Vol 87, No 6 (2023)

The role of the Valdai Hills and the Valdai Lake area in ensuring the fullness of the sources of the Volga River and its current trends against the background of climate change is presented. It is shown that the “water-making functions” of the upland landscape are initially determined by two general properties of the relief: its invariance as a “framework of life” and its changeable evolution under the influence of endogenous and exogenous factors. The “Cradle of the Volga” in relation to the Valdai Hills and specifically the Baltic-Caspian watershed is a set of conditions that allow the formation of runoff in the upper reaches of the river. Among the main ones that determine the conservation of runoff in the average annual volume are the state of rivers, lakes, and swamps, the minimization of anthropogenic impacts (regulation of runoff, plowing, catchment, deforestation, development and pollution of the coastline, etc.), and, in general, nature protected areas (creation of them at the source of the river). Based on the materials from the monitoring of the climate and hydrological regime of the region carried out by the Valdai branch of the State Hydrological Institute (Valdai), the main trends of the Volga River runoff factors in the upper reaches have been identified. The share of water-regulating, water-saving, and assimilation functions in the total volume of ecosystem services in the landscapes of the Valdai Hills is shown. It is concluded that the modern growth of recreational impact on the catchments of the sources of the Volga River can reduce the positive effect of the functioning of nature protected areas on them. The priority issues in preserving the “cradle of the Volga” should be the regulation of recreational loads on the landscapes of the Valdai Hills, rehabilitation of disturbed forest ecosystems, and monitoring of the volume and quality of runoff.

Two variants (methods) were used to calculate the contribution of anthropogenic and climatic factors to the change in the annual and seasonal runoff of the Volga River at Volgograd during periods of significant anthropogenic impact on waters (1930–2020 and 2011–2020) compared with the conditionally natural period of runoff formation (1879–1929). The first is based on comparing the anthropogenic change in runoff due to the influence of reservoirs and irretrievable water consumption with the total change in runoff for the comparison periods. In the second variant, the reconstructed conditionally natural runoff during periods of significant anthropogenic impact is compared with the total change in runoff, calculated by the relationship between the Volga River runoff and the runoff of rivers that are indicators of climatic conditions. It is assumed that climatic changes are mainly of natural origin. It is revealed that the influence of anthropogenic and climatic factors on the overall decrease in the annual runoff of the Volga River in comparison with the conditionally natural period is unidirectional and comparable. Both variants of the calculation give similar values for the ratio of anthropogenic and climatic factors in the total change in runoff in the 1930–2020 period. There are more significant differences in the calculations for the 2011–2020 period and in the assessment of seasonal changes, most noticeably manifested in the spring flood and in the winter. Anthropogenic and climatic factors act in the same direction, reducing the flow of the spring flood and increasing it in the winter, mainly due to anthropogenic factors. The existing differences in the ratio of factors can largely be explained by landscape transformations in the Volga River basin, including in river basins that are indicators of climatic conditions. The impact of such transformations on runoff is not taken into account in water management statistics, although in recent decades different types of economic activities in watersheds have largely offset each other in their impact on runoff. The share of anthropogenic factors in the Volga River runoff changes can vary widely depending on the type of water resources use which is be not always rational.

Basic information about the Upper Volga and Kama cascades of reservoirs is presented: water surface area, full and useful volume capacity, and average project power generation. The contribution of the considered cascades to the power generation of the entire Volga−Kama cascade of reservoirs is estimated. Data series have been generated on the annual inflow, discharge of water through hydroelectric facilities, and generation of electricity from 2002 to 2021, for several stations from 2004 to 2022. The relationship between the area of reservoirs and their capacity is shown, as well as the generation of electricity with the water content of individual years and periods. A relationship has been established between the inflow of water into the reservoirs and its discharge through the turbines of the hydroelectric power plants. Particular attention is paid to the Rybinsk reservoir, which performs over-year water storage. The generation of electricity in high-water, medium-water, and low-water years is calculated. The deviation of the actual electricity generation from the average design was estimated, based on which a conclusion was made about the efficiency of the hydroelectric power plants. The probability of electricity generation is determined depending on the predicted values of the river runoff.

