Western Siberian Rivers Research Articles

Environmental controllers for carbon emission and concentration patterns in Siberian rivers during different seasons

Despite the importance of small and medium size rivers of Siberian boreal zone in greenhouse gases (GHG) emission, major knowledge gaps exist regarding its temporal variability and controlling mechanisms. Here we sampled 11 pristine rivers of the southern taiga biome (western Siberia Lowland, WSL), ranging in watershed area from 0.8 to 119,000 km2, to reveal temporal pattern and examine main environmental controllers of GHG emissions from the river water surfaces. Floating chamber measurements demonstrated that CO2 emissions from water surface decreased by 2 to 4-folds from spring to summer and autumn, were independent of the size of the watershed and stream order and did not exhibit sizable (>30 %, regardless of season) variations between day and night. The CH4 concentrations and fluxes increased in the order “spring ≤ summer < autumn” and ranged from 1 to 15 μmol L−1 and 5 to 100 mmol m−2 d−1, respectively. The CO2 concentrations and fluxes (range from 100 to 400 μmol L−1 and 1 to 4 g C m−2 d−1, respectively) were positively correlated with dissolved and particulate organic carbon, total nitrogen and bacterial number of the water column. The CH4 concentrations and fluxes were positively correlated with phosphate and ammonia concentrations. Of the landscape parameters, positive correlations were detected between riparian vegetation biomass and CO2 and CH4 concentrations. Over the six-month open-water period, areal emissions of C (>99.5 % CO2; <0.5 % CH4) from the watersheds of 11 rivers were equal to the total downstream C export in this part of the WSL. Based on correlations between environmental controllers (watershed land cover and the water column parameters), we hypothesize that the fluxes are largely driven by riverine mineralization of terrestrial dissolved and particulate OC, coupled with respiration at the river bottom and riparian sediments. It follows that, under climate warming scenario, most significant changes in GHG regimes of western Siberian rivers located in permafrost-free zone may occur due to changes in the riparian zone vegetation and water coverage of the floodplains.

Major and trace elements in suspended matter of western Siberian rivers: First assessment across permafrost zones and landscape parameters of watersheds

In contrast to good understanding of chemical composition of the river suspended matter (RSM) of large rivers, small rivers remain strongly understudied, despite the fact that they can provide valuable information on mechanisms of RSM generation and transport depending on key environmental parameters of the watershed. This is especially true for permafrost-affected boreal and subarctic territories, subjected to strong modification due to permafrost thaw and landscape changes under climate warming. We selected Earth’s largest frozen peatland zone, the western Siberia Lowland (WSL) in order to test an impact of climate warming, permafrost thaw and landscape zone changes on riverine transport of particulate material from mainland to the Arctic Ocean. We sampled 33 small and medium size WSL rivers during spring flood, summer baseflow and autumn flood over a 1700 km gradient of climate and permafrost. Major and trace elements in particulate (>0.45 µm) and dissolved (<0.45 µm) fraction were analyzed. We hypothesize that future increase in active layer thickness and the change of dominant landscape from bogs and lakes to forest can be predicted via analyzing the actual pattern of RSM chemical composition across various permafrost zones and landscape parameters of WSL river watershed. We observed a minimum concentration of Li, Mg, Na, K, Rb, V, Cr, Zn, Cu, Co, Ni, Al, Ga, Y, REEs, Nb, W, Ti, Zr, Hf, Th and U in RSM collected from isolated and sporadic permafrost zones. Considering all seasons together, the presence of forest in the permafrost-bearing zone increased particulate concentrations of all alkalis and alkaline-earth elements, B, As, Nb, Mn, Co, Al, Ga, REEs, Ti, Zr, Hf, Th. This is consistent with element mobilization from mineral horizons that become available for interacting with soil fluids under forested regions. Lakes retained particulate alkaline-earths, Fe, Mn, Co, trivalent and tetravalent hydrolysates (TE3+, TE4+). The concentration of lithogenic low-soluble elements (TE3+, TE4+) in the RSM strongly increased with the river size (watershed area).Compared to the world RSM average, the WSL rivers exhibited lower concentrations of all elements except Mn and P and a low share of suspended elements relative to total (suspended + dissolved) forms of trace metals and of low-mobility (lithogenic) elements. Likely reasons for these features are: (i) low runoff and low RSM concentration as there is no rock and mineral substrate exposed to physical weathering in WSL peatland; (ii) organic, rather than mineral, nature of surrounding “solid” substrates and as a result, organic rather than silicate nature of RSM, and (iii) high DOC and Fe concentration leading to high concentrations of typically low-solubilty elements in the dissolved (<0.45 µm) fraction due to colloids.From a climate warming perspective, the increase in active layer thickness and involvement of mineral horizons into soil fluid migration in discontinuous to continuous permafrost zone will likely increase the share of particulate fraction in total element transport for many soluble (labile) elements and also lithogenic elements in WSL rivers. At the same time, permafrost boundary shift northward may decrease particulate concentrations of most major and TE in rivers of discontinuous permafrost zone. The lake drainage and forest colonization of tundra and bogs in the permafrost-affected part of WSL may increase the concentration of alkali and alkaline-earth elements, divalent metals and trivalent and tetravalent hydrolysates. As a result, export of particulate metal micronutrients and toxicants from the WSL territory to the Arctic Ocean may increase.

