Lake Formation Research Articles

The Global Distribution of Craters With Alluvial Fans and Deltas on Mars

AbstractWe present an inventory of alluvial fans and deltas within martian impact craters based on a systematic global survey of Context Camera images. Our database includes 314 fan‐hosting craters, with a total of 890 alluvial fans and 114 deltas. Alluvial fans and deltas are more widespread than previously reported (∼40°N to 54°S) and are strongly banded with respect to latitude. Most craters with alluvial fans occur at higher elevations (10°S–30°S) and along the dichotomy boundary (0°–10°N). Deltas occur at lower elevations (0°–40°N) where access to groundwater may have enabled the formation of lakes, and to a lesser extent in the highlands (0°–30°S). Alluvial fans in southern mid‐latitude craters preferentially formed along the northern and southern walls, which may reflect climatic control through solar insolation. The widespread distribution within the observed latitude bands and the similar Hesperian to Amazonian age of alluvial fan‐hosting craters is consistent with late‐stage synoptic precipitation.

Mechanism of landslide damming in Morzarrin Valley and its consequences, Lorestan Province, western Iran

Landslide dams are common geomorphic phenomena, especially in high relief mountains characterized by steep slopes and narrow valleys, where even small landslides can easily block the valleys and give rise to the formation of dam lakes. Mass movements and landslide dams are among active geohazards along river valleys of the Zagros Mountains of southwestern Iran, which pose serious risks to the local inhabitants and infrastructures. This paper explores the mechanism and consequences of a typical landslide dam in 2019 in the Morzarrin Valley in Lorestan Province, Iran. Meteorological data, satellite images and Google Earth images, geology and topography maps, as well as field observations were used to evaluate the morphometric characteristics of the landslide dam. Our investigations indicate that a heavy precipitation (rain and snowfall) triggered the occurrence of the landslide in marl and limestone formations. Moreover, high steepness of the slopes and river undercutting are other controlling factors on the occurrence of landslides in this basin, as indicated by the evidence of multiple landslides along the Morzarrin Valley. The studied landslide blocked the valley and formed a dam lake with an area of 3.3 km2. The landslide also destroyed and blocked the nearby road and caused damages in power lines and water transportation infrastructures and inundated fish farms. Digging a canal in the landslide dam and gradual discharge of the lake water reduced the landslide dam-break risks which particularly threatened the areas downstream.

Landscape Setting Drives the Microbial Eukaryotic Community Structure in Four Swedish Mountain Lakes over the Holocene.

On the annual and interannual scales, lake microbial communities are known to be heavily influenced by environmental conditions both in the lake and in its terrestrial surroundings. However, the influence of landscape setting and environmental change on shaping these communities over a longer (millennial) timescale is rarely studied. Here, we applied an 18S metabarcoding approach to DNA preserved in Holocene sediment records from two pairs of co-located Swedish mountain lakes. Our data revealed that the microbial eukaryotic communities were strongly influenced by catchment characteristics rather than location. More precisely, the microbial communities from the two bedrock lakes were largely dominated by unclassified Alveolata, while the peatland lakes showed a more diverse microbial community, with Ciliophora, Chlorophyta and Chytrids among the more predominant groups. Furthermore, for the two bedrock-dominated lakes—where the oldest DNA samples are dated to only a few hundred years after the lake formation—certain Alveolata, Chlorophytes, Stramenopiles and Rhizaria taxa were found prevalent throughout all the sediment profiles. Our work highlights the importance of species sorting due to landscape setting and the persistence of microbial eukaryotic diversity over millennial timescales in shaping modern lake microbial communities.

The Role of Glaciers in Hydropower Production in Nepal

Nepal is a mountainous country rich in water resources, with huge potential for hydropower generation. The Department of Electricity Development (DoED), which sits within the Nepalese Ministry of Energy, has published Guidelines for Study of Hydropower Projects to set out the official standards for the detailed study of hydropower projects in Nepal. The guide is regularly revised, with the latest revision having taken place in 2018, in order to ensure the long-term sustainability of the projects. Among the key issues considered are the linkages between glaciers and hydropower projects in Nepal under a changing environment. The formation of new glacial lakes and the potential for glacial lake outburst floods (GLOFs) are recent challenges in the Himalayan region. As such, any change impacting these processes may have serious consequences on hydropower projects or cause severe damage to these projects across the country, whether they are in the planning phase, under construction, or completed. This paper aims to make the connection between the status of hydropower projects in Nepal and the state of glaciers in the Himalayas, and suggests that advanced studies on glacial lakes and GLOFs are needed to ensure the long-term sustainability of hydropower projects under changing climate.

