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Despite causing harmful impacts on coastal communities and biodiversity for a few decades, eutrophication of marine systems has only recently gained public visibility. Representing a major land-based pollution, eutrophication is now considered the most striking symptom of intractable disruption of biogeochemical nutrient cycles at a global scale. The objective of this article is to analyze multi-scale dynamics of the problematization and regulation of ocean overfertilization. To do so, we build on a comprehensive literature review of previously published works that address the sociopolitical dimension of eutrophication issues and whose visibility we analyze with a critical perspective. We identify three stages that characterize the social history of marine eutrophication and how it was handled by public authorities. Although social mobilizations focus on emblematic sites, conflicts directly related to eutrophication symptoms spread in diverse hydro-social configurations. We conclude with a typology of four configurations associated with enduring nutrient pollution: noisy, overwhelming, silenced, and disturbing eutrophication.

International audience; Active biomonitoring permits the quantification of biological exposure to chemicals through measurements of bioavailable concentrations in biota and biological markers of toxicity in organisms. It enables respective comparison of the levels of contamination between sites and sampling campaigns. Caged gammarids are recently proposed as relevant probes for measuring bioavailable contamination in freshwater systems. The purpose of the present study was to develop a multi-pressure and multiscale approach, considering metallic contamination levels (from data based on active biomonitoring) as a response to pressures (combination of individual stressors). These pressures were anthropogenic land cover, industry density, wastewater treatment plant density, pressures on stream hydromorphological functioning, riverside vegetation and bioavailability factors. A dataset combining active biomonitoring and potentially related pressures was established at the French national scale, with 196 samplings from 2009 to 2016. The links between pressures and metallic contamination were defined and modelled via structural equation modeling (more specifically partial least squares - path modeling). The model enabled the understanding of the respective influences of pressures on metallic bioconcentration in caged sentinel organisms. Beyond validating the local influence of industries and wastewater treatment plants on metallic contamination, this model showed a complementary effect of driving forces of anthropogenic land cover (leading to human activities). It also quantified a significant influence of pressures on stream hydromorphological functioning, presence of vegetation and physico-chemical parameters on metal bioconcentration. This hierarchical multi-pressure approach could serve as a concept on how pressures and contamination (assessed by active biomonitoring) can be connected. Its future application will enable better understanding of environmental pressures leading to contamination in freshwater ecosystems.

International audience; Many freshwater ecological studies focused on the effects of environmental stressors induced by anthropogenic activities such as land use or alteration of hydromorphology and physico-chemistry conditions. While it is recognized as a potential major driver of ecological alteration, ecotoxicological stress is yet rarely explicitly considered. By combining ecological monitoring and field ecotoxicological approaches, the purpose of this research is to focus on the origin and levels of bioavailable contamination as well as toxicity in freshwater ecosystems taking into account various stream typologies and unraveling the relative impacts of other stressors on these two variables. Datasets of active biomonitoring at the French national scale were established, with 333 sites being investigated from 2009 to 2018. Bioavailable contamination (metallic and persistent organic substances) in freshwater ecosystems was assessed by bioaccumulation measurement in caged Gammarids. Stream toxicity was based on mortality and feeding activity of exposed organisms. For each site, integrated indicators of contamination and toxicity were computed with weighting chemical and biological measurements by national reference values. The link between environmental stressors and ecotoxicological indicators was modeled via Structural Equation Modeling. The model was adjusted according to the source of pollution and is reliable with the consideration of multi-scale and multi-stressor concepts. It enables to understand the role of driving forces (land use, hydromorphology, etc.) and their impact on the two outputs (contamination and toxicity). Its application improves the understanding of contamination and toxicity levels. It can also provide a prediction of risks of contamination and/or toxicity in aquatic environments.

The purpose of this study was to quantify the downstream impacts of different types of small dams on summer water temperature in lowland streams. We examined: (i) temperature regime upstream and downstream dams of different structural characteristics; (ii) relationships between stream temperature anomalies and climatic variables, watershed area, dam height, impoundment length and surface and residence time; (iii) the more significant variables explaining the different thermal behaviours, in order to account for dam diversity and functioning in future regional stream temperature models. Water temperature loggers were installed upstream and downstream 11 dams in the Bresse Region (France) and monitored at 30 min intervals during summer period (June to September), from 2009 to 2016 depending on the sites (2 sites were monitored during 2 summers, others only 1 summer, resulting in 13 time-series), with the opportunity to compare cold and hot summers. The small dams altered the downstream thermal regime for 23 % of the time-series with a > 1 °C elevation of the maximum daily temperature; for 77 % the range was in between −1 °C and +1 °C. The mean increase of the minimum daily temperature was 1 °C, with 85 % of the time-series showing an increase > 0.5 °C. The sites are grouped in three main types with specific responses of different temperature variables (maximum daily temperature (T max), minimum daily temperature (T min) and daily temperature amplitude). Two main types of impact were identified: an increase in the daily minimum temperatures associated with stability and even a slight reduction of the daily maximum temperatures for impoundments of low volume (residence time shorter than 0.7 day and an impoundment surface area smaller than 35 000 m2); and an increase of the daily minimum and maximum temperatures in the same orders of magnitude when the surface area of the impoundment is larger than 35 000 m2 and the residence time is longer than 0.7 day. This increase can reach 2.4 °C at certain structures and could impact the structure of aquatic communities and the functioning of the aquatic ecosystem. These determinants are candidate to generalize results, but this would necessitate the gathering of more precise information than the current dam descriptors in public databases.

