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The subsurface runoff in the permafrost zone shows considerable structural and seasonal specifics. The structural features are due, on the one hand, to the lithologically determined permeable zones of rock massifs and, on the other hand, the permeability governed by lithology. This permeability is a seasonal factor of water flow from the territory, and now it is the focus of studies in various aspects. The structural character is determined by the history of its geological and geocryological development: the runoff structures are most often inherited by the position of rocks of coarser lithological composition or features associated with former geocryological processes (fracturing, formation of cryogenic textures, local thermokarst, etc.). The spatial heterogeneity of the above-permafrost runoff was studied in the European North and in the mountains of the Northern Transbaikalia.

Hillslope water tracks are landmark features of permafrost landscapes, yet their origin and future evolution are debated. Water track networks are believed to be fully developed fluvial networks constrained by permafrost. Hence one potential evolution scenario under future climate is rapid thermo-erosional development of water tracks. Permafrost tundra environment near Vorkuta, European Russian Arctic, N67°17’, E63°39’, is a model ecosystem for this scenario, developing under changing climate and permafrost degradation.Figure 1 Hydrographical network of the study region, 30 km south of Vorkuta, European Arctic RussiaField works at the study site were carried out in September 2017 and repeated in 2021. Local streams and groundwater, from both boreholes and soil pits, were sampled for dissolved organic carbon (DOC) and nitrogen (DON), major ions, stable water isotopes and trace elements. Electrical resistivity tomography (ERT) was used to study permafrost distribution.First-order water tracks are minor linear depressions, occupied by Betula nana and rarely expressed in local topography, hosting fast subsurface runoff. Initial stages of permafrost perturbation, these forms are major pathways of DOC export from permafrost slopes, with mean DOC content is 29 ± 2 mg/L. Channelized runoff appears farther downslope, at the slope bend. Increased input from supra-permafrost groundwater is traced by Ca2+ increase, and rapid decline in DON content, from 0.1-0.3 mg/L to zero. At toeslopes adjacent to the Vorkuta R., larger streams coexist with polygonal depressions dissecting otherwise flat riverine terrace. In streams, the DOC content decreases to 12 ± 1.5 mg/L, while in depressions, it raises to 38-39 mg/L. Terrain perturbation by water tracks provides initial slope drainage and promotes fast DOC export from slope soils and its potential microbial consumption.Permafrost is discontinuous, and open taliks are present under water tracks and polygonal depressions, as shown by ERT survey. Taliks allow upward groundwater movement and drainage to the fluvial network. Sub-permafrost groundwaters were sampled from two boreholes, draining two major regional aquifers, and their traces were found in both large streams and minor water bodies of the region.

Spring floods in Sakha (Yakutia) Republic, Siberian Russia, annually induce a significant damage to the population and infrastructure of communities of this Arctic region. Most major urban settlements are protected from floods by dams and dikes, so rural areas take a heavy beat. In 2018, spring flooding severely hit numerous rural communities in the Amga River basin, central Yakutia, exposing deficient flood damage prevention and risk management practices in this Subarctic rural community. Hydrological data analysis shows that the 2018 flood had a 50-yr return period, and was caused by an ice jam in a nearby channel bend. Highest water stage is unrelated to both winter snow water equivalent or early May rainfall. The cold spells of late April and early May in Central Yakutia appear to promote ice-jam development in the middle section of the river, causing extreme water stage rise. Several river segments downstream Amga village, with shallow mid-channel sand bars with ground-fast ice during winter, impede ice movement during breakup that may lead to ice-jam formation. The Kritsky-Menkel distribution was used to evaluate a 100-yr flood water stage that was used in flood extent and depth mapping. Estimated tangible direct damage to the Amga village equals ₽5.1B, or $75.6M in 2018 prices, though the community reclaimed only ₽0.13B, or 2.5% of this total. Questionnaire survey revealed that most residents report important deterioration of drinking water quality and health after flooding.

International audience

Field studies, including high-frequency sampling for suspended sediment flux estimation, were conducted in 20142016 in the city of Igarka, at the outlet of the Yenisei River. During spring freshet of each year, multiple suspended sediment concentration (SSC) peaks were observed, irrelated to water discharge fluctuations. The form of hysteresis loops evidences the importance of input from local in-channel sediment sources, i.e. banks and bedforms, and scouring of bed material, deposited during winter, in observed sharp SSC peaks. On the falling stage of the freshet, longer peaks are related to sediment waves from major tributaries, notably the Nizhnyaya Tunguska River. Annual sediment load was calculated based on the daily water discharge and observed SSC data, using sediment rating curves and LOADEST models as two reference methods. Mean annual suspended sediment load of the Yenisei River in Igarka is estimated at 8.1 0.5 mln t., which significantly exceeds previously published values for the 19702001 period, from 4.6 to 5.9 mln t. Cumulative sediment load for 20142016 totals 24.2 2.1 mln t.

