecutive years (2012–2014), we measured daily to weekly concentrations of C, N, P, all major and 45 trace elements (TE) in filtered ( The spring flood (May and June) provided 50% of overall water and DOC, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Sb, and Pb flux and 60% of low-soluble TE (Al, Y, Nb, REEs, Ti, Zr, Hf and Th). The nutrients (K, Rb, Si, P, N) exhibited around 40% share of annual export during spring flood, whereas the export of soluble mobile elements (DIC, Cl−, SO42−, Li, B, Na, Mg, Ca, Sr, Mo and U) mainly occurred during winter (35–40%) with only 20–25% of annual flow provided by spring flood. The 3-year mean export fluxes of dissolved components were 30 to 50% lower than (Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cu, Cd, and Pb) or comparable to (±30% for all other elements including DOC and for DIC) previous estimates of this river from 2007 to 2008 and the historic data of major components from 1930 to 1950. In particular, there was no trend in mean monthly seasonal and annual concentrations and export fluxes of DOC, DIC, SO4, Cl since the beginning of chemical analysis between 1929 and 1930 and in Ca, Mg, Si, and Fe since the 1950's through the duration of this study (2012–2014). The lack of seasonal and annual increases in discharge, carbon, and element concentrations in the permafrost-free Severnaya Dvina River for >120 years of discharge and over 60 years of chemical composition measurements is at odds with the reported short-term trend (based on measurements that began in 1970s) showing that element export fluxes increased in other Arctic rivers due to on-going climate warming and permafrost thaw. Novelty statement Historical and contemporary measurements of element fluxes in the largest European Arctic river did not reveal sizeable changes in discharge and DOC, DIC, Ca, Mg, Fe, Si, SO4, Cl concentrations and fluxes over past >60 years.

International audience; The rising concern about the potential toxicity of synthetic gold nanoparticles (AuNPs) in aquatic environments requires a rigorous estimation of physico-chemical parameters of reactions between AuNPs and major freshwater microorganisms. This study addresses the interaction of 10-nm size, positively charged AuNPs with periphytic freshwater diatoms (Eolimna minima). The adsorption experiments on viable cells were performed in 10 mM NaCl and 5 mM NaCl + 5 mM NaHCO3 solution at a variable pH (3–10), at an AuNPs concentration from 1 µg/L to 10,000 µg/L, and an exposure time from a few minutes to 55 days. Three types of experiments, adsorption as a function of time (kinetics), pH-dependent adsorption edge, and constant-pH “Langmuirian” type isotherms, were conducted. In addition, long-term interactions (days to weeks) of live diatoms (under light and in the darkness) were performed. The adsorption was maximal at a pH from 3 to 6 and sizably decreased at a pH of 6 to 10. Results of adsorption experiments were modeled using a second order kinetic model, a Linear Programming Model, Freundlich isotherm, and a ligand binding equation for one site competition. The adsorption of AuNPs(+) most likely occurred on negatively-charged surface sites of diatom cell walls such as carboxylates or phosphorylates, similar to previously studied metal cations. Under light exposure, the AuNPs were stabilized in aqueous solution in the presence of live cells, probably due to the production of exometabolites by diatoms. The adsorbed amount of AuNPs decreased after several days of reaction, suggesting some AuNPs desorption. In the darkness, the adsorption and assimilation were stronger than under light. Overall, the behavior of positively charged AuNPs at the diatom–aqueous solution interface is similar to that of metal cations, but the affinity of aqueous AuNPs to cell exometabolites is higher, which leads to the stabilization of nanoparticles in solution in the presence of diatoms and their exudates. During photosynthetic activity and the pH rising above 9 in the vicinity of diatom cells, the adsorption of AuNPs strongly decreases, which indicates a decreasing potential toxicity of AuNPs for photosynthesizing cells. The present study demonstrates the efficiency of a thermodynamic and kinetic approach for understanding gold nanoparticles interaction with aquatic freshwater peryphytic microorganisms.

The geochemical processes in the river-sea mixing zone (the Marginal Filter of the Severnaya Dvina Rivers) are considered in this chapter. The general trend in transformation of the elements and components as a result of physical, chemical, and biogeochemical processes in this zone is the transition from dissolved forms of element existence into particulate suspended forms with the following sedimentation on the bottom. So, the Marginal Filter is a very effective barrier on the way of dissolved and suspended sedimentary materials from the continent to the sea.

