Search

International audience; In coastal systems, the multiplicity of sources fueling the pool of particulate organic matter (POM) leads to divergent estimations of POM composition. Eleven systems (two littoral systems, eight embayments and semi-enclosed systems and one estuary) distributed along the three maritime façades of France were studied for two to eight years in order to quantify the relative contribution of organic matter sources to the surface-water POM pool in coastal systems. This study was based on carbon and nitrogen elemental and isotopic ratios, used for running mixing models. The POM of the estuary is dominated by terrestrial material (93% on average), whereas the POM of the other systems is dominated by phytoplankton (84% on average). Nevertheless, for the latter systems, the POM composition varies in space, with 1) systems where POM is highly composed of phytoplankton (≥ 93%), 2) systems characterized by a non-negligible contribution of benthic (8 to 19%) and/or riverine (7 to 19%) sources, and 3) the Mediterranean systems characterized by the contribution of diazotroph organisms (ca. 14%). A continent-to-ocean gradient of riverine and/or benthic POM contribution is observed. Finally, time series reveal 1) seasonal variations of POM composition, 2) differences in seasonality between systems, and 3) an inshore-offshore gradient of seasonality within each system that were sampled at several stations. Spatial and seasonal patterns of POM composition are mainly due to local to regional processes such as hydrodynamics and sedimentary hydrodynamic (e.g. resuspension processes, changes in river flows, wind patterns influencing along-shore currents) but also due to the geomorphology of the systems (depth of the water column, distance to the shore). Future studies investigating the link between these forcings and POM composition would help to better understand the dynamics of POM composition in coastal systems.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU [TR2_IRSTEA]QUASARE; International audience; Watersheds are multidimensional objects and their understanding requires an interdisciplinary approach. The study of the Yzeron’s watershed, under growing pressure from suburban sprawl, displays important landcover changes since the beginning of the 20th century. This changes modifies the watershed functioning in terms of hydrology, morphology, physical chemistry and biology: increase of flooding frequency of low to medium intensity, introduction of poor quality water, forming spectacular incisions upstream and sanding up downstream, etc. Results allowed us to give several innovative management guidelines and stress the importance of fluvial geomorphology in interdisciplinary researches of small periurban hydrosystems.; Les bassins versants sont des objets d’étude multidimensionnels dont la compréhension exige une approche interdisciplinaire. L’étude du bassin versant de l’Yzeron, marqué par un fort étalement périurbain, présente d’importants changements d’occupation du sol depuis le début du XXe siècle. Cette évolution modifie le fonctionnement de ce bassin sur les plans hydrologique, morphologique, physico-chimique et biologique : élévation de la fréquence des crues d’intensité faible à moyenne, dégradation de la qualité des eaux, formation d’incisions spectaculaires en amont, ensablement en aval, etc. L’ensemble des résultats conduit à des préconisations de gestion innovantes et montre l’importance de la géomorphologie fluviale dans l’étude interdisciplinaire des petits hydrosystèmes périurbains.

International audience

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; Toxicokinetic (TK) models are relevant and widely used to predict chemical concentrations in biological organisms. The importance of dietary uptake for aquatic invertebrates has been increasingly assessed in recent years. However, the model parameters are estimated on limited specific laboratory data sets that are bounded by several uncertainties. The aim of this study was to implement a Bayesian framework for simultaneously estimating the parameters of a generic TK model for benthic invertebrate species from all data collected. We illustrate our approach on the bioaccumulation of PCB153 by two species with different life traits and therefore exposure routes: Chironomus riparius larvae exposed to spiked sediment for 7 days and Gammarus fossarum exposed to spiked sediment and/or leaves for 7 days and then transferred to a clean media for 7 more days. The TK models assuming first-order kinetics were fitted to the data using Bayesian inference. The median model predictions and their 95% credibility intervals showed that the model fit the data well. From a methodological point of view, this paper illustrates that simultaneously estimating all model parameters from all available data by Bayesian inference, while considering the correlation between parameters and different types of data, is a real added value for TK modeling. Moreover, we demonstrated the ability of a generic TK model considering uptake and elimination routes as modules to add according to the availability of the data measured. From an ecotoxicological point of view, we show differences in PCB153 bioaccumulation between chironomids and gammarids, explained by the different life traits of these two organisms.

International audience; A one-year monitoring study was conducted in a macrotidal estuary to assess the temporal variations and partitioning behavior of perfluoroalkyl and polyfluoroalkyl substances (PFASs). Surface water, suspended particulate matter (SPM), and invertebrates including zooplankton (copepods, mysids) and shrimps were sampled on a monthly basis in the Gironde Estuary (SW France). Environmental parameters such as suspended solid loads, salinity, and river water flow rate were highly variable at the study site. However, moderate seasonal variations were observed in terms of PFAS levels and profiles. Summed PFAS (S22PFASs) concentrations averaged 6.5 ± 2.7 ng L-1 in the dissolved phase and 3.0 ± 1.2 ng g-1 dry weight in the SPM. The S22PFASs was in the range of 1.7 - 13 ng g-1 wet weight in invertebrates. C5-C8 perfluoroalkyl carboxylates (PFCAs) generally prevailed in the dissolved phase, while perfluorooctane sulfonate (PFOS) was dominant in the SPM and biota. Suspended sediment-water partitioning coefficients Log KD and Log KOC were correlated with the perfluoroalkyl chain length, as were the particle bound fraction and bioaccumulation factors (Log BAF). Compound-specific Log BAFs varied within a limited range over the period surveyed. Biomagnification factors (mysids/copepods) were consistently >1 for PFOS, perfluorooctane sulfonamide, and long-chain PFCAs (perfluorodecanoate and perfluorododecanoate), suggesting biomagnification at the base of the estuarine food web.

International audience; The occurrence at different trophic levels of 17 poly- and perfluoroalkyl substances (PFASs), including perfluoroalkyl acids (PFAAs) and some of their precursors (e.g., perfluoroalkane sulfonamides, 6:2 fluorotelomer sulfonate), were investigated in riverine freshwater food webs in Southeastern France. Two fish species (Barbus barbus and Squalius cephalus) and various invertebrate taxa were collected at five locations to assess the spatial variability of trophic magnification factors (TMFs). Particular attention was devoted to sample and data processing to minimize potential biases associated with the TMF determination. Fish were significantly more contaminated than invertebrates (ΣPFAS = 7-1811 vs. 0.9-213 ng g-1 wet weight (ww)). Those from the Rhône River presented significantly higher levels due to high concentrations of perfluoroundecanoic acid (406 ng g-1 ww) and perfluorotridecanoic acid (566 ng g 1 ww) ascribed to an industrial point source. Perfluorooctane sulfonate (PFOS) was dominant at the other sites (range concentration = 3.6-134 ng g-1 ww). Two linear regression models were compared (i.e., Kendall regression vs. Generalized Linear Mixed-Effect Model, GLMM). Results showed that TMFs calculated using the non-weighted Kendall regression were higher than those obtained using the GLMM approach. GLMM-based TMFs were consistently > 1 for C9-C14 perfluorocarboxylic acids (PFCAs), PFOS and perfluorodecane sulfonate (PFDS), indicating their apparent biomagnification in the investigated food webs. Comparatively, 6:2 FTSA and N-ethylperfluorooctane sulfonamidoacetic acid (N EtFOSAA) were less often detected and were not significantly biomagnified, probably because of metabolization. TMF estimates were generally consistent across sites although some PFASs (in particular C9, C10 and C13 PFCAs) displayed higher variability, due to a unique extreme value that may have resulted from the contribution of unattributed precursor biotransformation.

