We studied the productivity level of some parts of Lake Onego. Four indicators were used: number of saprophytic bacteria, zooplankton biomass, chlorophyll-a concentration, and water transparency. The analysis included samples from 14 stations located at transects from the top of Kondopozhskaya Bay to the center of Lake Onego and from the top of Petrozavodskaya Bay to the center of the lake. Two periods of 20 years (the end of the last century and the beginning of the present one) were compared. The productivity level was estimated using fuzzy logic technology according to the Mamdani algorithm. The membership functions for each indicator included two terms: "low productivity" and "higher productivity"; the ranges of values for each term were set by an expert. The output membership function included two terms of rectangular shape with the values "low productivity" and "higher productivity". A total of 16 production rules were constructed; they, in turn, allowed to obtain 706 productivity level estimates for all stations. A bootstrapping was applied to assess the significance of differences. Comparison of data for the end of the last and beginning of the current century showed the following: There were no significant changes in productivity estimates at the transect "Petrozavodskaya Bay-the center of the lake". For the transect "Kondopozhskaya Bay-the center of the lake", there is an increase in productivity level, probably due to the appearance of new factors of anthropogenic impact: the trout farms. The advantage of the fuzzy logic modeling method is the clear theoretical meaning and simpler calculation technology compared to statistical classification methods.

The results of the diagnosis of the state and changes in the ecosystem of Onegskoe Lake (Lake Onego) and the watershed are presented using the developed information and analytical system “Lake Onego-watershed” (IAS), consisting of a comprehensive database (DB), a combined database of Roshydromet and Northern water problems institute/Karelian Research Center of the Russian Academy of Sciences on the nutrient load for the modern period 1995–2022, the ILLM mathematical model for assessing the removal of nutrients from the watershed and the formation of the nutrient load on the lake and the 3D-mathematical model SPLEM, developed for Lake Onego. Information was collected on the main sources of nutrient load in the Lake Onego catchment area, as well as available field observation data on the flow of nitrogen and phosphorus into the lake. The contribution of different nutrient sources coming from river runoff, diffuse sources, urban discharges and from trout farms was calculated for the lake and the main limnic areas. Based on data from field observations over the past 30 years and the results of numerical experiments using the SPLEM model with a grid resolution of 1 km it is shown that the ecosystem of the lake not only did not restored after the reduction in anthropogenic load after 1991, but eutrophication of waters in the lips and bays continues due to the influence of industrial and agricultural enterprises, trout farms and noticeable climate warming. Functional for the IAS “Lake Onego-catchment” to visualize the main modeling results on a 1 km grid was developed, and a web application interface has been created.

The article presents the results for 2014–2015 of chemical, microbiological and toxicological studies of the water quality of the urbanized tributary of Lake Onego (the River Neglinka). The high anthropogenic load on the studied river was revealed. The runoff of storm water reached one third of the river runoff. The maximum excess of maximum available concentration in storm water for BOD5 was 80–90-fold, for oil products – 50–60-fold, for suspended solids – 40-fold. The River Neglinka in the upper reaches (outside the urban area) is affected by a swampy catchment area. The chemical composition of the water (low pH values, high color index, CODCr and Fetot) reflected the influence of catchment area. The methodological problems were associated with identifying zones of anthropogenic impact against the background of the negative impact of natural factors on the water quality of the River Neglinka. In the calculation a modified specific combined water contamination index was used. This made it possible to determine zones of influence of the anthropogenic factor. Microbiological indicators (total bacterial abundant, total coliform bacteria, saprophytic bacteria) indicated a high degree of pollution of the River Neglinka and especially sanitary-indicative bacteria. The unsuitability of the River Neglinka for recreational use was revealed. Bioassay revealed the toxicity of the river water in the upper reaches. It was connected with the low pH due runoff of humic substances from swampy catchment area. The barrier role of groundwater, which led to an increase in the pH, and the complexing ability of humic substances, which reduced the bioavailability of heavy metals, stipulated non toxicity river water in urban areas. The study proved that the assessment of the quality of highly colored river waters is possible only with a comprehensive implementation of chemical, microbiological and toxicological studies.