The results of studies are presented for the elemental composition of peat from the Ilas ombrotrophic bog (White Sea drainage basin). The calculations of enrichment factors of trace elements over the section of the bog peat relatively to the average composition of the Earth’s continental crust showed that the concentrations of most of chemical elements is determined by the contributions of lithogenic and biogenic sources, and the content of trace elements is equal to the background level. Enrichment growth since the beginning of intense development of European industry until the early 21th century was revealed only for Zn, Sb, Pb, and Cd. These elements were supplied to the bog resulting from long-range air transport and precipitation from the atmosphere. No pronounced heavy-metal contamination caused by the Arkhangelsk agglomeration was revealed for the peat in the Ilas bog.

The release of major and trace elements (TEs) from mineral and organic-rich podzol soil horizons has been studied in batch reactors with live and dead soil heterotrophic Pseudomonas aureofaciens bacteria and in bacteria-free systems. Dissolved organic carbon (DOC) concentrations decreased and dissolved inorganic carbon concentrations increased over the course of experiments with live bacteria due to on-going DOC mineralization processes. Several families of major and trace elements could be distinguished, depending on their release patterns in bacteria-free systems and live bacteria-bearing systems. Live bacteria enhanced the release of Mg, Rb, Cd, Pb, Al, Fe and V from the mineral soil horizon and the release of Rb, Ni, Pb, As, Fe, V and La from the organic soil horizon relative to bacteria-free soil or dead bacteria experiments. Unexpectedly, K, Ca, Sr, Cu, Ti, Mn, Zn and As release from the mineral horizon and Mg, K, Ca, Sr, Ba, Cr, Ti, Mn and Zn release from the organic horizon decreased in the presence of live P. aureofaciens compared to bacteria-free and dead bacteria systems. Finally, live bacteria exhibited no effect on the release of Si, Al, Cu and Mo from the humic horizon and Ni, Mo, Cr, Ba, Si and La from the mineral horizon relative to the bacteria-free system. These results can be interpreted via a combination of several simultaneous processes, which occur in the soil–bacteria suspension and lead to changes in TE speciation and affinities to mineral surfaces and bacteria and include the following: 1) a slight decrease in the pH due to exometabolite production; 2) degradation of DOC and TE organic complexes by heterotrophic bacteria; 3) element adsorption at cell surfaces and biological uptake; and 4) element release from the soil mineral and organic particles. Compared to abiotic systems, the observed decreases in the concentrations of major elements and many heavy metals that leach from the soil in the presence of bacteria have important consequences regarding our understanding of the role of bacteria in element mobilizations from soil to rivers. It follows that chemical weathering in both organic and mineral horizons of podzol soil may not be strongly affected by heterotrophic bacterial activity; rather, the solution pH and DOC levels may control the intensity of element mobilization. The aqueous concentrations of many TEs (Fe, Al, La, Cr, Ni, Cd, Pb, Cu, and Rb) at the end of live-bacteria experiments were comparable with reported compositions of interstitial podzol soil solutions.

To reveal the geographical and inter-species variability of the major and trace element (TE) compositions of freshwater mussel shells across Eurasia, we used ICP MS after acid digestion to analyze 50 samples of shells from five species of the genus Margaritifera spp. (Bivalvia: Margaritiferidae) collected in 20 minor rivers located in NW Russia, Sakhalin, Amur basin, Kuril Islands, Kamchatka and Laos. The variations between replicates from the same site were smaller than the variations between samples from different localities or between different mollusk species. Using normed PCA, we observed significant biological and geographical controls of the trace element composition in freshwater shells, with five main species exhibiting distinct features of TE concentration corresponding to four major geographical locations. Four PCA factors explain 81% of the TE variability, which is closely linked to specific geographical location and weakly linked to the identity of the species. The first two factors (F1 × F2) are the element concentration and its biological affinity. The other two factors (F3 × F4) likely are the nutrient status of the river, corresponding to its proximity to wetlands or mountains, and the degree of the influence of volcanic/hydrothermal activity. The analysis of water samples collected during the active growth period in summer baseflow was used to quantify the distribution coefficients ( K d ) of trace elements between the aragonite shells and the river water. All species are significantly enriched in Mn relative to the river water, with distribution coefficients of up to 5. The other elements exhibit K d values that were similar for the five species. This suggests that the obtained distribution coefficients may be universal constants reflecting uptake of each element by the organism from the river water and its intracellular transport and biocalcification processes. Taken together, the chemical composition data for pearl mussel shells may not only reflect the geographical locality and species identity but also provide insights into biochemical processes of element uptake in the form of biominerals.

