Vol 52, No 5 (2025)

A study was carried out of the influence of the horizontal pressure gradient in inland water bodies (lakes and reservoirs) on the processes of formation of concentrations of dissolved gases. A three-dimensional hydrostatic model and a one-dimensional model based on averaging of three-dimensional equations over a horizontal section of a reservoir and complemented by parametrization of the pressure gradient to take into account gravitational oscillations (seiches) were used as tools for carrying out calculations. Based on the results of the numerical experiments, it can be concluded that the use of parameterization is of fundamental importance for describing the formation of concentrations of dissolved gases: turning off the pressure gradient in the model gives results corresponding to the Cato–Phillips formulation and does not allow one to correctly reproduce the distribution of gases in reservoirs of finite size. Parameterization of the influence of pressure gradient and horizontal diffusion in the one-dimensional LAKE model allows one to reproduce biogeochemical processes with sufficient accuracy, in accordance with the reference results obtained using the full three-dimensional model.

The most significant features of modeling the cycle of compounds of biogenic elements (nitrogen and phosphorus) and the dynamics of dissolved oxygen in the ecosystem of Lake Teletskoye are considered. The model was calibrated taking into account data from long-term observations of water quality in 1985-2003, as well as a scenario version of the hydrological regime in 2016. The analysis of the intra-annual variability for the state variables, external and internal fluxes of nitrogen and phosphorus compounds in the water is given. The permissible load of nitrogen and phosphorus on the lake is calculated. The model analysis showed that the lake's assimilation potential with respect to phosphorus compounds is insignificant, practically absent. In relation to nitrogen compounds, there is still a small reserve of self-purification. The water is clean not due to sufficient assimilation, but due to the fact that there has been a low anthropogenic load so far. The obtained model results indicate the urgent need to bring the research to a modern level, both in terms of the number for observation points of the monitoring network in characteristic zones, increasing the list of monitored indicators and the frequency of monitoring, and improving the quality of the instrumental and methodological base.

The elemental composition of the Sochi River waters undergoes sharp changes with shifts in hydrological phases. During floods, it is relatively rich, while during low-water periods, it is comparatively poor. In flood conditions, the river waters are enriched with 19 chemical elements relative to average continental river water concentrations (Clarke values), whereas only 7 elements show enrichment during low-water periods. However, the total concentrations of excess chemical elements are higher during low-water periods due to the presence of Ca and Mg, whose absolute concentrations are two orders of magnitude higher than those of the dominant flood macroelements (Fe and Al). This feature affects the overall water mineralization. During low-water periods, the average total mineralization of river water (109 mg/L) is 1.4 times higher than during floods (80 mg/L). During floods, the river waters become significantly enriched with rare earth elements (REEs), as well as Sn, Fe, Al, Mn, Zr, Cs, Pb, Th, Be, Ti, Co, Cu, Tl, V, Bi, and As. The active influx of these elements is attributed to abundant soil runoff and their ability to form organic and inorganic complexes, bind strongly with iron colloids, and adsorb onto soil colloid surfaces. In contrast, during the drier low-water period, when groundwater contributes more significantly to river flow, the concentrations of most elements, including REEs, decrease. Under the contrasting geological conditions of the studied area — where neutral argillites repeatedly alternate with alkaline marls — the low-water period is more influenced by geochemically depleted carbonate rocks. A comparative analysis of water composition during floods and low-water periods revealed a second group of elements — Ba, Sb, B, S, Na, U, Mo, K, Sr, Ca, Mg, Li, Re, Rb, Si, and Zn—whose influx into the river is associated with groundwater input and, consequently, the specific lithology. Studying variations in the elemental composition of the Sochi River waters across different hydrological phases allowed us to identify element groups whose elevated concentrations in a given phase are linked not with anthropogenic load but with the composition of the bedrock (in low-water periods) or intense soil runoff (in floods).

Contamination of the Kondopoga Bay and tributaries of Lake Onego with dibutyl phthalate (DBP), the most widespread and industrially used phthalic acid ester, was assessed. The water samples were analyzed for the content of organic substances, biogenic elements, heavy metals and the ionic composition of water, as well as lignosulfonates. The DBP concentration was measured using gas chromatography and mass spectrometry. Sampling was conducted during the period of ice formation in March 2023, in the water area of Kondopoga Bay, Lake Onego. This area was affected by wastewater discharges from the Kondopoga PPM. Samples were also collected in several small rivers near Petrozavodsk, receiving runoff from residential areas and landfills. In all analyzed samples, the DBP concentration exceeds the MAC for fishery reservoirs (1 microgram/l)). At the same time, there were no statistically significant correlations between the content of DBP and the marker components of wastewater (lignosulfonates and biogenic elements). However, statistically significant correlations between DBP concentration and the content of lithophilic elements (Fe, Mn, Si) as well as organic substances of natural origin (in terms of color, total organic carbon, dissolved organic carbon, and COD) were found, which suggests their joint intake from the catchment area. Thus, it has been revealed that the Kondopoga PPM does not significantly affect the content of DBP in the Kondopoga Bay of Lake Onego, and its sources of entry into the lake are mainly atmospheric precipitation, surface and river runoff. The increased DBP content in organic-rich river waters of the boreal zone may partially be of natural origin. The contamination of Lake Onego and its small tributaries, as identified in this study, is comparable to that of previously studied reservoirs in Russia and other countries.

The article examines water withdrawal changes in the territory of the former USSR after its collapse up to 2020. The water withdrawal dynamics and the structure of water use are analyzed both in the post-Soviet space as a whole and in individual sovereign states. A sharp decrease in water withdrawal, especially significant in the 1990s, was revealed for most states, including the largest water consumer, the Russian Federation. The actual water withdrawal in the post-Soviet space turned out to be several times less than predicted for this territory in a number of publications in the 1960s–1980s. Despite the general trend of decreasing water withdrawal in almost the entire post–Soviet space, this process took place at different rates in each sovereign state, most rapidly in the Baltic republics. The changes in the structure of water use are shown – the share of industry water use decreased, while the share of household and, to a lesser extent, agricultural water use increased. The dynamics of water withdrawal in the post-Soviet space and in the world are compared. While in the former USSR it generally decreased compared to the period before 1990, worldwide water intake increased mainly due to irrigated agriculture, and in a number of developed countries it decreased as a result of the introduction of a number of water-saving technologies.