La Binge Eating Scale (BES) est un outil utile pour evaluer et depister l'hyperphagie boulimique chez les sujets obeses, mais n'a jusqu'a present pas ete valide en francais. L'objectif de ce travail etait de tester les proprietes psychometriques de la version francaise de la Binge Eating Scale (BES), en etablissant sa structure factorielle, sa consistance interne et sa validite de construit en population non clinique et clinique. Resultats : La BES possede une structure mono-factorielle (expliquant 61 % de la variance en population non clinique et 46 % en population clinique), une tres bonne consistance interne et une tres bonne validite de construit vis-a-vis des comportements boulimiques. La validite de construit vis-a-vis du recours a des comportements compensatoires etait confirmee en population clinique et chez les sujets obeses ou en surpoids de la population non clinique mais pas chez les patients normo-ponderaux ou maigres de la population non clinique. Conclusion : La version francaise de la BES possede des proprietes psychometriques proches de la version originale. La BES est un outil utile pour evaluer et depister l'hyperphagie boulimique chez les sujets obeses, pouvant notamment etre utilise chez les patients candidats a la chirurgie bariatrique. [extrait du resume de l'editeur]

International audience

International audience; Wastewater treatment plant effluents from urban area are a well-known source of chronic multiple micropollution to the downstream living organisms. In this study, ecologically relevant laboratory-bred freshwater gastropods, Lymnaea stagnalis, were exposed for 29 days to raw effluents of a wastewater treatment plant in Lyon area (France). A time-course analysis of individual markers of immunocompetence (hemocyte density and viability, hemocyte NADPH activity, phenol oxidase activity, and capacity of phagocytosis) has shown slight trends of inflammatory-like responses induced by the 100% effluents. So far, no short-term hazard for L. stagnalis can be revealed. However, over the long term, such environmental stress-stimulating immune responses could provoke deleterious life history trade-offs because the immune system is known to be highly energy-consuming.

International audience; Modeling individual fish habitat selection in highly variable environments such as hydropeaking rivers is required for guiding efficient management decisions. We analyzed fish microhabitat selection in the heterogeneous hydraulic and thermal conditions (modelled in two-dimensions) of a reach of the large hydropeaking Rhône River locally warmed by the cooling system of a nuclear power plant. We used modern fixed acoustic telemetry techniques to survey 18 fish individuals (five barbels, six catfishes, seven chubs) signaling their position every 3 s over a three-month period. Fish habitat selection depended on combinations of current microhabitat hydraulics (e.g. velocity, depth), past microhabitat hydraulics (e.g. dewatering risk or maximum velocities during the past 15 days) and to a lesser extent substrate and temperature. Mixed-effects habitat selection models indicated that individual effects were often stronger than specific effects. In the Rhône, fish individuals appear to memorize spatial and temporal environmental changes and to adopt a "least constraining" habitat selection. Avoiding fast-flowing midstream habitats, fish generally live along the banks in areas where the dewatering risk is high. When discharge decreases, however, they select higher velocities but avoid both dewatering areas and very fast-flowing midstream habitats. Although consistent with the available knowledge on static fish habitat selection, our quantitative results demonstrate temporal variations in habitat selection, depending on individual behavior and environmental history. Their generality could be further tested using comparative experiments in different environmental configurations.

Les biomarqueurs sont des outils mis en oeuvre pour établir un diagnostic de risque environnemental. Leurs usages et leur intérêt, notamment dans la détermination du risque de pollution, sont devenus incontournables surtout depuis que la directive cadre européenne sur l'eau a imposé la surveillance de l'état écologique des cours d'eau.Cependant, le manque de connaissances sur la biochimie, la physiologie et le comportement des organismes aquatiques sentinelles utilisés limitent fortement l'utilisation optimale de ces outils. Quelles sont les connaissances disponibles sur les biomarqueurs ? Comment les utiliser et quelles sont les limites actuelles ? Autant de questions auxquelles cet article tente de répondre.

International audience; The present paper contains descriptions of two new species and one new genus: Latinopsis patagonica gen. nov., sp. nov., and Candona quasiincarum sp. nov. Both species were collected during a two-month Franco-Chilean expedition to Madre de Dios archipelago in January and February 2006. The following new systematic arrangements are proposed: L. anisitsi (Daday, 1905) comb. nov., L. columbiensis (Mehés, 1914) comb. nov., and L. falclandica (Vávra, 1898) comb. nov. Latinopsis anisitsi is redescribed from the type material and a lectotype is designated. Two species are excluded from the subfamily Candoninae, one of which is Danielocandona albida (Sars, 1901). After examination of the type material the species is reclassified as Neocypridopsis albida (Sars, 1901) comb. nov. A checklist of the known species of Candoninae of South America and the West Indies is provided.

International audience; Numerical clustering has frequently been used to define hierarchically organized ecological regionalizations, but there has been little robust evaluation of their performance (i.e., the degree to which regions discriminate areas with similar ecological character). In this study we investigated the effect of the weighting and treatment of input variables on the performance of regionalizations defined by agglomerative clustering across a range of hierarchical levels. For this purpose, we developed three ecological regionalizations of Switzerland of increasing complexity using agglomerative clustering. Environmental data for our analysis were drawn from a 400 m grid and consisted of estimates of 11 environmental variables for each grid cell describing climate, topography and lithology. Regionalization 1 was defined from the environmental variables which were given equal weights. We used the same variables in Regionalization 2 but weighted and transformed them on the basis of a dissimilarity model that was fitted to land cover composition data derived for a random sample of cells from interpretation of aerial photographs. Regionalization 3 was a further two-stage development of Regionalization 2 where specific classifications, also weighted and transformed using dissimilarity models, were applied to 25 small scale sub-domains' defined by Regionalization 2. Performance was assessed in terms of the discrimination of land cover composition for an independent set of sites using classification strength (CS), which measured the similarity of land cover composition within classes and the dissimilarity between classes. Regionalization 2 performed significantly better than Regionalization 1, but the largest gains in performance, compared to Regionalization 1, occurred at coarse hierarchical levels (i.e., CS did not increase significantly beyond the 25-region level). Regionalization 3 performed better than Regionalization 2 beyond the 25-region level and CS values continued to increase to the 95-region level. The results show that the performance of regionalizations defined by agglomerative clustering are sensitive to variable weighting and transformation. We conclude that large gains in performance can be achieved by training classifications using dissimilarity models. However, these gains are restricted to a narrow range of hierarchical levels because agglomerative clustering is unable to represent the variation in importance of variables at different spatial scales. We suggest that further advances in the numerical definition of hierarchically organized ecological regionalizations will be possible with techniques developed in the field of statistical modeling of the distribution of community composition.

Fluoxetine is a widely used antidepressant, frequently found in aquatic ecosystems. We investigated its effects on two freshwater prosobranch gastropods: Valvata piscinalis (European valve snail) and Potamopyrgus antipodarum (New Zealand mudsnail), which have different reproductive modes. The fecundity of V. piscinalis (cumulate number of eggs at day 42) was not affected with an NOEC of 100 mvg/L nominal concentration (69 microg/L measured concentration). The mudsnail P. antipodarum responded in a biphasic dose-effect curve at low concentrations. The cumulate number of neonates at day 42 had an LOEC of 100 microg/L (69 microg/L) and an NOEC of 33.3 microg/L (13 microg/L), whereas the embryos in the brood pouch at day 42 only showed an LOEC of 3.7 microg/L (1 microg/L). We also observed histological effects in P. antipodarum (gonadal thickness). Among the sexual steroids we measured only testosterone which varied, independent of reproduction. Moreover the use of two closely related species highlights the interspecific variability.