The present study aimed at testing the hypothesis that Fe adsorption and precipitation on bacterial phytoplankton likely cause significant isotopic fractionation with preferential adsorption of heavy isotopes on the cell surface. We measured the iron isotopic fractionation during the interaction of aqueous Fe with planktonic cyanobacteria ( Gloeocapsa sp ., Synehococcus sp., and Planthothrix sp.) in six independent experiments using two distinct Fe oxidation states (Fe(III) and Fe(II)) at pH 3 and 6. Isotopic analyses demonstrated that the Fe adsorption on bacterial planktonic biomass yields a clear enrichment of heavy isotopes on the cell surfaces, producing isotopically light δ 57 Fe values in solutions. The adsorption experiments with Fe(II) in the initial solution yielded a Δ 57 Fe cell-solution = 2.66 ± 0.14‰, whereas the adsorption experiments with Fe(III) in the initial solution yielded Δ 57 Fe cell-solution = 0.97 ± 0.19‰. Because these data approached closed system equilibrium isotopic fractionation lines rather than Rayleigh curves, the most likely mechanism is a steady state isotopic fractionation, linked with short-term reversible Fe adsorption on cells. In agreement with X-ray Absorption Spectroscopy structural data obtained on the same adsorption experiment samples (Gonzalez et al., 2014), the preferential enrichment of heavy Fe isotopes on the cell surfaces is attributed to the stronger covalent metal-ligand bonding (Fe O C/P) of octahedrally coordinated Fe with phosphoryl or carboxyl groups on the cell walls when compared with the Fe aquacomplexes (O Fe O) in solution. The larger isotopic fractionation factor in the experiments starting with Fe(II) results from the iron oxidation to Fe(III) which is itself accompanied by a strong isotopic effect. A natural case study of warm hydrothermal spring depositing Fe oxy(hydr)oxide with and without cyanobacterial biomass yielded an isotopic fractionation between the solid phase and aqueous solution (Δ 57 Fe solid-solution ) of 0.62 ± 0.16‰ (biotic) and 0.80 ± 0.06‰ (abiotic). This natural case study therefore confirms experimental results, albeit of smaller magnitude. These findings suggest that Fe adsorption on cyanobacteria cell surfaces in nature should produce cell enrichments in heavier isotopes relative to the coexisting aqueous solution.

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

To unravel the Mg isotope fractionation pathways within the continuous permafrost zone in the larch deciduous forest of Central Siberia, we measured the Mg isotopic composition of two large Siberian rivers (Nizhnaya Tunguska and Kochechum, which flow into the Yenisey), a small forested stream, and the major fluid and solid sources of Mg in the watershed: atmospheric precipitates, surface suprapermafrost flow, interstitial soil solutions, plant biomass, litter and mineral soils. The obtained results indicate a significant seasonal variation in riverine water Mg isotope signatures. During the winter baseflow, the Mg isotope composition of large rivers is significantly lighter than the source basaltic rocks and the atmospheric depositions. These differences support the presence of fluids enriched in lighter Mg isotopes, such as those affected by the mineral precipitation of secondary silicates or fluids that dissolve sedimentary carbonate rocks. During the spring flood and in the summer and fall seasons, the river fluid δ 26 Mg values increased by 0.2–0.3‰ and approached the Mg isotope composition of the ground vegetation (dwarf shrubs, mosses) and the soil organic horizon. Overall, the riverine waters were 0.3–0.7‰ lighter than the unaltered bedrock and the deep minerals soil horizons. The Mg isotopic compositions of Larix gmelinii organs (i.e., stem wood, roots and needles) exhibit a low variability. However, an enrichment of 0.2–0.3‰ in the δ 26 Mg of larch needles in the course of the growing season, from June to September can be observed. This enrichment most likely demonstrates uptake of isotopically heavier Mg by the plant in addition to the progressive thawing of the mineral soil (deepening of the active layer of the soil). Overall, the Mg isotope approach indicates the important contribution of vegetation (larch needles, mosses and dwarf shrubs) to the riverine Mg isotope signature and helps to reveal the contribution of isotopically light carbonate rocks in the large rivers of the Central Siberian Plateau.

