Low-water Years Research Articles

ВИЗНАЧЕННЯ НАТУРАЛІЗОВАНОГО СТОКУ ДНІПРА ЗА МЕТОДОМ ВІДНОВЛЕННЯ

The issue of determining the quantitative characteristics of the Dnipro River's streamflow and bringing them to natural indicators is quite relevant today. However, the history of studying this issue is quite long. A short review at the beginning of the article is devoted to this. For large regulated rivers, natural, anthropogenic, and naturalized flow are distinguished. In the study, based on the available data of regular instrumental observations, the naturalization of the Dnipro River's average annual flow was conducted using the restoration method. Additionally, a comparison with the actual flow was provided using the example of 2023. The average long-term naturalized flow of the Dnieper along the Locsmanska Kamianka (1818-2020) was obtained, which is 1648 m3/s (±31 m3/s) with a maximum of 3040 m3/s in 1877 and a minimum of 687 m3/s in 2015. The reduction in the natural runoff of the Dnipro River in 2023 due to the influence of reservoirs ranged from 4.8% for the Kyiv Reservoir to 14.8% for the Dnipro Reservoir. Analyzing the series of naturalized runoff of the Dnipro River over 203 years, it is worth noting that in the modern period, a historical minimum of average annual flow was observed. This is quite a concerning sign, as if the likelihood of low-water years similar to 2015 persists, and with the absence of the Kakhovka Reservoir, it will have severe consequences for the entire south of Ukraine. This situation could become especially critical if low water levels persist for several consecutive years, similar to 2019-2020 (with 98% reliability in the naturalized series). In the future, it is advisable to compare the given results with the average annual water consumption determined by other methods of naturalization, for example, through the use of the water balance.

Multi-objective simulation–optimization for water resources management and uses in multi-dam systems in low-water regions

One of the challenging issues in surface water resources management is the optimal operation of multi-dam systems. In addition to the applicability in determining the optimal pattern of operation of existing dams, this approach can be implemented in specifying the optimal capacity of under design dams. In this research, the simulation–optimization technique is used along with the reservoir zoning method in order to specify the optimal role curve of each of the dams in a multi-dam system (i.e., the Marun and Jarreh dams) in monthly intervals. The objective of this study is to develop a multi-objective algorithm on the basis of the zoning of reservoirs for the optimal operation of multi-dam systems. In this technique, instead of increasing the reliability of supplying demands in the whole period regardless the dry months, some of the inflow of rainy periods is stored in dam reservoirs to be consumed in dry months in order to mitigate the severity of deficiency. To examine the efficiency of the proposed model, the results obtained from the system operation in the current conditions are compared under two scenarios including optimal and reference. In the reference scenario, during 30-years, in some dry and low-water years, especially in the last six years of planning, the percentage of the demand supply is zero or less than five percent in several consecutive months. After optimizing the system, the minimum supply percentage in critical and dry months reaches 30 to 60 percent. Also, in the optimization scenario, the percentage of downstream ecological demands is improved. This research indicates that using the solution of this research leads to the better management of reservoirs in multi-dam systems and reduces the severity of deficiency in supplying various uses in low-water months.

Flooding and dam operations facilitate rapid upstream migrations of native and invasive fish species on a regulated large river

Dams commonly restrict fish movements in large rivers but can also help curtail the spread of invasive species, such as invasive bigheaded carps (Hypophthalmichthys spp). To determine how dams in the upper Mississippi River (UMR) affect large-scale invasive and native fish migrations, we tracked American paddlefish (Polyodon spathula) and bigheaded carp across > 600 river km (rkm) and 16 navigation locks and dams (LD) of the UMR during 2 years with contrasting water levels. In 2022, a low-water year, both native paddlefish and invasive bigheaded carp had low passage rates (4% and 0.6% respectively) through LD15, a movement bottleneck being studied for invasive carp control. In contrast, flooding in 2023 led to open-river conditions across multiple dams simultaneously, allowing 53% of paddlefish and 46% of bigheaded carp detected in Pool 16 to move upstream through LD15. Bigheaded carp passed upstream through LD15 rapidly (μ = 32 rkm per day) a maximum of 381 rkm, whereas paddlefish moved an average of 9 upstream rkm per day (maximum of 337 rkm). Our results can inform managers examining trade-offs between actions that enhance native fish passage or deter movements of invasive species. This understanding is critical because current climate change models project increases in flooding events like that observed during 2023.