The article presents an overview of the main hydrological and water management tasks and problems that have arisen in recent decades on the Lower Volga because of the construction and operation of the Volga-Kama cascade of reservoirs, anthropogenic changes in runoff as a result of economic activity, and the consequences of poorly predictable climatic changes. It is shown that the hydrological regime in the lower reaches of the Volga River has undergone significant changes, both as a result of regulation of runoff by reservoirs and due to climatic changes. The observed changes in flow fluctuations have led to serious changes in the aquatic environment and the entire ecosystem of the river. A number of negative consequences were predicted during the development of reservoir cascade projects, and the construction and operation processes were accompanied by the implementation of a set of compensatory measures of a fisheries’ nature. Nevertheless, the functioning of a complex water management system and insufficient attention to environmental problems led to the emergence of new environmental, technical, and scientific problems that required an integrated approach for their solution, and the effectiveness of the planned measures turned out to be insufficient. The study of the consequences of seasonal regulation of runoff by reservoirs, changes in the estimates of water resources, the involvement of new methods of studying the hydrological system, including multi-arm channels, and the analysis of anthropogenic-altered river sections allowed to obtain new results but at the same time to formulate a block of unresolved scientific problems. Among such problems, there is a need to solve such engineering and hydrological tasks as increasing the feasibility of forecasts of inflow to reservoirs, long-term forecasting of long-term fluctuations in runoff under conditions of ongoing climate change, obtaining up-to-date estimates of negative processes—deformation of riverbeds under anthropogenic impact. The latter is very important for the downstream of the Volgograd Hydroelectric Power Station. In terms of predicting the behavior of the ecosystems of the Lower Volga, with an assessment of their stability, further development of methods for assessing permissible impacts, the development of monitoring systems for their condition is required. The management of the Volga-Kama cascade of reservoirs is a complex scientific and technical task. Today, this management is carried out on the basis of dispatching rules dating back more than a dozen years. It is shown that modern management should be based on a coordinated system of priorities, including environmental criteria. The required optimization formulation of the task of finding optimal cascade control can be based, for example, on the search for a compromise solution at the level of agreement of the parties. A set of environmental and water management problems unsolvable for decades has been formed in the northern part of the Volga-Akhtuba floodplain as well as in the zone of the Western-subtidal ilmens (system of lakes in the Volga River Delta). To solve these problems, new methods of studying ecological systems under severe anthropogenic stress and appropriate engineering approaches that allow a comprehensive approach to achieving sustainable water resources management are considered. The problem of poorly predictable fluctuations in the level of the Caspian Sea and the problem of water resource management in the region in conditions of conflicting interests of users are touched upon. The main measures are discussed, whose implementation will mitigate the consequences of flow regulation for the ecosystem of the Lower Volga. Among the important system principles, the need for a basin approach is noted, which involves, at a minimum, the development of a General Scheme for the Use of Water Resources of the Volga River.

The Volga River has been the main Russian river for several centuries. The river, originating on the Valdai Hills, crosses several natural and climatic zones on its way to the Caspian Sea: from the southern taiga to the dry steppes of the Caspian Lowland. According to the latest data, 45% of industrial enterprises and 50% of agricultural production in Russia are concentrated in the river basin. The anthropogenic load on the river with its tributaries and their basins significantly exceeds the load on other large Russian rivers. The largest contaminated wastewater volumes fall on the share of Moscow, Samara, Nizhny Novgorod, Yaroslavl, Saratov, Ufa, Volgograd, Balakhna, Tolyatti, Ulyanovsk, Cherepovets, Naberezhnye Chelny and other large cities. All these negative processes occur against the background of ongoing climate change. The article analyzes the Roshydromet hydrochemical monitoring data of river waters in the Volga River basin for the 2000–2021 period by water bodies and federal subjects. Regardless of the year water content, almost 70% of hydrochemical monitoring stations in the Volga River basin correspond to the third quality class (“polluted”). An integral assessment of the water quality in the Volga River basin shows that the situation has not changed significantly since the end of the last century. To improve the ecological condition of the Volga River basin, it is necessary to implement a set of measures for the protection and reproduction of water resources in catchment areas, rationalize water use systems, and reduce the volume of freshwater intake. Reducing water consumption is a necessary condition for reducing the wastewater volume discharged and, consequently, the number of pollutants contained in it. One of the problems is that almost all types of water use harm the surface waters’ natural quality, including the Volga River basin.

