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[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples [Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; Resilience in river ecosystems requires that organisms must persist in the face of highly dynamic hydrological and geomorphological variations. Disturbance events such as floods and droughts are postulated to shape life history traits that support resilience, but river management and conservation would benefit from greater understanding of the emergent effects in communities of river organisms. We unify current knowledge of taxonomic‐, phylogenetic‐, and trait‐based aspects of river communities that might aid the identification and quantification of resilience mechanisms. Temporal variations in river productivity, physical connectivity, and environmental heterogeneity resulting from floods and droughts are highlighted as key characteristics that promote resilience in these dynamic ecosystems. Three community‐wide mechanisms that underlie resilience are (a) partitioning (competition/facilitation) of dynamically varying resources, (b) dispersal, recolonization, and recruitment promoted by connectivity, and (c) functional redundancy in communities promoted by resource heterogeneity and refugia. Along with taxonomic and phylogenetic identity, biological traits related to feeding specialization, dispersal ability, and habitat specialization mediate organism responses to disturbance. Measures of these factors might also enable assessment of the relative contributions of different mechanisms to community resilience. Interactions between abiotic drivers and biotic aspects of resource use, dispersal, and persistence have clear implications for river conservation and management. To support these management needs, we propose a set of taxonomic, phylogenetic, and life‐history trait metrics that might be used to measure resilience mechanisms. By identifying such indicators, our proposed framework can enable targeted management strategies to adapt river ecosystems to global change.

International audience; 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 (1) temperature regimes upstream and downstream of dams with different structural characteristics, (2) relationships between stream temperature anomalies and climatic variables, watershed area, dam height, impoundment length and surface area, and residence time, (3) the most significant variables explaining the different thermal behaviors, and (4) the dam thermal effect considering a biological threshold of 22 °C, with a calculation of both the number of days with a temperature above this threshold and the average hourly duration above this threshold. Water temperature loggers were installed upstream and downstream of 11 dams in the Bresse region (France) and monitored at 30 min intervals during summer (June to September) over the 2009-2016 period, resulting in 13 paired water temperature time series (two sites were monitored for two summers, allowing the opportunity to compare cold and hot summers). At 23% of the dams, we observed increased downstream maximum daily temperatures of more than 1 °C; at the remaining dams we bserved changes in the maximum daily temperature of -1 to 1°C. Across sites, the mean downstream increase of the minimum daily temperature was 1 °C, and for 85% of the sites this increase was higher han 0.5 °C. We hierarchically clustered the sites based on three temperature anomaly variables: upstream-downstream differences in (1) maximum daily temperature (diff Tmax), (2) minimum daily temperature (diffTmin), and (3) daily temperature amplitude (diffTamp). The cluster analysis identified two main types of dam effects on thermal regime: (1) a downstream increase in Tmin associated with Tmax either unchanged or slightly reduced for impoundments of low volume (i.e., a residence time shorter than 0.7 d and a surface area less than 35 000m2), and (2) a downstream increase of both Tmin and Tmax of the same order of magnitude for impoundments of larger volume (i.e., a residence time longer than 0.7 d and a surface area greater than 35 000m2). These downstream temperature increases reached 2.4 °C at certain structures with the potential to impair the structure of aquatic communities and the functioning of the aquatic ecosystem. Overall, we show that small dams can meaningfully alter the thermal regimes of flowing waters, and that these that these effects can be explained with sufficient accuracy (R2 = 0,7) using two simple measurements of small dam physical attributes. This finding may have importance for modelers and managers who desire to understand and restore the fragmented thermalscapes of river networks.

International audience; Channelization has increased in piedmont areas with urbanization and other anthropogenic alterations. Changes in riparian structures and in sediment dynamics have affected riparian biodiversity including aquatic macroinvertebrate richness. In this context, riverbank restoration becomes a major issue in preserving stream ecosystem functioning and associated services. As a relevant integrator of environmental changes in river systems, macroinvertebrate communities are likely to readily respond to a combination of anthropogenic disturbances. We aimed at assessing the response of the taxonomic and functional characteristics of benthic macroinvertebrate communities along a gradient of managed riverbank naturalness.