International audience; We investigated the relationships between the ecological status of wadeable rivers and the intensity of various stressors related with hydromorphological alterations, nutrient and organic matter contaminations. The French invertebrate-based multimetric index (I2M2), which efficiently responds to the effects of both physical and chemical and hydromorphological stressors, was used as descriptor of river reach ecological status. We developed a model focusing on the effects of hydromorphological and physical and chemical stressor gradients on the I2M2 in different physiographic contexts. The potential confounding effects of natural geographic conditions and watershed scale pressure gradients were taken into account and neutralized by gathering watersheds into homogeneous clusters integrated as an interaction factor in the model. Whatever effects were considered (general or within-spatial clusters), the I2M2 was impaired similarly by the same stressor types, being negatively influenced by an increase in BOD5, ammonium, nitrite, nitrate and total phosphorus concentrations. The I2M2 was also negatively influenced by variables describing hydromorphology at the reach scale, especially by the 'loss of sinuosity', 'increasing rates of bank erosion', 'flow reductions' and 'alteration of pool/riffle succession'. The I2M2 was generally more strongly impaired by physical and chemical pressures than by hydromorphological alterations.

International audience; The purpose of our approach was to take into account the nested spatial scales driving stream functioning in the description of pressures/ecological status links by analysing the results of a hierarchical model. The development of this model has allowed us to answer the following questions: Does the consideration of the indirect links between anthropogenic pressures and stream ecological status modify the hierarchy of pressure types impacting benthic invertebrates? Do the different nested scales play different roles in the anthropogenic pressures/ecological status relationship? Does this model lead to better understanding of the specific role of hydromorphology in the evaluation of stream ecological status? To achieve that goal, we used the Partial Least Square (PLS) path modelling method to develop a structural model linking variables describing (i) land use and hydromorphological alterations at the watershed scale, (ii) hydromorphological alterations at the reach scale, (iii) nutrients-organic matter contamination levels at the site scale, and (iv) substrate characteristics at the sampling site scale, to explain variation in values of a macroinvertebrate-based multimetric index: the French I2M2. We have highlighted the importance of land use effects exerted on both hydromorphological and chemical characteristics of streams observed at finer scales and their subsequent indirect impact on stream ecological status. Hydromorphological alterations have an effect on the substrate mosaic structure and on the concentrations of nutrients and organic matter at site scale. This result implies that stream hydromorphology can have a major indirect effect on macroinvertebrate assemblages and that the hierarchy of impacts of anthropogenic pressures on stream ecological status generally described in the literature - often determining strategic restoration priorities - has to be re-examined. Finally, the effects of nutrients and organic matter on macroinvertebrate assemblages are lower than expected when all the indirect effects of land use and hydromorphological alterations are taken into account.

International audience; In the field of macroecology, climate- and productivity-related factors are frequently identified as the strongest correlates of species-diversity patterns. These variables describe the action of climate on species, either directly by influencing physiological processes, or indirectly by controlling resource productivity or biomass. Being among the most vulnerable ecosystems to climate change, streams and rivers can experience both types of climate-induced effects and their consequences on communities. Here, we gather recent insights from multi-decadal studies investigating long-term responses of invertebrate communities to climatic and trophic changes in France. On the one hand, stream communities have been directly influenced by long-term hydroclimatic changes with a gradual increase in taxa exhibiting resistance and resilience strategies (e.g, small-sized organisms) at the expense of climate-sensitive taxa (e.g, typical from fast-running, cold waters). This general trend followed a latitudinal gradient supporting the predicted northwards colonisation/migration by Mediterranean species. On the other hand, additional long-term variations in invertebrate communities have been induced by trophic resource changes, either corresponding to a climate-induced trophic amplification, especially in headwaters, or related to water quality improvement. In both cases, trophic processes have promoted specialists of different resource types following either a productivity enhancement or a primary production transfer. As a result, these climatic and trophic changes have concomitantly contributed to the overall long-term increase in functional diversity of invertebrate communities throughout France. Nonetheless, beyond these present trends, invertebrate communities are threaten by the expected future warming due to distribution range contractions of the remaining sensitive taxa and/or competitive exclusions by the colonising tolerant taxa. These insights illustrate whether combining long-term and trait-based approaches can help to disentangle direct, indirect and confounding merged effects of environmental drivers on biological communities, with functional relevance for understanding and predicting community dynamics over broad spatial scales.

