The bioaccumulation of elements in the organs and tissues of the whitefish (Coregonus lavaretus L.) from various stretches of Imandra Lake under anthropogenic influence in the toxic load reduction period is considered. The accumulation of elements in the whitefish’s organs and tissues depends to a lesser extent on higher concentrations of toxic elements and the physiological state in water and to a greater extent on the tolerance thereto. The element redistribution in the whitefish’s liver and kidney in terms of its physiological state is modeled. The adaptive response strategy is observed most clearly in changes in iron and zinc metabolism.

An analysis of the problem of water bodies eutrophication as a global process is presented. The volumes increasing use of nitrogen and phosphorus on a planetary scale are shown, the dispersion of which leads to an increase in the content of nutrients in lakes and rivers. The results of original studies of remote lakes in the Arctic zone are presented, which showed an increase in the concentrations of nutrients in lakes in recent decades. A tendency has been revealed for an increase in the contents of nitrogen and phosphorus, as well as organic matter in lake waters, even in the absence of anthropogenic influence. It has been established that an increase in temperature and climate warming in the Arctic regions exert the main influence on the increase in the content of nutrients and the trophic status of lakes.

The problem of eutrophication of water objects as a global process is analyzed. The volumes of increasing planetary use of N and P, the dispersion of which together with climate warming leads to an increase in the nutrient content of lakes and rivers, are shown. The results of original studies of remote lakes of the Arctic zone are provided. The tendency toward an increase in the contents of N and P, as well as organic matter in water lakes even in case of the absence of anthropogenic impact, is revealed. It is proved that the climate warming mostly affects the increase in the nutrient content and the trophic status of lakes.

The paper is devoted to anthropogenic and biogeochemical processes that effect the formation of the water and bottom sediment (BS) of subarctic Imandra Lake. The data of long-term observations are presented that show changes in the chemical composition of the water during the period of maximum pollution and after the reduction in the anthropogenic load over the past 30 years. The concentrations of toxic metals in the water has decreased, but climate warming has increased the inflow of organic matter and nutrients, and this intensified the production processes. The enrichment of the water in heavy metals during the period of intense pollution resulted in the accumulation of these metals in the bottom sediments, with the highest concentrations of the metals found in the uppermost layers accumulated during the modern sedimentation period. The development of anoxic conditions in the bottom water horizons due to sedimentation and oxidation of organic matter leads to the circulation of metals and hampers their burial. Physicochemical and biogeochemical processes are considered as explaining the diffusion of metals to the surface of the bottom sediments and the accumulation of anomalously high concentrations of metals in the surface layers of BS despite the significant decrease in the concentrations of metals in water. A hypothesis is suggested for the beginning of initial diagenesis stage in bottom sediments.

The mechanisms of biogeochemical adaptation of fish to survival in the historically contaminated Imandra Lake were studied. The role of trace elements in the protective functions of the organism and their importance in the readaptation of organisms to improving the habitat was established. An elevated S to Se ratio indicates a high antioxidant status of fish from the historically contaminated part of the lake, while an increased accumulation of Fe, Cu, and Se can serve as a marker of liver pathologies, and of Zn and Co, of kidney pathologies.

Modeling of the dynamics of the nickel concentration in soils, water, and bottom sediments of lakes, caused by emissions into the atmosphere from the Pechenga Nickel Plant (Kola Peninsula) over the entire period of its operation, is considered. The technology of balanced identification, which makes it possible based on mathematical description of inhomogeneous geochemical processes occurring in ecosystems to combine heterogeneous experimental data and to develop a computer model with an optimal balance of complexity and closeness to the data, is used. The results including estimates of the retrospective state of the simulated objects and a forecast of their dynamics until 2030 are presented and discussed. According to model calculations, the intensity of Ni accumulation in the soil was 2.4 and it was twice as high as in bottom sediments during the periods of maximum deposition (1980–2005). According to the forecast model, after the shutdown of the plant, Ni accumulation in bottom sediments will begin to decrease and Ni will slowly leach from the soil with an intensity of 0.2 mg/(m2 yr).

— The paper discusses the distribution and origin of organic matter in natural waters with regard to the latitudinal geographic zoning in the European territory of Russia (ETR) and Western Siberia (WS) and demonstrates how conditions on the catchments and climate affect the content of autochthonous and allochthonous organic matter. Conditional coefficients of the ratios of these forms are calculated. The influence of the temperature factor on the content of autochthonous organic matter in the waters of the southern territories of the ETR and WS was proved by multivariate statistical methods of analysis. General trends and relations are identified in the distribution of lipids, proteins, and carbohydrates of the autochthonous and allochthonous organic compounds. The mechanism of biochemical transformation of bound carbohydrates of allochthonous organic compounds into free autochthonous ones via the microbial decomposition is demonstrated, which is more typical of waters in the southern regions of WS. The paper discusses how natural and climatic conditions can influence changes in concentrations of organic compounds in the lake waters and structural characteristics of these compounds (contents of aromatic and aliphatic fragments).

