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Rivers are increasingly used as superhighways for the continental-scale transportation of freight goods, but the ecological impact of large vessel traffic on river ecosystems is difficult to study. Recently, the temporary maintenance closure of lock and dam systems on the Illinois Waterway (USA) brought commercial vessel traffic to a halt along the river's length, offering a rare opportunity to study the response of the ecosystem before, during, and after an extended pause of this persistent anthropogenic disturbance. We observed improvements in main- and side-channel water quality and a redistribution of fish habitat-use during a months-long, near-complete reduction of large vessel traffic. Over 3600 water quality and 1300 fish community samples indicate that large vessel traffic reduction coincided with a 33 % reduction in turbidity as well as increased use of sampling strata near vessel navigation corridors by sound-sensitive and rheophilic fishes. Gizzard shad (Dorosoma cepedianum), the most abundant species in the system, also expanded their use of these 'impact' areas. Though inland waterway transport is an economically- and climate-friendly alternative to trucking and rail for the shipment of freight, our data suggest that intense vessel traffic may have profound physical and biological impacts across a large river. Monitoring and mitigation of ecological impacts of the ongoing expansion of inland waterway transport around the world will be critical to balancing large rivers as both useful navigation corridors and functional 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 © 2024 The US Geological Survey, The Author(s). Published by Elsevier B.V. All rights reserved.)

Climate change elevates the threat of compound heat and drought events, with their ecological and socioeconomic impacts exacerbated by human ecosystem alterations such as eutrophication, salinization, and river engineering. Here, we study how multiple stressors produced an environmental disaster in a large European river, the Oder River, where a toxic bloom of the brackish-water planktonic haptophyte Prymnesium parvum (the "golden algae") killed approximately 1000 metric tons of fish and most mussels and snails. We uncovered the complexity of this event using hydroclimatic data, remote sensing, cell counts, hydrochemical and toxin analyses, and genetics. After incubation in impounded upstream channels with drastically elevated concentrations of salts and nutrients, only a critical combination of chronic salt and nutrient pollution, acute high water temperatures, and low river discharge during a heatwave enabled the riverine mass proliferation of B-type P. parvum along a 500 km river section. The dramatic losses of large filter feeders and the spreading of vegetative cells and resting stages make the system more susceptible to new harmful algal blooms. Our findings show that global warming, water use intensification, and chronic ecosystem pollution could increase likelihood and severity of such compound ecoclimatic events, necessitating consideration in future impact models., (© 2024. The Author(s).)

River-floodplain ecosystems play a crucial role in connecting landscape patches through hydrological connectivity, but they are among the most threatened ecosystems. Floodplains provide important habitat for amphibians by connecting aquatic and terrestrial habitats. Modifications to floodplain hydrology can impact amphibian communities, yet few studies have examined amphibian metacommunities in floodplain wetlands.In this study, we assessed patterns in amphibian breeding abundance in one of the largest floodplains of the Danube River, Hungary, relative to hydrological connectivity and multi-scale variables at 30 waterbody sites. Our aim was to determine whether these patterns aligned with the pond-permanence gradient hypothesis, where breeding amphibian abundance is predicted to be highest in ephemeral ponds without large predatory fish. We used Bayesian hierarchical modelling to estimate multi-species abundance from repeated survey (count) data collected over one breeding season.We detected the eggs and larvae of four amphibian species. The best model of abundance included covariates describing two principal component axes associated with waterbody hydrology and landscape composition within a 500-m radius of a site. There was a positive relationship between mean community abundance at a site and hydrological disconnection from the main river channel; however, the common toad ( Bufo bufo ) was associated with hydrologically connected waterbodies. There was a positive relationship between mean community abundance and a high proportion of forest cover and low cover of agricultural land within a 500-m radius around a site, although this relationship was clear for only two species. There was no support for models containing the number of large predatory fish species detected at a site.Although our results showed that amphibian abundance declined with hydrological connectivity, based on model selection we could not ascribe this relationship to an increased number of large predatory fish species detected in waterbodies close to the main river channel. Differences in life history and habitat requirements are likely to have explained interspecific responses to hydrological connectivity. Our results underscore the importance of addressing amphibian abundance at multiple spatial scales in floodplain wetlands, as landscape composition partly explained patterns in abundance.Application of multi-species abundance modelling allowed us to investigate environmental relationships for common and infrequently detected species. Habitat restoration programmes in floodplains should provide waterbodies disconnected from main river channels as potential amphibian breeding sites and protect or restore forest as terrestrial habitat., Competing Interests: The authors declare there is no conflict of interest surrounding the research undertaken in this study, funding agencies, authors' affiliations or any other potential sources of conflict., (© 2023 The Authors. Freshwater Biology published by John Wiley & Sons Ltd.)