Toxigenic cyanobacteria and microcystins in the oligotrophic pelagic zone and mesotrophic bay of Lake Onego—the second largest lake in Europe—were found for the first time. Microscopic analysis revealed that Dolichospermum lemmermannii, D. circinale and D. spiroides dominated in bloom spots in the oligotrophic zone of the lake and D. flos-aquae and Microcystis aeruginosa OKin the eutrophic bay. The abundance of cyanobacteria in bloom spots is potentially hazardous for humans and animals. PCR-analysis showed that mcyA gene involved in microcystin biosynthesis was found in cyanobacteria of the genera Dolichospermum and Microcystis. Five structural variants of intracellular microcystins were detected in a trace amount using high-performance liquid chromatography–mass-spectrometry of high resolution. The most hazardous hepatotoxin, MC-LR, was found only in the eutrophic bay. In the present study, the reasons for the low cyanotoxin content in the phytoplankton dominated by Dolichospermum are discussed. The findings of our study make a significant contribution to the accumulation of facts which state that toxigenic cyanobacterial blooms can occur in large oligotrophic lakes.

The Kondopogskaya Bay of Lake Onego is under the influence of anthropogenic pressure due to the inflow of wastewater from a pulp and paper mill (the upper part) and trout farms (the central part). The primary production characteristics (photosynthesis, chlorophyll a, specific rate of photosynthesis, assimilation numbers) of the bay ecosystem during the “outbreak” of phytoplankton number and biomass in August 2021 are assessed. It is proved that the photosynthesis rate in the bay was determined by small diatoms during the research period. Diatom plankton cells with a volume of less than 600 µm accounted for 80-90% of the number of Bacillariophyta, the dominant group of the community. The photosynthesis values (150-330 µg/l•day) did not exceed the limits of oligo-mesotrophic ecosystems. The specific rate of photosynthesis (0.4-1.2 day–1) and daily assimilation numbers (22-40 µg C/µg Chl) were also temperate and did not indicate strong biogenic water pollution. It was revealed that the low content of chlorophyll a in phytoplankton biomass (0.13-0.39%) was mainly determined by a small number of productive green algae. The share of this phytoplankton group in the community biomass did not exceed 26%, in the number – 11%. At the same time, phytoplankton biomass (2.1-5.7 mg/l) and chlorophyll a concentrations (5.1-9.8 µg/l) reached values typical of meso-eutrophic ecosystems. Comparing the results of the study with long-term photosynthesis data showed that the trophic state of the central part of the bay, where large trout farms are located, has not changed. Long-term data on phytoplankton biomass indicate an increase in the trophic status of the central part of the bay at the present time. The inconsistency of the trophy level in terms of quantitative and functional indicators of phytoplankton may indicate the initial stage of eutrophication of the central part of the Kondopogskaya Bay as a result of the activities of trout farms.

An interdisciplinary study of microplastic (MP) contamination in the water area of Lake Onego was conducted within a project funded by the Russian Science Foundation. The aim of the project was to assess the current state of this large water body, specifically its contamination with synthetic polymer particles and the associated heavy metals, to identify the sources and areas of MP accumulation, patternsin its sedimentation and transport, and to conduct a hazard assessment of this pollution. The article provides an overview and a summary of the obtained results. Based on seasonal hydrochemical data for 2019–2021, the current state of the lake was identified and the degree of its contamination with microplastics, heavy metals, and other chemicals was determined. The highest MP content was found in the water and in the bottom sediments of the upper, most heavily contaminated, part of the Kondopoga Bay, where wastewater from the Kondopoga Pulp and Paper Mill enters the lake. Active accumulation of MP was detected in the bottom sediments of Lake Onego, its content being about twice that of the Baltic Sea. Spatial and seasonal patterns of MP distribution in the water column of Lake Onego were revealed. It has been established that with the current level of Lake Onego littoral area contamination by irregularly shaped MP particles sized about 100 microns, their negative impact on the population of invasive species, Baikal amphipod Gmelinoides fasciatus, is unlikely. Having applied SEM-EMF and Raman spectroscopy, we revealed the mechanism for mineralogical destruction of plastics driven by the crystallization and growth of microminerals, which leads to local ruptures of the plastic and accelerates its destruction. Methods for fractionation of MP particles and desorption of metals from their surface have been developed, making it possible to obtain comparable and reproducible results when analyzing the metal content on their surface. For the first time, models were suggested to simulate microplastic generation from a set of macrofragments through stochastic destruction and filtering of three-dimensional microplastic fragments on a grid. The simulation results are in good agreement with the ratios obtained during field experiments.The revealed relationships can be used to adjust the detected levels of microplastics in the nature depending on the mesh size of the net used in sampling.

