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[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; Eutrophication is one of the most common causes of water quality impairment of inland and marine waters. Its best-known manifestations are toxic cyanobacteria blooms in lakes and waterways and proliferations of green macro algae in coastal areas. The term eutrophication is used by both the scientific community and public policy-makers, and therefore has a myriad of definitions. The introduction by the public authorities of regulations to limit eutrophication is a source of tension and debate on the activities identified as contributing or having contributed decisively to these phenomena. Debates on the identification of the driving factors and risk levels of eutrophication, seeking to guide public policies, have led the ministries in charge of the environment and agriculture to ask for a joint scientific appraisal to be conducted on the subject. Four French research institutes were mandated to produce a critical scientific analysis on the latest knowledge of the causes, mechanisms, consequences and predictability of eutrophication phenomena. This paper provides the methodology and the main findings of this two years exercise involving 40 scientific experts.

Despite harmful impacts on coastal communities and biodiversity for a few decades, eutrophication of marine systems only recently gained public visibility. Representing a major land-based pollution, it is now considered as the most striking symptom of intractable disruption of biogeochemical nutrients cycles at a global scale, due to massive phosphate ore extraction and industrial synthesis of reactive nitrogen. The ambition of this article is to account for the protracted emergence of coastal eutrophication as a public problem. Based on a comprehensive literature review of previously dispersed works in sustainability, social and political sciences, the article analyses multi-scale dynamics of ocean overfertilization. We show that the experience of local people was usually insufficient to trigger stringent public policies, since the lack of effective public action was often presented as the result of local antagonisms and persistent scientific uncertainties, and identify three stages that characterize the social history of marine eutrophication and how it was handled – or not – by public authorities. Although social mobilizations against coastal eutrophication tend to focus on emblematic sites, socio-environmental conflicts directly related to eutrophication symptoms spread in diverse hydro-social configurations. Ultimately, we develop a typology of four configurations associated with enduring land-based nutrient pollution : noisy, overwhelming, silenced and disturbing eutrophication., Malgré les dommages qu’elle occasionne pour les populations humaines et la biodiversité littorales depuis parfois plusieurs dizaines d’années, l’eutrophisation des milieux marins n’a que très progressivement accédé à une visibilité dans l’espace politique et auprès d’un large public. Due à la production industrielle d’azote réactif et de l’extraction massive de minerai de phosphate, en particulier pour la fertilisation des cultures, cette pollution terrigène majeure est aujourd’hui considérée comme le symptôme le plus manifeste de la perturbation anthropique à grande échelle des cycles biogéochimiques des nutriments. Dans ce contexte, l’ambition de cet article est de rendre compte de l’émergence contrariée de l’eutrophisation côtière comme problème public. Fondé sur une revue systématique de la littérature internationale en sciences sociales et en sciences de la soutenabilité, littérature jusqu’à présent très dispersée, il propose une lecture critique des dynamiques multi-échelles de la surfertilisation des océans. Cette analyse met en évidence trois périodes majeures qui caractérisent l’histoire sociale de l’eutrophisation des milieux marins et examine la façon dont elle a été prise en charge, ou pas, par les autorités publiques. Dans la plupart des cas documentés, l’expérience vécue des populations a rarement suffi à déclencher des politiques publiques régulatrices, le manque d’efficacité de l’action publique étant souvent présenté comme résultant d’antagonismes locaux et d’incertitudes scientifiques persistantes. Si les mobilisations sociales contre l’eutrophisation côtière tendent à se cantonner à des sites emblématiques, les conflits socio-environnementaux directement reliés à des symptômes d’eutrophisation se déploient, en revanche, au sein d’une grande diversité de configurations hydro-sociales, dont nous proposons une typologie.

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.

