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

In contrast to numerous studies on the dynamics of dissolved ( &lt; 0.45&thinsp;µm) elements in permafrost-affected high-latitude rivers, very little is known of the behavior of river suspended ( &gt; 0.45&thinsp;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&thinsp;000&thinsp;km2 watershed) along a 1700&thinsp;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°&thinsp;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.</p

Using stable isotopes to assess surface water source dynamics and hydrological connectivity in a high-latitude wetland and permafrost influenced landscape

The research has been supported by the NERC/JPI SIWA project (NE/M019896/1); grant issued in accordance with Resolution of the Government of the Russian Federation No. 220 dated 9 April 2010, under Agreement No. 14.B25.31.0001 with Ministry of Education and Science of the Russian Federation dated 24 June 2013 (BIO-GEO-CLIM); grant RFBR No 17-05-00-348a; grant FCP “Kolmogorov” 14.587.21.0036, grant RNF No 15-17-1009, and grant RFBR No 17-55-16008. Stable water isotope data are available in the Natural Environment Research Council (NERC) Environmental Information Data Centre (EIDC) data repository (title: “Stable water isotopes in Western Siberian inland waters”, permanent identifier: https://doi.org/10.5285/ca17e364-638d-4949-befb-b18b3770aec6). We would like to acknowledge the Arctic-GRO and IAEA for their publicly available databases providing supporting data for our analyses. Stream flow data at Nikolskoe was provided by Sergey Vorobiev. Liliya Kovaleva is acknowledged for the artwork in Figure 9. We would like to thank the two anonymous reviewers and the handling editors for their constructive comments that improved the manuscript.Peer reviewedPublisher PD

High riverine CO2 emissions at the permafrost boundary of Western Siberia

Acknowledgements: The study was part of the JPI Climate initiative, financially supported by VR (the Swedish Research Council) grant no. 325-2014-6898 to J.K. Additional funding from RNF (RSCF) grant no. 18-17-00237, RFBR grant no. 17-55-16008 and RF Federal Target Program RFMEFI58717X0036 ‘Kolmogorov’ to O.S.P. and S.N.K. as well as NERC grant no. NE/M019896/1 to C.S. is acknowledged. The authors thank A. Sorochinskiy and A. Lim for assistance in the field, as well as M. Myrstener, M. Klaus and S. Monteux for advice on data analysis. L. Kovaleva is acknowledged for artwork.Peer reviewedPostprin

Seasonal dynamics of phytoplankton in acidic and humic environment in thaw ponds of discontinuous permafrost zone

Despite the high importance of shallow thaw ponds (thermokarst lakes) of Western Siberia in both surface coverage and carbon dioxide and methane emission to the atmosphere, their planktonic component remains poorly characterized. This work reports the first results of phytoplankton analysis of thaw lakes and ponds sampled during spring flood, open water season and ice formation. The lakes, located within the discontinuous/sporadic permafrost (66°N), are shallow (0.5–1.5 m depth), acidic (4.0 ≤ pH ≤ 6.1) and highly organic (10–40 mg.L−1 of DOC) with low concentrations of total dissolved solid (10–30 mg.L−1). In the plankton community of 20 lakes of variable size (from 700 m2 to 1.8 km2), we identified 134 taxa of algae with the dominance of green algae (33–60% of total), cyanobacteria (11–14%) and dinoflagellates (7–14%). The total cell number (N) ranged from 20 to 83 million cell.L−1 and the biomass (B) ranged from 0.1 to 37 mgwet.L−1 with the dominance of green algae, Dinophyta and Charophyta Ulothrix spp., Bambusina brebissonii. A Principal Component Analysis (PCA) revealed two possible factors responsible for phytoplankton variation: dissolved inorganic carbon, positively acting on cell number and the biomass of cyanobacteria, and DOC, Si and Fe, controlling the number of diatoms and green algae. In August, there was a general increase of both N and B as pH increased. Colony-forming cyanobacteria and green algae with thick capsules were highly abundant during all seasons. The specific acidic and organic-rich context of the shallow thermokarst waters subjected to full freezing in winter is one of the major factors limiting both the biodiversity and the biomass of the phytoplankton in these water objects.First study of phytoplankton seasonal dynamics in shallow (<1 m) acidic (4 ≤ pH ≤ 6) organic-rich thaw lakes of Western Siberia revealed the dominance of desmids and sheath-forming cyanobacteria and significant control of pH and inorganic carbon on the total cell number and biomass and abundance of cyanobacteria and Charophyta

High carbon emissions from thermokarst lakes of Western Siberia

The Western Siberia Lowland (WSL) is the world’s largest frozen peatland complex, however carbon emissions (CO2+CH4) from lakes in this region remain unknown. Here, the authors sample 76 lakes and show high carbon emissions from lakes across all permafrost zones in the WSL

Impact of snow deposition on major and trace element concentrations and elementary fluxes in surface waters of the Western Siberian Lowland across a 1700 km latitudinal gradient

