Reservoir Bays Research Articles

Morphological Characteristics and Annual Population Dynamics of Microcystis (Cyanobacteria) in Nanwan Reservoir (Xinyang, China)

Microcystis, a key genus of bloom-forming cyanobacteria in freshwater ecosystems, has garnered significant research interest due to its species diversity and population dynamics. This study investigated the water profiles and Microcystis populations at six stations in the Nanwan Reservoir (Xinyang, China) throughout 2022 to elucidate the morphological characteristics of Microcystis, analyze its population density patterns, and identify key environmental factors influencing its dynamics. The reservoir was classified as mesotrophic during most of the study period. Seven common Microcystis species were identified, including M. botrys, M. smithii, M. wesenbergii, M. firma, M. novacekii, M. aeruginosa, and a species suspected to be M. flos-aquae. The spatial and temporal distribution analyses revealed a bimodal fluctuation in Microcystis densities, with a monthly occurrence across stations except in August. The highest density, 1.71 × 107 cells/L, was recorded in May, while the lower densities were observed from July to September. The Mantel test results indicated that the nitrogen levels, particularly NO3−-N, were the primary factors influencing the Microcystis density. Additionally, both the reservoir bays and dam areas exhibited a high risk of Microcystis blooms. Effective management of nitrogen inputs, enhanced monitoring, and appropriate gate operations are recommended to mitigate the risk of Microcystis blooms in the Nanwan Reservoir.

Impact and Mechanism of Medium and Small Flood Regulation in the Three Gorges Reservoir on the Phytoplankton in Tributary Bays

The regulation of small- and medium-sized floods （RSMF） has become the main mode of regulation in the flood season of the Three Gorges Reservoir （TGR）. To study the response of phytoplankton in the tributary bays of the TGR to the RSMF, a typical eutrophic tributary of the TGR, Xiangxi River, was investigated for the spatiotemporal distribution characteristics of phytoplankton and nutrients in the main and tributary streams from 2020 to 2021. The response characteristics of phytoplankton in the tributary bays to the RSMF were analyzed. The results indicated that during the RSMF, the chlorophyll a （Chl-a） in the water body of the Xiangxi River decreased with the increase in the water level in front of the dam, whereas during the reservoir impounding at the end of flood season, the concentration of Chl-a increased again. During the RSMF, the Chlorophyta and Diatoma were the main communities of planktonic algae in the Xiangxi River. The phytoplankton community changed with the RSMF. When the water level fluctuation increased, diatoms were the main species, whereas when the water level fluctuation was small, blue and green algae were the main species. The concentration of Chl-a was more sensitive to changes in TN concentration. When the flow velocity was >0.25 m·s-1 or the suspended sediment content was >10 mg·L-1, the concentration of Chl-a in the water was inhibited. After 2010, the typical outbreak time of algal blooms in the Xiangxi River Reservoir Bay shifted to the flood season, with only two non-flood season algal blooms. Further attention needs to be paid to the response of algal blooms in the reservoir to small- and medium-sized flood control during the flood season.

Daily process and key characteristics of phytoplankton bloom during a low-water level period in a large subtropical reservoir bay.

Reservoirs, heavily influenced by artificial management, often harbor phytoplankton assemblages dominated by cyanobacteria or dinoflagellates, triggering significant changes in aquatic ecosystems. However, due to limited sampling frequency and insufficient attention to species composition, the bloom processes and key characteristics of phytoplankton community structure have not been systematically elucidated. During the low-water level period when blooms are most likely to occur (June to September) in a tributary bay of the Three Gorges Reservoir, daily sampling was conducted to investigate phytoplankton community composition, identify significant environmental factors, and evaluate important structure characteristics of phytoplankton community. The results showed that Microcystis aeruginosa maintained a clear dominance for almost a month in stage 1, with low Shannon and evenness but a high dominance index. Phytoplankton total density and biomass decreased drastically in stage 2, but Microcystis aeruginosa still accounted for some proportion. The highest Shannon and evenness but the lowest dominance index occurred in stage 3. Peridiniopsis niei occurred massively in stage 4, but its dominant advantages lasted only one to two days. NH4-N was responsible for the dominance of Microcystis aeruginosa, while TP and PO4-P was responsible for the dominance of Peridiniopsis niei; however, precipitation contributed to their drastic decrease or disappearance to some extent. The TN : TP ratio could be considered as an important indicator to determine whether Microcystis aeruginosa or Peridiniopsis niei dominated the phytoplankton community. Throughout the study period, physiochemical factors explained more variation in phytoplankton data than meteorological and hydrological factors. Pairwise comparisons revealed an increase in average β diversity with stage progression, with higher β diversities based on abundance data than those based on presence/absence data. Repl had a greater effect on β diversity differences based on presence/absence data, whereas RichDiff had a greater effect on β diversity differences based on species abundance data. Co-occurrence networks for stage 1 showed the most complex structure, followed by stage 4, while the network for stage 3 was relatively sparse, although the overall community division remained compact. This study provides a useful attempt to explore the status and changes in phytoplankton community structure during the bloom process through high-resolution investigation.

