Search

Dans le cadre du sixième appel d'offres (AO6) pour l'éolien en mer en France, Ifremer réalise l’étude pour identifier les zones de moindre contrainte pour les espèces halieutiques (poissons, mollusques, crustacés, invertébrés benthiques sensibles) dans le Golfe du Lion à la demande de la Direction Générale de l'Energie et du Climat (Ministère de la Transition Ecologique et Solidaire). La méthodologie pour calculer le risque d’effet a été adaptée à partir de la méthode proposée pour l’étude des compartiments granulats et avifaune au sud de la Bretagne afin de maintenir une similitude de concepts et de terminologies entre les différents appels d’offres. Les données des campagnes scientifiques MEDITS et PELMED ont été utilisées dans un premier temps pour créer des cartes de distribution (densité ou biomasse). Les cartes de distribution ont ensuite permis de calculer la représentativité de chaque espèce. Les données de débarquements géolocalisés de pêche ont également été utilisées pour calculer la représentativité des espèces. A partir de ces représentativités, de la vulnérabilité (statut de protection ou état du stock) et de la distribution des espèces, des cartes d’enjeu ont pu être créées. L’enjeu couplé à la sensibilité (effets biologiques potentiels de l’éolien flottant) des espèces a servi à calculer le risque d’effet. Le risque d’effet global (toutes espèces confondues) est très fort dans la partie ouest du Golfe du Lion : dans la macrozone A, en face de Port-la-Nouvelle, dans l’extrémité ouest de la macrozone B ; et dans la partie nord de la macrozone C. Le risque d’effet est faible au sud des macrozones et au large du Golfe du Lion. L’incertitude associée au risque d’effet a été évalué avec une technique de ré-échantillonnage appelée bootstrapping.

The objective of the present study was to document the knowledge about the biodiversity of benthic insect communities and their distribution patterns in the semi-arid bioclimatic stage in the streams of the Aurès Region (NE Algeria). The distribution patterns of communities were analyzed in relation to some environmental factors: physicochemical water parameters and global habitat characteristics, including human impact. The taxonomic biodiversity of six sampled streams (wadis) comprises 42 insect taxa, belonging to seven orders and 30 families, of which Coleoptera is the most diverse order (15 taxa), whereas Diptera, Trichoptera and Ephemeroptera dominate in terms of abundance. The human impact, flow velocity and some quality parameters of water (potential of hydrogen, nitrite, concentration of orthophosphates and conductivity) were identified as the most influential environmental variables, which allows the prediction of taxonomic diversity indicators. The classification and regression tree analysis (CART) for benthic insects shows the effect of environmental variables (habitat parameters and human impact in the arid region) on the diversity and distribution of insect orders. The RDA analysis showed that altitude, substrate type, human impact and physicochemical parameters of water (pH, flow velocity, conductivity and total dissolved solids) are the most important predictor variables that play an important role in the distribution patterns of benthic insects.