Ions of major salt composition and dissolved forms of some microelements (F, B, Sr, Rb, Cs, V, As, Mo, U) at the mouth of the Serebryanka R. (Sikhote Alin Reserve) are shown to feature conservative behavior in July 2009. The distribution of dissolved mineral phosphorus is shown to be controlled mostly by chemical processes (desorption from river suspension), even during vegetation period, while the role of biological consumption is secondary. The behavior of dissolved organic phosphorus and silicon is nearly conservative. A considerable amount of barium (up to 46% of its concentration in river water) is shown to be removed from solution, maybe because of its sorption on particulate matter of continental runoff. Ittrium and rare-earth elements (La, Ce, Pr, Nd, Dy, Ho) show an abrupt decrease in the concentrations of their dissolved forms at the initial stages of river water penetration into the sea. This decrease is supposedly due to coagulation and flocculation of organic and organic-mineral colloids.

This paper reports the current state of lake and wetland ecosystems in the north of Western Siberia and describes the mechanisms of their formation and succession. Elemental composition of lake water and macrophytes of the four most typical subarctic lake ecosystems in Western Siberia were analysed using ICP MS. We selected the species of Menyanthes trifoliata L. as an example of the biogeochemical system. The general dynamics of concentration of the chemical elements in M. trifoliata L. in all four ecosystems demonstrate the minimal concentrations of rare-earth elements, of which the mobility in fresh waters and the bioavailability are low. Similar properties are exhibited by all tri and tetravalent hydrolysates. We also calculated, at each of the four stages of development of the lake ecosystems, the coefficients of biological accumulation of chemical elements by M. trifoliata L. (Kb) relative to the water. This revealed that the M. trifoliata L. strongly accumulates heavy metals, such as Pb, Zn, Sr and...

This work extends our knowledge of anoxygenic phototrophic bacteria (APB) interactions and contributes to the database of aquatic microorganism trace element adsorption parameters, such as heavy metal pollutants and limiting micronutrients. The surface properties of a phototrophic anaerobic non-sulfur bacterium (Rhodopseudomonas palustris KR-95p), which is often considered a model microorganism for Precambrian anoxygenic primary producers, were studied using potentiometric acid-base titration at various ionic strengths. The electrophoretic mobility of viable cells was measured as a function of pH and ionic strength, as well as cation (Zn, Cd, and Pb) and anion (Mo, W, and Cr) concentration. Zn, Cd, Sr, Pb, Cu, Cs, Al, Ga, Sb, As, Ge, Tl, W, and Mo adsorption was studied as a function of pH at a constant initial element concentration, yielding the pH-dependent adsorption edge. Zn, Cd, Sr, Cu and Pb adsorption was also studied as a function of metal concentration in solution at a constant pH, producing a “Langmuirian” adsorption isotherm. The non-electrostatic linear programming method (LPM) was used to fit the experimental data and assess the number of surface sites and adsorption reaction constants involved in heavy metal and anion binding to the cyanobacteria surface. The total H/OH binding site number (80–480 μmol/gwet) for Rps. palustris encompasses the values reported for other APB (60–120 μmol/gwet) and cyanobacteria (50–200 μmol/gwet) examined using the same technique. For the cations, the adsorption edge follows the order Pb2 + > Cu2 + ≫ Cd2 + ≈ Zn2 + > Sr2 + > Tl+ > Cs+, which is similar to the element hydrolysis order. Trivalent hydrolysates (Al3 + and Ga3 +) demonstrated increased adsorption with a pH increase at 2 ≤ pH ≤ 4 followed by desorption from the bacterial surface at pH > 5–6 as negatively charged Al(OH)4− and Ga(OH)4−, similar to anions, such as MoO42 − and WO42 −. This behavior directly reflects the level of trace element complexation with two primary binding sites at the surface, carboxylate and phosphorylate, and certain electrostatic-like interactions between negatively charged anions and positive amine groups in acidic solutions. The main results of the present study are that the Rps. palustris exhibit trace element binding properties through their pH-dependence and overall adsorption capacity, which are similar to properties described earlier for other phototrophic bacteria, both anoxygenic bacteria and cyanobacteria. The absolute adsorption capacities for metal cations follow the order Rps. palustris