Colloidal transport of carbon and metals by western Siberian rivers during different seasons across a permafrost gradient

In contrast to fairly good knowledge of dissolved (<0.45 µm) and particulate (>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< 3 kDa fraction and medium molecular weight (MMW3 kDa-30 kDa) colloids. The LMW< 3 kDa fraction of OC increased in the order spring < autumn < summer, following progressive replacement of allochthonous medium and high molecular weight colloids in spring by autochthonous LMW organic ligands in summer; the latter possibly occurred due to exometabolites of plankton and periphyton. The LMW OC fraction became low again in autumn, presumably due to appearance of allochthonous DOM washed out by autumn rains from peat soil at maximum thawing depth. The size of the watershed had subordinate influence on colloidal distribution compared to seasons. The effect of landscape parameters of the watershed on the colloidal status of solutes was subordinate to seasonal and permafrost-zone controls. Overall, the ongoing environmental changes in WSL will likely decrease the proportion of mineral (Fe, Al – bearing) colloids of C and trace metals exported by rivers to the Kara Sea. As a result, the flux of dissolved C, micro-nutrients and metal toxicants may become increasingly bioavailable to coastal aquatic biota.

Enhanced particulate Hg export at the permafrost boundary, western Siberia

Arctic permafrost soils contain large amounts of organic carbon and the pollutant mercury (Hg). Arctic warming and associated changes in hydrology, biogeochemistry and ecology risk mobilizing soil Hg to rivers and to the Arctic Ocean, yet little is known about the quantity, timing and mechanisms involved. Here we investigate seasonal particulate Hg (PHg) and organic carbon (POC) export in 32 small and medium rivers across a 1700 km latitudinal permafrost transect of the western Siberian Lowland. The PHg concentrations in suspended matter increased with decreasing watershed size. This underlines the significance of POC-rich small streams and wetlands in PHg export from watersheds. Maximum PHg concentrations and export fluxes were located in rivers at the beginning of permafrost zone (sporadic permafrost). We suggest this reflects enhanced Hg mobilization at the permafrost boundary, due to maximal depth of the thawed peat layer. Both the thickness of the active (unfrozen) peat layer and PHg run-off progressively move to the north during the summer and fall seasons, thus leading to maximal PHg export at the sporadic to discontinuous permafrost zone. The discharge-weighed PHg:POC ratio in western Siberian rivers (2.7 ± 0.5 μg Hg: g C) extrapolated to the whole Ob River basin yields a PHg flux of 1.5 ± 0.3 Mg y−1, consistent with previous estimates. For current climate warming and permafrost thaw scenarios in western Siberia, we predict that a northward shift of permafrost boundaries and increase of active layer depth may enhance the PHg export by small rivers to the Arctic Ocean by a factor of two over the next 10–50 years.

Riverine particulate C and N generated at the permafrost thaw front: case study of western Siberian rivers across a 1700 km latitudinal transect