Ammonium and nitrate sources and transformation mechanism in the Quaternary sediments of Jianghan Plain, China

Excessive inorganic nitrogen (IN) compound content in groundwater is generally attributed to anthropogenic activities. Here, natural nitrogen sources in Quaternary sediments from aquifers and aquitards of Jianghan Plain (JHP), China were identified. Ammonium and nitrate content in groundwater samples collected from 129 well sites were determined through chemical analysis. Subsequent 4 boreholes were drilled at areas with high nitrogen concentration in the Quaternary aquifer. Indicators from hydrochemistry and soil geochemistry analysis, as well as optically stimulated luminescence dating and various of radioactive isotope δ14C-CO2 and stable isotopes including δ15N-NH4+, δ15N-total organic nitrogen (TON), δ15N-NO3−, δ18O-NO3−, δ18O-H2O, δD-H2O, and δ13C-total organic carbon (TOC) were used to identify high-concentration N compound sources and transformation mechanisms (NO3−: 0.02–770 mg L−1; NH4-N: 0–30.5 mg L−1) in the porous media. The thick clay layer protected the underlying media. Paleo-precipitation characteristics were preserved in the porewater; that is, it had not been affected by anthropogenic activities. The high nitrate concentration in the shallow oxidized aquifer was mostly attributed to manure and sewage (δ15N-NO3− was 14‰). The ammonium-N in the deep strata and part of ammonium-N in the shallow strata (aquifers and aquitards) were from natural sources, mainly from natural TON mineralization. Adsorption was an auxiliary factor for ammonium enrichment in the shallow strata, as were dissimilatory nitrate reduction to ammonium (DNRA) and low ammonia volatilization. Organic matter (OM) involved in mineralization was a mixture of lacustrine algae and terrigenous clastic sediments (from river upstream). The algae were traced to lake formation and frequent evolutionary changes in river environments, as indicated by alterations in sedimentary facies. The present findings may encourage researchers to consider natural IN sources' contribution to N contamination using quantitative models. They also serve as a valuable reference for understanding other pollutants' transformation mechanism in similar environments and provide research ideas for similar areas.

Evaluation of Glacial Lake Outburst Flood Susceptibility Using Multi-Criteria Assessment Framework in Mahalangur Himalaya

Ongoing recession of glaciers in the Himalaya in response to global climate change has far-reaching impacts on the formation and expansion of glacial lakes. The subsequent glacial lake outburst floods (GLOFs) are a significant threat to lives and livelihoods as they can cause catastrophic damage up to hundreds of kilometres downstream. Previous studies have reported the rapid expansion of glacial lakes and several notable destructive past GLOF events in the Mahalangur Himalaya, suggesting a necessity of timely and updated GLOF susceptibility assessment. Here, an updated inventory of glacial lakes across the Mahalangur Himalaya is developed based on 10-m Sentinel-2 satellite data from 2018. Additionally, the GLOF susceptibilities of glacial lakes (≥0.045 km2) are evaluated using a multi-criteria-based assessment framework where six key factors are selected and analyzed. Weight for each factor was assigned from the analytical hierarchy process. Glacial lakes are classified into very low, low, medium, high, and very high GLOF susceptibility classes depending upon their susceptibility index based on analysis of three historical GLOF events in the study area. The result shows the existence of 345 glacial lakes (>0.001 km2) with a total area of 18.80 ± 1.35 km2 across the region in 2018. Furthermore, out of the 64 glacial lakes (≥0.045 km2) assessed, seven were identified with very high GLOF susceptibility. We underline that pronounced glacier-lake interaction will likely increase the GLOF susceptibility. Regular monitoring and more detailed fieldworks for these highly susceptible glacial lakes are necessary. This will benefit in early warning and disaster risk reduction of downstream communities.

