Low Water Period Research Articles

РАСПРЕДЕЛЕНИЕ МОЛЛЮСКА ИЗ РОДА GYRAULUS (GASTROPODA, PLANORBIDAE) В СРЕДНЕМ ПРИТОКЕ САРАТОВСКОГО ВОДОХРАНИЛИЩА

Background.The Volga basin has been studied unevenly from an ecological point of view. The region of the Upper Volga can be rightly considered the best studied area. While the Lower Volga remains less investigated despite its significant influence on the complex of interrelated social, economic and ecological problems. The most informative assessment for the state of aquatic ecosystems is the state of macrozoobenthos which has various advantages over other approaches, first of all, consisting in species diversity and structure of bottom communities. Freshwater mollusks are one of their numerous groups. In the Volga basin there are representatives of two classes: Gastropoda and Bivalvia. Therefore, the aim of the work is to reveal the peculiarities of Gyraulusalbus distribution in the Samara River and to establish quantitative characteristics in different sections with different ecological conditions. Materials and methods. The study of malacofauna from the source to the river mouth was carried out in the Samara River. A total of 17 stations belonging to different sections were examined. Samples were taken during the low-water period. Near the shore, samples were collected using a hydrobiological scraper (blade length 0.2 m) and a quantitative frame. In deep water using Eckman-Burgey dredge (1/40 m2) with two replicates. The collected material was fixed with 95% ethanol solution, which was replaced with 70% after one week. Statistical processing was performed using Statistica 10.0, Microsoft Excel 2010 and in the R 4.0.5 programming environment and its vegan package. Results.SnailG. albus were recorded by us in sections of the river from its source to its mouth. Specimens of the species were recorded exclusively in the thickets of higher aquatic vegetation. Occurrence of the snail in the river biotopes was low and amounted to only 42% of all investigated stations. This is largely due to the natural rapid flow of water at most sites and hence the small area of macrophytes, which are important for the development of the species. The species prefers low-flow or standing water bodies, so the presence of a small reservoir on the river favored the quantitative indicators of the species in the river, reaching its peak just in this biotope. Morphological variability of the species' shells had no significant differences in the sections of the watercourse. The assessment of the influence of the most significant abiotic and biotic factors on the distribution of G. albus in the Samara River, fallen by the multivariate ordination method revealed three significantly correlated environmental variables: dissolved oxygen concentration, macrophyte area, and salinity level. Conclusions. The results of the study added to the existing gaps in the current composition and distribution of freshwater malacofauna in the region. A number of features of quantitative indicators reflecting features of G. albus habitat in conditions of lotic ecosystems were revealed.

МОРФОЛОГИЧЕСКИЕ ХАРАКТЕРИСТИКИ И ОСОБЕННОСТИ БИОЛОГИИ БАРБУСА СМИТА PUNTIOPLITES PROCTOZYSTRON (BLEEKER, 1865) В ДЕЛЬТЕ РЕКИ МЕКОНГ

Background. Fisheries in the Mekong River are characterized by high pressure and extremely low selectivity towards fishing targets, which greatly complicates the conservation and possible restoration of the region's biodiversity. Relevance. Knowledge of fish population structure and biology is essential for fishery management and rational use of resources; however, the fisheries of the region are predominantly artisanal, for which the information on catches is scarce. This work is aimed at a study of the morphological characteristics of Smith's barb Puntioplites proctozystron (Bleeker, 1865) and the distribution of its quantitative parameters. Methods. The data have been collected from the bottom trawl catches in the Mekong River Delta that were conducted using a beam trawl in the low water and flood periods of 2018–2022. Results. The average abundance and biomass of this species in fresh waters were 8.3±20.8 ind./ha and 114.7±229.4 g/ha, and in the estuary they were 0.6±2.7 ind./ha and 12.1±63.5 g/ha. These quantitative parameters for Smith's barb in the relatively shallow and low-flow Hau River and its estuarine channels were statistically significantly higher than in the rest of the delta estuary system (8.5±22.2 ind./ha and 110.7±248.7 g/ha as compared to 1.4±6.5 ind./ha and 25.0±90.1 g/ha). Examination of morphological characteristics showed a very low variability of traits in mature individuals; the coefficient of variation was less than 10 %. Conclusion. The obtained results indicate the absence of sexual dimorphism and different morphotypes in the population, provide the ground for minimum landing size recommendations, and can serve as a foundation for the further population research of this species.