The use of biospheric monitoring in the study of reservoirs in the Volga-Don interfluve of Russia

With anthropogenic activity, as well as with changes in climatic, hydrological and landscape regimes, significant structural and spatial shifts occur in existing ecosystems. The deterioration of water quality also significantly affects the state of coastal water zones, structural and species composition. In the course of monitoring the Tsimlyansk reservoir using the AQUA-1 automated watercraft, the quality of natural water was determined, formalized relationships between the abiotic and biotic components of the ecosystem were identified, the ecological state of the water intake zone was predicted, and the functioning of a number of structures that affect the regime and level of the reservoir. In order to improve the quality of water intake water, bioremediation was carried out using the planktonic microalgae Chlorella vulgaris, calculations of the invasion were made using computer programs. On the basis of the conducted monitoring studies, a hydrodynamic model of the reservoir bay was compiled, a model of an automated watercraft for biospheric monitoring was developed, an optimized scheme for the introduction of Chlorella vulgaris into the reservoir. The main biological indicators-indicators of water intake zones have been established, taking into account changes in the hydrological regime. The positive impact of the environmentally safe bioremediation of water at the water intakes of the Tsimlyansk reservoir in order to improve the quality of natural water used for drinking purposes and fish farming is shown.

The Hydrochemistry, Ionic Source, and Chemical Weathering of a Tributary in the Three Gorges Reservoir

Riverine dissolved matter reflects geochemical genesis information, which is vital to understand and manage the water environment in a basin. The Ganjing River located in the hinterland of the Three Gorges Reservoir was systematically investigated to analyze the composition and spatial variation of riverine ions, probe the source and influencing factors, and assess the chemical weathering rates and CO2 consumption. The results showed that the total dissolved solid value (473.31 ± 154.87 mg/L) with the type of “HCO3−–Ca2+” was higher than that of the global rivers’ average. The hydrochemical parameters were relatively stable in the lower reservoir area of the Ganjing River, which was largely influenced by the backwater of Three Gorges Reservoir. The carbonate weathering source contributed 69.63% of TDS (Total dissolved solids), which generally dominated the hydrochemical characteristics. The contribution rates of atmospheric rainfall were relatively low and stable in the basin, with an average of 4.01 ± 1.28%. The average contribution rate of anthropogenic activities was 12.05% in the basin and even up to 27.80% in the lower reservoir area of the Ganjing River, which illustrated that the impoundment of Three Gorges Reservoir had brought great challenges to the water environment in the reservoir bay. The empirical power functions were tentatively proposed to eliminate the dilution effect caused by runoff discharge on the basis of previous studies. Accordingly, the rock weathering rate was calculated as 23.54 t/km2 in the Ganjing River Basin, which consumed atmospheric CO2 with a flux of 6.88 × 105 mol/y/km2. These results highlight the geochemical information of tributaries in the hinterland of the Three Gorges Reservoir, have significant implications for understanding the impact of impoundment, and provide data support for the integrated management of water resources in the Ganjing River Basin.

The Study of Soil Bacterial Diversity and the Influence of Soil Physicochemical Factors in Meltwater Region of Ny-Ålesund, Arctic

Global climate change has caused the changes of the ecological environment in the Arctic region, including sea ice melting, runoff increase, glacial lake expansion, and a typical meltwater area has formed in the Arctic coastal area. In this study, the meltwater areas near six different characteristic areas of Ny-Ålesund in 2018 were taken as the research objects, and high-throughput sequencing of V3–V4 regions of all samples were performed using 16S rDNA. Among the soil samples of six glacial meltwater areas in Ny-Ålesund, Arctic, the meltwater area near the reservoir bay had the highest bacterial abundance, and the meltwater area near the sand had the lowest one. The dominant phyla in soil samples were Proteobacteria, Actinobacteria, Acidobacteria. The NH4+-N content in intertidal soil was higher than that in subtidal soil. Through WGCNA analysis and LEFSE analysis, it was found that the core bacteria significantly related to NH4+-N were basically distributed in the intertidal area. For example, Nitrosomonadaceae, Nitrospira and Sphingomonas were the core bacteria showed significant different abundance in the intertidal area, which have the ability to metabolize NH4+-N. Our findings suggest that NH4+-N plays an important role in soil bacterial community structure in the Arctic meltwater areas.

