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This study implements an entropy theory-based approach to infer bathymetry for 29 selected cross-sections along a 1740 km reach of the Congo River. A genetic algorithm optimization approach is used based on an analysis of near-surface velocity measurements to generate a random sample of 1000 bathymetry profiles from which the analysis is carried out. The resulting simulated bathymetry shows good agreement compared to the measurements obtained via Accoustic Doppler Current Profiler (ADCP), with a correlation that varies from 0.49 to 0.88. The bathymetry results are subsequently used to estimate the two-dimensional cross-sectional flow velocity distribution and, consequently, to calculate the river discharge. The mean errors observed for flow area, discharge, and mean velocity are found to be 2.7%, 1.3%, and 1%, respectively. This study demonstrates, for the first time, the successful application of an entropy-based approach to estimate bathymetry and discharge in large rivers and has significant implications for remote sensing applications. [ABSTRACT FROM AUTHOR]

The origin of the Amazon River is formed at the confluence of the Marañón and Ucayali rivers. Remote sensing and detailed hydrodynamics, sediment transport and bed morphology analysis under different hydrological conditions have been applied to understand the control mechanisms of the modern confluence, thus informing about ancient confluences. Results showed that: 1) meandering‐meandering confluences existed when bifurcated meandering channels from the Marañón River joined the meandering Ucayali River, 2) far‐field scale provided the boundary conditions for the near‐field scale processes. In the case of the Marañón River, the spatial frequency and displacement of incoming anabranching structures to the confluence location set the boundary conditions for the near‐field scale. In the case of the Ucayali River, the incoming hydrodynamics and bed morphology are governed by far‐field processes such as the occurrence of cutoffs, 3) high intensity secondary flows at large rivers were observed at far‐ and near‐field scales, where previous studies have reported that secondary flows are weak or nonexistence or mainly found downstream of confluences. Finally, 4) even though the Marañón River is larger compared with the Ucayali River, the confluence hydrogeomorphology is governed by the Ucayali River because of more developed and stronger secondary flows. [ABSTRACT FROM AUTHOR]

Blooms of toxin-producing cyanobacteria are an enduring public health threat in lakes and rivers. In addition to more commonly studied planktonic taxa in lakes, attached cyanobacteria covering riverbeds and lake littoral zones can produce anatoxins, potent neurotoxins of growing concern. However, relative to planktonic blooms, the geographical and temporal extent and ecology of anatoxin-producing benthic cyanobacteria are poorly documented. To increase understanding of the distribution of these cyanobacteria and their relationships with physicochemical variables, we surveyed sites throughout the Klamath River watershed in Northern California, USA, for anatoxins from benthic mats. We used visual surveys, composite mat samples, water samples, and samples of transported coarse particulate organic matter (CPOM) to quantify benthic cyanobacteria and anatoxin extent. Benthic anatoxins were widespread, adding to a growing body of evidence that anatoxins from benthic cyanobacteria may be more common than previously recognized. Anatoxin concentrations were highest in benthic mats compared with water column and CPOM samples. Anatoxin detection frequency, as indicated by anatoxin synthetase genes, was high in both transported CPOM and benthic mats (74 and 86%, respectively), and transported CPOM anatoxin concentrations reflected benthic mat anatoxin concentrations and cover. Relationships between observed taxa, toxin concentrations, and genetic source tracking indicated that Microcoleus was the dominant anatoxin producer. Clear, low-nutrient tributaries supported anatoxin concentrations as high as, and in some cases higher than, mainstem sites that had higher nutrients. Weak, negative relationships among water quality parameters and anatoxins suggest that some aspects of the tributary streams not captured in this analysis promote the proliferation of benthic Microcoleus and associated anatoxin production. Monitoring benthic mats, including the use of nets targeting sloughed benthic material, can inform public health notifications and document changes in the proliferation of benthic cyanobacteria and associated cyanotoxin production in rivers. [ABSTRACT FROM AUTHOR]

Adequate monitoring of river discharge is crucial for effective water resource management. However, this objective remains difficult to achieve in the context of large and ungauged river basins. This study assesses the performance of remote sensing applications for discharge monitoring in the lower reach of the Congo River, where daily discharge information is required to support many water resource operations. The approach is based on the use of Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing imagery to produce a daily time series of a ratio of reflectance values (C/M) for discharge monitoring. The validation of the approach is performed based on three-year water level data collected at the outlet gauging site and limited in situ Acoustic Doppler Current Profiler (ADCP) cross-section measurements for high and low flow seasons. The simulated discharge closely matches the observed values and falls within acceptable ranges, with errors below 10% and Nash-Sutcliffe coefficients ranging from 0.65 to 0.76 for ADCP and gauging station, respectively. [ABSTRACT FROM AUTHOR]

Silver Carp (Hypophthalmichthys molitrix) populations have established and expanded throughout the lower Mississippi River basin (LMRB). Information pertaining to Silver Carp population mixing among rivers within the LMRB is lacking. Documented relations between Silver Carp otolith and river water barium (Ba) and strontium (Sr) microchemical signatures may enable estimation of origins of Silver Carp in the LMRB. Replicate water samples and otoliths from 308 Silver Carp were collected from the Cache, Arkansas, White, Yazoo, St. Francis, L'Anguille, and Mississippi rivers, and Merrisach Lake (situated along a canal connecting the lower reaches of the Arkansas and White rivers) within the LMRB. Water and carp otolith microchemical signatures exhibited consistent differences among water bodies. A classification and regression tree model exhibited 80% accuracy when assigning carp collected from the White, Arkansas, and Mississippi rivers based on fish-water microchemical signatures. Model accuracy decreased as smaller rivers were incorporated into models. Predicted natal origin based on otolith microchemical signatures suggested the White River (43%) and the lower Mississippi River (39%) were the likely origins for ~ 82% of the Silver Carp sampled. Despite the prevalence of adult Silver Carp within the Arkansas River system, fewer (18%) appeared to have originated there compared to the White and Mississippi rivers. Long-term water sampling and additional isotopic measurements may refine analyses to better determine the relative contributions of Silver Carp from the smaller river systems. Population mixing of Silver Carp among tributary rivers appears to be common within the LMRB, and removal efforts may benefit from evaluating the magnitude of fish movement and connectivity among rivers. [ABSTRACT FROM AUTHOR]