Trophic resources use pathways between two coexisting freshwater shrimp (Palaemon argentinus and Macrobrachium borellii)

Context A better understanding of the use of different trophic pathways as a mechanism for adjusting interactions between coexisting omnivorous decapod species may help define the extent of their influence on energy flows in freshwater ecosystems. Aims Analyse the patterns of use of the benthic and littoral pathways by Macrobrachium borellii and Palaemon argentinus during a hydrological cycle in lakes of the middle Paraná River. Methods The study was conducted during one high-water (HW) and one low-water (LW) period in three lakes permanently connected to the middle Paraná River. We calculated the relative contributions of potential basal resources (benthic and littoral) to each species for each lake and hydrological period using mixing models. Key results It was observed that M. borellii feeds more in the littoral pathway and P. argentinus in the benthic pathway, especially in low water where we observed that the partitioning of resources was more pronounced. Conclusion The more aggessive species, M. borelli, during HW period quickly utilises the bioavailable material. Trophic dynamics and resource use are part of the coexistence mechanisms of both decapod species. Implications This may have important consequences in the aquatic trophic webs in which these organisms participate, because when segregating the use of resources, they intervene in different energetic pathways.

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.

Ecological and economic significance of the Middle Don sand arenas

The research purpose is a comprehensive assessment of the Middle part of the Don river sand massifs soil and hydrological conditions. The research objects are the sandy massifs of the Middle Don on an area of 527 thousand hectares. The sand arenas water balance dynamics for the period from November to March and for the period from April to October has been revealed. It has been established that atmospheric precipitation is the main source of river water supply. The basis of river systems flood filling are clay soils that form an intra-soil runoff. The low water period level is supported by sandy soils. A decrease in the density of plant formations contributes to an increase in groundwater supply. The total underground runoff reaches 599 million m3 from the sandy massifs of the Middle Don. The volume and dynamics of the moisture movement in the soil depend on the system of sandy areas use. Therefore, the load on sandy arenas should be regulated. Pasture farming should remain the dominant form of sand use. An effective method of sandy arenas afforestation is the planting of pine plantations according to the savanna type.

Elevating the logistics resilience of the Rhine-Alpine Corridor with the help of innovative vessel and cargo handling concepts

The Rhine-Alpine Corridor connects 70 million inhabitants and is home to Europe's biggest sea and inland ports and the Rhine as its most important waterway. Recent developments and events, such as the extreme low-water period in 2018 and the aggravating barge congestion in the seaports, have deteriorated the trust in the inland waterway network capacity of the Corridor. Hence, the availability and trustworthiness of IWT as a reliable transport mode is diminishing – possibly endangering the ambitious modal shift goals. In order to elevate logistics resilience, the challenges of low-water navigability and barge congestion are to be tackled with new solutions from naval architecture and marine engineering, i. e. innovative vessel concepts to ensure low-water navigability on the Rhine and a modular mobile terminal for additional transhipment capacity in the ports. The resulting concepts will be further examined regarding their operational verification and economic validation before being developed and deployed in their real settings.

