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Small lakes are important elements of the ecosystem, especially under conditions of climate change and active water use. Studying their condition is of key importance for understanding the water balance and biodiversity of the region. This study compares remote sensing techniques for small lakes using Landsat-8, Sentinel-2, Planet and unmanned aerial vehicle (UAV) data. The aim of the work is to determine the most effective approach for monitoring lake conditions by analyzing the accuracy of different methods and indices. The methods used include the analysis of multispectral data such as NDWI, MNDWI and AWEI, which allow the distinction between aquatic and non-aquatic objects. The scientific significance of the study lies in assessing the potential of modern remote sensing technologies for detailed monitoring of ecosystem changes. Practical significance of the work consists in providing recommendations for sustainable water resources management and development of adaptation strategies. The research methodology included processing satellite data of different resolutions, accuracy verification using UAV reference data, and application of spectral indices for water surface mapping. Results showed that high-resolution imagery (PlanetLab data) most closely matched field observations. The spectral indices NDWI, MNDWI and AWEI showed different accuracy depending on data characteristics and lake features. The analysis confirms the effectiveness of an integrated approach using high-resolution data and spectral indices for monitoring the condition of small lakes. The practical value of the study lies in optimizing the monitoring of water bodies and maintaining their ecological sustainability. [ABSTRACT FROM AUTHOR]

Numerous policies have been proposed by international and supranational institutions, such as the European Union, to surveil Earth from space and furnish indicators of environmental conditions across diverse scenarios. In tandem with these policies, different initiatives, particularly on both sides of the Atlantic, have emerged to provide valuable data for environmental management such as the concept of essential climate variables. However, a key question arises: do the available data align with the monitoring requirements outlined in these policies? In this paper, we concentrate on Earth Observation (EO) optical data applications for environmental monitoring, with a specific emphasis on ocean colour. In a rapidly changing climate, it becomes imperative to consider data requirements for upcoming space missions. We place particular significance on the application of these data when monitoring lakes and marine protected areas (MPAs). These two use cases, albeit very different in nature, underscore the necessity for higher-spatial-resolution imagery to effectively study these vital habitats. Limnological ecosystems, sensitive to ice melting and temperature fluctuations, serve as crucial indicators of a climate in change. Simultaneously, MPAs, although generally small in size, play a crucial role in safeguarding marine biodiversity and supporting sustainable marine resource management. They are increasingly acknowledged as a critical component of global efforts to conserve and manage marine ecosystems, as exemplified by Target 3 of the Kunming–Montreal Global Biodiversity Framework (GBF), which aims to effectively conserve 30% of terrestrial, inland water, coastal, and marine areas by 2030 through protected areas and other conservation measures. In this paper, we analysed different policies concerning EO data and their application to environmental-based monitoring. We also reviewed and analysed the existing relevant literature in order to find gaps that need to be bridged to effectively monitor these habitats in an ecosystem-based approach, making data more accessible, leading to the generation of water quality indicators derived from new high- and very high-resolution satellite monitoring focusing especially on Chlorophyll-a concentrations. Such data are pivotal for comprehending, at small and local scales, how these habitats are responding to climate change and various stressors. [ABSTRACT FROM AUTHOR]

Changes in the macrozoobenthos of two northern lakes differing in degree of humification of water over the 50-year period that have passed since the first studies were considered. In the lake with water uncolored by humus, the benthos biomass increased, and in the humified one, it decreased. The changes that have occurred are due to climate warming, especially pronounced in winter. It was concluded that even closely located bodies of water can respond differently to climate change. Depending on the nature of the catchment area and the morphology of the lakes, either an increase in their productivity due to the supply of nutrients or a decrease due to humification can be observed. [ABSTRACT FROM AUTHOR]

Primary studies of the concentrations of rare elements in the sediments of two lakes on King George Island (Kitezh and Glubokoe) showed that their geochemistry reflects the geological features of the area. Compared to the composition of the upper part of the Earth's crust, the studied sediments are enriched in Cu, Cd, V, Tl, Mn, Ti, and P. Similar patterns have been identified in the geochemistry of volcanic and sedimentary rocks of the Fildes Peninsula. Trends in REE changes generally follow their behavior in rocks, but the overall REE concentration in sediments of lakes is higher, which may be due to the presence of organic matter accumulating in sediments of water bodies. Unlike the aquatic environment, the chemical composition of sediments does not reflect the significant influence of the activities of polar stations. However, small increases in Pb and Sb concentrations in the upper sediments suggest the influence of long–range atmospheric transport of the contaminants. [ABSTRACT FROM AUTHOR]