Unraveling the effects of hydrological connectivity and landscape characteristics on reservoir water quality

Dam construction and reservoir operation altered the landscape and hydrological process of reservoir bays, affecting reservoir water quality. However, many landscape and hydrological connectivity metrics are highly correlated and may introduce redundancies and misleading results when use conventional multivariate regression techniques. Knowledge concerning the pure effects of landscape and hydrological connectivity metrics are crucial for understanding nonpoint pollution processes and guiding water quality protection strategies in reservoirs. Based on water quality monitoring data for six years (2015–2020) from 66 reservoir bays of the Danjiangkou Reservoir in China during both flood discharge periods (FDPs) and water storage periods (WSPs), machine learning approaches (boosted regression trees and random forest) were conducted to decipher the effects of hydrological connectivity and landscape characteristics on water quality. The results showed that landscape composition, landscape configuration, and topography had the combined importance of 46.69%, 31.48%, and 10.14% on the overall water quality changes during the FDPs, respectively. However, landscape configuration was the largest importance factor controlling overall water quality for the WSPs with the combined importance of 38.57%. For the FDPs, the top two importance variables of overall water quality variation were the proportions of shrub and agricultural land in the reservoir bay. For the WSPs, the top two importance variables were flow length and index of connectivity. For specific water quality parameters, the highest importance factor controlling the variation in total nitrogen, total phosphorus, ammonia nitrogen, nitrate and chlorophyll a were landscape configuration, while the landscape composition had the highest importance on the variation in permanganate index, suggesting landscape characteristics affected water quality with specific responses to distinct water quality parameters. These findings emphasize the distinct roles of landscape and hydrological characteristics on water quality and provide important information for the efficient formulation of water quality protection strategies in reservoirs.

How has the eutrophication evolved in the tributary bay of the Three Gorges Reservoir area

AbstractThe Three Gorges Reservoir on the Yangtze River is the largest water control project in the world. While exerting great benefits (i.e., flood control, hydropower generation, inland river navigation and scenic tourism), the eutrophication of the tributary bay of the Three Gorges Reservoir has become one of the main environmental problems. This paper is to study the causes of water environment evolution in the tributary bay and investigate the driving force of eutrophication succession after the Three Gorges Reservoir enters the regular operation. By considering the Meixi River on the left bank of the mainstream of the Three Gorges Reservoir area (a typical tributary), this paper developed a three-dimensional hydrodynamic, water quality and water eutrophication mathematical model for the Meixi tributary bay, calibrated with measured data about hydrological regime (water level, flow), hydrodynamic factors (velocity) and water quality (water temperature, Chl-a, TP, TN, etc.). The annual variation of Chl-a concentration in the tributary bay was simulated, and the response relationship between the variation of Chl-a concentration and water conditions of the mainstream and tributary bay (e.g., reservoir water level, reservoir bay velocity, exogenous nutrient input, water temperature stratification and other factors) was analyzed. Results show that the water storage operation of the Three Gorges Reservoir contributes to the low flow velocity maintenance (≤0.05 m/s) in the tributary bay, the backward flow of the mainstream and the sufficient nutrients carried by the tributary water; the water temperature stratification is more likely to occur in the slow detention area in the middle-upper part of the bay in spring and summer, which provides a potential driving force for algae blooms. With the continuous decline of pollution load input in the reservoir basin, the algae blooms in tributary bay was the result of the combined action of low water level operation, low flow velocity (≤0.02 m/s), a large number of non-point source loads input with rainfall and runoff (the proportion of wet year is >70%), and obvious water temperature stratification in shallow water area, and the suitable meteorological conditions are the main inducing factors. Therefore, since the ecological regulation cannot be applied to the multitudinous tributary bays, the non-point source pollution control in the tributary bay is the key to controlling factor.