Spatio-seasonal patterns of the impact of wastewater treatment plant effluents on antibiotic resistance in river sediments

There is a growing concern about the risk of antibiotic resistance emergence and dissemination in the environment. Here, we evaluated the spatio-seasonal patterns of the impact of wastewater treatment plant (WWTP) effluents on antibiotic resistance in river sediments. To this purpose, sediment samples were collected in three river basins affected by WWTP effluents in wet (high-water period) and dry (low-water period) hydrological conditions at three locations: (i) upstream the WWTPs; (ii) WWTP effluent discharge points (effluent outfall); and (iii) downstream the WWTPs (500 m downriver from the effluent outfall). The absolute and relative abundances of 9 antibiotic resistance genes (ARGs), 3 mobile genetic element (MGE) genes, and 4 metal resistance genes (MRGs) were quantified in sediment samples, as well as a variety of physicochemical parameters, metal contents, and antibiotic concentrations in both sediment and water samples. In sediments, significantly higher relative abundances of most genes were observed in downstream vs. upstream sampling points. Seasonal changes (higher values in low-water vs. high-water period) were observed for both ARG absolute and relative abundances in sediment samples. Chemical data revealed the contribution of effluents from WWTPs as a source of antibiotic and metal contamination in river ecosystems. The observed positive correlations between ARG and MGE genes relative abundances point out to the role of horizontal gene transfer in antibiotic resistance dissemination. Monitoring plans that take into consideration spatio-temporal patterns must be implemented to properly assess the environmental fate of WWTP-related emerging contaminants in river ecosystems.

Прогнозирование притока воды в Цимлянское водохранилище

Methods for short-, medium-, and long-term forecasting of water inflow into the Tsimlyansk Reservoir have been developed. The methods are based on climatic and anthropogenic changes in the conditions for the inflow formation over the past decades. Their verification showed satisfactory and good results. Average daily water inflow discharges are predicted throughout the year with a lead time of 1 to 10 days based on the hydrograph extrapolation method. The resulting forecasts are used to predict the volume of water inflow for 5 and 10 days. The monthly inflow for the low-water period of the year from June to February of the next year is predicted according to its dependence on the inflow for the previous month. In long-term forecasting of the volume of the water inflow into the reservoir for the second quarter, the forecast of the inflow layer for the spring flood period and the precipitation layer averaged over the catchment area for March obtained by V. D. Komarov's method is taken into account. The proposed system of methods provides the reasonable use of water resources of the Tsimlyansk Reservoir in modern conditions. Keywords: reservoir, inflow, water discharge, volume, forecast, lead time, error, accuracy

Current State of Flooding and Water Quality of Nokoue Lake in Benin (Ouest Africa)

A thorough literature review was conducted in order to discover the previous studies that have been done in relation to the problems of flooding and water pollution of Nokoue lake (Benin, West Africa), to identify the limitations of these previous studies, to draw lessons in order to propose how to overcome them. This bibliographic synthesis has shown that previous studies related to the flooding issue have focused on the dynamics of understanding the genesis of flooding. These studies range from the oldest conducted in 1979 to the most recent conducted in 2016. The major results of these studies in relation to floods are hydrodynamic techniques allowing to evaluate in a punctual way the hydrological regime of the Nokoue lake. In other words, they are solutions allowing to reconstitute the floods generated by the river waters. It appeared that these results of flood reconstitution are difficult to generalize because of the complexity of the hydrographic network of Nokoue lake. The hydrodynamics of Nokoue lake is influenced differently by its main water tributaries (the Sô River, the Ouémé River, the Porto Novo Lagoon and the Atlantic Ocean). Therefore, a decision-making issue on planning and flood management must be motivated by a decision support tool. It is moreover recommended in these studies the resumption of the process of hydraulic techniques periodically during the period of high water in order to take advantage of the hydrological behavior of Nokoue lake in terms of overflow which are at the origin of the floods. The need for innovative decision-making solutions on flood planning and management in order to reduce disasters is still a priority for decision-makers. These innovative solutions are undoubtedly the flood forecasting. On the water quality of Nokoue lake, the oldest study conducted dates back to 1987 and the most recent one in 2018. In these studies, water quality is evaluated in two seasons: the low water season (December to mid-May) and the high-water season. It was found that the salinity of the lake increased significantly with an average of 16 ppt during the low water period while during the high-water period, freshwater inflows from the tributaries invaded the lake and prevented water from the Atlantic Ocean from entering. The concentrations of inorganic nutrients in the lake increase from low water to high water. However, the quantification to date of nutrient loads from external sources as well as internal sources to the lake have not been quantified. This implies that further research on the water quality of the lake could be conducted. Prevention actions should consider a predictive monitoring of the water quality index of Nokoue lake.