International audience; Taking the nested scales of stream functioning into account in analysing the links between pressures and ecological status calls for the development of hierarchical models on the monitoring datasets. We aimed at answering the following questions: Does the indirect links between pressures and ecological status modify the classically observed impact hierarchy of pressures? Do the different nested scales play a different role in the pressures-ecological status relationship? Do hydromorphological alterations play a specific role in ecological status evaluation? To achieve that goal, we used the PLS path modelling method to develop a structural model linking latent variables built on (i) land use, and hydromorphological pressures descriptors at watershed scale, (ii) hydromorphological alterations assessed at reach scale, (ii) nutrients-organic matter contamination levels, and (iv) substrate samples to explain the score variation in the French monitoring macroinvertebrate based indicator I2M2. This method allows one to express the total effect of a variable as the sum of its direct and indirect effects. As a first important result, we have highlighted the importance of land use effect exerted on both hydromorphology and physico-chemistry and their translation as an indirect effect on biological condition of streams. We have also demonstrated that hydromorphological alterations had an effect on substrates structure and nutrients and organic matter concentrations. This study also reveals that hydromorphology has a major effect on macroinvertebrates indicator, thus indirect. Comparatively, nutrients and organic matter total effect on macroinvertebrates communities appears lower than expected since we take into account all the indirect effects of land use and hydromorphological alterations.

International audience; We built a corpus of models capable of explaining the variability of the biological indices used in the French surveillance monitoring network and also predict the ecological status of non-monitored water bodies. Benthic macroinvertebrates, diatoms and fish indices have been used to determine the ecological status of 1100 sites of the monitoring network distributed homogeneously over national territory.The pressures taken into account to explain and predict ecological status cover three spatial scales: catchment, reach, site. The set of predictive data cover three types of pressure: land use pressure, hydromorphological pressure and physico-chemical pressure measured at catchment, reach and site scale, respectively.We showed that the parameters characterising the load of nutrients and organic matter had a predominant effect on the three biological compartments, and that land use variables played an integrating role of the different pressures acting on rivers and explained a major part of their degradation. On the contrary, we also showed that it was more difficult to characterise the role of the hydromorphological descriptors measured at the intermediate scale of the reach due to the difficulty of characterising the links between scales.The three predictive models developed demonstrated good performances to evaluate biological condition and are of great interest for managers as it permits using a set of pressure data to successively predict the status of water bodies for which biological monitoring data are unavailable.

International audience; Rivers are complex systems for which it is hard to make reliable assessments of causes and responses to impairments. We present a holistic risk-based framework for river ecosystem assessment integrating all potential intervening processes and functions. Risk approaches allow us to deal with uncertainty both in the construction of indicators for magnitude of stressors and in the inference of environmental processes and their impairment. Yet, here we go further than simply replacing uncertainty by a risk factor. We introduce a more accurate and rigorous notion of risk with a transcription of uncertainty in causal relationships in probability distributions for the magnitude of impairment and the weight of different descriptors, with an associated confidence in the diagnostic. We discuss how Bayesian belief networks and Bayesian hierarchical inference allow us to deal with this risk concept to predict impairments and potential recovery of river ecosystems. We developed a comprehensive approach for river ecosystem assessment, which offers an appealing tool to facilitate diagnosis of the likely causes of impairment and predict future conditions. The ability of the risk approaches to integrate multi-scale quantitative and qualitative descriptors in the identification of multiple stressor sources and pathways in the stream network, and their impairment of specific processes and structures is illustrated for the national-level risk analysis for hydromorphology and pesticide pollution. Not only does the risk-based framework provide a more complete picture of environmental impairments, but it also offers a comprehensive, user-friendly tool to instruct the decision process.

Connectivity may be structural , based on adjacency of landscape features, or functional , based on how that adjacency translates to movement of organisms. We present a modelling approach that elucidates both aspects of connectivity to identify vital corridors and conservation priorities in a river network. For the dendritic network structure of river systems, at first a graph theoretic structure is developed to model the river network at the segment scale. To derive functional connectivity, a Bayesian hierarchical modelling of species dispersal is applied to infer the influence of riparian corridor characteristics to the species colonization. The integration of the functional and structural component is realized with a graph-theoretic connectivity measure. With this approach, the European otter colonization of the Loire river basin over 25 years is modelled on the basis of large datasets on riparian corridor land use and hydromorphological characteristics of a 17,000 km river network. Channel straightening and riparian forest fragmentation are determined to be key elements to the functional connectivity. Road infrastructure is distinguished as a critical habitat factor, but not so much an obstacle for the species movement in the riparian corridor. Integration of the Bayesian model posterior colonization probability in the integrated connectivity analysis reveals the importance of the river network density to the otter colonization and locates conservation priorities mainly in the lower parts of the river basin. Synthesis and applications Both functional and structural connectivity are essential elements in the contexts of ecological network identification for species conservation and recovery. We successfully developed an integrated modelling of both components of connectivity that highlighted the importance of the downstream basin for a well-connected ecological network for the otter.

