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Microplastic contamination of lakes and rivers is an emerging environmental issue. Sources, environmental fate, in-situ behaviour, concentration and harmful impacts of microplastics on aquatic life are the focus of this review paper. Present review summarises the current state of information about microplastics in riverine ecosystems around the world. The tiny plastic particles can serve as substrate as well as transporters of a variety of toxicants, including recalcitrant chemical compounds from miscellaneous sources having potential to seriously harm people's health. Further, intake and entanglement of microplastics can inflict a number of adverse bio-physico-chemical impacts on people and other living creatures. Secondary microplastics are produced by the disintegration of bigger size primary plastic particles and ultimately end up in the terrestrial and aquatic habitats. Comprehensive information on microplastic pollution in fresh water ecosystems is still limited on a single platform. This review critically addresses the microplastic pollution in rivers, sources, and its impact around the world. Further, possible replacements for plastics like modified starch, cellulose, esters of cellulose, polylactic acid etc. derived from biomass and microorganisms are also examined. [ABSTRACT FROM AUTHOR]

Climate change and the reliance on carbon-intensive fuels have made electromobility necessary to reduce greenhouse gas (GHG) emissions in transport. This study analyses the potential environmental impact of a shallow-draught vessel operating within a section of Colombia’s Atrato River basin by estimating CO₂-equivalent emissions across various technological alternatives (conventional, hybrid, and electric) using a life cycle analysis. Data on engine performance, fuel type, and operating conditions were gathered. A battery propulsion system was modelled using both ‘conventional’ and renewable energy sources. The analysis focused on four impact categories: global warming potential (GWP), acidification potential (AP), eutrophication potential (EP), and photochemical ozone creation potential (POCP). Results indicated significant reductions with renewable energy: 92.6% in GWP, 94.2% in AP, 82.4% in EP, and 93.7% in POCP. The selection of energy sources for electricity generation is crucial in assessing the viability of battery technology for sustainable shipping. [ABSTRACT FROM AUTHOR]

Recently, the impact of climate change has led to an increase in the scale and frequency of extreme rainfall and flash floods. Due to this, the occurrence of floods and various river disasters has increased, necessitating the acquisition of technologies to prevent river disasters. Owing to the nature of rivers, areas with poor accessibility exist, and obtaining information over a wide area can be time-consuming. Artificial intelligence technology, which has the potential to overcome these limits, has not been broadly adopted for river detection. Therefore, the current study conducted a performance analysis of artificial intelligence for automatic river path setting via the YOLOv8 model, which is widely applied in various fields. Through the augmentation feature in the Roboflow platform, many river images were employed to train and analyze the river spatial information of each applied image. The overall results revealed that the models with augmentation performed better than the basic models without augmentation. In particular, the flip and crop and shear model showed the highest performance with a score of 0.058. When applied to rivers, the Wosucheon stream showed the highest average confidence across all models, with a value of 0.842. Additionally, the max confidence for each river was extracted, and it was found that models including crop exhibited higher reliability. The results show that the augmentation models better generalize new data and can improve performance in real-world environments. Additionally, the RivDet artificial intelligence model for automatic river path configuration developed in the current study is expected to solve various problems, such as automatic flow rate estimation for river disaster prevention, setting early flood warnings, and calculating the range of flood inundation damage. [ABSTRACT FROM AUTHOR]

This article introduces a methodology utilizing the Analytical Hierarchy Process (AHP) integrated with a Geographic Information System (GIS) to classify sub-basins within a large river basin in terms of pollution levels.The research uses data from the Haraz River basin, located in northern Iran near the Caspian Sea. The river basin under investigation comprises seven sub-basins. The primary pollution sources in this region include domestic wastewater from urban areas, effluents from fish farms, discharge from sand and gravel mines, sewage from restaurants and tourism centers, as well as land use (agriculture, forests, and rangelands). In addition to these pollution-related factors, other criteria such as basin area, river length, road network length, and slope were also considered.Using scores assigned by experts and leveraging the Expert Choice software, all sub-basins, and factors contributing to river pollution were identified. According to the findings, urban domestic wastewater was the most significant contributor to pollution in the study Basin, accounting for 42.2% of the total pollution. The sub-basins were classified according to their final weighted scores, identifying those with the highest and lowest pollution levels.The studied approach offers substantial advantages in terms of time, cost, and resource efficiency. [ABSTRACT FROM AUTHOR]