Small lakes (areas ranging from 0.01 km2 to 1 km2) are highly sensitive to climate change and human activities. However, few studies have investigated the long-term intra-annual trends in the number and area of small lakes and their driving mechanisms in the Qinghai–Tibet Plateau (QTP). As a significant water tower in northwest China, the Qilian Mountains region (QMR) in the QTP is essential for sustaining regional industrial and agricultural production, biodiversity, and human well-being. We conducted an analysis of the dynamics of small lakes in the QMR region. In this study, we employed Geodetector and examined nine factors to investigate the driving mechanisms behind the long-term variations in the small lake water bodies (SLWBs). We specifically focused on understanding the effects of single-factor and two-factor interactions. The results indicate that the number and area of small lakes had a fluctuating trend from 1987 to 2020. Initially, there was a decrease followed by an increase, which was generally consistent with trends in the large lakes on the QTP. All basins had far more expanding than shrinking lakes. The area of seasonal SLWBs in each basin was increasing more rapidly than permanent SLWBs. The distribution and trends in the area and number of small lakes varied widely across elevation zones. Runoff, snow depth, and temperature contributed the most to SLWB changes. Human activities and wind speed contributed the least. However, the main drivers varied across basins. The impact of two-factor interactions on SLWB changes in basins was greater than that of single factors. Our results provide useful information for planning and managing water resources and studies of small lakes. [ABSTRACT FROM AUTHOR]

The problem of eutrophication of the waters in remote Arctic regions is discussed as a consequence of climate warming and global dispersion of phosphorus. The analysis of long-term monitoring results of water quality from 1990 through 2018 (once every four to five years) provides evidence that the total concentrations of phosphorus and nitrogen, as well as organic matter, had increased by the last decade, which is confirmed by reliable relationships with temperature conditions. The fluxes of phosphorus into lakes from drainage areas were calculated using V.V. Bouillon's model and turned out to grow during the last decade. The trophic status indicator (TSI) of the lakes shows that the number of oligotrophic lakes has decreased and the number of meso- and eutrophic ones has increased even where no influence of any anthropogenic factors was identified. [ABSTRACT FROM AUTHOR]

Species distribution and assemblage structuring are influenced by a combination of species dispersal mode and the dispersal routes used. Habitat connectivity is particularly important for passively dispersing taxa such as freshwater molluscs. In addition, current anthropogenic eutrophication affects the structure of assemblages by reducing native fauna and promoting the spread of generalist species. Here, we examined mollusc assemblages in two systems of small lakes differing in hydrological connectivity. The assemblages of 22 isolated lakes in Albania were mainly controlled by the distance between the lakes with a lower contribution of environmental conditions and lake area. In contrast, assemblages of 52 interconnected lakes in Czechia were driven primarily by environmental conditions. However, as lake trophic status increased, the assemblages in Czechia became more homogeneous in species composition as high trophic status filtered out all species except generalists. These assemblages from 33 eutrophic lakes were strongly determined by environmental variables, whereas the remaining assemblages from 19 low trophic lakes were structured by a combination of spatial and environmental variables. We conclude that hydrological connectivity between lakes is crucial for the distribution of molluscs, but eutrophication may influence the importance of individual mechanisms structuring mollusc assemblages. [ABSTRACT FROM AUTHOR]

The Local Government and the Government Agency shape the Seven Crater Lakes. The present study focused on understanding the predominant Governments and Lake Governance's concept vis‐a‐vis the small lakes and their basin communities. These foremost authorities are intertwined, and Lake Governance's essential criteria interplayed and continuous to the responsibility. Although the City Government of San Pablo City and the Laguna Lake Development Authority (LLDA) have improved the small lake's situations and they are satisfactorily functioning, serious issues still remain at present and into the future. Focusing on the criteria's lessons, Pandin Lake, Yambo Lake, Mohicap Lake and Sampaloc Lake have been ameliorated to varying degrees. In contrast, Bunot Lake, Palakpakin Lake and Calibato Lake continue to struggle with deficiencies. Thus, over the dual governments need to exhibit greater commitment, decisiveness and effectiveness if the Seven Crater Lakes are to flourish in development and conservation. Furthermore, while the Structuring Government and Administering Water criteria are adequate, completing the Developing Tourism, accomplishing the Regulating Fishery and substantially subsidizing the Supporting Finance in the City Government and the LLDA remain deficient. Accordingly, the main target of the paired Governments' over time is to address the remaining challenges facing the Seven Crater Lakes. [ABSTRACT FROM AUTHOR]

Various components of lake systems located in different landscape zones in southern West Siberia were studied for contents of natural and artificial radionuclides, following the requirements of the state standards (GOST). This work aims at assessing the radiation state of lacustrine sapropel sediments in the Baraba lowland and Kulunda plain, taking into account their natural features and the degree of contamination during nuclear tests. It was found out that the values of the total effective specific activity (As) of natural radionuclides in all of the sapropel lacustrine sediments are significantly lower than the standard value (according to the requirements of the GOST). Some sapropel horizons in the lakes contain excess 137Cs reserves that are twice as high as the global background. Such lakes tend to be spatially constrained to areal traces of radioactive fallouts after nuclear tests at the Semipalatinsk test site and undoubtedly belong to lake systems whose waters and soils on catchments were primarily contaminated with radiocesium. [ABSTRACT FROM AUTHOR]