Temporal changes in limno-morphometric characteristics in a floodplain lake within Cross River ecosystem during low water period

Iyieke Lake is one of the floodplain lakes within the middle reaches of the Cross River, it is a major foraging and breeding site of several fish species. It is not directly connected to any river, so the water level depends on seasonal inundation by the Cross River. With gradual changes in precipitation and consequent alteration in flooding pattern, and increased agricultural activities around the lake, there are indications of steady annual decline in water level and quality, and lake area. In order to understand the effect of these changes on the aquatic biota, the morphology and some limnological parameters of the lake were studied during low water period (March-May) in 2005, 2011 and 2019 at interval of 6.5 years. Water samples were collected from the lake and the limno-morphological parameters measured at the littoral and limnetic zones of the lake following standard procedures. The results showed that monthly rainfall was significantly (p<0.05) lower in 2019 compared to 2005 and 2011, while minimum and maximum temperature trended conversely (p<0.05). The mean total dissolved solids (TDS) increased from 13.00mg/l in 2005 to 39.33mg/l in 2019 and conductivity trended the same. Mean nitrate (0.92mg/l) and phosphate (1.78mg/l) were higher in 2019 compared to 2005 and 2011. Contrarily, transparency decreased from 0.45m in 2005 to 0.19m in 2019. Similarly, mean dissolved oxygen (3.80mg/l), maximum length (443.20m) and width (314.50m) declined significantly toward 2019 (p<0.05). Lake length, transparency, conductivity and TDS that were seemingly good predictors of water deterioration could be useful in modelling, which is vital in conserving the biodiversity of the Cross River floodplain ecosystem.

Improving measures to improve the hydrological regime of the Kuban water basin on the example of the Pshish River

The article discusses ways to improve the hydrological regime of the Pshish River in the Kuban water basin. An effective way to reduce damage from floods and floods is to use simulation mathematical models of floods, taking into account joint work, so in the context of a progressive shortage of fresh water, especially in southern Russia, studies of the water resources of the Kuban River basin, especially medium and small rivers, are of particular relevance. Hydrologically, the Pshish River and the Krasnodar Reservoir remain poorly studied, so when the time of flood comes, the level of the water's edge increases significantly, since they will be active feeding boundaries for groundwater in the protected area, and at low low water periods they are drains. When the water levels in the reservoir are less than 29 m, and this is the time of the period of low water level in the river. Pshish in the area of the low-pressure earth dam, and the impact of the water level on the protected area is significantly reduced. The coastline of the Krasnodar reservoir recedes from the transverse low-pressure dam far to the northwest, exposing the previously flooded river bed. Taking into account the emerging database on the real technical condition of hydraulic structures of the flood control system of the Lower Kuban, obtained using non-destructive methods and satellite technologies. Simulation mathematical modeling makes it possible to optimize the operating mode of spillways of the flood control system of the Lower Kuban, namely for a low-pressure earthen dam for summer and winter floods, for the conditions for the occurrence of congestion and the occurrence of surge phenomena on the river. All this makes it possible to develop specific anti-flood measures before, during and after the passage of the flood. The effectiveness of engineering flood protection largely depends on the technical condition of the flood control system in the Lower Kuban. Simulation mathematical modeling allows you to determine those parts of the system that require priority investment.

FEATURES OF THE CONTENT OF MICROELEMENTS MO, MN, ZN IN THE GLACIER WATER OF THE CENTRAL CAUCASUS FOR THE PERIOD 2019-2021

The results of a study of the content of the main microelements (Mo, Mn, Zn) in the waters of three glacial rivers of the Central Caucasus with glacial feeding during winter low water periods and summer rain floods are presented. It is shown that in the dynamics of their concentrations there is a downward trend from the zone of the upper reaches to the zone of entry into the low-mountain zone and the features of the level of pollution inherent in each river in the upper reaches. The studies were carried out over a three-year period — from 2019 to 2021. The main water pollutants in the rivers Malka, Baksan, Terek have been identified. The concentrations of trace elements in the water of mountain rivers during the main phases of the hydrological regime are presented. A comparative interannual analysis was carried out.