When investigating the fields of biogeography and macroecology, climate- and productivity-related variables are frequently identified as the strongest correlates of species-diversity patterns. These variables have been usually merged under the climate/productivity hypothesis and describe the direct and indirect actions of climate on species. Being among the most vulnerable ecosystems to climate change, streams and rivers are expected to be influenced both by climatic and trophic (i.e. productivity-related) factors. We propose here to distinguish the relative influence of the two processes on large-scale, long-term changes in the functional diversity of freshwater invertebrate communities over two decades in France. To this end, we designed two functional indices using invertebrate traits to surrogate the respective mechanisms: climate vulnerability and feeding specialisation. Using Geographically Weighted Regression (GWR) models, we showed that trends in both indices, along with the initial regional species-pools, have significantly contributed to the overall long-term increase in functional diversity of invertebrate communities. In addition, we highlighted a strong geographical differentiation in the contribution patterns with the climate vulnerability effect decreasing with latitude and the feeding specialisation effect being higher in headwaters than in large rivers. Finally, taking into account this non-stationarity in the ecological processes and responses using GWR models allowed explaining about 75% of the long-term changes in the community diversity. Consequently, this study offers sound perspectives in predicting the future patterns of trends in functional diversity of communities under different scenarios of environmental changes, like climate and/or land-use. This article is protected by copyright. All rights reserved.

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; L’eutrophisation touche de nombreux lacs, réservoirs, rivières et zones côtières, en France et dans le monde. Elle génère des perturbations majeures pour les écosystèmes aquatiques et a des impacts sur les biens et les services associés, sur la santé humaine et sur les activités économiques. Cet ouvrage présente les connaissances scientifiques disponibles sur ce phénomène. Il identifie les leviers d’action existants et les dispositifs mis en place au niveau national et international pour surveiller et lutter contre l’eutrophisation.

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.

Damming is one of the most widespread impairments of river systems around the world. The formula-tion of scientifically justified guidelines for restoration and remediation of impairments requires betterunderstanding of the relationships between alteration and stream condition. The present study examinesrelationships between the presence and density of dams and biological metrics of river health in the con-text of a variety of environmental drivers over the Loire river basin. We hypothesized that dam densitymeasured at supra-reach level would show more significant influence on river health than the local leveldensity, and further that the impact of dams is best estimated with measures for the functional traits ofbiotic assemblages. An extensive dataset of fish (169 sites) and invertebrate (211 sites) communities inthe Loire river basin, described with metrics of density of ecological guilds, taxonomic richness and lifehistory traits, and coupled with reach hydromorphology and catchment characteristics was constructed.Generalized linear modeling was performed in order to quantify dam impact and investigate the impor-tance of regional- and local-scale measures of dam density to the structure of biotic communities. Theanalysis showed that community structure at the basin scale responded significant to dam presence andconfirmed that the strongest relationships were observed for specific functional trait-based metrics. Forthe macroinvertebrates the observed impact counts up to 25% of the variance in the trait-based qual-ity indices, whereas for fish communities the dam density only explains up to 12%. Macroinvertebrateresponses were stronger at higher scale level, and especially the upstream context explained on its own70% of the observed impairment. For fish communities, the local context prevails and explained up to70% of the dam impact. These results can be explained by the biotic processes ruling community assem-bly in the specific groups, passive dispersal for the invertebrates and migrations between habitats forfish. The geographic context furthermore explains the differentiation in these responses, reflecting themetacommunity structure of invertebrate assembly over the river basin. We conclude that for upstreamparts of the river basin, locally based management actions can be successful in restoring biotic integrity,whereas more downstream, dam removal actions require more integrated measures at regional ratherthan local scale.

