Functioning Of River Ecosystems Research Articles

River metabolic fingerprints and regimes reveal ecosystem responses to enhanced wastewater treatment.

Although many studies have examined how improvements in wastewater treatment impact river nutrient concentrations and loads, there has been much less focus on measuring river metabolism to evaluate the wider aquatic ecosystem benefits of reducing nutrient inputs to rivers. The objectives of this study were to evaluate the effects of enhanced wastewater treatment (nitrification) on river metabolism in the Grand River, Canada's largest river draining into Lake Erie. Metabolic fingerprints and regimes (calculated from high-frequency dissolved oxygen [DO] measurements) were used to visualize whole-river ecosystem functional responses to these wastewater treatment upgrades. There was a 60% reduction in ecosystem respiration during summer, in response to reductions in effluent total ammonia inputs, causing a shift from net heterotrophy to net autotrophy, and contraction of river metabolic fingerprints. This resulted in major improvements in summer DO concentrations, with reductions in the percentage of days during summer that DO minima fell below water-quality guidelines for protection of aquatic early life stages, from 88% to ≤16%. The results also point to potential cascading impacts on coupled phosphorus and nitrogen cycles, which may generate further improvements in river water quality. During the summer, high rates of river metabolism and nutrient retention may result in measured water-column nutrient concentrations potentially underestimating nutrient pressures. This study also demonstrates the value of combining river metabolism with nutrient monitoring for a more holistic understanding of the role of nutrients in river ecosystem health and function.

Dynamic Simulation of Ecological Flow Based on the Variable Interval Analysis Method

Ecological flow is an important basis for maintaining the structure and function of river ecosystems, and ensuring the sustainable development of economies and societies in river basins. In order to solve the problems of unclear concepts of ecological flow, difficulty in adapting to dynamic changes in demands, and the hydrological conditions and poor operability of calculated results of a practical application, a variable interval analysis method (VIAM) was proposed to calculate the ecological flow. The method comprehensively considered a variety of variable factors, such as spatial–temporal scale changes, hydrological condition changes, ecological service object changes, and calculation method changes. On the basis of a relatively fixed ecological base flow, a variable lifting amount was added to determine the ecological flow, and the ecological flow was a variable interval. Taking the Wei River as an example, the VIAM was validated and applied. With the support of a knowledge visualization integrated platform, the ecological flow simulation system of the Wei River was constructed. The results show that: (1) the VIAM makes the ecological flow calculation more scientific and reasonable, and the ecological flow of the Wei River from the upper reaches to the lower reaches increases gradually under the influence of water inflow, sewage discharge, and erosion and deposition of sediment, and the annual total water demand of the upper limit of ecological flow in a dry year is 1.04 billion m3, 1.63 billion m3, 2.29 billion m3, 4.09 billion m3, and 4.66 billion m3; (2) the variable interval is used to describe the ecological flow, which has strong applicability and operability; (3) the simulation system can quickly adapt to the demand changes in practical application, and provide visual decision support for managers. The VIAM provides new ideas and references for comprehensively promoting the control of the ecological flow.

Analysis of the influence paths of land use and landscape pattern on organic matter decomposition in river ecosystems: Focusing on microbial groups

Organic matter decomposition (OMD) is one of the important river ecosystem functions. Changes in land use and landscape pattern (LULP) have a serious influence on the OMD in neighboring river ecosystems. However, there is limited information on the influence paths of LULP on organic matter decomposition in river ecosystems. In this study, cotton strip (CS) as a substitute for investigating OMD, was introduced to the delineated catchments in Luanhe River Basin in China, meanwhile combining with remote sensing interpretation, water quality analysis, microbial sequencing, and redundancy analysis (RDA) to identify the dominant LULP metrics, water quality parameters, and microbial groups controlling the OMD. Then the structural equation models (SEMs) were used to connect these dominant controlling factors to track the influence paths of LULP on OMD in river ecosystems. RDA results indicated that construction land (CON), farmland (FAR) and landscape shape index (LSI) in LULP, total nitrogen (TN), chemical oxygen demand (COD) and pH in water quality, bacterial phyla Planctomycetes and Firmicutes, as well as fungal phyla Chytridiomycota and Basidiomycota were the dominant factors controlling the OMD (quantified by tensile strength loss (TSL) and respiration (RES)). These four microbial phyla contributed significantly to OMD. SEMs further proposed three paths to explain the mechanism of LULP influencing on OMD, which were CON - TN - Firmicutes - TSL, CON - TN - Chytridiomycota - RES, and FAR - COD - Chytridiomycota - TSL. CON promoted OMD mainly through enhancing TN content in river water to increase Firmicutes and Chytridiomycota. FAR increased Chytridiomycota by decreasing COD in river water, promoting OMD. These results will deepen our understanding of the influence of LULP on river ecosystem functions and provide valuable information for policymakers and managers to carry out watershed land planning and river management in the future.

