Summer Low Water Research Articles

Research of the Lagoon Estuaries of Vaygach Island in the 2023 Summer Low Water Period

Research of the Lagoon Estuaries of Vaygach Island in the 2023 Summer Low Water Period

HYDROLOGICAL REGIME OF THE IKVA RIVER (SOUTHERN BUG BASIN)

This article reveals the issue of a detailed study of the hydrological regime of small plain rivers in the presence of data from regular observations. The Ikva River, the object of our study, belongs to the Southern Bug basin and is its small tributary, on which a hydrological indicators monitoring station has been operating since 1939. Since 1955, a continuous series of observations has been available, which allowed us to carry out a detailed analysis and description of the main hydrological characteristics – levels (H, cm) and water flows (Q, m3/s), to evaluate their fluctuations in time, cyclicity and the relationship Q= f(H). The construction of the corresponding graphs confirmed that the Ikva River is characterized by cyclic flow fluctuations, and since 1965 we have already observed two complete cycles of fluctuations in water level lasting about 30 years. At the moment (2022), the flow indicators record the minimum of the low-water phase of the second cycle, so we can expect an increase in the flow in the near future and the transition to a new cycle. We have also determined that the amplitude of water level fluctuations of the Ikva River at the post in the village of Stara Sinyava over many years is 60 cm, and varies from a minimum of 75 cm (1957) to 135 cm (1981), that is, a little more than 0.5 meters in total. This agrees quite well with the literature data and estimates of other authors, considering the plain nature and small size of this object. The long-term course of the water levels of the Ikva River is characterized by a slight increase, while the long-term fluctuations of the average water flow at this station also do not have a large amplitude: from 0.66 m3/s (2020) to 3.64 m3/s (1979) i.e. 2.98 m3/s. At the same time, the general trend line for multi-year cost fluctuations shows, on the contrary, a tendency to decrease them. Therefore, we can state that the graphs of multi-year costs and levels are not synchronous, which is evidence of the manifestation of vertical channel deformations in the area of the post. As the water level increases, the decrease in water consumption is a direct sign of siltation of the riverbed in this area and the raising of the bottom level due to accumulative processes over a long period. The largest amplitudes are characterized by the parameters of the maximum runoff, that is, the amplitudes of the maximum levels (∆Нmax = 168 cm) and maximum flows (∆Qmax = 92.9 m3/s), which is not surprising, because we are talking about the characteristics of the period of floods and inundations, which are always marked by significant fluctuations in time. An interesting fact, identified for us for the first time, is that the characteristics of the minimum flow of the closed period of the channel are characterized by higher amplitudes than the characteristics of the open period. Therefore, the summer low water is more pronounced than the winter low water, which means that in the warm period (summer), the lack of precipitation more clearly provokes a decrease in water levels and flows in the channel system than during the winter period. The reason can be both winter thaws and the specifics of the groundwater regime. Key words: hydrological regime; water level; water flows; hydrological cycle; low water phase; high water phase; relationship Q=f(H).

Study of Marginal Filter of Mesotidal Estuary of Indiga River (Barents Sea Basin)

The article provides brief information on the study of the features of the marginal filter of the mesopotential estuary of the Indiga River in the Barents Sea in the summer low water of 2022.

Calculation of Seasonal Erosion on the Oka River Riverbanks Using Geodetic Modeling

Abstract—Directed erosion of riverbanks stands out among the dangerous geomorphological processes on large lowland rivers. In the middle reaches of the Oka river, horizontal channel deformations make a significant contribution to regional lithodynamics and the reduction in the area of floodplain lands. We carried out field geological and geomorphological studies in the valley of this large tributary of the Volga, which revealed the complex facies architecture of the floodplain. The forecast for riverbank erosion near the city of Ryazan has recently declined due to the unstable water regime of the Oka river. For a detailed assessment of the consequences of destabilization of the coastal slopes, their surface was surveyed using a total station and aerial photography from a UAV. Regular observations of erosion by the seasons of the hydrological year allowed us to obtain actual data on the redistribution of soils along the height of the slope. We have found that erosion in summer low water is three times weaker than during high water. The predominance of collapses of the uppermost (0.0–2.0 m from the day surface) part of the erosion fronts was also revealed. The article also discusses possible reasons for the mobilization of the geological filling of the river bank, arising from local differences in the Pleistocene-Holocene evolution of the morpholithic system of the Oka river floodplain and the fixation of geological information in it.