International audience; When considering the development of conservation strategies for threatened plant communities it is crucial to understand their resilience to environmental change, taking into account current decline and the occurrence of further habitat fragmentation and climatic changes. Many recent works describe resilience character and elements, but there is little focus on the metrics and indices that describe elements of stability and specific resistance or resilience over the community composition matrix. Communities with strong niche selection might be restricted to specific resistance strategies to cope with environmental changes. This would result in a community at greater risk from increasing fragmentation and climatic changes. In a 35 years survey of relic calcareous grasslands, we looked at measures to identify the resilience mechanisms for stability in the presence and abundance of species. We used techniques of partitioning of temporal beta diversity in nestedness and turnover components, analysis of functional strategy changes and dissimilarity analysis to detect changes in between -plot diversity and exchanges. Contrary to expectations, we observe strong resilience with different stabilizing mechanisms both at plot level and exchanges between plots. At the scale of our grassland complex, response diversity and environmental stochasticity allow for the maintenance of high biodiversity under natural perturbations and gradual human -induced environmental changes. This highlights the importance of dispersal, recruitment dynamics and microsite diversity. Community resilience is more than just the sum of species resilience strategies; adaptive management strategies need more emphasis on the variability of conditions, as this can enable or disrupt important community resilience mechanisms.

National audience; Nous présentons les premiers résultats du projet IBBHIS. Ces premiers résultats concernent le lien entre volume de bois mort et biodiversité saproxylique. Nous comparons différentes plateformes statistiques pour estimer ces relations. Les différentes plateformes donnent des résultats proches. Les premiers résultats indiquent une relation qui varie dans l'espace, et des seuils de bois mort qui varient aussi d'un massif à l'autre.

D’une façon générale, un corridor représente une emprise spatiale garante de la connectivité dans un réseau écologique. Pour les cours d’eau, cette notion est non seulement liée à une zone spatialement identifiée comme riparienne, ou corridor rivulaire, qui se définit comme une bande de végétation naturelle située le long d'un cours d'eau, Mais, c’est également un milieu où se cumulent de nombreuses fonctionnalités écosystémiques : zone tampon, filtre d’épuration, zone de provision et de rétention de nutriments, habitat, écotone et couloir de connexion, de contact et d’échange. L’étude du corridor rivulaire est par conséquent indissociable de celle de la rivière, de son paysage et de son bassin versant. Quelles sont les échelles pertinentes à considérer pour appréhender la continuité écologique des corridors rivulaires? Comment construire une approche qui tienne compte de l’échelle de réalisation des processus d’échange et de contact ? Le focus de mes travaux au laboratoire d’hydroécologie quantitative repose sur les cours d’eau à l’échelle large de la France avec une attention particulière portée à leur structure et leur fonctionnement hydromorphologique. Les altérations physiques, la fragmentation des habitats, mais aussi la pollution se présentent comme des pressions emboîtées à différentes échelles, qui peuvent se cumuler au sein des réseaux hydrographiques. Pour correctement identifier leurs impacts et pouvoir y remédier, il fallait mobiliser de nouveaux concepts et bâtir un programme de recherche à moyen terme pour développer de nouvelles méthodes d’analyse hiérarchique, notamment pour caractériser la notion de connectivité. Le travail repose sur une sélection de variables spatiales d’intérêt, concrétisée ensuite par leur extraction géomatique à partir de bases de données couplées à des systèmes d’informations géographiques ou à partir de documents cartographiques, incluant par exemple l’imagerie à très haute résolution spatiale. Ces caractéristiques, résumées par des indicateurs spatiaux qui renseignent les ruptures de continuité, sont ensuite utilisées pour explorer avec un nouveau regard et une ouverture du champ spatial (réseaux hydrographiques, effets amont aval) des relations fonctionnelles entre corridor et différents processus ou réponses écologiques.