Flooding is one of the greatest disasters that produces strong effects on the ecosystem and livelihoods of the local population. Flood frequency is expected to increase globally making its risk assessment an urgent issue. In spring‐summer 2017, an extreme flooding occurred in the Indigirka River lowland of Northeastern Siberia that inundated a large area. In this study, the extent and climatic drivers of the flooding were determined using the results of field observations, satellite images, and climate reanalysis dataset, and its possible effects on the ecosystem were discussed. In 2017, a significant lowland area of around 16,016 km² was covered with water even in July, which was 5,217 km² (around 4% of the total area) greater than the water‐covered area in 2015 when usual hydrological condition in the area was observed. The hydrographic signature obtained for the Indigirka River water level in 2017 was unusual. Although the water level rose sharply at the end of May (which was typical for the Arctic region), it did not fall afterwards and even increased again to an annual daily maximum value in the middle of July. The climate reanalysis dataset obtained for the temporal–spatial variations of snow water equivalent, snowmelt, and runoff over the lowland revealed that a large amount of snowmelt runoff in June and July 2017 produced a large water‐covered area and unusually high river water levels that lasted until summer. Snow depth from winter to spring was largest in 2017 over the period from 2009 to 2017, and the surface of the lower reach of the lowland was partially covered with snow even in the end of June due to the extreme snowfall that occurred in October 2016. Such unusual hydrological conditions waterlogged most trees over the lowland, which caused serious ecosystem devastation and changes in the material cycle.

International audience; The export of organic carbon export by the rivers to the oceans either as particulate organic carbon (POC) or dissolved organic carbon (DOC) is very sensitive to climate change especially in permafrost affected catchments where soils are very rich in organic carbon. With global warming, organic carbon export in both forms is expected to increase in Arctic regions. It should affect contemporary biogeochemical cycles in rivers and oceans and therefore modify the whole food web. This study tries to understand complex processes involved in sediment, POC and DOC riverine transport in the Yenisei River basin and to quantify their respective fluxes at the river outlet. The SWAT (Soil and Water Assessment Tool) hydrological model is used in this study to simulate water and suspended sediment transfers in the largest Arctic river. POC and DOC export have been quantified with empirical models, adapted from literature for the study case. First, the hydrological model has been calibrated and validated at a daily time step for the 2003–2008 and the 2009–2016 periods respectively, and its output has been compared with field data for water and sediment fluxes. Based on conceptualization of transfer processes, calibration on climate and soil properties has been performed in order to correctly represent hydrology and sediment transfer in permafrost basins. Second, calibration of empirical models for DOC/POC transport have been performed by comparing their output with field data, available from 2003 to 2016. Our study reveals that SWAT is capable of correctly representing hydrology, sediment transfer, POC and DOC fluxes and their spatial distribution at a daily timescale, and outlines the links between these fluxes and permafrost features. Our simulation effort results in specific sediment, POC and DOC fluxes of 2.97 t km−2 yr−1, 0.13 t km−2 yr−1 and 1.14 t km−2 yr−1 for the period 2003–2016 which are in the range of previous estimates. About 60% of the total fluxes of sediment, DOC and POC to the Arctic Ocean are exported during the two months of the freshet. Spatial analysis show that permafrost-free areas have returned higher daily organic carbon export than permafrost affected zones, highlighting the thawing permafrost effect on carbon cycle in climate change feedback.

The Yenisei River has the highest annual discharge of all the rivers draining into the Arctic Ocean and therefore any change in the chemical flux composition could have a profound effect on the nutrient input to the ocean. The hydrological cycle of this region is predicted to change because of changing precipitation patterns and thawing permafrost. By studying the seasonal changes in the geochemistry of the river, information on which end-member sources are important under different hydrological conditions can be gained and therefore provide a basis to model future change. In this study we present a 7-month time-series of water chemistry samples collected at Igarka near the mouth of the Yenisei. We investigate seasonal variation in major cation chemistry, radiogenic Sr ( 87 Sr / 86 Sr ), stable Li ( δ 7 Li ) and stable Mg ( δ 26 Mg ) isotopes. Temporal variation in major cation chemistry was consistent with seasonal changes in the relative contribution of end-members previously identified from smaller rivers in this region: snow, shallow soil (organic layer and leaf litter) and deeper soil/groundwater. Temporal variation in 87 Sr / 86 Sr values, a source tracer, was also broadly consistent with seasonal changes in the contribution of the aforementioned end-members to river chemistry. However, an additional contribution from atmospheric dust, which is a minor component of major cation fluxes, is required to account for the observed increase in 87 Sr / 86 Sr values during the spring flood. Variations in Li isotopes are observed, with lower values during spring flood. Although there is a relationship between 87 Sr / 86 Sr and δ 7 Li , the variation in δ 7 Li values is unlikely to be due to changes in source inputs. Rather, they are consistent with decreased isotope fractionation during high discharge as a result of the short water residence time inhibiting processes known to fractionate Li isotopes such as adsorption and secondary mineral formation. The seasonal variation in δ 26 Mg values is negligible, but the inter-annual variation observed between 2012 and 2015 may be due to changes in permafrost extent.