Renaturyzacja rzek szansą dla ochrony populacji brzegówki Riparia riparia w Polsce

The regulation and reconstruction of rivers and their valleys, apart from drastic hydrological changes, often lead to the change or disappearance of the habitats of valuable plant and animal species. Particularly vulnerable to the loss of breeding sites are species directly associated with precipitous banks and river slopes, which are formed as a result of erosive and landslide processes. Intensive hydrotechnical treatments, such as straightening of the channels or elimination of irregularities of the river banks, resulted in the inhibition of the desirable natural river processes. Bird species native to Poland that require the above nesting conditions, include: sand martin Riparia riparia, kingfisher Alcedo atthis and bee-eater Merops apiaster. More and more actions are taken to restore rivers to a near-natural state. The aim of restoration is not only to increase retention capacity, protect against floods, social and economic benefits, but also to improve the overall functioning of river ecosystems and preserve biodiversity within their valleys. Renaturation includes activities such as the creation of exposed slopes that mimic erosive undercuts, the removal of bank reinforcements or the maintenance of bank gaps, which promote their occupation by the aforementioned bird species. In addition to predation, the loss of suitable breeding sites is the greatest threat to the sand martin population, such as the American mink Neovison vison, the fox Vulpes vulpes and the locally raccoon dog Nyctereutes procyonoides. A regulated river, where the implemented hydrotechnical measures disrupt the functioning of natural river processes, also causes losses in bird broods due to flash floods that destroy many nests together with eggs or nestlings. Sand martins in many places have stopped using riverbeds as breeding places, occupying anthropogenic habitats which, however, have certain limitations and threats. Renaturation is therefore an important measure to be taken in places where past regulations have caused the greatest damage to the environment. The development of anthropogenic areas should be supported in accordance with the principles of sustainable use of natural resources.

Method for monitoring environmental flows with high spatial and temporal resolution satellite data.

Monitoring environmental flows is crucial to maintaining the function and stability of river and lake ecosystems. However, current methods for monitoring environmental flows are expensive and ground based, and the accuracy of the results needs to be verified to evaluate the environmental flows. This evaluation is hampered by the problem of data shortages, such as hydrological and ecological data. In this study, a method for monitoring environmental flows is proposed using multisource high spatial and temporal resolution satellite data. A case study in the Yongding River Basin demonstrates that the method is feasible for monitoring the environmental flows of rivers in semiarid and arid areas. The results show that the environmental flows and months with large water discharges and shortages in the three control sections of the Yongding River Basin were different. Moreover, the downstream river width rarely met the environmental water demand, achieving this only for one period from 2017 to 2019 according to the three typical types of years (an average water year, a dry year, and an extremely dry year). This method and the results have applications in planning environmental flows and could improve the comprehensive management of the ecological environment in river basins.

Disentangling responses to natural stressor and human impact gradients in river ecosystems across Europe