1. Assuming that recruitment variation is one of the main sources of fish population and assemblage changes, it is necessary to understand how natural variations in the environment influence 0+ fish abundance. Temperature regimes play an important role in enhancing both spawning activity and survival during early larval fish development. Flow regime variation, which is a powerful source of stream disturbance, is another factor to be taken into account. 2. Responses to these variables need to be assessed using long-term datasets, since standard statistical approaches fail to provide a causal structure or to quantify the different effects. We therefore used a 26-year dataset to evaluate the respective effects of seven derived independent variables describing the effects of temperature and flow regimes on the 0+ juvenile abundance of eight fish species in the River Rhone. 3. A clustering procedure using the Kendall tau rank correlation coefficient was implemented and identified three groups of fish according to their synchronic variations in juvenile abundance; i.e. varying with decreasing juvenile abundance, slightly increasing juvenile abundance and increasing juvenile abundance. These clusters provided the basis for building hierarchical log-Poisson generalized linear models. The Bayesian paradigm gives a reliable framework for model selection, and the best model was determined using the Bayes Factor. 4. The posterior distribution of the regression parameters was coherent with what was expected based on knowledge of the biology of the different species. It indicates that temperature regime drives 0+ juvenile abundance but that flow regime also plays an important regulating role. The models thus detected evidence of the consequences of specific flow events such as larval drift and an increase in available habitat during higher flow discharges. 5. Our study illustrates the advantages of using a hierarchical modelling approach to quantify ecological effects by improving discrimination between the different sources of uncertainty, leading to better precision when estimating regression parameters.

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.

Hydrological and morphological characteristics of streams and rivers influence a wide array of ecological processes and patterns ; they define the aquatic habitat template. Interdisciplinary approaches are required to study physical-biological interactions ; increased collaboration between ecologists and experts in morphology, hydrology and hydraulic engineering is particularly desirable. In this paper, we present our experience of aquatic habitat modelling. In particular, we indicate how statistical instead of mechanistic hydraulic descriptions simplify the input field data required to estimate instream habitat suitability. We have also conducted significant biological validations of habitat model predictions expressed at the fish community level. A better quantification of instream habitat suitability is meaningful when associated with the understanding of the large-scale processes governing stream equilibrium. In this context, the knowledge of bankfull discharge, at which the self-maintenance of the river morphology occurs, is of particular importance. The identification of key hydraulic variables and periods for population dynamics and vital processes are challenging for the near future. A greater understanding of physical-biological interactions will not only yield deeper insights into the ecological organization of streams and rivers, it will also improve our ability to predict how flow alterations caused by various human activities affect these vital ecosystems. Our progresses depend mainly on of our ability to produce biologically validated models.

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.

La question des debits reserves dans les cours d'eau a l'aval d'ouvrages derivant l'eau pour differents usages comporte plusieurs dimensions relevant de choix de societe et d'evaluations techniques faisant appel a differentes approches. Un rappel des differentes techniques mobilisables, depuis les methodologies purement hydrologiques jusqu'aux approches plus complexes tenant compte du biologique montre que l'eventail des aides a la decision est deja bien etoffe. Par ailleurs les connaissances sur le fonctionnement des hydrosystemes, en particulier sur le point precis du lien entre l'hydrologie et l'ecologie des cours d'eau sont loin d'etre negligeables. La difficulte recurrente pour obtenir un consensus de decision est analysee par rapport a un manque de clarte dans la definition des objectifs, ou par une non acceptation des evolutions de la societe en matiere de preoccupation environnementale. Comme souvent dans ce genre de situation, le debat de fond est esquive et il est demande aux scientifiques de revoir leur copie, et d'affiner encore leurs methodes. Parmi les differentes issues envisageables figurent en premier lieu des etudes de demonstration, ou, apres une evaluatin prealable des quantites d'eau a delivrer, on s'attache a suivre et a quantifier l'evolution reelle du cours d'eau et de sa biologie. Seul desormais ce retour d'experience permettra de franchir une nouvelle etape. Encore faut-il s'engager franchement dans cette voie, sous peine d'avoir a subir de nouvelles reglementations du type de la loi relative a la peche en eau douce, jugees par d'aucuns trop arbitraires

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.

Cette note expose, à la demande d'utilisateurs potentiels, le protocole précis de mise en oeuvre de la méthode des microhabitats développée au CEMAGREF de Lyon depuis 1985 et adaptée de l'IFIM de l'US Fish and Wildlife Service. Les principes des modèles inclus dans la méthode sont présentés. Les protocoles de mesures sont expliqués en fonction du modèle hydraulique et de la méthode de couplage des informations hydrauliques et biologiques. Les limites d'application sont ensuite exposées.

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.

[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.