The condition of the aquatic environment, particularly in protected areas of high ecological value such as the Narew River, requires detailed monitoring to identify and minimise the impact of anthropogenic factors on the ecosystem. This study focused on the content of heavy metals in bottom sediments and macrophytes of the Narew River, emphasising the influence of human activities and natural factors on this ecologically valuable ecosystem. Pb, Cr, Zn, Cd, Fe, and Mn concentrations were analysed in sediment samples, and ten macrophyte species were collected at 11 sampling points along the river. A geochemical index (Igeo) and multivariate statistical analyses were employed to identify sources of contamination. The digested samples (sediments and plants) were analysed for Pb, Cr, Cu, Zn, Ni, Cd, Fe, and Mn using flame atomic absorption spectrometry (AAS) on an ICE 3500 Thermo Scientific spectrometer, with a measurement error below 5%, validated against certified reference materials. The study results indicated that most metals, including Ni, Cr, Co, Fe, and Mn, predominantly originate from natural geological processes. In contrast, Zn, Cd, Cu, and Pb were identified as being enriched due to anthropogenic activities. An analysis of macrophytes revealed varied patterns of metal accumulation, which correspond to the bioavailability of metals and their environmental concentrations. Comprehensive statistical analyses provided insights into the predominant sources of metal contamination, closely associated with industrial emissions, agricultural runoff, and transportation activities. The integration of sediment and macrophyte monitoring allowed for a thorough evaluation of the Narew River ecosystem, facilitating the identification of key pollution sources. These findings highlight the critical need for measures to mitigate anthropogenic contributions of heavy metals—particularly from industrial, agricultural, and transportation sectors—to safeguard the Narew River's unique ecological and natural heritage. [ABSTRACT FROM AUTHOR]

Marine tourism is authorized in Jakarta Bay's Angke Kapuk mangrove forest. Maritime vessel activities, maintenance, and land reclamation can pollute nearby aquatic environments and sedimentary deposits. This study examines lead (Pb), a heavy metal, in water and sediment samples to measure contamination. Lead pollution in aquatic habitats can harm aquatic organisms and humans through bioaccumulation in the food chain. The sampling was done twice in August 2023, seven days apart. This technique was done at three stations with different activities. Microwave Plasma-Atomic Emission Spectroscopy (MP-AES) was used to measure lead amounts in the samples. The water sample analysis showed 0.0022-0.0092 mg/L, matching Indonesian Government Regulation No. 22 of 2021 standards. Conversely, sediment samples showed 0.067-0.200 mg/kg, which is below the quality criteria set by ANZECC&ARMCANZ in 2000 for Australia and New Zealand and CCME in 2001 for Canada. Despite low pollution according to recognized criteria, heavy metals in ecotourism zones require government and public attention. Additional information, in-depth research on water contamination, and heightened awareness of the impacts of heavy metals may be necessary. [ABSTRACT FROM AUTHOR]

A survey was conducted in 12 areas viz., Naini, Arail, Shringverpur, Jhusi, Baluva Ghat, Daraganj, Jamunipur, Phaphamau, Mankameshwar, Chhatnag, Mecferson Lake and Sangam Ghat near the river Ganga and Yamuna at Prayagraj, U.P. in the year 2024. Sixty soil samples were collected during the month of January, March, May, July and September, respectively. Six genera of plant-parasitic nematodes viz., Meloidogyne sp. Pratylenchus sp., Rotylenchus sp, Tylenchulus sp., Helicotylenchus sp. and Heterodera sp. were found in 12 above mentioned areas. Meloidogyne sp. Heterodera sp., Rotylenchus sp., and Pratylenchus sp. were predominant followed by Tylenchulus sp. and Helicotylenchus sp. Maximum number of Meloidogyne sp., Heterodera sp., Rotylenchus and Pratylenchus sp. were found in the sample collected during the month of January followed by September, March, July and May, respectively, in the area Naini, Arail, Shringverpur, Jhusi followed by Balua Ghat, Daraganj, Jamunipur, Phaphamau, Mankameshwar, Chhatnag, Macpherson Lake area and Sangam Ghat area, respectively. Minimum number of Tylenchulus and Helicotylenchus sp. were found in Naini, Arail and Jhusi areas in the samples collected during January and September months. [ABSTRACT FROM AUTHOR]