Abstract Rivers are dynamic ecosystems in which both human impacts and climate‐driven drying events are increasingly common. These anthropogenic and natural stressors interact to influence the biodiversity and functioning of river ecosystems. Disentangling ecological responses to these interacting stressors is necessary to guide management actions that support ecosystems adapting to global change. We analysed the independent and interactive effects of human impacts and natural drying on aquatic invertebrate communities—a key biotic group used to assess the health of European freshwaters. We calculated biological response metrics representing communities from 406 rivers in eight European countries: taxonomic richness, functional richness and redundancy, and biomonitoring indices that indicate ecological status. We analysed metrics based on the whole community and a group of taxa with traits promoting resistance and/or resilience (‘high RR’) to drying. We also examined how responses vary across Europe in relation to climatic aridity. Most community metrics decreased independently in response to impacts and drying. A richness‐independent biomonitoring index (the average score per taxon; ASPT) showed particular potential for use in biomonitoring, and should be considered alongside new metrics representing high RR diversity, to promote accurate assessment of ecological status. High RR taxonomic richness responded only to impacts, not drying. However, these predictors explained little variance in richness and other high RR metrics, potentially due to low taxonomic richness. Metric responsiveness could thus be enhanced by developing region‐specific high RR groups comprising sufficient taxa with sufficiently variable impact sensitivities to indicate ecological status. Synthesis and applications. Metrics are needed to assess the ecological status of dynamic river ecosystems—including those that sometimes dry—and thus to identify priority sites requiring action to tackle the causes of environmental degradation. Our results inform recommendations guiding the development of such metrics. We propose concurrent use of richness‐independent ‘average score per taxon’ indices and metrics that characterize the richness of resistant and resilient taxa. We observed interactions between aridity, impacts and drying, highlighting that these new metrics should be region specific, river type specific and adaptable, promoting their ability to inform management actions that protect biodiversity in river ecosystems responding to climate change.

Method for Environmental Flows Regulation and Early Warning with Remote Sensing and Land Cover Data

Environmental flows play a vital role in ecosystem and water resource management. The regulation and management of environmental flows can improve the function and stability of river and lake ecosystems. However, current methods for assessing environmental flows mainly emphasize water management, and there is no complete set of regulations or early warning systems, especially in arid and semiarid basins. In this study, we proposed a method for environmental flows regulation and early warning with remote sensing and land cover data and carried out a case study in the Yongding River Basin, which is a basin typical of arid and semiarid areas. The results show that from 2001 to 2014 the mean precipitation was 17.90 × 109 m3, and the mean water consumption was 19.42 × 109 m3, indicating that the basin water budget was clearly unbalanced and that there was an overall deficiency. Notably, from 2005 to 2014 and in 2014, the available consumable water was less than the water consumption required for human activities, which both showed a trend of further reduction; therefore, long-term and annual early warnings should have been issued. The methods applied in this study and the study outcomes could help in the development of comprehensive management and ecological restoration plans, further improving the ecological environments of river basins.

Animal legacies lost and found in river ecosystems

Animals can impact freshwater ecosystem structure and function in ways that persist well beyond the animal’s active presence. These legacy effects can last for months, even decades, and often increase spatial and temporal heterogeneity within a system. Herein, we review examples of structural, biogeochemical, and trophic legacies from animals in stream and river ecosystems with a focus on large vertebrates. We examine how the decline or disappearance of many native animal populations has led to the loss of their legacy effects. We also demonstrate how anthropogenically altered animal populations, such as livestock and invasive species, provide new legacy effects that may partially replace lost animal legacies. However, these new effects often have important functional differences, including stronger, more widespread and homogenizing effects. Understanding the influence of animal legacy effects is particularly important as native animal populations continue to decline and disappear from many ecosystems, because they illustrate the long-term and often unanticipated consequences of biodiversity loss. We encourage the conservation and restoration of native species to ensure that both animal populations and their legacy effects continue to support the structure and function of river ecosystems.

How environmental stress leads to alternative microbiota states in a river ecosystem: A new insight into river restoration

Catastrophic shifts in river ecosystems can abruptly degrade their structures and functions, often reducing the efficacy of traditional remediation targeting physicochemical properties. Alternative stable states theory can not only explain this phenomenon but also provide a new insight into river restoration; however, little is known about the existence and implications of alternative stable states in a river. Considering the important role of benthic microbiota in sustaining river ecosystem structures and functions, ecological theory and high-throughput sequencing were combined to firstly investigate multi-stability in microbial communities and its relationship with environmental factors in river sediments. The Nanjing reach of the Yangtze River was selected as the study area because of its huge spatial heterogeneity and varying degrees of pollution. Bimodal distributions combined with temporal variations of microbiota status provided direct evidence of bistability by showing the instability at the intermediate. In addition, environmental stress, particularly concentrations of NH4+−N and NO3−−N, was identified as an important driver of alternative microbiota states from the perspectives of the behavior of bistable ecosystems. Comparison of α-diversity indices and network properties between two alternative microbiota states revealed that the diversity and co-occurrence pattern of microbial communities will be high if they are settled in favorable environments (i.e., comprehensive sediment quality identification index > 3.7). Key taxa, including Clostridiales, Nitrospirales and Myxococcales, were discerned by combining LEfSe and network analysis, and their strong interspecies interactions were believed to be an important factor in triggering alternative microbiota states. This study suggests alternative stable states theory should be considered in river remediation to better understand the response of river ecosystems to environmental stress and the effect of hysteresis, benefiting the implementation of effective monitoring and restoration strategies in a river of urban area.