Abiotic Factors and Their Role in the Development of Phytoplankton in the Lower Volga

Based on field observations carried out during the 2015–2020 summer low water period, the interannual variability of abiotic characteristics and chlorophyll content in the Lower Volga is considered. In years with different thermal conditions and water content, the temperature, transparency, color and electrical conductivity of water are characterized by small variability and demonstrate changes from north to south, according to the zonal features of the Volga cascade. The average nutrient content (0.81–0.99 mg/L Ntot and 101–134 μg/L Ptot) changes insignificantly in the Saratov and Volgograd reservoirs, but decreases in the unregulated lower part of the Volga. The content of N-N\({\text{O}}_{3}^{ - }\) and P-P\({\text{O}}_{4}^{{3 - }}\) in the total nitrogen and phosphorus pool respectively, is 4–9 and 69–74%, the ratio Ntot/Ptot 10 indicates a possible nitrogen limitation of phytoplankton. The Chl a content corresponds to the mesotrophic category in the Saratov and Volgograd reservoirs (5.3 ± 0.6 and 7.2 ± 0.9 μg/L), and eutrophic in the lower section (13.9 ± 1.5 μg/L). The trophic status of the Lower Volga has not changed in comparison with the last decade of the 20th century. It was found that abiotic factors have a weak effect on the Chl a content in the Saratov reservoir, moderate in the Volgograd reservoir and almost completely control the development of phytoplankton in the unregulated lower part of the Volga (R2 = 0.21, 0.59, and 0.91). The data obtained supplement the observations of previous years and form the basis for long-term monitoring of ecosystems of large artificial reservoirs.

ВЛИЯНИЕ ВЕТРОВОГО АПВЕЛЛИНГА И СТОКА РЕКИ АМУР НА ТЕРМОХАЛИННУЮ СТРУКТУРУ ВОД У СЕВЕРО-ВОСТОЧНОГО ПОБЕРЕЖЬЯ ОСТРОВА САХАЛИН

The impact of the wind-driven upwelling and the Amur River discharge on the thermohaline water structure off the northeastern coast of Sakhalin was analyzed using hydrographic data аnd satellite information on the sea surface temperature distribution. The interaction of upwelling water and the coastal current depends on wind conditions and the Amur river runoff. Coastal upwelling develops at relatively low river runoff values (summer low water). The increase in the Amur River discharge during the summer flood enhances the interaction of the upwelling and the coastal buoyancy current. The Amur river runoff flows directly along the shore, which tears cold upwelling water off the coast. The advection of the cold upwelling water from the coast towards the open sea increases with the consecutive alternation of upwelling and downwelling events.

Hydrochemistry of Medium-Size Pristine Rivers in Boreal and Subarctic Zone: Disentangling Effect of Landscape Parameters across a Permafrost, Climate, and Vegetation Gradient

We studied two medium size pristine rivers (Taz and Ket) of boreal and subarctic zone, western Siberia, for a better understanding of the environmental factors controlling major and trace element transport in riverine systems. Our main objective was to test the impact of climate and land cover parameters (permafrost, vegetation, water coverage, soil organic carbon, and lithology) on carbon, major and trace element concentration in the main stem and tributaries of each river separately and when considering them together, across contrasting climate/permafrost zones. In the permafrost-bearing Taz River (main stem and 17 tributaries), sizable control of vegetation on element concentration was revealed. In particular, light coniferous and broadleaf mixed forest controlled DOC, and some nutrients (NO2, NO3, Mn, Fe, Mo, Cd, Ba), deciduous needle-leaf forest positively correlated with macronutrients (PO4, Ptot, Si, Mg, P, Ca) and Sr, and dark needle-leaf forest impacted Ntot, Al, and Rb. Organic C stock in the upper 30–100 cm soil positively correlated with Be, Mn, Co, Mo, Cd, Sb, and Bi. In the Ket River basin (large right tributary of the Ob River) and its 26 tributaries, we revealed a correlation between the phytomass stock at the watershed and alkaline-earth metals and U concentration in the river water. This control was weakly pronounced during high-water period (spring flood) and mostly occurred during summer low water period. Pairwise correlations between elements in both river systems demonstrated two group of solutes—(1) positively correlated with DIC (Si, alkalis (Li, Na), alkaline-earth metals (Mg, Ca, Sr, Ba), and U), this link originated from groundwater feeding of the river when the labile elements were leached from soluble minerals such as carbonates; and (2) elements positively correlated with DOC (trivalent, tetravalent, and other hydrolysates, Se and Cs). This group reflected mobilization from upper silicate mineral soil profile and plant litter, which was strongly facilitated by element colloidal status, notably for low-mobile geochemical tracers. The observed DOC vs DIC control on riverine transport of low-soluble and highly mobile elements, respectively, is also consistent with former observations in both river and lake waters of the WSL as well as in soil waters and permafrost ice. A principal component analysis demonstrated three main factors potentially controlling the major and TE concentrations. The first factor, responsible for 26% of overall variation, included aluminum and other low mobile trivalent and tetravalent hydrolysates, Be, Cr, Nb, and elements strongly complexed with DOM such as Cu and Se. This factor presumably reflected the presence of organo-mineral colloids, and it was positively affected by the proportion of forest and organic C in soils of the watershed. The second factor (14% variation) likely represented a combined effect of productive litter in larch forest growing on carbonate-rich rocks and groundwater feeding of the rivers and acted on labile Na, Mg, Si, Ca, P, and Fe(II), but also DOC, micronutrients (Zn, Rb, Ba), and phytomass at the watershed. Via applying a substituting space for time approach for south-north gradient of studied river basins, we predict that climate warming in northern rivers may double or triple the concentration of DIC, Ca, Sr, U, but also increase the concentration of DOC, POC, and nutrients.