Inter-annual changes in zooplankton in the Volga delta kultuk zone in summer (low-water period)

The paper presents the results of our studies of inter-annual changes in the structure of summer zooplankton in the kultuk zone of the Volga delta depending on hydrological and meteorological conditions. The study shows the main trends in zooplankton differences in a series of low-water years. It was found that in low-water years in the kultuk zone with low runoff, short floods and weak watering of floodplain territories, zooplankton was characterized by low species richness, reduced average individual mass of crustaceans and the number of Rotifera, but a high proportion of the number of juvenile Copepoda. In the year when the water level decreased before the flood during the period of temperature increase, and then a rapid rise with the inflow of cold waters and the removal of fish larvae, zooplankton was characterized by a minimum species richness and quantitative values of Rotifera, but increased biomass of Cladocera and the Shannon index. In every low-water year, with a stable and relatively high water level before the flood, fish spawning in the kultuk zone, biomass of zooplankton reduced due to Cladocera, and the number of species in the sample. In every mid-water year, the flood had the largest runoff and prolonged, increased flooding of the floodplain, zooplankton was characterized by the maximum total and specific species richness, abundance of Rotifera, total biomass on account of Cladocera, and the individual mass of crustaceans, the Shannon index, but the minimum proportion of juvenile Copepoda.

Features of underground flow formation to the Golovesnya river (Desna basin) during the dry period 2007-2021

Purpose. To analyze the peculiarities of the dynamics of underground flow on the catchment of the Golovesnya River, a right-bank tributary of the Desna River, during the dry period of 2007-2021 in comparison with the period of 1960-1985 - before the beginning of noticeable climatic changes. Methods. The hydrodynamic finite-difference method of calculating the specific consumption of groundwater based on the data of routine observations of the levels of groundwater and surface water, the hydrodynamic method of calculating the components of the groundwater balance. Results. The specific flow of groundwater to the Golovesnya River was calculated based on the data of observations for 2007-2021; the share of groundwater flow in the total flow of the river was determined, changes in the dynamics of infiltration nutrition and the inflow of groundwater to the river were revealed, which can be associated with the sign of the charge of the static electric field of the surface layer of the atmosphere, an increase in air temperature, and an increase in the volume of moisture retention in the aeration zone after reducing GWT. Underground flow to the river largely compensates for the losses and stabilizes the river flow in low-water years and during prolonged hydrological drought. Important factors in the regulation of the groundwater regime in low-water periods (in addition to precipitation) are the level and flow of water in the river, as well as the loss of moisture due to the saturation of the aeration zone, and therefore, the lithological and granulometric composition of this zone. Losses in the aeration zone are also an important regulatory factor of balance and river flow in the scale of the Desna River catchment. The largest volumes of underground runoff to the Golovesnya River for 2007-2021 were set for the multi-water year 2016, the smallest - for 2021. By 2016, the chronological graphs show clearer seasonal patterns: repeatability of underground flow fluctuations in the spring and autumn seasons; opposite flow fluctuations in winter and spring and a relatively stable summer flow; typical for autumn are maximum, and for summer always minimum values ​​of reserves and infiltration recharge of groundwater. In the abundant water year of 2016, infiltration recharge and groundwater reserves during autumn and winter sharply decrease and acquire negative values ​​due to a significant decrease in GWT in the previous period, an unfavorable course of temperature and precipitation distribution, and increased outflow to the river. In 2017-2021, the seasonal differences in the recharge of the river with groundwater are almost equalized: the role of recharge increases during the summer period, and decreases during the spring and autumn seasons. The role of the condensation mechanism of moisture transfer in the aeration zone is increasing. During the summer, the lateral inflow of groundwater to the river was the highest in 2016-2018. Conclusions. Calculations and analysis of the dynamics of infiltration feeding and groundwater flow to the Golovesnya River have been performed. Changes in groundwater supply and discharge, especially in the period after 2015, have been identified, which can be interpreted as the consequences of adverse weather and climate conditions in 2014-2015. In 2018-2021, there was a decrease in groundwater and surface water resources, which corresponds to signs of hydrological drought.