The paper presents the results of methane flux and its concentration measurements in the reservoirs of the Volga cascade: Ivankovskoye, Rybinskoye, Gorkovskoye, Kuybyshevskoye, and Volgogradskoye reservoirs. The article summarizes the materials from the 2017–2023 seasonal observations archive. Measurements of the gas flux were carried out by the floating chamber method, the methane concentration determination in the samples was carried out by the headspace method. The spatial and seasonal variability of both methane content and its emissions depending on the coefficient of water exchange, weather conditions, the nature of bottom sediments, and depth was revealed. High values of methane concentration and methane flux are observed in the presence of stratification, while during vertical mixing, the flux values decrease significantly. The highest methane flux values are characteristic of the heavily populated by macrophytes shallow Shoshinskiy reach of the Ivankovskoye reservoir (up to 334 mgC-CH₄/(m² day)), the flooded left bank floodplain of the Gorkovskoye reservoir (up to 548 mgC-CH₄/(m² day)), where they are associated with weak flow and intra-mold circulation, and also for Chesnava bay of the Rybinskoye reservoir (up to 1086 mgC-CH₄/(m² day)), associated with anthropogenic pollution and low flow rates. In the bays of Kuybyshevskoye and Volgogradskoye reservoirs that receive inflows with increased mineralization, stratification may increase due to density stratification, the formation of zones with oxygen deficit, and increase in methane flux despite the small amount of organic matter in sediments. The example of the Gorkovskoye reservoir shows the effect of the dam on the spatial structure of methane flux and concentration. Comparison with generalized data on specific methane flows from moderate water reservoirs showed that in the Volga cascade, these values are lower in all months of the open water period except August.

The paper summarizes the data from long-term observations of hydrometeorological parameters in the Caspian macro-region. The average annual air temperature over the past 30 years at stations in the Russian part of the Caspian Sea has increased by 1.0°C and the temperature of the surface water layer by 0.3°C. Currently, the total river runoff into the sea is about 275 km³. The volume of annual runoff from all rivers flowing into the Caspian Sea went down in the 1996–2020 period compared to the 1961–1990 period. The intensity of the decrease in river runoff in the 1996–2020 period averaged 0.12 km³ per year, while the flow of the Volga and Kura rivers decreased most intensively. In conditions of warming and decreasing river runoff, the Caspian Sea level continues to decline, which began in the late 1990s. Due to increasing water scarcity in the Volga River, the level of the Caspian Sea is going down. The trend started in the late 1990s. By the beginning of 2023, the average sea level had reached –28.70 m abs, which is about 2 m lower compared to the level in 1995. The drained coastal territories are assessed at more than 22 thous. km², mainly in the northern shallowest part of the sea. The changes in the wind regime and the observed increase in the average monthly and yearly wind speeds are compared against those in the standard reference period (1961–1990). It has been established that the easterly and westerly winds, which cause storm surges with devastating impact on coastal territories, have the greatest repeatability. The statistics of surges observed at four marine stations are given for the 2010–2021 period. The amplitude of the wind-induced level fluctuations in the Lagan area reaches a maximum value of 3.0–3.5 m, while it is about 1 m in Makhachkala. An analysis of the seasonal variability of surges is also given.