International audience; We present the first measurements of solutes, invertebrates, and microbial activity in the semi-perched hyporheic, parafluvial, and riparian flowpaths of an ephemeral river channel. Dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) concentrations decreased as water from an adjacent river mainstem moved through the flowpaths. DOC, DON, and DOP processing rates decreased with increasing mainstem flow and increased with parafluvial zone length. These patterns suggest that the surface water zones of perched river systems are organic nutrient sources to subsurface flowpaths and that parafluvial zones of these systems are strong sinks for organic matter. No longitudinal changes were detected in NO3 concentrations, and relationships between NO3 processing and hydrological variables were not significant. NO3 concentrations were uniformly high, and microbial activity and DOC and dissolved reactive phosphorus (DRP) concentrations were low, suggesting that biological NO3 removal was carbon- or phosphorus-limited. Invertebrate assemblages also varied between subsurface zones: density and taxon richness in the hyporheic and parafluvial zones were higher than in the riparian zone, and evenness was higher in the riparian zone than in the hyporheic or parafluvial zones. Distinct invertebrate assemblages in riparian zones may reflect greater hydrologic stability compared with hyporheic and parafluvial zones.; Nous présentons les premières mesures des solutés, des invertébrés et de l'activité microbienne dans les voies de passage hyporhéiques semi-perchées, parafluviales et riveraines du chenal d'une rivière éphémère. Les concentrations de carbone organique (DOC), d'azote (DON) et de phosphore (DOP) dissous diminuent à mesure que l'eau provenant du cours principal d'une rivière adjacente traverse les diverses voies de passage. Les taux de transformation de DOC, DON et DOP décroissent lorsque le débit augmente dans le cours principal et s'accroissent en fonction de la longueur de la zone parafluviale. Ces patrons laissent croire que les zones d'eau superficielle des systèmes de rivières perchés servent de source de nutriments organiques pour les voies de passage souterraines et que les zones parafluviales de ces systèmes sont d'importants pièges de matière organique. Nous ne détectons aucun changement longitudinal des concentrations de NO3 et il n'y a pas de relation significative entre la transformation de NO3 et les variables hydrologiques. Les concentrations de NO3 sont uniformément élevées, alors que l'activité microbienne et les concentrations de DOC et de phosphore réactif dissous (DRP) sont faibles; ces observations indiquent que le retrait biologique de NO3 est limité par le carbone ou par le phosphore. Les peuplements d'invertébrés varient aussi d'une zone souterraine à une autre: la densité et la richesse en taxons sont plus élevées dans les zones hyporhéiques et parafluviales que dans la zone riveraine et l'équitabilité est plus grande dans la zone riveraine que dans les zones hyporhéiques et parafluviales. Les peuplements particuliers d'invertébrés dans les zones riveraines peuvent être le reflet d'une plus grande stabilité hydrologique par comparaison aux zones hyporhéiques et parafluviales.

Low levels of pharmaceuticals have been detected in many countries in surface waters. As a wide range of pharmaceuticals can reach aquatic environments, a selection of molecules to survey is the first step before implementing a monitoring program. We used a simple equation to calculate Predicted Environmental Concentrations (PECs), adapted from the European Medicine Agency model used for the Environmental Risk Assessment (ERA) of human pharmaceutical. Excretion fractions for pharmaceuticals were determined for 76 compounds. Using year 2004 French drug consumption data, we determined aquatic PECs for 112 parent molecules and several metabolites. Considering excretion fractions of pharmaceuticals can lead to drastically reduce predicted concentrations reaching the aquatic environment and help to target environmentally relevant pharmaceuticals and metabolites. Calculated PECs using the described methodology are consistent with French field measurements. The simple model for calculating PECs can be used as a valuable estimation of the exposure. Risk quotient ratios were also calculated. Due to the lack of ecotoxicological data, the use of PEC/PNEC ratios is not enough informative to prioritize pharmaceuticals likely to pose a risk for surface waters. Alternative ways to prioritize risk to pharmaceuticals, combining PEC, pharmacological, and ecotoxicological data available from the literature, should be implemented.

[Departement_IRSTEA]MASpecial Issue on the Tribolium Genome; The Tribolium genome contains 21 nuclear receptors, representing all of the six known subfamilies. This first complete set for a coleopteran species reveals a strong conservation of the number and identity of nuclear receptors in holometabolous insects. Two novelties are observed: the atypical NR0 gene knirps is present only in brachyceran flies, while the NR2E6 gene is found only in Tribolium and in Apis. Using a quantitative analysis of the evolutionary rate, we discovered that nuclear receptors could be divided into two groups. In one group of 13 proteins, the rates follow the trend of the Mecopterida genome-wide acceleration. In a second group of five nuclear receptors, all acting early during the ecdysone cascade, we observed an even higher increase of the evolutionary rate during the early divergence of Mecopterida. We thus extended our analysis to the twelve classic ecdysone transcriptional regulators and found that six of them (ECR, USP, HR3, E75, HR4 and Kr-h1) underwent an increase in evolutionary rate at the base of the Mecopterida lineage. By contrast, E74, E93, BR, HR39, FTZ-F1 and E78 do not show this divergence. We suggest that coevolution occurred within a network of regulators that control the ecdysone cascade. The advent of Tribolium as a powerful model should allow a better understanding of this evolutionary event.

Anticholinesterase insecticides constitute a major portion of modern synthetic pesticides and the assessment of cholinesterase (ChE) inhibition is widely used as a specific biomarker for evaluating the exposure of non-target organisms to these pollutants. However, most studies on this biomarker were developed on vertebrates and among invertebrates, gastropod mollusks are rarely used. However, gastropods are important members of aquatic habitats and therefore present a high ecological relevance for freshwater ecosystems. In this context, ChE activities were characterized in two freshwater gastropod mollusks, Potamopyrgus antipodarum and Valvata piscinalis, in order to ascertain their value as sentinel species. Firstly, characterization of ChE activities was performed using different substrates (acetylcholine iodide, butyrylcholine iodide and propionylcholine iodide) and specific inhibitors (eserine, iso-OMPA and BW284c51). Secondly, in vivo effect of a widely used organophosphate insecticide, chlorpyrifos, was tested on ChE activity in both species. Results suggested that P. antipodarum possesses two isoforms of cholinesterases, one isoform which properties are intermediate between an acetyl and a propionyl ChE, and one minor isoform which correspond to a butyryl ChE, while V. piscinalis seems to possess only one isoform which displays typical properties of an acetyl ChE. Chlorpyrifos induced no effect on V. piscinalis ChE. In contrast, P. antipodarum activity was significantly decreased by environmental realistic chlorpyrifos concentrations (2.86 and 14.2 nM) after seven days of contact. The present study suggests that P. antipodarum may be employed as a biological indicator for assessing pesticide contamination.

International audience; Inundation marks the shift from a terrestrial ecosystem to an aquatic ecosystem in ephemeral rivers. The forms and rates of responses by aquatic invertebrates and sediment microbes to inundation depend on desiccation resistance during preceding dry periods.As desiccation resistance is likely to vary with dry period duration, we assessed invertebrate and microbial responses to variable lengths of inundation in sediments from an ephemeral reach of the Selwyn River, New Zealand. Microbial response variables were dissolved oxygen consumption and non-specific esterase activity. Sampling sites along the reach had been continuously dry for 1592 d prior to sample collection. The onset of flow simulated by a 17-d experimental inundation led to the appearance of aquatic invertebrates in all samples, but the assemblages varied with the length of the preceding dry period. Taxon richness decreased linearly with dry period length while density decreased exponentially. These patterns indicate that a large number of individuals from desiccation-sensitive taxa were eliminated soon after flow ceased, and a low-density assemblage composed of a small number of desiccation-resistant taxa persisted during prolonged dry periods. As with invertebrate density, sediment respiration and non-specific esterase activity decreased with length of dry period, and were characterized by exponential decay functions. The results of the inundation experiments suggest that a temporal ecotone exists for about one week after the disappearance of flowing water, and before the terrestrial system stabilizes.