ШУ ӨЗЕНІНІҢ МЫСАЛЫНДА СУ ТАРАТУДЫ ОҢТАЙЛАНДЫРУ ӘДІСІ

A methodology has been developed for assessing and assigning a coefficient of "infringement" of water supply to irrigated agricultural consumers and natural and economic complexes. The issues of optimizing water distribution in the context of uncertainty of the inflow of water resources are considered. To solve the multi-purpose problem, a method was proposed for optimizing water distribution with a criterion condition for limiting the infringement of environmental launches in the interval of low-water and medium-water years. The article discusses the issues of optimizing water distribution in the event of a lack of water inflow. A methodology was developed for assessing and assigning a "infringement" factor for the "pressure" coefficient of water supply to water consumers and natural and economic complexes of irrigated agriculture. The most important negative environmental result is a decrease in runoff both during the year and in the long-term period, as well as an unnatural increase in the cycle of low-water years. The criterion for limiting environmental effluents between low-water and medium-water years has been considered to solve a multipurpose issue. To preserve river ecosystems the most important task at the present stage is the scientific substantiation of the permissible volumes of receiving and establishing the environmental flow of rivers. In addition, this environmental regulation has common properties for all watercourses. However, the ecosystem of each river has its own characteristics and characteristics, which are determined by geographical location, climatic, morphological, hydrological and other conditions. Therefore, depending on the individuality and uniqueness of ecosystems, appropriate research should be carried out for each of them to assess all types of anthropogenic impact factors and the state of the ecosystem.

Оптимизационный алгоритм управления водными ресурсами водохранилищ для обоснования диспетчерских графиков

The rules for the use of reservoir water resources need to be constantly updated, considering a significant number of factors affecting the effectiveness of management. Anthropogenic changes in morphometric functions, partial siltation of dead volume, and changes in basic hydrological characteristics have a significant impact on reservoir parameters and flow regulation regime. Justification of the regulatory regime remains an urgent and traditionally difficult engineering task of the IRP, discussed at professional meetings and in scientific publications. The article discusses a methodological approach based on the introduction of a given control algorithm into the process of assigning an interval request to the reservoir. In this case, the request is formulated as a two-parameter power function of the predicted resource for the estimated time interval (month). The degree indicator and the relative length of the range of uninterrupted water requirements coverage are the arguments of the query function. Nomograms illustrating the influence of the degree indicator on the outline of the dependence of requirements on the reservoir are constructed. In our opinion, this approach significantly reduces the Pareto set, excluding a significant part of the set of formal optima. The algorithm of the proposed model is focused on two-criteria optimization, where the relative values of the total annual water output and the sum of the relative interval ordinates of water consumption are considered as criteria. The unified functional is formed by linear convolution of criteria. The model was tested on the example of the resources of the Zhizdra River for a series of two low-water years. In the process of balance modeling and optimization, Excel tools are used, including “solution search” and VBA procedures. It is noted that it is necessary to use more powerful optimization algorithms for calculations based on multiyear hydrological series.

Inter-annual changes of zooplankton in the kultuk zone of the Volga River delta in the spring period

The studies conducted in spring have shown the main trends in changes in the structure of zooplankton in the kultuk zone of the Volga River delta in years that differ in hydrological and temperature regimes. It was revealed that in low-water years (2012, 2014), with a decrease in the volume of runoff, water level, and a reduction in the duration of floods, zooplankton was characterized by relatively low species richness, high biomass of Copepoda and Cladocera. At the same time, the highest rates of specific species richness, biomass and abundance of all zooplankton groups were observed at spring of a low-water year (2014), which was characterized by a runoff volume during the flood of 101 km3, a high pre-flood water levels, the absence of a sharp and significant dilution, as well as an early warm spring and gradual warming of the waters. In the year (2012), characterized by a volume of runoff during the flood period of 114 km3, a decrease in water level and a sharp increase in temperature before the flood, and then its rapid rise with dilution by cold waters, zooplankton was distinguished by the minimum species richness, a low number of ecological groups and low abundance of Cladocera, but a high proportion of juvenile copepods (fine filter feeders) and in terms of biomass of active euryphagous predators and euryphagous collectors. In a medium-water year (2013) with a large volume of runoff during the flood of 140 km3, with early and high and long floods, zooplankton was distinguished by a high total number of species encountered, but a minimum abundance and biomass, which is associated with the “dilution effect” and an increase in the areas of flooded rich in higher aquatic vegetation.