Abstract. In contrast to numerous studies on the dynamics of dissolved (&lt;0.45 µm) elements in permafrost-affected high-latitude rivers, very little is known of the behavior of river suspended (&gt;0.45 µm) matter (RSM) in these regions. In order to test the effect of climate, permafrost and physio-geographical landscape parameters (bogs, forest and lake coverage of the watershed) on RSM and particulate C, N and P concentrations in river water, we sampled 33 small and medium-sized rivers (10–100 000 km2 watershed) along a 1700 km N–S transect including both permafrost-affected and permafrost-free zones of the Western Siberian Lowland (WSL). The concentrations of C and N in RSM decreased with the increase in river watershed size, illustrating (i) the importance of organic debris in small rivers which drain peatlands and (ii) the role of mineral matter from bank abrasion in larger rivers. The presence of lakes in the watershed increased C and N but decreased P concentrations in the RSM. The C:N ratio in the RSM reflected the source from the deep soil horizon rather than surface soil horizon, similar to that of other Arctic rivers. This suggests the export of peat and mineral particles through suprapermafrost flow occurring at the base of the active layer. There was a maximum of both particulate C and N concentrations and export fluxes at the beginning of permafrost appearance, in the sporadic and discontinuous zone (62–64∘ N). This presumably reflected the organic matter mobilization from newly thawed organic horizons in soils at the active latitudinal thawing front. The results suggest that a northward shift of permafrost boundaries and an increase in active layer thickness may increase particulate C and N export by WSL rivers to the Arctic Ocean by a factor of 2, while P export may remain unchanged. In contrast, within a long-term climate warming scenario, the disappearance of permafrost in the north, the drainage of lakes and transformation of bogs to forest may decrease C and N concentrations in RSM by 2 to 3 times.

Permafrost Boundary Shift in Western Siberia May Not Modify Dissolved Nutrient Concentrations in Rivers

Identifying the landscape and climate factors that control nutrient export by rivers in high latitude regions is one of the main challenges for understanding the Arctic Ocean response to ongoing climate change. This is especially true for Western Siberian rivers, which are responsible for a significant part of freshwater and solutes delivery to the Arctic Ocean and are draining vast permafrost-affected areas most vulnerable to thaw. Forty-nine small- and medium-sized rivers (10–100,000 km2) were sampled along a 1700 km long N–S transect including both permafrost-affected and permafrost-free zones of the Western Siberian Lowland (WSL) in June and August 2015. The N, P, dissolved organic and inorganic carbon (DOC and DIC, respectively), particular organic carbon (POC), Si, Ca, K, Fe, and Mn were analyzed to assess the role of environmental parameters, such as temperature, runoff, latitude, permafrost, bogs, lake, and forest coverage on nutrient concentration. The size of the watershed had no influence on nutrient concentrations in the rivers. Bogs and lakes retained nutrients whereas forests supplied P, Si, K, Ca, DIC, and Mn to rivers. The river water temperature was negatively correlated with Si and positively correlated with Fe in permafrost-free rivers. In permafrost-bearing rivers, the decrease in T northward was coupled with significant increases in PO4, Ptot, NH4, pH, DIC, Si, Ca, and Mn. North of the permafrost boundary (61° N), there was no difference in nutrient concentrations among permafrost zones (isolated, sporadic, discontinuous, and continuous). The climate warming in Western Siberia may lead to a permafrost boundary shift northward. Using a substituting space for time scenario, this may decrease or maintain the current levels of N, P, Si, K, Ca, DIC, and DOC concentrations in rivers of continuous permafrost zones compared to the present state. As a result, the export flux of nutrients by the small- and medium-sized rivers of the Western Siberian subarctic to the Arctic Ocean coastal zone may remain constant, or even decrease.

Trace element transport in western Siberian rivers across a permafrost gradient

Abstract. Towards a better understanding of trace element (TE) transport in permafrost-affected Earth surface environments, we sampled ∼ 60 large and small rivers (&lt; 100 to ≤ 150 000 km2 watershed area) of the Western Siberian Lowland (WSL) during spring flood and summer and winter baseflow across a 1500 km latitudinal gradient covering continuous, discontinuous, sporadic and permafrost-free zones. Analysis of ∼ 40 major and TEs in the dissolved (&lt; 0.45 µm) fraction allowed establishing main environmental factors controlling the transport of metals and TEs in rivers of this environmentally important region. No statistically significant effect of the basin size on most TE concentrations was evidenced. Two groups of elements were distinguished: (1) elements that show the same trend throughout the year and (2) elements that show seasonal differences. The first group included elements decreasing northward during all seasons (Sr, Mo, U, As, Sb) marking the underground water influence of river feeding. The elements of the second group exhibited variable behavior in the course of the year. A northward increase during spring period was mostly pronounced for Fe, Al, 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 springtime northward decrease was observed for Ni, Cu, Zr and Rb. The increase in element concentration northward was observed for Ti, Ga, Zr and Th only in winter, whereas Fe, Al, rare earth elements (REEs), Pb, Zr, and Hf increased northward in both spring and winter, which could be linked to leaching from peat and transport in the form of Fe-rich colloids. A 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). Finally, B, Li, Cr, V, Mn, Zn, Cd, and Cs did not show any distinct trend from S to N. The order of landscape component impact on TE concentration in rivers was lakes &gt; bogs &gt; forest. The lakes decreased export of Mn and Co in summer and Ni, Cu, and Rb in spring, presumably due to biotic processes. The lakes enriched the rivers in insoluble lithogenic elements in summer and winter, likely due to TE mobilization from unfrozen mineral sediments. The rank of environmental factors on TE concentration in western Siberian rivers was latitude (three permafrost zones) &gt; season &gt; watershed size. The effect of the latitude was minimal in spring for most TEs 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 versus bog water feeding determined the pattern of TE concentration and fluxes in rivers of various sizes as a function of season. Comparison of obtained TE fluxes in WSL rivers with those of other subarctic rivers demonstrated reasonable agreement for most TEs; the lithology of base rocks was the major factor controlling the magnitude of TE fluxes. Climate change in western Siberia and permafrost boundary migration will essentially affect 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 plant–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 with merely active layer thickening and permafrost boundary shift.