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The high levels of nitrate (NO3−) in the surface water have contributed to eutrophication and other eco-environmental damages worldwide. Although the excessive NO3− concentrations in rivers were often attributed to anthropogenic activities, some undisturbed or slightly disturbed rivers also had high NO3− levels. This study utilized multi-pronged approaches (i.e., river natural abundance isotopes, 15N-labeling techniques, and qPCR) to provide a comprehensive explanation of the reason for the high NO3− levels in a river draining forest-dominated terrene. The river natural abundance isotopes (δ15N/δ18O-NO3−) indicated that the soil source (i.e., soil organic nitrogen-SON and chemical fertilizer-CF) were the primary contributors to the NO3−, and the NO3− removal was probably prevalent in the basin scale. The 15N-labeling techniques quantitatively showed that denitrification and anammox were stronger than nitrification in the soils and sediments. Structural equation models suggested that nitrification in the soils was regulated by NH4+-N contents, which, in turn, were closely related to fertilization in spring. Denitrification and anammox were largely controlled by elevation and functional gene abundances (i.e., nirK and hzsB, respectively). The hydrological isotopes (i.e., δD/δ18O-H2O) indicated that the transport of NO3− from soil to the river was related to the intensity of runoff leaching to the soil, In contrast, the riverine NH4+ was largely from point sources; thus, increasing runoff led to a dilution effect. This study clearly showed that soil biogeochemistry and hydrological condition of a river basin jointly shaped the high NO3− levels in the almost undisturbed river. [ABSTRACT FROM AUTHOR]

The state of Michigan is 253,800 km2 in size with abundant freshwater habitats, including lakes, streams, ponds, and rivers that are ideal for freshwater red algae from the order Batrachospermales. In addition, there are numerous herbarium records, but approximately 60% are more than 20 years old. Recent collections have been from a small geographic area and only a handful of specimens have associated DNA sequences that are often needed for accurate species identification. We surveyed broadly in the Upper and Lower Peninsula, revisiting previously sampled sites and exploring new localities. Freshwater red algae were collected from 19 sites that varied from small streams, rivers, and lake inlet/outlets with a corresponding range in water temperature, pH, and conductivity. Four genera were collected, Batrachospermum, Paludicola, Sheathia, and Virescentia, with species identifications verified with rbcL gene sequencing. The genus Sheathia was the most abundant (15 sites) and represented by two species, S. grandis and S. involuta. At seven sites, we found Batrachospermum gelatinosum, whereas Paludicola communis and Virescentia viride-americana were each collected once. Although these four genera have been previously known from the state, this study provided the first rbcL sequence for B. gelatinosum and P. communis in Michigan. At one location, we confirmed the presence of Virescentia viride-americana 30 years after it had first been collected, and likewise, we confirmed B. gelatinosum at another site 27 years later. Sheathia grandis was recently described from only two locations in nearby states. This study was the first report in Michigan and added considerably to the number of known locations. This research has yielded new records, species identification with DNA sequence, and expanded habitat information. [ABSTRACT FROM AUTHOR]

Globally scarce and ecologically valuable, the lowland chalk streams of southern and eastern England experience extensive eutrophication pressures arising from intensive agriculture. Mitigation measures are required to restore natural chalk stream functioning and the reintroduction of the Eurasian beaver (Castor fiber) could provide a solution. Here, we investigated the impact upon chalk stream hydrochemistry of the reintroduction of beavers to a 6-ha enclosure on the headwaters of the River Glaven, Norfolk. Over a two-year period (March 2022 – May 2024), 190 river water samples were collected across control and impact sites displaying minor-to-major hydrological disturbance from beaver activity, with samples analysed for nitrate (NO3), phosphate (PO4), and dissolved organic carbon (DOC). Results revealed significant reductions in nutrient concentrations downstream of the beaver enclosure (NO3 = -43%; PO4 = -51%), as well as significantly lower concentrations relative to the agricultural control site (NO3 = -64%; PO4 = -86%). Conversely, DOC concentrations were significantly higher downstream of the enclosure (+ 94%) and compared to the control (+ 272%). Greater reductions in nitrate and phosphate during the summer (NO3 = -47%; PO4 = -61%) compared to winter (NO3 = -37%; PO4 = -38%) indicated biological assimilation within the beaver wetland as a likely causal mechanism, whilst lower dissolved oxygen concentrations within the beaver ponds indicated a role for denitrification in nitrate removal. Overall, these results demonstrate that beaver wetlands can significantly mitigate eutrophication risk in agriculturally impacted chalk streams and provides further evidence in support of their wider reintroduction to English catchments. [ABSTRACT FROM AUTHOR]