Large rivers are characterized by large water discharges, high suspended sediment fluxes and low slope, and typically display multiple channels that are separated by large complex bars. The most common channel style found in these rivers is characterized by the alternating presence of single and multiple channel threads. Mid‐channel compound bars separate a main deeper channel from shallower secondary channels, leading to low‐order braiding and low to moderate sinuosity. Despite the importance of this type of river for global terrestrial sediment transport and the interpretation of ancient fluvial successions, integrated depositional models for large multi‐channel rivers are still not fully developed. This paper interprets the channel morphodynamics and depositional architecture of such large rivers by investigating the distinctive features of their laterally‐accreting mid‐channel bars in the Solimões–Amazonas River. This is achieved by examination of temporal series of satellite images, quantification of bedforms using multibeam echosounding surveys, analysis of shallow seismic and ground penetrating radar surveys of selected areas, and on‐site field observations and sample collections. Such mid‐channel bars produce directional variability in planform scroll bar accretion of up to 180°. As these bars – and their associated channels – evolve, they become progressively shallower, due to the bifurcation of the two channels and the resultant partitioning of discharge that leads to a gradual reduction in transport capacity within the outer channel. The preserved successions of this process in the alluvial plain are characterized by fining‐upward trends, with larger cross‐strata sets at mid‐depths and internal erosional surfaces marking distinct cycles of bar development with potentially differing palaeocurrent trends. The new depositional models proposed for these mid‐channel bars and channels constitute a basis for the recognition of large multi‐channel river deposits in the ancient rock record. [ABSTRACT FROM AUTHOR]

Ecosystem structure and its heterogeneity shape ecosystem processes. Ecosystem heterogeneity has been characterized in smaller stream ecosystems dominated by benthic processes. However, in larger river ecosystems structured by water column characteristics including suspended sediment and phytoplankton, ecosystem heterogeneity has not been directly observed. We assessed flow‐dependent ecosystem structure along 230 km of a large, highly managed Great Plains river (The Kansas River) by analyzing 1‐dimensional, downstream color profiles across flow conditions derived from satellite imagery. River color is a robust metric that reflects the combined state of several important large‐river habitat features, specifically suspended sediment, chromophoric dissolved organic matter, and phytoplankton. We found that at flows above a flow threshold that we call Qpatch (240 m3 s−1), the entire river was uniformly yellow. At flows below Qpatch, the river was generally greener and often had patches of very green water that occurred upstream of run‐of‐river dams. Comparing color with in situ data showed the color patches were likely areas of elevated chlorophyll‐a concentrations from phytoplankton accumulation, indicating that the patches reflected biological processes. Flows were below Qpatch on 77% of days during the period of record (1985–present), indicating that the ecosystem spends significant time in a patchy state. Our findings uniquely demonstrate that the water column characteristics structuring temperate, large‐river ecosystems can be patchy. Plain Language Summary: An ecosystem represents a collection of smaller areas, or patches, that play different ecological roles. We can see and walk through patches in forests, however within flowing aquatic ecosystems like large rivers, it is difficult to see and characterize patches. Here, we present direct observations of downstream patches along a river and how they change across streamflow conditions. We measure spatial variation using satellite‐derived water color observations as a proxy for ecosystem properties along a highly managed Great Plains river, The Kansas River. Increases in algae floating in the river should make the river greener, while increases in sediment should make the river more yellow. We found that at high flows above a distinct threshold, the entire river was uniformly yellow. At flows below the threshold, the river was greener and often had particularly green patches behind small, in‐river dams. Comparing our color observations with in‐stream sensor measurements indicated that the green patches were likely caused by elevated algae accumulation and not a reduction in sediment. This work thus revealed a surprising feature of large rivers: they may have stable patches created largely by biological processes. Key Points: We use 1‐D profiles of water color on a large, managed Great Plains river to assess shifts in ecosystem structure across flow conditionsThe 77% percentile flow marked a threshold: above, the river was uniformly yellow. Below, the river was greener and showed green patchesIn situ data suggested these green patches were biologically driven, caused by increased phytoplankton growth upstream of run‐of‐river dams [ABSTRACT FROM AUTHOR]

Multimetric indices play a pivotal role in assessing river ecological quality, aligning with the European Water Framework Directive (EU WFD) requirements. However, indices developed specifically for large rivers are uncommon. Our objective was to develop a fish-based tool specifically tailored to assess the ecological quality in Portuguese large rivers. Data were collected from seven sites in each of three Portuguese large rivers (Minho, Guadiana, and Tagus). Each site was classified using an environmental disturbance score, combining different pressure types, such as water chemistry, land use, and hydromorphological alterations. The Fish-based Multimetric Index for Portuguese Large Rivers (F-MMIP-LR) comprises four metrics: % native lithophilic individuals; % alien individuals; % migrant individuals; and % freshwater native individuals, representing compositional, reproductive, and migratory guilds. The index showed good performance in separating least- and most-disturbed sites. Least-disturbed sites were rated 'high' or 'good' by F-MMIP-LR, contrasting with no such classification for most-disturbed sites, highlighting index robustness. The three rivers presented a wide range of F-MMIP-LR values across the gradient of 'bad' to 'high', indicating that, on a large spatial extent, the biological condition was substantially altered. The F-MMIP-LR provides vital information for managers and decision-makers, guiding restoration efforts and strengthening conservation initiatives in line with the WFD. [ABSTRACT FROM AUTHOR]

Apocorophium lacustre – a species of benthic amphipod native to American and European estuaries along the North Atlantic Ocean – has rapidly expanded outside of its native range and is now established in the Illinois, Upper Mississippi, and Ohio river systems, USA. A. lacustre is considered high risk for colonization and disruption of the Laurentian Great Lakes’ benthic communities. To further our understanding of factors influencing A. lacustre distribution and its threat to the Great Lakes, zoobenthic and habitat data were collected from colonization samplers (i.e., rock bags) deployed at 370 sites along the Illinois Waterway. A. lacustre was found in the lower six pools of the Illinois Waterway and was the most abundant amphipod collected in those pools. Our results parallel other studies in that A. lacustre was not observed upstream of Dresden Island Pool, but A. lacustre was found ~11 km farther upstream of any previous records. Generalized linear mixed effects modeling indicated that parameters pertaining to food availability, water quality, and impoundment influenced A. lacustre abundance. Model averaging identified five statistically significant variables: A. lacustre abundance was negatively associated with turbidity, fluorescent dissolved organic matter, and vegetation density and positively associated with temperature and downstream distance (i.e., closer to the next downstream dam). Our findings of what factors influence A. lacustre abundance should be of broad interest to risk assessment and invasion forecasting in other regions where A. lacustre have been or may be introduced. [ABSTRACT FROM AUTHOR]

Abstract: The water hyacinth, Pontederia crassipes, is a free-floating aquatic plant native to South America, which has colonized tropical rivers in several continents and has become dominant in floodplains. Aim This study aimed to evaluate the relationship between leaf length and leaf biomass (as an indirect phenometric estimation) and to compare the accuracy of the indirect phenometric estimation (which is a non-destructive method) with that of the direct estimation of aboveground biomass (which is destructive). Methods Pontederia crassipes green leaves of all sizes were collected from a floodplain lake of the Paraná River (Argentina). The leaves were oven-dried in the laboratory to obtain the constant dry weight. To determine the accuracy the indirect phenometric estimation was compared with the direct estimation of aboveground biomass. The relationship between leaf weight and leaf length was evaluated by regression analysis. The length of the 279 green leaves collected ranged between 7 and 115 cm. Results The non-destructive method was a good predictor of leaf biomass (R2 = 0.87 p < 0.0001). No significant differences were found between the dry weight obtained directly and that estimated by the indirect method. Conclusions Our results suggest that leaf length is a good attribute to estimate the aboveground biomass of P. crassipes. This method can contribute to diminish the impact of the direct method of harvest of P. crassipes and can be applied in experimental studies aimed to determine the leaf life span and primary productivity of P. crassipes clones.