Benthic diatoms have long been considered as an interesting compartment for monitoring aquatic environments quality. Then, within the implementation of the Water Framework Directive (WFD), adopted since 10/23/2000, they are identified as one of the key biological quality elements, making it possible to assess the ecological status of different categories of aquatic environments, including rivers from continental Europe and certain overseas territories. Because of its legal status, New Caledonia is not really part of the European Union and WFD has no legal vocation for application there. However, integrated and sustainable management of water resources is an important concern for local authorities and managers. In order to complete the ecological information already provided on watercourses by 2 biological indices based on benthic invertebrates (the Biotic Index of New Caledonia or IBNC, developed since 1999, and the recent Bio-Sedimentary Index or IBS), on the initiative of the OEIL and with the support of DAVAR and CNRT, a Research & Development Program aiming at the development of a new diatomic index has been implemented under responsibility of the Asconit-Irstea consortium, assisted by the local private consultant Bioeko. Carried out between October 2012 and 2017, this program enabled the acquisition of 210 complete surveys coupling diatomic inventories and physico-chemical conditions at the station, collected during 4 sampling campaigns covering the 2 main climatic seasons. At the toltal, 466 different taxa could be inventoried, many of which being previously poorly known or even unknown.Function of the quantity of ecological information capitalized, 217 sufficiently encountered freshwater taxa participate in the calculation of the new IDNC. Many of them do not provide specific information on the level of anthropogenic alteration of the river (Taxons +). Other taxa with a distribution clearly favored by anthropogenic pressure gradients were selected using the TITAN software, and constitute alert taxa (Taxa -). Specific lists of alert taxa have thus been identified with respect to 7 different anthropogenic gradients.This iconographic guide is intended to allow the reliable identification of the IDNC's taxa (i.e. taxa really participating in the calculation of the index score). Some marine taxa identified during the study are also illustrated. It is useful to recognize them: indeed, their identification in more than marginal numbers in a given sample would be a sign of a coastal influence exerted at the level of the sampled site (transition zone), such a situation getting outside the validity domain of IDNC.This identification guide consists of 2 volumes: Volume 1 describes each index taxon individually. Volume 2 (i.e. this document) compiles illustrations of morphologically-close taxa in order to be able to compare them and facilitate their routine identification.; Les diatomées benthiques sont considérées de longue date comme un compartiment d'intérêt pour surveiller la qualité des milieux aquatiques. Aussi, dans le cadre d'application de la Directive-Cadre sur l'Eau (DCE), adoptée depuis le 23/10/2000, elles ont été identifiées comme l'un des maillon-clés permettant d'évaluer l'état écologique de différentes catégories de milieux aquatiques de l'Europe continentale et de certains territoires ultramarins, dont les cours d'eau. Du fait de son statut juridique, la Nouvelle-Calédonie n'est pas partie intégrante de l'Union Européenne et la DCE n'a pas vocation légale à s'appliquer. Cependant, la gestion intégrée et durable de la ressource en eau est une préoccupation importante des autorités et gestionnaires locaux. Afin de venir compléter l'information écologique déjà apportée sur les cours d'eau par 2 indices biologiques basés sur les invertébrés benthiques (l'Indice Biotique de Nouvelle-Calédonie ou IBNC, mis au point depuis 1999, et l'Indice Bio-Sédimentaire ou IBS, de production plus récente), à l'initiative de l'OEIL et avec l'appui de la DAVAR et du CNRT, un programme de Recherche-Développement visant la mise au point d'un nouvel indice diatomique a été mis en place, dont la réalisation a été confiée au consortium Asconit-Irstea, avec l'appui du bureau d'études local Bioeko. Réalisé entre Octobre 2012 et 2017, ce programme a permis l'acquisition de 210 relevés complets couplant inventaires diatomiques et conditions physico-chimiques à la station, collectés au cours de 4 campagnes de prélèvement couvrant les 2 saisons climatiques principales. En tout, 466 taxons différents, ont pu être inventoriés, dont beaucoup étaient antérieurement mal connus voire inconnus.En fonction du niveau d'information écologique capitalisé, 217 taxons d'eau douce suffisamment rencontrés participent effectivement au calcul du nouvel IDNC. Bon nombre d'entre eux n'apportent pas d'information particulière sur le niveau d'altération anthropique de la rivière (Taxons +). D'autres taxons, à répartition clairement favorisée par des gradients de pression anthropique, ont été sélectionnés à l'aide du logiciel TITAN et constituent des taxons d'alerte (Taxons -). Des listes spécifiques de taxons d'alerte ont ainsi été identifiées vis-à-vis de 7 gradients différents d'anthropisation.Le présent guide iconographique est destiné à permettre l'identification fiable des taxons indiciels de l'IDNC (i.e. les taxons qui participent effectivement au calcul de la note indicielle). Quelques taxons halins identifiés en cours d'étude sont également illustrés. Il est utile de les reconnaître. En effet, leur identification dans un effectif plus que marginal dans un relevé donné serait le signe d'une influence littorale exercée au niveau du site prélevé (zone de transition), situation particulière sortant du domaine de validité de l'IDNC.Le présent guide d'identification est composé de 2 volumes : le Volume 1 décrit chaque taxon indiciel individuellement. Le Volume 2 (présent document) compile des illustrations de taxons morphologiquement proches afin de pouvoir les comparer et de faciliter leur identification en routine.