Paleomonsoonal shifts during ∼13700 to 3100 yr BP in the central Ganga Basin, India with a severe arid phase at ∼4.2 ka

We present a multiproxy record of grain size and stable carbon isotope from the Lilaur lake, Ganga Basin, India to understand the history of lake formation linked to changes in Indian monsoon precipitation during ~13714 to 3073 calibrated year before Present (cal yr BP). A comparison is made between Lilaur lake proxy record with those from other parts of South Asia as well as North Atlantic to understand extent and causes of monsoon variability and its influence on the fauna and flora of the region. Chronology of lake core was constrained using AMS 14C and optically stimulated luminescence (OSL) dates. This study suggests a transition from river to lake during ~5800 to 5189 cal yr BP which is supported by reduced precipitation with weakening of the Indian summer monsoon (ISM). This river to lake transition culminated in a severe arid phase during 4250 to 4050 cal yr BP (4.2 ka event), corresponding to enhanced El Niño activity, southward shift of the Inter-Tropical Convergence Zone, and aridification of India when the ISM was weak.

Estimating Stable Measured Values and Detecting Anomalies in Groundwater Geochemistry Time Series Data Across the Athabasca Oil Sands Area, Canada

Regional groundwater monitoring in the Athabasca region of Alberta, Canada, provides information on groundwater quality and geochemical changes over time, including data useful for evaluating potential impacts of industrial activity such as oil sands mining and in situ operations. Data collected from over 5000 wells from the 1950s to 2014, including 161 wells from government’s monitoring network, were used to develop and apply bootstrap techniques for the detection of changes in groundwater geochemistry over time and at specific points in time. Increasing temporal anomalies were identified in Cl, TDS, B, and naphthenic acids in the McMurray formation across 2003 and 2008, while decreasing anomalies were found for SO4. Temporal variance for 15 indicators was quantified for a smooth bootstrap approach to arrive at stable values representative of the most recent samples taken from wells in the study area. Stable values revealed sampling bias in the Devonian, Grand Rapids, Empress, Channel Beverly, and Muriel Lake formations suggesting expansion of sampling may be necessary. Although temporal anomalies were found in the McMurray formation, sampling bias was not identified. The entropy and relative magnitude of time series were evaluated to identify candidate wells for continued observations, which consist of wells with low measurements and low entropy that are near active industry lease boundaries. Temporal anomalies, stable values, and entropy were combined into type-well information to provide plots for visual inspection and interpretation. Stable values are useful for regional mapping, for detecting future changes and trends, and for identifying areas of interest warranting further investigation.

Sedimentary stratigraphy of Lake Chalco (Central Mexico) during its formative stages

Lake Chalco lies south of the Basin of Mexico and has been the subject of studies related to Late Quaternary climate variability. In 2016, the International Continental Scientific Drilling Program “MexiDrill Project” recovered a 520-m sediment record from Lake Chalco. Magnetic susceptibility measurements revealed substantial changes in sediment physical properties between 343 and 285 m depth, suggesting changes in composition associated with fluctuations in the depositional environment. We targeted sediments in the 343–285 m interval for high-resolution facies analysis, to develop a model of Lake Chalco formation. We identified three facies associations, using sediment composition, texture, mineralogy and micro-morphological characteristics: (1) detrital facies, consisting of laminated silt, massive sand, stratified silty sand, clast-supported gravel and matrix-supported gravel; (2) biogenic facies, which include diatom ooze and bivalve coquina; and (3) volcaniclastic facies, represented by clast-supported pumice deposits. We propose that formation of Lake Chalco occurred in four stages, which we identified by changes in sediment characteristics. The first stage was an alluvial delta environment, in which debris and hyper-concentrated flows were the main sediment transport agents. The second was characterized by turbulent flows in a fluvial deltaic environment, which alternated with laminar flows associated with floodplains. The third stage was a time of fluvio-lacustrine transition in the basin, with formation of the previously identified Paleo-Chalco-I Lake, in response to wet conditions. During the fourth stage, a deep eutrophic lake formed (Paleo-Chalco-II), with an origin that appears to have been related to regional volcanism. Our working age-depth model indicates establishment of the lake at ca. 400 ± 46 ka. This paper presents the only available record of the transition from alluvial to lacustrine sedimentation of Lake Chalco. Our results allow us to establish (1) how the lake was formed and what the phases of its development were, (2) how a major volcanic event altered and transformed the lacustrine sedimentation, and (3) which climatic conditions dominated during the lake formation. The age for the onset of the lacustrine sedimentation in Chalco is for the first time constrained to around 400 ka. This enables to expand our knowledge of the climate for a time for which there is no information from terrestrial records of tropical North America.