/ D'une façon générale, un corridor représente une emprise spatiale garante de la connectivité dans un réseau écologique. Pour les cours d'eau, cette notion est non seulement liée à une zone spatialement identifiée comme riparienne, ou corridor rivulaire, qui se définit comme une bande de végétation naturelle située le long d'un cours d'eau, Mais, c'est également un milieu où se cumulent de nombreuses fonctionnalités écosystémiques : zone tampon, filtre d'épuration, zone de provision et de rétention de nutriments, habitat, écotone et couloir de connexion, de contact et d'échange. L'étude du corridor rivulaire est par conséquent indissociable de celle de la rivière, de son paysage et de son bassin versant. Quelles sont les échelles pertinentes à considérer pour appréhender la continuité écologique des corridors rivulaires? Comment construire une approche qui tienne compte de l'échelle de réalisation des processus d'échange et de contact ? Le focus de mes travaux au laboratoire d'hydroécologie quantitative repose sur les cours d'eau à l'échelle large de la France avec une attention particulière portée à leur structure et leur fonctionnement hydromorphologique. Les altérations physiques, la fragmentation des habitats, mais aussi la pollution se présentent comme des pressions emboîtées à différentes échelles, qui peuvent se cumuler au sein des réseaux hydrographiques. Pour correctement identifier leurs impacts et pouvoir y remédier, il fallait mobiliser de nouveaux concepts et bâtir un programme de recherche à moyen terme pour développer de nouvelles méthodes d'analyse hiérarchique, notamment pour caractériser la notion de connectivité. Le travail repose sur une sélection de variables spatiales d'intérêt, concrétisée ensuite par leur extraction géomatique à partir de bases de données couplées à des systèmes d'informations géographiques ou à partir de documents cartographiques, incluant par exemple l'imagerie à très haute résolution spatiale. Ces caractéristiques, résumées par des indicateurs spatiaux qui renseignent les ruptures de continuité, sont ensuite utilisées pour explorer avec un nouveau regard et une ouverture du champ spatial (réseaux hydrographiques, effets amont aval) des relations fonctionnelles entre corridor et différents processus ou réponses écologiques.

National audience; La loutre est inféodée au corridor rivulaire. Sa recolonisation du bassin de la Loire, suivie par l'ONCFS depuis 30 ans, dépend des éléments de paysage de ce corridor. Le développement d'un modèle bayésien pour analyser la dynamique de recolonisation a permis l'identification de ces facteurs d'intérêt.

The aim of this study was to develop an operational Object-Based Image Analysis procedure for delimiting current riparian areas and characterizing their composition (herbaceous, shrub, hardwood and softwood vegetation) from available National Vector Spatial (NVS) and Very High Spatial Resolution Imagery (VHSRI) data in France. This procedure was designed and implemented over a reach of the dynamic Allier River (118 km). Results are excellent in delimiting current riparian areas at the date of the image whatever the VHSRI data source used (92 % for orthophotos 0.5 m, 90 % for Rapideyes images 5 m). The work on the characterization of vegetation composition illustrates the interest of using orthophotos for (1) delineating forest patches using Haralick textures and 2) identifying tree species using both spectral and textural information at tree crown scale. Further work will consist in assessing the delimitation process at various riparian landscapes (i.e., distinct river sizes and anthropogenic contexts) and exploiting information from archive Spot5 time-series images to improve characterization of the riparian area.