Dispersal behaviour of fish expanding their range is an important component of invasion success and can evolve along dispersal pathways. Understanding the movement biology of invasive species during the spread phase of a new invasion is important for developing targeted management strategies. This study determined the extent and movement patterns of two tilapia species, Oreochromis mossambicus and Pelmatolapia mariae, in the Mitchell River catchment, northern Australia, during the spread phase of the invasion. Tilapia were only found in three locations within one sub-catchment of the Mitchell River. Strontium isotopes of tilapia otoliths revealed different movement patterns among these three locations, with active dispersal to one of the locations from both other locations. Movements made by P. mariae mostly occurred within the first two years of life. These movement patterns demonstrate active habitat seeking behaviour, mostly by juveniles, that lead to the successful establishment of tilapia at new locations within a catchment following introduction. The movement patterns revealed in this study were used to recommend priority management actions to limit the risk of tilapia spreading to vulnerable floodplain habitats and other river systems in the Gulf of Carpentaria. These include monitoring within the sub-catchment containing established tilapia and control measures applied to the established local populations to limit population growth, limiting the risk of downstream spread by reducing dispersal probability. [ABSTRACT FROM AUTHOR]

There is concern over potential toxic elements (PTEs) impacting river ecosystems due to human and industrial activities. The river's water, sediment, and aquatic life are all severely affected by the release of chemical and urban waste. PTE concentrations in sediment, water, and aquatic species from river ecosystems are reported in this review. Among the PTEs, chromium (Cr), cadmium (Cd), lead (Pb), and nickel (Ni) revealed high pollution levels in water and aquatic species (fish and shellfish) at many rivers. The Karnaphuli, Ganga, and Lee rivers have high levels of Pb and Cd contamination, while the Buriganga and Korotoa rivers' water had notable Ni contamination. A number of rivers with PTEs showed ecological risk as a consequence of the sediment's potential ecological risk (PER), the pollutant load index (PLI), and the geoaccumulation index (Igeo). A comprehensive study suggests elevated PLI values in river sediments, indicating significant pollution levels, particularly in the Buriganga River sediment, marked by high Igeo values. The PER of the Shitalakshya and Buriganga rivers was marked as very high risk, with an Eir > 320, while the Dhaleshwari and Khiru rivers showed 'high risk', with 160 = Eir < 320. It was found that fish and shellfish from the Buriganga, Turag, and Swat rivers have a high concentration of Cr. PTE pollution across several river sites could pose health toxicity risks to humans through the consumption of aquatic species. The CR value shows the carcinogenic risk to human health from eating fish and shellfish, whereas an HI value > 1 suggests no carcinogenic risk. The occurrence of other PTEs, including manganese (Mn), arsenic (As), and nickel (Ni), significantly increases the ecological risk and concerns to aquatic life and human health. This study emphasises the importance of PTE toxicity risk and continuous monitoring for the sustainability of river ecosystems. [ABSTRACT FROM AUTHOR]

Abstract Water quality management is a critical aspect of environmental sustainability, particularly in arid and semi-arid regions such as Iran where water scarcity is compounded by quality degradation. This study delves into the causal relationships influencing water quality, focusing on Total Dissolved Solids (TDS) as a primary indicator in the Karkheh River, southwest Iran. Utilizing a comprehensive dataset spanning 50 years (1968–2018), this research integrates Machine Learning (ML) techniques to examine correlations and infer causality among multiple parameters, including flow rate (Q), Sodium (Na+), Magnesium (Mg2+), Calcium (Ca2+), Chloride (Cl−), Sulfate (SO4 2−), Bicarbonates (HCO3 −), and pH. For modeling the causation, the “Back door linear regression” approach has been considered which establishes a stable and interpretable framework in causal inference by focusing on clear assumptions. Predictive modeling was used to show the difference between correlation and causation along with interpretability modeling to make the predictive model transparent. Predictive modeling does not report the causality among the variables as it showed Mg is not contributing to the target (TDS) while the findings reveal that TDS is predominantly positive influenced by Mg, Na, Cl, Ca and SO4, with HCO3 and pH exerting negative (inverse) effects. Unlike correlations, causal relationships demonstrate directional and often unequal influences, highlighting Mg as a critical driver of TDS levels. This novel application of ML-based causal inference in water quality research provides a cost-effective and time-efficient alternative to traditional experimental methods. The results underscore the potential of ML-driven causal analysis to guide water resource management and policy-making. By identifying the key drivers of TDS, this study proposes targeted interventions to mitigate water quality deterioration. Moreover, the insights gained lay the foundation for developing early warning systems, ensuring proactive and sustainable water quality management in similar hydrological contexts.

