Hydrological Seasons Research Articles

Tracing nitrogen sources and transformation characteristics in a large basin with spatially heterogeneous pollution distribution

This study used dual stable isotopes to examine nitrate sources and geographical distribution in the Liao River Basin (LRB), one of China's seven major river basins. During a normal hydrological season in April 2021, water samples were taken from the main streams of the Liao River (MLR), Shuangtaizi River (STR), Hun River (HR), Taizi River (TZR), and Daliao River (DLR). Monitoring results indicated that 93% of the water samples had a total nitrogen level exceeding the Class IV limit (1.5 mg/L) of the ‘Environmental Quality Standards (EQS) for surface water’, indicating a serious nitrogen pollution status. 71.3% of the total nitrogen on average was in the form of nitrate. The scatterplots of δD-H2O and δ18O-H2O showed that water in TZR and DLR were mainly affected by precipitation, while MLR, STR and HR were additionally impacted by evaporation and groundwater. The overall δ15N and δ18O of NO3− varied from 7.7‰ to 17.9‰ and 0.6‰–11.2‰, respectively. The correlations between δ15N-NO3- and δ18O-NO3-, along with attribution results from the Bayesian isotopic mixing model, indicated a predominant role of manure/sewage (MS) pollution in affecting river nitrate, accounting for 78% of total nitrate in MLR and 72% in DLR. A positive correlation between δ15N-NO3- and δ18O-NO3- in MLR indicated the occurrence of denitrification process. Overall, attribution results showed that the primary nitrate sources varied in different river systems within such a large basin, mainly due to spatially varied land use and human activities. Tailored nitrogen management strategies should be implemented to address the main anthropogenic pressures.

Influence of hydrological variability and life history strategy on riverine fish assemblages in the Australian wet‐dry tropics

AbstractRiverine fish assemblages are strongly influenced by attributes of the flow regime. Tropical savannah river systems have distinct and predictable hydrologic seasonality, reflecting the wet‐dry climate, but can vary substantially in terms of dry season flow permanency and wet season flow‐pulse characteristics. Understanding how flow permanence and variability influence fish assemblages, and whether these factors can be used to predict responses to future hydrological change, are key knowledge gaps that impede effective management. We examined the influence of hydrological variability on the structure and diversity of freshwater fish assemblages across rivers of the wet‐dry tropics of northern Australia. We found distinct fish assemblages that varied predictably across three hydrological river types: Intermittent, Perennial Stable and Perennial Flashy flow regimes. This distinction emerged despite a common species pool across the region. Species richness was greatest in rivers with Perennial Stable flow regimes, whereas beta‐diversity was greatest in Intermittent rivers. However, life history strategies of constituent species were generally poor predictors of species abundances within each hydrological river type. The distinct fish assemblages evident among hydrological classes may provide some cautious ability to both predict potential fish assemblage changes with future hydrological changes (e.g. if perennial streams became more flashy or intermittent), and to predict fish assemblages expected in unsampled rivers with particular hydrological characteristics. Our findings provide further support for the importance of maintaining regional flow‐habitat heterogeneity and the connectivity between hydrological river types, and their essential role for conserving tropical fish species diversity into an uncertain hydrological future.

Features of the Distribution of Black Sea Ichthyoplankton in Conditions of Activation of Atmospheric Processes in the Summer Hydrological Season of 2021

Features of the Distribution of Black Sea Ichthyoplankton in Conditions of Activation of Atmospheric Processes in the Summer Hydrological Season of 2021

Water level regime variation is a crucial driver for taxonomic, functional, and phylogenetic diversity in seasonally flooded tropical forests