Simple Summary: Aquatic habitats in urban areas are often important for conservation of local biodiversity. Although Odonata are widely used as ecological indicators of freshwater habitat integrity and health, our understanding and knowledge of their ecological requirements in urban landscapes is not yet complete. Therefore, the taxonomic and functional diversity of Odonata assemblages was analyzed in a semi-natural wetland in the Croatian capital in the summers of 2020 and 2023. The two main habitat types, anthropogenically disturbed and natural oxbow lakes, mostly had comparable assemblage metrics. However, we found significant differences in relation to the time scale, where most metrics were lower in 2023, indicating the negative impact of extreme climate events (including droughts) that occurred in this region after 2020. As even some species of conservation concern were detected, our results indicate that semi-natural urban wetlands, especially natural oxbow lakes, have great potential to function as good habitats for Odonata. As the human population in urban areas is continuously growing, urbanization is one of the greatest threats to biodiversity. To mitigate the negative effects, the inclusion of blue zones (aquatic habitats) in modern urban development practices is strongly recommended, as they could be beneficial for the local biodiversity conservation. Odonata are a flagship group and are widely used in freshwater conservation as ecological indicators of habitat integrity and health. However, our understanding of their ecological requirements in urban landscapes is not yet complete. Therefore, we analyzed the taxonomic and functional diversity of Odonata in a semi-natural wetland in the Croatian capital. This study was conducted in the summers of 2020 and 2023. Most taxonomic and functional assemblage metrics were comparable between the two main habitat types, anthropogenically disturbed and natural oxbow lakes. However, significant differences were found in relation to the time scale, where most metrics were lower in 2023, indicating the negative impact of extreme climate events (including droughts) that occurred in this region after 2020. With 19 species recorded, our results indicate that semi-natural urban wetlands, especially natural oxbow lakes, have great potential to function as good habitats for Odonata, where even some species of conservation concern were detected. When developing landscape management plans in urban areas, it is essential to consider the importance of habitat heterogeneity in terms of good structure of aquatic macrophytes (presence of submerged, emergent and floating vegetation), which would ensure the most suitable habitat conditions for local Odonata species. [ABSTRACT FROM AUTHOR]

Meteorological and hydrological forcings influence phytoplankton at very short-time scales. The effect of turbulence, dilution, light, and nutrients are highly dynamic. Yet, our knowledge of short-term phytoplankton dynamics associated with discharge disturbances and nutrient inputs remains elusive, especially in large rivers. Based on every three-day monitoring, we studied phytoplankton in the middle Loire River (France) and related to the daily variations in water discharge and the physical and chemical parameters. We focused on summer phytoplankton (2013 and 2014), where dissolved inorganic phosphorus concentration was potentially limiting growth. We identified eight discharge events, which increased suspended matter concentration and decreased chlorophyll-a concentration. The most significant environmental drivers of phytoplankton composition were discharge and water temperature, a sensitive proxy for meteorological forcing at short-time scale. The phytoplankton composition responded to changes in hydrology along with three distinct assemblage types, where even small water discharge increase induced a community response. Meroplanktic algae being able to withstand sedimentation and resuspension could take advantage of hydrological peaks, following the benthic retention hypothesis. Our results suggest that short-term dynamics are crucial to understanding community organization and functioning in large river plankton, with meroplankton playing a decisive role in maintaining phytoplankton diversity and ecosystem functioning. [ABSTRACT FROM AUTHOR]

The phytoplankton functional group (FG) classification system sensu Reynolds enables evaluating the ecological status of rivers using the Q(r) compositional index. Here, we apply the Q(r) index to analyze the ecological conditions of the Southern Bug River, at the entire river length, in the early 20th century, testing it first on historic river phytoplankton data. Moreover, we combined the FG approach with the saprobic index and taxonomic richness to assess the ecological status of the river more reliably. The Bray–Curtis Similarity index highlighted the spatial clustering of river sites that corresponded well to the bioregions of the Eastern Lowlands and the Pontian Province. The Q(r) index revealed a higher variation in ecological status among sites than the saprobic index. Therefore, we argue that the FG approach provides a sensitive ecological status indication approach for river phytoplankton, including historical human impacts. The method may improve understanding of reference conditions and assessing the ecological status of Ukrainian rivers, as requested by the European Water Framework Directive. [ABSTRACT FROM AUTHOR]

Objective: This study compiled data sets from multiple research efforts from 2010 to 2018 to describe patterns in the presence and density of larval lampreys in deep water habitats across 430 river kilometers of the lower and middle main‐stem Columbia River. Methods: We used logistic regression to evaluate the influence of landscape‐level factors on Pacific Lamprey Enthosphenus tridentatus and Lampetra spp. presence. Additionally, we used N‐mixture models to estimate larval lamprey densities in six river mouths in the spring and fall of multiple years. Result: At the landscape‐level, the models suggested that the probability of presence for both Pacific Lampreys and Lampetra spp. decreased with increasing distance from the ocean, distance from the closest upstream tributary river mouth, and distance from the nearest main‐stem riverbank. The probability of presence also varied by upstream tributary river mouth. The probability of larval presence in river mouths was an order of magnitude greater than in reservoir pools. Evaluating river mouth habitats, larval lamprey densities varied seasonally, annually, and among river mouths, ranging from 0.04 to 9.63 larvae/m2. Results generally suggested broader distributions and higher densities within river mouths during spring when flows were high compared to the fall when flows were lower, although not in all river mouths or across all years. Larval densities increased in the Wind and Klickitat rivers (the most consistently examined tributary river mouths) over the study period. Conclusion: Our findings suggest that the main‐stem Columbia River supports larval lamprey rearing year‐round. Probability of presence was highest and variable among river mouths, suggesting the importance of some river mouths as rearing habitats. Understanding shifts (seasonal, annual, and those as result of changes in environmental conditions) in lamprey presence and density could inform how specific management actions (e.g., dewatering for in‐river work) and their timing could affect larval lampreys in rivers. Impact statementThis research demonstrated that the main‐stem river habitats provide year‐round rearing for lampreys and tributary river mouth habitats are of particular importance. Understanding changes in seasonal and annual shifts in populations could inform management and conservation actions for lampreys in large rivers systems. [ABSTRACT FROM AUTHOR]