Les cours d’eau et leurs ripisylves constituent des trames naturelles structurant fortement les paysages. Pour en connaitre l’état de conservation ou d’altération à large échelle, il est possible d’utiliser des outils performants et d’analyser différents supports d’imageries. L’information extraite peut être simplement cartographiée ou être résumée par des indicateurs spatiaux qui vont renseigner les compositions d’essences arborées, leurs arrangements spatiaux, leurs emprises spatiales et les ruptures de continuité. Ces caractéristiques sont ensuite utilisées pour explorer avec un regard nouveau et une ouverture du champ spatial (réseau, effets amont aval) des relations fonctionnelles entre corridor et différents processus ou réponses écologiques. Cette construction d’indicateurs homogènes sur tout le réseau hydrographique métropolitain a permis de rechercher des relations spécifiques et quantitatives aussi bien avec des réponses physico-chimiques (qualité de l’eau), qu’avec des potentiels de répartition de mammifères (loutre et castor). On détaille ici l’analyse menée au travers de la loutre sur le bassin de la Loire. L’existence de corridors rivulaires boisés ajoutée à une absence d’altération du milieu physique des cours d’eau offrent des situations favorables pour la colonisation par cette espèce. Ces situations ont été cartographiées en prenant en compte la densité du réseau hydrographique. Ces cartographies identifient des trames structurelles et fonctionnelles répondant à des besoins écologiques à différentes échelles. Elles constituent un support efficace pour orienter les stratégies de gestion visant le renforcement et la protection de cet espace. / Rivers and their corridors constitute natural networks that strongly structure the landscape. To build knowledge on their conservation status or alterations at large scale, different sources and methods of image analysis nowadays exist. Remotely sensed information can be used for cartography purposes or embedded in spatial indicators that can inform on spatial configuration, fragmentation and continuity, or riparian forest composition. These characteristics are then used to explore the functional relationships between the corridor and different processes and ecological responses through a new regard and network analysis methods. Building homogeneous indicators over the entire French hydrographic network has allowed us to investigate specific and quantitative relationships not only in regard to physicochemical responses (e.g. water quality), but also in relation to the potential spatial distribution of mammals (e.g. otters and beavers). We describe here an analysis concerning otters in the Loire watershed. The presence of wooded riparian corridors combined with a lack of alteration of the physical environment of rivers offer favorable conditions for colonization by this species. Such configurations were mapped while taking into account the density of the hydrographic network. Results identify structural and functional networks which meet the ecological needs of the species at different scales. They provide effective support to guide management strategies aimed at strengthening and protecting such areas.

La faune benthique est au coeur de l’évaluation écologique des cours d’eau depuis les années soixante, où ont été proposés les premiers indices biotiques. Ces macroinvertébrés de par leurs exigences et leurs modes de vie constituent des signatures temporelles précieuses qu’il convient d’analyser et d’interpréter avec grand soin : si des évolutions temporelles sont constatées, quels en sont les principaux déterminants ? Voit-on des signes d’amélioration de la qualité de l’eau ? Quels paramètres en sont responsables ? Voit-on des tendances temporelles imputables à des changements de climat ? Le présent rapport détaille le processus de recueil et de sélection des sites et des données. Des premiers résultats riches d’enseignements ont pu être mis en évidence.

La faune benthique est au coeur de l’évaluation écologique des cours d’eau depuis les années soixante, où ont été proposés les premiers indices biotiques. Ces macroinvertébrés de par leurs exigences et leurs modes de vie constituent des signatures temporelles précieuses qu’il convient d’analyser et d’interpréter avec grand soin : si des évolutions temporelles sont constatées, quels en sont les principaux déterminants ? Voit-on des signes d’amélioration de la qualité de l’eau ? Quels paramètres en sont responsables ? Voit-on des tendances temporelles imputables à des changements de climat ? Le présent rapport détaille le processus de recueil et de sélection des sites et des données. Des premiers résultats riches d’enseignements ont pu être mis en évidence.

Macroinvertebrate communities are one of the longest applied biotic indicator for running waters. Since the approval of the Water Framework Directive, in 2000, survey networks have been widely implemented in most Member States. One of the main issues for the assessment of stream biotic condition is the understanding of invertebrate community functioning in the context of changing environmental conditions. Still, only few studies are based on long time series. In France, national biological monitoring networks have been routinely sampled since 1992. Furthermore, many watercourses are surveyed since the 1970s-1980s. This data is of great importance for several reasons: 1) It contributes to the identification of temporal patterns of stability and persistence to calibrate assessment methods and 2) It allows the analysis of long time invertebrate community trends.