Longitudinal Variations in Physiochemical Conditions and Their Consequent Effect on Phytoplankton Functional Diversity Within a Subtropical System of Cascade Reservoirs

The social and environmental impacts of large dams are quantifiable and have been well documented, while small dams have often been presumed to be less environmentally damaging than large dams. The purpose of this study was to analyze longitudinal gradients in environmental, hydrodynamic variables and their impact on phytoplankton function, within a cascade of four reservoirs (XuanMiaoGuan, XMG; TianFuMiao, TFM; XiBeiKou, XBK; ShangJiaHe, SJH) and one reservoir bay (Huangbohe Bay, HBH), located from upstream to downstream in the Huangbo River, Hubei Province, China. Our results showed that water temperature, total nitrogen, and soluble silicate increased along the cascade reservoir system, while the concentration of dissolved oxygen and total phosphorus decreased. We identified 16 phytoplankton functional groups, and the predominant groups, including D (Synedra and Stephanodiscus hantzschii), E (Dinobryon divergens), Lo (Dinoflagellate: Peridinium bipes and Peridiniopsis), X2 (Chroomona), and Y (Cryptomonas), changed longitudinally from up to down in the cascade reservoirs. The number of dominant functional groups increased along the longitudinal gradient, indicating that the function of the phytoplankton community was more stable. Functional group D was the dominant phytoplankton functional group among the four reservoirs, and Lo group was dominant except SJH. The phytoplankton functional groups in the HBH have been completely changed due to the backwater jacking of the main stream of the Yangtze River. Euphotic depth, suspended solids, and nutrients were apparently the key factors driving variations in phytoplankton functional groups among the reservoirs. Notably, the patterns we observed were not all consistent with the cascading reservoir continuum concept (CRCC) that typically characterizes large rivers. Thus, our findings contribute to the further theoretical development of the CRCC, which may not apply widely to all cascade systems.

Comparison Between Tributary and Main Stream and Preliminary Influence Mechanism of CO2 Flux Across Water-air Interface in Wanzhou in the Three Gorges Reservoir Area

The main stream of the Three Gorges Reservoir area in Wanzhou and its tributary (the Pengxi River) were selected as a survey area to monitor the CO2 concentration. Twelve related indicators were selected during the blooming period from April to September 2019, which were divided into Climate factors, Water environment factors, Carbon source factors, Nutrient factors, and Sediment factors. These factors were considered for further discussion of the impact pathways and contribution to CO2 flux. The average CO2 fluxes of Gaoyang (the Pengxi River), Huangshi (the Pengxi River), and Wanzhou (the main stream) were (1.445±1.739), (3.118±2.963), and (2.899±1.144) mmol·(m2·h)-1, respectively, showing that Gaoyang < Wanzhou < Huangshi. The CO2 flux of tributary showed a large variation, while the main stream had a relatively small variation, which is a stable "source" of CO2. The main stream of the Yangtze River, as a hub for the transportation of biomass from land to sea, has higher carbon concentration and higher flow rate than its tributaries, which makes the CO2 flux of the main stream usually larger than that of the tributary. However, the difference in hydrological conditions result in spatial differences in CO2 flux at different points of the same tributary. Gaoyang is located in the reservoir bay, which is conducive to the growth of phytoplankton and the CO2 flux is lower; Huangshi is located in a river with a faster flow rate. The backwater support and backflow of the main stream make the CO2 flux significantly greater than that at Wanzhou. The effects of various indicators on the CO2 flux are also markedly different in the tributary and main stream. Temperature (T), DO, dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) have significant effects on CO2 fluxes in the tributary, while NH4+-N has a significant impact on CO2 fluxes in the main stream. Nutrient factors and carbon source factors contribute 32.37% and 27.25%, respectively, to CO2 flux, accounting for more than half of the total, followed by climate factors, water environment factors, and sediment factors, which contribute 18.81%, 13.49%, and 8.08%, respectively. Reservoir CO2 emission control can focus on controlling the eutrophication and carbon sources; phenomena such as global warming and sedimentation will also have a certain impact on the CO2 emission of reservoirs.

Phytoplankton community structure and driving mechanism of its construction process in autumn in Zhelin Reservoir, Lake Poyang Basin