Berth planning and real-time disruption recovery: a simulation study for a tidal port

With the increasing volume of container freight transport, future port planning is crucial. Simulation models provide a means to gain insight in the effects of terminal expansions. Detailed simulations incorporate berth allocation: assigning vessels a time and location at the quay wall, where the vessel is loaded and unloaded. This article develops decision models for both offline preliminary berth planning and for online recovery of this plan during simulation. First, we develop an optimisation-based approach that incorporates realistic aspects—cyclic vessel arrivals, tidal windows, and minimisation of vessel draught during low water periods—in order to develop a cyclic baseline berth allocation plan. The approach can proactively incorporate slack for increased robustness. Exploiting a constraint-based solver, we can obtain optimal or satisficing solutions for a year’s operation of a large port. The resulting preliminary berth plan is used as a basis for the arrival times. However, disruptions can occur, such as vessel arrival and loading times varying from the planned. Hence, second, we develop a real-time disruption management decision model. This multi-level heuristic approach reacts to disruptions while minimising perturbation of the original berth plan. Computational experiments with a high-resolution simulator show our recovery approach finds good solutions until a tipping point of disturbance. Results also show that when the expected occupation of a terminal is higher, strengthening robustness of the preliminary plan has increased importance. The approach described in the article is implemented for a major European inland tidal port, forming the basis of a simulation-based decision support tool for operational planning and exploring port expansion options.

Remote Monitoring of NH3-N Content in Small-Sized Inland Waterbody Based on Low and Medium Resolution Multi-Source Remote Sensing Image Fusion

In applying quantitative remote sensing in water quality monitoring for small inland rivers, the time-frequency of monitoring dramatically impacts the accuracy of time-spatial changes estimates of the water quality parameters. Due to the limitation of satellite sensor design and the influence of atmospheric conditions, the number of spatiotemporal dynamic monitoring images of water quality parameters is insufficient. Meanwhile, MODIS and other high temporal resolution images’ spatial resolution is too low to effectively extract small inland river boundaries. To solve the problem, many researchers used Spatio-temporal fusion models in multisource data remote sensing monitoring of ground features. The wildly used Spatio-temporal fusion models, such as FSDAF (flexible spatial-temporal data fusion), have poor performance in heterogeneous changes of ground objects. We proposed a spatiotemporal fusion algorithm SR-FSDAF (Super-resolution based flexible spatiotemporal data fusion) to solve the problem. Based on the FSDAF, it added ESPCN to reconstruct the spatial change prediction image, so as to obtain better prediction results for heterogeneous changes. Both qualitative and quantitative evaluation results showed that our fusion algorithm obtained better results. We compared the band sensitivity of the images before and after fusion to find out that the sensitive band combination of NH3-N has not changed, which proved that the fusion method can be used to improve the time-frequency of NH3-N inversion. After the fusion, we compared the accuracy of linear regression and random forest inversion models and selected the random forest model with better accuracy to predict the NH3-N concentration. The inversion accuracy of NH3-N was as follows: the R2 was 0.75, the MAPE was 23.7% and the RMSE was 0.15. The overall concentration change trend of NH3-N in the study area was high-water period < water-stable period < low water period. NH3-N pollution was serious in some reaches.