Benthic diatoms have long been considered as an interesting compartment for monitoring aquatic environments quality. Then, within the implementation of the Water Framework Directive (WFD), adopted since 10/23/2000, they are identified as one of the key biological quality elements, making it possible to assess the ecological status of different categories of aquatic environments, including rivers from continental Europe and certain overseas territories. Because of its legal status, New Caledonia is not really part of the European Union and WFD has no legal vocation for application there. However, integrated and sustainable management of water resources is an important concern for local authorities and managers. In order to complete the ecological information already provided on watercourses by 2 biological indices based on benthic invertebrates (the Biotic Index of New Caledonia or IBNC, developed since 1999, and the recent Bio-Sedimentary Index or IBS), on the initiative of the OEIL and with the support of DAVAR and CNRT, a Research & Development Program aiming at the development of a new diatomic index has been implemented under responsibility of the Asconit-Irstea consortium, assisted by the local private consultant Bioeko. Carried out between October 2012 and 2017, this program enabled the acquisition of 210 complete surveys coupling diatomic inventories and physico-chemical conditions at the station, collected during 4 sampling campaigns covering the 2 main climatic seasons. At the toltal, 466 different taxa could be inventoried, many of which being previously poorly known or even unknown.Function of the quantity of ecological information capitalized, 217 sufficiently encountered freshwater taxa participate in the calculation of the new IDNC. Many of them do not provide specific information on the level of anthropogenic alteration of the river (Taxons +). Other taxa with a distribution clearly favored by anthropogenic pressure gradients were selected using the TITAN software, and constitute alert taxa (Taxa -). Specific lists of alert taxa have thus been identified with respect to 7 different anthropogenic gradients.This iconographic guide is intended to allow the reliable identification of the IDNC's taxa (i.e. taxa really participating in the calculation of the index score). Some marine taxa identified during the study are also illustrated. It is useful to recognize them: indeed, their identification in more than marginal numbers in a given sample would be a sign of a coastal influence exerted at the level of the sampled site (transition zone), such a situation getting outside the validity domain of IDNC.This identification guide consists of 2 volumes: Volume 1 describes each index taxon individually. Volume 2 (i.e. this document) compiles illustrations of morphologically-close taxa in order to be able to compare them and facilitate their routine identification.; Les diatomées benthiques sont considérées de longue date comme un compartiment d'intérêt pour surveiller la qualité des milieux aquatiques. Aussi, dans le cadre d'application de la Directive-Cadre sur l'Eau (DCE), adoptée depuis le 23/10/2000, elles ont été identifiées comme l'un des maillon-clés permettant d'évaluer l'état écologique de différentes catégories de milieux aquatiques de l'Europe continentale et de certains territoires ultramarins, dont les cours d'eau. Du fait de son statut juridique, la Nouvelle-Calédonie n'est pas partie intégrante de l'Union Européenne et la DCE n'a pas vocation légale à s'appliquer. Cependant, la gestion intégrée et durable de la ressource en eau est une préoccupation importante des autorités et gestionnaires locaux. Afin de venir compléter l'information écologique déjà apportée sur les cours d'eau par 2 indices biologiques basés sur les invertébrés benthiques (l'Indice Biotique de Nouvelle-Calédonie ou IBNC, mis au point depuis 1999, et l'Indice Bio-Sédimentaire ou IBS, de production plus récente), à l'initiative de l'OEIL et avec l'appui de la DAVAR et du CNRT, un programme de Recherche-Développement visant la mise au point d'un nouvel indice diatomique a été mis en place, dont la réalisation a été confiée au consortium Asconit-Irstea, avec l'appui du bureau d'études local Bioeko. Réalisé entre Octobre 2012 et 2017, ce programme a permis l'acquisition de 210 relevés complets couplant inventaires diatomiques et conditions physico-chimiques à la station, collectés au cours de 4 campagnes de prélèvement couvrant les 2 saisons climatiques principales. En tout, 466 taxons différents, ont pu être inventoriés, dont beaucoup étaient antérieurement mal connus voire inconnus.En fonction du niveau d'information écologique capitalisé, 217 taxons d'eau douce suffisamment rencontrés participent effectivement au calcul du nouvel IDNC. Bon nombre d'entre eux n'apportent pas d'information particulière sur le niveau d'altération anthropique de la rivière (Taxons +). D'autres taxons, à répartition clairement favorisée par des gradients de pression anthropique, ont été sélectionnés à l'aide du logiciel TITAN et constituent des taxons d'alerte (Taxons -). Des listes spécifiques de taxons d'alerte ont ainsi été identifiées vis-à-vis de 7 gradients différents d'anthropisation.Le présent guide iconographique est destiné à permettre l'identification fiable des taxons indiciels de l'IDNC (i.e. les taxons qui participent effectivement au calcul de la note indicielle). Quelques taxons halins identifiés en cours d'étude sont également illustrés. Il est utile de les reconnaître. En effet, leur identification dans un effectif plus que marginal dans un relevé donné serait le signe d'une influence littorale exercée au niveau du site prélevé (zone de transition), situation particulière sortant du domaine de validité de l'IDNC.Le présent guide d'identification est composé de 2 volumes : le Volume 1 décrit chaque taxon indiciel individuellement. Le Volume 2 (présent document) compile des illustrations de taxons morphologiquement proches afin de pouvoir les comparer et de faciliter leur identification en routine.