In large rivers, floods are affected by the mosaic of geomorphic and geologic settings of the fluvial corridor. Here, we assess the role of geomorphology on the downstream flood dynamics of the Araguaia River, the largest free-flowing river in Central Brazil. The study integrates and advances existing flood-type classifications. We assess the factors that govern flood hydrograph properties and their downstream propagation by using flow time series, conducting statistical analysis, and evaluating geomorphic and flood metrics. Our findings highlight the role of geomorphology in the transmission of floods. In the upper and lowermost fluvial segments, the geological characteristics of the valley are a major factor. In the intermediate section, two main factors modulate the floods. The wide and complex floodplain plays a major role through storage and buffer effect for floods, and water diversion from the main system to a huge abandoned channel by avulsion governs seasonal flow transfers. The Araguaia is the most geodiverse floodplain of the Amazon–Cerrado ecotone, and floods play a fundamental ecological role in the river–floodplain environments. The combination of diverse factors controlling the flood mechanisms has to be considered when implementing conservation plans for the fluvial corridor and effective river management strategies. [ABSTRACT FROM AUTHOR]

The connectivity of large rivers is impaired by human activities, which could cause severe consequences to hydrodynamics, water quality. To clarify the changes in hydrological connectivity of large rivers and their effects on nutrients, a composite index method of river connectivity in longitudinal, lateral and vertical dimensions was developed in this study. Taking the middle reaches of the Yangtze River as an example, the hydrological connectivity of typical hydrological years and periods in the region was analyzed, and the responses of critical nutrient indexes to varied river connectivity was assessed. The results showed that significant temporal and spatial variations in river connectivity were observed, with better river connectivity in the wet year than the dry year, and worse connectivity in headwaters, tributaries, or downstream of gates and dams than other river reaches. This was mainly due to the degree of river fragmentation (DOF) and the degree of regulation (DOR) with a relative importance of 81.28% and 56.07%, respectively, implying that gate and dam interception was the main cause of impaired river connectivity in the study area. Statistical methods indicated that the impaired connectivity in the middle reaches of the Yangtze River implied a stronger retention of nutrients by dams, and that retention effect was greater during the flood period than the non-flood period. The stronger negative correlation between connectivity and TP (correlation coefficient = −0.58) than TN (correlation coefficient = −0.46) during the flood period revealed that phosphorus was more influenced by river connectivity. The results of this study provide important information on water resources and water quality for the management of large rivers.

Abstract: Aim Additive diversity partitioning has been used to explain the accumulation of diversity at different spatial scales with relative success. In lotic ecosystems, the spatial extent is extremely relevant in studies of diversity accumulation, because it encompasses environmental variation that causes changes in the observed communities. Despite of previous knowledge on the effect of extent on biological communities and diversity accumulation, little is known about the topic in aquatic insect communities in large rivers. In this context, we studied the effect of spatial extent and environmental variation on diversity components, alpha and beta, in Ephemeroptera, Plecoptera and Trichoptera (EPT) groups in Xingu River rapids. Methods The sampling was carried out in October 2015 in the dry period of the region, in nine rapids in the Xingu, Bacajá and Iriri rivers. At each collection site, five Surber samples were taken. We also recorded pH, dissolved oxygen, electrical conductivity, water temperature, and geographic coordinates. We used additive diversity partitioning to separate the diversity components α and β. For the spatial component, we generated the spatial filters using PCNM (Principal Coordinates of Neighbour Matrices) and partitioned the variance between space and environment using partial Redundancy Analysis (pRDA). Results We collected 12,249 individuals in 27 genera within 11 families in the EPT orders. The greatest accumulation of diversity was observed among rapids of the river, when the β diversity in this spatial extent was greater than the expected. The spatial structure was an indirect effect at this extent, since it is a relevant drive to environmental variables. Conclusions The results indicate that the effect of spatial extent on rapids is a contributing factor in the diversity components of aquatic insect communities in large river rapids. To the conservation and management of this environment is necessary cover as many rapids as possible, since the preservation of only a few rapids can mean a substantial loss of regional diversity.

The extinction of the Chinese paddlefish Psephurus gladius is examined in the context of transnationalism, technology transfer, and the compressing timescape of human activity, not just from the perspective of Psephurus, but also sturgeons and other long-lived, ancient and not-so-ancient declining fish species. Information is presented and questions raised as to why the extinction of Psephurus occurred, what broader transnational and technological trends may have led to it, and what can be learned and done to save the remaining Acipenseriform and other vulnerable species. Despite Psephurus (and its close relatives) surviving through millions of years of evolutionary time, its rapid descent to extinction, a result of a combination of overharvest, dam construction blocking spawning migrations, and pollution, is best understood in a broader geopolitical context of transfer of technologies for river development and use without adequate concurrent introduction of ecological knowledge needed for species persistence. The slowly developing life histories of Psephurus and many other fishes in a rapidly compressing timescape had led to their formerly adaptive life histories becoming maladaptive in the wild. Biologists and managers must start thinking more about what measures must be implemented immediately to maintain biodiversity of these long-lived but now ill-adapted species in the wild in an increasingly human-dominated, timescape-compressed world. [ABSTRACT FROM AUTHOR]

The annual entrainment of early life history stages of fishes (ELH) into the cooling system of the largest power plant in the Vistula River basin was assessed using passive capture techniques and DNA metabarcoding. Hydrological and thermal conditions during the 2022 breeding season were also analyzed. A total of 5,011 ELH individuals identified to four families and 23 species were recorded. ELH densities upstream of the power plant were an order of magnitude higher than they were downstream. Along with the phenology of occurrence and species composition of drift, this indicated very high (probably close to 100%) ELH mortality during passage through the cooling system. Taking into account low water discharge at constantly high water intake during the season, the absolute estimate of ELH individuals entrained into the cooling system was > 103 × 106. The power plant entrains a notable proportion of one-quarter to one-half of the total ELH drifting by, especially during low-flow periods. Together with the very high abundance of two invasive Ponto-Caspian gobies, the magnitude of the entrainment of ELH into the Kozienice Power Plant presents a truly alarming picture. [ABSTRACT FROM AUTHOR]

Variation in water colour is a remarkable characteristic of Amazonian rivers and reflects their limnological properties and the geomorphology of sub-basins. We present here a literature-based study to examine the relationships between fish species turnover and abiotic properties of Amazonian rivers with contrasting water colours. We analysed fish records and water physicochemical properties (pH, colour, turbidity, dissolved oxygen, ammonia and suspended solids) of eight Amazonian rivers with white-, black- and clearwaters. Rivers with similar water colour shared more fish species than those that contrasted in colour. Increased differences in abiotic parameters imply an increased dissimilarity in fish species composition. Species composition is also related to distance among rivers with high dissimilarity observed in rivers distant to each other. The fish species turnover could be ultimately driven by the geological history of rivers which provides different opportunities to speciation and biotic interchange. Water types likely influence species turnover by selecting fishes with different limits of physiological tolerance and specialized use of different habitat types. Our findings suggest that river water colours are reliable proxies for historical and ecological mechanisms affected fish species distribution. Antropic disturbances of Amazonian rivers with distinct water colours could threaten unique fish assemblages. [ABSTRACT FROM AUTHOR]