Mountain lakes are unique and often isolated freshwater habitats that harbour a rich biotic diversity. This high conservation value may be reflected by diatoms, a group of algae that is known for its reliability as a bioindicator, but which has not been studied extensively in mountain lakes of the northern European Alps. In this study, the conservation value of these lakes was assessed by characterizing the number, share, and abundance of diatom Red List (RL) taxa and their relationship with environmental variables, diatom α and β diversity (assemblage uniqueness). For this purpose, linear regression models, generalized linear models, and generalized additive models were fitted and spatial descriptors were included when relevant. Of the 560 diatom taxa identified, 64% were on the RL and half of these were assigned a threat status. As hypothesized, a decreasing share of RL species in sediment and littoral samples at higher trophic levels was reflected by higher total phosphorous content and lower Secchi depth, respectively. Species-rich lakes contained a high number of RL taxa, contrasting our hypothesis of a logarithmic relationship. In turn, RL abundance increased with uniqueness, confirming our initial hypothesis. However, some of the most unique sites were degraded by fish stocking and contained low abundances of RL species. The results demonstrate the importance of oligotrophic mountain lakes as habitats for rare freshwater biota and their vulnerability in light of human impact through cattle herding, tourism, damming, and fish stocking. Additional conservation efforts are urgently needed for mountain lakes that are still underrepresented within legal conservation frameworks. Species richness and uniqueness reflect complementary aspects of RL status and thus should be applied jointly. Uniqueness can indicate both pristine and degraded habitats, so that including information on human impacts facilitates its interpretation. [ABSTRACT FROM AUTHOR]

Factors of formation of phosphorus load on lakes of various landscapes (from tundra to steppe zone) are considered. The calculations of the balance model showed that the phosphorus load is predominantly determined by the conditional water exchange, specific catchment area, and runoff module. Statistical analysis demonstrated that phosphorus fluxes in lakes are determined by the cumulative impact of landscape (swamp and forest areas), climatic (annual precipitation, sum of active temperatures, duration of the vegetation period). Lakes from the tundra to forest-steppe zones are characterized by the low (mesotrophic) trophicity, while lake from the steppe zone reveals the high (eutrophic) trophicity. The factual phosphorus loads in lakes during the autumn homothermy were calculated and analyzed compared to the critical loads during the period of spring mixing. [ABSTRACT FROM AUTHOR]

• Due to climate change the surface of floodplain water bodies decreases substantially. • The share of small lakes and ponds increases. • Small floodplain lakes may be a substantial source of CO 2 emission. • Carbon is buried mostly in insoluble forms. Small floodplain lakes (SFLs), characterized by their diminutive size (<10,000 m2), have been consistently overlooked in assessments of organic carbon (C) stock and the impacts of climate changes. This study aims to ascertain both the quantity and quality of carbon stored within the sediments of SFLs. Furthermore, we endeavour to evaluate the influence of ongoing climate change on the floodplain lake structure within the continental humid climate zone on the example of the Vistula River valley and estimate the CO 2 emission from dry floodplain lakes. The sedimentary organic carbon content (TOC) ranged from 2.3–64 g kg−1, averaging at 3.4 g kg−1. Consequently, the sediments in the analysed SFLs of the river section potentially harbour up to 5,785 Mg TOC. Notably, the abundance of easily soluble carbon fractions (humic and fulvic acids) was relatively low (∼15 %), implying a stable immobilization of organic C compounds and minimal impact of sediments on water quality. Satellite imagery analysis for the years 2017–2020 revealed a 31 % reduction in the total lake surface area within a 100-km-long segment of the Vistula River. The decreasing surface area of floodplain lakes and rising mean air temperatures increase CO 2 emissions and have an additional impact on climate warming. Our research underscores that investigating lake C storage concerning climate change demands a nuanced approach. While higher temperatures stimulate primary production, the reduction in lake surface area and the escalating role of small lakes, such as SFLs, in C storage should be paramount considerations. [ABSTRACT FROM AUTHOR]

Extremely high uranium concentrations (>100 times average crustal content) are established in the recent sediments of small lakes of the northern Murmansk region. It is substantiated that the high uranium concentrations in the sediments of the lakes of the northern Murmansk region were mainly controlled by natural uranium migration from magmatic and metamorphic rocks bearing uranium mineralization (Litsa geological district). The sediments of the studied lakes display a tight correlation of uranium with Mo and rare earth elements usually accompanying uranium in parental rocks. The main chemical fractions of uranium in the lake sediments are revealed. It is shown that organic matter significantly affects the accumulation of this element in the lake sediments. [ABSTRACT FROM AUTHOR]