Spatiotemporal patterns of northern lake formation since the Last Glacial Maximum

The northern mid- to high-latitudes have the highest total number and area of lakes on Earth. Lake origins in these regions are diverse, but to a large extent coupled to glacial, permafrost, and peatland histories. The synthesis of 1207 northern lake initiation records presented here provides an analog for rapid landscape-level change in response to climate warming, and its subsequent attenuation by physical and biological feedback mechanisms. Our compilation reveals two peaks in northern lake formation, 13,200 and 10,400 years ago, both following rapid increases in North Atlantic air temperature. Placing our findings within the context of existing paleoenvironmental records, we suggest that solar insolation-driven changes in climate (temperature and water balance) that led to deglaciation and permafrost thaw likely contributed to high rates of northern lake formation during the last Deglacial period. However, further landscape development and stabilization dramatically reduced rates of lake formation beginning ∼10,000 years ago. This suggests that temperature alone may not control future lake development; rather, multiple factors must align to enable a landscape to respond with an increase in lake area. We propose that land surfaces strongly geared toward increased lake formation were highly conditioned by glaciation. Thus, it is unlikely that warming this century will cause lake formation as rapid or as widespread as that during the last Deglacial period.

A holistic view of Shisper Glacier surge and outburst floods: from physical processes to downstream impacts

We observed the surge velocity, terminus advance, lake formation and outburst, as well as its downstream impacts at Shisper Glacier in the Karakoram, Pakistan and suggest potential nature-based risk-reduction solutions. A recent surge started in late 2017 with increased velocity since April 2018 and a resulting terminus advance from June 2018. Bi-modal peak velocity of 19.2 ± 0.16 m/day was observed in April-May 2018 and May-June 2019. Also, the terminus advance blocked the river from the adjacent Muchuhar Glacier repeatedly since November 2018. Lake outbursts were observed in June 2019 and April 2020. Relying on observations of the lake area and peak discharge of 142 m3 s−1 in 2019 and 85 m3 s−1 April 2020, outburst were simulated using the BASEMENT software. Simulations and field observations show that even at high discharge, damages were mainly observed along the main river channel, causing strong bank erosion rather than widespread inundation of land. The ice-dammed lake is potentially hazardous until the blocked stream completely disappears in future. Our results suggest that the biggest lake outburst hazard lies in its erosion potential with damages to infrastructure closest to the river and large sediments transport to the downstream Hunza River.

Evidence of ice streaming and ice tongue shutdown in western Latvia: revealed from the mapping of crevasse-squeeze ridges

Glacial geomorphological mapping of western Latvia using a 1-m-resolution digital elevation model generated from airborne LiDAR data has revealed two sets of mega-scale glacial lineations (MSGLs), one of which is superimposed by crevasse-squeeze ridges (CSRs). CSRs occur as a dense ridge network with a dominant orientation of ridges perpendicular to the ice flow direction. The landform assemblage is interpreted as evidence for two separate phases of fast ice flow with different ice flow directions during the overall deglaciation of the Fennoscandian Ice Sheet (FIS). The first fast ice flow phase occurred from the northwest by the Usma Ice Lobe that extended in the Eastern Kursa Upland. The second fast ice flow occurred from the north by the Venta Ice Tongue in a narrow flow corridor limited mainly to the Kursa Lowland. Active ice streaming caused ice crevassing perpendicular to the ice flow direction and formation of CSRs by squeezing of subglacial till into basal crevasses. A good preservation of the CSRs and general lack of recessional moraines suggest widespread stagnation and ice mass melting after the shutdown of the Venta Ice Tongue followed by the formation of the Venta-Usma ice-dammed lake and glaciolacustrine deposition in the lowest areas of lowland. Our data provide the first evidence of CSRs in the south-eastern terrestrial sector of the FIS suggesting the dynamic ice streaming or surging behaviour of the ice lobes and tongues in this region during deglaciation.