Co‐loading of mercury (Hg) with dissolved organic carbon (DOC) is a key driver of the observed spatial and temporal Hg patterns among aquatic ecosystems. Their strong biogeochemical coupling has spurred the use of DOC as a predictor of Hg concentrations and exports in boreal regions where sampling logistics for Hg are costly and complex. Yet relationships between Hg and methylmercury (MeHg) with DOC have recently been shown to be highly variable in terms of slope and strength, suggesting that mechanisms other than co‐transport along the land‐water continuum may drive the relationship between Hg and DOC across landscapes. In this study, we explore the relationship between Hg and MeHg with DOC across 18 boreal rivers collectively draining over 350,000 km2 of the eastern James Bay territory (Québec), comprising watersheds with a wide range of vegetation, water residence time and riverine DOC concentrations and optical properties. Our results show that although a large portion of the variation in Hg and MeHg is explained by concentrations of DOC, Hg‐DOC and MeHg‐DOC relationships and ratios vary greatly both spatially and temporally. We show that ratios and strength of the coupling can be predicted from system hydrology, with declines in Hg:DOC and increase in MeHg:DOC ratios and stronger coupling during the seasonal progression to warmer temperatures, higher water evaporation, and longer residence time. Our study highlights the role of seasonal hydrology and biogeochemical processing in governing Hg, MeHg and DOC patterns in boreal rivers. Plain Language Summary: Different forms of mercury and organic carbon may have similar behaviors in rivers, which facilitates understanding of the processes in the landscapes and in the water that controls the inputs and the losses of these elements. Seasonal and geographic differences in the factors behind this behavior, however, may break this similarity and highlight key processes of environmental importance. Here we show how organic carbon and mercury loaded from land tend to be strongly associated across 18 rivers found across a >350,000 km2 boreal landscape, especially during periods of high flow and low temperature that favor passive transport of these elements. Higher concentrations and proportions of biomagnifiable neurotoxic methylated mercury relative to total mercury and organic carbon concentrations, were found during warm and low flow seasons that favored high biological transformation of the mercury and carbon pools during the riverine transit from land to ocean. The amount and nature of the mercury and carbon that is loaded from land to water, and that is transformed in rivers thus greatly varies across seasons, with implications for future trends in climate and hydrology. Key Points: Hg:DOC and MeHg:DOC ratios were as variable over seasons than spatially across a 350,000 km2 boreal landscapeHg and dissolved organic carbon (DOC) were mostly coupled under conditions of high flow and low biogeochemical processingHg and colored DOC were preferentially lost during high processing seasons compared to bulk DOC and MeHg [ABSTRACT FROM AUTHOR]

Understanding the spatial patterns of dissolved organic matter (DOM) and factors that influence them is crucial for maintaining river ecosystem functions and riverine health, considering the significant role of DOM in water quality and aquatic ecosystems. Nevertheless, there is limited knowledge regarding the spatial variation of DOM bioavailability and the factors driving them in large river systems. This study involved 39 sampling locations along the main stem of the Changjiang River, spanning its entire length (>5000 km) during a dry season. Spatial patterns of DOM were assessed by measurements of DOC concentrations and eight fluorescence DOM indices, namely fluorescence index (FI-A and FI-B), Trytophan/Tyrosine, Humic A, Humic C, humification indices (HIX-A and HIX-B), and Freshness index (β/α). The results revealed that the water DOM in the main stem of the Changjiang River primarily originated from terrestrial sources. A decline in DOM bioavailability was observed from the upper to the lower basin, aligning with the carbon processing prediction rather than the river continuum concept (RCC). The pure effect of physicochemical factors (25.30%) was greater than that of geographic factors (9.40%). The internal transformation processes determined the significant longitudinal decreases of DOM bioavailability. While no significant difference in DOM bioavailability was observed between reaches before and after the dams, the construction of dams was found to improve DOM bioavailability at the subsection scale and reduce the spatial autocorrelation of DOM bioavailability across the entire basin. • Dissolved organic matter (DOM) bioavailability exhibited a longitudinal decrease along the river in the natural reaches. • The longitudinal decrease in DOM bioavailability was primarily attributed to internal transformation processes. • Damming resulted in an increase in DOM bioavailability at the subsection scale. • Documented the spatial variation of DOM along the 5,000 km course of the Changjiang River. [ABSTRACT FROM AUTHOR]

Sturgeon populations are declining worldwide and are the target of extensive conservation efforts. Addressed in several pieces of legislation, sturgeons have received considerable attention as flagship or umbrella species. Despite the need for a better understanding of the distribution and population status, the use of traditional sampling methods failed in the past, thereby hampering reliable assessments, a prerequisite for conservation. Here, we describe the development and application of an environmental DNA (eDNA) metabarcoding approach for detecting rare sturgeons in large rivers. Exemplarily, we developed a reference database for five native Danube sturgeons (Acipenser stellatus, Acipenser gueldenstaedtii, Acipenser ruthenus, Acipenser nudiventris, and Huso huso) and two non-native species (Acipenser baerii and Acipenser transmontanus), assessed these ex situ, and used eDNA as a detection tool along the entire length of the Danube (Europe, ~ 2850 km) and major tributaries. In ex situ analyses, all assays yielded positive amplifications for the assessed sturgeon species. In the Danube, the presence of A. ruthenus was confirmed at 14 of 29 sites (48.3%), and in 2 of 18 tributary sites (11.1%), providing the first comprehensive large-scale biogeographical snapshot of this species. Relative number of reads assigned to A. ruthenus varied between 0 and 2.5%, with sites registering positive detections being clustered in 3 sections of the Danube. Our findings enabled us to confirm the advantages of eDNA monitoring over traditional sampling methods for comprehensive whole-river snapshot studies of sturgeons conducted on a large geographical scale, and therefore we consider it to be a promising approach for application in conservation measures, fisheries management, scientific studies, and adaptive management plans for sturgeons on a global scale. [ABSTRACT FROM AUTHOR]

In the context of global climate change, a significant increase in the active layer thickness (ALT) of permafrost is expected in the current century. This process has been observed by researchers over the past few decades. If the current climate trend continues, an increase in ALT may have a significant impact on the concentration of organic matter in Arctic river waters. The relationship between the thickness of the seasonally thawed layer of permafrost and the concentration of dissolved organic matter in river waters has been explored using clustering, one-way ANOVA, and cross-tabulation analysis. The data set for analysis included original details on the content of organic matter in the rivers of Eastern Siberia (in terms of COD, BOD5, and the color of the water), phytoplankton abundance and biomass, and data on the permafrost active layer thickness (ALT) in the catchments. It was revealed that in the areas of catchments where the ALT is deeper, the content of organic matter in the rivers is lower than in areas with a shallow, seasonally thawed permafrost. Our results are consistent with the existing conceptual model of the influence of ALT on the chemistry of river waters in the cryolithozone. This knowledge is important for predicting the chemical composition of the Arctic rivers, eutrophication, and the rate of inflow of dissolved solids into the Arctic Ocean under the current conditions of ALT deepening. [ABSTRACT FROM AUTHOR]