International audience; Recent progress in very high spatial resolution imagery (VHSRI) has increased the availability of fine-scale land cover data over extensive areas. This new spatial information might improve our understanding of how land cover affects stream ecosystems.Land cover information was investigated in whole catchments and riparian areas in Normandy (France) and related to stream macroinvertebrates at 155 sites. The first model was based on the land cover data obtained via moderate spatial resolution imagery (MSRI) at the catchment scale. The second and the third models were additionally based on riparian land cover data both locally (at the site) and upstream. The riparian land cover data were derived from the MSRI for the second and from the VHSRI for the third model.Riparian vegetation (at a distance from the channel of 5–100 m) was poorly detected by MSRI when compared to VHSRI. The model based on higher resolution data at the riparian scale (i) ensured that relationships identified at the riparian corridor scale were independent from those at whole catchment scale, (ii) identified the influence of riparian vegetation on the aquatic environment as being most pronounced when using data from a 20-m wide strip (i.e. 20 m on each bank for a total of 40 m) and (iii) disentangled the effects of roads from other urban infrastructure.This study confirms the advantages of using very high resolution data in landscape approaches to the study of aquatic ecosystems. It provides accurate spatial information at the riparian scale that improves interpretation of the influence of land cover on the ecological condition of streams and allows identification of relevant features for management.

Global change calls for an understanding of how temperature and flow regimes influence aquatic ecosystems. Fish assemblages are a major component of river ecosystems and are thought to exhibit more integrative informative responses than single species to environmental variations, whether rare and sudden or gradual and continuous. The use of long-term datasets is thus of primary importance, allied to statistical modeling. For each of three previously identified species clusters, we performed Bayesian variable selection and inference within a hierarchical log Poisson Generalized Linear Model using a spike and slab normal prior to pinpoint which subset of environmental variables is of importance for each fish assemblage. Fish counts from electrofishing experiments are known to provide overdispersed data and, not surprisingly, the contribution of recorded environmental effects is found to be weak compared with those of other intra-assemblage sources of variation. The posterior distribution of the regression parameters is in coherence with what was expected from biological knowledge of the three species clusters. In particular, thermophilic species tend to benefit from warmer waters, whereas the recruitment of cold water species decreases due to global warming effects. Our study provides an example of the advantages of hierarchical modeling for quantifying interspecies ecological effects and selecting common environmental variables of importance.

Les avantages présumés de couverts forestiers riverains pour l’écosystème aquatique comprennent la purification, le contrôle thermique, l’apport de matière organique et d’habitats, ce qui peut améliorer la qualité physico-chimique et biotique. Toutefois, ces effets bénéfiques pourraient être atténués par de multiples facteurs de stress de l’agriculture intensive et de l’urbanisation dans les bassins versants en amont. Nous avons examiné la relation entre couvert forestier riverain et la qualité physico-chimique et indices d’intégrité biotique dans de vastes ensembles de données à grande échelle. La mesure des conditions hydromorphologiques et du couvert forestier riverain selon différentes largeurs des zones tampons pour 59 × 103 secteurs de rivière s’étendant sur 230 × 103 km du réseau fluvial français ont été couplés avec des données pour les variables physico-chimiques et biotiques prélevés sur le réseau national de surveillance. Des régressions linéaires généralisées et des régressions par quantiles ont servi à déterminer les réponses des variables physico-chimiques et des indices d’intégrité biologique des macroinvertébrés et poissons à la couverture de ripisylve dans les sélections de stress intermédiaire pour les rivières d’ordres 2 à 4. Des réponses significatives au couvert forestier ont été trouvées pour les nutriments et les indices biologiques. Selon ces réponses, un taux de ripisylve de 60 % dans un corridor de 10 m correspond aux limites du bon état des variables physico-chimiques et indices biotiques. Pour la zone tampon de 30 m, la réponse observée suggère que la couverture de ripisylve d’au moins 45 % correspond avec le bon état écologique de l’écosystème aquatique. Ces réponses cohérentes indiquent un potentiel important pour l’amélioration de la qualité du milieu aquatique en rétablissant la forêt riveraine. Les effets sont plus importants dans un environnement de pression unique, mais restent quand même importants dans des environnements avec multiple pressions. / Claimed benefits of riparian forest cover for the aquatic ecosystem include purification, thermal control, organic matter input and habitat provision, which may improve physicochemical and biotic quality. However, these beneficial effects might be flawed by multiple stressor conditions of intensive agriculture and urbanization in upstream catchments. We examined the relationship between riparian forest cover and physicochemical quality and biotic integrity indices in extensive large scale datasets. Measurements of hydromorphological conditions and riparian forest cover across different buffer widths for 59×103 river stretches covering 230×103 km of the French river network were coupled with data for physicochemical and biotic variables taken from the national monitoring network. General linear and quantile regression techniques were used to determine responses of physicochemical variables and biological integrity indices for macroinvertebrates and fish to riparian forest cover in selections of intermediate stress for 2nd to 4th order streams. Significant responses to forest cover were found for the nutrient variables and biological indices. According to these responses a 60% riparian forest cover in the 10 m buffer corresponds to good status boundaries for physicochemical and biotic elements. For the 30 m buffer, the observed response suggests that riparian forest coverage of at least 45% corresponds with good ecological status in the aquatic ecosystem. The observed consistent responses indicate significant potential for improving the quality of the aquatic environment by restoring riparian forest. The effects are more substantial in single-stressor environments but remain significant in multi-stressor environments.