Hydrochemical and geophysical data collected during a hydrological survey in September 2017, reveal patterns of small-scale hydrological connectivity in a small water track catchment in the north-European Arctic. The stable isotopic composition of water in different compartments was used as a tracer of hydrological processes and connectivity at the water track catchment scale. Elevated tundra patches underlain by sandy loams were disconnected from the stream and stored precipitation water from previous months in saturated soil horizons with low hydraulic conductivity. At the catchment surface and in the water track thalweg, some circular hollows, from 0.2 to 0.4 m in diameter, acted as evaporative basins with low deuterium excess (d-excess) values, from 2‰ to 4‰. Observed evaporative loss suggests that these hollows were disconnected from the surface and shallow subsurface runoff. Other hollows were connected to shallow subsurface runoff, yielding d-excess values between 12‰ and 14‰, close to summer precipitation. ‘Connected’ hollows yielded a 50% higher dissolved organic carbon (DOC) content, 17.5 ± 5.3 mg/L, than the ‘disconnected’ hollows, 11.8 ± 1.7 mg/L. Permafrost distribution across the landscape is continuous but highly variable. Open taliks exist under fens and hummocky depressions, as revealed by electric resistivity tomography surveys. Isotopic evidence supports upward subpermafrost groundwater migration through open taliks under water tracks and fens/bogs/depressions and its supply to streams via shallow subsurface compartment. Temporal variability of isotopic composition and DOC in water track and a major river system, the Vorkuta River, evidence the widespread occurrence of the described processes in the large river basin. Water tracks effectively drain the tundra terrain and maintain xeric vegetation over the elevated intertrack tundra patches.

It is commonly assumed that methane (CH4) released by lakes into the atmosphere is mainly produced in anoxic sediment and transported by diffusion or ebullition through the water column to the surface of the lake. In contrast to that prevailing idea, it has been gradually established that the epilimnetic CH4 does not originate exclusively from sediments but is also locally produced or laterally transported from the littoral zone. Therefore, CH4 cycling in the epilimnion and the hypolimnion might not be as closely linked as previously thought. We utilized a high-resolution method used to determine dissolved CH4 concentration to analyze a Siberian lake in which epilimnetic and hypolimnetic CH4 cycles were fully segregated by a section of the water column where CH4 was not detected. This layer, with no detected CH4, was well below the oxycline and the photic zone and thus assumed to be anaerobic. However, on the basis of a diffusion-reaction model, molecular biology, and stable isotope analyses, we determined that this layer takes up all the CH4 produced in the sediments and the deepest section of the hypolimnion. We concluded that there was no CH4 exchange between the hypolimnion (dominated by methanotrophy and methanogenesis) and the epilimnion (dominated by methane lateral transport and/or oxic production), resulting in a vertically segregated lake internal CH4 cycle.

Groundwater icings, typical features of permafrost hydrology, are indicative of hydrothermal interactions between surface and ground waters, and permafrost. Their main morphological parameters, i.e., icing area and volume, are generally estimated with low accuracy. Only scarce field observational data on icing volume and seasonal development exist to date. Our study evaluates and compares performance of several widely used techniques of icing morphometric estimation, based on field data, collected on a giant Icing #2 in the Samokit River basin, southern Yakutia. Groundwater icing area was estimated by: (a) staking, (b) unmanned aerial vehicle (UAV) surveys, and (c) satellite imagery analysis. Icing #2 area in late February was between 1.38·106 m2 and 1.68·106 m2, icing volume, between 1.73·106 m3 and 4.20·106 m3, depending on the technique used. Staking is the least accurate, but also the only direct technique, which is hence used as a baseline tool in our study. Staking-based assessment of icing morphometry is the most conservative, while UAV-based estimates of icing area are higher by 14% to 17%, and of icing volume, by 74% to 142%, compared to staking. The latter appears, in our case, to be the least accurate method, although a direct one. It requires a sufficient number of staking points and transects, which should be set up to represent all icing zones, i.e., channel branches and alluvial islands. Photogrammetry based on UAV surveys has numerous advantages, i.e., higher precision of a per pixel icing volume calculation, based on an ice-free valley bottom digital surface model (DSM), and potential reusability of a resulting DSM. However, positioning precision suffers from the overlay of multiple flyovers required because of battery replacements, and, in our case, an insufficient number of ground control points. Satellite imagery along with B.L. Sokolov’s empirical approach were used to estimate the annual maximum icing area and volume, and the empirical estimates tend to converge to satellite-based values. Finally, all thing being equal, UAV-based photogrammetry shows higher precision in estimating the icing morphometrical parameters.

Arctic lakes emit methane (CH

Permafrost hydrology is an emerging discipline, attracting increasing attention as the Arctic region is undergoing rapid change. However, the research domain of this discipline had never been explicitly formulated. Both &lsquo, permafrost&rsquo, and &lsquo, hydrology&rsquo, yield differing meanings across languages and scientific domains, hence, &lsquo, permafrost hydrology&rsquo, serves as an example of cognitive linguistic relativity. From this point of view, the English and Russian usages of this term are explained. The differing views of permafrost as either an ecosystem class or a geographical region, and hydrology as a discipline concerned with either landscapes or generic water bodies, maintain a language-specific touch of the research in this field. Responding to a current lack of a unified approach, we propose a universal process-based definition of permafrost hydrology, based on a specific process assemblage, specific to permafrost regions and including: (1) Unconfined groundwater surface dynamics related to the active layer development, (2) water migration in the soil matrix, driven by phase transitions in the freezing active layer, and (3) transient water storage in both surface and subsurface compartments, redistributing runoff on various time scales. This definition fills the gap in existing scientific vocabulary. Other definitions from the field are revisited and discussed. The future of permafrost hydrology research is discussed, where the most important results would emerge at the interface between permafrost hydrology, periglacial geomorphology, and geocryology.