Floodplains contribute significantly to terrestrial ecosystem service provision but are also among the most vulnerable and degraded ecosystems worldwide. Heterogeneity in floodplain properties arises from variations in river-specific flood regimes, watershed characteristics, and valley morphology, influencing seasonally flooded forests' taxonomic, functional, and phylogenetic diversity. This study addresses persisting knowledge gaps in floodplain ecology, focusing on the seasonally dry tropics. We explore the relationships between flood regime, environmental conditions, vegetation composition, functional and phylogenetic diversity, and the impact of environmental variables on above-ground biomass (AGB) and ecological strategies. The study spans six rivers in southeastern Brazil's main river basins: Rio Grande and São Francisco. We identified five eco-units in each floodplain based on flooding regimes and surveyed six plots per eco-unit. We measured trees with DBH > 5 cm and collected functional traits, along with detailed soil, climate, and water level data. We calculated plot-level floristic composition, taxonomic, functional, and phylogenetic diversity, wood density, and AGB. Functional and phylogenetic dissimilarity were analyzed, and the effects of climate, soil, and hydrological variables were quantified using generalized linear mixed models. We show how flood frequency and duration affect floristic composition across the floodplains. Taxonomic and phylogenetic diversity responded to climate, soil, and hydrological variables, while functional diversity responded primarily to hydrological variables, emphasizing the role of environmental filtering. Hydrological seasonality, soil fertility, and flood regime emerged as key factors shaping community structure and ecological strategies in the studied seasonally flooded tropical forests. Plot-level AGB responded to phosphorus but not to climate or hydrological variables. The study also highlights functional and phylogenetic dissimilarities among eco-units and basins, indicating potential climate change impacts.

Factors of macrozoobenthos formation in low-mountain lakes of the Russian Altai

The current state of macrozoobenthos of six low-mountain lakes of the Russian Altai was studied in different hydrological seasons (May, July, September) 2022: Aya (Aiskoe), Beloe, Kireevo, Kolyvanskoe, Koksha, and Svetloe. The aim of the article is to study the factors of formation of benthic invertebrate communities of foothill lakes of the Russian Altai. In total 156 species from 9 classes of invertebrates were identified in the zoobenthos of the studied lakes, the highest percentage of occurrence was recorded for chironomids and oligochaetes. According to the taxonomic composition of macrozoobenthos, most of the studied lakes of the Russian Altai (Aya, Beloe, Kireevo and Kolyvanskoe) were close to flatland lakes. Two lakes (Koksha and Svetloe) combined characteristics of both flatland and highland lakes. The abundance and biomass of zoobenthos in lakes Aya and Kireevo corresponded to the oligotrophic level, in lakes Beloe and Kolyvanskoe to the mesotrophic level, and in lakes Koksha and Svetloye to the eutrophic level. The structural characteristics of macroinvertebrates are indicators of the state of lake ecosystems. Therefore, in order to maintain the health of lake ecosystems, it is important to determine the limiting factors for macroinvertebrate community composition and structure. The influence of environmental factors on the composition and structure of macrozoobenthos of foothill lakes of the Russian Altai was studied. The relationship of 10 main indicators of zoobenthos structure with 30 hydro physical and hydrochemical indicators was analyzed. Using principal component analysis, multiple regression method, correlation and canonical analyses, it was revealed that the greatest influence on the development of benthic invertebrate communities in the studied lakes of the Russian Altai was exerted by nutrients, permanganate oxidability and soil character and water temperature.

Influence of the hydrological regime of lake buyo on fish community of three floodplains in the Tai national park (southwestern Côte d’Ivoire)

Floodplains play an important role in the ecological functioning of the areas on which they depend. These plains are also of socio-economic interest to the local population, particularly in terms of fishing activities. The fish fauna of three Lake Buyo floodplains (Néma, Libériakôbro and Gah) was studied in relation to the lake's hydrological regime. The aim of this study was to evaluate the influence of the hydrological seasons of Lake Buyo on the structure of the fauna considered. Sampling of fish community was carried out monthly during an annual cycle using experimental fishing. The structure of the fish community was analyzed by determining taxonomic composition, taxon abundances (Ar) and the Shannon-Weaver diversity (H') and Pielou equitability (E) index. Temporal dynamics of the studied parameters were analyzed according to three hydrological seasons: flood season, high water season and recession season. Results showed that total specific richness of ichthyofauna of the studied plains was 38 species, and the richness observed at the different hydrological seasons varied significantly (p < 0.05). The Cyprinidae family was dominant in the abundances recorded at all seasons (48.34% ≤ Ar ≤ 85.5%). It should be noted that the studied ichthyofauna exhibited relatively low diversity and equitability with reference to diversity index (1.42 ≤ H' ≤ 1.46 and 0.28≤ E ≤ 0.29).