Existing methods for connectivity analysis still encounter difficulties in explaining functional relationships between network structure and ecological patterns over larger territories or complex structures like dendritic river networks. We propose a method that addresses the problem of scale and resolution in the connectivity analysis of dendritic network structures, illustrated here for the re-colonization of the French Loire river basin by the European otter. The ecological niche factor approach is applied to infer favourable habitat in the river network based on large scale data of land use and hydro-morphology of river segments for the entire river basin. These analyses identified the stressors to the riparian zone of channel straightening, urbanisation and forest fragmentation as the principal factors explaining otter occurrence. Using this estimate of habitat favourability, we used the Integral Index of Connectivity to quantify habitat availability and connectivity in the dendritic river network. When we calculate the integral index of connectivity over different spatial extents by constraining network distances, the scale-sensitivity of the network’s connectivity emerges. Accounting for high mobility by entering larger network distances in the analysis identifies conservation networks and priorities mainly in downstream parts of the river basin, whereas with smaller network distances, more restricted high quality areas in central and upstream parts are highlighted. The presented approach performed better than distribution modelling approaches in explaining species occurrence over the river network and confirms the crucial aspect of connectivity in otter re-colonization.

Une demarche faisant appel a la methode des microhabitats a permis d'estimer l'habitat potentiel lie aux structures minerales et hydrauliques du chenal dans trois cours d'eau salmonicoles du Massif Central. Cette methode a permis d'evaluer une surface ponderee utile (SPU) de cours d'eau ou capacite d'accueil potentielle pour les differents stades de Truite fario en fonction de variables physiques (hauteur d'eau, vitesse de courant et substrat). Le recours aux calculs des SPU permet de s'affranchir de l'heterogeneite physique entre sites liee a l'hydromorphologie; il est alors possible d'aborder l'influence d'autres facteurs environnementaux sur un nombre raisonnable de sites et de campagnes. Les comparaisons entre cours d'eau des rapports biomasse observee/SPU ont mis en evidence de forts ecarts entre stations attribuables a des differences d'habitat hydromorphodynamique et d'environnement vegetal. Appuye par une estimation des differentes structures d'abris, l'exemple propose souligne l'importance de la vegetation rivulaire arboree comme un des facteurs responsable de la structuration des populations de truites. La station depourvue de vegetation rivulaire arboree presente une biomasse totale de truite par SPU faible de 13 g/m 2 . Inversement, le site possedant une vegetation arboree creant de nombreuses caches par les systemes racinaires dans un chenal domine par du sable et pauvre en abri mineral heberge une biomasse de 65 g/m 2 . La capacite d'accueil physique potentielle de ces types de cours d'eau devrait, par consequent, etre abordee non seulement en tenant compte de l'habitat hydromorphodynamique estime par la methode des microhabitats, mais egalement en tenant compte de l'influence de vegetation rivulaire arboree qui offre differentes structures d'abris a l'interieur du cours d'eau.

The well-documented re-colonisation of the French large river basins of Loire and Rhone by European otter and beaver allowed the analysis of explanatory factors and threats to species movement in the river corridor. To what extent anthropogenic disturbance of the riparian zone influences the corridor functioning is a central question in the understanding of ecological networks and the definition of restoration goals for river networks. The generalist or specialist nature of target species might be determining for the responses to habitat quality and barriers in the riparian corridor. Detailed datasets of land use, human stressors and hydro-morphological characteristics of river segments for the entire river basins allowed identifying the habitat requirements of the two species for the riparian zone. The identified critical factors were entered in a network analysis based on the ecological niche factor approach. Significant responses to riparian corridor quality for forest cover, alterations of channel straightening and urbanisation and infrastructure in the riparian zone are observed for both species, so they may well serve as indicators for corridor functioning. The hypothesis for generalists being less sensitive to human disturbance was withdrawn, since the otter as generalist species responded strongest to hydro-morphological alterations and human presence in general. The beaver responded the strongest to the physical environment as expected for this specialist species. The difference in responses for generalist and specialist species is clearly present and the two species have a strong complementary indicator value. The interpretation of the network analysis outcomes stresses the need for an estimation of ecological requirements of more species in the evaluation of riparian corridor functioning and in conservation planning.

With the increasing appreciation of global warming impacts on ecological systems, in addition to the myriad of land management effects on water quality, the number of literature citations dealing with the effects of water temperature on freshwater fish has escalated in the past decade. Given the many biological scales at which water temperature effects have been studied, and the growing need to integrate knowledge from multiple disciplines of thermal biology to fully protect beneficial uses, we held that a survey of the most promising recent developments and an expression of some of the remaining unanswered questions with significant management implications would best be approached collectively by a diverse research community. We have identified five specific topic areas of renewed research where new techniques and critical thought could benefit coldwater stream fishes (particularly salmonids): molecular, organism, population/species, community and ecosystem, and policy issues in water quality. Our hope is that information gained through examination of recent research fronts linking knowledge at various scales will prove useful in managing water quality at a basin level to protect fish populations and whole ecosystems. Standards of the past were based largely on incipient lethal and optimum growth rate temperatures for fish species, while future standards should consider all integrated thermal impacts to the organism and ecosystem.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]GEUSI; Social and scientific factors are deeply enmeshed in each other within the development and the use of ecological indicators (EI). Yet low research has assessed which factors contribute to selecting ecological indicators on the long-term. This article proposes to study the historical construction of EI by examining ecological, political, and social background of specific places where EIwere developed, in France on lakes and rivers. Our major findings in France were that ecological indicators were never optimised for the present market or political arena. Instead EI development was typically recycling previous tools that were elaborated for other purposes by environmentally committed outsiders, without regular funding. We found that regular funding for monitoring an EI was only provided when it matched an institution's goal. Beyond the geographically limited relevance of the case studies, these results therefore improve the theoretical framework we deploy when constructing or relying on indicators.