The vulnerability of soil organic matter (SOM) sequestered in permafrost-affected soils to climate change plays one of the key roles in the global carbon (C) cycle. However, it still remains unclear how changing soil and site-specific factors, associated with the changing depth of the permafrost table due to thawing, influence the spatial distribution and variability of soil organic carbon (SOC) and total nitrogen (N) stocks in high-latitude mineral soils. The relationships between the spatial variation of SOC and N stocks (0–30 cm) and active layer (AL) thickness, thickness of the organic layer (OL), soil acidity, Al and Fe hydroxides as well as plant- and microbial-derived C inputs were studied using ordinary statistics and geostatistics within six landscape patches (16 m2) in the Siberian forest-tundra ecotone underlain by warm and discontinuous permafrost. At deeper permafrost table, SOC and N stocks (0–30 cm) were lower and, according to the semivariogram analysis, an overall homogenization of SOC and N distribution at the analyzed scale occurred. Total N and SOC stocks were spatially independent from root-derived organic matter distribution (i.e. the concentration of suberin-derived monomers) at shallow AL patches, whereas there was a significant positive spatial correlation within deep AL and non-permafrost soils. Hence, the development of root systems and an increase in rooting depth, leading to “hot spots” of SOM accumulation at intensively rooted soil patches, was observed as a result of deeper AL. Total N and SOC stocks within deeper AL and non-permafrost subsoils were also positively spatially correlated with the concentration of Fe and Al hydroxides, demonstrating the importance of organo-mineral associations for SOM stabilization in soils with lower permafrost table. This study confirmed that deepening of the AL in boreal forest ecosystems may lead to an overall homogenization of SOM distribution and simultaneous development of distinct mechanisms of SOM accumulation and stabilization.

A quantitative assessment is made of suspended sediment load, including particulate organic matter and organic carbon, in 2014 for the small streams of the Northern Yenisei region, in the taiga–tundra transition zone (near the city of Igarka, Krasnoyarsk krai). It was found that the suspended sediment concentration (SSC) of the streams under investigation fluctuated between 2 and 18 mg/L during the summer–autumn low-water period of 2014. The proportion of dissolved organic matter (DOM) in the total sediment yield varied from 16.4% to 74.1%, depending on landscape-geomorphological conditions for suspended sediment formation: it is higher for streams with tundra catchments and lower on forest watersheds underlain by sandy and clayey loams. The DOM content varies from catchment to catchment from 1.63 to 2.42 mg/L, and the mean concentration of dissolved organic carbon (DOC) is estimated at 0.73 to 1.09 mg C/L. It is shown that the local channel transformations serve as the main source of POM and DOC input to the water of two out of three streams under study. Surface runoff or fast subsurface flow in the organic soil horizon is the external source of DOM input to the water of the third stream during flooding. Regional empirical dependencies were obtained, which correlate the water discharge, total SSC and the proportion of DOM are obtained. The long-term proportion of DOM in the annual suspended sediment flow of the Graviika river makes up 25% and DOC, 11%, or, in absolute values, 406 and 183 t/year, and in units of layer 1.26 and 0.57 t/km2, respectively.

International audience; Permafrost peatlands are important carbon stocks currently experiencing rapid evolution after permafrost thaw. Following thaw, dissolved organic matter (DOM) is a potentially important pathway for the release of permafrost carbon. This study investigates the origin and composition of DOM across sites at different stages of thaw in a discontinuous permafrost area of North Siberia. We determine the optical properties, molecular composition, stable (δ13C) and radiocarbon (14C) content of DOM. Early stages of thaw are characterized by high DOC concentrations, high aromaticity, contribution of vegetation-derived DOM, and a high contribution of permafrost carbon. In contrast, in later stages, the microbial contribution to DOM increases, and only modern carbon is detected. This work links DOM composition with its radiocarbon content in permafrost peatlands. It shows that DOM originating from previously frozen permafrost peatland is highly aromatic and previously processed. It highlights the variability of post-thaw carbon dynamics in boreal and arctic ecosystems.

