Element transport in the Taz River, western Siberia

The riverine export fluxes of dissolved carbon, nutrient and metals from the land to the Arctic Ocean are fairly well quantified for five large Arctic rivers but remain virtually unknown for mid-sized Eurasian rivers, notably those draining through the permafrost zone. Because such rivers can most rapidly respond to on-going climate warming and permafrost thaw in the Arctic, their current hydrochemical composition and elemental yields are badly needed for judging the level of changes in the very near future. Towards quantifying the annual export fluxes and assessing the mechanisms of seasonal variability of river solutes, we monitored the pristine subarctic Taz River (Swatershed = 150,000 km2), which drains through boreal forest and peatlands in the discontinuous and continuous permafrost zone, on a weekly to monthly basis over a 3 year period. Based on seasonal pattern of riverine solutes (70% of annual Mn flux occurred in winter. A number of elements present in the snowpack exhibited sizable (> 45%) export during spring flood (Zn, Cu, Pb, Cd, Sb and Cs). The 3 years mean export fluxes (yields) of dissolved components were comparable to or 30–50% lower than those of other large and medium sized Arctic rivers. This was due mostly to a lack of fresh unaltered rocks and a dominance of peatlands within the Taz River watershed. Elevated concentrations of redox-sensitive micro-nutrients (such as Fe and Mn) occurring during winter baseflow can be linked to disproportionally large floodplain zone of this river which can act, especially in the river's lower reaches, as a stratified lake thereby releasing high amounts of redox-sensitive elements from the sediments. The role of suboxic zones in the Arctic boreal riverine landscape may be more important than previously thought, and may allow explaining anomalously high concentrations of some metals (i.e., Mn) reported in Arctic Ocean surface waters. It is anticipated that climate warming in the region may increase the contribution of winter flow and enhance the export of soluble elements and some nutrients (such as Si, Mn and Co)

Size distribution, surface coverage, water, carbon, and metal storage of thermokarst lakes in the permafrost zone of the Western Siberia Lowland

Despite the importance of thermokarst (thaw) lakes of the subarctic zone in regulating greenhouse gas exchange with the atmosphere and the flux of metal pollutants and micro-nutrients to the ocean, the inventory of lake distribution and stock of solutes for the permafrost-affected zone are not available. We quantified the abundance of thermokarst lakes in the continuous, discontinuous, and sporadic permafrost zones of the western Siberian Lowland (WSL) using Landsat-8 scenes collected over the summers of 2013 and 2014. In a territory of 105 million ha, the total number of lakes >0.5 ha is 727,700, with a total surface area of 5.97 million ha, yielding an average lake coverage of 5.69% of the territory. Small lakes (0.5–1.0 ha) constitute about one third of the total number of lakes in the permafrost-bearing zone of WSL, yet their surface area does not exceed 2.9% of the total area of lakes in WSL. The latitudinal pattern of lake number and surface coverage follows the local topography and dominant landscape zones. The role of thermokarst lakes in dissolved organic carbon (DOC) and most trace element storage in the territory of WSL is non-negligible compared to that of rivers. The annual lake storage across the WSL of DOC, Cd, Pb, Cr, and Al constitutes 16%, 34%, 37%, 57%, and 73%, respectively, of their annual delivery by WSL rivers to the Arctic Ocean from the same territory. However, given that the concentrations of DOC and metals in the smallest lakes (<0.5 ha) are much higher than those in the medium and large lakes, the contribution of small lakes to the overall carbon and metal budget may be comparable to, or greater than, their contribution to the water storage. As such, observations at high spatial resolution (<0.5 ha) are needed to constrain the reservoirs and the mobility of carbon and metals in aquatic systems. To upscale the DOC and metal storage in lakes of the whole subarctic, the remote sensing should be coupled with hydrochemical measurements in aquatic systems of boreal plains

Seasonal dynamics of organic carbon and metals in thermokarst lakes from the discontinuous permafrost zone of western Siberia