Although the interaction between Fe and microorganisms has been extensively studied, the main physico-chemical factors controlling the mechanisms of Fe adsorption and precipitation on bacterial cell walls remain poorly understood. In this study, we quantified thermodynamic parameters of the Fe adsorption reaction and characterized the speciation of Fe adsorbed on the surface of cyanobacteria and soil heterotrophic bacteria. For this purpose, the molecular mechanisms of iron interaction with typical aquatic and soil bacteria were investigated by combining batch macroscopic adsorption experiments with atomic-level Fe K-edge X-ray absorption fine structure spectroscopy (XAFS). Three cyanobacteria species ( Synechococcus sp., Planktothrix sp. and Gloeocapsa sp.) and aerobic heterotrophic soil rhizobacterium ( Pseudomonas aureofaciens ) were used for Fe 3 + and Fe 2 + adsorption experiments. These experiments were carried out for a wide range of initial iron concentration (4.5–57.3 μM) and pH (2.0–6.5). Surface adsorption data were rationalized using a Linear Programming Model (LPM), which allowed quantification of the surface adsorption constants and the number of binding sites. XAS (XANES and EXAFS) analysis of adsorbed iron demonstrated the predominance of O-coordinated Fe 3 + species. Moreover, XANES data treatment using a linear combination fit of reference compounds suggested that the atomic environment of iron adsorbed onto soil bacterial surfaces was dominated by phosphoryl moieties with a lesser amount of carboxylates and some contribution of Fe(III)-oxy(hydr)oxide component. Complete oxidation of Fe(II) to Fe(III) was observed in the solid phase as determined by XANES analysis. Binding of Fe(III) to carboxylate groups was only significant for capsular cyanobacteria ( Gloeocapsa sp.). The relative proportions of various Fe species at the cell surface determined by thermodynamic analysis of the macroscopic data and by XAS are in a good agreement. Our results suggest that, in the presence of surface organic ligands, the oxidation of divalent iron does occur, but the polymerization of formed Fe(III)oxy(hydr)oxides is partially inhibited and adsorbed iron in the form of both Fe–O–Fe polymers and individual Fe atoms attached to phosphoryl moieties. The presence of EPS reduces metal-cell binding capacity and enhances Fe polymerization at the bacterial surface.

Stable Ca and radiogenic Sr isotope compositions were measured in different compartments (stream water, soil solutions, rocks, soils and soil leachates and vegetation) of a small permafrost-dominated watershed in the Central Siberian Plateau. The Sr and Ca in the area are supplied by basalt weathering and atmospheric depositions, which significantly impact the Sr isotopic compositions. Only vegetation significantly fractionates the calcium isotopes within the watershed. These fractionations occur during Ca uptake by roots and along the transpiration stream within the larch trees and are hypothesised to be the result of chromatographic processes and Ca oxalate crystallisations during Ca circulation or storage within plant organs. Biomass degradation significantly influences the Ca isotopic compositions of soil solutions and soil leachates via the release of light Ca, and organic and organo-mineral colloids are thought to affect the Ca isotopic compositions of soil solutions by preferential scavenging of 40Ca. The imprint of organic matter degradation on the δ44/40Ca of soil solutions is much more significant for the warmer south-facing slope of the watershed than for the shallow and cold soil active layer of the north-facing slope. As a result, the available stock of biomass and the decomposition rates appear to be critical parameters that regulate the impact of vegetation on the soil–water system in permafrost areas. Finally, the obtained δ44/40Ca patterns contrast with those described for permafrost-free environments with a much lower δ44/40Ca fractionation factor between soils and plants, suggesting specific features of organic matter decomposition in permafrost environments. The biologically induced Ca isotopic fractionation observed at the soil profile scale is not pronounced at the scale of the streams and large rivers in which the δ44/40Ca signature may be controlled by the heterogeneity of lithological sources.