International audience; A sociologist's and an ecologist's critical view of the Rhone river restoration programme. A ten-year physical and ecological restoration programme was defined for the Rhone River in 1998. Initially, one of its main objectives was to increase the minimum flow in several bypassed sections, with the clear goal of improving the fluvial habitat and the general ecological functioning of the river. A complex consultation process which brought together the hydropower industry, regional civil organisations, and local civil representatives was adopted to define more precisely the local measures to be taken. In the course of this process, the programme underwent a progressive change from purely ecological to more socially motivated outcomes such as improving amenity values and flood defence. We studied how increasing the minimum flow is a topic that can or cannot be discussed by the actors during the consultation process. For example, there is less discussion about the ecological value than about the economic value of the restoration programme between the hydropower industry and the local elected members. But, the various actors readily debate with the scientists about floods and sedimentary transport, linked with local knowledge. We applied a multidisciplinary approach, involving sociology and ecological sciences, to question the restoration programme and to analyse its hybrid results in terms of both the ecological and amenity values and at the same time to understand the governance process.; Il est assez commun que dans un processus de politique publique donnant large place à la concertation, l'objet initial soit déplacé. Il en est ainsi de ce cas d'étude qui, partant de la question des débits réservés, aboutit à celle de la lutte contre les inondations. Pour saisir cette trajectoire tracée aussi bien par la résistance du milieu aquatique que par les interactions humaines que celui-ci construit, il a fallu le regard croisé de l'écologue et du sociologue. L'hybridation est réussie, mais son efficacité tient aussi à une mise en critique des « utopies gestionnaires et scientifiques » qui voudraient un alignement pur et simple des différents types de savoirs et une heuristique propre à la dynamique des apprentissages sociaux. Asymétries, contradictions et ambivalences sont toujours là et la question de l'efficacité environnementale d'une gouvernance vertueuse reste posée. La Rédaction Mots-clés : restauration écologique ; concertations ; hydrosystème fluvial ; écologie et sociologie ; Rhône Résumé – Acté en 1998, le Programme décennal de restauration hydraulique et écologique du Rhône s'est fixé comme objectif principal d'augmenter les débits réservés dans les bras court-circuités du fleuve. Cet objectif était initialement pensé comme une action de restauration écologique de milieux naturels fortement perturbés. Un processus concomitant de concertations a plusieurs fois déplacé l'intérêt initial vers des projets d'élaboration d'un territoire fluvial, puis d'un outil de gestion contre les crues. L'approche interdisciplinaire appliquée, entre sociologie et écologie, interroge la capacité d'une telle action environnementale à aboutir à des résultats hybrides, relevant à la fois de l'amélioration d'un écosystème fluvial et d'un processus de gouvernance.

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

The functioning of running water ecosystems is controlled by the interaction of several physical parameters, the knowledge of which is beiing improved. Currently, the CEMAGREF, LYON, is developing a methodology allowing the description and the modelling of three of these parameters which have been selected on the basis of their importance for the biotic communities.namely, i stream velocity, ii water depth, Hi bed material. A division of the study reach into discrete cells provides a differenciated picture of the spatial variability of the hydrodynamic parameters measured at a given discharge, the mathematical modelling of water level integrates time variability. A reach on the Filliere river (Northern French) examplifies this method., Une bonne connaissance du fonctionnement des écosystèmes d'eau courante nécessitela prise en considération d'un certain nombre de variables physiques supposés les régir. Le CEMAGREF de Lyon développe actuellement une méthodologie permettant de décrire et modéliser trois de ces variables jouant un rôle essentiel pour la communauté biotique : la vitesse du courant, la hauteur d'eau et la granulométrie du lit. Un découpage de la station en cellules discrètes permet d'obtenir une image claire de la variabilité spatiale des conditions hydrodynamiques observées, un modèle mathématique de calcul de ligne d'eau autorisant l'appréciation de leur variabilité temporelle. L'exemple d'une station étudiée sur un cours d'eau de montagne donne une bonne idée des résultats ainsi obtenus., Malavoi J.R., Souchon Y. Méthodologie de description, quantification des variables morphodynamiques d'un cours d'eau à fond caillouteux : exemple d'une station sur la Fillière (Haute-Savoie) / A methodology for the description and the quantification of the morphodynamic variables along a gravel bed river : a reach of the Fillière river (Haute-Savoie) as an example. In: Revue de géographie de Lyon, vol. 64, n°4, 1989. Dynamique et gestion des cours d'eau. pp. 252-259.