This paper presents an overview of the Danube municipalities on the Bulgarian coast, with a particular focus on their spatial and socio-economic characteristics as territorial units. The paper outlines the structural postulates that highlight the importance of the Danube coast for the regional development of the Danube region and the development of the Bulgarian geographical space. The paper goes on to present a characterization of the Danube region in a more general context as a part of the pan-European space, together with an outline of the development of socio-geographical processes and phenomena. In practice, the region presents many challenges for forming regional development policies and interest in the area in terms of tourism and investment. The paper presents relevant conclusions and recommendations for developing the Bulgarian municipalities along the Danube.

Esinmirin River is an important historic ancient river in Ile-Ife, the source of the Yoruba Kingdom that was associated with mystical power in stabilizing the ancient city during the period of war that would have destroyed it. The water resource needs investigation because of the recent anthropogenic and industrial activities that could affect the river. The study examines the river's physicochemical, heavy metals, and bacteriological parameters in the upstream, midstream, and downstream sections to comprehend the pollution levels of the Esinmirin River. Nine samples were collected in May 2023 by composite method at various sections using a systematic sampling technique. Twenty-one parameters including the physical, chemical, heavy metals, and bacteriological were examined. A significant departure from WHO, and SON permissible water standard limits in temperature, iron, and the various bacteria found in the research, brings to light the alarming pollution levels of the river. Though temperature (29.9 °C–30.9 °C) and iron (0.7 mg/L-1.3 mg/L) in the 3 sections were above the standard guidelines while lead, copper, and cadmium were absent, all other physicochemical parameters were within the limits. The pH values were highest in the upstream, EC and TDS in the midstream, and temperature in the downstream. At the same time, the chemical parameters and iron increase progressively from upstream to downstream. However, TBC, Escherichia Coliform, Klebsiella species, Staphylococcus Aureus species, and Enterobacter species in all the sections indicated a high level of contamination. The physical, chemical, heavy metal and bacteriological parameters were significantly related mostly at p > 0.01 and on a few occasions at p > 0.05. The study recommends awareness campaigns, routine monitoring, and water treatment before use, to protect public health.

Domestication is a process in which animals are bred in captivity under controlled resource availability. Compared with wild-type phenotypes, animals with domesticated phenotypes exhibit reduced stress sensitivity and cognitive abilities. The pigmentation of domesticated phenotype animals is a morphological change, one of those that is considered a "domestication syndrome". In fish, the impact of pigmentation on behaviour and physiology has rarely been examined. We compared the performance of two phenotypes of the common carp Cyprinus carpio : a wild-coloured phenotype and an orange-coloured phenotype of koi carp. The fish were exposed to short-term stress conditions, after which blood samples were collected to obtain biochemical indices. The maze and field experiments were used to observe individuals' movement activity, exploratory behaviour, and ability to find food in the experimental maze. The fish were equipped with radio tags for the field experiment. In the riverine environment, movement activity and preferred temperatures during light/dark cycles were observed. Presuming that the orange-coloured carp exhibit reduced cognitive ability, we hypothesized that they would exhibit i) reduced exploratory behaviour and ii) lower stress sensitivity than wild-coloured carp. Our results revealed mostly nocturnal activity in koi carp. The koi carp needed more time to explore the maze, as expected, but contrary to our assumption they showed greater stress levels accompanied by greater movement activity. This behaviour was similar for different maze setting. The wild-coloured carp were active during both day and night and exhibited greater left-sided lateralization and cognitive skills, allowing them to find food faster. For the wild-coloured phenotype, body temperature was significantly correlated with all the other observed variables. Our results suggest potentially lower welfare of the koi carp in mixed aquaculture, e.g., a lower ability to use feeding resources than the wild-coloured carp. [Display omitted] • Behavioural and physiological traits differed between coloured carp phenotypes. • Wild-coloured carp explored the environment more effectively. • Behaviour of the wild-coloured phenotype correlated with a proactive coping style. • Koi phenotype showed higher sensitivity to stress and mostly nocturnal activity. • Mixing of coloured fish may reduce the welfare of phenotypes sensitive to stress. [ABSTRACT FROM AUTHOR]