Despite relatively good knowledge of the biogeochemistry of Siberian thermokarst lakes during summer base flow, their seasonal dynamics remains almost unexplored. This work describes the chemical composition of 130 thermokarst lakes ranging in size from a few m2 to several km2, located in the discontinuous permafrost zone. Lakes were sampled during spring flood, just after the ice break (early June), the end of summer (August), the beginning of ice formation (October) and during the full freezing season in winter (February). The lakes larger than 1000m2 did not exhibit any statistically significant control of the lake size on dissolved organic carbon (DOC), the major and trace element concentrations over three major open water seasons. On the annual scale, the majority of dissolved elements including organic carbon increased their concentration from 30 to 500 %, with a statistically significant (p summer>autumn>winter. The ice formation in October included several stages: first, surface layer freezing followed by crack (fissure) formation with unfrozen water from the deeper layers spreading over the ice surface. This water was subsequently frozen and formed layered ice rich in organic matter. As a result, the DOC and metal (Mn, Fe, Ni, Cu, Zn, As, Ba and Pb) concentrations were highest near the surface of the ice column (0 to 20 cm) and decreased by a factor of 2 towards the bottom. The main implications of discovered freeze-driven solute concentrations in thermokarst lake waters are enhanced colloidal coagulation and removal of dissolved organic matter and associated insoluble metals from the water column to the sediments. The measured distribution coefficients of a TE between amorphous organo-ferric coagulates and lake water (<0.45 μm) were similar to those reported earlier for Fe-rich colloids and low molecular weight (<1 kDa, or <1–2 nm) fractions of thermokarst lake waters, suggesting massive coprecipitation of TE with amorphous Fe oxyhydroxide stabilized by organic matter. Although the concentration of most elements was lowest in spring, this period of maximal water coverage of land created a significant reservoir of DOC and soluble metals in the water column that can be easily mobilized to the hydrological network. The highest DOC concentration observed in the smallest (<100m2) water bodies in spring suggests their strongly heterotrophic status and, therefore, a potentially elevated CO2 flux from the lake surface to the atmosphere

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

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 (< 10 to &le; 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 (< 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 < 100 to > 10 000 km². Environmental factors are ranked by their increasing effect on DOC, DIC, δ¹³C_DIC, and major elements in western Siberian rivers as follows: watershed area < season < 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 (< 1000 km² watershed) rivers DOC, DIC and ionic composition and this change will be mostly pronounced in summer

Effect of mosses and lichens on the elemental composition and dynamics of carbon in the water of thermokarst lakes

The influence of the plant substrate on the formation of the elemental composition of water and the dynamics of carbon (DOC and CO2) in thermokarst lakes in the discontinuous permafrost zone of Western Siberia was studied. Mesocosm experiments were conducted during 3 weeks on large thermokarst lake waters interacting in 30-L tanks with the dominant ground vegetation (lichen Cladonia sp. аnd moss Sphagnum sp.). As a result of mesocosm experiments is that lichen is able to change the chemical composition of melt water more strongly than mosses. An increase in the DOC concentration upon contact with lichen shows a rapid increase in the DOC concentration (2–3 weeks) at a high substrate concentration. The increase in conductivity, DOC and SUVA254, and concentrations of CO2 and CH4 in lake water in the presence of moss and lichen in the first week of the experiment are within the range of values characteristic of natural thermokarst subsidence and lakes. Thus, the conducted field experiments on setting up mesocosms with the addition of the dominant vegetation of flat-hilly frozen bogs (mosses and lichens) can serve as experimental models of the formation of the elemental composition and the formation of dissolved greenhouse gases in thermokarst subsidence

Organic and organo-mineral colloids in discontinuous permafrost zone

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 (<0.22 μm) and low-molecular-weight (<1 kDa) fractions exhibited an order of magnitude decrease in DOC/Fe in the landscape continuum “depressions and permafrost subsidence → thaw ponds → thermokarst lakes → streams → rivers”. Thermodynamic modeling and on-site size separation suggested that a number of trace elements (TEs), including alkaline earth elements and several micronutrients (Zn, Ba, Mn, and Ni), decreased the degree of their binding to DOM along the landscape continuum, whereas the majority of insoluble TEs (Al, Fe, Co, Cd, Cu, Pb, REEs, Th, and U) remained complexed with DOM in the LMW<1 kDa fraction. Two primary sites of colloid generation included (i) ground vegetation and peat leaching, which supplied DOM complexes of divalent metals and organo-Al entities to thaw ponds and lakes; and (ii) Fe2+ oxidation and TE co-precipitation with Fe hydroxides in the presence of surface DOM at groundwater discharge sites within the riparian/hyporheic zones of rivers. Under a warming climate scenario, an increase in the thickness of the thawing depth will intensify the input of inorganic components from deep mineral horizons and possibly underground waters thus producing the enrichment of large lakes in Fe-rich colloids and particles. The speciation of divalent metal micronutrients (Cu, Ni, and Co) and toxic metals (Al, Cd, Pb, and U) that are complexed within DOM will most likely remain conservative. Overall, the WSL’s surface water colloidal composition may shift from DOM-rich and DOM-Al-rich to Fe-rich, and the export of low-soluble trivalent and tetravalent hydrolysates from the soil to rivers will increase