Soil moisture dynamics and evapotranspiration water consumption in spring maize

In the present study the dynamics of soil reservoir and evapotranspiration in dry farmland were thoroughly analyzed based on the long-term positioning test and investigation of soil moisture dynamic changes of spring maize. It was found that the vertical distribution curve of annual average soil water content in spring maize field was “single peak and single valley” type. Compared with wet (high water) years, the regulation depth of soil reservoir in the field during the growth period of Spring Maize in dry years moved up and becomes shallow; The soil moisture of Spring Maize in dry (low water) years was more stable than that in wet years. Under the two precipitation years, the “water level” of soil reservoir showed the characteristics of first rising, then falling, and then rising patterns. This study clarified the water source of evapotranspiration water consumption during the growth period of spring maize, evaluated the water balance of farmland ecosystem, and a preliminary understanding of the formation and restoration process of soil dry layer, which provided data support and theoretical basis for improving the practice of existing knowledge of production practice and sustainable development of dry farming. Bangladesh J. Bot. 52(2): 473-478, 2023 (June) Special

Soil moisture dynamics and evapotranspiration water consumption in spring maize

In the present study the dynamics of soil reservoir and evapotranspiration in dry farmland were thoroughly analyzed based on the long-term positioning test and investigation of soil moisture dynamic changes of spring maize. It was found that the vertical distribution curve of annual average soil water content in spring maize field was “single peak and single valley” type. Compared with wet (high water) years, the regulation depth of soil reservoir in the field during the growth period of Spring Maize in dry years moved up and becomes shallow; The soil moisture of Spring Maize in dry (low water) years was more stable than that in wet years. Under the two precipitation years, the “water level” of soil reservoir showed the characteristics of first rising, then falling, and then rising patterns. This study clarified the water source of evapotranspiration water consumption during the growth period of spring maize, evaluated the water balance of farmland ecosystem, and a preliminary understanding of the formation and restoration process of soil dry layer, which provided data support and theoretical basis for improving the practice of existing knowledge of production practice and sustainable development of dry farming. Bangladesh J. Bot. 52(2): 473-478, 2023 (June) Special

ANTHROPOGENIC TRANSFORMATION OF THE LYUTITSA RIVER BASIN

The Liutytsia is a typical small river of the Polissya part of the Volyn region. It flows through the territory of Rozhyshche and Kopachivka united territorial communities. The river is 37 km long, with a catchment area of 208 km2, 3.6% forest cover, 1.4% marshland, and 60.5% ploughed. About 10,000 people live within the basin. The territory has long been developed. Agricultural use predominates. Specialisation: growing potatoes, cereals, industrial crops, dairy and meat farming and processing of agricultural products. In the structure of land use in the basin, 87.6% of the land is used for agricultural purposes. All land available for agricultural use has been ploughed and is actively used. Within the basin, the permissible land use limits are exceeded. This contributes to the aggravation of the environmental situation and requires the implementation of measures for the rational use of natural resources and nature protection. 8.8% of the basin's territory is occupied by settlements, industrial, transport, communications, etc. The basin's water resources are also actively used. Most of the water is used for water supply to the population, industry and agriculture. In a year of 95% runoff availability, total water withdrawals exceed 20% of the annual runoff, and irreversible water consumption in the basin is 15%. In the future, runoff shortages may become a problem in low-water years. The frequency of dry years has been increasing recently. The concentration of most chemicals in the river water does not exceed the maximum permissible concentration. The content of ammonium nitrogen exceeds the per capita values by 15.6 times in the first and 2.92 times in the river channel 2, nitrite nitrogen by 1.7 times and 1.91 times, respectively, and total iron by 16 times and 2.4 times. The excessive content of nitrogen compounds is caused by surface runoff from urban areas, fields, farms, and spontaneous solid waste dumps. The area of drained land within the basin is 8,606 thousand hectares, with a land reclamation rate of 41.4%. There are 5 drainage systems within the basin. Soil overdrainage is widespread within the basin's drainage systems, leading to loss of soil cohesion, loss of vegetation cover and deflation. With distance from the drainage network, water drainage is worse, there are waterlogged areas, rewetting occurs due to inefficient drainage channels that are silted and overgrown with vegetation. Some reclaimed areas have not been ploughed for many years and are overgrown with selfseeding. Hazardous exogenous processes are occurring within the basin: karst, secondary waterlogging, and siltation of the riverbed. Soils are also undergoing negative changes. Erosion processes are occurring, the depth of the humus horizon is decreasing, and the content of humus and plant nutrients is decreasing. Environmental problems in the basin include: violation of water protection zones, ploughing and rewetting of the floodplain; lack of hydroecological monitoring in the river basin; poor condition of drainage systems; lack of soilprotective technologies for growing crops, violation of recommendations for the use of drained land; illegal landfills in the basin; low forest cover, lack of protected areas within the basin, lack of an effective local ecological network.
 Keywords: river basin, geoecological state of the basin, sources of anthropogenic impact within the basin, anthropogenic transformation of the basin.