Environmental policies fall short in protecting freshwater ecosystems, which are heavily threatened by human pressures and their associated stressors. One reason is that stressor effects depend on the context in which they occur and it is difficult to extrapolate patterns to predict the effect of stressors without these being contextualized in a general frame. This study aims at improving existing decision-making frameworks such as the DPSIR approach (Driver-Pressure-State-Impact-Response) or ERA (Environmental Risk Assessment) in the context of stressors. Here, we delve into stressor-impact relationships in freshwater ecosystems and develop a guideline which includes key characteristics such as stressor type, stressor duration, location, the natural levels of environmental variables to which each ecosystem is used to, among others. This guideline is intended to be useful in a wide range of ecosystem conditions and stressors. Incorporating these guidelines may favor the comparability of scientific results and may lead to a substantial advancement in the efficacy of diagnosis and predictive approaches of impacts., 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 © 2021 Elsevier B.V. All rights reserved.)

Urban surface runoff from storms impacts the water quality dynamics of downstream ecosystems. While these effects are well-documented in mesic regions, they are not well constrained for arid watersheds, which sustain longer dry periods, receive intense but short-lived storms, and where stormwater drainage networks are generally isolated from sewage systems. We used a network of high-frequency in situ water quality sensors located along the Middle Rio Grande to determine surface runoff origins during storms and track rapid changes in physical, chemical, and biological components of water quality. Specific conductivity (SpCond) patterns were a reliable indicator of source, distinguishing between runoff events originating primarily in urban (SpCond sags) or non-urban (SpCond spikes) catchments. Urban events were characterized by high fluorescent dissolved organic matter (fDOM), low dissolved oxygen (including short-lived hypoxia <2 mg/L), smaller increases in turbidity and varied pH response. In contrast, non-urban events showed large turbidity spikes, smaller dissolved oxygen sags, and consistent pH sags. Principal component analysis distinguished urban and non-urban events by dividing physical and biogeochemical water quality parameters, and modeling of DO along the same reach demonstrated consistently higher oxygen demand for an urban event compared to a non-urban event. Based on our analysis, urban runoff poses more potential ecological harm, while non-urban runoff poses a larger problem for drinking water treatment. The comparison of our results to other reports of urban stormwater quality suggest that water quality responses to storm events in urban landscapes are consistent across a range of regional climates., Competing Interests: Declaration of competing interest The authors do not declare any conflict of interest in submitting this manuscript for publication., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Although river restoration has increased rapidly, observations of successful ecological recovery are rare, mostly due to a discrepancy in the spatial scale of the impact and the restoration. Rivers and their ecological communities are a product of four river facets-hydrology, geomorphology, ecology and biogeochemistry-that act and interact on several spatial scales, from the sub-reach to the reach and catchment scales. The four river facets usually affect one another in predictable pathways (e.g., hydrology commonly controls geomorphology), but we show that the order in which they affect each other and can be restored varies depending on ecoregion and hydroclimatic regime. Similarly, processes at different spatial scales can be nested or independent of those at larger scales. Although some restoration practices are dependent of those at higher scales, other reach-scale restoration efforts are independent and can be carried out prior to or concurrently with larger-scale restoration. We introduce a checklist using the four river facets to prioritize restoration at three spatial scales in order to have the largest positive effect on the entire catchment. We apply this checklist to two contrasting regions-in northern Sweden and in southern Brazil-with different anthropogenic effects and interactions between facets and scales. In the case of nested processes that are dependent on larger spatial scales, reach-scale restoration in the absence of restoration of catchment-scale processes can frankly be a waste of money, providing little ecological return. However, depending on the scale-interdependence of processes of the river facets, restoration at smaller scales may be sufficient. This means that the most appropriate government agency should be assigned (i.e., national vs. county) to most effectively oversee river restoration at the appropriate scale; however, this first requires a catchment-scale analysis of feedbacks between facets and spatial scale interdependence., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Riparian vegetation is a crucial component of fluvial systems and serves multiple socio-ecological functions. The objective of this review is to follow the scientific trajectory of studies of riparian vegetation throughout history and across regions and fields of knowledge. Such a synthesis is challenging because riparian vegetation is an open co-constructed socio-ecological system at the crossroads of the biosphere, hydrosphere, lithosphere, atmosphere and anthroposphere; thus, it exhibits a wide range of ecological patterns and functioning depending on climatic, morphological and land-use contexts. To address this, we used qualitative and quantitative approaches in our review of the scientific literature. From the scientific perspective, how riparian vegetation is studied has changed over time (e.g. development of modeling and geomatic approaches) and varies among fluvial systems and geographic areas (e.g. its relation to groundwater is usually studied more in Oceania and Asia than on other continents). This review revealed the lack of a single and well-identified scientific community that focuses on riparian vegetation. This is probably due to the nature of the subject, which includes diverse fields of knowledge and several applied issues: biodiversity, forestry, water quality, hydromorphology, restoration, ecology, etc. Some topics are actively regenerated (e.g. biogeomorphological approaches) and others are emerging, which reflects general trends in ecology (e.g. functional approaches). The literature review indicates that a substantial amount of knowledge already exists; therefore, a major priority of our study is to produce a clear and integrative understanding of riparian zone functioning to address the inherent complexity of these zones and remain valid across a wide diversity of geographical contexts. It is also essential to develop detailed analysis of the sociocultural dimension of riparian vegetation to understand the ecology of riparian zones and to improve riparian vegetation management according to local recommendations in order to maintain and improve its functions and services in the face of global changes., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The majority of food web studies are based on connectivity, top-down impacts, bottom-up flows, or trophic position (TP), and ecologists have argued for decades which is best. Rarely have any two been considered simultaneously. The present study uses a procedure that integrates the last three approaches based on taxon-specific secondary production and gut analyses. Ingestion flows are quantified to create a flow web and the same data are used to quantify TP for all taxa. An individual predator's impacts also are estimated using the ratio of its ingestion (I) of each prey to prey production (P) to create an I/P web. This procedure was applied to 41 invertebrate taxa inhabiting submerged woody habitat in a southeastern U.S. river. A complex flow web starting with five basal food resources had 462 flows >1 mg·m -2 ·yr -1 , providing far more information than a connectivity web. Total flows from basal resources to primary consumers/omnivores were dominated by allochthonous amorphous detritus and ranged from 1 to >50,000 mg·m -2 ·yr -1 . Most predator-prey flows were much lower (<50 mg·m -2 ·yr -1 ), but some were >1,000  mg·m -2 ·yr -1 . The I/P web showed that 83% of individual predator impacts were weak (<10%), whereas total predator impacts were often strong (e.g., 35% of prey sustained an impact >90%). Quantitative estimates of TP ranged from 2 to 3.7, contrasting sharply with seven integer-based trophic levels based on longest feeding chain. Traditional omnivores (TP = 2.4-2.9) played an important role by consuming more prey and exerting higher impacts on primary consumers than strict predators (TP ≥ 3). This study illustrates how simultaneous quantification of flow pathways, predator impacts, and TP together provide an integrated characterization of natural food webs., (© 2018 by the Ecological Society of America.)