Research conducted on Brown trout populations downstream of impoundments has showed the influence of several natural constraints. First, population dynamics analysis of 3 Brown trout (Salmo trutta) populations, along with a multiple-sites analysis (53 stations) of relationships between by-passed sections populations and their physical habitat templet, showed several structuring factors. The first filter is stream width. On top of that, natural flood events constrain the populations. Furthermore, habitat fragmentation related to the size of each dam affects juveniles variability, while flow replenishment along the bypassed section parlty determines trout abundance. The second step consisted in characterizing the physical habitat in which the different salmonid regulated reaches are to be found, for the entire hydroelectric EDF (Electricité de France) facilities. 15 types were established, based on their mountain range (Alps, Pyrénées and Massif Central), on the combination of two major hydromorphological variables (stream gradient and mean annual streamflow), and on the flow-sediment regime. Finally, litterature general knowledge on impacts of impoundments on trout populations and specific knowledge from the multiple-sites analysis were combined with the different types of regulated reaches physical habitats. General knowlege on stream habitats sensitivity of a given area can be gained from this combination. Using these results, it is possible to build an ecological risk assessment framework for bypassed reaches trout populations : this framework assess the risk related to a given impoundment, risk which comes on top of preexisting physical natural constraints defined according to the type the reaches belong to., Les recherches menées sur les populations de truite à l'aval des barrages ont mis en évidence l'influence de nombreuses contraintes naturelles. Dans un premier temps, une analyse de la dynamique de 3 populations de truite (Salmo trutta), combinée à une analyse multi-sites (53 sites) des relations entre les populations et leur cadre d'habitat physique en TCC, ont mis en évidence différents éléments structurants. Le premier filtre est la largeur du cours d'eau. A cela se surimpose un forçage par les crues naturelles. En outre, le niveau de fragmentation du réseau hydrographique lié à la taille du barrage influence la variabilité du stade juvénile, tandis que le degré de reconstitution du débit le long du TCC détermine en partie l'abondance de truite. Dans un second temps, le travail a consisté à caractériser pour l'ensemble du parc hydroélectrique EDF le cadre géophysique général dans lequel s'inscrivent les différents types de tronçons de cours d'eau salmonicoles soumis à l'influence d'ouvrages hydroélectriques. 15 types ont ainsi été définis sur la base de leur appartenance à l'un des trois massifs Alpes, Pyrénées et Massif Central, de la combinaison de 2 caractéristiques hydromorphologiques majeures (pente et module), et du régime hydrosédimentaire. Finalement, le croisement des connaissances générales issues de la littérature sur les impacts des ouvrages sur les populations de truite, des connaissances spécifiques acquises via l'analyse multi-sites avec les types de situation ouvrages/milieu permet de tirer des enseignements généraux sur les sensibilités a priori des habitats des cours d'eau d'une région.