Characterization of a West African Coastal Lagoon System: Case of Lake Nokoué with Its Inlet (Cotonou, South Benin)

The purpose of this work was to investigate the physical and chemical dynamics of Lake Nokoué for its efficient management. For this purpose, two sampling campaigns per month from five stations (North, South, Central, East and West) were conducted for a period of one year (November 2020 to November 2021). Physic and chemical parameters (temperature, salinity, depth, water transparency, pH, dissolved oxygen and total dissolved solids) were measured and wet substrate samples were collected to study the granulometry. Data analysis revealed that Lake Nokoué is mainly affected by two regimes: flooding and low water. Flooding, which is not directly related to rainfall, did not begin until one month after the major rainy season in June. The sources that contributed to the flooding of Lake Nokoué were the freshwater tributaries coming mainly from the Ouèmé River and the flow of the Sô River from August to November. The inflow of fresh water contributed to the decrease in salinity and transparency of the lake from the east to the south. During the low water period (from December to July), Lake Nokoué is characterized by an increase in salinity and transparency from the south to the northeast due to the massive intrusion of sea water into the lake. The highest dissolved oxygen levels are observed in the south and center (5.92 ± 0.46 mg/L) while it varies greatly in the north and west (Eichhornia crassipes concentration zone) during flooding. The average annual depth of Lake Nokoué was 1.47 ± 0.66 m with an average annual pH of 6.85 ± 0.56.

Plastic capture methods in the water bodies, a review of world experience

Over the past twenty years, the plastic pollution problem in the water bodies has reached an alarming scale. The easy-to-use, light, waterproof material has the significant drawback, it is the very long decomposition period, which has led to the 368 million tons of plastic accumulation over the past 70 years, and the accumulation continues. Plastic environmental pollution is the urgent problem for the water bodies in Ukraine too. The source of plastic entering water bodies is primarily temporary waste landfills from which plastic is washed into rivers and lakes during rains, by wind and by flood. The rivers carry plastic throughout the river floodplain, polluting riverbeds and banks during the flood. In the work, the analysis of the world experience in the area of the plastic capture devices and the possibility to use these devices for the mountain rivers conditions in Ukraine was assessed. The peculiarities of the hydrological regime of the mountain rivers are the transportation of plastic during floods, significant water levels fluctuations, the danger for people being in the riverbed during the flood, high water speeds up to the 5 m/s, the large amount of litter, which in consists of the plastic, tree trunks, branches and other large debris. It was assessed the booms, trash traps and trash racks for catching litter in water outlets and temporary streams. Plastic collecting facilities such as floating boats, catamarans, and robots were not assessed, because their use during the flood is dangerous, and the small water depths in the rivers do not allow to use them effectively during the low water period. Devices for plastic capture for the mountain rivers should be autonomous, strong, have the big litter capacity, be ecological friendly, able to work with rapid water level change and under high water speed. Analysis of the existing devices shows that these requirements will be met by expensive segment. At the same time, it is known that the plastic capture in the water bodies costs in 10 times higher than the cost of collecting and sorting plastic in the populated areas. So, to solve the problem of plastic pollution in the water bodies by the expensive devices is not right way. First of all, in order to reduce plastic pollution in water bodies, it is necessary to create conditions to prevent plastic to get into the rivers, namely: voluntary limitation of the plastic usage, manufacture responsibility for the use of recyclable plastic, active informing society about the plastic harm to the environment and the necessity to collect and sort it.

Effect of climate change on earthworks of infrastructure: statistical evaluation of the cause of dike pavement cracks

The flood protection embankments of Hungary and Europe face numerous challenges. Some dike bases were constructed more than 200 years ago; since then, they have been elevated and extended. Because of these iterative adaptations, the dikes bear many construction errors, which can trigger failures and slides. Due to climate change, droughts and low-water periods of the rivers in central Europe are becoming more frequent. As a result of these effects, the water balance of the dikes can alter and desiccate in the long term. The most staggering fissures appeared on dikes built from clays susceptible to volume change. The General Directorate of Water Management ordered a comprehensive survey of dike pavement cracks in Hungary. This was one of the most extensive surveys of such kind. Hungary has some 4400 km of primary flood protection embankments, out of which 1250 km is paved. There are multiple reasons why the pavement of an embankment can crack. The main features of crack patterns related to clays with shrink-swell potential are identified. The results of international studies and the present survey are synthesised. The main objective of this paper is to draw a correlation between drought (aridity) zones, plasticity index of the soil samples, and crack thickness.