In a changing climate with a warming trend in air temperature, river water temperature increases as a result of heat exchange with the atmosphere. Moreover, of the different types of anthropogenic activity impacting rivers, the construction of dams appears to have multi-dimensional effects on the river environment, and it especially affects the thermal condition of rivers. The aim of the study is to identify and assess the impact of these two distinct sources of water temperature distortion in relation to the natural thermal conditions of rivers. In the study, linear trend analysis and a complex wavelet transform are used. The analysis focuses on daily river water temperature data for time periods before and after the construction of selected reservoirs in the Polish Carpathians, and on daily air temperature data for neighboring meteorological stations. Three rivers were selected for analysis: (1) Dunajec River, 22km downstream of the Czorsztyn-Sromowce Wyżne reservoir complex, (2) Ropa River, 16km downstream of the Klimkówka Reservoir, and (3) Wisłok River, 33km downstream of the Besko Reservoir. Research has shown that the significant increasing trends identified for water temperature are weaker than analogous trends in air temperature. The Czorsztyn-Sromowce Wyżne and Klimkówka reservoirs appear to exert considerable influence on natural air-water temperature synchronization, because the phase difference increases 5-fold in comparison with conditions prior to the construction of the reservoirs. The weakening of the natural air-water temperature synchrony implies diminished impact of air temperature on stream water temperature. However, this creates an opportunity for preparing appropriate management practices mitigating an increasing temperature trend in order to shape more favorable (natural) thermal conditions for native aquatic biota in impounded rivers., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The Amazon River watershed and its associated plume comprise a vast continental and oceanic area. The microbial activities along this continuum contribute substantially to global carbon and nutrient cycling, and yet there is a dearth of information on the diversity, abundance, and possible roles of viruses in this globally important river. The aim of this study was to elucidate the diversity and structure of virus assemblages of the Amazon River-ocean continuum. Environmental viral DNA sequences were obtained for 12 locations along the river's lower reach ( n = 5) and plume ( n = 7). Sequence assembly yielded 29,358 scaffolds, encoding 82,546 viral proteins, with 15 new complete viral genomes. Despite the spatial connectivity mediated by the river, virome analyses and physical-chemical water parameters clearly distinguished river and plume ecosystems. Bacteriophages were ubiquitous in the continuum and were more abundant in the transition region. Eukaryotic viruses occurred mostly in the river, while the plume had more viruses of autotrophic organisms ( Prochlorococcus , Synechococcus ) and heterotrophic bacteria ( Pelagibacter ). The viral families Microviridae and Myoviridae were the most abundant and occurred throughout the continuum. The major functions of the genes in the continuum involved viral structures and life cycles, and viruses from plume locations and Tapajós River showed the highest levels of functional diversity. The distribution patterns of the viral assemblages were defined not only by the occurrence of possible hosts but also by water physical and chemical parameters, especially salinity. The findings presented here help to improve understanding of the possible roles of viruses in the organic matter cycle along the river-ocean continuum. IMPORTANCE The Amazon River forms a vast plume in the Atlantic Ocean that can extend for more than 1,000 km. Microbial communities promote a globally relevant carbon sink system in the plume. Despite the importance of viruses for the global carbon cycle, the diversity and the possible roles of viruses in the Amazon are poorly understood. The present work assesses, for the first time, the abundance and diversity of viruses simultaneously in the river and ocean in order to elucidate their possible roles. DNA sequence assembly yielded 29,358 scaffolds, encoding 82,546 viral proteins, with 15 new complete viral genomes from the 12 river and ocean locations. Viral diversity was clearly distinguished by river and ocean. Bacteriophages were the most abundant and occurred throughout the continuum. Viruses that infect eukaryotes were more abundant in the river, whereas phages appeared to have strong control over the host prokaryotic populations in the plume.