Stable (Cu and Mg) and radiogenic (Sr and Nd) isotopic compositions in filtrates and ultrafiltrates of various size fractions have been measured in waters of subarctic watersheds (NW Russia) and in temperate rivers and lakes of the south boreal zone. A large volume of samples were filtered in the field using cascade filtration and ultrafiltration employing progressively decreasing pore sizes (100, 20, 10, 5, 0.8, 0.4, 0.22, and 0.1 μm; 100, 10 and 1 kDa) followed by element isotopic analysis using thermal ionization mass spectrometers and a Neptune multicollector ICP-MS. In the boreal watershed underlain by Archean and Proterozoic rocks, the 87 Sr/ 86 Sr ratio decreased in the 1–100 kDa ultrafiltrates and dialysates by 0.0001–0.0004 units compared to the 0.45 μm filtrates. Despite the dominance of colloids in the Nd speciation in surface waters, the isotopic value of Nd in the filtrates and ultrafiltrates remained constant within the uncertainty of the measurements. We hypothesize the absence of an atmospheric input of silicate dust for Nd but the presence of marine aerosols for Sr. It follows that the Sr in the investigated surface waters has a short residence time compared to the time required for achieving isotopic equilibrium between the colloidal (1 kDa–0.22 μm) and truly dissolved ( Despite the dramatically different structures of the metal–dissolved organic matter (DOM) complexes for Cu 2 + and Mg 2 + , the results of the present work reveal a high homogeneity of stable isotope compositions between colloidal (1 kDa–0.22 μm) and ultrafiltered (

Significant and systematic variations of iron isotopic composition in surface water sample fractions obtained by frontal cascade filtration and ultrafiltration have been recorded in (1) subarctic organic-rich boreal river and stream, mire, lake and soil solutions in northern taiga zone (Karelia, NW Russia) and (2) temperate river and lake waters of the southern boreal zone (Central Russia). Water samples were filtered in the field employing progressively decreasing pore size from 100 μm to 1 kDa followed by iron isotope analysis. In all river samples, there was a gradual increase of δ57Fe relative to IRMM-14 with decreasing pore size, from +0.4 ± 0.1‰ at 100 μm up to +4.2 ± 0.1‰ at 10 kDa fraction in the subarctic zone and from −0.024 ± 0.2‰ at 100 μm up to +1.2 ± 0.2‰ at 10 kDa in the temperate zone. In the series of filtrates/ultrafiltrates of subarctic and temperate streams and rivers, the δ57Fe value decreases with increasing molar Fe/Corg ratio. Therefore, small-size, Fe-poor, C-rich colloids (1–10 kDa) and Low Molecular Weight (LMW) fractions of oxygenated water exhibit strong enrichment in heavy isotope whereas High Molecular Weight Fe-rich colloids (100 kDa–0.22 μm) and particles (1–100 μm) are isotopically lighter and closer to the continental crust Fe isotope composition. The relative enrichment of 1–10 kDa ultrafiltrates in heavy isotopes suggests that low molecular weight ligands bind Fe more strongly (Fe–O–C bonds) than Fe(III)oxy(hydr)oxides (Fe–O–Fe bonds), in accord with quantum mechanics principles. Highly positive δ57Fe of the LMW fraction of labile and potentially bioavailable Fe in small subarctic rivers may turn out to be a very important source of isotopically heavy Fe in the Arctic Ocean. The mechanisms involved in the production of this isotopically heavy Fe may lead this tracer to become a new indicator of environmental changes occurring in the boreal zone.

Towards a better understanding of acid–base properties and metal adsorption capacities of the first primary producers on Earth, the surface chemistry of non-sulfur anoxygenic phototrophic bacteria (APB) Rhodobacter blasticus f-7 was characterized using a combination of potentiometric acid–base titration methods and electrophoretic mobility measurements as a function of pH (3 to 11) and ionic strength (0.001 to 1.0 M). Surface titrations were performed using limited residence time reactors taking into account the cell-wall bound Ca and Mg from the culture media for net proton balance calculations. Electrophoretic mobilities of live APB cells were investigated in 0.001–0.5 M NaCl at pH of 1 to 11 and different Zn, Cd and Pb concentrations. Adsorption of Zn, Cd, Pb, Cu, Co, Ni, Sr, Al, Ga, Ge, Mo, and W was studied at 25 °C in 0.01 M NaNO3 as a function of pH and metal concentration in batch reactors. A competitive Langmuir sorption isotherm in conjunction with a linear programming optimization method (LPM) was used to fit experimental data and assess the number and nature (carboxylate, phosphoryl/phosphodiester and amine) of surface sites and adsorption reaction constants involved in the binding of trace metals to the Rhodobacter blasticus f-7 surface. We found that the total H/OH binding site number (60–120 μmol/gwet) for APB is comparable to that of cyanobacteria studied previously by the same technique (50–200 μmol/gwet). Similarly, LPM adsorption parameters for Zn, Cu, Pb and Cd for APB are in close agreement with those observed for the cyanobacteria. As such, results of the present study indicate similar affinity of both bacteria cells surfaces to divalent metal micronutrients, most likely due to the dominance of carboxylate and phosphorylate binding at rather high metal loading.