The Lena River (Lena R.) heat flux affects the Laptev Sea hydrology. Published long-term estimates range from 14.0 to 15.7 EJ·a−1, based on data from Kyusyur, at the river outlet. A novel daily stream temperature (Tw) dataset was used to evaluate contemporary Lena R. heat flux, which is 16.4 ± 2.7 EJ·a−1 (2002–2011), confirming upward trends in both Tw and water runoff. Our field data from Kyusyur, however, reveal a significant negative bias, −0.8 °C in our observations, in observed Tw values from Kyusyur compared to the cross-section average Tw. Minor Lena R. tributaries discharge colder water during July–September, forming a cold jet affecting Kyusyur Tw data. Major Tw negative peaks mostly coincide with flood peaks on the Yeremeyka River, one of these tributaries. This negative bias was accounted for in our reassessment. Revised contemporary Lena R. heat flux is 17.6 ± 2.8 EJ·a−1 (2002–2011) and is constrained from above at 26.9 EJ·a−1 using data from Zhigansk, approximately 500 km upstream Kyusyur. Heat flux is controlled by stream temperature in June, during the freshet period, while from late July to mid-September, water runoff is a dominant factor.

Water regime and sedimentary features of the middle Lena River reach near Yakutsk, central Yakutia, were studied to assess their control over fluvial thermal erosion. The Lena River floodplain in the studied reach has complex structure and embodies multiple levels varying in height and origin. Two key sites, corresponding to high and medium floodplain levels, were surveyed in 2008 to describe major sedimentary units and properties of bank material. Three units are present in both profiles, corresponding to topsoil, overbank (cohesive), and channel fill (noncohesive) deposits. Thermoerosional activity is mostly confined to a basal layer of frozen channel fill deposits and in general occurs within a certain water level interval. Magnitude-frequency analysis of water level data from Tabaga gauging station shows that a single interval can be deemed responsible for the initiation of thermal action and development of thermoerosional notches. This interval corresponds to the discharges between 21,000 and 31,000 m 3 s − 1 , observed normally during spring meltwater peak and summer floods. Competence of fluvial thermal erosion depends on the height of floodplain level being eroded, as it acts preferentially in high floodplain banks. In medium floodplain banks, thermal erosion during spring flood is constrained by insufficient bank height, and erosion is essentially mechanical during summer flood season. Bank retreat rate is argued to be positively linked with bank height under periglacial conditions.

Midlatitude anthropogenic mercury (Hg) emissions and discharge reach the Arctic Ocean (AO) by atmospheric and oceanic transport. Recent studies suggest that Arctic river Hg inputs have been a potentially overlooked source of Hg to the AO. Observations on Hg in Eurasian rivers, which represent 80% of freshwater inputs to the AO, are quasi-inexistent, however, putting firm understanding of the Arctic Hg cycle on hold. Here, we present comprehensive seasonal observations on dissolved Hg (DHg) and particulate Hg (PHg) concentrations and fluxes for two large Eurasian rivers, the Yenisei and the Severnaya Dvina. We find large DHg and PHg fluxes during the spring flood, followed by a second pulse during the fall flood. We observe well-defined water vs. Hg runoff relationships for Eurasian and North American Hg fluxes to the AO and for Canadian Hg fluxes into the larger Hudson Bay area. Extrapolation to pan-Arctic rivers and watersheds gives a total Hg river flux to the AO of 44 ± 4 Mg per year (1σ), in agreement with the recent model-based estimates of 16 to 46 Mg per year and Hg/dissolved organic carbon (DOC) observation-based estimate of 50 Mg per year. The river Hg budget, together with recent observations on tundra Hg uptake and AO Hg dynamics, provide a consistent view of the Arctic Hg cycle in which continental ecosystems traffic anthropogenic Hg emissions to the AO via rivers, and the AO exports Hg to the atmosphere, to the Atlantic Ocean, and to AO marine sediments.

Published suspended sediment data for Arctic rivers is scarce. Suspended sediment rating curves for three medium to large rivers of the Russian Arctic were obtained using various curve-fitting techniques. Due to the biased sampling strategy, the raw datasets do not exhibit log-normal distribution, which restricts the applicability of a log-transformed linear fit. Non-linear (power) model coefficients were estimated using the Levenberg-Marquardt, Nelder-Mead and Hooke-Jeeves algorithms, all of which generally showed close agreement. A non-linear power model employing the Levenberg-Marquardt parameter evaluation algorithm was identified as an optimal statistical solution of the problem. Long-term annual suspended sediment loads estimated using the non-linear power model are, in general, consistent with previously published results.

The above mentioned article was originally scheduled for publication in the special issue on Ecology of Tundra Arthropods with guest editors Toke T. Høye . Lauren E. Culler. Erroneously, the article was published in Polar Biology, Volume 40, Issue 11, November, 2017. The publisher sincerely apologizes to the guest editors and the authors for the inconvenience caused.

Modification of the hydrological cycle and, subsequently, of other global cycles is expected in Arctic watersheds owing to global change. Future climate scenarios imply widespread permafrost degradation caused by an increase in air temperature, and the expected effect on permafrost hydrology is immense. This study aims at analyzing, and quantifying the daily water transfer in the largest Arctic river system, the Yenisei River in central Siberia, Russia, partially underlain by permafrost. The semi-distributed SWAT (Soil and Water Assessment Tool) hydrological model has been calibrated and validated at a daily time step in historical discharge simulations for the 2003–2014 period. The model parameters have been adjusted to embrace the hydrological features of permafrost. SWAT is shown capable to estimate water fluxes at a daily time step, especially during unfrozen periods, once are considered specific climatic and soils conditions adapted to a permafrost watershed. The model simulates average annual contribution to runoff of 263 millimeters per year (mm yr−1) distributed as 152 mm yr−1 (58%) of surface runoff, 103 mm yr−1 (39%) of lateral flow and 8 mm yr−1 (3%) of return flow from the aquifer. These results are integrated on a reduced basin area downstream from large dams and are closer to observations than previous modeling exercises.