Can vegetation clearing operations and reprofiling of bars be considered as an ecological restoration measure? Lessons from a 10‐year vegetation monitoring program (Loire River, France)

Maintenance operations in regulated rivers are often implemented as preventive measure to maintain wide, smooth channels and to limit the risk of flooding. By clearing vegetation, removing roots and lowering sediment bar elevation, these works can recreate pioneer habitats and related plant communities. Using a before‐after‐control‐impact design with monitoring of riparian vegetation over 10 years, we evaluated the effects of fluvial maintenance works on plant richness and composition in an island complex located in a Nature Reserve along the Middle Loire River. Our results showed that artificial rejuvenation operations had a significant short‐term negative effect on richness. However, in the few years following the work, the riparian communities established on the rejuvenated island became more diverse, with a large proportion of annual plants, contributing to the increased species pool of the Nature Reserve. In addition, we found that temporal changes in species richness were strongly influenced by hydrological conditions, with a peak in biodiversity observed during prolonged summer low water. This highlights the importance of considering flow variations to more accurately assess the ecological benefit of restoration operations on riparian vegetation. Overall, as successional stages were more advanced at the island complex scale, fluvial maintenance works have allowed the recreation of sandy pioneer habitats exposed to flooding. These habitats have promoted the establishment of species‐rich communities without favoring the installation of invasive alien species. From this view, the maintenance works have increased the mosaic of habitats within the Nature Reserve and have restored environmental conditions favorable to early‐successional species.

Nutrient availability modulates the effect of water abstraction on the metabolism of 2 lowland forested streams

Climate change predictions for Southern Europe indicate an increase in the frequency and duration of summer low flows and water scarcity in streams. Droughts can cause substantial changes in aquatic communities and biogeochemical processes because they modify stream environmental conditions. Among the many physical, chemical, and biological variables that influence stream metabolism, nutrients may affect algae and heterotrophic microorganisms, and nutrient concentrations may vary with reduction in water discharge. We experimentally manipulated stream discharge and used a before–after control–impact paired design to assess how reduction of stream discharge affected metabolism (i.e., ecosystem respiration [ER] and gross primary production [GPP]). The study was done in 2 lowland forested streams in northwestern Spain with contrasting nutrient concentrations (i.e., mesotrophic: Caselas stream; eutrophic: Pego stream). In the 2 streams, metabolism was estimated before and after discharge manipulation. Prior to discharge reduction, the 2 streams were heterotrophic (i.e., GPP∶ER < 1), and GPP and ER were related in the eutrophic Pego. Discharge reduction increased GPP at the impacted reaches of the mesotrophic Caselas and decoupled GPP and ER at the Pego. An information-theoretic approach was used to assess which combinations of physical, chemical, and biological variables were most important to explain the variation in ER and GPP under the different hydrologic conditions. The observed differences between the 2 streams suggest that the metabolic response to stream drought can be modulated by the interplay between nutrient availability and the density of consumers feeding on resources, among other environmental variables. We show that longer summer periods and reduced stream discharge have the potential to increase daily hypoxia in nutrient-rich lowland stream ecosystems. Increased hypoxia can threaten biodiversity of stream ecosystems and reduce consumer pressure on basal instream resources, such as algae, bacteria, and fungi, which may, in turn, favor instream GPP. In addition, drying conditions seemed to favor autotrophic over heterotrophic activity under moderate nutrient availability (i.e., increase in the GPP∶ER ratio in the impacted Caselas reaches). Therefore, drought conditions not only affect overall daily rates of metabolic activity, but also the relative importance of different energy sources and organic matter for instream function. Our results show that discharge reduction caused by increased water scarcity, due to both climate change and water demand by human activities, can influence energy flow and organic matter dynamics through effects on the metabolism of forested lowland streams.