International audience; Detection and assessment of the impact of pollution on biological resources imply increasing research on early-warning markers such as metallothioneins in metal exposure. Metallothioneins are cytosolic, low-molecular-weight proteins, involved principally in essential metal homeostasis and non-essential metal detoxication. Metallothionein synthesis could be influenced by abiotic (season) or biotic (reproduction process) factors directly or indirectly by its effect on metal bio-accumulation (i.e., sex, weight). In view of using metallothioneins as metal-exposure biomarkers in Gammarus pulex, this study attempts to define the effect of several factors (sex, weight/size and season) on the level of this protein. Metallothionein levels recorded in individuals over a large range of weights indicate a negative correlation between them. Inversely in our conditions, no difference was observed between male and female organisms. During field study, metallothionein level changes were observed with the highest levels in autumn and winter periods. The highest metallothionein levels were observed after the reproduction period, perhaps with the metabolic needs of biologically available essential metal such as zinc.

International audience; Bioassays can be used in aquatic toxicology to provide individual determinations, however ecotoxicology is now attempting to assess the impact of pollution on populations. The main issue is how to infer the impact on an entire population of the toxic effects observed in individuals. At the individual level, Dynamic Energy Budget in Toxicology (DEBtox) theory provides a set of mechanistic models of survival, reproduction and growth continuously as a function of time and exposure concentration, in which the parameters used have clear biological meanings. These models have been designed for the analysis of data provided by the internationally standardized toxicity tests, and sometimes make it clear which is the mode of action of the contaminant. Matrix population models directly yield the population growth rate, the most robust endpoint in risk assessment at the population level. By combining DEBtox theory and matrix population models, we extrapolate every effects of the toxic compound on the individual (reduced fecundity, growth and survival) to the population level. Both lethal and sublethal effects are integrated into a single parameter, the population growth rate, which is calculated continuously against exposure concentration. We can thus compare the consequences at the population level of choosing one or another assumption about the mode of action of the contaminant at the individual level. We used various complementary matrix population models, in order to perform a complete sensitivity analysis, highlighting critical demographic parameters in the evolution of population growth rate as a function of contaminant concentration. Here, we apply this method to a test organism commonly used in ecotoxicology, Daphnia magna, through a case study of cadmium contamination.

International audience; To date, aquatic hyphomycetes have mainly been considered as a source of carbohydrates, mineral elements and proteins for detritivores in detritus-based headwater streams. Yet, consumers are highly dependent on other molecules, such as essential fatty acids, to complete their biological cycle. These molecules might be limiting in detritus-based ecosystems since they are primarily synthesized by autotrophic organisms. We investigated: (i) if aquatic hyphomycetes are able to synthesize polyunsaturated fatty acids (PUFAs); and (ii) if the abundance of phosphorus, often considered as a limiting factor in headwater streams, could affect the proportions of PUFAs in aquatic hyphomycetes. All hyphomycete species tested synthesized high amounts of PUFAs (C18 omega 3 and omega 6) and the proportions of these essential fatty acids varied with P availability. This study sheds new light on the importance of aquatic hyphomycetes in the detritus-based stream food web, but also on potential co-variations between mineral nutrient limitation and the availability of essential fatty acids for consumers.

The paper presents a new index for assessing water trophy and organic pollution. It is based on only true aquatic macrophytes – being calculated on species score, coefficient of ecological amplitude and degree of cover. The method was tested in an acidic lowland river and an alkaline mountain river, and is shown to be validated by bio-indication scales based on macrophyte communities. The practical interest is discussed regarding the Water Framework Directive.

International audience; 1. Many aspects of the flow regime influence the structure of stream communities, among which the minimum discharge left in rivers has received particular attention. However,instream habitat models predicting the ecological impacts of discharge management often lack biological validation and spatial generality, particularly for large rivers with many fish species. 2. The minimum flow at Pierre-Be´nite, a reach of the Rhone river bypassed by artificial channels, was increased from 10 to 100 m3 s)1 in August 2000 (natural mean discharge 1030 m3 s)1), resulting in a fivefold increase in average velocity at minimum flow. Fish were electrofished in several habitat units on 12 surveys between 1995 and 2004. 3. Principal components analysis revealed a significant change in the relative abundance of fish species. The relative abundance of species preferring fast-flowing and/or deep microhabitats increased from two- to fourfold after minimum flow increase. A change in community structure confirmed independent quantitative predictions of an instream habitat model. This change was significantly linked to minimum flow increase, but not to any other environmental variables describing high flows or temperature at key periods of fish life cycle. The rapidity of the fish response compared with the lifespan of individual species can be explained by a differential response of specific size classes. 4. The fish community at Pierre-Be´nite is in a transitional stage and only continued monitoring will indicate if the observed shift in community structure is perennial. We expect that our case study will be compared with other predictive tests of the impacts of flow restoration in large rivers, in the Rhone catchment and elsewhere.; Cinq ans après augmentation du débit minimum à Pierre-Bénite, tronçon court-circuité du Rhône Français, les espèces d'eau courante ont doublé en proportion. Ce changement valide des prédictions quantitatives des modèles d'habitat réalisées avant restauration du débit. Il s'agit d'une première validation de prédictions concernant les communautés de poissons.

In the boreal forest, watershed logging may increase runoff as well as chemical loading, including nutrient, dissolved organic carbon and mercury, to lakes. Since they are exposed directly to nutrients and contaminants exported from the watershed, littoral communities such as periphyton may respond quickly to watershed disturbances. The objectives of this study were to evaluate the response of periphyton to watershed logging using a BACI (Before/After Control, Impact) statistical approach, and to develop a predictive tool to facilitate the elaboration of practical logging policies aimed at reducing Hg loading to lakes. In this study, we compare the periphyton biomass as well as their total mercury and methyl-mercury levels in 18 boreal Canadian shield lakes. During the ice-free season from 2000 to 2002, eight lakes were monitored before and after logging whereas the others served as controls. The BACI statistical analyses reveal a significant impact of logging on periphyton biomass (decrease; 0.6 to 1.5-fold) and methyl-mercury accumulation (increase; 2 to 9.6-fold). This study demonstrates that periphyton responds quickly to disturbances of the watershed. Our results suggest that the periphyton and watershed characteristics could serve as good management tools and logging should be limited in watersheds with a mean slope below 7.0%.; En forêt boréale, la coupe forestière peut augmenter l'écoulement et l'apport d'éléments chimiques aux lacs tel que le carbone organique dissous et le mercure. Les communautés littorales, comme le périphyton, peuvent être exposées directement aux apports de contaminants exportés du bassin versant, et ainsi répondre rapidement aux perturbations de ce dernier. Les objectifs de cette étude étaient d'évaluer la réponse du biofilm périphytique aux coupes forestières en utilisant une approche statistique de type BACI, et de développer des outils prédictifs utiles pour l'élaboration de politiques forestières visant la réduction des apports de Hg dans les lacs. Dans cette étude, nous avons échantillonné 18 lacs boréaux du bouclier canadien et comparé la biomasse et les concentrations de mercure total et méthyl-mercure du périphyton. Durant la saison libre de glace de 2000 à 2002, huit lacs ont été échantillonnés avant et après la coupe alors que les autres ont servi de témoins. Les analyses statistiques BACI révèlent un impact significatif des coupes sur la biomasse (diminution; 0.6 à 1.5 fois) et sur les concentrations de méthyl-mercure (augmentation; 2 à 9.6 fois). Cette étude démontre que le périphyton répond rapidement à une perturbation du bassin versant. Nos résultats suggèrent que le périphyton et les caractéristiques du bassin versant peuvent être de bons outils de gestion et que la coupe forestière devrait être limitée lorsque la pente moyenne est inférieure à 7.0%.