Modification of the hydrological cycle and, subsequently, of other global cycles is expected in Arctic watersheds owing to global change. Future climate scenarios imply widespread permafrost degradation caused by an increase in air temperature, and the expected effect on permafrost hydrology is immense. This study aims at analyzing, and quantifying the daily water transfer in the largest Arctic river system, the Yenisei River in central Siberia, Russia, partially underlain by permafrost. The semi-distributed SWAT (Soil and Water Assessment Tool) hydrological model has been calibrated and validated at a daily time step in historical discharge simulations for the 2003–2014 period. The model parameters have been adjusted to embrace the hydrological features of permafrost. SWAT is shown capable to estimate water fluxes at a daily time step, especially during unfrozen periods, once are considered specific climatic and soils conditions adapted to a permafrost watershed. The model simulates average annual contribution to runoff of 263 millimeters per year (mm yr−1) distributed as 152 mm yr−1 (58%) of surface runoff, 103 mm yr−1 (39%) of lateral flow and 8 mm yr−1 (3%) of return flow from the aquifer. These results are integrated on a reduced basin area downstream from large dams and are closer to observations than previous modeling exercises.

Chronic, low intensity herbivory by invertebrates, termed background herbivory, has been understudied in tundra, yet its impacts are likely to increase in a warmer Arctic. The magnitude of these changes is however hard to predict as we know little about the drivers of current levels of invertebrate herbivory in tundra. We assessed the intensity of invertebrate herbivory on a common tundra plant, the dwarf birch (Betula glandulosa-nana complex), and investigated its relationship to latitude and climate across the tundra biome. Leaf damage by defoliating, mining and gall-forming invertebrates was measured in samples collected from 192 sites at 56 locations. Our results indicate that invertebrate herbivory is nearly ubiquitous across the tundra biome but occurs at low intensity. On average, invertebrates damaged 11.2% of the leaves and removed 1.4% of total leaf area. The damage was mainly caused by external leaf feeders, and most damaged leaves were only slightly affected (12% leaf area lost). Foliar damage was consistently positively correlated with mid-summer (July) temperature and, to a lesser extent, precipitation in the year of data collection, irrespective of latitude. Our models predict that, on average, foliar losses to invertebrates on dwarf birch are likely to increase by 6–7% over the current levels with a 1 °C increase in summer temperatures. Our results show that invertebrate herbivory on dwarf birch is small in magnitude but given its prevalence and dependence on climatic variables, background invertebrate herbivory should be included in predictions of climate change impacts on tundra ecosystems. This study is a joint contribution of the Herbivory Network (http://herbivory.biology.ualberta.ca) and the Network for Arthropods of the Tundra (NeAT; https://tundraarthropods.wordpress.com/). Dwarf birch distribution maps were kindly provided by Kyle Joly. Sample collection during 2014 was facilitated by INTERACT (http://www.eu-interact.org/). ICB was supported by a postdoctoral fellowship funded by the Icelandic Research Fund (Rannsóknasjóður, grant nr 152468-051) and AXA Research Fund (15-AXA-PDOC-307); MtB and EK were supported by the Nordic Centre of Excellence TUNDRA, funded by the Norden Top-Level Research Initiative ‘‘Effect Studies and Adaptation to Climate Change’’; EMS and KAB were supported by COAT (Climate-ecological Observatory of the Arctic Tundra); AB was supported by MOBILITY PLUS (1072/MOB/2013/0) and the Polish-American Fulbright Commission; CGB was supported by IUT 20-28, EcolChang e Center of Excellence; BCF and TK were supported by the Academy of Finland (project 256991); MMPDH was supported by The Netherlands Organization for Scientific Research (NWO-ALW, VIDI grant 864.09.014); DSH was supported by the Natural Sciences and Engineering Research Council of Canada; AH was supported by the Research Council of Norway (grant 244557/E50); JL was funded by the German Research Foundation DFG (project WI 2680/8-1); MM-F was supported by a NERC IRF fellowship NE/L011859/1; SN was supported by the Villum foundation’s Young Investigator Programme (VKR023456); JS was supported by Kempestiftelserna and the Research Foundation Flanders (FWO); AS and NS were supported by the grant of RFBR (project 16-44-890108), grant of UB of RAS (project 15-15-4-35) and IEC “Arctic” of Yamal Government Department of Science and Innovation; LES and PAW were supported by the UK Natural Environment Research Council (NERC) grant NE/K000284/1; MVK and VZ were supported by the Academy of Finland (project 276671). Scopus