The paper discusses modeling the dynamics of nickel concentration in soils, water, and the bottom sediments of lakes caused by atmospheric emissions from the Pechenganickel plant, Kola Peninsula, throughout its whole operation period. The applied technology of balanced identification makes it possible to use a mathematical description of heterogeneous geochemical processes in ecosystems to combine heterogeneous experimental data and build up a computer model with an optimal balance of its complexity and fitting quality of the data. The model is used to analyze the spatial and temporal variability of natural objects in the zone of distribution of atmospheric pollution (nickel) from the Pechenganickel plant. The paper presents and discusses results of this study, including estimates of the retrospective state of the simulated objects (before the start of the intense studies) and a forecast of their dynamics until 2030. According to the model calculations, the intensity of Ni accumulation in the soil and bottom sediments was 2.35 and 4.48 mg/(m2 year) during the maximum deposition periods (1980–2005), whereas the model predicts a decrease in the intensity of Ni accumulation in the bottom sediments (0.23 mg/(m2 year)) and slow Ni leaching from the soil (0.19 mg/(m2 year)) after the shutdown of the plant.

— The paper analyzes the effect of ever increasing anthropogenic impacts on land waters and analyzes V.I. Vernadsky’s works on natural waters and their significance for assessing modern biogeochemical processes. The paper demonstrates the scale of the influx of chemical elements and compounds into the modern biosphere as a result of the emission of greenhouse gases, nitrogen and phosphorus dissemination, acid-forming gases, and metals. Key changes in some regions and the biosphere as a whole are highlighted. The consequences of anthropogenically induced processes are illustrated by the example of a remote Arctic region, the northern Kola Peninsula in Russia: the effects of climate warming and the acidification and eutrophication of the waters and their enrichment in metals. In the wake of V.I. Vernadsky’s ideas about the role of land waters in supporting the life necessities of the planet’s human population, approaches to assessing water quality from the standpoint of the ecological paradigm are described.

-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.

The paper presents results of a long-term (1990–2018) study of changes in the geochemistry of land waters in the Kola region as a consequence of climate warming and a regional- and global-scale decrease in the emission of acid-forming gases. The work is based on materials acquired by studying 75 small lakes in the region every four to five years in the period of time of 1990 through 2018. Reliable trends toward a temperature rise over a 28-year study period were revealed based on the analysis of weather archives. It was found out that the content of anthropogenic sulfates in the water significantly decreased and the acid-neutralizing capacity of waters increased due to the reduction in the anthropogenic sulfur emissions into the atmosphere. An increase in the content of organic matter and nutrients in the water of lakes has been proven, which is reliably associated with an increase in the regional temperatures. A number of lakes in acid-vulnerable regions retain critical values of the acid-neutralizing capacity of waters, which may be associated with both local and transregional transport of polluted air masses. The analysis of the chemical variability the waters in a long-term series of observations demonstrates the evolutionary development of lakes and changes in the biogeochemical cycles as a consequence of the transformation of the watersheds under the influence of a decrease in acid deposition from the atmosphere on the catchment areas and climate warming in the region.

Bioaccumulation of the main pollutants in the organs of whitefish, as well as their haematological parameters, were examined dynamically over a 40-year period in historically contaminated Lake Imandra. A quantitative histological analysis was performed to assess the physiological state of whitefish and histopathologies of organs, as well as their physiological and biochemical functions in the current period of toxic load decline. Biological reactions of whitefish from the historically contaminated area have been greatly modified in contrast to those of whitefish from the never contaminated area of the lake, and this shift persisted even after approximately 20 years of toxic load decline. First, high antioxidant status supports the body's systems, smoothing over the negative consequences of metal toxicity, phagocytosis and inflammatory reactions. Moreover, the defence mechanism of whitefish from the historically contaminated area actively uses the oxidative systems of nonspecific immunity. Second, the adaptive strategy is aimed at improving gas exchange without compensatory proliferation of gill structure, which increases their functional surface and reduces the distance to the bloodstream, as well as increasing haemoglobin in maturing erythrocytes. Third, the higher efficiency of endo- and phagocytosis was confirmed by detecting increased monocytes and macrophages in the peripheral blood and decreased melano-macrophage centres in the fish kidney. Elevated accumulation of Fe, Cu, and Se may serve a sign of liver pathology, while elevated accumulation of Zn and Co already indicates kidney pathology, which is confirmed by histopathological alterations.