International audience; While many metals are known to accumulate in sediments, knowledge about the resulting ecotoxicological effects on sediment microbial communities is scarce. The present study aimed at evaluating the structural and functional impact of chronic exposure to environmental concentrations of copper (Cu) and arsenic (As), alone or mixed together, on river sediment microbial communities. Natural uncontaminated surface sediments collected in a French River (Ain) were spiked with As and Cu at a nominal concentration of 40 mg/kg and then were exposed for 21 days in laboratory channels with overlying waters. The response of heterotrophic microbial communities to metals was evaluated both in terms of genetic structure (using ARISA analysis) and functional potential (using exo-enzymatic, metabolic and qPCR analyses). A pollution induced community tolerance (PICT) approach was also performed to assess if the exposure led to an increase in the capacity of microbial communities to tolerate metals. Our results showed rapid and marked effects of Cu alone on the structure and the functions of the exposed communities. Chronic Cu exposure also induced an increase in community tolerance to Cu, as observed by PICT measurement using beta-glucosidase activity. In contrast, the effects of As were mostly undetectable. Under mixture exposure (Cu+As), the effects were similar or higher than those provoked by Cu alone, depending on the measured parameter. Altogether those findings reveal that metals accumulation in sediments can impact exposed microbial communities thus affecting their functional role in aquatic ecosystems.

International audience; Turbulence and aeration are reduced in many streams during low-flow periods as a consequence of drought or water abstraction, thus affecting invertebrate interactions and pivotal ecosystem processes such as the breakdown of organic matter (OM). These effects can be larger in the hyporheic zone (HZ), the ecotone connecting the surface stream and groundwater, especially when fine sediments reduce hydraulic conductivity. In addition, OM breakdown in the HZ could depend on the availability ofOMin the benthic zone (BZ), because the latter would not only be a more accessible, and thus preferred, food resource, but also more easily scoured downstream. In a laboratory microcosm experiment of 28 days duration, we manipulated aeration, sediment size and location ofOM(either all buried or half buried with half on the surface, simulating the HZ and BZ respectively). Six mayfly (Habroleptoides) individuals and four stonefly (Capnioneura) individuals were enclosed in each microcosm and the consumption of OM was measured. Lack of aeration reduced oxygen saturation from 94 to 66%, reducing OM consumption particularly on the surface, in contrast with our expectations. As hypothesised, the availability of surface OM significantly reduced invertebrate consumption of buried OM. Habroleptoides performed better than Capnioneura, especially in fine sediments. The results suggest that reduced turbulence can affect invertebrate trophic interactions as well as the decomposition of OM, depending on sediment grain size and the location of OM.