Phylogenetic and functional diversity could be better indicators of macroinvertebrate community stability

It is essential to understand biodiversity’s contribution to maintaining river ecosystem functioning and stability, which will us help to develop more effective strategies for river ecosystem conservation. However, knowledge regarding the relationship between multidimensional characteristics of biodiversity and ecosystem functioning and stability in aquatic ecosystems remains limited. This study examined the relationships between macroinvertebrate multidimensional diversity, secondary productivity, and secondary productivity/biomass (P/B) ratios in natural river ecosystems to examine which kind of diversity could best indicate community stability. In this study, macroinvertebrates were extensively sampled from Chishui River (CSH, an undammed river) and Heishui River (HSH, a dammed river) in April and September 2019. We comparatively analyzed seasonal variations in different types of diversity (species diversity, SD; phylogenetic diversity, PD; and functional diversity, FD), secondary productivity, and P/B ratios between the two rivers. Structural equation models were used to reveal the relationships between multidimensional diversity, secondary productivity, and P/B ratios. The results showed that SD significantly decreased during September both in the undammed CSH which has dramatic seasonal hydrological fluctuations, and in dammed HSH which has stable seasonal hydrological conditions. These findings indicated that SD could not clearly distinguish the key factors that cause changes in biodiversity. Conversely, both PD and FD significantly declined during September in the undammed CSH, but they did not significantly change in the dammed HSH. This result indicated that PD and FD are more sensitive than SD for identifying the effects of disturbances on biodiversity in these natural river ecosystems. After severe hydrological disturbance, although species abundance, biomass, biodiversity, and secondary productivity decreased in CSH, the still high value of P/B ratios indicated the high functional redundancy of communities, which further demonstrated the high stability of macroinvertebrates in CSH. Structural equation models revealed that the effects of PD and FD on secondary productivity and P/B ratios were more significant than those of SD in both rivers, which suggested that PD and FD may be better indicators of macroinvertebrate community stability than SD in these natural river ecosystems. Our study provides evidence that biological functional traits and evolutionary history can help achieve a more complete understanding of biodiversity patterns that maintain river ecosystem functioning and stability.

Effects of chronic exposure of antibiotics on microbial community structure and functions in hyporheic zone sediments

Microbial communities in hyporheic zones (HZ) provide vital biogeochemical functions such as contaminant degradation for river ecosystems. Antibiotics are contaminants that have been increasingly detected in HZ sediments. In this study, sediments from different HZ locations in a contaminated river, Maozhou river, China were sampled and analyzed using qPCR and high-throughput sequencing to investigate the effect of antibiotic contamination on microbial community structures and functions in HZ sediments. Results indicated that types and concentrations of antibiotics in HZ sediments were heterogeneously distributed that were largely consistent with the distribution of antibiotic sources. Sediments near animal farm and hospital contained higher antibiotic concentrations compared with those from mainstream. The distribution of ARGs was well correlated with antibiotics. Bacterial indicator genera indicating differences between mainstream area and other sampling areas were positively correlated with antibiotics, suggesting the influences of antibiotics on reshaping microbial community structures. PICRUSt revealed positive relationships between antibiotics and predicted functional genes involved in defense, signal transduction, and recombination and repair. This imply the defensive response of microbial communities on antibiotic attack. These results indicated that antibiotic contamination in the watershed posed a potential risk on HZ microbial community structures and functions, which may further threaten river ecosystem functions.