СТАТИСТИЧЕСКИЙ АНАЛИЗ ВОДНОГО РЕЖИМА РЕКИ АМУР ДЛЯ ЦЕЛЕЙ ПРОГНОЗА

The Amur is navigable along its entire length, and it has a great transport importance for the Far East region. In years with spring-summer-autumn periods of low water level, the Amur River navigation suffers great economic losses. In such years, the volume of cargo transportation and the movement of passenger ships are disrupted, the work of water intakes deteriorates, and water supply to the population and enterprises is hampered. In the Khabarovsk Territory, material damage is sometimes commensurate with the damage from floods. More than a century of observations of the Amur regime near Khabarovsk made it possible to carry out a statistical analysis of the characteristic water level dynamics in three water phases: spring flood, summer low-water period and rain floods. The territory climate with cold dry winters and warm humid summers determines a dual maximum runoff in the Amur regime, reduced in spring and high in summer. It is noteworthy that both maximum runoffs have a steady downward trend in the dynamics of the highest water levels for 1896–2021. However, the height of the spring flood wave, in contrast to the annual maximums, decreases in dynamics more intensively (at a rate of 10–12 cm / 10 years and 5–7 cm / 10 years, respectively). The lowest water levels observed after the flood wave (summer low water period) have a long-term trend in dynamics, parallel to the spring trend. A similar trend in the Amur regime is associated with the variability of the regional climate and is synchronous with global warming characterized by an increase in surface air temperature, which contributes to an increase in evaporation from the water surface, and therefore, to a decrease in river runoff. The performed assessment of the Amur water regime during the navigation period makes it possible, by means of trend components, to orient the hydrologist-forecaster on the distribution of the Amur water content in in the coming season.

Сезонная изменчивость концентрации хлоридных ионов в воде Куйбышевского водохранилища

According to long-term observations in the period 2001–2019. regularities of seasonal variability of the content of chlorides in the water of the Kuibyshev reservoir were studied. Stationary hydrochemical observation point is located in the outlet section of the reservoir. To study the causes of seasonal variability in chloride concentrations, hydrological data were used at the inlet (Cheboksary and Nizhnikamsk waterworks) and outgoing (Zhigulevsk waterworks) sections of the Kuibyshev reservoir. It was found that over the 19-year observation period, the range of seasonal fluctuations in average monthly chloride concentrations was 14–42 &lt;math xmlns="http://www.w3.org/1998/Math/MathML"&gt;&lt;mfrac&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mi&gt;g&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;msup&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;/mfrac&gt;&lt;/math&gt;. Seasonal variability of chloride content is pronounced and is characterized by alternating maxima and minima of chloride concentration. The winter maximum is observed in April before the beginning of the spring flood, and the summer maximum is observed in July before the beginning of the autumn low water. The spring minimum is observed in May at the peak of the spring flood, and the autumn minimum is observed in December before the freeze-up begins. The seasonal variability of chlorides includes four periods (I, II, III, IV), which are formed as a result of the interaction of genetically heterogeneous water masses in the reservoir. Period I is characterized by a gradual increase in the concentration of chlorides due to the inflow of groundwater during the winter low water. The short-term period II is characterized by a sharp decrease in the concentration of chlorides due to the entry of soil-surface waters into the reservoir during the spring flood. Period III is characterized by an increase in the concentration of chlorides due to an increase in the role of soil and groundwater during the summer low water period. Period IV is the longest and is characterized by a gradual decrease in the concentration of chlorides during the autumn low water period. The revealed patterns of seasonal variability of chlorides are unchanged and were observed annually during 2001–2019. However, the values of chloride concentrations significantly depended on the hydrometeorological conditions of a particular year. In dry years, the concentration of chlorides increased, and in high-water years, they decreased in all hydrological seasons of the year.