Changes in a brown trout (Salmo trutta L.) population result from interaction among various mechanisms which are dependent on environmental conditions and biotic processes. In reaches influenced by the presence of dams, the instream flow in the bypassed section is not the only parameter which affects the population. Flood episodes, the general connectivity of the bypassed section, and the characteristics of the substrate which define the availability and quality of spawning grounds may also have a crucial impact. The design and fine-tuning of tools which take environmental parameters into account can improve our understanding of the dynamics of such influenced populations. In this perspective, a deterministic model (MODYPOP) has been developed in an attempt to integrate all these factors and to test the effect of different long-term scenarios of influenced flow regimes on the structure of trout populations. MODYPOP was applied to three populations and three reaches (on the Roizonne, Neste d'Aure and Lignon du Forez rivers in France). For each stream, experiments were carried out on a bypassed section downstream of a hydropower station, before and after an increase in the minimum instream flow due to relicensing. These experiments allowed integrating into MODYPOP local phenomena (impact of flood episodes, impact of flushing, impact of downstream migration of juveniles and adults) affecting the populations during the study period and then calibrating them. To estimate the change in the population due to the increase in minimum instream flow, different long-term simulations were run, selecting discharge patterns at random. These scenarios help to evaluate the time required for the population to return to a range close to habitat saturation after an improvement in the hydraulic habitat or following a flood event. These applications have enabled determining the relative importance of changes in population density due to different types of events. Copyright © 2008 John Wiley & Sons, Ltd.

The conclusions of numerous stream restoration assessments all around the world are extremely clear and convergent: there has been insufficient appropriate monitoring to improve general knowledge and expertise. In the specialized field of instream flow alterations, we consider that there are several opportunities comparable to full-size experiments. Hundreds of water management decisions related to instream flow releases have been made by government agencies, native peoples, and non-governmental organizations around the world. These decisions are based on different methods and assumptions and many flow regimes have been adopted by formal or informal rules and regulations. Although, there have been significant advances in analytical capabilities, there has been very little validation monitoring of actual outcomes or research related to the response of aquatic dependent species to new flow regimes. In order to be able to detect these kinds of responses and to better guide decision, a general design template is proposed. The main steps of this template are described and discussed, in terms of objectives, hypotheses, variables, time scale, data management, and information, in the spirit of adaptive management. The adoption of such a framework is not always easy, due to differing interests of actors for the results, regarding the duration of monitoring, nature of funding and differential timetables between facilities managers and technicians. Nevertheless, implementation of such a framework could help researchers and practitioners to coordinate and federate their efforts to improve the general knowledge of the links between the habitat dynamics and biological aquatic responses.

International audience; Despite the many habitat simulations that have been undertaken around the world, not enough biological monitoring has been performed following flow manipulations. It is difficult, however, to refine flow management decisions without a better understanding of the links between amounts, durations and seasonality of flow deliveries and population dynamics. Trout populations were monitored before and after flow alterations in five trout streams, involving 17 study sites over a 4- to 12-year period, depending on the sites. A comparison of the trout populations observed to theoretical Habitat/population models pointed up several helpful lessons. Various factors slow increases in population size, including the availability and quality of spawning grounds, the general connectivity of the bypass section (BPS) and severe spate events. In addition to these site-dependent factors, hydrological dynamics may explain why it is so difficult to clearly identify relationships between habitat availability and real fish stocks. Moreover, opportunities to observe population changes are improved when the pre-enhancement instream flow value is very low, and when there is a considerable difference between pre- and post-enhancement values. A population dynamics model that incorporates different habitat limitations and demographic background can be a very precious tool to improve understanding of the different situations and to build scenarios of population recovery.

Introduction to the special Issue, Editorial : Introduction présentant la thématique de l'ensemble des articles

The real impact on downstream fish populations of a change in management of a hydropower installation, in particular, the impact of an increase in instream minimum flow, can be difficult to assess. Other factors, in addition to the simple habitat limitations in low-flow periods, can influence the evolution of a fish population over time. It has often observed in French streams that the 0+ individuals appear limited by strong discharge in the first months after their emergence (March to May). A dynamic model of a trout populations (MODYPOP) has been applied to the river Roizonne in the French Alps, upstream and downstream of a hydropower station, in order to estimate the effect of different discharge time series on trout population dynamics. Trout populations were monitored by means of annual inventories at two study sites, one with minimum flow and the other with natural flow. At each site, available habitat was described and simulated as it changed with discharge, according to the ‘microhabitat’ method (EVHA, derived from PHABSIM). Habitat time series were built on the basis of discharge time series. MODYPOP simulations, integrating habitat and discharge time series, were compared with observed fish numbers. Results indicated that fluctuations in discharge during the post-emergence period played a major role in the dynamics of the total population. Predictions were significantly improved when the impact of strong discharge on emerging fry was integrated in the model. Copyright © 2003 John Wiley & Sons, Ltd.