The results of our bacterioplankton study (total abundance; saprophytic, hydrocarbon oxidizing and phenol resistant bacteria; total microbial number, and coliform bacteria) in an urbanized tributary of Lake Onego in 2015 are presented. The lower reaches of the Lososinka River flow across the territory of Petrozavodsk city (Karelia) and receive 14 untreated drains of the urban storm sewers. Differences in the temporal abundance dynamics of bacteria which are the indicators of oil pollution, sanitary condition and saprobity were found in the reference and urban parts of the river. These changes are not related to the hydrological and temperature regime of the river and reflect the influence of the pollutant drainage from the urban area on the formation of the river bacterial community. A significant increase in all studied indicators of the quantitative development of bacterioplankton in the urban part of the river as compared to the reference part was revealed. The number of heterotrophic bacteria of various ecological-trophic groups decreases in the lake water by 8–16 times due to dilution, as early as 500 m from the mouth of the river. A significant decrease in the numbers of hydrocarbon oxidizing bacteria in the river water and an increase in sanitary-indicative microorganisms are shown to occur over four years. The Lososinka River on the territory of the Petrozavodsk city is assessed as polluted with oil products and organic matter of fecal origin and unsuitable for recreation according by the level of indicator bacteria.

The Petrozavodsk Bay of Lake Onego is characterized by favorable temperature, food and oxygen conditions for the functioning of relict crustaceans Monoporeia affinis (Lindström, 1855) population. The analysis of the size-age population structure was performed for this species for the first time. In 2018, the spring and autumn state of the M. affinis population differed. The contribution to the total number of young crustaceans with a body length of 1.5–2.0 mm and 2.1–3.0 mm in May and September was distinguished. The number of these two size groups changed inversely from May to September, which indicated the growth processes of juveniles. The total contribution of young crustaceans to the total population at different stations varied within 40–50% in May and 20–40% in September. Based on the analysis of size-frequency histograms and the method of principal components, two age cohorts of crustaceans with a body length of 3.1–7.0 mm (the first cohort, age 1 year) and 7.1–10.0 mm (the second cohort, age 2 years) were identified. The proportion of the first cohort in the total population of M. affinis was on average 12% in May and September. The proportion of the second cohort in May was on average 2%, and in September it increased to 8%. The data obtained are in good agreement with two age cohorts of M. affinis in other lakes of Karelia.

The trophic state and water quality of Lake Onegо have been assessed under climate warming and changes in anthropogenic load over the past 30 years. The water body retains its natural oligotrophic state during the summer stratification according to the concentration of Chl a. A small amount of readily mineralizable organic matter in water determines the low level of development of saprophytic bacteria, corresponding to xenosaprobic and β-oligosaprobic waters. Only Kondopogskaya Bay in Lake Onego is characterized by a higher trophic level (mesotrophic) and water saprobity (β-mesosaprobic) due to pollution by wastewater from the PPM and waste from trout farms. The local bloom of cyanobacteria in the open area of the lake was observed during the anomalous heating of the epilimnion in the summer of 2022 for the first time in the 50-year history of research. The increase in the concentration of humic substances in the water of the bays as a result of climate warming at this stage did not lead to a change in the level of saprophytic bacteria.