Himalayan Cryospheric Science: A Paradigm Shift By IRS 1C/1D DATA

Himalayan region is a water tower (W.T.) of Asia due to a large concentration of cryosphere. The area generates a large amount of water and used by the millions of people living in the Indo-Gangetic plains. The W.T. provides a sustainable source of water for Indus, Ganga, and Brahmaputra river basins. By considering the importance of the Himalayan cryosphere, the field-based glaciological programme started in the mid-1970s. It provided limited information about the Himalayan cryosphere. Therefore, based upon minimal observations, numerous conclusions were made about glacier mass, length, and area loss, leading to the erroneous conclusion by the Intergovernmental Panel on Climate Change (IPCC) in 2007. At the same time, the results from a cryosphere programme of the Indian Space Research Organization (ISRO) started to arrive, where satellite data of Indian Remote Sensing Satellite (IRS) 1C and 1D were analysed. The information helped to resolve IPCC controversy and provided invaluable insight into Himalayan cryosphere. New models, techniques, and methods were developed in the ISRO programme, providing information on the distribution of snow and glaciers, the formation of glacier lakes, glacier retreat, and mass loss. The information was unique and otherwise not available to the scientific community. The data were also extensively used for developmental activities and to assess national security. These include monitoring of snow in Ladakh, hydropower development in Himachal Pradesh, and risk assessment from glacier lakes in Uttarakhand. The methods and techniques are still being used or improved upon, making remote sensing as an indispensable tool to study the Himalayan cryosphere.

Late Pleistocene Catastrophic Landslide from the Balaganchik Ridge: Evidence from the Mitoga 2 Reference Section (Western Kamchatka)

A new reference section of the Okhotsk seaside of Kamchatka in the Mitoga 2 River area is studied and dated for the first time (14C and 230Th/U). Sedimentary deposits were correlated with the previously known sections in the Khomutina‒Mitoga interfluve. It has been established that the sequence of “gray silts and clays” represents deposits of a large lake-type estuary, which began to swamp about 90–80 ka BP, and all sediments overlapping the silts began to form no earlier than 90 ka BP (second half of MIS 5). Deposits of a catastrophic collapse (clastic mass transport over about 100 km, area ≥1500 km2, volume ≥15 km3), which descended from the Balaganchik Ridge about 90‒80 ka BP, were identified. Two main facies were established: dispersed basal layer (“moraine-type loam” sequence) and landslide proper sediments (conglomerates). Valleys of the Bystraya and Plotnikova rivers were blocked by a collapse, resulting in the formation of a large dammed lake. The catastrophic drainage of the lake could occur about 37 ka BP. Deposits related to the dam breakthrough are recorded between the Mitoga 2 River and Zuikovo Settlement on the Okhotsk coast.

Radiocarbon dating of organic-rich deposits: Difficulties of paleogeographical interpretations in highlands of Russian Altai

The high mountainous southeastern part of Russian Altai is characterized by complicated sedimentation history. As a result of tectonic movements, Paleogene, Neogene, and even more old Carboniferous and Jurassic organicrich deposits had been partly uplifted and exhumed on the ridge’s slopes, where during the Pleistocene, they were affected by various exogenous processes including glaciation, glacio-fluvial erosion, winnowing activity of ice-dammed lakes, sliding during lake-draining events, followed by further intensive Holocene erosion, pedogenesis, and permafrost formation/degradation. Remobilized ancient organic matter had been involved into geomorphic and pedogenesis processes and affected the results of radiocarbon dating. Numerous radiocarbon ages obtained revealed several typical problems in interpretation of dating results, which was confirmed by multidisciplinary investigations of associated sediments in a wider regional context. This article presents a discussion on obtained apparent radiocarbon dates of organic material from ten sections of the SE Altai. In addition to radiocarbon analysis, in each case multidisciplinary study was carried out in order to properly interpret obtained dates, as well as to explain the inability of directly using apparent <sup>14</sup>C ages as a geochronological basis for paleogeographical reconstruction. The analysis presented is of vital importance for establishing the chronology of formation of large ice-dammed lakes and their cataclysmic draining; revealing chronology and paleoenvironmental conditions of pedogenesis in the highlands of the SE Altai; and estimating the range and magnitude of the tectonically driven topography rebuilding in the post-Neogene time.