The hyporheic zone and its interactions with coarse surface sediments is increasingly reported by aquatic ecologists because the water exchanges between surface and subsurface are important factors for the understanding of the ecosystem functioning. However, the hyproheic oligochaete assemblages have received less attention than other assemblages such as crustaceans. In addition, studies investigating the incidence of pollution in watercourses have mostly focused on the benthic zone and have neglected the hyporheic zone. Some examples are given from an unpolluted glacial river (Roseg), polluted plains rivers (Moselle, Rhône) and a protected wetland in an urbanized environment. The hyporheic zone kept the memory of past and present incidences of pollution, in particular when downwellings of polluted surface waters to the hyporheic zone predominated. The Active hydrologic Exchange Describers between surface and subsurface (AED oligochaete species) were the same in the glacial river Roseg, the rivers Rhône and Moselle and the urbanized wetland. The predominance of pollution-tolerant species like Limnodrilus hoffmeisteri was observed in polluted groundwater as well as in polluted surface coarse sediments. Moreover, the urbanized wetland exhibited a high species richness, suggesting that the hyporheic zone is a reservoir of species. The oligochaete communities enable biologists to simultaneously assess the pollution incidence, the permeability of coarse habitats, the water exchanges between surface and subsurface, and give an approximate measure of the metabolic activities in the sediments. Consequently, the simultaneous study of surface and hyporheic oligochaete assemblages is of great interest when considering the ecological functioning of watercourses and the incidence of pollution inputs.

We investigated the relationships between different environmental variables and the spatial distribution patterns of the stoneloach (Barbatula barbatula) at the stream system, the stream site, and the mesohabitat (riffle/pool) scales in south-western France. Stoneloach occurred at 240 sites (out of 554 sampling sites), chiefly close to the source, in areas at low elevation and with weak slopes. Population density at a site was primarily influenced by physical conditions. Stream width was positively related to the probability of presence of stoneloach within the stream system, but negatively related to local density. These results indicate that stoneloaches can occur in a wide range of streams, but they are less abundant in wide rivers, probably because of lower habitat heterogeneity. Slope was negatively correlated to both fish presence at the regional scale and local density, suggesting that stoneloach’s swimming performance were weak under greater erosive forces. These results suggested that the distribution of populations and the density of stoneloach were governed by the suitability of physical habitat. Multi-scale studies of factors influencing a species’ distribution allow to integrate patterns observed at different scales, and enhance our understanding of interactions between animals and their environment. The use of few pertinent variables in successful final models could reduce the effort and cost of data collection for water management applications.

International audience; In order to better assess the influence of organic matter on the bioavailability of hydrophobic organic contaminants, the effect of algae and POM of bacterial origin on the bioaccumulation of benzo[a]pyrene in Daphnia magna was evaluated. The bioaccumulation was monitored with increasing concentrations of particulate organic matter (POM) and dissolved organic matter (DOM).In all experiments, the presence of POM greatly reduced the bioaccumulation of benzo[a]pyrene. The reduction was more pronounced in the presence of algae, for which we observed a 99%-reduction effect in the presence of 6×105 cell/mL (equivalent to 5.3 mg C/L). The bioaccumulation of benzo[a]pyrene was decreased by 49% by organic matter of bacterial origin at 4.7 mg C/L.Assuming that benzo[a]pyrene was partitioned between water, DOM and POM and supposing that D. magna accumulated free benzo[a]pyrene via respiration and POM-bond benzo[a]pyrene via ingestion, bioaccumulation data allowed to estimate the dietary uptake rate of benzo[a]pyrene as well as partitioning coefficients KPOC and KDOC.Despite the ingestion of contaminated particles, we could not observe any dietary uptake of benzo[a]pyrene in daphnids. We verified, as usually supposed, that the bioaccumulation of benzo[a]pyrene to D. magna occurs mainly via direct contact. Very high partitioning coefficients (log KPOC between 5.2 and 6.2) were estimated. This study pointed out the great influence of biogenic organic matter on the fate and the bioavailability of benzo[a]pyrene in aquatic ecosystems.

International audience; Despite IFIM worldwide success, some criticisms have not been sufficiently addressed in the literature: lack of sufficient validation of the relationships between potential available habitat and biomass of fish, particularly in warmwater streams; complexity of habitat modelling; too narrow focus on selected fish species habitat instead of entire riverine ecosystem; complexity and expense of implementation. First, we briefly address the general context of ecological flows methods. Second, we present some successful validations of microhabitat applications at the fish population (Brown trout, Salmo trutta, L. 1758) and community levels. Finally, we present the results of the statistical analysis and modelling of about one hundred Phabsim simulations. The functions of habitat (WUA) versus discharge could be predicted by synthetic hydraulic variables, in particular the Froude and Reynolds numbers. A simplified alternative to Phabsim, named Estimhab opens the way to habitat measurements in a great number of sites, particularly useful to view habitat at entire watershed level.

International audience; DEBtox model is a biologically based model used to analyse aquatic toxicity data (Kooijman and Bedaux, 1996). To date, it has not been used to analyse sediment survival tests, mainly because this would require daily counting of survivors, which is difficult for benthic organisms. In the present study, we adapted survival toxicity tests with the midge Chironomus riparius to permit survival data analysis with DEBtox. To validate the adaptation proposed, we exposed organisms to two chemicals, copper and methiocarb. We exposed larvae of second, third and fourth instar to different concentrations of the tested compounds and two different diets to assess the influence of diet and instar on DEBtox parameter estimates. Daily counting of organisms did not affect survival and did not lead to much more effort when compared to usual tests. Moreover, the analysis profited much from use of the DEBtox model. It was possible, with only survival data to estimate and validate the kinetics of the compounds, to predict survival during the recovery of exposed organisms and to assess the influence of food availability on toxicity. Food availability did not influence methiocarb toxicity, but copper was more toxic to food-limited organisms when a threshold concentration was exceeded. Comparison of parameters estimate also helped in understanding the differences in toxicity responses between instars. For the two compounds we studied, the difference was entirely explained by differences in threshold values.; Le modèle DEBtox est un modèle à fondement biologique utilisé pour l'analyse des données de toxicité aquatique (Kooijman et Bedaux, 1996). Jusqu'à présent, il n'a jamais été utilisé pour analyser les données des tests de survie sur sédiment, ce qui est principalement du à la difficulté de suivre la survie des organismes benthiques jour après jour. Ici, nous avons adapté les tests de survie avec Chironomus riparius pour permettre l'analyse des données avec DEBTox. Pour valider notre approche, nous avons exposé les organismes à deux contaminants, le cuivre et le mercaptodiméthur (un pesticide). Trois stades larvaires différents (deuxième, troisième et quatrième) et deux régimes alimentaires (ad libitum et limitant) ont été considérés. Le décompte quotidien des survivants n'a pas altéré la bonne marche du test et n'a pas donné lieu à beaucoup plus d'effort qu'un test classique. De plus, nous avons pu tirer des bénéfices de l'utilisation de DEBtox. Il a ainsi été possible, à partir uniquement des données de survie, d'estimer la cinétique des composés, de prédire la survie au cours de la phase de dépuration, et de caractériser l'influence de la nourriture. Le manque de nourriture n'influe pas sur la toxicité du pesticide mais augmente celle du cuivre. Quant à la différence entre stades, elle s'est caractérisée uniquement par une différence entre les concentrations seuils d'effet.