Effect of hydrological variability on suspended sediment load at a river junction: a case study

Abstract Confluences act as crucial intersection in a fluvial system as they regulate the flow, sediment, and geomorphological stability. Two of the natural occurrences that have an effect on hydro-morphological processes that characterize the channel are sediment movement and stream discharge. However, assessments of suspended sediment distribution patterns across channel confluences and functions of tributaries on sediment transfer in downstream streams are still inadequately explored. To fulfil this, a year-long field investigation was conducted around river confluence at various time scales during the hydrological season. The bathymetry of the confluence was performed using digital echo-sounding equipment, electro-magnetic current meter, and differential global positioning equipment. This study uses in situ measurement and empirical techniques to quantify the spatiotemporal distribution of suspended sediment particles. Furthermore, Yang's formula was used to analyze the sediment concentration, and several statistical standards were employed to establish a differentiation between predicted and observed data. The results illustrated that a good agreement has been achieved among the calculated and measured statistics based on the correlation coefficient value. According to the findings, 8% fewer errors in the quantification of suspended sediment were induced in the tributary than in the main river because of the very low flow of the tributary. The present ramifications can help increase our database and understanding of the dynamics of major river confluences.

Method for identification of hydrological seasons in the semi-arid Caatinga biome, Brazil

ABSTRACT Semi-arid regions are strongly dependent on the rainfall regime. Yet season identification is still ambiguous and clear definitions are lacking regarding which variables and criteria should be used. The objective of this work is to establish a method for hydrological season partitioning in the semi-arid Caatinga biome in northeastern Brazil considering precipitation, soil moisture and vegetation. The following four periods were employed for this purpose: (i) dry–rainy transition, (ii) rainy season, (iii) rainy–dry transition and (iv) dry season. The method was applied to the Aiuaba experimental basin (AEB) from 2003 to 2022. We observed a large inter-annual variability in the duration of seasons and a tendency for the rainy–dry transition season to increase, facts that may indicate changes in the hydrological regime of the region. This novel combination of precipitation, soil moisture, and vegetation data for identification of hydrological seasons within the Caatinga biome allows a detailed seasonal hydrological behaviour analysis.

Ichthyoplankton in the northern part of the Black Sea under prolongation of summer hydrological season in 2020

The species diversity and spatial distribution of ichthyoplankton in the shelf and deep-sea waters of the northern half of the Black Sea near the Crimean Peninsula and the shores of the Caucasus under the conditions of prolongation of the summer hydrological season 2020 for September–October are presented. The high temperatures of the upper layer of the sea, peculiar of the summer spawning season, caused a continuation of productive spawning of warm-water fish. Eggs and larvae of 19 species from 12 families were identified in the ichthyoplankton. The maximum number of eggs was 302 ind./m2, and larvae — 58 ind./m2. Eggs and larvae of the mass commercial species Engraulis encrasicolus (L., 1758) dominated, whose share in the total population was 92.9 and 84.2% respectively. The highest abundance of ichthyoplankton corresponded to areas with minimal dynamic activity and maximum warming within the limits of coastal-shelf quasi-stationary anticyclonic vortices characteristic of the summer hydrological season.

Influence of surface mining on seasonal hydrology response to storms across eastern Kentucky, USA

ABSTRACT Mountain Top Removal and Valley Fill (MTR/VF) practices have drastically altered the surface cover, topography and hydrology of many watersheds across the Appalachian region of the US. These practices strip the bedrock from the ridges and peaks of watersheds, before removing the coal seams and depositing the waste fill into adjacent valleys. Existing research has generated conflicting outcomes as to the resulting hydrological impacts in response to storms. This creates potential issues for subsequent mitigation projects seeking to recreate prior hydrological conditions and riparian ecosystems. Our study focused on the potential influence of MTR/VF practices for a series of mined and unmined watersheds across the Eastern Coalfield of Kentucky. We analyzed rainfall-runoff response, focusing on how quickly rainfall was converted to quickflow and how much water left the catchment during storms for the 2022 water year. Lag times were shortened for the mined watersheds while quickflow coefficients reduced when vegetation cover increased. Valley fill-in mined watersheds also appears to create a delayed secondary release of quickflow from headwater locations during more extreme storms. These findings may assist future reclamation/mitigation practices for mined watersheds across Eastern Kentucky aiming to correctly recreate the hydrologic conditions that resemble those of unmined landscapes.