Characteristics of (micro)plastic transport in the upper reaches of the Yangtze River

Many studies focus on the transport of plastic from rivers to oceans while little attention was paid to the plastic transport in the upper reaches of rivers. Transport process of plastic from upstream to downstream in the whole river basin scale is still poorly understood. In this work, five sections in the upper reaches of the Yangtze River were investigated to characterize the features of plastic transport. Plastic abundance and flux were 293 to 156,667 n/m3 and 1.2 to 34,711 g/s, respectively. Plastic flux peaked at or right after the first flood peak in most sections, but plastic abundance was the highest in the normal or low water period. The first flood peak caused a temporary rise of plastic flux that last a short duration. Transport of plastic was not limited to water surface, and the Three Gorges Dam showed a peak elimination effect on plastic transport. Annual discharge of plastic was 1392 to 9532 tons and 6.2 × 1014 to 175 × 1014 particles at different sections. An increasing trend was observed for both plastic mass and quantity going downstream. Results showed that river plastic flux is highly variable and influenced by the dam, which should be considered in future to develop better monitoring strategies and to further improve the model.

Hydrological Regime and Fish Predation Regulate the Zooplankton Community Size Structure in a Tropical Floodplain Lake

Floodplain ecosystems are characterised by alternating flood and drought periods that can affect the structure of the aquatic community. Dynamic changes in the hydrological regimes from flooding to dry periods influence the migration and dispersal of aquatic fauna and the exchange of particulate matter and nutrients. Riverine floodplains are among the most productive ecosystems; however, increasing pressure from anthropogenic activities has altered the hydrological regimes, threatening aquatic biodiversity. In this study, we examined the temporal patterns of zooplankton community size structure and fish density during three distinct hydrological events in a tropical floodplain lake, Lake Tempe, Indonesia. We included fish density data and three contrasting hydrological conditions, moderate-, high-, and low-water periods, as the environmental factors regulating zooplankton community structure. In high- and low-water conditions, the ecosystem heterogeneity was characterised by high chlorophyll-a, total nitrogen, and total phosphorus concentrations; high fish density; and high zooplankton abundance and biomass. During the early flood period, the ecosystem was characterised by lower concentrations of trophic indicators and significant decreases in zooplankton abundance and biomass, as well as decreased fish density. While there was no clear association between hydrological conditions and zooplankton size structure, our findings indicate that fish predation probably suppressed zooplankton size diversity in Lake Tempe, shown by the dominant contribution of small-sized zooplankton towards total abundance and biomass under all hydrological conditions. Our results indicate that the patterns of environmental variables, zooplankton community, and fish density are affected by hydrological conditions, highlighting the role of water level fluctuation as the driving factor for zooplankton community structure. Our results also indicated that fish predation led to the development of a small-sized population of zooplankton in Lake Tempe.

Riverbed morphology and hydrodynamics in the confluence of complex mega rivers - A study in the Branco and Negro rivers, Amazon basin

The study of the morphology and hydrodynamics of large rivers has advanced in recent decades. Nonetheless, there are a few studies with surveyed data carried out at the confluences of the mega rivers (Q > 17,000 m³s−1), especially those from the Amazon basin. The Negro River is the main river in the northwestern Amazon and is considered the sixth-largest in the world in terms of water discharge, has a complex multichannel pattern and a peculiar geological configuration. This article aims at analyzing the bed morphology and hydrological processes in the confluence region between the Branco and Negro rivers. Field surveys with echo-sounding and Acoustic Doppler Current Profiler were carried out over an area of 31 km2 during the low water period of 2021 year. The results of this survey made it possible to identify the main morphological characteristics of the riverbed in the confluence hydrodynamic zone between Branco and Negro River, as well as the dynamics of the velocity, streamflow, and transport of suspended sediment of these important northwestern Amazonian rivers. Analysis of bed morphology and their neotectonic control are also discussed. These results presented in this work contribute to expanding the knowledge about the confluence of large tropical rivers with significant bed discordance and differences in the density of flows.