Permafrost coverage, watershed area and season control of dissolved carbon and major elements in western Siberian rivers

Abstract. Analysis of organic and inorganic carbon (DOC and DIC, respectively), pH, Na, K, Ca, Mg, Cl, SO4 and Si in ~ 100 large and small rivers (&lt; 10 to ≤ 150 000 km2) of western Siberia sampled in winter, spring, and summer over a more than 1500 km latitudinal gradient allowed establishing main environmental factors controlling the transport of river dissolved components in this environmentally important region, comprising continuous, discontinuous, sporadic and permafrost-free zones. There was a significant latitudinal trend consisting in a general decrease in DOC, DIC, SO4, and major cation (Ca, Mg, Na, K) concentration northward, reflecting the interplay between groundwater feeding (detectable mostly in the permafrost-free zone, south of 60° N) and surface flux (in the permafrost-bearing zone). The northward decrease in concentration of inorganic components was strongly pronounced both in winter and spring, whereas for DOC, the trend of concentration decrease with latitude was absent in winter, and less pronounced in spring flood than in summer baseflow. The most significant decrease in K concentration from the southern (&lt; 59° N) to the northern (61–67° N) watersheds occurs in spring, during intense plant litter leaching. The latitudinal trends persisted for all river watershed size, from &lt; 100 to &gt; 10 000 km2. Environmental factors are ranked by their increasing effect on DOC, DIC, δ13CDIC, and major elements in western Siberian rivers as follows: watershed area &lt; season &lt; latitude. Because the degree of the groundwater feeding is different between large and small rivers, we hypothesize that, in addition to groundwater feeding of the river, there was a significant role of surface and shallow subsurface flow linked to plant litter degradation and peat leaching. We suggest that plant-litter- and topsoil-derived DOC adsorbs on clay mineral horizons in the southern, permafrost-free and discontinuous/sporadic permafrost zone but lacks the interaction with minerals in the continuous permafrost zone. It can be anticipated that, under climate warming in western Siberia, the maximal change will occur in small (&lt; 1000 km2 watershed) rivers DOC, DIC and ionic composition and this change will be mostly pronounced in summer.

Siberian River Run‐off in the Kara Sea: Characterisation, Quantification, Variability and Environmental Significance

After the end of the Cold War, the number of scientific publications dealing with Russian Arctic seas increased dramatically These include compilations of Soviet‐era data sets, as well as new data collected by international expeditions since the early 1990s. Several large, multidisciplinary projects were organized through Russian‐German research partnership focusing on the Laptev and Kara seas.Notably the Siberian River Run‐off (SIRRO) project was aimed at investigating the effects of the discharge of western Siberian rivers on the Kara Sea. The importance of this topic is justified by the critical role of runoff in the formation and maintenance of the Arctic Ocean ice cover, and in controlling the deep‐sea thermohaline convection in the Nordic seas. The Kara Sea receives more than one‐third of the total runoff into the Arctic Ocean, predominantly from the Ob and Yenisey rivers, which drain a huge catchment area extending to the slopes of the Tibetan Plateau.

Toward an ice‐free Arctic ocean

The strong salinity stratification of the Arctic Ocean prevents substantial ice‐free conditions in winter by suppressing convection and reducing upward heat flux from the Atlantic Water. These conditions would be significantly altered in the sensitive southern Eurasian basin if suggested diversions of western Siberian rivers were accomplished.