Longitudinal patterns and linkages in benthic fine particulate organic matter composition, respiration, and nutrient uptake

AbstractLongitudinal changes in the structure and function of river ecosystems have long been recognized, yet our understanding of how such patterns shape elemental cycles remains limited. In particular, while benthic fine particulate organic matter (POM, 0.7–1000 μm) may control many stream nutrient cycles, less is known about longitudinal patterns or controls of benthic POM‐associated nutrient uptake. We conducted a survey of benthic POM‐associated respiration and nutrient uptake as well as microbial biomass (bacteria and algae) and benthic POM composition in four size classes (0.7–53 μm, 53–106 μm, 106–250 μm, and 250–1000 μm) in six streams in the forested South Fork Eel River watershed (California), encompassing a longitudinal gradient in light availability and primary production. Benthic POM at downstream sites was composed of smaller particles with lower organic matter content that were richer in nitrogen and autotrophic material. Areal respiration and nutrient uptake rates increased 11‐ to 67‐fold with stream size. While microbial activity rates did not increase with stream size, benthic POM‐associated microbial biomass increased 20‐fold with stream size, and closely tracked a 15‐fold increase in light availability, and primary production. Thus, microbial biomass, not activity, determined longitudinal patterns in benthic POM‐associated areal nutrient uptake and respiration rates. We attribute longitudinal patterns in microbial biomass to increases in light availability and primary production. Our findings help clarify the role of local (primary production) and upstream processes in shaping ecosystem structure and function.

Combining Hydrologic Simulations and Stream‐network Models to Reveal Flow‐ecology Relationships in a Large Alpine Catchment

AbstractFlow regimes profoundly influence river organisms and ecosystem functions, but regulatory approaches often lack the scientific basis to support sustainable water allocation. In part, this reflects the challenge of understanding the ecological effects of flow variability over different temporal and spatial domains. Here, we use a process‐based distributed hydrological model to simulate 23 years of natural flow regime in 100 bioassessment sites across the Adige River network (NE Italy), and to identify typical nivo‐glacial, nivo‐pluvial, and pluvial reaches. We then applied spatial stream‐network models (SSN) to investigate the relationships between hydrologic and macroinvertebrate metrics while accounting for network spatial autocorrelation and local habitat conditions. Macroinvertebrate metrics correlated most strongly with summer, winter, and temporal variation in streamflow, but effects varied across flow regime types. For example (i) taxon richness appeared limited by high summer flows and high winter flows in nivo‐glacial and pluvial streams, respectively; (ii) invertebrate grazers increased proportionally with the annual coefficient of flow variation in nivo‐glacial streams but tended to decline with flow variation in pluvial streams. Although local land‐use and water quality also affected benthic communities, most variation in macroinvertebrate metrics was associated with spatial autocorrelation. These findings highlight the importance of developing environmental flow management policies in ways that reflect specific hydro‐ecological and land use contexts. Our analyses also illustrate the importance of spatially‐explicit approaches that account for auto‐correlation when quantifying flow‐ecology relationships.

Rewilding watersheds: using nature’s algorithms to fix our broken rivers

Rewilding is an ecological restoration concept that promotes the natural recovery of ecosystems, through (initial) active or passive removal of human influence. To support the application of rewilding approaches in rivers and their watersheds, we propose a framework to assess ‘rewilding potential’ based on measurement of basic river ecosystem functions (e.g. restoring flood and nutrient pulses), including examples of specific indicators for these processes. This includes a discussion of the challenges in implementing rewilding projects, such as lack of spatio-temporal data coverage for certain ecosystem functions or tackling ongoing problems once active management is removed. We aim to stimulate new thinking on the restoration of wild rivers, and also provide an annotated bibliography of rewilding studies to support this.