Hydrochemical water quality monitoring of natural water bodies of the Ural river basin

A general characteristic of the river basin of the interstate Ural river and information on the economic use of the Ural river in its upper, middle and lower reaches are given. Information on the hydrology of the liquid and solid flow of the Ural river is presented. Hydrochemical monitoring of water bodies of the Ural river basin was conducted during the flood period, during the summer low water period and during the autumn low water period of 2017–2018. The hydrochemical monitoring of the water quality in natural reservoirs of the Ural drainage basin made it possible to identify an excess of the MPCs for residential use and for fishery of heavy metal ions in the water of the examined reservoirs. An excess of cadmium ions by (1.2–1.4) MPC for residential use was found in the Ilek river during its low water as well as in the Ural river near the border with the Russian Federation during the flood period in the amount of (3.1–3.4) MPC for residential use and near the village Zharsuat in the period of summer and autumn low water in the amount of (1.5–2.6) MAC for residential use. An excessive concentration of lead ions by (1.2–1.4) of MPC for fresh water fisheries in the middle and lower reaches of the Ural river at different times of the year was found. Excessive concentrations of ions of different heavy metals in comparison with their MPC for fresh water fisheries were found in all water bodies in different periods of the year. The greatest excess of zinc ions in comparison with its MPC for fresh water fisheries was observed during low water.

Flow rate regime of the Western Urals’s rivers

The flow rate is one of the most important elements of the river’s water regime. Establishing patterns in river flow rates’ changes within a year and by season is of great importance for the hydrological forecasts for spring floods, rain floods and hydrological calculations. By now, there are few publications on this area, both in Russia and abroad. The initial data were divided into 5 hydrological seasons – winter and summer low water, rise and fall of spring floods and autumn rain floods. For each season, an analysis of river flow rate over a period (1936-2013) was done. The average flow rate in rivers varied greatly depending on the water regime’ phase and the type of terrain in which the river flows. For all seasons, the amplitude of fluctuations in the flow rate on the plain rivers is less than on the mountain ones. So, in mountain rivers, flow rates vary from 0.04 to 2.42 m/s, and on flat rivers from 0.02 to 1.43 m/s. As well the pairwise and multiple correlation coefficients of flow rates for each morphometric and catchment characteristics were calculated. The highest correlation coefficients were obtained for the dependency between the average flow rate and the watershed elevation (0.30-0.75) and the watershed slope (0.42-0.76). The multiple correlation coefficients between the average flow rate and all catchment’s morphometric characteristics varied from 0.97 to 0.99. Results verification on an independent data demonstrated that the relative error was on average 2%.

Hydrological-stenobiontic method for determining environmental flows from reservoir

In the practice of using river resources accumulated in reservoirs, there is a typical problem of unreasonably large water intake for industrial-household needs to the detriment of the aquatic ecosystem. An important tool for balancing these links is to provide environmental flows based on a comprehensive analysis of river functioning patterns. And in terms of a progressing negative impact of reservoirs on the integrity of river ecosystems, the choice of indicator hydrobiota for the calculation of environmental flows should be considered insufficiently substantiated. The solution of this problem, by filling the appropriate methodological niche, allowed substantiating the hydrological-stenobiontic method for determining environmental flows. The developed solutions are based on the minimum possible values of tolerance of aquatic ecosystems stenobionts to water velocity. Five groups of macrozoobenthos represent relevant target organisms. The hydrological calculations presented in the paper are based on the data of daily water flow rate for 80 years and the results of field studies of the river channel depth in the low water period. On this basis, it was determined that for lowland parts of rivers, the flow velocity in the tailwater of reservoirs should be at least 0.2 m/s. Comparison of the curve of the average monthly water velocity dynamics of 95 % runoff availability with the minimum corresponding requirements of stenobionts allowed determining the most threatening period of the year for the aquatic ecosystem – summer low water. For a reservoir in the lowland parts of the river, based on the developed method, the calculations substantiate an increase in the minimum volume of environmental flows by 40 % relative to the current one. It is also estimated that the average annual and average second volumes of environmental flows should be about 38 % of the respective river runoff. The obtained results are close to those found on rivers in China, Iran and the United States in the framework of a comprehensive analysis of hydrological, hydraulic and hydrobiological parameters of the aquatic ecosystem