Mid‐Holocene rainfall seasonality and ENSO dynamics over the south‐western Pacific

AbstractEl Niño–Southern Oscillation dynamics affect global weather patterns, with regionally diverse hydrological responses posing critical societal challenges. The lack of seasonally resolved hydrological proxy reconstructions beyond the observational era limits our understanding of boundary conditions that drive and/or adjust El Niño–Southern Oscillation variability. Detailed reconstructions of past El Niño–Southern Oscillation dynamics can help modelling efforts, highlight impacts on disparate ecosystems and link to extreme events that affect populations from the tropics to high latitudes. Here, mid‐Holocene El Niño–Southern Oscillation and hydrological changes are reconstructed in the south‐west Pacific using a stalagmite from Niue Island, which represents the period 6.4–5.4 ka BP. Stable oxygen and carbon isotope ratios, trace elements and greyscale data from a U/Th‐dated and layer counted stalagmite profile are combined to infer changes in local hydrology at sub‐annual to multi‐decadal timescales. Principal component analysis reveals seasonal‐scale hydrological changes expressed as variations in stalagmite growth patterns and geochemical characteristics. Higher levels of host rock‐derived elements (Sr/Ca and U/Ca) and higher δ18O and δ13C values are observed in dark, dense calcite laminae deposited during the dry season, whereas during the wet season, higher concentrations of soil‐derived elements (Zn/Ca and Mn/Ca) and lower δ18O and δ13C values are recorded in pale, porous calcite laminae. The multi‐proxy record from Niue shows seasonal cycles associated with hydrological changes controlled by the positioning and strength of the South Pacific Convergence Zone. Wavelet analysis of the greyscale record reveals that El Niño–Southern Oscillation was continuously active during the mid‐Holocene, with two weaker intervals at 6–5.9 and 5.6–5.5 ka BP. El Niño–Southern Oscillation especially affects dry season rainfall dynamics, with increased cyclone activity that reduces hydrological seasonality during El Niño years.

Ichthyoplankton in the Northern Part of the Black Sea under the Prolongation of Summer Hydrological Season in 2020

Ichthyoplankton in the Northern Part of the Black Sea under the Prolongation of Summer Hydrological Season in 2020

Regional variability of the Black Sea ichthyoplankton state during the change of the spring hydrological season to the summer

The species diversity and spatial distribution of ichthyoplankton in the coastal and open waters of the northern part of the Black Sea and the southwestern part of the Sea of Azov in June 2020 are presented. The species diversity and abundance of ichthyoplankton changed in accordance with the regional conditions of warming of the sea upper layer during the formation of a vertical thermal structure of the summer type. The most favorable conditions for the survival of ichthyoplankton were observed in the open and coastal waters of the Western Sector of research in the initial phase of the summer hydrological season.