International audience; This chapter emphasizes the role of riparian vegetation in regulating and protecting river ecological integrity, based on a study of a river catchment (25 000 km²; 6000 km river network) located in the North of France. Restoring riparian vegetation is supposed to enhance the river ecosystem integrity and its ecosystem services. To reveal this relationship, at first a Riparian Area Land Cover (RALC) map for all rivers of the catchment was produced from high and very high spatial resolution earth observation data using Object-Based Image Analysis (OBIA) methods. Fine-scale land cover information was obtained to assess reliably riparian vegetation conditions and human pressure at riparian corridor scale. The land cover information was assembled at three distinct spatial scales: the local riparian corridor, the upstream riparian corridor (using RALC map), and the upstream watershed (using CORINE Land Cover database). Both for the local riparian corridor and the upstream corridor the land cover data were gathered for a range of buffers. Ecological integrity of the rivers was measured using macroinvertebrate community composition. Responses to the land cover at the distinct scale levels were investigated. Results show the benefic influence on the macroinvertebrate community for the riparian forest and grassland vegetation in a 20m-buffer on both sides of the river, locally and on the whole upstream network. These results highlight the interest of fine-scale earth observation data interpretation in the prioritization and design of riparian corridor restoration strategies at catchment scale. With this fine-scaled information, new reliable spatial indicators (e.g., continuity, width and uniformity…) can be explored in order to better understand the contribution of riparian vegetation to maintain river ecological integrity and ecosystem services.

International audience

International audience

International audience; Spatial analysis using fine-scale information over broad territories is essential to define efficient restoration strategies from local to national scale. We designed an OBIA dedicated to produce operationally reliable fine-scale information over broad territories. The originality of our OBIA lies particularly in the top-down approach for the construction of the classification tree and the use of „knowledge-based rules‟ classification technique. The implementation of this OBIA over the two study areas – (i) the Normandy region for riparian area land cover mapping (5600 km² riparian area) and (ii) fours departments over the Languedoc-Roussillon region (22644 km²) – demonstrates the operability of our approach (time-efficient, reproducible, transferable, portable). Broad scale spatial analysis conducted from resulting maps demonstrate the interest of using fine-scale information and highlight that OBIA, following our approach, will be at very short run a broadly applicable method to carry out such analysis.

International audience

International audience; Restoring or preserving the ecological quality of aquatic ecosystems is a major objective of Water Framework Directive (WFD). A pending question deals with the relative influence of anthropic pressures from local to watershed scale on river ecological status in order to better orient restoration strategies. For this purpose, a regional approach studying the relationships between land cover (a driving force of the main anthropic pressures) and biological WFD standards is required. This study mobilizes three complementary fields of research: 1- the use of suitable land cover data at each functioning scale: the upstream watershed (UW), the upstream riparian (UR) and the local riparian scale (LR) ; 2- the quantification of synthetic spatialized indicators of land cover reflecting the impact mechanisms; 3- the development of pressure/state statistical spatialized models (PSM) that quantify the links between biological indicators assessed at station level and land cover spatial indicators over each scale. Several riparian buffers were tested in order to better localize the areas to be restored. The corresponding methods were developed and implemented over lower French Normandy river networks (6000 km long; 157 macroinvertebrate stations, a part of Tables Calcaires hydroecoregion). CLC database was used for quantifying land cover at UW scale and very high spatial resolution imagery over riparian scales (UR and LR). Results show for instance the significant riparian tree vegetation (over a 20m wide strip on both sides of the river) influence on macroinvertebrate indicator. Such results are very useful for decision-makers that can estimate the interest of investing in restoration strategies by anticipating their effects in terms of Water Framework Directive standards. In the near future, new spatial indicators at riparian scale and new biological indicators will be used in PSM models over different hydroecoregions with a particular attention to the spatial and temporal inaccuracies of data.

International audience; The definition of restoration strategies on riparian corridor requires an improved understanding at regional scale of the relative influence of both human surrounding pressures (at different scales, from watershed to local riparian corridor) and riparian vegetation on river ecological status. This work brings new routine methodologies for (i) accurate and fine-scale mapping of land cover within riparian corridors over large extent in combining information from remotely-sensed images at very high spatial resolution and ancillary data; (ii) building spatial indicators reflecting impact mechanisms on river ecological status of both human pressures along rivers and riparian vegetation; (iii) building spatialized pressure/impact models at regional scale. These methodologies were developed and implemented over the Herault watershed (1150 km, 2650 km², 3 ecoregions, southern France) and rivers of the Normandy Region (6000 km, 25000 km², nordwest France). First, detailed fine-scale riparian corridor land cover maps were produced on the two studied areas with high accuracy (89%) from an object-oriented classification procedure combining information from orthophotos (0.5 m pixels), Spot 5 XS (10 m pixels) satellite images, and complementary spatial thematic data. Then, several spatial indicators were defined and built. For example, six types of indicators specific to the role of riparian forest have been defined: (1) length and (2) area indicating the presence and intensity of this vegetation along the river; (3) connectivity (number of gaps/km of river) and (4) length of gaps reflecting the role of thermal regulation related to the shadow cast by the vegetation, and (5) the average width and (6) uniformity (varying width) reflected with the connectivity indicator the ability of this vegetation to act as a buffer. Finally, introduction of these indicators in Pressure/Impact models highlights the influence of herbaceous and tree riparian vegetation on a 20 m buffer width on macroinvertebarte community. Remotely sensed riparian corridor indicators are a key issue to monitor and manage riverine landscape.