• Riverine N 2 O dynamics change in response to variation in urbanization intensity. • Urbanization affects N 2 O dynamics via hydrological, biogeochemical and microbial processes. • Riverine NO 3 − availability and functional gene abundance increase with urban percentage. • Dissolved oxygen saturation and flow velocity decrease with urban percentage. • Denitrification contribution to N 2 O production increases with urban land percentage. Human-disturbed rivers are globally significant sources of atmospheric nitrous oxide (N 2 O). Yet, the underlying mechanisms of urbanization impact on riverine N 2 O dynamics are not well understood. This study unveiled the effects of urbanization on N 2 O dynamics by integrating hydrological, biogeochemical and microbial processes in a river with various urbanization intensities. Riverine NO 3 − concentration enhanced with increasing urban land percentage, primarily because of the increased proportional contribution of sewage & manure source. The 15N site preference and relevant isotopic evidences revealed that the proportion of denitrification derived N 2 O increased from 60 % to 76 %, with the urban land percentage increasing from 〈 5 % to 〉 22 %, which was caused by decreases in flow velocity and dissolved oxygen saturation, increases in NO 3 − concentration and N 2 O-denitrifying genes. The non-negligible contribution of nitrification to N 2 O production (∼ 40 %) in lower-urbanized river stretches may be attributed to aerobic conditions and lower impermeable riparian zone facilitating the occurrence of in-river nitrification and the access of in-soil nitrification to river. Urbanization-mediated decreases in flow velocity and dissolved oxygen and increases in nitrogen availability and denitrification process resulted in an increase in N 2 O concentration and flux, with N 2 O concentration approximately four times higher in higher-urbanized river reaches (50.7 ± 26.3 nmol/L) than in lower-urbanized river reaches (14.4 ± 2.5 nmol/L). In addition, increased proportional contribution of sewage & manure source also provides the possibility for exogenous N 2 O inputs with urban expansion. These findings contribute to deepening our understanding of how urbanization drives N 2 O dynamics in river systems. [Display omitted] [ABSTRACT FROM AUTHOR]

It is important to discover what change led to the improvement in European macroinvertebrate biodiversity in the period from 1990-2000s and what prevents further desirable gains from taking place today. A 30-year data set from 1,457 macroinvertebrate monitoring sites spread across England, with 65,032 discrete observations was combined with 41 chemical, physical, habitat, and geographic variables. This data set was analyzed using generalized linear mixed-effect models and generalized additive mixed models. To include all combinations of the variables required to address each question, required over 20,000 model runs. It was found that no variables were more consistently and strongly associated with the overall family richness than Zn and Cu. Zn and Cu led both for the era of large gains in richness up to 2005 and also in the later period of 2006-2018 when few further gains were made.

The discharge of treated wastewater from wastewater treatment plants (WWTPs) into river systems is a significant source of pollution, introducing a range of chemical and biological pollutants that impact the chemical and ecological quality status of rivers. This study evaluates the effect of a secondary treated wastewater effluent on the Onyar River, in the northeast Spain. Water and biofilm samples were collected at one upstream and four downstream sampling points (up to 2.8 km from the discharge point) across four seasons. A wide array of pollutants, including metals, pharmaceuticals, microplastics (MPs), per- and polyfluoroalkyl substances (PFAS), antibiotic resistance genes (ARGs), among other emerging pollutants, were detected downstream, with significant differences between upstream and downstream concentrations. Our results show that WWTP discharge also altered biofilm microbiome composition and ARGs presence, being these changes distinguishable from seasonal variations. Nevertheless, a partial recovery further downstream (525 m) was observed for biofilm microbiome and ARGs composition. These findings highlight the value of microbiome analysis in assessing wastewater impacts on river ecosystems and emphasize the need for further research to improve pollutant attenuation and biofilm recovery strategies in river streams., Competing Interests: Declaration of Competing Interest ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025. Published by Elsevier Ltd.)