PROSPECTS AND PROBLEMS OF USING LOCAL WATER RESOURCES FOR IRRIGATION IN THE BASINS OF SMALL RIVERS OF THE FOREST-STEPPE OF UKRAINE

On the example of a separate agricultural farm located in the basin of the small Manzhelia River within the Left Bank Forest Steppe, the approaches to the selection of potential sources of irrigation and the specifics of determining the volumes of local water resources intended to be used for irrigation, as well as the areas of possible irrigation in the absence of existing irrigation systems, are given. The results of the research indicate that the prospects for the development of land irrigation on farmland can be mainly provided subject to the combined use of surface runoff accumulated in ponds on the Manzhelia River and groundwater admissible for extraction, taking into account their quality. It was determined that influenced by a complex of anthropogenic factors, the river runoff sharply decreased compared to natural conditions, and the feeding of river course ponds during the entire low water period occurs only due to lateral inflow. Based on calculations it was determined that in average and low-water years, the volumes of surface and ground inflow to the cascade of ponds for the period from June to September are smaller than evaporation losses. Under such conditions, the use of the river runoff for irrigation is possible only due to the accumulation of flood and, partially, high water runoff. The calculations of flood runoff volume for March - April at the gate of the lower pond indicate the impossibility of using water from it for irrigation in very low-water years, as well as the dependence of runoff use for irrigation in low-water years on the pre-flood filling level of the ponds. It was determined that up to 0.8 million m3 of water can be used for irrigation in medium-water years, and up to 1.4 million m3 in high-water years, which will provide irrigation on an area of 400 and 700 hectares, respectively (having an irrigation rate of 2000 m3/ha). The possibility of installing at least 40 water intake wells within the territory of the farm with a total flow rate of 20-24 thousand m3/day and a total water intake during the irrigation period of about 1.5 million m3 has been substantiated. This will make it possible to irrigate 750 hectares of land having an irrigation rate of 2000 m3/ha, and at least 1000 hectares having an irrigation rate of 1500 m3/ha. It is focused on the mandatory preliminary investigation of water quality for irrigation, which for many small rivers and aquifers is a limiting factor when using local water resources for the construction of irrigation systems.

Water Flow Changes In The Don River (European Russia) During 1891–2019

The Don River Long near Razdorskaya Village had long phases (lasting 33–86 years) of increased/decreased naturalized annual and seasonal water flow, and their properties for 1891–2019 were identified. Long-term changes in the annual and snow-melt flood flow occurred in the opposite phase relative to changes in the winter and summer-autumn flow. Annual hydrographs in the phase of decreased flow were characterized by an increase in water discharge during the low-water seasons of the year, but a noticeable decrease in daily flood water discharge and maximum water discharge. The share of high-water years (years with a flow exceedance probability equal to or less than 25%) in the phase of increased flow is significantly higher than the share of low-water years (years with a flow exceedance probability equal to or more than 75%). And on the contrary. At the same time the cumulative share of low- and high-water years remains relatively stable. The total changes in the annual and seasonal flow, caused by both anthropogenic and climatic factors, throughout the entire period of modern global warming (since 1989) consisted in a decrease of the annual and snow-melt flood flow and an increase of flow values during low-water seasons.

Extreme Low Flow during Long-Lasting Phases of River Runoff in the Central Part of the East European Plain

In the rivers of the central part of the East European Plain (the Volga at Staritsa, the Oka at Kaluga, and the Don at Stanitsa Kazanskaya), long phases (10–15 years or more) of increased/decreased annual and seasonal runoff have occurred, as well as differences in the frequencies of extremely low flow conditions from the late 19th century to 2020. Phase boundaries were identified by cumulative deviation curves and statistical homogeneity. The frequencies of specific water flow values were estimated using the empirical curves of the exceedance probability of annual and seasonal water flows based on their long-term time series. In the century-long changes of rivers considered, two long contrasting phases were revealed. These phases are characterized by increased and decreased runoff of hydrological seasons. Near simultaneously, a phase of increased runoff was first observed for the freshet season. On the contrary, phases of decreased runoff were first observed for low-water seasons. The runoff phases differ significantly in duration and differences in flow. Significant differences were revealed in the frequency of low-water years for a low runoff with an exceedance probability above or equal to 75% and above or equal to 95%.