International audience; Preservation and restoration of river ecosystems requires an improved understanding of the mechanisms through which they are influenced by landscape at multiple spatial scales from the overall upstream watershed to the local riparian corridor. This research is dedicated to the statistical analysis of the role of riparian vegetation in regulating and protecting river ecological status. It is particularly focussed on the relevance of land use indicators and the spatial footprint over which they are calculated, for the assessment and implementation of efficient and realistic preservation and restoration strategies in the riparian corridor. The method was implemented over the Normandy river network (6000 km long river network; 155 ecological stations). It analysed (i) the potential of Very High Spatial Resolution (VHRS, metric) remote sensing imagery for a fine scale mapping of the Riparian Area Land Cover (RALC); (ii) the use of GIS techniques to produce spatial indicators at riparian scale; and (iii) the design of Regionalized Pressures/Impacts (RPI) models studying relationships between land cover indicators and indicators of the stream biological response. The overall objective is to provide quantitative and spatialised basis for the design of a regional restoration strategy for the riparian corridor. In a first phase, we elaborated a generic classification procedure (Tormos et al., submitted-010), that produces RALC maps in different relief, climate and geology contexts. This procedure uses information from orthophotos (0.5 m pixels) and Spot 5 XS (10 m pixels) image data, and complementary spatial thematic data. It produces a reliable detailed (62 classes) RALC map. In a second phase, we derived from this RALC map, using automated GIS techniques, several spatial indicators that quantify the proportion of a given land cover category within a wide range of riparian footprints. A footprint is a buffer with a given lateral distance to the river and given longitudinal distances upstream and downstream from the ecological station. Finally, we developed RPI models (Wasson et al., 2010) based on these spatial indicators at riparian scale over the Normandy river region. Thanks to the fine RALC mapping and the indicators computed on a spectrum of riparian footprints it was possible to identify and localize more precisely the different pressures and to demonstrate the specific influence of riparian vegetation (on a 20m wide strip on both sides of the river) on river ecological status at regional level. In the near future, new spatial indicators at riparian scale, incorporating knowledge of human impact and riparian vegetation influence on aquatic ecosystems (Tormos et al., in press-2010), and new biological indicators will be used in RPI modeling in order to prioritize riparian corridor restoration.

Since about 90% of the natural floodplain area of rivers in Europe has been reclaimed and now lacks river dynamics, nature rehabilitation along rivers is of crucial importance for the restoration of their natural function. Flood protection, self-purification of surface water, groundwater recharge, species protection and migration are all involved in this process. It is now generally recognised that rivers form natural arteries in Europe but are also of economic importance and are recognisable cultural landscape. Many examples are already available of successful small river restoration projects. Several species thought to be extinct have now reappeared and characteristic species have also expanded in recent years. This paper concentrates on the concept of setting targets for river restoration as exemplified by the Meuse River. A modelling exercise shows the restraints of current habitat configuration and the potential for habitat restoration along the river. A policy analysis, using a strategic approach, illustrates the influence of the decision making process on the targets for natural river development. River dynamics play a key factor in determining the potential for persistent populations of target animal species along the river, with the help of an expert system (LARCH, Landscape ecological Analysis and Rules for the Configuration of Habitat). The potentials for the increase of dispersion and biodiversity and the maximisation of ecological benefits at different scales, are also considered.

De te verwachten effecten van het Grensmaasproject op het gedrag van de rivier, zodat ook prognoses over de invloed op de bosontwikkeling mogelijk worden