Distribution pattern of macroinvertebrate community and its relationships with environmental factors in the Yongding River Basin

Human disturbances have altered global stream ecosystems in multiple ways. Understan-ding spatio-temporal dynamics of aquatic organism composition and their relationships with environmental factors play an important role in revealing changes in the structure and function of river ecosystems. The macroinvertebrates and environmental parameters were sampled in the Yongding River Basin at spring (March), summer (July), and autumn (November) in 2017. The results showed that chironomids were the dominant group in the Yongding River Basin, including Orthocladius, Chironomus, Glyptotendipes, and Polypedilum. Results of the cluster analysis showed significant spatial variations of macroinvertebrate community. Sampling sites were clustered into two groups based on the similarities of macroinvertebrate composition in the Yongding River. Sampling sites belonging to group 1 mainly located in the Sanggan River and Dongyang River, with Orthocladius sp.being the dominant species. Sampling sites belonging to group 2 mainly located in the Yang River, Guishui River and main section of the Yongding River, with Glyptotendipes sp. being the dominant species. The biomass, Shannon index, Margalef index, Pielou evenness index and taxa richness of group 2 were significantly higher than those of group 1. Higher values of biological indices indicated better ecological condition of the stream ecosystem. The density, biomass and diversity indices of summer were significantly lower than those of both spring and autumn. Results of Canonical correspondence analysis (CCA) showed that the spatio-temporal distribution of macroinvertebrate in the Yongding River was mainly influenced by water temperature, ammonium, pH, dissolved oxygen, and total phosphorus. From the perspective of hydrological characteristics, flow velocity and flow capacity were significantly correlated. The significant positive correlations between hydrological parameters of velocity and capacity and biological indices of density and EPT% in group 2 indicated the preference of fast flow to sensitive taxa of EPT (Ephemeroptera, Plecoptera, and Trichoptera). The negative correlations between flow capacity and biodiversity indices implied the adverse effects of high flow on macroinvertebrate biodiversity. Our results confirmed that the composition and biodiversity of macroinvertebrate were affected by both water environment and hydrology, which reflected the multiple human activities in aquatic ecosystems of the Yongding River. It is important to control water contamination and sustain environmental flow at the specific reaches for the restoration of Yongding River.

Single-Stream Recycling Inspires Selective Fish Passage Solutions for the Connectivity Conundrum in Aquatic Ecosystems.

Barrier removal is a recognized solution for reversing river fragmentation, but restoring connectivity can have consequences for both desirable and undesirable species, resulting in a connectivity conundrum. Selectively passing desirable taxa while restricting the dispersal of undesirable taxa (selective connectivity) would solve many aspects of the connectivity conundrum. Selective connectivity is a technical challenge of sorting an assortment of things. Multiattribute sorting systems exist in other fields, although none have yet been devised for freely moving organisms within a river. We describe an approach to selective fish passage that integrates ecology and biology with engineering designs modeled after material recycling processes that mirror the stages of fish passage: approach, entry, passage, and fate. A key feature of this concept is the integration of multiple sorting processes each targeting a specific attribute. Leveraging concepts from other sectors to improve river ecosystem function may yield fast, reliable solutions to the connectivity conundrum.

Heterogeneity of ecosystem function in an “Anthropocene” river system

Physical heterogeneity is a strong driver of ecosystem function in rivers, but it is not clear whether this relationship persists in “Anthropocene” rivers: those affected by pronounced and persistent anthropogenic stressors. Such stressors can result in regime shifts of rivers, altering not only ecosystem structure and function, but also their heterogeneity. This study examines the heterogeneity of the physical template and ecosystem function of the Illinois River (Illinois, USA), as an example of an Anthropocene River. This river was biologically dead for most of its length in the mid 1900′s because of multiple anthropogenic stressors. A systemic reduction in physical heterogeneity of the Illinois River also resulted in simplification of its physical environment. Multiple lines of evidence demonstrate the physical simplification of the river channel caused the homogenization of ecosystem function. The significant overlap in trophic niche spaces, convergence of isotope ratios, dominance of benthic contributions to higher-level consumers, increased food chain lengths, plus the emergence of only two food webs indicate a simpler river ecosystem. Limited attention to the role of heterogeneity in anthropogenically modified river systems not only restricts understanding of resilience in rivers, but also the application of resilience thinking to managing these globally important ecosystems.