研究环境过滤过程和空间扩散限制过程在构建水生浮游植物群落结构中的作用是了解这些因素如何驱动物种分布和影响群落结构的关键步骤.为了揭示鄱阳湖流域柘林水库浮游植物群落结构特征与环境因子的关系，以及明确环境因子和空间扩散限制性因子在浮游植物群落构建过程中的影响机制，于2020年10月，对柘林水库33个采样点的浮游植物和水质理化进行调查分析.共鉴定浮游植物7门122种，其中，以绿藻门种类最多，为34属62种，占总物种数的50.81%，硅藻门次之，为11属27种.柘林水库浮游植物优势种类主要是蓝藻门中的伪鱼腥藻属（Pseudoanabaena）、浮鞘丝藻属（Planktolyngbya）、小尖头藻属（Raphidiopsis）以及硅藻门中的针杆藻属（Synedra）.柘林水库浮游植物细胞丰度的变化范围为0.93×10⁶~172.12×10⁶ cells/L，平均值为95.42×10⁶ cells/L，生物量的变化范围为0.95~22.35 mg/L，平均值为9.35 mg/L.上游修河水域浮游植物生物多样性指数显著高于库心和库湾水域，库心与库湾水域之间浮游植物生物多样性指数差异性不明显.柘林水库上游修河水域浮游植物群落结构与库心和库湾水域存在明显分离，群落结构的差异性主要受水体透明度、电导率、氨氮和硝态氮的影响.变差分解结果显示，空间扩散限制性作用在驱动柘林水库浮游植物群落构建过程中占据主导地位.;Evaluation of the relative influences of environmental and spatial processes in structuring aquatic phytoplankton metacommunities is an essential step for understanding the species spatio-temporal distributions. To reveal the relationships between community structures of phytoplankton and the environment as well as clarify the driving mechanism of environmental factors and spatial diffusion limiting factors on phytoplankton community structure in Zhelin Reservoir, Lake Poyang Basin, the phytoplankton and water quality physicochemical characteristics of 33 sampling sites were investigated and analyzed in October 2020. A total of 122 species belong to 7 genera were identified, with 62 species in 34 genera were Chlorophyta, accounting for 50.81% of the total species, followed by Bacillariophyta with 27 species in 11 genera. The dominant species of phytoplankton in Zhelin Reservoir are Pseudoanabaena, Planktolyngbya and Raphidiopsis of Cyanophyta and Synedra of Bacillariophyta. The cell abundance of phytoplankton in the Zhelin Reservoir varied from 0.93×10⁶ to 172.12×10⁶ cells/L with an average of 95.42×10⁶ cells/L, and the biomass varied from 0.95 to 22.35 mg/L with an average of 9.35 mg/L. The phytoplankton biodiversity index in the upstream Xiuhe tributary area was significantly higher than that in the center of the reservoir area and the reservoir bay area, while no significant difference in the phytoplankton biodiversity index between the center of the reservoir area and the reservoir bay area was found. The phytoplankton community structure in the Xiuhe tributaries of Zhelin Reservoir was separated from that in the center reservoir and reservoir bay, and the differences were mainly affected by water transparency, electrical conductivity, ammonia nitrogen and nitrate nitrogen. The results of variation partitioning showed that the spatial diffusion limiting effect was dominant in driving the phytoplankton community structure in Zhelin Reservoir.

Sources and routes from terrestrial exogenous pollutants affect phytoplankton biomass in reservoir bays

Abstract Reservoir bays, at the terrestrial and water boundary, where water fluidity slows down and self-purification ability turns weak, hence they are especially sensitive to terrestrial exogenous pollutants, even resulting in eutrophication. According to N:P, water nutrient types can be divided into N limited, P limited and N + P limited classes. Phytoplankton biomass is represented by chlorophyll a, which is one of the sensitive indicators of water eutrophication. Comprehensively tracing non-point pollution from terrestrial exogenous pollutants (fertilizer, soil release, anthropogenic discharge) to water nutrients that happen in reservoir bays is of great significance. This paper identified the dominant environmental variables and nutrients' limited types of reservoir bays at storage and discharge periods, and constructed a partial least squares structural equation model (PLS-SEM) to explore the impacts of terrestrial exogenous pollutants. Results showed that in the storage period, water contamination mainly came from residential discharge and soil endogenous release, and the total contribution rate reached 61%. In the discharge period, with the increase of rainfall–runoff erosion, the explanatory ability of land use, topography and landscape pattern to water quality increased, up to 58%. The dominant nutrient limited types of reservoir bays were P limited (35%–47%) and N + P limited (35%–59%) at both stages, N limited situations were less than 20% and generally appeared in the storage period. Whatever the nutrient limited type was, phosphorus always had a higher effect on phytoplankton biomass. In the N limited situation, nitrogen came mainly from soil release (total effect = 0.6) and phosphorus from fertilizer (total effect = 0.22) and soil release (total effect = 0.17). In the P limited situation, all three sources had almost high effects on nitrogen, phosphorus, and phytoplankton biomass. In the N + P limited situation, anthropogenic discharge was the main source of nutrients and the primary threat factor for phytoplankton biomass. The approaches employed in this study could be generalized to other basins and the results were significant for early warning and controlling water eutrophication.