Status of several large-river darter species is uncertain because of difficulties sampling deep-water habitats. We characterized the darter (Family: Percidae) community in main and side channel macrohabitats of the upper Mississippi River using a small-mesh benthic trawl at sites in five navigation pools and a portion of the lower St. Croix River encompassing nearly 200 river kilometers in 2016 and 2017. We captured six darter species in conjunction with a survey to assess crystal darter (Crystallaria asprella) (state endangered) status and estimated density (n/700 m2) and population size for selected species in navigation pools. No crystal darter were collected in 83 trawl tows, including tows made at historical crystal darter locations. However, a total of 154 western sand darter (Ammocrypta clara) (globally vulnerable) were captured with density estimates ranging among pools from 1.0 to 9.6 in main channel and 1.0 to 5.0 in side channel macrohabitats. The largest population estimate was 33,286 (95% confidence limit: 17,974–52,725) for western sand darter in all side channels in Pool 7. A total of 71 river darter (Percina shumardi) were captured with zero caught in some pools to a maximum mean density of 17.5/700 m2 in Pool 3. Highest population size was 14,829 (8260–25,127) for river darter in the lower St. Croix River. A total of 43 logperch (Percina caprodes) and 143 johnny darter (Etheostoma nigrum) were captured but exhibited clumped spatial distributions that hindered population estimates. Only three mud darter (Etheostoma asprigene) and one slenderhead darter (Percina phoxocephala) were captured in deep-water habitats. Crystal darter absence supports continued state endangered classification. However, our density and population estimates for western sand darter and river darter represent the first such estimates for the upper Mississippi River and perhaps the world and should be used as baselines for future comparisons. [ABSTRACT FROM AUTHOR]

Regular diversity surveys are important for monitoring changes in the molluscan fauna's species richness and composition in time, especially in areas of large river floodplains, which are biodiversity hotspots characterised by rapid and dynamic habitat changes. This work brings an annotated list of the terrestrial molluscan fauna from the Slovak part of the Danube Plain and contains several original findings based on field observations. Snails and slugs were collected using visual searches, snails were also sampled using leaf litter collections. A total of 81 terrestrial gastropod species (45% of the total number of land gastropods in Slovakia) from 27 families were found in the 45 sites in the whole surveyed territory. The highest number of species (max. 25 species, median = 18) was recorded in flooded forest habitats, followed by non-flooded forest habitats (max. 20 species, median = 15), the least species occurring in open habitats sensu lato (max. 14, median = 9). The ordination (MDS) showed that open wet communities/sites formed an isolated, relatively compact cluster, flooded and non-flooded gastropod communities form more similar, albeit relatively clearly separated clusters. Communities in open dry sites are the most species-specific and heterogeneous. [ABSTRACT FROM AUTHOR]

Recent evidence has shown that Arctic regions have warmed about twice as much as elsewhere on the planet over the last few decades, and that high‐latitude permafrost–periglacial processes and hydrological systems are notably responsive to rising temperatures. The aim of this paper is to report on the thermal regime of islands located along the Lena River floodplain, upstream of the city of Yakutsk (eastern Siberia). Four islands were monitored using waterproof dataloggers and continuous monitoring of frozen soil in contact with ice breakup of the Lena River. For each of these islands, we measured: (a) ground surface temperature, air and frozen soil temperatures at different depths; and (b) submersion duration during the flood. Our results show that within a zone of thick and continuous permafrost, the Lena floodplain is notably heterogeneous, with a combination of permanently and seasonally frozen islands. The ice breakups seem to have a negligible impact on the ground thermal regime. Our study confirms that relatively young (<30 years old) islands, composed of fine sand material, appear less prone to permafrost formation compared to older islands with ice‐rich silty material. [ABSTRACT FROM AUTHOR]

Predictive modeling of phytoplankton transformation in large East Siberian rivers in response to global climate changes was performed. Artificial neural networks and the space-for-time substitution approach have been applied to our analysis. As a result, we determined that, under the trend towards an increase in the ice-free period on subarctic rivers, the likely response of planktonic algae communities will be (1) an increase in the phytoplankton abundance and risk of "algal bloom," (2) an increase in the number of species due to invasions, (3) a decrease in the phytoplankton cell size, and (4) reduction in the number of monotypic taxa in the flora. The aquatic ecosystems of the rivers studied by us are still largely non-impact. This allowed us to evaluate the effect of climate change on phytoplankton, rather than local anthropogenic factors. [ABSTRACT FROM AUTHOR]

Context: Untangling relationships between landscape patterns shaped by human stressors and related response of fish communities is important for identifying biodiversity patterns and conservation targets, yet in large rivers this knowledge is extremely limited. Objectives: Our study focuses on how human stressors within a riparian landscape zone, including both riparian land use and in-channel stressors, explained the fish community structure in a large river. Methods: We studied fish community patterns along the upstream-downstream gradient of the Yangtze River, China. The curve estimation was used to test correlations between fish metrics and the distance from the estuary. We linked human stressors to fish metrics by multivariate generalized linear models. Results: We collected a total of 63 freshwater fish species from 6,147 specimens. Limnophilic species had the highest richness, represented by 30 specie. The predominant riparian land uses in the studied reaches were cropland (65.3% ± 13.1%) and urban land (19.7% ± 13.6%). There were strong negative correlations between riparian land use (e.g., urban land) and in-channel stressors (e.g., shoreline modification, navigation, and fishing pressure) and fish assemblages, especially limnophilic fish abundance, biomass, and richness. Conclusions: These results demonstrate influences of both riparian land use and in-channel stressors on fish communities, and highlight the use of landscape descriptors as a valuable approach to assess linkages between human pressures and fish diversity in large river systems. Management recommendations include: establishing or rehabilitating riparian buffers, improving commercial navigation management, implementing shoreline protection measures, and reinforcing fishing laws and regulations. [ABSTRACT FROM AUTHOR]

Abstract Objectives Mayflies (Insecta: Ephemeroptera) were collected from the Ohio River, Wabash River and White River in Indiana during July and August 2019, with the goals of confirming the continued existence of historic populations of species and discovering previously undocumented populations. Data description Notable new data for Ephoron album (Say) (Polymitarcyidae), Heptagenia elegantula (Eaton) (Heptageniidae), Pentagenia vittigera (Walsh) (Palingeniidae), and Tortopsis primus (McDunnough) (Polymitarcyidae) are reported.

The Ganges River Dolphin Platanista gangetica has been classified as Endangered in the IUCN Red List of Threatened Species. The IUCN changed its status from ‘Vulnerable’ to ‘Endangered’ in 1996 as the species population was declining in its entire distribution range. It is, however, classified as ‘Critically Endangered’ in Nepal. Historically, the freshwater cetacean has been documented in the Karnali, Koshi, Narayani, and Mahakali basins. With their population and distribution range in decline, the Ganges River Dolphin (GRD) is no longer found in the Mahakali River system, which demarcates and traverses the Western border of India and Nepal. This study examines the status and distribution of the GRD in the river systems of Nepal during the monsoon of 2016. The national dolphin population survey was conducted in the three largest river basins in Nepal—Karnali, Narayani, and Koshi. Each of the three basins represent the extreme upstream limit of the GRD distribution in Ganges River basin. The national population survey included both a boat-based survey and shore-based synchronized counting in each of the three river systems. Fifty-two (Best-High-Low: 52-61-50) dolphins were counted during the entire nationwide survey, conducted in July–August, 2016. Researchers gathered social-data from locals residing alongside the observed basin, giving priority to artisanal fishers and those subsisting to some degree from the rivers known to host the river dolphin. A questionnaire survey of ninety-two residents from riparian villages adjacent to the GRD hotspots sheds light on the local perspectives towards dolphin conservation coupled with an assessment of their socio-economic status; artisanal fishing practices; and their awareness of dolphin conservation. According to the survey, notable threats to dolphin conservation are prey depletion; non-availability of suitable habitat; habitat fragmentation and a low level of awareness. Based on the counting outcomes and social survey, recommendations have been put forward for the conservation of this species.