Small lakes are numerous in the landscape and closely connected to the terrestrial environment, which strongly influences the system scale carbon cycling. However, despite their importance in large-scale carbon budgets, small lakes remain understudied compared to large lakes. We investigated oxygen and carbon dynamics in four small Danish forest lakes over a year. Continuous pH measurements were used to establish a high-frequency time series of CO2 partial pressure and 1169 direct measurements of air–water CO2 flux were performed using floating chambers. Net ecosystem oxygen production (NEP) was derived from free-water oxygen measurements in order to quantify the contribution of in-lake aerobic metabolism to the air–water CO2 flux. We found that the forest lakes, on average, were tenfold CO2 supersaturated. The two most intensively studied lakes had mean CO2 effluxes of 36.3 mol m−2 year−1. The CO2 effluxes exceeded NEP during all months implying that the CO2 generated by aerobic respiration alone could not account for the observed CO2 efflux. The observed discrepancy is likely promoted by a hydrologic CO2 input and/or anaerobic sediment processes generating CO2 without a concurrent consumption of O2. A broad-scale national analysis showed that the CO2 efflux increased as lake size decreased despite lower gas exchange velocity. Small lakes also showed higher excess CO2 efflux compared to O2 influx. Overall, small lakes and forest lakes in particular have high CO2 effluxes and high CO2 supersaturation. However, the contribution of hydrological inputs and anaerobic sediment processes to the net CO2 efflux remains elusive. [ABSTRACT FROM AUTHOR]

Theoretical pelagic primary production of phytoplankton and benthic primary production of periphyton were modelled for two small lakes in Estonia (Northeast Europe). Although located only 500 m apart, the water colour and light attenuation of these two lakes differed markedly. The Secchi depth (SD) in the clear‐water lake was 4.5 m and only 0.47 m in the dark‐water lake. The total phosphorus (TP) concentrations were, respectively, 15 μg/l and 28 μg/l. An empirical model whose inputs were morphometric, light conditions and dissolved organic carbon parameters obtained from in situ measurements was employed for the present study. The model calculated primary production with a time‐step of 10 min, and a spatial resolution of 10 cm, from sunrise to sunset and from lake surface to lake bottom. The primary production of periphyton and phytoplankton was almost equal in the clear lake, whereas only phytoplankton contributed to whole‐lake primary production in the dark lake because of the stronger light attenuation in the water column. The results of the present study indicated the depth‐distribution profiles differed dramatically between the two lakes. The clear lake had a deep, U‐shaped curve, with the productive layer reaching considerable depth soon after sunrise and maintaining a similar profile throughout the light hours. In contrast, the dark lake production declined rapidly with increasing depth, whereas the profile changed over the day reaching the greatest depth at noon. [ABSTRACT FROM AUTHOR]

Small lakes are understudied compared to medium- and large-sized lakes, but have recently received increased attention due to their abundance and importance for global scale biogeochemical cycles. They have close terrestrial contact, extensive environmental variability, and support high biodiversity among them. Temporal and spatial variability of water temperature, oxygen, and stratification-mixing dynamics were examined during a year in nine small Danish lakes. We found that diel mean surface water temperatures were similar among lakes while the diel range decreased with increasing water depth. Vertical temperature stratification occurred on 47% of the days during the entire year and 64% of summer days, usually with daytime stratification and nocturnal convective mixing. The probability of daytime stratification increased with higher incident irradiance, higher air temperature, and lower wind speed. During spring, daytime stratification caused differences in oxygen saturation between surface and bottom waters. These findings offer new insights on the high variability of water temperature and oxygen in time and space in small temperate shallow lakes. The variable water temperature and the regular stratification-mixing processes will have a pronounced influence on biogeochemical cycles. Also, these features are expected to affect the performance and evolutionary process of organisms associated with small lakes. [ABSTRACT FROM AUTHOR]

More than half of the freshwater lakes in the Philippines are small with surface areas of <2 km 2 . The dynamics in these lakes are different from those in the bigger lakes. This study was conducted to determine the organic pollutants and their sources in three of the seven lakes of San Pablo City in Laguna, Philippines: lakes Palakpakin, Sampaloc, and Pandin. Gas Chromatography-Mass Spectrometry (GC–MS) and Liquid Chromatography - Tandem Mass Spectrometry (LC-MS/MS) were used in the targeted and non-targeted analysis of the lake water samples. The three lakes are all volcanic crater lakes but are exposed to different anthropogenic activities, which includes domestic activities, livelihood (farming and aquaculture) and eco-tourism. Due to the presence of rice fields and fruit plantations, chlorpyrifos was detected in the three lakes while other pesticides like cypermethrin, picolinafen and quinoxyfen were additionally found in Lake Sampaloc, which is the biggest of the three lakes and located within the urbanized section of the city. Traces of different surfactants (linear alkylbenzene sulfonates, secondary alkyl sulfonates, alkyl sulfates, alkyl ether sulfates), biocide benzalkonium chloride, insect repellent diethyltoluamide, antibiotics (sulfadiazine and sulfamethoxazole), hypertension drug telmisartan, phosphate-based fire retardants, and artificial sweeteners (acesulfame, cyclamate, saccharin and sucralose) were detected in lakes Sampaloc and Palakpakin. The same surfactants, artificial sweeteners, insect repellant and phosphate-based fire retardants were also found in Lake Pandin, which is mainly used for eco-tourism activities like swimming and boating. The results of this study suggest that the organic pollutants present in the small lakes can be linked to the various human activities in the immediate lake environment. Because small lakes are more prone to environmental stresses, human activities in the said lakes must be regulated to ensure sustainable development. [ABSTRACT FROM AUTHOR]