Thermokarst lake waters across the permafrost zones of western Siberia

This work describes the hydrochemical composition of thermokarst lake and pond ecosystems, which are observed in various sizes with different degrees of permafrost influence and are located in the northern part of western Siberia within the continuous and discontinuous permafrost zones. We analysed the elemental chemical composition of the lake waters relative to their surface areas (from 10 to 106 m2) and described the elemental composition of the thermokarst water body ecosystems in detail. We revealed significant correlations between the Fe, Al, dissolved organic carbon (DOC) and various chemical elements across a latitude gradient covering approximately 900 km. Several groups of chemical elements that reflect the evolution of the studied water bodies were distinguished. Combining the data for the studied latitude profile with the information available in the current literature demonstrated that the average dissolved elemental concentrations in lakes with different areas depend specifically on the latitudinal position, which is presumably linked to (1) the elements leached from frozen peat, which is the main source of the solutes in thermokarst lakes, (2) marine atmospheric aerosol depositions, particularly near the sea border and (3) short-range industrial pollution by certain metals from the largest Russian Arctic smelter. We discuss the evolution of the chemical compositions observed in thermokarst lakes during their formation and drainage and predict the effect that changing the permafrost regime in western Siberia has on the hydrochemistry of the lakes

Organic and organo-mineral colloids in discontinuous permafrost zone

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 (<0.22 μm) and low-molecular-weight (<1 kDa) fractions exhibited an order of magnitude decrease in DOC/Fe in the landscape continuum “depressions and permafrost subsidence → thaw ponds → thermokarst lakes → streams → rivers”. Thermodynamic modeling and on-site size separation suggested that a number of trace elements (TEs), including alkaline earth elements and several micronutrients (Zn, Ba, Mn, and Ni), decreased the degree of their binding to DOM along the landscape continuum, whereas the majority of insoluble TEs (Al, Fe, Co, Cd, Cu, Pb, REEs, Th, and U) remained complexed with DOM in the LMW<1 kDa fraction. Two primary sites of colloid generation included (i) ground vegetation and peat leaching, which supplied DOM complexes of divalent metals and organo-Al entities to thaw ponds and lakes; and (ii) Fe2+ oxidation and TE co-precipitation with Fe hydroxides in the presence of surface DOM at groundwater discharge sites within the riparian/hyporheic zones of rivers. Under a warming climate scenario, an increase in the thickness of the thawing depth will intensify the input of inorganic components from deep mineral horizons and possibly underground waters thus producing the enrichment of large lakes in Fe-rich colloids and particles. The speciation of divalent metal micronutrients (Cu, Ni, and Co) and toxic metals (Al, Cd, Pb, and U) that are complexed within DOM will most likely remain conservative. Overall, the WSL’s surface water colloidal composition may shift from DOM-rich and DOM-Al-rich to Fe-rich, and the export of low-soluble trivalent and tetravalent hydrolysates from the soil to rivers will increase

Elemental composition of macrophytes of thermokarst lakes in Western Siberia

Relevance. Macrophytes are one of the key participants in accumulation of chemical elements in lake ecosystems, but despite this, the issue of elemental composition of macrophytes of thermokarst lakes in Western Siberia and accumulation of chemical elements relative to the sediments and pore water remains practically unexplored. The aim of the research is to describe the formation of elemental composition of macrophyte species of thermokarst lakes in the north of Western Siberia and to identify the possibility of their use in biomonitoring. The objects of research were macrophyte plants (Hippuris vulgaris L., Glyceria maxima (Hartm.) Holmb., Comarum palustre L., Ranunculus spitzbergensis Hadac, Carex aquatilis Wahlenb s. Str., Menyanthes trifoliata L.), sediments and pore waters of thermokarst lakes of the north of Western Siberia. Methods. The elemental composition of the samples was studied by inductively coupled plasma mass spectrometry (ICP/MS, Agilent Technologies, 7500 se), the concentration of anions in water samples was determined by liquid chromatography (Dionex ICS/2000), the dissolved organic carbon was defined by infrared spectroscopy TOC/VCSN, Shimadzu), the organic carbon content of the sediments was determined by infrared spectrometry (Horiba Jobin Yvon Emia/320V C/S Analyzer). Statistical processing of data was carried out using the STATISTICA 6.0 software package. Results. The coefficients of biological accumulation of chemical elements in macrophytes relative to sediments and pore water were calculated for four key thermokarst lakes. It has been shown that macronutrients (Na, Mg, Ca), some heavy metals and metalloids (Ni, Cu, Zn, Co, As, Cd), as well as B and Mo are actively accumulated in water plants of thermokarst lakes of Western Siberia. High coefficients of accumulation of heavy metals indicate a significant phytoremediation function of macrophytes in a given territory