Dynamics of dissolved heavy metals in reservoir bays under different hydrological regulation

Reservoirs play a crucial role in the drinking water supply for solving the uneven distribution of water resources. Reservoir bays, which serve as direct source areas and initial collection areas of pollutants, are crucial areas for drinking water safety. Systematic observations of heavy metal pollution in reservoir bays are required and urgent under different hydrological regulation. Water samples were collected from 65 bays in the Danjiangkou Reservoir which is the water source of the world’s longest trans-basin water diversion project during the storage and flood discharge period from 2015 to 2019. We investigated the temporal and spatial variation in eight dissolved heavy metals, chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), and lead (Pb), and assessed their human health risks. The driving factors of high-risk metals were identified by constructing a structural equation model (SEM). The results showed that the concentrations of heavy metals decreased after 5 years of reservoir operation and varied significantly (p < 0.05) between the storage period and flood discharge period. The concentrations of Cr, Mn, Cd and Pb were higher in the storage period, but the other four metals (Ni, Cu, Zn, As) had the reverse trend. Notably, the As, Mn, and Pb in individual bays exceeded the water quality standard threshold. The human health risk assessment indicated that only As posed a potential carcinogenic risk (1.29E-04) in the flood discharge period. Land use and water physicochemical properties were the main factors affecting As concentrations, and they explained 32% and 44% of the variability of As in the storage and flood discharge periods, respectively. This study provided critical insights into the periodic dynamics and driving factors of the concentration of heavy metals in reservoir bays, and formulated effective management measures for water quality management.

Characteristics of surface water quality and stable isotopes in Bamen Bay watershed, Hainan Province, China.

Bamen Bay is located at the intersection of the Wenjiao River and Wenchang River in Hainan Province (China), where mangroves have been facing a threat of water quality deterioration. Therefore, it is imperative to study the characteristics of the surface water quality on a watershed scale. Water samples were collected three times from 36 monitoring sites from 2015 to 2016. It was found that nitrate was the main inorganic nitrogen form and all the surface water types were alkaline. Meanwhile, aquaculture water had high content of nitrogen, total phosphorus, chlorophyll a (Chl.a), total organic carbon (TOC), and chemical oxygen demand (COD). Significant spatial and temporal variations were found for most parameters. However, stable isotopes of δD and δ18O indicated that river water mainly originated from atmospheric precipitation and experienced strong evaporation. The water chemistry and isotopes of the Bamen Bay, mangroves, and aquaculture water were initially affected by the mixing of fresh water and seawater, followed by evaporation. The river and reservoir water chemistry were mainly controlled by water–rock interactions and cation exchange as deduced from the ionic relationships and Gibbs plots. These interactions involved the dissolution of calcite-, bicarbonate-, carbonate-, and calcium-containing minerals. Oxidized environments (river, reservoir, and Bamen Bay) were conducive for nitrification, while anaerobic conditions (mangrove and aquaculture water) were beneficial to the reduced nitrogen forms.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ ВОЛНОВОГО ДВИЖЕНИЯ ВОДЫ В ВОДОХРАНИЛИЩЕ, ВЫЗВАННОГО ВТОРЖЕНИЕМ В НЕГО ОБВАЛЬНООПОЛЗНЕВОГО МАССИВА

The construction of dams and reservoirs in mountainous and foothill areas poses a number of urgent tasks for designers and researchers related to the wave movement of water in a reservoir with a complex geometric configuration. The collapse of significant masses of rock into the reservoir basin as a result of a landslide phenomenon provokes high surface waves, leading to catastrophic natural disasters in the form of victims and destruction. Designers, construction organizations and maintenance services are required to assess the expected wave increase in water level through the dam crest, as well as the zone and degree of flooding of the area in the reservoir bays and along the river gorge, depending on the geometric, kinematic and dynamic characteristics of potentially possible landslide massifs, mudslides and avalanche flows. In this way, you can predict and then prevent or mitigate the consequences and damage that can cause the formation of destructive waves. In addition to the above problem, this article develops a mathematical model of the wave movement of water in a reservoir, when the movement is caused by the intrusion of a landslide rock mass or a high-speed mudflow into its bowl. The model is the initial boundary value problem of hydrodynamics and hydraulics of gravitational waves. In contrast to previous works, the developed mathematical model takes into account the planned non-prismatic configuration of the reservoir and changes in the water depth in the longitudinal direction of the reservoir. Taking these factors into account significantly clarifies the numerical values of the amplitude of the wave formed, as well as the values of the flow rate, speed and volume of water poured over the dam crest. In the General initial-boundary value problem, the coefficients of the main differential equation are variables that depend on the spatial coordinate. In the General formulation, this creates great difficulties in the analytical solution of the problem and has not been solved by anyone in the whole world to date. In this article was found and applied original and effective substitution, i.e. replacing a variable that in two special cases based on the coefficients from the spatial coordinates that led basic differential equation initial-boundary value problem to the equation with constant coefficients, and thus substantially easier way of solving the initial-boundary value problem. In the above-mentioned special cases, the initial-boundary value problem is solved by strict analytical methods of mathematical physics. For each case, a set of calculation formulas is obtained for calculating the amplitude of the waves formed, as well as for the flow rate and volume of water poured over the dam crest.