Transformation of Volga river runoff in multiyear aspect

The article describes in detail all the most significant components of the hydrological regime in the lower reaches of the Volga. As a result of the regulation of the Volga runoff by the Volgograd hydroelectric dam in 1958, the ecological conditions of natural reproduction of fish changed significantly: the areas of spawning grounds decreased, the hydrological regime was violated, which led to deformation of the spring flood regime, intra-annual redistribution of runoff. Their size is of fundamental importance for the fisheries of the Volga-Caspian basin. Attention is drawn to the deep deformation of all flood indicators that occurred after the regulation of the Volga runoff on the Lower Volga, while in the worse direction for the reproduction of aquatic biological resources. The process of degradation of aquatic biological resources of the Volga-Caspian reflects the lack of the minimum hydroecological conditions necessary to ensure the formation of resilient juvenile fish in the process of their natural reproduction in the overwhelming number of years. The modern operation of the Volga-Kama cascade of reservoirs does not meet the requirements of the Volga-Caspian fisheries. There is a tendency to increase intraannual redistribution of runoff, due to high winter releases of water into the lower reaches of the Volgograd hydroelectric complex and low spring releases. The system of management and intersectoral distribution of water resources during the flood does not currently meet the necessary hydroecological conditions under which it is possible to form resilient fish offspring and, as a consequence, preserve and increase stocks of the most valuable commercial fish species. The main reasons for the decrease in water reserves are determined by the regulation of the Volga runoff and as a result of this reduction in the volume of water supply to the lower reaches of the Volgograd hydroelectric complex. Especially this negative manifestation of a sharp deterioration in the flooding of spawning grounds occurs in low-water years, when the priority is to fill the reservoirs of the cascade to a normal retaining level in order to ensure the generation of hydroelectric power during the inter-war period (summer, autumn, winter), the operation of water transport, the implementation of water intake for irrigation, utility purposes, etc.

Assessment of the state of aquatic bioresources and the feasibility of involving floodplain lakes of the Ob river in the upper reaches of the Novosibirsk hydroelectric power station in fishing

An overview of typical lakes of the floodplain system of the river is presented. Ob in the upper reaches of the Novosibirsk hydroelectric power station. Data on the species structure, abundance and biomass of zooplankton, zoobenthos and fish are presented. Most of the lakes of the left-bank floodplain of the Ob have an elongated channel-like shape and a constant hydrological connection with the channels of the Ob river. The lakes are located in a low floodplain and are completely flooded by flood waters even in low-water years. The area of the lakes does not exceed 40 hectares. The zooplankton of the lakes is represented by 16 species, the total number varied from 360 copies/m3 (lake Epanchino) to 36 530 copies/m3 (lake Komendantskoye), the biomass was 13.8–229.0 mg/m3. According to the development of zooplankton, all the floodplain lakes studied belong to low-feeding, ultra-oligotrophic type reservoirs, the lowest productivity class. 13 species were found in the zoobenthos of floodplain lakes, the total number varied from 172 specimens/m2 (lake Chernoe) to 860 specimens/m2 (lake Baigachevskoe), biomass — from 0.513 to 4.196 g/m2. On the development of zoobenthos lake. Epanchino refers to medium–fed, mesotrophic type reservoirs, the other three — to low-fed, oligotrophic type reservoirs, low productivity class. The main species of ichthyofauna of floodplain lakes are pike (Esox lucius Linnaeus), river perch (Perca fluviatilis Linnaeus) and silver carp (Carassius gibelio Bioch). Pike at the age of 3+ — 4+ years dominates in lake populations, perch — 2+ years. The biomass of the ichthyofauna is 15,3–45,8 kg/ha. According to the ichthyomass, floodplain lakes of the lower reaches belong to the oligotrophic and mesotrophic type of reservoirs, low and medium productivity class.