Wetlands and lakes formation and evolution on the Lower Danube Floodplain during Middle and Late Holocene

River floodplains are amongst the most dynamic features which are continuously changing their shape and structure in relation to climate, vegetation, human pressure and base-level variability. In this study, we focus on the lower reach of Danube (upstream of its delta) and investigate the formation and transformations of wetlands and lakes during the last 8000 years using a multi-proxy methodology. We identified two main stages of floodplain landscape changes which are divided by a major shift in the regime of the most important controlling factor of this region which is the sea level. The transgressive stage covers the 8000-5500 BP period with sustained sea level rise (6-3 mm/yr) when floodplain dynamics acted to adapt to the ever-changing base level. Consequently, successive transitions between wet and dry conditions have been recorded as intertwined (thick) coarse-grained and (thinner) fine-grained sedimentary units. The latter stage (5500 BP - present) begins once with abrupt sea-level rise deceleration which fostered the expansion of persistent wetlands and lakes within meta-stable floodplain. The depositional evidence of this stage is composed of fine-grained sediments and peat. The transition between the two floodplain stages corresponds to the blooming phase of lakes, marshes and secondary channels which altogether persisted until the 20th century when during the communist period large floodplain areas were subject to drainage and desiccation works and their transformation into arable lands.

Features of the Formation of Lakes in the Cryogenic Regions of the Upper Kolyma, Northeast Siberia

Long-term observations of the evolution of the Elikchan lakes (Kolyma Upland, Maimandzha Mountains), which form a "chain" that stretches across the flat watershed separating the Upper Kolyma and the Sea of Okhotsk drainages, make it possible to determine how slope, thermokarst processes, and ecology affected landscape changes within this area. Clastic material coming from the slopes of the Maimandzha Mountains formed dams, which created large lakes within the Okhotsk basin (Elikchan-4 Lake, Elikchan-3 Lake). The origin of the lakes belonging to the Kolyma basin is the result of active thermokarst processes associated with the thawing of ice wedges, the development of bogs, the confluence of small lakes and the formation of new larger reservoirs. Such thermokarst processes were some of the main factors in the origin of Elikchan-1 Lake. The continuous palynological record and radiocarbon dating of the Elikchan-1 Lake sediments reflect the successive changes of biocenoses, which correspond to the general pattern of the evolution of the vegetation cover in the Upper Kolyma basin and in Northern Priokhotye. This record shows a change in plant communities over at least the past 9 000 years with a climatic optimum at ca. 8 000 - 6 100 years ago. Comprehensive analysis of Elikchan-1 Lake also emphasizes the significant discrepancies between the boundaries of Holocene subdivisions in the Far Eastern region and the European chrono-stratigraphy for the Holocene. Attempts to resolve the problems of Far East stratigraphy by comparison to the traditional divisions for Europe are a serious mistake. Moreover, a complete analogy of the Far Eastern subdivisions of the Holocene with the European chronological standard should not be expected, just as it is inappropriate to use the УEuropeanФ terminology in the Far Eastern reconstructions. The influences of the primary factors that determine the Holocene events in the Far East sharply differ from those of Europe, including the specific features of the regional climates as they respond to global forcing factors, diversity of the vegetation cover, and variations in the timing of changes in the biocenoses. Given such differences, it is quite natural that equating the Holocene divisions between the two regions is unacceptable. Radiocarbon dating at the base of the Elikchan-1 Lake sedimentary column indicates that the site was originally a peat bog in the Early Holocene with subsequent lake formation. Comparison of radiocarbon dates from the Elikchan-1 peat with other peat deposits in the region suggests that the Early Holocene was a time of active formation and fairly widespread development of peat bogs in the mountainous regions of the Kolyma and Northern Priokhotye.

Long-term dynamics of a cladoceran community from an early stage of lake formation in Lake Fukami-ike, Japan.