Phytoplankton photosynthesis in Lake Onego was measured in 1989-2006. An attempt was made to calculate photosynthesis by daily assimilation numbers and chlorophyll a concentration measured in 2007-2021 to supple-ment data on the primary production. Daily assimilation numbers were calculated by simultaneously measured photosynthesis and chlorophyll in 1989-2006 for different areas and seasons of a limnically complex water body. A comparative statistical analysis of the size-structural characteristics of phytoplankton in 1989-2006 and 2007-2021 was performed to assess the possibility of using the obtained assimilation numbers to restore photosynthesis values. Comparison of the average cell volume for the phytocenosis and the ratio of diatoms and smaller non-diatoms showed their similarity in both periods in the main water area of the lake. Only in the central sector of Kondopoga Bay, which has been influenced by biogenic loads from the trout farms since the 2000s, the average cell volume decreased significantly and the proportion of diatom plankton also decreased. Photosynthesis was not calculated for this sector. The calculated assimilation numbers were similar for almost the entire water area of the lake. The maximum daily values were observed in summer with medians from 11.8 to 18.4 µg C/µg Chl in different parts of the water body. In Kondopoga Bay, which during both study periods was experiencing a biogenic load of wastewater from the pulp and paper mill, their median values in summer reached 40.3 and 29.6 µg C/µg Chl day–1 in the top and open parts, respectively. It was possible to restore 197 values of photosynthesis by chlorophyll a measured in 2007-2021and by the calculated assimilation numbers in the surface water layer of different areas in Lake Onego in different seasons.

For the first time in Lake Onega, the reproduction features of the alien amphipod Gmelinoides fasciatus (Stebbing, 1899) were studied based on research in 2010–2011. The period of reproduction in the conditions of the reservoir (May–September) were established, the body length ranges of egg-bearing females, the average and maximum sizes of breeding individuals, as well as fertility were determined. During the study period, a decrease in the average size of females from May–June to August–September was noted, which is associated with the beginning of reproduction of females of the summer generation and the continued reproduction of females of the last year's generation. Equations were calculated that make it possible to predict the fecundity of females by body length, which indicates similar patterns of generative growth of G. fasciatus on the littoral in the northern bays of Lake Onega. Generally, the fecundity of the amphipod is higher in Lake Onega compared to the fecundity of the same species in Lake Ladoga, Neva Bay, Lake Arakhley and the Bratsk Reservoir. This phenomenon is probably associated with the geographical location of Lake Onega, a higher latitude and a longer photoperiod.

For Karelian lakes, it is shown that, as the water color increases, an increase in the total phosphorus content in water leads to a slower increase in the concentration of chlorophyll a compared to the generally accepted Dillon–Riegler dependence. This is explained by the fact that a significant amount of phosphorus is associated with iron in complexes with humic substances, which is indirectly confirmed by a significant dependence of the concentration of total phosphorus on the water color. An equation for calculating the chlorophyll a concentration using the total phosphorus value for water bodies of Karelia not affected by anthropogenic influence has been proposed for the first time. An overestimation of the real trophic status of high-color waters, determined based on the total phosphorus value, can lead to an unreasonably high permissible anthropogenic phosphorus load on water bodies in Karelia.

To indicate the potential role of Gmelinoides fasciatus, an invasive species of Lake Onego, in the inclusion of microplastics into food webs, several indicators were evaluated: its ability to ingest microplastics, the preferred size ranges, and the ingestion intensity. For this purpose, irregularly shaped polystyrene copolymer particles (acrylonitrile butadiene styrene plastics, artificially crushed) of four size classes (<50, 50-100, 100-250, >250 µm) were used. Gmelinoides fasciatus actively ingested microplastic particles, and in treatment with particles of 100-250 µm in size, the consumption rate was the highest. The crustaceans that survived the experiment ingested smaller particles than the deceased ones. Based on the size-frequency distributions of the ingested particles and the same in the suspension, crustaceans preferred smaller particles than those in suspension. The mean size of the ingested particles was 100 ± 5 µm. However, considering the actual concentration of microplastic fragments in the sediments of Lake Onego, in natural conditions, a negative effect of microplastic fragments on the G. fasciatus population is unlikely. At the same time, the ability of the invasive species G. fasciatus to consume microplastics and their active integration into the food webs of Lake Onego through consumption by fish can be considered reliable factors of the entry of microplastics in the fish of Lake Onego. Environ Toxicol Chem 2022;41:184-192. © 2021 SETAC.