Towards a better understanding of chemical composition of snow and its impact on surface water hydrochemistry in poorly studied Western Siberia Lowland (WSL), dissolved (melted snow) and particulate (> 0.45 μm) fractions of snow were sampled in February 2014 across a 1700-km latitudinal gradient (c.a. 56.5 to 68° N) in essentially pristine regions. Concentration of dissolved Fe, Co, Cu, As, La, increased by a factor of 2 to 5 north of 63° N. The pH, Ca, Mg, Sr, Mo and U dissolved concentration in snow water increased with the increase in concentration of particulate fraction (PF), which was also correlated with the increase in calcite and dolomite proportion in the mineral fraction, suggesting an enrichment of meltwater by these elements during dissolution of carbonate minerals. The concentrations of Al, Fe, Pb, La and other insoluble elements in Comparison of major and trace elements in dissolved fraction of snow with lakes and rivers of western Siberia across the full latitude profile revealed significant atmospheric input of a number of trace elements. The snow water concentration of DIC, Cl, SO 4 , Mg, Ca, Cr, Co, Ni, Cu, Mo, Cd, Sb, Cs, W, Pb and U exceeded or were comparable with spring-time concentration in thermokarst lakes of the region. The spring-time river fluxes (May–June, representing the snow melt period) of DIC, Cl, SO 4 , Na, Mg, Ca, Rb, Cs, metals (Cr, Co, Ni, Cu, Zn, Cd, Pb), metalloids (As, Sb), Mo and U in the discontinuous to continuous permafrost zone (64–68° N) can be fully explained by melting of accumulated snow. Therefore, the present study demonstrates significant and previously underestimated atmospheric input of many major and trace elements to their riverine fluxes during spring flood. The impact of snow deposition strongly increased northward, in discontinuous and continuous permafrost zones of frozen peat bogs, which is consistent with the decrease of the impact of rock lithology on river chemical composition in the permafrost zone of WSL, relative to the permafrost-free regions.

Thaw of frozen peat in discontinuous permafrost zone produces a significant number of thermokarst lakes, which are known to contribute to Green House Gases (GHG) emission in the atmosphere. In palsa peatland of western Siberia, the thermokarst lake formation includes soil subsidences, lichen submergence and peat abrasion, leading to lateral spreading of the lake border, often intensified by ground fires. Mesocosm experiments were conducted during 3weeks on two thermokarst lake waters interacting in 30-L tanks with surface horizon of peat, the dominant ground vegetation (lichen Cladonia sp.) and the ash produced by lichen burning at 450°C. The obtained results allowed a better understanding of physico-chemical factors controlling the enrichment of thermokarst lake water in organic carbon and metals, and evaluating CO2 sequestration/emission potential. The changes of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), major element and divalent metal concentration in response to peat and lichen biomass addition were less than a factor of 2 over full duration of the experiment. Iron (Fe) concentration in the lake water decreased by a factor of 2 to 3 after the addition of peat and lichen biomass. The concentration of low-soluble trivalent and tetravalent hydrolysates decreased by ca. 30 to 50%, presumably due to their co-precipitation with Fe hydroxide. The dissolved carbon dioxide (CO2) in tank with lichen increased by a factor of 5.5±0.5, likely due to respiration of algal component in closed environment. Strong enrichment of the lake water in DIC, P, K, Ca, Mg, Si, Al, Ti, Mn, Mo, Rb, As, Sb and U upon the ash addition persisted over full duration of experiments and was significant (p