An increase in nutrient levels due to eutrophication has considerable effects on lake ecosystems. Cladocerans are intermediate consumers in lake ecosystems; thus, they are influenced by both the bottom‐up and top‐down effects that occur as eutrophication progresses. The long‐term community succession of cladocerans and the effects cladocerans experience through the various eutrophication stages have rarely been investigated from the perspective of the early‐stage cladoceran community assemblage during lake formation. In our research, long‐term cladoceran community succession was examined via paleolimnological analysis in the currently eutrophic Lake Fukami‐ike, Japan. We measured the concentration of total phosphorus and phytoplankton pigments and counted cladoceran and other invertebrate subfossils in all layers of collected sediment cores, and then assessed changes in the factors controlling the cladoceran community over a 354‐year period from lake formation to the present. The cladoceran community consisted only of benthic taxa at the time of lake formation. When rapid eutrophication occurred and phytoplankton increased, the benthic community was replaced by a pelagic community. After further eutrophication, large Daphnia and high‐order consumers became established. The statistical analysis suggested that bottom‐up effects mainly controlled the cladoceran community in the lake's early stages, and the importance of top‐down effects increased after eutrophication occurred. Total phosphorus and phytoplankton pigments had positive effects on pelagic Bosmina, leading to the replacement of the benthic cladoceran community by the pelagic one. In contrast, the taxa established posteutrophication were affected more by predators than by nutrient levels. A decrease in planktivorous fish possibly allowed large Daphnia to establish, and the subsequent increase in planktivorous fish reduced the body size of the cladoceran community.

Assessment of Spatio-Temporal Landscape Changes from VHR Images in Three Different Permafrost Areas in the Western Russian Arctic

Our study highlights the usefulness of very high resolution (VHR) images to detect various types of disturbances over permafrost areas using three example regions in different permafrost zones. The study focuses on detecting subtle changes in land cover classes, thermokarst water bodies, river dynamics, retrogressive thaw slumps (RTS) and infrastructure in the Yamal Peninsula, Urengoy and Pechora regions. Very high-resolution optical imagery (sub-meter) derived from WorldView, QuickBird and GeoEye in conjunction with declassified Corona images were involved in the analyses. The comparison of very high-resolution images acquired in 2003/2004 and 2016/2017 indicates a pronounced increase in the extent of tundra and a slight increase of land covered by water. The number of water bodies increased in all three regions, especially in discontinuous permafrost, where 14.86% of new lakes and ponds were initiated between 2003 and 2017. The analysis of the evolution of two river channels in Yamal and Urengoy indicates the dominance of erosion during the last two decades. An increase of both rivers’ lengths and a significant widening of the river channels were also observed. The number and total surface of RTS in the Yamal Peninsula strongly increased between 2004 and 2016. A mean annual headwall retreat rate of 1.86 m/year was calculated. Extensive networks of infrastructure occurred in the Yamal Peninsula in the last two decades, stimulating the initiation of new thermokarst features. The significant warming and seasonal variations of the hydrologic cycle, in particular, increased snow water equivalent acted in favor of deepening of the active layer; thus, an increasing number of thermokarst lake formations.

Evaluation of Glacial Lakes and Catastrophic Floods on the Northern Slopes of the Kyrgyz Range

The changing climate in the 20th and 21st centuries has had a profound impact on glacial lake formation and downwasting. The rapid receding of glaciers due to increased atmospheric temperature has caused glacial lake outburst floods (GLOFs) in the nival–glacial belt region on the northern slopes of the Kyrgyz mountain range over the last 20 years. Catastrophic events downstream due to GLOFs are increasing in this region and could affect the natural environment, human lives, and property. This study aims to evaluate the spatial distribution and growth of glacial lakes on the northern slopes of the Kyrgyz range using semiautomated remote sensing and field techniques. We recorded 273 glacial lakes and examined the characteristics of 5 small GLOFs that occurred between 2000 and 2012 due to moraine collapse. Further, the findings highlight alarmingly rapid changes and a high probability that these lakes will burst soon. Remote sensing, geographic information system, and statistical techniques combined with field-based knowledge are effective in identifying and monitoring the catastrophic nature of GLOFs on the northern slopes of the Kyrgyz range. The study recommends creating a spatial database inventory of both glacial lakes and GLOFs in the region using high-resolution satellite images and in-situ field techniques.