GIS technologies were used to study the spatial distribution of zones with different trophic conditions in the water area of Lake Onego. Empirical data on the trophic conditions of waters sampled in 1982–2020 were as the basis for the map development. Two periods, before and after 2000, were considered separately to assess the impact of climate change. As indicators of trophic conditions, the number of saprophytic bacterioplankton, biomass of crustacean zooplankton, concentration of chlorophyll “a” and water transparency were used. All characteristics were converted to a normal distribution, and the values at individual points were interpolated for the entire water area of the lake, which was presented as a network of 544 squares. Each cell of the water area was characterized by four values of indicators. To assess trophic conditions, multivariate statistics (principal component analysis) and an expert system (Bayesian classifier) were used. The first principal component can be considered as the integral value of trophic conditions in a given part of the water area. The Bayesian classification method allows to get an estimate of the probability of classifying each cell in the water area as “high trophic conditions” and “low trophic conditions” and assign a significance threshold (p = 0.05). The cartograms built on the basis of both methods are basically the same. Most of Lake Onego area is characterized as low trophic conditions. The vast area with high trophic conditions was identified in the northwestern part of Lake Onego where on the coast large cities are located (Petrozavodsk and Kondopoga), which is associated with active anthropogenic pollution in the last century. In recent years, due to industry recession, trophic conditions in this area has sharply decreased, with the exception of Kondopozhskaya Bay, where there is an increase in water pollution as a result of trout farms.

The review reports the main results of the studies carried out by NWPI KarRC RAS in the institute’s major research areas over the past 30 years. Information is provided on some studies in national priority R&D areas, and on the activities implemented under regional and international grant-funded projects and applied initiatives. Some results of research on the White Sea, Lakes Ladoga and Onego, lake-river systems, and groundwater are reported. A summary is given of important practical developments ordered by federal and regional ministries and departments, companies and organizations, and implemented under the public drinking water supply programme. The information systems designed and implemented for these developments to be used by relevant organization are introduced. An overview of the results of studies carried out by NWPI collaboratively with Russian and foreign institutes and universities is given, namely regarding research on water resources, water quality, White Sea ecosystems, Russia’s largest lakes, and under-ice conditions in North Russian lakes.

Studying and forecasting the consequences of the climate change impact on aquatic ecosystems are among the important tasks of hydroecology and hydrobiology.Over the past 30 years, according to data of meteorological stations on the catchment area of Lake Onego-the largest reservoir of Northwestern Russia-the average annual air temperature is steadily increasing.In the winter of 2019-2020, an abnormally high air temperature was recorded, which exceeded the climatic norm by 5-9°С.According to satellite data, in winter 2020, for the first time in the 65-year history of observations, there was no ice cover on most of the open part of Onego.To assess the consequences of an abnormally warm winter for the ecosystem of Onego, its state in the spring-summer period was studied.In June 2020, the water temperature, the concentration of chlorophyll "a," and photosynthesis were measured, and the structural parameters of phytoplankton in Onego were studied using standard methods.Based on the data from the temperature sensors of the buoy station, it was found that the spring thermal bar passed 10-15 days earlier than the average long-term periods, the temperature stratification of water was established 15-20 days earlier.The temperature of the surface water layer in Onego in June 2020 was 5-8°C higher than the average long-term values for the period of spring mixing and corresponded to the period of summer heating of water.In the open part of the lake, a shift in the phenological phases of phytoplankton development was observed, in particular, its summer composition, the seasonal maximum of chlorophyll "a," and primary production were formed a month earlier.In the Kondopoga Bay of Onego, which was exposed to the highest anthropogenic phosphorus load, the level of phytoplankton development first reached the α-eutrophic state.

The total biomass of an invasive amphipod, Gmelinoides fasciatus, in Lake Onega has been estimated for the first time based on our own data and published data; it ranges from 1.6 to 2.2 thousand t of wet weight for the entire water body. Its production over the growing season varies from 2.9 to 4.0 thousand t. The biotope with the richest stock of this species (reed thickets, where the biomass of the crustacean can reach 39 g/m2) is located mainly in the northern part of the lake. The possibility of considering G. fasciatus a potential commercial species with an estimated total allowable catch of up to 1.5–2.0 thousand t per year is discussed.