EFFECTS OF THE VERTICAL HETEROGENEITY OF WATER MASSES ON THE STABILITY OF INDUSTRIAL WATER SUPPLY IN INDUSTRY-INTENSIVE AREAS

The stability of water supply systems is one of the main factors for reliable operation of large industrial complexes. This problem is considered through the case of the Azot branch of JSC URALCHEM in the city of Berezniki, which derives raw process water from the Kama River (Kama storage reservoir). A characteristic feature of this water body is a highly variable hydrological regime. During the summer low water period, it is characterized by low current velocities. In winter, when the water level in the reservoir declines, a typical river flow regime is observed. In addition, the water body is exposed to heavy human impact. The bulk of the load comes from non-declared non-point (diffuse) sources. Their characteristic feature is high suspended solids content, and, accordingly, the density of the effluents. Their behavior is fundamentally different from the processes of dilution and migration of effluents with neutral buoyancy. Traditional methods of calculating dilution processes cannot be used to describe them. A two-layer flow is formed, where the content of basic ions in the surface horizon is more than an order of magnitude lower than near the bottom. Early in July 2020, a significant increase in the content of chlorine and sodium ions was observed at the water intake facility of the Azot branch, causing a shutdown of the plant. The causes of the phenomenon had to be identified. The putative causes were emergency discharges of concentrated waste from the sludge dump on the shore or contamination by the wastewater entering the Kama River below the intake facility due to backflow. These situations can be modeled taking into account the vertical heterogeneity of water masses based on the coupling of hydrodynamic models in one-, two-, and three-dimensional formulation. As a result, it was shown that the only cause of the emergency could be water intake from the Kama River bottom flow.

ГИДРОЛОГИЧЕСКИЕ ОСОБЕННОСТИ И ГЕОЭКОЛОГИЧЕСКОЕ СОСТОЯНИЕ МАЛЫХ ВОДОТОКОВ ПОЛЬДЕРНЫХ ТЕРРИТОРИЙ КАЛИНИНГРАДСКОЙ ОБЛАСТИ6

The paper presents the results of research into the hydrological features and geoecological state of small watercourses in the polder territories of the Kaliningrad region. The work is focused on the largest polder massif of the region located on the territory of the Neman lowland in the Slavsky urban district. There was carried out geoecological monitoring of surface watercourses in the following seasons: summer (July 15, 2020), autumn (October 15, 2020), winter (February 3, 2021), and spring (March 27, 2021). For the monitoring we selected watercourses that in their totality could characterize the river network of the polder massif as a whole: the rivers Zlaya, Shlyuzovaya, Nemoninka, and Osa. Subsequently, water samples were taken for hydrochemical analysis, and the hydrometric characteristics of the rivers were measured at background and control points. In order to more objectively characterize the hydrological features of the river network, in addition to the results obtained during the monitoring, we used data on long-term hydrological observations. The research provides information on the state of the watercourses and the influence of anthropogenic and natural factors on them. Monitoring of the geoecological state has shown that they are to a greater or lesser extent susceptible to pollution and, in general, have a ‘bad quality’ water class. The main pollutants identified in the course of research were: nitrites, ammonium, phosphates, total iron, and oil products. There are also inconsistencies with the norms of maximum permissible concentrations in terms of biological consumption of oxygen and dissolved oxygen that are noted during the period of activity of living organisms. The geoecological state was found to be linked to the water regime, weather conditions, natural and agricultural cycles. A non-standard course of the water regime phases was noted, namely: autumn-winter floods, not very pronounced high water, and summer low water. The current situation of the river network can be characterized as unfavorable but still having a potential for correction due to the properly selected environmental protection measures.

Особенности многолетней динамики развития гидрохимических показателей воды Шершневского водохранилища

The article presents an analysis of the long-term dynamics of the hydrochemical conditions of the water of the Shershnevsky reservoir for 1972-2020 during the spring flood and summer low water. The features of the development of water quality indicators over time are determined: pH, mineralization, turbidity, color, suspended solids, the content of dissolved oxygen and organic substances by permanganate oxidability and BPK5, as well as changes in the concentrations of ammonium, nitrite, nitrate nitrogen and phosphates. In the water of the Shershnevsky reservoir for the period 1972-2020, trends of a significant decrease in mineralization, turbidity and permanganate oxidability were noted in both phases of the hydrological mode. In the summer low water period, a significant increase in chromaticity, oxygen content in water and orthophosphates was detected.. The revealed features of changes in the hydrochemical regime indicate an increase in the processes of anthropogenic eutrophication of the Shershnevsky reservoir – the only drinking source of the Chelyabinsk agglomeration and make it possible to predict the state of the aquatic ecosystem. The information obtained can be implemented in the process of making management decisions on environmental protection measures for the Shershnevsky reservoir.