Understanding how fis assemblages vary is a major goal of ecology and bioindication. In this PhD thesis, advanced statistical tools were used to identify which descriptors of temperature and flow regimes, that are among the most essential components of fish natural environment, do generate interannual variations of juvenile assemblages of cyprinid fish in the upper River Rhone. By using datasets of water temperature, flow and electric fishing samples over the 1980-2005 period, three groups of species have been determined based on their synchrone response to environmental variations and have been used to develop to types of Bayesian hierarchical models : - a Poisson regression, for which a selection of variable was performed, using the Bayes Factor criterion. this first model allowed for the quantification of the effects of the selected variables on the interannual variations of the different species abundance. - a model with shared latent variable, assuming the existence of a common source of variation for the environmental and the biological data, the Hypersignal. This model underlined the relative importance of the environemental variables in determining the assemblages structure. While their effects are generally treated separately, the joint effect of the temperature and flow regimes on the structure and the interannual variations of juveniles fish assemblages was put forward here., La compréhension des déterminismes des communautés de poissons et de leurs variations est un enjeu majeur, tant en écologie qu'en bioindication. Dans ce travail doctoral, nous avons mis en place des outils de statistiques avancées afin d'identifier les aspects des régimes thermique et hydrique, constituants essentiels de l'environnement naturel des poissons, responsables des variations des assemblages de juvéniles de cyprinidés du haut Rhône. En utilisant des chroniques de températures de l'eau, de débits et d'échantillonnages par pêche électrique sur la période 1980-2005, nous avons déterminé trois groupes d'espèces présentant des réponses synchrones aux variations d'environnement, et développé deux types de modèles hiérarchique, s'appuyant sur ces groupes, selon une perspective bayésienne :- un modèle de régression poissonienne, pour lequel nous avons utilisé une procédure de choix de modèle fondée sur le critère du Facteur de Bayes. Ce premier modèle nous a permis de sélectionner les variables d'intérêt et de quantifier leurs effets sur les variations interannuelles d'abondances des différentes espèces. - un modèle à facteur latent partagé, résumant l'influence commune d'une variable latente, l'hypersignal, sur les variations de l'environnement et des proportions relatives des groupes d'espèces. Nous avons ainsi souligné les importances relatives des variables environnementales dans la structuration des communautés. Alors que leurs effets sont généralement discutés séparément, nous avons mis en évidence l'influence conjointe des régimes thermique et hydrique sur la structuration et les variations interannuelles des assemblages de juvéniles de poissons en grandes rivières.