International audience; Addition of large wood (LW, wood pieces longer than 1 m and wider than 10 cm) into stream channels is a common restoration practice aimed at enhancing habitat diversity and fish populations, as well as the abundance and diversity of benthic invertebrates. Nevertheless, there is some controversy regarding the effects of LW restoration on invertebrate assemblages, and the effects could differ depending on the season of the year as well as on the scale of observation (habitat vs reach scale). In this study we analysed the effects of a LW restoration experiment performed in 4 mountain streams following a BACI (Before-After/Control-Impact) design. We sampled benthic invertebrates in 3 main habitats (fine inorganic sediments, called gravel; coarse inorganic sediments, called cobbles; and particulate organic matter, called POM) in winter and summer before and after the addition of LW into experimental reaches, and compared the results to those obtained from upstream control reaches. LW addition promoted the retention of gravel and organic matter, resulting in an overall decrease in the areal cover of cobbles and a significant increase in the cover of organic matter in summer. Invertebrate richness was highest in cobbles and lowest in POM, whereas density and biomass were highest in POM and lowest in gravel. At the habitat scale, LW addition promoted invertebrate and shredder richness, diversity and biomass in summer, but the opposite effect was found in winter. Community composition changed significantly with wood addition, most notably as a result of increased density of elmids, limnephilids and limoniids, and decreased density of baetids. Density of limnephilids increased 20-fold and that of limoniids 5-fold. At the reach scale, LW addition enhanced the biomass of invertebrates and shredders in summer but the effects were opposite in winter. LW addition did not affect invertebrate density. The results show the effects of LW restoration on invertebrates to differ among seasons. Positive effects on biomass occur in summer, when retention by LW enhances food availability compared to unrestored reaches, whereas effects are slightly negative in winter, a period of large food availability.

/ Les effets d'une contamination sur des organismes sont évalués dans un premier temps en étudiant la toxico-cinétique, c'est-à-dire le lien entre la concentration d'exposition et la concentration bioaccumulée par l'organisme. En effet, la bioaccumulation de contaminants métalliques ou organiques par diverses espèces aquatiques est un phénomène très variable, puisqu'il dépend à la fois des caractéristiques du milieu, des propriétés des contaminants mais aussi de l'espèce considérée. Différents modèles dits toxico-cinétiques (ou biodynamiques) ont été développés pour décrire l'accumulation de contaminants dans les réseaux trophiques aquatiques (Luoma et Rainbow, 2005). Dans ces modèles, l'organisme est souvent considéré comme un compartiment unique ; la bioaccumulation de contaminants est alors décrite comme la résultante de flux entrants (absorption) et sortants (élimination). Le processus d'absorption peut se faire par voie dissoute et/ou trophique. Le régime alimentaire des organismes aquatiques est reconnu pour être une importante voie de bioaccumulation de contaminants. Le processus d'élimination inclut l'excrétion, la métabolisation et la dilution par la croissance. À ce jour, des modèles existent pour décrire l'accumulation de composés persistants peu métabolisables dans des organismes aquatiques variés. Cependant, la prise en compte de la biotransformation reste problématique malgré son importance ; il s'agit d'un processus clé pouvant atténuer la bioaccumulation des substances et varie considérablement selon les espèces et les contaminants (Arnot et al., 2008). De même, les études incluant la dépendance à la concentration dans les modèles actuels sont peu nombreuses, toutefois à considérer puisqu'il existe physiologiquement des phénomènes de saturation. À ce jour, il n'existe pas de cadre générique de modélisation réunissant l'ensemble de ces processus (absorption avec éventuellement effet de saturation, élimination avec éventuellement biotransformation) pour les contaminants organiques persistants. Ce projet de recherche a pour objectif de développer un tel cadre générique de modélisation biodynamique en s'appuyant sur des données expérimentales obtenues en conditions contrôlées en réalisant des cinétiques d'accumulation et d'élimination de composés organiques, notamment émergents, par différentes espèces aquatiques présentant des traits biologiques variés. Trois espèces d'invertébrés benthiques d'eau douce (Physa acuta, Chironomus riparius et Gammarus fossarum) ont été sélectionnées ; les substances modèles incluent notamment le PCB 153, l'hexabromocyclododécane et un polybromodiphényl-éther. Les paramètres du modèle générique pour chaque couple espèce-contaminant seront estimés par inférence Bayésienne à partir des résultats expérimentaux.