Small waterbodies, including ponds and small lakes, low-order streams, ditches and springs, are the most numerous freshwater environments globally, are critical for freshwater biodiversity and are increasingly recognised for their role in ecosystem service delivery. Small waters often represent the best remaining examples of intact freshwater habitats and are the most likely to remain unpolluted, often being a refuge for species which have disappeared from larger, more damaged, waterbodies. Practically all water-related ecosystem services are initially mediated by small waters and some, such as carbon cycling, may be dominated by them. Small waters are exposed to all the threats affecting larger waters, and some experienced only by small waters. Despite this, small waters remain the least investigated part of the water environment and are largely excluded from water management planning. We identify the priorities for research to underpin better protection of small waters and recommend policy actions needed to better integrate small waters into the management of catchments and landscapes. The primary requirements are to identify reliable monitoring programmes for small waters, develop effective measures to protect the biodiversity and ecosystem services they provide and ensure that regulators take full account of this critical part of the water environment. [ABSTRACT FROM AUTHOR]

The seasonal dynamics of freshwater lake ice and its interactions with air and snow are studied in two small subarctic lakes with comparable surface areas but contrasting depths (4.3 versus 91 m). Two, 2.9 m long thermistor chain sensors (Snow and Ice Mass Balance Apparatuses), were used to remotely measure air, snow, ice, and water temperatures every 15-min between December 2021 and March 2022. Results showed that freeze-up occurred later in the deeper lake (Ryan Lake) and earlier in the shallow lake (Landing Lake). Ice growth was significantly faster in Ryan Lake than in Landing Lake, due to cold water temperatures (mean (T w ¯) =0.65 to 0.96°C) persisting beneath the ice. In Landing Lake, basal ice growth was hindered because of warm water temperatures (T w ¯ =1.5 to 2.1°C) caused by heat released from lake sediments. Variability in air temperatures at both lakes had significant influences on the thermal regimes of ice and snow, particularly in Ryan Lake, where ice temperatures were more sensitive to rapid changes in air temperatures. This finding suggests that conductive heat transfer through the air-water continuum may be more sensitive to variability in air temperatures in deeper lakes with colder water temperatures than in shallow lakes with warmer water temperatures, if snow depths and densities are comparable. This study highlights the significance of lake morphology and rapid air temperature variability on influencing ice growth processes. Conclusions drawn aim to improve the representation of ice growth processes in regional and global climate models, and to improve ice safety for northern communities. • Two autonomous ice sensors were deployed in two Canadian subarctic lakes. • Air, snow, ice, and water temperatures measured at 15-min intervals for 4 months. • Ice temperatures were more sensitive to variable air temperatures in the deep lake. • Ice growth in shallow lake was inhibited by heat released from lake sediments. • Small lakes may act as significant regional sources of conductive heat. [ABSTRACT FROM AUTHOR]

Aquatic community body size distributions are highly predictable with decreasing abundance and increasing body size. This basic relationship has led to significant increases in our understanding of the internal regulation processes of aquatic communities. However, most of our understanding of the patterns of community size structure is derived from large aquatic systems with little known about the dynamics of small lakes. Processes that promote predictable, or deterministic, community size structure likely differ with levels of biodiversity and disturbance patterns, both of which frequently co-vary with ecosystem size. Here we examine the influence of lake size, fish species richness, and natural disturbance regime on fish community size structure in six small lakes (<200 ha) on Beaver Island, Michigan, USA. Fish communities in three of the six lakes exhibited a deterministic size structure and it appears that disturbance regime is the most obvious barrier to developing and/or maintaining stable and predictable community size structure. In this study, lakes with less than 10 species and lakes experiencing periodic winterkills exhibited stochastic size structure. Lake size did not show any clear relation to fish community size structure. Collectively our results shed some light on the conditions that promote (or do not promote) deterministic size structure. [ABSTRACT FROM PUBLISHER]