Aquatic macroinvertebrates are often the subject of biomonitoring efforts because they are ubiquitous in most systems and are known to be suitable indicators of water quality. The vast majority of biomonitoring efforts that use macroinvertebrates are tailored towards small, wadeable streams, whereas methods for sampling macroinvertebrates in non-wadeable streams (i.e., large rivers) are often less available. We compared the use of a wood sampler to collect aquatic macroinvertebrates with two more commonly used samplers (Hester-Dendy and leaf packs) to assess its suitability for sampling non-wadeable systems in the Georgia Coastal Plain. All three types of samplers were deployed at three sites on each of the Savannah and Ogeechee River for approximately 30 days during the fall of 2014. Mean, standard deviation, and variance components were examined from 53 common bioassessment metrics and 2 multi-metric indices to assess for potential differences in colonizing macroinvertebrates between the samplers. Only 9 of the metrics examined scored significantly different between sampling devices, however, assemblages colonizing the three sampling devices differed (PERMANOVA; F14,37 =1.6078, P = 0.001). Results suggest assemblage differences were primarily driven by the proportions of taxa collected by each device, rather than by different taxa colonizing devices altogether. Estimates of variance components attributed a large percentage (i.e., >20%) of the variability encountered to differences between sites, rather than devices. Our study shows that wood samplers are comparable to other devices commonly used for collecting macroinvertebrates from non-wadeable streams in the Georgia Coastal Plain. Furthermore, wood samplers can provide a suitable alternative for bioassessment, although some differences in the proportions of taxa collected with alternative devices should be expected. Determining the precision and overall efficiency of alternative sampling devices is an important step towards developing standard operating procedures for the bioassessment of large coastal plain rivers.

The metacommunity theory is a framework that explains the interdependence of local factors and regional processes as community drivers. In rivers, it has been hypothesized that the metacommunity structure and the relative importance of dispersal and local environmental conditions may vary from headwaters toward lowlands. The aims of this study were (1) to analyze the benthic metacommunity structure along the longitudinal dimension of the Paraguay‐Paraná system, and (2) to assess the relative importance of dispersal (spatial structure) and niche‐based processes as drivers of these structures. We used data of oligochaetes assemblages in the studied system and analyzed the Elements of Metacommunity Structure in different river sections. Moreover, we performed a variance partitioning analysis to determine the relative importance of spatial and environmental variables. In the upper section, we found a gradient structure (Gleasonian) and in the lower section we found random and quasi‐Clementsian structures. Similarly, environmental variables were the main structuring factor in the upper section while spatial variables were more important in the delta. The present study provides evidence that metacommunity structure and the underlying mechanisms that shape it, change along the longitudinal dimension of a large South American River. However, we emphasize the necessity of further studies assessing other taxonomic groups and other large South American Rivers. [ABSTRACT FROM AUTHOR]

In European countries, electrofishing by wading is widely applied to sample fish communities in rivers. In deeper rivers, electrofishing even by boat is considered only suitable to sample the shallow, littoral zone. The monitoring sampling methods concerning fish in the Bulgarian sector of the Danube River are electrofishing and drifting gill nets. The scope of this study is to compare different fish sampling approaches in order to identify the most appropriate for this sector, which could be also applicable for the whole lower Danube River stretch. According to the results, concerning Lower Danube River upstream of its delta, fish monitoring by boat electrofishing during day and night altogether with beach seine should be used; drifting gill nets could contribute valuable data in some cases. These sampling methods could also unveil the basic characteristics of alien fish populations. [ABSTRACT FROM AUTHOR]

The Niagara River, which connects two Great Lakes (Erie and Ontario) and forms a border between Canada and the United States, has experienced decades of abiotic and biotic disturbance as well as long-term restoration efforts. Given the iconic riverscape and importance as a binational fisheries resource, a biodiversity assessment of the mainstem Niagara River fish assemblage is overdue. Here, fish assemblage and habitat data from a standardized boat electrofishing program of the Niagara River were combined with species trait data related to substrate associations, diet preferences, reproductive strategies, and body size to quantify biodiversity patterns among river sections (sites above and below Niagara Falls), seasons (spring, summer, fall), and years (2015–2017). Sixty-five species were captured representing a variety of trait combinations. Significant differences in functional dispersion and divergence (i.e., functional diversity) were observed between river sections, seasons, and (or) years. The fish community captured in the lower river in spring 2015 had both the highest average functional dispersion (2.08 ± 0.32 SD) and divergence (0.88 ± 0.04 SD) compared to the other seasonal sampling efforts, but relatively few fishes were captured (n = 686). Although non-native fishes represented a small portion of the catch over the 3 years (8.6% of catch), the seasonal presence (spring and fall) of mostly introduced large-bodied salmonids expanded functional trait space in the lower river during these periods. The importance of rare species on functional diversity metrics suggests further insight on local species detection probabilities is needed to understand if differences in functional diversity reflect ecological patterns or are driven by sampling design. [ABSTRACT FROM AUTHOR]

Mobile hydroacoustic sampling is increasingly being used to monitor fish populations in large rivers; however, several factors may influence the ability to sample fishes with this gear in these environments. This study sought to address the effects of vessel speed, wind speed, the coefficient of variation (CV) of transducer pitch angle, and beam compensation (BC) on hydroacoustic detectability to advance and inform mobile, horizontally oriented hydroacoustic sampling in large rivers. A series of four replicate surveys was conducted past 23 artificial targets at three vessel speeds in a large river. Wind speed data during surveys were obtained, and post‐processing of hydroacoustic data was conducted separately under maximum BC values of 6 and 12 dB. Results revealed significant negative effects of wind speed and transducer pitch CV on buoy detectability, as well as negative interactions between vessel speed and wind speed, with detectability decreasing as wind speed increased, particularly at slower vessel speeds. We suggest this may be due to increased vessel and transducer motion during periods of increased wind speed. Detectability also significantly increased under an expanded BC due to a greater proportion of the water volume being analyzed; however, further work is necessary before implementing greater BC settings in large rivers. These results ultimately display the interactive and negative effects of wind speed and vessel speed on horizontal hydroacoustic detectability in large rivers, revealing important considerations for hydroacoustic monitoring and sampling efforts in these systems. [ABSTRACT FROM AUTHOR]