Geritz, Gyllenberg, Jacobs, and Parvinen show that two similar species can coexist only if their strategies are in a sector of parameter space near a nondegenerate evolutionarily singular strategy. We show that the dimorphism region can be more general by using the unfolding theory of Wang and Golubitsky near a degenerate evolutionarily singular strategy. Specifically, we use a PDE model of river species as an example of this approach. Our finding shows that the dimorphism region can exhibit various different forms that are strikingly different from previously known results in adaptive dynamics.

Most river systems are impacted by sewage effluent. It remains unclear if there is a lower threshold to the concentration of sewage effluent that can significantly change the structure of the microbial community and its mobile genetic elements in a natural river biofilm. We used novel in situ mesocosms to conduct replicated experiments to study how the addition of low-level concentrations of sewage effluent (nominally 2.5 ppm) affects river biofilms in two contrasting Chalk river systems, the Rivers Kennet and Lambourn (high/low sewage impact, respectively). 16S sequencing and qPCR showed that community composition was not significantly changed by the sewage effluent addition, but class 1 integron prevalence (Lambourn control 0.07% (SE ± 0.01), Lambourn sewage effluent 0.11% (SE ± 0.006), Kennet control 0.56% (SE ± 0.01), Kennet sewage effluent 1.28% (SE ± 0.16)) was significantly greater in the communities exposed to sewage effluent than in the control flumes (ANOVA, F = 5.11, p = 0.045) in both rivers. Furthermore, the difference in integron prevalence between the Kennet control (no sewage effluent addition) and Kennet sewage-treated samples was proportionally greater than the difference in prevalence between the Lambourn control and sewage-treated samples (ANOVA (interaction between treatment and river), F = 6.42, p = 0.028). Mechanisms that lead to such differences could include macronutrient/biofilm or phage/bacteria interactions. Our findings highlight the role that low-level exposure to complex polluting mixtures such as sewage effluent can play in the spread of antibiotic resistance genes. The results also highlight that certain conditions, such as macronutrient load, might accelerate spread of antibiotic resistance genes., (Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The spatiotemporal distribution of microbial diversity, community composition, and their major drivers are fundamental issues in microbial ecology. In this study, the planktonic bacterial and microeukaryotic communities of the Jiulong River were investigated across both wet and dry seasons by using denaturing gradient gel electrophoresis (DGGE). We found evidence of temporal change between wet and dry seasons and distinct spatial patterns of bacterial and microeukaryotic communities. Both bacterial and microeukaryotic communities were strongly correlated with temperature, NH4-N, PO4-P, and chlorophyll a, and these environmental factors were significant but incomplete predictors of microbial community composition. Local environmental factors combined with spatial and temporal factors strongly controlled both bacterial and microeukaryotic communities in complex ways, whereas the direct influence of spatial and temporal factors appeared to be relatively small. Path analysis revealed that the microeukaryotic community played key roles in shaping bacterial community composition, perhaps through grazing effects and multiple interactions. Both Betaproteobacteria and Actinobacteria were the most dominant and diverse taxa in bacterial communities, while the microeukaryotic communities were dominated by Ciliophora (zooplankton) and Chlorophyta (phytoplankton). Our results demonstrated that both bacterial and microeukaryotic communities along the Jiulong River displayed a distinct spatiotemporal pattern; however, microeukaryotic communities exhibited a stronger distance-decay relationship than bacterial communities and their spatial patterns were mostly driven by local environmental variables rather than season or spatial processes of the river. Therefore, we have provided baseline data to support further research on river microbial food webs and integrating different microbial groups into river models.