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; We reviewed 219 papers and built an inventory of 532 items of ecological evidence on multiple stressor impacts in rivers, lakes, transitional and coastal waters, as well as groundwaters. Our review revealed that, despite the existence of a huge conceptual knowledge base in aquatic ecology, few studies actually provide quantitative evidence on multi-stress effects. Nutrient stress was involved in 71% to 98% of multi-stress situations in the three types of surface water environments, and in 42% of those in groundwaters. However, their impact manifested differently along the groundwater-river-lake-transitional-coastal continuum, mainly determined by the different hydro-morphological features of these ecosystems. The reviewed papers addressed two-stressor combinations most frequently (42%), corresponding with the actual status-quo of pressures acting on European surface waters as reported by the Member States in the WISE WFD Database (EEA, 2015). Across all biological groups analysed, higher explanatory power of the stress-effect models was discernible for lakes under multi-stressor compared to single stressor conditions, but generally lower for coastal and transitional waters. Across all aquatic environments, the explanatory power of stress-effect models for fish increased when multi-stressor conditions were taken into account in the analysis, qualifying this organism group as a useful indicator of multi-stress effects. In contrast, the explanatory power of models using benthic flora decreased under conditions of multiple stress

2ème Conférence Internationale I.S. Rivers, Lyon, FRA, 22-/06/2015 - 26/06/2015; International audience; In order to study the relationship between substrates and benthic macrofauna in a regulated river section of the Durance River following management measures implemented to favor sediment unclogging (e.g. artificial flow releases from a dam), a high-frequency monitoring program was initiated in 2014 (the first year after a major flood). The development of the benthic macroinvertebrate community structure following the disturbance event was studied. During the first two months after the flood event, very low taxonomic richness and abundance values reflected the direct impacts of the flood. Later, a taxonomic diversification was observed, leading to more balanced communities four months after the flood event. The consideration of the role of biofilm development, larval growth dynamics (size classes) and a functional analysis approach will ultimately lead to an improved understanding of the relationship between substrates and benthic invertebrate communities under various current conditions. These results of the first year of study (recolonisation post-flood) will serve as a comparative basis for the biological monitoring of the efficiency of flow releases from dams.; Afin d'étudier, dans des mesures de gestion permettant le décolmatage des substrats (ex : lâchers d'eau depuis un barrage), la relation entre l'état des substrats et la macrofaune benthique dans un tronçon en régime réservé, un premier suivi haute-fréquence a été initié à la suite d'un épisode naturel de crue en janvier 2014 en moyenne Durance. La structure des communautés de macroinvertébrés benthiques en lien avec l'éloignement temporel de la perturbation a été étudiée. Durant les deux premiers mois suivant cet épisode de crue, des valeurs faibles de richesses taxonomiques et d'abondances reflétaient les impacts directs de la perturbation. Puis, une diversification taxonomique a été observée, aboutissant à la présence de communautés d'avantage équilibrées quatre mois après l'épisode de crue. La prise en compte de l'influence du développement du biofilm, de la dynamique de développement larvaire (classes de taille) de certains taxa et d'une démarche d'analyse fonctionnelle originale permettra d'améliorer la compréhension entre colmatage des substrats et communautés d'invertébrés benthiques dans diverses ambiances d'écoulement. Ces résultats de la première année d'étude (recolonisation suite à une crue) serviront par la suite de base comparative pour le suivi de l'efficacité de lâchers d'eau.