Transformation of the water runoff of the Volga River after the creation of the Zhiguli hydroelectric complex

For the Volga River, studies of interannual changes in water discharges in the period 1958-2021 were carried out. Systematic hydrological observations were carried out at the Zhiguli hydroelectric complex on the border of the Middle and Lower Volga. 97% of the water runoff of the entire Volga is regulated in this section in the seasonal, weekly and daily range. It was found that the average water flow was 7704 m3/s. The amplitude of interannual fluctuations was 5270-10431 m3/s. Temporal changes in the average annual water discharges were characterized by cyclicity, including the change of low-water and high-water phases. From 1958-1975 a low-water phase was observed, from 1976-1996 - high-water and since 1997-2021 - again shallow. A comparison of the historical (1877-1955) and modern (1958-2021) periods showed that over 144 years, the average water flow of the Volga River has not changed much. However, as a result of the regulation of water flow in the period 1958-2021 the value of water discharges in high-water years decreased, while in low-water years it increased.

Water Level and Temperature as the Main Factors Responsible for the Formation of Conditions for Aboriginal Fish Fauna Effective Reproduction in the Kremenchuk Reservoir

Modern dynamics of the main abiotic environmental factors responsible for fish fauna effective reproduction in the Kremenchuk Reservoir are discussed in the paper. Annual dynamics of water level and temperature were analyzed. It has been found that the main factor responsible for the rate of breeding stock maturation in the Kremenchuk Reservoir is water temperature dynamics rather than spawning temperatures. It is underlined that the operation of hydroelectric facilities and the spawning campaign must be synchronized to ensure sustainable fisheries. The drainage of spawning grounds in low-water years results in the decrease in their area and, as a consequence, in the formation of low-yielding generations. It is recommended to optimize the annual dynamics of water level according to the needs of fisheries.

Photosynthetic activity of plankton in saline lakes under climatic fluctuations conditions

Climate change causes the alternation of high-water and low-water years, which is reflected in morphometric characteristics of lakes. Changes in the depth and volume of water bodies affect the structural and functional activity of the ecosystem, including the growth and development of primary producers. The photosynthetic activity of water body plankton was shown on the example of Dabasa-nor lake and Kudzhertai lake located in the steppe territory of the South-Eastern Transbaikalia. The studied lakes differ in their hydrochemical composition. The content of chlorophyllain Dabasa-nor lake is lower than in Kudzhertai lake. Degraded form of chlorophylla- pheophytin is present only in Dabasa-nor lake, which currently has the least depth of its filling. Carotenoids, as more stable forms of pigments, dominate in the pigment diversity of lake plankton. Chlorophyllcwas not detected in any of the plankton of both lakes. Factor analysis of the main components showed the interdependence of a number of abiotic agents with the pigment characteristic of phytoplankton. Thus, under the current conditions of the period of lake water availability recovery after a long dry period, the photosynthetic activity of the water body ecosystem is experiencing certain difficulties.

Interannual variability of the functional state of bream (Abramis brama, L.) of the delta Volga in the pre-spawning period

Bream is an important fishing object of the Volga-Caspian region. Its catches here in the middle of the last century reached 60 thousand tons, while currently they do not exceed 14 thousand tons. The study of the functional state of bream in the pre-spawning period makes it possible to determine the success of spawning, predict the survival of offspring at the early stages of ontogenesis. During the spawning periods (2007–2017 and 2021), the functional state of female and male bream caught in the waters of the delta Volga was studied. To assess the physiological state, the following biochemical parameters of blood were analyzed: the amount of hemoglobin, total serum protein, β-lipoproteins, cholesterol, total lipids, triglycerides, inorganic phosphorus, glucose, activity of alkaline phosphatase and aspartate aminotransferase, generally accepted methods of hematological and biochemical studies of blood and blood serum were used. The work used generally accepted methods of hematological and biochemical studies of blood and blood serum. As a result, there were statistically significant differences in the values of such indicators as the level of hemoglobin in the blood, cholesterol and β-lipoproteins cholesterol, glucose between females and males were noted. Significant interannual differences in the values of the studied indicators were revealed. The flow regime and the volume of spring flood had a decisive influence on the functional state of bream in the prespawning period. Deviations from the values of these indicators from the limits of reference values characteristic of fish and bream, in particular, taken from literary sources, were usually observed in low-water years (hemoglobin, β-lipoproteins, total lipids). The average level of correlation (r = 0.50) between the value of total whey protein and cholesterol was established in bream, which indicates a close relationship between protein and lipid metabolism. Thus, the physiological state of the Lower Volga bream in the pre-spawning period of high-water years can be characterized as relatively favorable.