Linking water environmental factors and the local watershed landscape to the chlorophyll a concentration in reservoir bays

The frequency of harmful algal blooms caused by eutrophication is increasing globally, posing serious threats to human health and economic development. Reservoir bays, affected by water environment and local watershed landscape, are more prone to eutrophication and algal blooms. The chlorophyll a (Chl a) concentration is an important indicator for the degree of eutrophication and algal bloom. Exploring the complex relationships between water environment and landscape background, and Chl a concentration in the reservoir bays are crucial for ensuring high-quality drinking water from reservoirs. In this study, we monitored Chl a concentrations of 66 bays in Danjiangkou Reservoir and the related water quality parameters (e.g., water temperature, turbidity, nutrients) in waterbodies of these reservoir bays in the storage and discharge periods from 2015 to 2018. Partial least squares-structural equation modeling (PLS-SEM) was used to quantify the relationship between water environmental factors and watershed landscapes, and Chl a concentrations in reservoir bays. The results showed that mean Chl a concentration was higher in storage period than that in discharge period. Two optimal PLS-SEMs explained 66.8% and 53.6% of Chl a concentration variation in the storage and discharge periods, respectively. The net effect of water chemistry on Chl a concentration was more pronounced during the discharge period (total effect = 0.61, 37% of the total effect on Chl a), while the net effect of land-use composition on Chl a concentration was more significant during the storage period (total effect = 0.57, 30% of the total effect on Chl a). The landscape pattern had significant indirect effects on Chl a concentration, especially during the discharge period (indirect effect = −0.31, 19% of the total effect on Chl a). Our results provide valuable information for managers to make rational decisions, thereby contributing to the prevention of eutrophication and algal blooms in reservoir bays.

Comparative Analysis of Chlorophyll a Content in Freshwater and Marine Waterbodies

The data on chlorophyll content in the water and bottom sediments in freshwater Rybinsk Reservoir (Upper Volga) and Aniva Sea Bay (Sea of Okhotsk) are summarized. The average concentration of chlorophyll a in plankton of the reservoir is 23.0 ± 1.9 μg/L, in the bay 0.77 ± 0.06 μg/L, in the bottom sediments 144.2 ± 14.9, and 8.2 ± 0.7 μg/g in the dry sediment, respectively. Correlations between pigment concentrations in the euphotic zone, in the aphotic bottom layer, the whole column of water, and the upper layer of bottom sediments, as well as the relationship of pigments with depth (within 6–100 m) and transparency (from 1 to 18 m), were revealed. It is shown that the general relations for two waterbodies are approximated by nonlinear equations with determination coefficient values (R2) from 0.37 to 0.93. The patterns of the relationship between pigment indices are similar in both waterbodies.

Study on the mechanism of the influence of flood storage at the end of the Three Gorges Reservoir on the phosphorus forms in the sediments of the tributary reservoir bay

This paper studies the influence of the impounding process during flood recession in the TGR on the distribution and rerelease of sediment phosphorus forms in the Xiangxi Bay in 2016. Influenced by the main stream of the Three Gorges Reservoir (TGR) flowing backward during impoundment, the water environmental conditions, sediment grain size and sediment-forming environment of the tributary bays change correspondingly. In this study, it is found that the water temperature (WT), turbidity and oxidation–reduction potential (ORP) of the overlying water in the Xiangxi Bay decrease, while the pH increases after impoundment in the TGR. The backward flow of the main stream containing a large amount of sediments increases the sediment content of the tributary bay, and the difference in sediment particle size between the main stream and tributaries narrows after resedimentation. The phosphorus adsorbed on the sediments increases the total phosphorus (TP) in the sediments of the Xiangxi River to 1.3 times its value before water impoundment. NaOH-P and HCl-P in the Xiangxi River sediments account for 42% and 38% of the TP, respectively, and the contents of the various phosphorus forms are ranked in the following order: NaOH-P > HCl-P > organic phosphorus (OP). After impoundment, HCl-P accounts for 67% of the TP, and the relative contents of the phosphorus forms are ranked as: HCl-P > OP > NaOH-P. Orthophosphate (PO43−-P) in the Xiangxi sediments before and after impoundment acts as a source, and the PO43−-P diffusion flux increases from approximately − 0.0029 to 0.0059 mg (m2 d)−1 before impoundment to 0.0067–0.1071 mg (m2 d)−1 after impoundment, which is mainly due to the increased difference in concentration of PO43−-P [ρ(PO43−-P)] between the sediment interstitial water and overlying water after impoundment. After nutrient recharge of the main stream of the Yangtze River, ρ(PO43−-P) of the overlying water is 3.7 times its value before impoundment, and after the release of NaOH-P in the sediments, ρ(PO43−-P) of the interstitial water is 8.3 times its value before water impoundment. Hence, the risk of nutrient release from the sediments in the Xiangxi Bay increases.