International audience; We reviewed 219 papers and built an inventory of 532 items of ecological evidence on multiple stressor impacts in rivers, lakes, transitional and coastal waters, as well as groundwaters. Our review revealed that, despite the existence of a huge conceptual knowledge base in aquatic ecology, few studies actually provide quantitative evidence on multi-stress effects. Nutrient stress was involved in 71% to 98% of multi-stress situations in the three types of surface water environments, and in 42% of those in groundwaters. However, their impact manifested differently along the groundwater-river-lake-transitional-coastal continuum, mainly determined by the different hydro-morphological features of these ecosystems. The reviewed papers addressed two-stressor combinations most frequently (42%), corresponding with the actual status-quo of pressures acting on European surface waters as reported by the Member States in the WISE WFD Database (EEA, 2015). Across all biological groups analysed, higher explanatory power of the stress-effect models was discernible for lakes under multi-stressor compared to single stressor conditions, but generally lower for coastal and transitional waters. Across all aquatic environments, the explanatory power of stress-effect models for fish increased when multi-stressor conditions were taken into account in the analysis, qualifying this organism group as a useful indicator of multi-stress effects. In contrast, the explanatory power of models using benthic flora decreased under conditions of multiple stress

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE; International audience; The study of biological traits have enhanced the understanding of the changes in the macroinvertebrate communities of the Rhône River during the last thirty years, as well as the potential effects of hydroclimatic factors and thermal discharges on the structure and the functioning of these communities at the regional scale. If every section of the Rhône had specific features, we observed over time a trend towards a higher uniformisation of invertebrate communities, especially in the Lower section. The strong impacts of the alien species and the water warming subsequent to the 2003 heat wave have been detected in the Lower Rhône and the Middle Rhône: the communities of the Middle Rhône gradually exhibit profiles closer to those of the communities of the Lower Rhône. The Upper Rhône was less colonized by alien species but was impaired by the global warming: its communities exhibited biological profiles closer to those of communities of further-downstream zones. In this site, the thermal discharges have led to a lower diversity of the communities and a higher occurrence of eurythermic species. Hence the benthic macrofauna of the Rhône River seems to have reacted quickly and strongly to environmental changes and to the arrival of invasive species. However numerous trait adaptations being common to Mediterranean and alien species, it seems complex to evaluate the respective weight of each of these potential sources of impairment. Predicting trends in invertebrate community composition is a complex objective because of the competition between native and/or invasive species in addition to man-induced environmental variation (flow, temperature). However, if biological invasion does not occur continuously but only based on specific events (especially hydroclimatology), we can legitimately believe that this drift will continue with the arrival of new Ponto-Caspian species via the Danube-Main Canal, their usual way to western and southern Europe. The common feature of these different species is that they are essentially predators or filterers, thermophilic and euryecic, and efficient functional competitors. Finally, this study once again emphasizes the importance of long-term monitoring in the study of biological communities in the context of global warming.

The sampling of benthic arthropods is one of several common approaches to monitor and assess ecosystem health in both lotic and lentic systems. This type of environmental effects monitoring has a number of drawbacks that support the development of new methodologies to improve our ability to detect and mitigate effects in the field. We propose an enzymatic technique to assess the status of arthropod communities and ecosystem health rapidly and efficiently. The method is based on measuring the activity of free chitobiase, an arthropod moulting enzyme, in natural waters. The rationale behind using chitobiase activity and how it could be applied to general field monitoring and assessment situations are discussed. An example of results obtained from field level monitoring using this assay is presented from the Oir River catchment and one of its tributaries, the La Roche, in Lower Normandy, France. Chitobiase activity was detected and quantified with low variability in the Oir and La Roche with the enzyme's activity statistically related (p < 0.0001, r2 = 0.77) to standard water quality physico-chemical parameters using multiple linear regression. A decrease in chitobiase activity was noted downstream of a sewage treatment plant releasing effluent into the Oir. This is the first time chitobiase activity has been measured in a freshwater ecosystem as an indicator of ecosystem health. However, extensive validation is required before chitobiase activity can be used in an environmental monitoring context.