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

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

The chemical composition of thermokarst lake ecosystem components is a crucial indicator of current climate change and permafrost thaw. Despite high importance of macrophytes in shallow permafrost thaw lakes for control of major and trace nutrients in lake water, the trace element (TE) partitioning between macrophytes and lake water and sediments in the permafrost regions remains virtually unknown. Here we sampled dominant macrophytes in thermokarst lakes of discontinuous and continuous permafrost zones in the Western Siberia Lowland (WSL) and measured major and trace elements in plant biomass, lake water, lake sediments and sediment porewater. All six plant species (Hippuris vulgaris L., Glyceria maxima (Hartm.) Holmb., Comarum palustre L., Ranunculus spitzbergensis Hadac, Carex aquatilis Wahlenb s. str., Menyanthes trifoliata L.) sizably accumulated macronutrients (Na, Mg, Ca), micronutrients (B, Mo, Nu, Cu, Zn, Co) and toxicants (As, Cd). Accumulation of other trace elements, including rare earth elements (REE), in macrophytes relative to pore waters and sediments was highly variable among species. Using miltiparametric statistics, we described the behavior of ТЕ across two permafrost zones and identified several group of elements depending on their sources in the lake ecosystems and their affinity to sediments and macrophytes. Under future climate warming and shifting the permafrost border to the north, we anticipate an increasing uptake of heavy metals and lithogenic low mobile elements such as Ti, Al, Cr, As, Cu, Fe, Ni, Ga, Zr, and REEs by macrophytes in the discontinuous permafrost zone and Ba, Zn, Pb and Cd in the continuous permafrost zone. This may eventually diminish transport of metal micronutrients and geochemical tracers from soils to lakes and rivers and further 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 (

International audience; Despite the importance of surface waters of permafrost landscapes in carbon (C) emission and dissolved C and metal storage and export, the majority of available observations in high latitude aquatic systems deal with punctual or seasonal sampling without accounting for diurnal variations in temperature and primary productivity-respiration cycles. Towards providing comprehensive understanding of diel variations in CO2 emission, organic C and element concentrations in lakes of frozen peatlands, we monitored, each 2 h over 2 days, the water temperature, pH, CO2 fluxes, CO2, CH4, dissolved organic and inorganic carbon (DOC and DIC, respectively), nutrients, carboxylic acids, bacterial number, and major and trace elements in two acidic (pH = 3.6 and 4.0) and humic (DOC = 15 and 35 mg L−1) thermokarst lakes of discontinuous permafrost zone in Western Siberia. We discovered a factor of 2 to 3 higher CO2 concentrations and fluxes during the night compared to daytime in the high-DOC lake. The emission fluxes in the low-DOC lake increased from zero to negative values during the day to highly positive values during the end of night and early morning. The methane concentration varied within a factor of 5 without any link to the diurnal cycle. The bulk of dissolved (< 0.45 μm) hydrochemical parameters remained highly stable with ±10% variation in concentration over 2 days of observation (DOC, DIC, SUVA254nm, carboxylates (formate, oxalate, puryvate and glutarate), Mn, Fe, Al, other trace elements). Concentrations of Si, P, K, Cu varied within ±20% whereas those of Zn and Ni ranged by a factor of 2 to 4 without any link to diurnal pattern. Overall, the impact of diel cycle on CH4, DOC, nutrient and metal concentration was below 10%. However, neglecting night-time period may underestimate net CO2 emission by ca. 30 to 50% in small organic-rich thaw ponds and switch the CO2 exchange from uptake/zero to net emission in larger thermokarst lakes. Given the dominance of large lakes in permafrost regions, the global underestimation of the emission flux may be quite high. As such, monitoring CO2 concentrations and fluxes in thermokarst lakes during months of extended night time (August to October) is mandatory for assessing the net emissions from lentic waters of frozen peatlands.

The flood zone of the Ob River, the largest (in watershed area) river of the Arctic Ocean basin, is tens of km wide and, after the Amazon's Varzea, is the world's second largest flooding territory. To better understand the biogeochemistry of the Ob River and adjacent surface waters, we studied, in May and July 2014, the dissolved and colloidal organic carbon and trace metals in small rivers, lakes, and flooded water bodies connected and disconnected with the mainstream as well as the Ob River itself. All major and trace elements were distributed among two major categories depending on their pattern of dependence on the dissolved organic carbon (DOC) concentration. Dissolved inorganic carbon (DIC), Na, Mg, Ca, sulfate, Sr, Mo, Sb and U exhibited a general decrease in concentration with the increase of the [DOC]. The lowest concentration of these elements was observed in DOC-rich humic, acidic (4.9 ≤ pH ≤ 6.1) upland lakes fed by surrounding bogs. These elements marked the influence of underground feeding in July during summer baseflow, which was most visible in flood lakes in the Ob riparian zone and the Ob River itself. In May, the flood lakes were statistically similar to the Ob River. The elevated concentration of DOC (up to 60 mg/L) in the upland lakes was not correlated with groundwater-related elements, suggesting a lack of significant groundwater feeding in these lakes. In contrast, insoluble, usually low mobile elements (Al, Fe, other trivalent hydrolysates, Ti, Zr, Hf) and some metals (Cr, Zn, Ni, Pb) demonstrated a steady increase in concentration with increasing DOC, with the lowest values observed in the Ob River and the highest values observed in small tributaries and organic-rich upland lakes in July. It follows that these elements are limited by their main carriers – organic and organo-ferric colloids, rather than by the availability of the source, peat and mineral soil or plant litter. While for the majority of non-colloidal, groundwater-fed elements with high mobility (DIC, Na, Mg, Ca, K, Sr…) the small tributaries can be used as representatives of the Ob main stream, this is not the case for low mobility “insoluble” elements, such as Fe, Al, trivalent and tetravalent hydrolysates, and metal micronutrients (Cu, Zn, and Mn). The low soluble elements and divalent metals exhibited a much lower concentration in the river mainstream compared to that in the flood lakes, upland lakes and small rivers. This difference is significantly more pronounced in the baseflow in July compared to the spring flood in May. Presumably, autochthonous processes, such as the photo-oxidation and bio-oxidation of organo-ferric colloids and phytoplankton uptake are capable decreasing the concentration of these elements in the river mainstream.