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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; 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.

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.