Turbidity is commonly used as a proxy to estimate suspended sediment content in streams, and for hydroecological purposes. The scope of this paper is to give an outlook to wider applications of nephelometric turbidimetry as a method. Uncalibrated turbidity records in conjunction with water chemistry data prove useful in detecting watershed reaction to single hydrological events during the spring flood in Arctic Russia. The turbidimetric survey technique was applied to study the spatial variability of sediment yield features on small rivers of the south-eastern part of Sakhalin Island. Suspended sediment concentration (SSC) vs. turbidity relation follows the geological features of the terrain and reflects the land-use intensity within the watersheds. For our Igarka key site, a logarithmic regression model was developed as an instrument of SSC calculation with turbidity data for each of the four studied watersheds. A regional regression model was developed for this site, and supplementary water optics data (filtered sample turbidity) was employed to increase the reliability of SSC calculations. Our results show that factors influencing turbidity, namely water colour and sediment grain size, have to be considered in multivariate models, to minimize errors and acquire an understanding of what kind of physical response is actually measured by nephelometry-based instruments.

Major theoretical prerequisites for the application of regression analysis are considered as applied to calculating suspended sediment given observational data on water discharge and sediment load in rivers. A concept of sediment transport curve as a calculation model based on regression analysis is introduced. The role of the probabilistic structure of raw data in the determination of the optimal form of sediment transport curve and the potential structure of errors of regression models is discussed. The most widely used theoretical models of curves, as well as the methods and algorithms for assessing regression coefficients are analyzed. The application limits and the accuracy of the method are derived from its stochastic nature, and the most common methodological mistakes in its use are discussed.

Preliminary analysis of long-term hydrological data shows that sediment dynamics of Russian Arctic rivers is largely affected by hysteresis effects in relation of water discharge to suspended sediment concentration (SSC). The role of large-scale geomorphic and geocryological conditions in sediment transport is still relatively understudied. This research aims to assess the links between hydrogeomorphology and regularities of sediment formation and movement in Russian Arctic rivers. A dataset containing information on measured water discharges and SSC for 27 gauges on 16 medium and large rivers of the Russian Arctic was used in this research. Clockwise hysteresis is typical during spring events, while in summer counterclockwise and ‘figure eight’ curves are widely observed. The results show that the form of the rating curve can be attributed to the dominant sediment source, dominant channel pattern and, to certain extent, to the cross-section position within the river basin. Seasonality in hysteresis effects reflects the role frozen ground dynamic plays in sediment flux formation. Thus, reaction of permafrost landscapes on the widely observed climate shift should lead to significant changes in sediment transfer systems.

For determining the water regime characteristics we suggest a modification of the technique which is based on taking into consideration the parameters of alluvium ridge movement and which has been used in evaluating the annual runoff of traction load on the rivers in the north of Siberia and in the north-east of Russia. The intrazonal character of the runoff of traction load is substantiated. We examine the role of geological and hydroclimatic conditions and ascertain a correlation between the flow rate of traction load and water flow rates.

The water temperature characteristics of the Lena River at basin outlet during the summer season (June–September) are considered. The analysis is based on a long-term data series covering the period from the beginning of observation (1936) to the present time (2012) at Kusur (Kyusyur) gauging station and complementary data at several stations downstream and one station upstream. These additional data are rarely used, but their analysis is important for understanding processes in the basin outlet area. The differences between the stream surface temperatures at Kusur station and 200 km downstream to the north at Habarova (Khabarova) station have almost always been an anomalously large and negative for the considered period since the beginning of observation during open water season from July to September. The description of this difference and its analysis are presented. To sort the problem out, we consider the observational data in terms of the hydrology and morphology of the Lena River delta and main channel area and apply statistical and deterministic modelling approaches. The inability of water temperature observational data at Kusur station to represent the mean cross-sectional temperature is addressed. The analysis of the water temperature trends at the Kusur and Habarova stations is also presented.

Regularities in the manifestation of hysteresis effect in the relationship between water discharge and suspended load in rivers in the permafrost zone of Siberia and Far East are studied for individual phases of water regime. The existing typifications of hysteresis curves, the formation mechanisms of suspended load peaks in permafrost zone rivers are considered. Data of regime observations are used to determine the predominant types of hysteresis curves discharge-sediment load for 27 gages on 16 large rivers in the region. The role of permafrost conditions and processes in the formation of the hysteresis effect is identified and a relationship between the type of the hysteresis curve and the predominant sediment source is established.

