Nº 3 (2024)

The territory of Karelia is a unique geographical region, where currently more than 62,000 lakes function in a humid climate, being at different stages of the evolution of their ecosystems. In this study, we analyzed the data on the chemical composition of the bottom sediments of Karelian lakes collected during the period 1965-2020. The patterns of the formation of the chemical composition of the bottom sediments of lakes are discussed. It is shown that in the lakes of the southeastern part of the Fennoscandian Crystal Shield, the bottom sediments of a mixed type are currently being formed: iron-humus-silicon, iron-silicon-humus, or humus-iron-silicon. There are small lakes where the bottom sediments accumulate either silicon (diatomite), iron (lake ore), or organic matter.

The work is based on the E.A. Gofman’s collection of recent ostracods. Here we present summarized data on our results of studying 45 near-shore sampling sites and previously published data, which were the first one to investigate the distribution of recent ostracods in the Caspian Sea and to discuss the influence of such factors as bottom sediments type, water temperature and salinity. Overall, distribution of the ostracods in the Caspian Sea shows a remarkable depth control. The near-shore ostracod assemblage of the Caspian Sea indicates shallow water conditions. Predominant species tolerates temperature and salinity seasonal changes. In northern area assemblage is dominated by Cyprideis torosa and contains abundant euryhaline species tolerant to reduced salinity ranges reflecting the river influence, significant temperature changes and unstable hydrological regime. In the Central and Southern Caspian Sea, the assemblage is mostly represented by the Tyrrhenocythere amnicola donetziensis and other stenohaline species. The analysis of the recent near-shore ostracods of the Caspian Sea allows to conclude that salinity, along with water depth, are the leading factors determining the composition of ostracod assemblages.

As a continuation of regular research to obtain information about mechanisms and sources of air pollution above the water area of Lake Baikal, we present the results of the expeditionary studies on the concentrations of РМ₁₀, polycyclic aromatic hydrocarbons and gaseous elemental mercury in the near-water layer of the atmosphere above Lake Baikal in August 2023. On the route of the vessel along the perimeter of the lake, the concentrations of pollutants in the near-water atmosphere increased near the local sources of air pollution located on the coast of the southern basin (Listvyanka, Slyudyanka and Baikalsk) as well as at the source of the Angara River with the northwesterly transport from the industrial cities of the Baikal region. Over the study period, the РМ₁₀ concentrations averaged 6.0 µg/m³, PAHs–1.1 ng/m³, and gaseous elemental mercury–0.75 ng/m³, which was lower than the values recorded during wildfires between 2016 and 2020 in some areas of Siberia. The resulting concentrations of the investigated air components did not exceed air quality standards. Pairwise correlations during the study period were high between РМ₁₀ and PAHs (0.71) and low between PAHs and mercury (0.21).

The characteristics of the composition, ecological-geographical, and functional structure of the phytoplankton dominant complexes of three different types of lakes in the Nizhny Novgorod Volga region (Klyuchik, Svetloyar, and Svyatoye Dedovskoye) are given. Lake Klyuchik is a rare type of gypsum, highly mineralized “blue” lake; unique in terms of its supply source, the role of which is played by the underground river with high water consumption, and has a weakly expressed stratification. Lakes Svyatoye Dedovskoye and Svetloyar are dimixic, light-water, low-mineralized, of hydrocarbonate class, and with neutral pH values that are fed by rainwater. All lakes belong to specially protected natural areas. Analysis of the algal flora of the studied lakes showed the taxonomic significance of the divisions of Cyanobacteria, Chlorophyta, Bacillariophyta, Ochrophyta, and Euglenophyta, constituting more than 70% of the total species richness. The composition of the dominant species contained 114 taxa of algae (26.38% of the total composition): in Lake Svyatoye Dedovskoye, greens and diatoms predominated (50%), in Lake Svetloyar, euglenids predominated (25%), in Lake Klyuchik, diatoms predominated (more than 40%). Among 13 dominants (from 5 divisions) with high values of DF>10, Dt>10, and pF>20, dinoflagellates from the functional group L₀ (Ceratium hirundinella, Peridinium cinctum) were noted in all lakes, with maximum development in the summer stratification. In the group of diatoms, representatives of centric diatoms of codon B (species of the genus Cyclotella) predominated in each water body, reaching maximum development rates under conditions of water mixing. The composition of the remaining dominant groups in each reservoir was determined by its limnological features. Using the method of multivariate analysis of variance (PERMANOVA), a statistically significant (P-value=0,001) low degree of similarity of the dominant and functional phytoplankton complexes was shown, which may indicate the uniqueness of algae cenogenesis in each of the studied lakes due to the influence of a certain combination of factors.