Projections of change in high‐flow extremes with global warming vary widely among, and within, large midlatitude river basins. The spatial variability of these changes is attributable to multiple causes. One possible and little‐studied cause of changes in high‐flow extremes is a change in the synchrony of mainstem and tributary streamflow during high‐flow extremes at the mainstem‐tributary confluence. We examined reconstructed and simulated naturalized daily streamflow at confluences on the Columbia River in western North America, quantifying changes in synchrony in future streamflow projections and estimating the impact of these changes on high‐flow extremes. In the Columbia River basin, projected flow regimes across colder tributaries initially diverge with warming as they respond to climate change at different rates, leading to a general decrease in synchrony, and lower high‐flow extremes, relative to a scenario with no changes in synchrony. Where future warming is sufficiently large to cause most subbasins upstream from a confluence to transition toward a rain‐dominated, warm regime, the decreasing trend in synchrony reverses itself. At one confluence with a major tributary (the Willamette River), where the mainstem and tributary flow regimes are initially very different, warming increases synchrony and, therefore, high‐flow magnitudes. These results may be generalizable to the class of large rivers with large contributions to flood risk from the snow (i.e., cold) regime, but that also receive considerable discharge from tributaries that drain warmer basins. Key Points: Projected changes in extreme high flows at river confluences are due partly to changes in mainstem‐tributary hydrograph synchronyDecreasing synchrony between snowmelt‐dominated basins dampens anthropogenically forced increases in high flowsUnder large forcing, increased synchrony between a historically snowmelt‐dominated and rainfall‐dominated basin increases high flows [ABSTRACT FROM AUTHOR]

The following paper aims to quantify the bedload transport in the Paraná river in the Porto São José cross section (22°45’52”S; 53°10’34”W), between Porto Primavera and Itaipu dams, Brazil. In the used method, the bedload transport is estimated from the height and the displacement of the dunes along a longitudinal profile. The results were compared with those obtained from classical bedload transport equations. In the Porto São José cross section, the estimated average bedload transport applying the Dune Displacement Method (DDM) was 3,157 t d-1, which corresponds to an average annual bedload transport of 1,152,325 t yr-1. Applying the Van Rijn equation the average bedload transport was calculated in 2,830 t d-1 (1,032,950 t yr-1), while using the Engelund-Fredsøe equation the average bedload transport found was 3,135 t d-1 (1,144,378 t yr-1). The obtained values using different methods presented some coherence each other, which means that these results can be used as a starting point to establish bedload transport estimations in the Upper Paraná river.

Aquatic macroinvertebrates are often the subject of biomonitoring efforts because they are ubiquitous in most systems and are known to be suitable indicators of water quality. The vast majority of biomonitoring efforts that use macroinvertebrates are tailored towards small, wadeable streams, whereas methods for sampling macroinvertebrates in non-wadeable streams (i.e., large rivers) are often less available. We compared the use of a wood sampler to collect aquatic macroinvertebrates with two more commonly used samplers (Hester-Dendy and leaf packs) to assess its suitability for sampling non-wadeable systems in the Georgia Coastal Plain. All three types of samplers were deployed at three sites on each of the Savannah and Ogeechee River for approximately 30 days during the fall of 2014. Mean, standard deviation, and variance components were examined from 53 common bioassessment metrics and 2 multi-metric indices to assess for potential differences in colonizing macroinvertebrates between the samplers. Only 9 of the metrics examined scored significantly different between sampling devices, however, assemblages colonizing the three sampling devices differed (PERMANOVA; F14,37 =1.6078, P = 0.001). Results suggest assemblage differences were primarily driven by the proportions of taxa collected by each device, rather than by different taxa colonizing devices altogether. Estimates of variance components attributed a large percentage (i.e., >20%) of the variability encountered to differences between sites, rather than devices. Our study shows that wood samplers are comparable to other devices commonly used for collecting macroinvertebrates from non-wadeable streams in the Georgia Coastal Plain. Furthermore, wood samplers can provide a suitable alternative for bioassessment, although some differences in the proportions of taxa collected with alternative devices should be expected. Determining the precision and overall efficiency of alternative sampling devices is an important step towards developing standard operating procedures for the bioassessment of large coastal plain rivers. [ABSTRACT FROM AUTHOR]

Reduced body size is among the universal ecological responses to global warming. Our knowledge on how altered body size affects ecosystem functioning in ectothermic aquatic organisms is still limited. We analysed trends in the cell size structure of phytoplankton in the middle Danube River over a 34-year period at multiple levels: (1) average cell size of assemblages (ACS), (2) within the centric diatom community and (3) in the dominant centric diatom taxon: Stephanodiscus. We asked whether global warming and human impacts affected the average cell size of phytoplankton. Also, whether the altered size structure affected how chlorophyll-a, as an ecosystem functioning measure, relates to the ACS of phytoplankton. The cell size of phytoplankton decreased significantly at all organisation levels, and the assemblages became more dispersed in cell size over time. Environmental variables related to global warming and human impacts affected the ACS of phytoplankton significantly. The relationship between chlorophyll-a and the ACS of phytoplankton shifted from negative linear to broad and then narrow hump shape over time. Longer water residence time, warming and decline in nutrients and suspended solids decrease the ACS of phytoplankton in the middle Danube and expectedly in other large rivers. Our results suggest that cell size decrease in phytoplankton, especially of centric diatoms, constrains planktic algal biomass production in large rivers, independently of algal density. Such cell size decrease may also affect higher trophic levels and enhance the more frequent occurrence of "clear-water" plankton in large, human-impacted rivers under global change. [ABSTRACT FROM AUTHOR]

Most grain size monitoring is still being conducted by manual sampling in the field, which is time consuming and has low spatial representation. Due to new remote sensing methods, some limitations have been partly overcome, but methodological progress is still needed for large rivers as well as in underwater conditions. In this article, we tested the reliability of two methods along the Old Rhine River (France/Germany) to estimate the grain size distribution (GSD) in above‐water conditions: (i) a low‐cost terrestrial photosieving method based on an automatic procedure using Digital Grain Size (DGS) software and (ii) an airborne LiDAR topo‐bathymetric survey. We also tested the ability of terrestrial photosieving to estimate the GSD in underwater conditions. Field pebble counts were performed to compare and calibrate both methods. The results showed that the automatic procedure of terrestrial photosieving is a reliable method to estimate the GSD of sediment patches in both above‐water and underwater conditions with clean substrates. Sensitivity analyses showed that environmental conditions, including solar lighting conditions and petrographic variability, significantly influence the GSD from the automatic procedure in above‐water conditions. The presence of biofilm in underwater conditions significantly altered the GSD estimation using the automatic procedure, but the proposed manual procedure overcame this problem. The airborne LiDAR topographic survey is an accurate method to estimate the GSD of above‐water bedforms and is able to generate grain size maps. The combination of terrestrial photosieving and airborne topographic LiDAR methods is adapted to assess the GSD over several kilometers long reaches of large rivers. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]