Small lakes are potentially effective environmental sensors; they react quickly to anthropogenic stressors. We studied the long-term response of water chemistry to reduced acid deposition and climate warming in the Kola Arctic region of Russia based on monitoring data from 75 lakes. Monitoring was carried out once every 4–5 years in 1990–2018, with analysis for major anions and cations, dissolved organic carbon (DOC), and heavy metals (Ni and Cu). Analysis of archive data on the weather allowed us to reliably identify trends toward a systematic temperature increase over the past 28 years. The population of the lakes under study was proven to generally show a decrease in the concentrations of anthropogenic sulfates and the strengthening of the acid-neutralizing capacity (ANC) of the waters during this period. The concentrations of both DOC and nutrients (Ptot and Ntot) in the lake waters were determined to increase. This phenomenon can be explained by the following two mechanisms: a decrease in the deposition of strong acids and climate warming. We suggest that the effects of multiple factors on the surface waters result in an irreversible evolution of the lakes; hence, the term recovery does not adequately reflect the processes occurring in this industrially well-developed part of the Arctic.

The characteristics of the development of anthropogenically induced processes in the land waters of the Arctic basin, such as eutrophication, acidification and toxic pollution in a changing climate, are characterized. The main changes in ecosystems and periods of occurrence of the most dangerous situations are shown. The criteria for diagnosing adverse processes and the need to tighten water quality standards for the waters of the Arctic regions are substantiated.

The mechanisms of fish adaptation to survival in the historically contaminated Lake Imandra were studied. The role of trace elements in the protective functions of the organism and their importance in the re-adaptation of organisms to improving the habitat was established. The lake whitefish (Coregonus lavaretus L.) unable to migrate for large distance was chosen as the object of research. The indices of red blood as an indicator of fish homeostasis, as well as the role of white blood cells in the activation of the immune system were examined. The causes of the occurrence of histopathologies of organs and tissues are explained. Data on the accumulation of trace elements in the body of fish from this lake are presented. The principal difference in the bioaccumulation of elements is the intense metabolism of Se. An elevated S to Se ratio indicates a high antioxidant status of fish from the historically contaminated part of the lake, while an increased accumulation of Fe, Cu, and Se can serve as a marker of liver pathologies, and Zn and Co, of kidney pathologies.

This paper reviews currently available evaluations of the effects of continuously increasing anthropogenic loads on water resources. The increase in the fluxes of elements and compounds into the environment, such as the emission of greenhouse gases and dispersion of nutrients (nitrogen and phosphorus), acidifying gases, and toxic elements and compounds that adversely affect water quality, are considered. The significance of fresh waters as a life support factor for human populations is demonstrated. Examples illustrate how key anthropogenic-induced processes develop in land waters under the effect of anthropogenic loads, as exemplified by the Russian Kola regions. Climate warming and the increasing dispersion of elements are demonstrated to result in the eutrophication of surface waters, even in areas remote from anthropogenically impacted regions. Although the emissions of acidifying gases diminish, the waters are still acidified in acid-vulnerable areas, and the chemical compositions of the waters have been significantly modified over the past decades, indicating that the changes in the chemical composition of the waters are irreversible. A new feature of the waters is distinguished: the toxicity of the habitats for aquatic organisms. The novelty of the work was to highlight the bridge between anthropogenic loads on surface water on a planetary scale and their consequences in certain regions, which reflect changes in water quality. Arguments are presented for establishing a theoretical approach for evaluating critical loads.

On the basis of long-term studies of the Kola North lakes, which have been exposed to the negative effects of atmospheric precipitation of technogenic acids for many years due to the operation of metallurgical industries, an assessment of biogeochemical changes in the lakes after a decrease in anthropogenic load and under conditions of concomitant climate warming is made. Reliable trends in changes in a number of hydrochemical indices of 75 lakes over the past 30 years have been proven: a decrease in the contents of technogenic sulfates and an increase in the acid-neutralizing capacity of water (ANC), as well as an increase in the concentration of organic matter (DOC) and nutrients (P tot , N tot ) in lake waters. Evidence of the evolution of the biogeochemical status of the lakes is provided, the term “recovery” does not characterize the processes that are developing in this industrially developed region of the Arctic in the modern period of decreasing atmospheric pollution and concomitant climate warming.