ОЦЕНКА ПРОСТРАНСТВЕННО-ВРЕМЕННОЙ ДИНАМИКИ ЗАГРЯЗНЕНИЯ РЕКИ КРАСНОЙ В КАЛИНИНГРАДСКОЙ ОБЛАСТИ

Today, the Kaliningrad region has considerablr strategic significance for the Russian Federation. Due to the fact thatthe region is separated from the main part of the country, the quality of water resources is considered a substantial factor for its economicwell-being. One of the main tools in this area is hydrochemical and hydrological monitoring of surface watercourses. The purpose ofthe work is to assess the spatio-temporal dynamics of the Krasnaya River pollution for 4 hydrological seasons in 2022-2023. Monitoringwas carried out during the autumn (10/15/22), winter (01/15/23), spring (04/23/23), and summer (07/19/23) hydrological seasons,during which water samples were taken at 4 hydraulic stations, and hydrometric characteristics were measured to calculate water flowrates. Water samples were examined for the relevant chemical indicators, on the basis of which integral indicators of water qualitywere determined. In turn, their spatio-temporal variability was determined and cartographically expressed. As a result of the study, thepaper provides information about the state of the watercourses and the influence of anthropogenic and natural factors on them. Thespecific combinatorial index of water pollution showed that the river is polluted from source to mouth. Intra-annual variability wasstudied using the WPI and has a similar spatial interpretation, water quality decreases from source to mouth with slight deviations.Temporal variability has developed in such a way that autumn is the most polluted season, while the remaining seasons have nearlyequal average water pollution indices. The main pollutants can be divided into systematic (petroleum products, iron, BOD5, COD) andnon-systematic (sulfate phosphates, ammonium, and low dissolved oxygen). A correlation was discovered between chemical pollutionand the quantitative characteristics of river flow, natural cycles of aquatic and shore vegetation, and vehicle washing. The emissionsof iron and petroleum products do not fit into any specific regular system: the sources of the former are groundwater, of the latter –anthropogenic activities. In general, the situation with water quality on the Krasnaya River is rated as satisfactory.

Особенности разработки нормативов допустимого воздействия на малые реки Севастопольского региона

The aim of the study is the identification of uncertainties to improve information support for the standards of permissible impact (SPI) elaboration for small rivers of the Sevastopol region. Materials and methods. The initial data were the results of surface water bodies monitoring in the Sevastopol region, other materials on the Chernaya River basin, characterizing the conditions for the formation of runoff and the quality of waters of small rivers. Monitoring data has been provided by the territorial bodies of Roshydromet, Rospotrebnadzor, Rosprirodnadzor and State Unitary Enterprise of Sevastopol for Water Use (SUES "Vodokanal"). The shortcomings of information support for the elaboration of SPI are revealed. Pollutants were ranked according to their importance for the ecosystem of the Chernaya River tributaries and distribution in water bodies, the water quality standards are substantiated. The list of pollutants in descending order of importance for the ecosystem includes: phosphates, nitrites, ammonium ion, BOD5, suspended solids, iron, manganese, copper, magnesium, calcium, nickel, zinc, phenols, sulfates, surfactants, oil products. The most common pollutants (indicators of pollution) in the tributaries of the Chernaya River are BOD5, nitrites, phenols, manganese, iron and copper (excesses of standards are recorded for almost all objects). MPC for objects of fishery importance were adopted as standards for SPI elaboration. The exception was BOD5, for this indicator the hygienic standard was used. Assumptions are proposed that allow solving the problem of elaboration SPI under conditions of incomplete information. The calculations of the runoff volume for the years of 50 % and 95 % security, SPIchem for priority pollutants on the main hydrological seasons were performed. Analysis of the results showed that SPI differ significantly by hydrological seasons (up to 48 times) and by each indicator of pollution for different tributaries, which is especially pronounced (more than 10 times) for the Uzundzha and Kalenda Rivers in terms of BOD5, iron, phenols and phosphates. The results obtained confirms the need for differentiated regulation of the permissible impact on individual tributaries of the Chernaya River. When developing the SPI for the small rivers of the Sevastopol region, normative-methodological, informational, large-scale and target uncertainties were identified. The assumptions proposed in the work make it possible to solve practical problems of management in the field of use and protection of water bodies, but do not reduce the relevance of measures aimed at improving the information support for the SPI elaboration. Measures aimed at improving the information support for the SPI elaboration includes: organizing access to the monitoring data of the territorial body of Roshydromet («Crimean UGMS»), increasing the frequency of observations on tributaries of the Chernaya River, organization of systematic observations in the background sections and in the zones of influence of diffuse sources of pollution.

ДИНАМИКА КОНЦЕНТРАЦИЙ РАСТВОРЕННЫХ ФОРМ ТЯЖЕЛЫХ МЕТАЛЛОВ В ВОДЕ РЕКИ МОСКВЫ ПО ДАННЫМ МОНИТОРИНГОВЫХ ИССЛЕДОВАНИЙ В 2021-2023 ГОДА