1. One current approach to the prediction of community characteristics is to use models of key local-scale processes (e.g., niche dimensions) affecting individuals and to estimate their effects over larger scales. We tested this approach, focusing on how the hydraulic habitat structures fluvial fish communities. We used a recent statistical habitat model to predict fish community characteristics in eleven reaches in the Rhône river basin in France. Predictions were made 'blindly', as most reaches were not used to calibrate the model. The model reflects species preferences for local hydraulics. We made predictions of the fish community from the local hydraulic conditions found in the reaches under low flow conditions. We predicted the overall abundance and the relative abundance (both as indices) of fish species, specific size classes, and species traits (reproductive, trophic, morphological and others). We summarised our predictions of the relative abundance of species as two 'community structure indices' using Principal Component Analysis. Our predictions from low flow hydraulics were compared with long-term observations of fish communities. The relative abundance of species actually observed depended largely on zoogeographic factors within the Rhône basin, which could not be predicted by the model. The model predicted 13 % of the variance in the indices of relative abundance at the species level and 23 % of this variance at the trait level for all zoogeographic regions combined. When focused on reaches within a geographic region, however, the model explained up to 47 % of the same variance. Therefore, geographic regions act as 'filters' on relative abundance of species, but hydraulics do affect fish communities within a given geographical context. For the synthetic 'community structure indices', we obtained good predictions from hydraulics independently of the geographical context (variance explained up to 95 %). These indices were linked to simple key hydraulic characteristics of river reaches (Froude and/or Reynolds number). They enabled interpretations of the links between hydraulics, geomorphology, discharge and community patterns. These links were consistent with existing knowledge of species and their traits. In addition to the above validations, the habitat model partly explained the observed effects of impoundment on fish communities. These results show that stream hydraulics strongly impact fish community structure. Consequently, they confirm that community characteristics can be predicted using models of the local-scale habitat requirements of the species forming the community., Une approche possible pour prédire les caractéristiques des communautés aquatiques consiste à modéliser les processus clés (ex: préférences d'habitat) à l'échelle des individus, et d'estimer leurs effets à plus large échelle. Nous avons testé cette approche pour prédire les caractéristiques de communautés de poissons en fonction de l'hydraulique fluviale. 2. Un modèle d'habitat statistique a été utilisé pour estimer les caractéristiques des communautés de 11 tronçons de cours d'eau du bassin du Rhône. Des prédictions ont été faites 'à l'aveugle', sur des sites non-utilisés pour construire les modèles. Le modèle d'habitat reflète les préférences locales des espèces. Nous en avons déduit les caractéristiques attendues des communautés sachant l'hydraulique des tronçons à l'étiage. Nous avons estimé des indices d'abondance globale et d'abondance relative des espèces, de leurs classes de taille, et de leurs traits biologiques (reproduction, morphologie, alimentation...). Les indices d'abondances relatives ont été résumés sous forme d'indices de structure de la communauté par Analyse en Composantes Principales. Les indices de structure de la communauté, eux, sont bien prédits (jusqu'à 95 % de variance expliquée) sur l'ensemble des sites. Ils sont liés à des résumés hydrauliques simples des tronçons (nombres de Froude, de Reynolds). Ces indices permettent une interprétation synthétique du rôle de l'hydraulique sur les peuplements, en accord avec les connaissances existantes sur les espèces et leur biologie. 5. Par delà ces validations, le modèle a permis d'expliquer en partie l'effet de l'aménagement du fleuve sur la structure des communautés. Ces résultats démontrent l'importance de l'hydraulique sur la structure des communautés de poissons. Ils confirment que certaines caractéristiques des communautés peuvent être prédites à partir de modèles ciblés sur les exigences locales des espèces de ces communautés.

