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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.

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; 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

[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.