This paper reports the results of an extensive investigation of water chemistry in the small lakes of European Russia and Western Siberia along a climatic gradient. It was demonstrated that small lakes unaffected by any direct contamination can be used as indicators of natural geochemical conditions of water formation, as well as global and regional fluxes of airborne pollution and climate warming. A novel concept was developed for within- and between-zone variability in water chemistry over vast areas of tundra, taiga, forest, and steppe, and contributions of natural and anthropogenic factors to its formation under present-day conditions were estimated. A proposed predictive scenario showed that climate warming will result in an increase in water salinity in southern regions and ubiquitous phosphorus enrichment in terrestrial waters; the hydrologic and geochemical conditions of water formation in northern Siberia will change significantly in response to permafrost thawing. Zonal features in the development of anthropogenically-induced processes in terrestrial surface waters (acidification, eutrophication, and metal enrichment) were determined. It was demonstrated that, in addition to naturally acidified lakes with high contents of humic acids, acid lakes of anthropogenic origin occur over the whole humid region discussed here, and acidification processes were characterized for each subregion. The trophic status of lakes and limitation of their bioproductivity with respect to nutrients were estimated. The concentrations and distribution of trace elements were analyzed in terrestrial waters from various climatic zones of European Russia and Western Siberia, and the first estimates were obtained for the mean concentrations and coefficients of migration of a wide range of elements in terrestrial freshwaters. We distinguished a group of metal (Mo, As, U, Bi, Sb, Cd, Ag, Se, Re, Pb, Cd, W, etc.) the enrichment of which in natural waters results from their global dispersion in the environment. Experimental results and natural observations are presented on the processes of metal ion complexation with humus substances, and sequences of their increasing activity in competing for organic ligands were derived. Data are presented on the speciation of metals depending on natural water chemistry in the tundra, taiga, and steppe zones. The pioneering investigations on the geochemistry of natural waters allowed us to substantiate new regional norms for water quality. [ABSTRACT FROM AUTHOR]

This paper reports the results of an extensive investigation of water chemistry in the small lakes of European Russia and Western Siberia along a climatic gradient. It was demonstrated that small lakes unaffected by any direct contamination can be used as indicators of natural geochemical conditions of water formation, as well as global and regional fluxes of airborne pollution and climate warming. A novel concept was developed for within- and between-zone variability in water chemistry over vast areas of tundra, taiga, forest, and steppe, and contributions of natural and anthropogenic factors to its formation under present-day conditions were estimated. A proposed predictive scenario showed that climate warming will result in an increase in water salinity in southern regions and ubiquitous phosphorus enrichment in terrestrial waters; the hydrologic and geochemical conditions of water formation in northern Siberia will change significantly in response to permafrost thawing. Zonal features in the development of anthropogenically-induced processes in terrestrial surface waters (acidification, eutrophication, and metal enrichment) were determined. It was demonstrated that, in addition to naturally acidified lakes with high contents of humic acids, acid lakes of anthropogenic origin occur over the whole humid region discussed here, and acidification processes were characterized for each subregion. The trophic status of lakes and limitation of their bioproductivity with respect to nutrients were estimated. The concentrations and distribution of trace elements were analyzed in terrestrial waters from various climatic zones of European Russia and Western Siberia, and the first estimates were obtained for the mean concentrations and coefficients of migration of a wide range of elements in terrestrial freshwaters. We distinguished a group of metal (Mo, As, U, Bi, Sb, Cd, Ag, Se, Re, Pb, Cd, W, etc.) the enrichment of which in natural waters results from their global dispersion in the environment. Experimental results and natural observations are presented on the processes of metal ion complexation with humus substances, and sequences of their increasing activity in competing for organic ligands were derived. Data are presented on the speciation of metals depending on natural water chemistry in the tundra, taiga, and steppe zones. The pioneering investigations on the geochemistry of natural waters allowed us to substantiate new regional norms for water quality. [ABSTRACT FROM AUTHOR]

Bacterial abundance and the rates of sulfate reduction (SR) and total organic matter decomposition (D) were studied in the bottom sediments of nine lakes in the vicinity of Vilnius (Lithuania) during the ice-free seasons of 2006-2009. During the spring mixing of the water, aerobic processes of organic matter decomposition prevailed in the bottom sediments of most lakes, while anaerobic processes predominated (up to 80-90% D) in summer and early autumn. SR rates in the bottom sediments made up 0.16-2.6 and 0.09-2.0 mg S/(dm day) for the medium-depth and shallow lakes, respectively. The highest numbers of sulfate-reducing bacteria (up to 10 cells/cm) and SR rates were observed in summer. SR rate in mediumdepth lakes increased with development of anaerobic conditions at the bottom and elevated sulfate concentrations (up to 96.0 mg/dm). In shallow lakes, where O concentration at the bottom was at least 6.7 mg/L, SR rates increased with temperature and inflow of fresh organic matter, especially during cyanobacterial blooms. The average SR rates in the bottom sediments of the lakes of urbanized areas were 4 times higher than in the shallow lakes of protected areas. Accumulation of organic matter and its intensive decomposition during summer may enhance the processes of secondary eutrophication of these small and shallow lakes. [ABSTRACT FROM AUTHOR]

Abstract: Sediment structure, rock-magnetic and bio-geochemical records obtained from sapropel core samples in Lake Beloye, southern Western Siberia, indicate an abrupt ecosystem change at 3.4 calibrated ka BP. The lake changed from eutrophic to oligotrophic, its vegetation — from carbon-fixing macrophytic angiosperms to calcium-fixing macrophytic algae and angiosperms, and, as a result, the type of sedimentation shifted from peaty sapropel to carbonate-rich sapropel. Those changes could be induced by climate, which was warmer and wetter before 3.4ka BP and cooler and drier after this. Nevertheless, our data show that those ecosystem changes occurred when the lake became shallower to get about 1m depth and started to freeze to the bottom in winter time. The full freezing of the lake led to the deposition of carbonates, which resulted in: i) death of carbon-utilizing macrophytic angiosperms; and ii) winter precipitation of calcium carbonate. In summer, additional portions of Ca2+ and HCO3 − ions come into the lake from the surrounding CaCO3 rich loess sediments with ground water. The Beloye Lake thus represents an example of interrelated regional climatic and local ecological factors, which combination resulted in the 3.4cal. ka BP dramatic change of its ecosystem. [Copyright &y& Elsevier]