Миграция тяжелых металлов в системе «береговой грунт – донные отложения – растения» реки Ходца в период летней межени 2019 года

The article describes the purpose of the work, which is determining the distribution and relationships between the composition of pollutants in coastal soil, bottom sediments and higher aquatic vegetation in the small river Khodtsa. There have been presented the data of the laboratory research based on the results of the field work onselecting samples, on concentration of toxicants (cadmium, lead, iron, nitrogen, ammonium and petroleum products) in deposit media, as well as &#x0D; in Carex aquatilis plants of the small river Hodza. This plant species is limiting throughout the river due to the low intensity of biological absorption. The studies were carried out during the summer low water season in 2019 on the river section from the source (Elektrostal city) to the river mouth in the area of Pavlovsky Posad. In all the studied objects there have been found increased concentrations of iron. In the coastal ground and bottom sediments the pollution with heavy metals is manifested to a much greater extent: at the source and intermediate point. Petroleum products and ammonia &#x0D; nitrogen are distributed unevenly in space. A correlation analysis of the experimental data obtained in the components of the environment of the studied territory (the Khodtsa river) was performed. &#x0D; In general, the highest measurement results are observed in the upper reaches of the small river Khodtsa in the industrial city of Elektrostal. The obtained data on the heavy metals migration &#x0D; in the system “сoastal ground – bottom sediments – higher aquatic vegetation” of the small river Khodtsa can be successfully used as indicators an environmental monitoring system and serve as the basis for organizing further research, as well as for developing a strategy for environmental management and environmental protection in the Moscow Region.

Decadal trends and ecological shifts in backwater lakes of a large floodplain river: Upper Mississippi River

Shallow lakes are typically found in one of two stable states, a macrophyte-dominated clear water state or a turbid state due to excessive phytoplankton and suspended sediment. Whether shallow backwater lakes in large river floodplains exhibit similar alternate stable states is less understood. This study considers mechanisms, interactions and feedbacks associated with a shift in environmental conditions and biotic community structure in backwater lakes of a hydrologically dynamic floodplain river system. We use long-term data from backwater lakes to show an increase in submersed aquatic vegetation, improved water quality, and resulting shifts in the community structure of aquatic vegetation and fish following a 4 year period of summer low water discharge on the Upper Mississippi River. Backwater lakes in our study span a gradient of environmental conditions. Backwater lakes located in the upper reach of our study area were chronically turbid and support only sparse aquatic macrophytes, whereas those downriver exhibited clearer water and abundant vegetation. An increase in submersed aquatic vegetation in the lower backwater lakes resulted in a fish community shift to more vegetation-associated species. A lesser response in submersed aquatic vegetation abundance and fish community shift was observed in the upper, more turbid backwater lakes. The combination of vegetative cover and turbidity were key environmental variables associated with fish community structure in lower backwater lakes. Turbidity was the key environmental variable associated with submersed aquatic vegetation in both upper and lower backwaters. Providing further insight into the physical, chemical and biological interactions associated with ecological shifts will help guide management and restoration decisions towards more resilient, macrophyte-rich floodplain backwaters.

Изменение водности реки Волги в районе заповедного острова Бахиловский

The ecological state of the protected Islands Seredysh and Shalyga (now Bakhilovsky island) depends on the water content and flow of the Volga River. We have analyzed the long-term changes in the water flow of the Volga River for the period 1958-2017 in the alignment Zhiguli dam, located 12 km upstream from the island. According to the average annual water consumption, there are three periods that differ from each other in water content: low-water period (1958–1976), high-water period (1977–1997) and the period of average water content (1998–2017), with extremely low-water (1967, 1973, 1975, 1976, 1977, 1996) and extremely high-water (1966, 1979, 1981, 1990, 1991, 1994) years. In highwater years, during the passage of the spring flood, the island is almost completely flooded, and in low-water years, during the summer low water, the area of the island increases and changes its configuration.