Effect of local watershed landscapes on the nitrogen and phosphorus concentrations in the waterbodies of reservoir bays.

Reservoir bays, which are affected by the reservoir and watershed characteristics, are the initial and most sensitive areas in the evolution process of reservoir water quality. However, the relationship between the watershed characteristics and nitrogen and phosphorus concentrations in reservoir bays is poorly understood. We selected 66 bays from the Danjiangkou Reservoir and sampled twice per year (storage and discharge periods) from 2015 to 2018 to monitor the total nitrogen (TN) and total phosphorus (TP) concentration in the waterbodies of the reservoir bays. Four types of watershed characteristic indices (topographic variables, soil variables, land-use composition, and landscape patterns) around these bays were obtained. We quantified the relationship between the TN and TP concentrations and watershed characteristics in the waterbodies of the reservoir bays using partial least squares regression (PLSR). The results showed that the mean concentrations of TN and TP in the storage period (TN:1.69mg·L-1, TP:0.088mg·L-1) were higher than those in the discharge period (TN:1.22mg·L-1, TP:0.063mg·L-1). The optimal PLSR models explained 67.9% and 82.5% of the TN concentration variability, and 65.4% and 67.2% of the TP concentration variability during the storage and discharge period, respectively. Based on the variable importance in the projection (VIP) values, soil erodibility had significant effects on the TN and TP concentrations. The key factors affecting the TN concentration were the slope gradient, basin relief, topographic wetness index, forest and agricultural land use, whereas the factors controlling the TP concentration were the landscape shape index, edge density, Shannon's diversity index and grass land use, although the TP concentration was also controlled by the patch density and contagion during the storage period, and by mean patch size and largest patch index during the discharge period. This study provides critical insights into sustainable landscape planning and effective reservoir water quality management.

Introducing Nature-Saving Technologies as an Environmental Imperative in the Development of Regions

The article deals with the conservation and restoration of water resources, which is one of the basic factors of regional development. O.V. Inshakov paid attention to this factor highlighting natural resources (land, water, minerals, forests and others) with a certain set of indicators of quantity, structure and quality in the structural and logical model of the development of Volgograd region – 2030. One of the key directions of the civilization development in the 20th century was the search and practical application of a new class of technological and technical solutions in the field of water conservation with the ecological imperative “preserve nature for future generations”. This implies the gradual elimination of their practices of economic activity processes that can lead to irreversible consequences in the ecosystem of the planet. In this context, the issues raised in the article on the study and preservation of natural water quality in the South of Russia are very justified and relevant. As a result of the anthropogenic impact (pollution by industrial, agricultural and municipal effluents), nitrogen, phosphorus, chlorine-containing substances causing fatal mutations and the process of “blooming” of water bodies are concentrated in excess in natural water. Many countries face the problem of “blooming” of water bodies as a result of intensive growth of blue-green algae. The importance of solving this problem is explained by the fact that the toxins entering water from the biological activity of blue-green algae are very dangerous for human health and other organisms. Scientific literature provides examples of human diseases from using water with a significant amount of cyanobacteria blooms. When “blooming” biomass of blue-green algae accumulates in the coastal part and causes technical difficulties in supplying water to the water supply network, the formation of overseas zones and the death of hydrobionts. Existing methods of combating “blooming” have a number of significant drawbacks, for example, mechanical methods require high financial costs, and chemical ones are environmentally unsafe. The article presents the results of the scientific research of the All-Russian Research Institute of Irrigated Agriculture, Volgograd (Volgograd) on using biotechnology for natural water purification. The experiment on introducing Chlorella vulgaris IGF no. C-111 microalgae into the bays of the Volgograd reservoir was carried out on the basis of preliminary compilation of the hydrological characteristics of the reservoir bays, determination of hydrobiological and hydrochemical qualities of water. The aim of the work was to substantiate the technology of introducing Chlorella vulgaris IFR no. C-111 strain into the bays of the Volgograd reservoir and to obtain data confirming the scientific hypothesis – the expediency of using Chlorella vulgaris IFR no. C-111 strain to improve the hydrobiological and hydrochemical composition of natural water.