The paper presents a generalized algorithm for the simulation of multiyear cycles in variations of the chemical composition of lake waters with regard for the seasonal specifics of hydrogeochemical processes. Data were obtained on the behavior of the hydrogeological system during a time span of 500-1000 years. Each of the simulated model cycles involved a successively alternating 'summer-winter' time periods. Terrestrial exchange fluxes between reservoirs, groundwater inflow, falls of atmospheric precipitate, and the evaporation of lake water were taken into account for summer periods, whereas winter conditions were simulated as corresponding to the development of the ice phase, the absence of water exchange fluxes, a change from oxidizing to reducing conditions, and the burial of solid phases in the sediments. The results of our physicochemical simulations with the use of data on the composition of natural hydrogeological systems are in good agreement with natural observations and make it possible to realistically predict the evolution of small lakes in the Ol'khon area. [ABSTRACT FROM AUTHOR]

Lake ice cover is described by its thickness, temperature, stratigraphy and overlying snow layer. When the ratio of ice thickness to lake size is above ∼10−5, the ice cover is stable; otherwise, mechanical forcing breaks the ice cover, and ice drifting takes place with lead-opening and ridging. This transition enables a convenient distinction to be made between small and large lakes. The evolution of the ice cover on small lakes is solved by a wholly thermodynamic model, but a coupled mechanical–thermodynamic model is needed for large lakes. The latter indicates a wide distribution of ice thickness, and frazil ice may be formed in openings. Ecological conditions in large lakes differ markedly from those in small lakes because vertical mixing and oxygen renewal may take place during the ice season, and the euphotic zone penetrates well into the water column in thin ice regions. Mesoscale sea ice models are applicable to large lakes with only minor tuning of the key parameters. These model systems are presented and analysed using Lake Peipsi as an example. As the climate changes, the transition size between small and large lake ice cover will change. [ABSTRACT FROM AUTHOR]

During a yearlong observation, settling fluxes of seston in the epilimnion and hypolimnion of Lake Viitna Linajärv varied from 230 to 1400 mg m.2 d.1. Most of the seston consisted of particulate organic matter (POM). The POM content in the dry matter of surface sediments sampled from the entire lake floor was on average over 50%. Seasonal changes in the distribution of chlorophyll a in the lake and the content of POM reveal the important role of fresh planktonic particles in the deposition. A strong correlation between POM and particulate inorganic matter in the settling matter during stratification indicates flocculent settling of the mineral particles. Resuspension from the littoral zone results in the focusing of sediment into the deep basin of the lake. [ABSTRACT FROM AUTHOR]

In small lakes (<10 ha) the process of sedimentation is not influenced very strongly by wind and wave activity and spatio-temporal variations in the composition of sediments are related with the topography of the current basin. Investigations on surface sediments (LOl, grain-size composition) in two small Estonian lakes - Lake Viitna Linajärv and Lake Väike Juusa - showed that up to 50% of the lithological composition of sediment is determined by the slope inclination, distance to the shore, and water depth. A composite dimensionless parameter (CP) developed enables to use the same approach to the description of the location of the site in lakes of different size, bottom topography, and hypsographic curve. Using the CP value it is possible to estimate the location of the sampling site in either an accumulation area (A area) or erosion-transportation area (E + T area) with A < CP = 2.5 ± 0.5 < E + T. [ABSTRACT FROM AUTHOR]

The mining company Karelian Pellet in NW Russia extracts iron ore and processes it locally into iron pellets. The production operations have effects on the environment in the form of air pollution (SO2 and dust) and waste water emissions. The waste waters from the process and the mining pits are let out into a dammed basin, formerly the natural Lake Kostomuksha. This basin flows north-east through several small lakes (e.g., Poppalijärvi, Kento) to the larger lake Middle Kuito and the White Sea. For these small lakes an exceptionally high mineral content, high pH value, and high concentrations of potassium, lithium and nitrogen in the water have been characteristic. However, the total phosphorus content (6–9 μg l-1) is slightly lower than in the Lake Upper Kuito (11–13 μg l-1) which acts as a reference lake. Biota from bacteria to fish were quantitatively sampled in August 2000 and 2001. Our results suggest a twice higher biomass of both phytoplankton (mainly picoalgae) and fish (biomass per unit effort) in the lakes downstream from the mine in comparison to the reference lake. Zooplankton and zoobenthos biomass both peak in L. Kento, the lake in the middle of the outflow series. The fish fauna (seven to eight species caught) is the same in all lakes and is dominated by perch and roach. Both grow well and roach show best growth in L. Poppalijärvi, next to the waste basin. Perch gills show some histopathological changes which do not, however, appear to affect either growth or reproduction. [ABSTRACT FROM AUTHOR]