This study aimed to investigate the concentration of potentially toxic elements (PTEs) such as cadmium (Cd), arsenic (As), lead (Pb), mercury (Hg), and nickel (Ni) in river sediments across China. Additionally, it performed a non-dietary risk assessment for the exposed population. We searched international databases, including Web of Science, PubMed, Scopus, and Google Scholar (for gray literature), covering the period from January 1, 2010, to February 30, 2023. Ultimately, we included 136 papers comprising 190 studies or data reports. Our findings revealed that the highest Arsenic concentrations were found in the Mawei River, Xiangjiang River, and Fuyang River sediments. The highest Lead concentrations were detected in the North River sediment, and the Yangtze, Xiangjiang, and North Rivers showed the most significant Cadmium levels. The rank order of PTEs based on the percentage of significant non-carcinogenic risk (toxicity hazard quotient, THQ > 1) in adults was as follows: arsenic (87%) > lead (29%) > cadmium (24%) > mercury (18%) > nickel (4%). In adolescents, the ranking was as follows: arsenic (95%) > lead (84%) > cadmium (62%) > mercury (28%) > nickel (18%). Our findings indicate that the non-carcinogenic risk in most of the studied locations in China is unacceptably high due to arsenic, lead, and cadmium (THQ > 1). Furthermore, the carcinogenic risk of arsenic in the majority of the studied areas (99%) was also deemed unacceptable (cancer risk > 1E-6). As such, the pollution from toxic elements in the sediments of China's rivers requires urgent attention., Competing Interests: Declarations. Ethics approval: Not applicable. Consent to participate: The authors declare their consent to participate in this article. Consent for publication: The authors declare their consent to publish this article. Competing interests: The authors declare no competing interests., (© 2025. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Urbanization can significantly drive biodiversity loss in river ecosystems, yet the underlying mechanisms require further study. Here, we used a trait-based approach to investigate temporal succession and variation in the dissimilarity of phytoplankton community functional traits along an urbanizing subtropical river over 11 years - during which time the downstream of catchment underwent rapid urbanization. Our results indicated that urbanization altered the interannual succession of phytoplankton. The phytoplankton communities in the rural region were mainly shaped by a specialist trade-off between extreme lotic strategies (single cell, high maximum growth rate and high silica demand) in river habitat, and extreme lentic strategies (colonial, toxin production and nitrogen fixation abilities) in reservoir habitat. Conversely, in the urban region, generalist strategies with intermediate trait combinations (moderate mobility and mixotrophic ability) dominated the communities in both river and reservoir habitats. Time-lag analysis of functional dissimilarity showed lower, or even no significant variations of functional beta diversity in the urban region. Further decomposition of functional beta diversity indicated a reduced rate of functional turnover in urban river compared with that in rural river and a decrease in functional nestedness in urban reservoir. Paired differences between river and reservoir in the urban region exhibited convergent succession by functional turnover. The convergent succession and homogenization in the urban region made the variation in phytoplankton functional structure more unpredictable in a random forest model, and diminished the relationship between functional dissimilarity and environmental factors compared to the rural region. Our study shows how urbanization shapes the phytoplankton functional structure and causes homogenization in functional trait composition. The insight gained enhance our ability to assess and predict the environmental impacts of urbanization on aquatic ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier Inc. All rights reserved.)