Evaluation of interregional consistency in associations between neonicotinoid insecticides and functions of benthic invertebrate communities in rivers in urban rice-paddy areas

Neonicotinoid insecticides pose risks that need to be managed for conservation of aquatic ecosystems. In this study, we evaluated the associations between the estimated environmental concentrations of two neonicotinoid insecticides (imidacloprid and dinotefuran) and the total abundances of seven functional feeding groups (FFGs) of benthic invertebrate communities in rivers in urban rice-paddy areas in four Japanese regions. Regional datasets of benthic invertebrate communities and environmental variables available for Japan were analyzed. The associations between neonicotinoid exposure and benthic functional groups in each region were evaluated by applying a partial redundancy analysis to each regional dataset. We then examined whether there was an interregionally consistent pattern in the observed associations to ascertain the general applicability of the associations. In two of the four regions, the associations of the total abundances of the seven FFGs with neonicotinoid concentrations were significant, suggesting negative effects of imidacloprid and dinotefuran on river ecosystem functions in these two Japanese regions. Moreover, although the associations in the remaining two regions were not significant, the pattern of associations of the total abundances of six of the FFGs (shredders, filter feeders, collectors, grazers, predators, and scavengers) with imidacloprid concentrations seemed to be consistent among the four regions. This implies broad-scale negative effects of imidacloprid on river ecosystem functions in urban rice-paddy areas. We did not, however, find any interregionally consistent patterns in the associations with dinotefuran concentrations. This may be related to the multicollinearity with the imidacloprid concentrations and/or the low maximum dinotefuran concentration relative to the toxicity values of this neonicotinoid. Therefore, the association between dinotefuran and river ecosystem functions requires additional investigation. We believe that this type of hypotheses-generating research using country-wide biomonitoring and exposure databases can be a great aid in future ecological risk assessment studies.

Long-term agricultural contamination shaped diversity response of sediment microbiome

The pollution caused by agricultural production poses a threat to the ecological integrity of river ecosystems, altering the structure and function of river ecosystems. Differences in microbial community structure provide useful information about the impact of agricultural pollution on the biological integrity of ecosystems, but generally convey little information regarding ecosystem functions. In this study, using Illumina MiSeq sequencing technology based on the 16S rRNA gene, river sediment samples associated with four different types of agricultural pollution were comprehensively analyzed. The results show that the total organic carbon (TOC) content was highest at the YZS site (animal husbandry sewage) among the assayed sites, but the species richness and uniformity were lowest at this site, which may have been caused by the high nutrient source of the sewage. Furthermore, in the three YZS samples affected by the long-term discharge of aquaculture tail-water, the unique genus Dechloromonas and the genus Candidatus-Competitor were observed, which are strongly correlated with phosphorus conversion. The formation of network modules may correspond to the coexistence of functional bacteria accustomed to multiple niche combinations under different agricultural pollution conditions in river sediments. According to the PICRUSt functional prediction, the bacterial community in the agricultural polluted river sediment primarily harbored 46 subfunctions, exhibiting richness of functions. Overall, our results provide a more comprehensive understanding of the structure and ecological processes associated with the aggregation of bacterial communities, which is beneficial for the management of river environments.

Historical Changes in the Ecological Connectivity of the Seine River for Fish: A Focus on Physical and Chemical Barriers Since the Mid-19th Century

To understand the long-term fate of fish assemblages in the context of global change and to design efficient restoration measures in river management, it is essential to consider the historical component of these ecosystems. The human-impacted Seine River Basin is a relevant case that has experienced the extinction of diadromous fishes over the last two centuries and has recently witnessed the recolonization of some species. One key issue is to understand the historical evolution of habitat accessibility for these migratory species. Thanks to the unique availability of historical, mainly hand-written sources of multiple types (river engineering projects, navigation maps, paper-based databases on oxygen, etc.), we documented and integrated, in a geographic information system-based database, the changes to physical and chemical barriers in the Seine River from the sea to Paris for three time periods (1900s, 1970s, and 2010s). The potential impact of these changes on the runs of three migratory species that have different migratory behaviors—Atlantic salmon, allis shad, and sea lamprey—was evaluated by ecological connectivity modeling, using a least-cost approach that integrates distance, costs, and risks related to barriers. We found that accessibility was contrasted between species, emphasizing the crucial role of the migration type, period, and level of tolerance to low dissolved oxygen values. The highest disruption of ecological connectivity was visible in the 1970s, when the effects of large hypoxic areas were compounded by those of impassable navigation weirs (i.e., without fish passes). As the approach was able to reveal the relative contribution of physical and chemical barriers on overall functional connectivity, it may constitute a model work in assessing the functioning of large river ecosystems.