The processes of the migration and concentration of trace elements during sedimentation in small continental lakes in various landscape zones of the south of Western Siberia have been studied. We provide a quantitative assessment of the concentration levels and changes in the regional geochemical background of Cd, Hg, Sb, Zn, and Pb in sapropel deposits over the past 200 years. It was shown that complex natural processes determined by a combination of azonal factors play a fundamental role in the formation of the geochemical and mineral compositions of the bottom sediments of small lakes in various landscape zones in the south of Western Siberia. These consist of: the formation of sedimentary material in the lake catchment depending on the relief, geology, soil, and vegetation cover, as well as anthropogenic influences; the formation of authigenic organic and mineral matter as a result of biological, biochemical, and physicochemical processes; and the deposition of a complex mixture of allochthonous and autochthonous matter at the bottom of a lake, which flows under conditions of prolonged ice formation (anaerobic conditions). [ABSTRACT FROM AUTHOR]

We studied 46 small, drainless lakes in various landscape types: The sub-taiga (Vasyugan plain), forest–steppe (Baraba lowland), and steppe and subzone of ribbon forests (Kulunda plain). Sampling of lake components (sediments, water, and biota) was performed. The materials were analyzed via a combination of modern analytical methods (atomic absorption spectroscopy, X-ray fluorescence, scanning electron microscopy and X-ray diffractometry). It was found that in the south of Western Siberia, lakes with a bicarbonate-sodium water composition are widespread against the background of general landscape zoning. This composition contributes to the abundant growth of biota in the lakes, which leads to the processes of authigenic carbonate formation from calcite–dolomite series and aragonite on geochemical barriers, i.e., drifting biota–water, submerged biota–water, and water–bottom sediments against a background of terrigenous demolition and organic matter accumulation. The article shows the differences in the composition and structure of low-temperature carbonate minerals formed on various geochemical barriers. It was found that low-magnesium calcite and aragonite are the most common authigenic carbonates in small lakes in the south of Western Siberia and are formed on all three geochemical barriers in lakes. High-magnesium calcites and Ca-excess dolomites are formed only at the water–bottom sediment barrier in lakes with HCO3–Na and Cl–HCO3–Na water composition at pH > 9 and with a total dissolved solids > 3 g·L−1 (in some lakes of HCO3-Na composition with a TDS < 3 g·L−1 and pH > 9). [ABSTRACT FROM AUTHOR]

The morphology and mineralogical and geochemical compositions of the freshwater ferromanganese formations (FMF) of Lake Onego (NW Russia) and small lakes located in its catchment area were studied. The lake waters, bottom sediments and FMF were analyzed by a set of modern methods of geochemistry, mineralogy, and crystal chemistry (powder X-ray diffraction, IR spectroscopy, electron microscopy, ICP–MS analysis, atomic absorption, etc.). A detailed description of the microscopic structure in comparison with the geochemical characteristics of the FMF provides new information on the role of biota in the formation and behavior of individual elements at various stages in the nodule formation process. This study shows the homogeneous composition of microconcretions—only manganese or only ferruginous—in bottom sediments throughout the entire water area of Lake Onego and the rhythmic structures of the nodules, formed by macro- and microlayers with mineralized microbiota. The layers are composed of either crystalline Mn mineral phases (pyrolusite, rhodochrosite) or crystalline Fe mineral phases (siderite, goethite). The separation of Mn and Fe mineral phases in the nodules proceeded during their formation and diagenesis. The examined chemical and mineral compositions, textures, and structures of the nodules are a testament to the hydrogenic source of their ore substance and the formation of FMF is controlled primarily by redox environments at the water–sediment interface. [ABSTRACT FROM AUTHOR]

Remote sensing of ice phenology for small lakes is hindered by a lack of satellite observations with both high temporal and spatial resolutions. By merging multi-source satellite data over individual lakes, we present a new algorithm that successfully estimates ice freeze and thaw timing for lakes with surface areas as small as 0.13 km2 and obtains consistent results across a range of lake sizes. We have developed an approach for classifying ice pixels based on the red reflectance band of Moderate Resolution Imaging Spectroradiometer (MODIS) imagery, with a threshold calibrated against ice fraction from Landsat Fmask over each lake. Using a filter derived from the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) surface air temperature product, we removed outliers in the time series of lake ice fraction. The time series of lake ice fraction was then applied to identify lake ice breakup and freezeup dates. Validation results from over 296 lakes in Maine indicate that the satellite-based lake ice timing detection algorithm perform well, with mean absolute error (MAE) of 5.54 days for breakup dates and 7.31 days for freezeup dates. This algorithm can be applied to lakes worldwide, including the nearly two million lakes with surface area between 0.1 and 1 km2. [ABSTRACT FROM AUTHOR]