Riverine export fluxes of organic carbon (OC), major and trace elements remain at the forefront of environmental research in Arctic and subarctic regions, due mostly to high sensitivity of river hydrochemical parameters to climate warming and, at the same time, global importance of OC, nutrients and toxicants delivered by rivers to the Arctic Ocean. In contrast to reliable information on export fluxes of carbon and metals from the mainland to the Arctic Ocean by large and mid-size Arctic rivers, the majority of these studies quantify either dissolved (< 0.45 µm) or particulate suspended matter (PSM) fluxes, without mechanistic analyses of element speciation in most labile, low molecular weight (LMW) or colloidal form. Here we assessed colloidal versus LMW (< 3 kDa) and suspended (> 0.45 µm) export of OC, major and trace elements in a large Siberian river (Ob) and its smaller tributaries, situated within a boreal taiga / wetland zone. The main differences between Ob and its small tributaries are (i) higher dissolved OC and dissolved and particulate Fe concentrations in tributaries, due to input from surrounding bogs, (ii) much higher PSM load (clays) in the large river (Ob) compared to smaller tributaries; and (iii) strong underground water input for the Ob River, especially during baseflow, which is less pronounced for its tributaries. These major environmental factors were largely responsible for specific features of colloidal vs particulate export for the Ob River and its tributaries. Annual export fluxes normalized to the watershed area (yields) were similar for most elements in dissolved (< 0.45 µm) fraction between the Ob and the tributaries, exempting Fe, Mn, Co and Zn which were higher in tributaries essentially due to input from wetlands. Export of Mo, V, W and U was higher in the Ob River due to pronounced groundwater influence. Colloidal (3 kDa - 0.45 µm) yields were also generally higher in the tributary compared to Ob, except for those soluble elements of groundwater input (Sr, Mo, W, U). The particulate suspended (> 0.45 µm) yield of all elements, except Mn, was much higher in the Ob River when compared to its smaller tributaries. Overall, elemental fluxes of small wetland-draining tributaries of the Ob River can be considered analogous to the small rivers of the permafrost-free portion of the Arctic coast. Such small rivers are more sensitive to processes occurring at the watershed level, hence being an efficient potential sentinel for environmental changes. Fluxes in large Arctic coast rivers are more conservative and are strongly controlled by the effects of PSM interaction with river water at high flow and groundwater loading at base flow. Global significance of our findings is that elemental dissolved (< 0.45 µm) yields of small Artic rivers draining coastal wetlands and boreal forests can be adequately (within a factor of 2 to 3, comparable to inter-annul variations and uncertainties) approximated by those currently available for mid-sized and large rivers., Competing Interests: Declaration of competing interest We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome., (Copyright © 2025 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Coastal Louisiana is known for saltwater intrusion that threatens wetlands, aquifers, and rivers. However, the extent of saltwater intrusion is not well understood. This study develops an innovative framework with airborne electromagnetic (AEM) data to map chloride concentration distributions for wetlands in the Mississippi River deltaic plain and Chenier plain as well as for the Mississippi River Valley alluvial aquifer (MRVA) and Chicot aquifer. Moreover, the framework maps chloride concentrations along the Mississippi River and Atchafalaya River. Key components in the framework include the establishment of resistivity-to-chloride concentration transformation, 3D resistivity architecture building through geostatistics, and the employment of a lithologic model. The transformation functions correlate AEM resistivity data with porewater salinity measurements and groundwater and river chloride samples. The results show that AEM data reliably infers soil water chloride concentrations and correlates well with the distribution of various marsh types. AEM data reveals extensive saltwater presence at depth and near the coast, originating from salt domes and the Gulf of Mexico, respectively. The saltwater upconing pattern in the Chicot aquifer is likely due to excessive groundwater withdrawals. The AEM data also confirms a distinct tongue of saltwater intruding into the Atchafalaya Basin from the Gulf. The AEM data helps to identify faults that are obscured or eroded at the surface, which appear as leaky barriers in the subsurface where dramatic changes in chloride concentration are apparent. Finally, this study uses the AEM data to infer the presence of an extensive seawater wedge in the Mississippi River and Atchafalaya River., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025. Published by Elsevier Ltd.)

Freshwater ecosystems face significant threats, including pollution, habitat loss, invasive species, and climate change. To address these challenges, management strategies and restoration efforts have been broadly implemented. Across Europe, such efforts have resulted in overall improvements in freshwater biodiversity, but recovery has stalled or failed to occur in many localities, which may be partly caused by the limited dispersal capacity of many species. Here, we used a comprehensive dataset comprising 1327 time series of freshwater macroinvertebrate communities ranging from 1968 to 2021 across 23 European countries to investigate whether dispersal capacity changes with the ecological quality of riverine systems. Sites experiencing improvements in ecological quality exhibited a net gain in species and tended to have macroinvertebrate communities containing species with stronger dispersal capacity (e.g., active aquatic and aerial dispersers, species with frequent propensity to drift, and insects with larger wings). In contrast, sites experiencing degradation of ecological quality exhibited a net loss of species and a reduction in the proportion of strong dispersers. However, this response varied extensively among countries and local sites, with some improving sites exhibiting no parallel gains in macroinvertebrates with higher dispersal capacity. Dispersal capacity of the local species pool can affect the success of freshwater ecosystem restoration projects. Management strategies should focus on enhancing landscape connectivity to create accessible "source" areas and refugia for sensitive taxa, especially as climate change reshapes habitat suitability. Additionally, biodiversity initiatives must incorporate adaptive decision-making approaches that account for the site-specific responses of macroinvertebrate communities to changes in ecological quality., (Global Change Biology© 2025 The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)