International audience; Community convergence across biogeographically distinct regions suggests the existence of key, repeated evolutionary mechanisms relating community characteristics to the environment. However, convergence studies at the community level often involve only qualitative comparisons of the environment and may fail to identify which environmental variables drive community structure. We tested the hypothesis that the biological traits of fish communities on two continents (Europe and North America) are similarly related to environmental conditions. Specifically, from observations of individual fish made at the local scale (few m2) within French streams, we generated habitat preference models linking traits of fish species to local scale hydraulic conditions (Froude number). Using this information, we then predicted how hydraulics and geomorphology at the larger stream reaches scale (length of streams including several pool-riffle sequences) should quantitatively influence the trait composition of entire communities. Trait composition for fish in stream reaches with low Froude number at low flow or high proportion of pools was predicted as non-benthic, large, fecund, long-lived, non-streamlined, and weak swimmers. We tested our predictions in contrasting stream reaches in France (n=11) and Virginia, USA (n=76), using analyses of covariance to quantify the relative influence of continent versus physical variables on fish traits. Results indicated that trait proportions in the communities differed across continents (up to 55 % of the variance in each trait explained), but, within continents, they were also related to the hydraulic and geomorphic variables (up to 54 % of the variance within continents explained). In particular, a synthetic description of fish traits was well predicted from the Froude number independently of the continent. In addition, the effect of physical variables was comparable across continents for most traits, confirming our predictions qualitatively and quantitatively. Therefore, despite phylogenetic and historical differences between continents, fish communities of France and Virginia exhibit convergence in biological traits related to hydraulics and geomorphology. This convergence reflects morphological and behavioral adaptations to physical stress in streams. This study supports the existence of a habitat template for ecological strategies. Some key quantitative variables that define this habitat template can be identified by characterizing how individual organisms use their physical environment, and by using dimensionless physical variables which are suited to reveal common energetic properties in different systems. Overall, quantitative tests of community convergence are efficient tools to demonstrate that some community traits are predictable from environmental features.; Les traits des communautés de poissons (morphologie, comportement, reproduction) répondent de façon comparables aux conditions hydrauliques dans des tronçons de cours d'eau français et nord-americains. Ces observations sont quantitativement prévisibles par des observations faites en France à une autre échelle : celle des microhabitats au sein des tronçons de cours d'eau.

International audience; Hydrological and biotic forces constrain brown trout (Salmo trutta) population dynamics, but tests of their role across numerous streams are uncommon. In 30 French stream reaches, using 5-8 samples (1 per year) each, we investigated whether the year-to-year seasonal hydrology influenced annual trout densities within reaches, and whether the relationships were shared by all reaches. We also searched for intraspecific interactions between and within cohorts. Trout data were age class (0+, 1+, and adults) densities. For each year, hydrology was described using 13 variables, each computed for a reproduction, emergence, and growth period related to the biological cycle of trout. We used anal-yses of covariance (ANCOVA) to test how trout densities at year n - 1 and hydrology at year n influenced trout densi-ties at year n. High flows during emergence significantly reduced the 0+ densities, consistently across the 30 reaches. Then, 1+ and adult densities were linked, respectively, to 0+ and 1+ densities from the previous year. Analyses also re-vealed density-dependent survival mechanisms for the 0+ cohort, suggesting intracohort competition. Therefore, hydrol-ogy constrains trout dynamics only during the critical emergence period, after which intracohort interactions regulate the 0+ density. Such mechanisms, validated across 30 environmentally different reaches, seem to be fundamental to trout population dynamics.; Les forces hydrologiques et biotiques imposent des contraintes à la dynamique de population des Truites brunes; cependant, on a rarement évalué leur rôle simultanément dans un grand nombre de cours d'eau. À partir de 5-8 échantillons (1 par année) récoltés dans chacun de 30 tronçons de cours d'eau français, nous avons examiné si les variations de l'hydrologie d'année en année influencent la densité annuelle des truites dans un tronçon et si les relations obtenues s'appliquent à tous les tronçons. Nous avons aussi cherché à trouver des interactions intra-spécifiques au sein des cohortes et d'une cohorte à l'autre. Nos données consistaient en des densités des différentes classes d'âges (0+, 1+ et adulte). Nous avons mesuré, chaque année, 13 variables hydrologiques, regroupées selon les périodes d'émergence, de reproduction et de croissance du cycle biologique des truites. Des analyses de covariance (ANCOVA) nous ont permis de vérifier comment la densité des truites de l'année n -1 et l'hydrologie de l'année n pouvaient influencer la densité des truites de l'année n. Des débits élevés durant l'émergence réduisaient significativement les densités des truites d'âge 0+, de façon comparable dans tous les 30 tronçons. De plus, les densités des truites d'âges 1+ et adulte étaient reliées respectivement aux densités des poissons d'âges 0+ et 1+ de l'année précédente. Les analyses ont aussi mis en évidence des mécanismes de survie reliés à la densité chez la cohorte d'âge 0+, ce qui semble indiquer l'existence de compétition au sein de la cohorte. L'hydrologie impose donc des contraintes à la dynamique de population des truites seulement durant la période critique de l'émergence, après quoi ce sont les interactions au sein de la cohorte qui contrôlent la densité des poissons d'âge 0+. De tels mécanismes, observés dans 30 tronçons qui diffèrent par leurs conditions environnementales, semblent être des caractéristiques fondamentales de la dynamique de population des truites.

Young-of-the-Year (YOY) cyprinid recruitment success was investigated annually over a 16-year period (from 1983 to 1998) in relation with the annual hydrological regime in a large regulated river (the Rhône River, France). The annual discharge regime was divided among 3 seasons based on the biological cycle of fishes (wintering, reproduction, and growth periods), and characterised by descriptors of average, high and low flow conditions, and overall variability. Co-inertia analysis revealed two distinct effects of hydrology on YOY recruitment success. The first resulted in a sudden shift in the YOY community organization, and was the consequence of two unpredictable (of extremely high magnitude in regard with the long-term mean value in a given time interval) consecutive floods, in October 1993 (110-year return-flood) and January 1994 (50-year flood). The resulting scouring of the substratum seems to have had a favourable effect on recruitment. The second, weaker effect was only observed in the 5 years after the 1993 and 1994 floods. It revealed the role of seasonality in hydrological conditions, because it separated high and variable discharge during the spawning period (favourable for barbel and bleak) from low discharge during this season (favourable for roach, rudd and nase). The results were consistent with previous knowledge concerning these species, and functional interpretations confirmed general expectations. Our findings support habitat template theories that attribute a major role to environmental variability (including 'disturbance history') in determining community characteristics. Finally, these results provide the first steps for a rational management of seasonal discharge in large regulated streams., Nous avons étudié le succès de recrutement annuel des Cyprinidés sur une période de 16 ans (1983-1998) en relation avec le régime hydrologique annuel dans un grand fleuve régulé (le Rhône). Le régime hydrologique annuel a été divisé en 3 saisons basées sur le cycle biologique des Cyprinidés (hiver, reproduction et croissance), et caractérisé par des descripteurs des conditions moyennes, de hauts et bas débits, ainsi que de la variabilité globale. Une analyse de co-inertie a révélé 2 effets distincts de l'hydrologie sur le succès de recrutement. Le premier s'est traduit par un changement très net dans l'organisation de la communauté alevine (forte augmentation des abondances et de la richesse spécifique), et est la conséquence de 2 crues consécutives de très fortes amplitudes (imprévisibles), en Octobre 1993 (crue de période de retour estimée à 110 ans) et Janvier 1994 (crue cinquantenale). Il semblerait que le nettoyage (décolmatage) du substrat consécutif à ces 2 événements ait agit favorablement sur le recrutement. Le second effet est plus faible, et n'est décelable que pendant les 5 années qui font suite aux crues de 1993-1994. Il met en évidence le rôle de la saisonnalité des conditions hydrologiques, en séparant les débits forts et variables durant la saison de reproduction (favorables au barbeau et à l'ablette) des débits faibles pendant la reproduction (favorable au gardon, rotengle et hotu). Ces résultats sont pertinents avec les connaissances que l'on a de ces espèces, ainsi que les interprétations fonctionnelles (traits biologiques). Nos résultats sont en accord avec les théories basées sur 'l'habitat template' qui attribuent un rôle prépondérant à la variabilité environnementale (incluant 'l'histoire des perturbations') dans la déterminations des caractéristiques biologiques et fonctionnelles de la communauté piscicole. Finalement, ces résultats peuvent servir de base à une gestion rationnelle des débits saisonniers dans les grands cours d'eau aménagés.