Towards a better understanding of trace element transport in permafrost-affected Earth surface environments, we sampled ∼ 60 large and small rivers (< 100 to ≤ 150 000 km2 watershed area) of Western Siberia Lowland (WSL) during spring flood and summer and winter base-flow across a 1500 km latitudinal gradient covering continuous, discontinuous, sporadic and permafrost-free zones. Analysis of ∼ 40 major and trace elements in dissolved (< 0.45 μm) fraction allowed establishing main environmental factors controlling the transport of metals and trace elements in rivers of this environmentally important region. No statistically significant effect of the basin size on most TE concentration was evidenced. Three category of trace elements were distinguished according to their concentration – latitude pattern: (i) increasing northward in spring and winter (Fe, Al, Ga (only winter), Ti (only winter), REEs, Pb, Zr, Hf, Th (only winter)), linked to leaching from peat and/or redox processes and transport in the form of Fe-rich colloids, (ii) decreasing northward during all seasons (Sr, Mo, U, As, Sb) marking the underground water influence of river feeding and (iii) elements without distinct trend from S to N whose variations within each latitude range were higher than the difference between latitudinal ranges (B, Li, Ti (except summer), Cr, V, Mn, Zn, Cd, Cs, Hf, Th). In addition to these general features, specific, northward increase during spring period was mostly pronounced for Fe, Mn, Co, Zn and Ba and may stem from a combination of enhanced leaching from the topsoil and vegetation and bottom waters of the lakes (spring overturn). A spring time northward decrease was observed for Ni, Cu, Zr, Rb. The southward increase in summer was strongly visible for Fe, Ni, Ba, Rb and V, probably due to peat/moss release (Ni, Ba, Rb) or groundwater feeding (Fe, V). The Principal Component Analysis demonstrated two main factors potentially controlling the ensemble of TE concentration variation. The first factor, responsible for 16–20 % of overall variation, included trivalent and tetravalent hydrolysates, Cr, V, and DOC and presumably reflected the presence of organo-mineral colloids, as also confirmed by previous studies in Siberian rivers. The 2nd factor (8–14 % variation) was linked to the latitude of the watershed and acted on elements affected by the groundwater feeding (DIC, Sr, Mo, As, Sb, U), whose concentration decreased significantly northward during all seasons. Overall, the rank of environmental factors on TE concentration in western Siberian rivers was latitude (3 permafrost zones) > season > watershed size. The effect of the latitude was minimal in spring for most TE but highly visible for Sr, Mo, Sb and U. The main factors controlling the shift of river feeding from surface and subsurface flow to deep underground flow in the permafrost-bearing zone were the depth of the active (unfrozen) seasonal layer and its position in organic or mineral horizons of the soil profile. In the permafrost-free zone, the relative role of carbonate mineral-bearing base rock feeding vs. bog water feeding determined the pattern of trace element concentration and fluxes in rivers of various size as a function of season. Comparison of obtained TE fluxes in WSL rivers with those of other subarctic rivers demonstrated reasonable agreement for most trace elements; the lithology of base rocks was the major factor controlling the magnitude of TE fluxes. The climate change in western Siberia and permafrost boundary migration will affect essentially the elements controlled by underground water feeding (DIC, alkaline-earth elements (Ca, Sr), oxyanions (Mo, Sb, As) and U). The thickening of the active layer may increase the export of trivalent and tetravalent hydrolysates in the form of organo-ferric colloids. Plant litter-originated divalent metals present as organic complexes may be retained via adsorption on mineral horizon. However, due to various counterbalanced processes controlling element source and sinks in plants – peat – mineral soil – river systems, the overall impact of the permafrost thaw on TE export from the land to the ocean may be smaller than that foreseen by merely active layer thickening and permafrost boundary shift.

Active processes of permafrost thaw in Western Siberia increase the number of soil subsidencies, thermokarst lakes and thaw ponds. In continuous permafrost zones, this process promotes soil carbon mobilisation to water reservoirs, as well as organic matter (OM) biodegradation, which produces a permanent flux of carbon dioxide (CO2) to the atmosphere. At the same time, the biogeochemical evolution of aquatic ecosystems situated in the transition zone between continuous permafrost and permafrost-free terrain remains poorly known. In order to better understand the biogeochemical processes that occur in thaw ponds and lakes located in discontinuous permafrost zones, we studied ~30 small (1–100,000 m2) shallow (