Background. The Moskva River is a prime example of a natural urban watercourse subjected to strong and varied anthropogenic pressure. For many years, this river has been characterized by increased content of heavy metals. The exceedance of the maximum allowable concentrations of harmful substances in the waters of water bodies used for fishery can result in disruption of the normal functioning of aquatic ecosystems. Relevance. The summarized data collected over the course of monitoring surveys of the Moskva River for three years will be indicative of the relative contribution of natural and anthropogenic sources into its pollution. The aim of this work is to identify the dynamics of spatial and temporal distribution of heavy metals in the Moskva River water and its relation to hydrological seasons, as well as to assess the anthropogenic pressure exerted by the city of Moscow on the river. Methods. Water samples were collected in 2021-2023 during four hydrological seasons. Identification of heavy metals in the collected samples has been carried out using the atomic absorption method. Results. The analysis of the content of dissolved heavy metals (iron, cadmium, cobalt, manganese, copper, nickel, lead, and chrome) in the Moskva River water in various seasons of 2021-2023 has been conducted, and the same was done for zinc in 2023. The dynamics of the spatial and temporal distribution of these heavy metals has been identified, as well as its dependence on the hydrological phases. The influence of the urban infrastructure on the composition of the Moskva River water has been elucidated. Within the investigated area, the exceedance of the values prescribed by the water quality standards for the water bodies used for fishery (MACfish) has been recorded. Conclusion. The waters of the Moskva River have been characterized as polluted, mainly with iron, manganese, copper, and zinc. For lead, chrome, cobalt, nickel, and cadmium, no exceedance of the MACfish has been recorded. It has been found that the majority of the investigated elements were exceeding the values prescribed by the established standards in the spring season, but their concentrations decreased in summer.

Regional Variability of the State of Ichthyoplankton in the Black Sea during the Change from the Spring Hydrological Season to the Summer

Regional Variability of the State of Ichthyoplankton in the Black Sea during the Change from the Spring Hydrological Season to the Summer

Метазойный микрозоопланктон Севастопольской бухты в весенний период: видовое разнообразие и структура сообщества

The original results of studies of metazoan microzooplankton (MM) in different locations of the Sevastopol Bay and the nearest open seashore at the end of the spring hydrological season are presented. Using the Primer 5 software package, changes in the abundance, species composition and structure of the MM community were analyzed. Samples were taken in 3 areas of Sevastopol Bay, differing in the degree of pollution and trophicity of the water. MM sampling, temperature and salinity measurements were carried out in three layers of the water column: from the surface to a 10-meter depth. The abundance of organisms, species diversity indices (Margalef, Pielou, Simpson, Shannon), the degree of similarity and difference of communities were calculated for successive layers: surface, middle (0-5 m) and bottom (5-10 m), as well as on average for the whole column of water. The species diversity of the MM community during the study period was generally moderately high. The middle layer of water at all stations was characterized by the highest species richness. In spatial terms, a decrease in species diversity was observed in the direction from the open seashore into the bay. Against the backdrop of an increase in water temperature from the end of May to the first ten days of June, a significant increase in the abundance of MM was recorded. In May, the average abundance in the 10-meter layer in different water areas ranged from 10 to 40 thousand ind./m3, and at the end of the first ten days of June it increased by 1.5-3.6 times. In both periods there was a trend of increasing abundance from open waters deeper into the bay, coinciding with the temperature trend of local water areas. The absolute maximum of abundance was noted in June in the surface layer in the inner part of the bay – more than 720×103 ind./m3. Quantitative changes in abundance were accompanied and largely determined by changes in the qualitative composition of MM. At the beginning of the period, the main role in the abundance and determination of similarities/differences in the community structure was played by native species of copepods, rotifers, and mollusk veligers. When the water warmed above 18-19 ºС, the role of the heat-loving invader, the copepod Oithona davisae Ferari and Orsi, 1984, sharply increased. The maximum abundance of the non-native species in the local water areas from open waters to the internal waters of the bay increased by more than an order of magnitude: from 23 to 550 ×103 ind./m3. The direction of changes in the abundance of O. davisae in the local water areas studied coincided with an increase in the level of their pollution and trophicity: from the open seashore towards the depths of the bay, both the absolute and relative abundance of the invader and its role in the community structure increased. This testifies to the indicator properties of this species. In general, the changes in abundance, species diversity and community structure of MM in local water areas reflect both seasonal and spatial changes in their trophic status in the natural gradient of the open seaside – the internal space of the Sevastopol Bay and can be used for its indirect assessment.