In order to better understand the chemical composition of snow and its impact on surface water hydrochemistry in the poorly studied Western Siberia Lowland (WSL), the surface layer of snow was sampled in February 2014 across a 1700 km latitudinal gradient (ca. 56.5 to 68° N). We aimed at assessing the latitudinal effect on both dissolved and particulate forms of elements in snow and quantifying the impact of atmospheric input to element storage and export fluxes in inland waters of the WSL. The concentration of dissolved+colloidal (&lt; 0.45 µm) Fe, Co, Cu, As and La increased by a factor of 2 to 5 north of 63° N compared to southern regions. The pH and dissolved Ca, Mg, Sr, Mo and U in snow water increased with the rise in concentrations of particulate fraction (PF). Principal component analyses of major and trace element concentrations in both dissolved and particulate fractions revealed two factors not linked to the latitude. A hierarchical cluster analysis yielded several groups of elements that originated from alumino-silicate mineral matrix, carbonate minerals and marine aerosols or belonging to volatile atmospheric heavy metals, labile elements from weatherable minerals and nutrients. The main sources of mineral components in PF are desert and semi-desert regions of central Asia. The snow water concentrations of DIC, Cl, SO4, Mg, Ca, Cr, Co, Ni, Cu, Mo, Cd, Sb, Cs, W, Pb and U exceeded or were comparable with springtime concentrations in thermokarst lakes of the permafrost-affected WSL zone. The springtime river fluxes of DIC, Cl, SO4, 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 explained solely by melting of accumulated snow. The impact of snow deposition on riverine fluxes of elements strongly increased northward, in discontinuous and continuous permafrost zones of frozen peat bogs. This was consistent with the decrease in the impact of rock lithology on river chemical composition in the permafrost zone of the WSL, relative to the permafrost-free regions. Therefore, the present study demonstrates significant and previously underestimated atmospheric input of many major and trace elements to their riverine fluxes during spring floods. A broader impact of this result is that current estimations of river water fluxes response to climate warming in high latitudes may be unwarranted without detailed analysis of winter precipitation

Minor contribution of small thaw ponds to the pools of carbon and methane in the inland waters of the permafrost-affected part of the Western Siberian Lowland

International audienceDespite the potential importance of small (2) thaw ponds and thermokarst lakes in greenhouse gas (GHG) emissions from inland waters of high latitude and boreal regions, these features have not been fully inventoried and the volume of GHG and carbon in thermokarst lakes remains poorly constrained. This is especially true for the vast Western Siberia Lowland (WSL) which is subject to strong thermokarst activity. We assessed the number of thermokarst lakes and their size distribution for the permafrost-affected WSL territory based on a combination of medium-resolution Landsat-8 images and high-resolution Kanopus-V scenes on 78 test sites across the WSL in a wide range of lake sizes (from 20 to 2 × 108 m2). The results were in fair agreement with other published data for world lakes including those in circum-polar regions. Based on available measurements of CH4, CO2, and dissolved organic carbon (DOC) in thermokarst lakes and thaw ponds of the permafrost-affected part of the WSL, we found an inverse relationship between lake size and concentration, with concentrations of GHGs and DOC being highest in small thaw ponds. However, since these small ponds represent only a tiny fraction of the landscape (i.e. ~1.5% of the total lake area), their contribution to the total pool of GHG and DOC in inland lentic water of the permafrost-affected part of the WSL is less than 2%. As such, despite high concentrations of DOC and GHG in small ponds, their role in overall C storage can be negated. Ongoing lake drainage due to climate warming and permafrost thaw in the WSL may lead to a decrease in GHG emission potential from inland waters and DOC release from lakes to rivers

Carbon storage and burial in thermokarst lakes of permafrost peatlands

Thermokarst (thaw) lakes of the Western Siberian Lowland (WSL), the World´s largest permafrost peatland, contain important but poorly constrained stocks of organic carbon (OC) and nitrogen. These lakes are highly vulnerable to climate warming and permafrost thaw. The present work aims to quantify the OC and total nitrogen (TN) stocks and accumulation rates in sediments of 11 thermokarst lakes in the WSL across a permafrost gradient, from isolated to discontinuous and continuous permafrost. We found an increase in OC and TN stocks in lake sediments (0–30 cm) from the northern taiga with sporadic permafrost (285 Tg C and 10.5 Tg N) to the tundra zone with continuous permafrost (628 Tg C and 26 Tg N). The upper 30 cm thermokarst lake sediments of the permafrost-affected WSL store 1250 ± 35 Tg C and 50 ± 1.4 Tg N). The OC accumulation rates in thermokarst lake sediments ranged from 36 to 250 g C m−2 year−1, which is 5 to 10 times higher than C accumulation rates in peatlands of western Siberia. The total OC accumulation in lakes of WSL is 7.8 ± 0.7 Tg C year−1. This is about 24–47% of the C emission from the WSL thermokarst lakes, implying that it represents an important factor in the C budget to consider in order to understand impacts of climate change and permafrost thaw on the C cycle

Trace element transport in western Siberian rivers across a permafrost gradient

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. <br><br> 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. <br><br> 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