Evidence for climate change effects on biodiversity at global scale is now unequivocal. Among impaired ecosystems, running waters are particularly vulnerable to climate fluctuations. Changes in aquatic community structure and composition are then considered as integrative signals of the ecological responses to these climate changes. Under certain circumstances, these signals can be also exacerbated, confounded or potentially obscured by other abiotic variations.Therefore, the aim of this PhD was to assess the relative effect of different drivers on longterm trends in benthic macroinvertebrate communities, in the context of global climate change. Our investigations were focused more precisely on the Middle Loire River since, as lowland large river, it is particularly concerned by the potential impact of multiple stressors. Regarding the choice of the biological model, benthic fauna has been selected according to its acknowledged interest in bioassessment of running waters, especially thanks to a great diversity of potential responses to environmental disturbances and a number of methodological advantages.First, we investigated the temporal changes of ten major abiotic parameters over three decades (1977-2008). We highlighted the gradual warming of the Loire River (c. +1.2°C in the mean annual temperature over the three decades), coupled with a significant drop in mean discharge (c. -25%), both trends being exacerbated during the warm period (May-August). In the same time, although these changes were expected to induce a rise in the trophic level of the river, we emphasized a confounding effect of the wastewater treatment improvement (i.e. phosphorus input reduction), leading mainly to a drop in phosphate concentrations and a phytoplankton limitation.Second, we assessed the long-term structural and functional responses (i.e. over a 30-year period) of invertebrates of the Loire River to both major concomitant trends. On the one hand, we highlighted that water warming and to a lesser extent discharge reduction were significantly involved in the disappearance or decrease in rheophilic and psychrophilic taxa (e.g. Chloroperlidae). On the other hand, they explained also a major part of the appearance and increase of limnophilic and thermophilic taxa, including invasive species (e.g. Corbicula sp.). In terms of functional responses, these changes were illustrated by an adaptive evolution of the biological trait profiles in agreement with a priori predictions that is possible to make in a theoretical framework. However, this shift towards a generalist and pollution tolerant assemblage was partially confounded by improvement in water quality, explaining the settlement of new pollution-sensitive taxa during the last years (e.g. Philopotamidae). Although no taxonomic or functional resilience was observed, this trend was translated, via biological traits, into a probable transfer of trophic resources from phytoplankton to periphytic biofilms and macrophytes.Finally, we explored the multi-site spatial variability of these biotic and abiotic trends and we showed that our results as a whole, which supported already a number of observations in Europe, exhibited also a strong homogeneous pattern along the Middle Loire River (on nearly 300 km) and among different hydrosystems (e.g. Loire, Seine, Meuse)., Les effets du changement climatique sur la biodiversité à l’échelle du globe sont maintenant sans équivoque. Parmi les écosystèmes affectés, les cours d’eau sont particulièrement vulnérables aux fluctuations du climat. Les modifications de structure et de composition des communautés aquatiques constituent alors un signal intégrateur des réponses écologiques à ces changements climatiques. Dans certaines circonstances, ce signal peut également être exacerbé, modéré ou potentiellement masqué par d’autres variations abiotiques.L’objectif de ce travail de thèse était donc d’évaluer l’effet relatif de différents facteurs de forçage sur les tendances d’évolution à long-terme des communautés de macroinvertébrés benthiques de grands cours d’eau, dans un contexte de changement climatique global. Nos investigations ont ciblé plus spécifiquement la Loire moyenne car, en tant que grande rivière de plaine, elle est particulièrement concernée par les problèmes liés aux stress multiples. En ce qui concerne le choix du compartiment biologique, la faune benthique a été sélectionnée pour son intérêt reconnu en bioévaluation des cours d’eau, notamment grâce à une grande diversité de réponses potentielles aux perturbations environnementales et à un certain nombre d’avantages méthodologiques.Dans un premier temps, nous nous sommes appliqués à caractériser les modifications temporelles de dix paramètres abiotiques majeurs sur trois décennies (1977-2008). Nous avons notamment mis en évidence le réchauffement graduel de la Loire (c. +1,2°C en moyenne annuelle sur les trois décades), couplé à une réduction significative du débit moyen (c. -25%), les deux tendances étant exacerbées en période chaude (mai-août). Dans le même temps, alors que ces modifications étaient susceptibles de provoquer une augmentation du niveau trophique du fleuve, nous avons souligné l’existence d’un effet confondant de l’amélioration des traitements d’épuration (i.e. réduction des apports en phosphore), se traduisant principalement par la baisse des concentrations en phosphates et la limitation des organismes phytoplanctoniques.Dans un second temps, nous nous sommes intéressés aux réponses structurelles et fonctionnelles long-terme (i.e. 30 ans) des invertébrés de la Loire à ces deux évolutions concomitantes majeures. En premier lieu, nous avons constaté que le réchauffement et, dans une moindre mesure, la réduction du débit sont impliqués dans la disparition ou le déclin progressif de taxons rhéophiles et psychrophiles (e.g. Chloroperlidae). En parallèle, ces modifications hydroclimatiques expliquent une majeure partie de l’apparition et de la colonisation de taxons limnophiles et thermophiles, comprenant certaines espèces invasives (e.g. Corbicula sp.). En termes de réponses fonctionnelles, ces changements s’illustrent par une évolution adaptative des profils de traits biologiques cohérente avec les prédictions a priori qu’il est possible de faire dans un cadre théorique. Toutefois, cette dérive progressive vers un assemblage généraliste et polluotolérant est partiellement confondue par l’amélioration de la qualité d’eau, qui explique l’apparition de nouveaux taxons polluo-sensibles lors des dernières années (e.g. Philopotamidae). Bien qu’aucune résilience taxonomique ou fonctionnelle ne soit constatée, cette tendance se manifeste, via les traits biologiques, par un transfert probable des ressources trophiques depuis les organismes phytoplanctoniques vers des biofilms épibenthiques et des macrophytes.Pour finir, nous avons exploré la variabilité spatiale multi-sites de ces tendances biotiques et abiotiques et montré que l’ensemble de ces résultats, qui corrobore déjà un certain nombre d’observations en Europe, constitue également un patron homogène le long de la Loire moyenne (sur près de 300 km) et entre différents hydrosystèmes (e.g. Loire, Seine, Meuse).