Метазойный микрозоопланктон Севастопольской бухты в весенний период: видовое разнообразие и структура сообщества

The original results of studies of metazoan microzooplankton (MM) in different locations of the Sevastopol Bay and the nearest open seashore at the end of the spring hydrological season are presented. Using the Primer 5 software package, changes in the abundance, species composition and structure of the MM community were analyzed. Samples were taken in 3 areas of Sevastopol Bay, differing in the degree of pollution and trophicity of the water. MM sampling, temperature and salinity measurements were carried out in three layers of the water column: from the surface to a 10-meter depth. The abundance of organisms, species diversity indices (Margalef, Pielou, Simpson, Shannon), the degree of similarity and difference of communities were calculated for successive layers: surface, middle (0-5 m) and bottom (5-10 m), as well as on average for the whole column of water. The species diversity of the MM community during the study period was generally moderately high. The middle layer of water at all stations was characterized by the highest species richness. In spatial terms, a decrease in species diversity was observed in the direction from the open seashore into the bay. Against the backdrop of an increase in water temperature from the end of May to the first ten days of June, a significant increase in the abundance of MM was recorded. In May, the average abundance in the 10-meter layer in different water areas ranged from 10 to 40 thousand ind./m3, and at the end of the first ten days of June it increased by 1.5-3.6 times. In both periods there was a trend of increasing abundance from open waters deeper into the bay, coinciding with the temperature trend of local water areas. The absolute maximum of abundance was noted in June in the surface layer in the inner part of the bay – more than 720×103 ind./m3. Quantitative changes in abundance were accompanied and largely determined by changes in the qualitative composition of MM. At the beginning of the period, the main role in the abundance and determination of similarities/differences in the community structure was played by native species of copepods, rotifers, and mollusk veligers. When the water warmed above 18-19 ºС, the role of the heat-loving invader, the copepod Oithona davisae Ferari and Orsi, 1984, sharply increased. The maximum abundance of the non-native species in the local water areas from open waters to the internal waters of the bay increased by more than an order of magnitude: from 23 to 550 ×103 ind./m3. The direction of changes in the abundance of O. davisae in the local water areas studied coincided with an increase in the level of their pollution and trophicity: from the open seashore towards the depths of the bay, both the absolute and relative abundance of the invader and its role in the community structure increased. This testifies to the indicator properties of this species. In general, the changes in abundance, species diversity and community structure of MM in local water areas reflect both seasonal and spatial changes in their trophic status in the natural gradient of the open seaside – the internal space of the Sevastopol Bay and can be used for its indirect assessment.

Abiotic and biotic factors influencing heavy metals pollution in fisheries of the Western Amazon

The escalating industrial and artisanal extraction of natural resources in the Amazon Basin has centered it into the spotlight of global environmental concern. This study deals with the environmental problems of heavy metals pollution and biomagnification, which stem from mining, agricultural, petrochemical, and industrial discharges. We conducted an extensive investigation, analyzing 360 fish specimens representing 58 species, to assess the concentrations of 11 metals (Al, As, Cd, Cr, Cu, He, Mn, Ni, Pb, Zn, and Hg) along the Ecuadorian sections of the Napo and Pastaza watersheds. Stable isotope analyses (δ15N and δ13C) were employed to determine their trophic positions and potential biomagnification risks. Sampling was carried out during two distinct hydrological seasons to capture seasonal variations in metal concentrations. Furthermore, we estimated species-specific daily heavy metal intake levels. The results of our study revealed that 15 fish species and 53 individual specimens exhibited heavy metal concentrations surpassing recommended standards, with elevated levels of Al, As, and Hg posing significant risks to human consumers with daily intakes of 0.46 kg/day. Notably, our investigation unveiled concerning trends, including increased metal concentrations, Hg biomagnification within fish populations from the Pastaza watershed, and an association between smaller fish size and higher metal content. This study provides a crucial baseline for monitoring future environmental changes and understanding the persistent impacts of heavy metal pollution in the Ecuadorian Amazon region and the broader Western Amazon. It underscores the urgent need for sustainable environmental management practices to mitigate the escalating threat to these vital ecosystems.