International audience; The feeding activity and subsequent assimilation of the products resulting from food digestion allow organisms to obtain energy for growth, maintenance and reproduction. Among these biological parameters, we studied digestive enzymes (amylase, cellulase and trypsin) in Gammarus fossarum to assess the impact of contaminants on their access to energy resources. However, to enable objective assessment of a toxic effect of decreased water quality on an organisms’ digestive capacity, it is necessary to establish reference values based on its natural variability as a function of changing biotic and abiotic factors. To limit the confounding influence of biotic factors, a caging approach with calibrated male organisms from the same population was used. This study applied an in situ deployment at 23 sites of the Rhone basin rivers, complemented by a laboratory experiment assessing the influence of two abiotic factors (temperature and conductivity). The results showed a small effect of conductivity on cellulase activity and a significant effect of temperature on digestive enzyme activity but only at the lowest temperature (7 °C). The experimental conditions allowed us to define an environmental reference value for digestive enzyme activities to select sites where the quality of the water impacted the digestive capacity of the organisms. In addition to the feeding rate, this study showed the relevance of digestive enzymes as biomarkers to be used as an early warning tool to reflect organisms’ health and the chemical quality of aquatic ecosystems.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA; By modifying the physical environment, ecosystem engineers can have inordinately large effects on surrounding communities and ecosystem functioning. However, the significance of engineering in ecosystems greatly depends on the physical characteristics of the engineered habitats. Mechanisms underlying such context-dependent impact of engineers remain poorly understood even though they are crucial to establish general predictions concerning the contribution of engineers to ecosystem structure and function. The present study aimed to decrypt such mechanisms by determining how the environmental context modulates the effects of ecosystem engineers (bioturbators) on microorganisms in river sediments. To test the effects of environmental context on the role of bioturbators in sediments, we used mesocosms and recreated two sedimentary contexts in the laboratory by adding a layer of either fine or coarse sand at the top of a gravel-sand matrix. For each sediment context, we examined how the sediment reworking activity of a bioturbating tubificid worm (Tubifex tubifex) generated changes in the physical (sediment structure and permeability) and abiotic environments (hydraulic discharge, water chemistry) of microorganisms. Microbial characteristics (abundances, activities) and leaf litter decomposition a major microbially-mediated ecological process were measured to evaluate the impact of bioturbation on biotic compartment. Our results showed that the permeability, the availability of oxygen and the activities of microorganisms were reduced in sediments covered with fine sand, in comparison with sediments covered with coarse sand. Tubifex tubifex significantly increased permeability (by about six-fold), restored aerobic conditions and ultimately stimulated microbial communities (resulting in a 30% increase in leaf litter breakdown rate) in sediments covered with fine sand. In contrast T. tubifex had low effects in sediments topped by coarse sand, where O2 was already available for hyporheic microorganisms. Our study supports the idea that context dependency mainly modulates the effects of engineering by controlling the ability of engineers to create changes on abiotic (O2 in the present study) factors that are limiting for surrounding communities.

[Departement_IRSTEA]Eaux; International audience; The distribution of eukaryotic plankton was investigated in the English Channel and the North Sea during the MICROVIR cruise in summer 2007. The size distribution of autotrophic, heterotrophic eukaryotes and species composition was analyzed with a focus on two major divisions, Haptophyta and Chlorophyta, targeted by 18S rRNA probes. Picoeukaryotes (

International audience; 1. The hyporheic zone plays a key role in hydrological exchange and biogeochemical processes in streambed sediments. The clogging of sediments caused by the deposition of particles in the bed of streams and rivers can decrease sediment permeability and hence greatly affect hyporheic microbial processes. 2. The main objective of this study was to determine the influence of sediment clogging on hyporheic microbial processes in three French rivers (the Usses, Drome and Isere). In each river, microbial abundance and activity were studied at three depths (10, 30 and 50 cm) in the sediment at one unclogged (high porosity) and one clogged site (low porosity). 3. The results showed that the sediment clogging had inconsistent effects on microbial processes in the three rivers. Increases (Usses) or decreases (Drome and Isere) in both aerobic and anaerobic processes were detected at the clogged sites compared to unclogged sites. These results suggest that microbial changes because of the sediment clogging are mainly mediated by the residence time of water within the hyporheic sediments. 4. A single model predicting the effect of clogging on hyporheic microbial processes cannot be applied generally to all rivers because the degree of clogging creates heterogeneous effects on flow rates between surface and interstitial waters. As a consequence, the influence of heterogeneous clogging on surface water-hyporheic exchanges needs to be evaluated by water tracing and hydraulic modelling to determine the links between microbial processes and hydraulic heterogeneity induced by clogging in hyporheic sediments.

International audience; 1. A substantial portion of particulate organic matter (POM) is stored in the sediment of rivers and streams. Leaf litter breakdown as an ecosystem process mediated by microorganisms and invertebrates is well documented in surface waters. In contrast, this process and especially the implication for invertebrates in subsurface environments remain poorly studied. 2. In the hyporheic zone, sediment grain size distribution exerts a strong influence on hydrodynamics and habitability for invertebrates. We expected that the influence of shredders on organic matter breakdown in river sediments would be influenced strongly by the physical structure of the interstitial habitat. 3. To test this hypothesis, the influence of gammarids (shredders commonly encountered in the hyporheos) on degradation of buried leaf litter was measured in experimental systems (slow filtration columns). We manipulated the structure of the sedimentary habitat by addition of sand to a gravel-based sediment column to reproduce three conditions of accessible pore volume. Ten gammarids were introduced in columns together with litter bags containing alder leaves at a depth of 8 cm in sediment. Leaves were collected after 28 days to determine leaf mass loss and associated microbial activity (fungal biomass, bacterial abundance and glucosidase, xylosidase and aminopeptidase activities). 4. As predicted, the consumption of buried leaf litter by shredders was strongly influenced by the sediment structure. Effective porosity of 35% and 25% allowed the access to buried leaf litter for gammarids, whereas a lower porosity (12%) did not. As a consequence, leaf litter breakdown rates in columns with 35% and 25% effective porosity were twice as high as in the 12% condition. Microbial activity was poorly stimulated by gammarids, suggesting a low microbial contribution to leaf mass loss and a direct effect of gammarids through feeding activity. 5. Our results show that breakdown of POM in subsurface waters depends on the accessibility of food patches to shredders.

International audience; Présentation de la restauration physique du fleuve et de ses effets.