Every spring, riverine communities throughout the Arctic face flood risk. As the river ice begins to thaw and break up, ice jams—accumulation of chunks and sheets of ice in the river channel, force melt water and ice floes to back up for dozens of kilometers and flood vulnerable communities upstream. Via a comparative analysis between two flood-prone communities in Alaska and Yakutia (Siberia), this study examines key components of flood risk—hazards, exposure, and vulnerability, and existing practices in flood risk reduction in rural Arctic. The research sites are two rural communities—Galena (Yukon River) and Edeytsy (Lena River), which sustained major ice-jam floods in May 2013. The data was acquired through a combination of direct observations on site, review of documents and archives, focus group discussions, and surveys. Five focus groups with US and Russian representatives from disaster management agencies revealed a few similar patterns as well as significant differences in flood risk reduction strategies. The main differences included higher reliance on mechanical and short-term ice jam and flood mitigation efforts (e.g., ice-jam demolition) in the Russian Arctic, and lack of a centralized flood management model in the US. Surveys conducted among population at risk during the site visits to Edeytsy (November 2015) and Galena (March 2016) revealed higher satisfaction levels with the existing flood risk reduction efforts among Edeytsy residents. Survey respondents in Galena indicated the lack of ice jam removal and other flood prevention measures as the key drawback in the existing flood management. Historical analysis, conducted via the disaster Pressure and Release (PAR) model, revealed that springtime flood risk in both regions results from complex interactions among a series of natural processes that generate conditions of hazard, and human actions that generate conditions of communities’ exposure and vulnerability. The analysis revealed colonial heritage, top-down governance, and limited inclusion of local communities in the decision-making as the driving forces of vulnerability in both regions. Seasonal weather patterns and regional river channel morphology determine the location, severity, and duration of floods. The analysis also revealed the importance of continuous communication between all stakeholders in timely and effective flood risk management in both regions.

A long–term daily streamflow dataset, covering the period from 1925 to 2013, was compiled for the Lena River basin, with an average record length of 49 years. Time–series of mean annual daily flow (MADF) and extreme (maximum, Qmax, and minimum, Qmin) daily flows were subject to trend detection and change–point detection analysis. Significant changes result mostly from rapid 'breakpoint' homogeneity disruptions. Thirty one time–series showed trends in MADF, 10, in Qmax, and 32 of the 55 records with non–zero Qmin, significant at p ≤ 0.05. Upward trends prevail in both mean annual and extreme flows, with average magnitudes of 47% (MADF), 56% (Qmax) and 68% (Qmin). Two to three stations in each subset showed downward trends (averaging –20%, –39% and –38%, respectively). Abrupt changes are observed in the 1990s and early 2000s mostly in the headwaters of the basin, underlain by discontinuous permafrost.

Role of changing climatic conditions on permafrost degradation and hydrology was investigated in the transition zone between the tundra and forest ecotones at the boundary of continuous and discontinuous permafrost of the lower Yenisei River. Three watersheds of various sizes were chosen to represent the characteristics of the regional landscape conditions. Samples of river flow, precipitation, snow cover, and permafrost ground ice were collected over the watersheds to determine isotopic composition of potential sources of water in a river flow over a two year period. Increases in air temperature over the last forty years have resulted in permafrost degradation and a decrease in the seasonal frost which is evident from soil temperature measurements, permafrost and active-layer monitoring, and analysis of satellite imagery. The lowering of the permafrost table has led to an increased storage capacity of permafrost affected soils and a higher contribution of ground water to river discharge during winter months. A progressive decrease in the thickness of the layer of seasonal freezing allows more water storage and pathways for water during the winter low period making winter discharge dependent on the timing and amount of late summer precipitation. There is a substantial seasonal variability of stable isotopic composition of river flow. Spring flooding corresponds to the isotopic composition of snow cover prior to the snowmelt. Isotopic composition of river flow during the summer period follows the variability of precipitation in smaller creeks, while the water flow of larger watersheds is influenced by the secondary evaporation of water temporarily stored in thermokarst lakes and bogs. Late summer precipitation determines the isotopic composition of texture ice within the active layer in tundra landscapes and the seasonal freezing layer in forested landscapes as well as the composition of the water flow during winter months.

Frozen ground within river channels is widely observed on most Russian Arctic rivers with sand-clay alluvium. Within-channel permafrost determines high long-term stability and site-specific trends in channel development, affecting northern rivers navigation conditions. Extensive field studies on 200-km reach of Lena River in Central Yakutia, largest in the region, show that navigation conditions are majorly impaired by permafrost-af fected narrowing, increasing length and curvature of fairways. Economical effects of such impairment, including gross operational costs, dredging operation and new fairways development expenses, were estimated based on statistic data provided by Lena Basin State Waterways & Navigation Authority. Average additional gross operating costs (per 1 km of fairway length) were estimated about US $60 to $100 per ship passage, including ship maintenance costs, fuel and crew expenses. Furthermore, above 1.5 M m 3 of bed material were excavated within the studied reach during years 2003-2007 to maintain safe ship operations, adding another us $6 M to the total expenses. Study results reveal, that permafrost and related channel dynamics add to the northern navigation costs. Facilitation of the latter includes forecasts of permafrost-in duced channel alterations. A probabilistic model using hydrological data was developed in order to assess the spatial extent of within-channe l permafrost and its potential impact on channel dynamics. Modeling results for the studied 200-km Lena river reach appear to be consistent with field observations, thus allowing introduction of the model in forecasting and decision-making processes during waterway development planning.

For short-term forecast of ice-jam levels, a model of river ice jamming, based on numerical solution of Sen-Venan equations using Militeev’s implicit scheme was developed. The model was enlarged with a simple model of ice-jam length increase. Computation of an observed ice jam was used for model verification. Computing velocity vectors on this model allows estimation of dynamic load on facilities within the river valley during flooding. Results of the research revealed the origin of extremely high ice-jam stages. High roughness factor of ice lower surface causes high stage rise upstream the jam.