International audience; Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in frequent and major changes in the ohysical conditions of the fish habitat. The microhabitat methodology, derived from the IFIM, focuses on minimum flow studies in by-pass sections, but has been adapted to two rivers subject to daily flow fluctuations descriptors to take into account the temporal aspects of peaking flows and their effects on trout habitat, i.e. flow and habitat chronologies analysed in duration and frequency. Hydropeaking and the natural upstream flow regime were compared. The results show that habitat variations are closely related to the flow regime and site morphology; instances, hydraulic refugia are crucial for organisms to withstand the variations of physical variables. This approach helps in better understanding the physical limiting factors in situations of short-term flow fluctuations.; Le fonctionnement par éclusées engendre des fluctuations de débits à l'aval des ouvrages, qui s'accompagnent de modifications rapides et brutales des paramètres physiques de l'habitat des poissons. La méthode des microhabitats, dérivée de l'IFIM américain, a d'abord cherché à résoudre les problèmes de définition des débits réservés dans les secteurs court-circuités. Elle a été ici adaptée pour des rivières sujettent à éclusées (Ance du Nord et Oriège). Ce qui a supposé l'addition de nouveaux descripteurs de l'habitat pour tenir compte de ces aspects temporels, en particulier par la truite fario. La chronologie de débits et des habitats est analysée en terme de durée et fréquence. Les situations à éclusées sont comparées avec celles des secteurs témoins. Les résultats indiquent que les variations d'habitat sont très liés au règime des débits et à la morphologie ; les effets des éclusées sur les paramètres d'habitat différent dans les secteurs à profil encaissé de celles à profil évasé. Dans les deux cas, l'existence de refuges hydrauliques est essentielle pour que les organismes puissent supporter les variations des paramètres physiques. Cette approche aide à mieux comprendre l'effet des facteurs physiques limitants dans des situations de variations de débit à très court terme.

The quantification of management impacts on fish populations requires a reliable estimation of the local hydraulic variability. In the case of complex natural flows, deterministic hydaulic models are expensive and not adapted to the description of local velocities. Statistical descriptions of the velocity distribution as a function of easily obtained input variables are therefore an attractive alternative. Existing velocity data on several French stream segments with intermediate -to largescale roughness were analysed statistically to define a shape parameter of the point velocity frequency distributions. Dimensional analysis was used to model this shape parameter, and thereby the velocity distributions, as a function of simple average descriptors of stream reaches (discharge, mean roughness, mean depth, and mean width). Such predictive models of the physical habitat availability for fish in the probability domain can provide stream managers with cost-effective tools., La quantification des impacts de la gestion sur les populations de poisson nécessite de disposer d'estimations fiables de la variabilité hydraulique locale de l'habitat. Dans le cas de débits naturels complexes, les modèles hydrauliques déterminants sont chers et non adaptés à la description des vitesses locales. Des descriptions statistiques de la distribution des vitesses en fonction de variables plus aisément accessibles présentent une alternative interessante. Des données disponibles de vitesse sur plusieurs tronçons de cours d'eau français avec des rugosités médianes à grandes mailles ont été analysées statistiquement pour définir un paramètre de forme des distributions de fréquence des vitesses ponctuelles. Une analyse dimensionnelle a été utilisée pour modéliser ce paramètre de forme, ainsi que les distributions de vitesse, en fonction de simples descripteurs moyens du tronçon (débit, rugosité moyenne, hauteur d'eau moyenne et largeur moyenne). De tels modèles prédictifs de la disponibilité de l'habitat physique des poissons dans le domaine des probabilités est de nature à doter le gestionnaire des cours d'eau d'outils de décision d'un coût acceptable.

The actual main result of habitat simulation procedures is a static relationship between an index of potential habitat, e.g. Weighted Usable Area (WUA), versus discharge in a study reach representative of a stream. This paper presents a new methodology to analyse timing and magnitude of physical habitat variations. Three options are presented : the habitat time series, the habitat duration curves, and the continuous under threshold habitat duration curves (CUT curves). The last option is a new procedure to interpret habitat chronicles. It determines continuous durations during which total WUA in a study reach was lower than a given threshold. The assumption according to which some durations/thresholds values could represent limiting events for fish population dynamics was illustrated with surveys of two wild brown trout populations. We studied the relationship between spawning habitat conditions and the relative density of 0+ the year after. In this case a continuous duration of more than 20 days with spawning habitat conditions lower than 80 % of the optimum conditions, seemed to limit the number of 0+. Finally, this new procedure was presented like a potential helping tool to interpret natural discharge chronicle in a management point of view.; Le principal résultat des procédures de simulation de l'habitat est une relation statique entre un indice d'habitat potentiel, c'est-à-dire la Surface Utilisable Pondérée (WUA) et le déversement dans un cours d'eau représentatif du point de vue de l'étude. Cet article représente une nouvelle méthodologie d'analyse de la durée et de l'étendue des variations physiques de l'habitat. Trois options sont présentées : (i) la série de durée de l'habitat, (ii) les courbes de durée de l'habitat et (iii) les courbes de durée continue d'habitat (courbes CUT) sous le seuil (courbes CUT). La dernière option est une nouvelle procédure d'interprétation des chroniques de l'habitat. Elle permet de déterminer les durées continues pendant lesquelles la WUA totale d'un cours d'eau représentatif du point de vue de l'étude était inférieure à un seuil donné. La supposition selon laquelle certaines valeurs de durée/seuil freineraient la dynamique de la population des poissons est illustrée par les études de deux populations de truites brunes sauvages. Une étude a été faite de la relation entre les conditions de l'habitat de frai et la densité relative de 0+ l'année suivante. Une durée continue de plus de 20 jours avec des conditions d'habitat de frai inférieures à 80 % des conditions optimales semblaient limiter le nombre de truites 0+. Cette nouvelle procédure a été présentée comme un outil d'interprétation utile de l'évolution du déversement naturel du point de vue de la gestion.