International audience

International audience; Multilevel biomarker studies are now a classical approach for the monitoring of contaminated environments. Nevertheless, even if the population constitutes a level of interest for environmental management, the characterization of in situ effects of contaminants at this level reminds difficult notably because it also integrates plastic, adaptive and neutral variability related to physical-chemical habitat or phylogeograhical constraints. In predictive approaches, the experimental difficulty to assess impacts of chemical compounds at the population scale is currently addressed by modelling techniques. With two environmental relevant species, we develop this methodology in a diagnostic framework by coupling population modelling and in situ caging. Hence, we expect to enhance the ecological relevance of in situ toxicity assessment and to develop biologically integrated ecotoxicological indicators. Our approach proceeds in two steps. (i) Population models are developed to mechanistically link life history traits (survival, growth, reproductive activity, fecundity) and the dynamics of reference native populations all along a year. For this, we use a dual approach combining laboratory and field experiments. The latter consisting in a demographic follow-up based on monthly population census (densities, size distributions) and an individual approach with field organisms caged in situ (reproduction, growth, survival). (ii) Effects of contamination, observed at the organism level through the exposure of transplanted individuals caged in contaminated stations, are projected into the dynamics of these reference populations in order to propose a diagnostic assessment of water quality at the population level.

International audience

National audience

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA; National audience; Le Rhône est le quatrième fleuve européen et son bassin versant correspond au quart du territoire français. Depuis la seconde partie du 19ème siècle, le bassin versant, le corridor fluvial et le chenal ont subit des transformations, qui ont modifié radicalement la production et le transfert des sédiments. Quelques chiffres suffisent à illustrer les profondes modifications sédimentaires que connaît ce grand fleuve depuis quelques décennies. En 1950, le Rhône charriait 1 Million m3.a-1 de sables et graviers ; la valeur actuelle est estimée à 0,2 Million m3.a-1. Cette chute est liée d'une part à une extraction massive de matériaux alluvionnaires et d'autre part, à une disparition progressive de la torrentialité du bassin versant. Le 20ème siècle correspond donc à une mutation considérable des conditions d'alimentation, puis de transfert et de stockage sédimentaires, qui modifient la nature des aléas et des contraintes de l'occupation du sol à proximité du fleuve. C'est dans ce contexte de crise sédimentaire majeure que s'inscrit cette étude dédiée à la compréhension des liens étroits entre flux sédimentaires fluviatiles et polluants métalliques et organiques. Surimposée à cette pénurie de sédiments, la présence de contaminants hydrophobes dans les sédiments du Rhône implique la mise en ½uvre de programmes de recherche permettant de comprendre l'évolution séculaire et décennale de ces polluants. Quatre sites, situés sur le Rhône, en aval et en amont de l'agglomération lyonnaise ont fait l'objet de carottages courts. Les séquences ont été prélevées dans des environnements fluviatiles ayant archivé l'histoire récente des flux sédimentaires et des contaminants associés. Les comptages gamma (Césium et Plomb 210) ont permis d'établir une chronologie précise de la dynamique fluviatile. L'archivage exhaustif des crues constitue également un complément de calage du modèle d'âge. La susceptibilité magnétique et les mesures granulométriques autorisent une reconstitution du fonctionnement hydro-sédimentaire du Rhône à l'échelle annuelle. Les changements de texture, de flux ainsi que l'image de Passega sont des proxies sédimentaires sensiblement affectés par les aménagements (construction de barrages et de retenues). L'interprétation des profils de Plomb et de PCB est plus complexe, eu égard à la complexité des mécanismes et des modalités de la sédimentation fluviatile ; bien que nous ayons choisi des sites caractérisés par une décantation fine, les séquences sédimentaires étudiées enregistrent aussi les événements de type "crue". Les polluants dosés ayant une forte affinité particulaire, il convient donc de prendre en compte le lien étroit entre dynamique sédimentaire et concentration en métaux (Pb) et composés organiques (PCB). Néanmoins, Les sédiments du Rhône sont marqués par une baisse significative de la teneur en Plomb, les valeurs actuelles rejoignant progressivement le bruit de fond géochimique. Quant aux PCB, les tendances sont plus complexes car la contamination est souvent diffuse ; les différences entre les sites amont et les sites aval sont significatives et confirment la difficulté de relier les sources chimiques et les sources géographiques. Les modèles sur lesquels nous travaillons actuellement permettront de comprendre et de préciser l'origine des PCB identifiés dans les séquences historiques des sédiments du Rhône.

National audience; La concentration démographique dans les villes se poursuit et se poursuivra au cours des prochaines décennies (Europe, Monde) Étalement des couronnes périurbaines Imperméabilisation partielle des BV => modification du cycle de l'eau DCE impose d'atteindre (préserver) le bon état écologique d'ici 2015 (bon potentiel écologique pour les masses d'eau fortement modifiées) Directive cadre inondations (2007) vise à concilier gestion des inondations - changement climatique - bon état écologique L'OTHU travaille sur les inondations par ruissellement (péri)urbain.

International audience; The monitoring of contaminated environments via multilevel biomarker studies is a classical approach in ecotoxicology. Nevertheless, mechanistic links are rarely set up between the different levels of biological organization (sub-organism, organism, population). Population models are now recognized as useful tools to solve this extrapolation issue in predictive approaches, but environmental realism of these models could be improved in order to yield more pertinent risk assessment at the population level. This work proposes a new way to take advantage from the complementary nature of population modelling and in situ caging methodologies. On the basis of case studies with two environmental relevant species, the main purpose is to improve the extrapolation procedure by linking in situ biomarkers classically used in ecotoxicology at the organism level (laboratory bioassays or in situ biotests) and their consequences at a level of ecological interest: the population. Our approach proceeds in two steps. (i) Population models are developed to mechanistically link life history traits (survival, growth, reproductive activity, fecundity) and the dynamics of reference native populations all along a year. For this, we use a dual approach combining laboratory and field experiments. The latter consisting in a demographic follow-up based on monthly population census (evolution of densities and age-size structures) and an individual approach with field organisms caged in situ (reproduction, growth, survival). (ii) Effects of contamination, observed at the organism level through the exposure of transplanted individuals caged in contaminated stations, will be projected into the dynamics of these reference populations in order to propose a diagnostic assessment of water quality at the population level.

International audience; This study is a part of a large research project aiming at developing an ERA tiered framework for sediment management, in the context of integrated management of contaminated sediment, site restoration and sustainable navigation. The purpose of this study is to assess sediment quality by exploring the relationships between chemical contamination and benthic community structure using classical taxonomy and functional traits approaches. During falls 2004-2005, macroinvertebrates were collected in 59 sites in the St. Lawrence River, especially in its three fluvial lakes and in the harbour zone of Montreal. Organic (PCBs, PAHs, petroleum hydrocarbons), inorganic (As, Cd, Cu, Cr, Hg, Ni, Pb and Zn) contaminants and sediments characteristics (e.g. grain size, metal-binding phases, nutrients) were measured in whole sediment. Taxonomy and functional traits of benthic macroinvertebrates in the St. Lawrence River will be used to assess the relative impact of chemical contamination and sediment characteristics applying multivariate analysis and variance partitioning. We will compare the potential of taxonomy and functional traits approaches for assessing sediment quality in comparison with chemical sediment quality guidelines classification. The preliminary results and the implication for the development of an ERA tiered framework will be discussed.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA; National audience; In fall 2005, fish contamination by dioxin-like PCBs above the threshold for fish consumption was observed in the Rhone river, in the vicinity of Lyon (France). This observation triggered a series of investigations on sediment contamination along the mainstem of the Rhone. In addition to surface sampling in depositional areas along a ~120 km reach, short cores were collected from 3 locations and analyzed for PCBs and age-dating radionuclides. These data could help regional authorities identify the principal PCB sources among the potential ones, provided that distinct congeners source patterns can be identified. PCB congener pattern analysis in sediments is challenging because weathering processes can modify the original patterns. Further, in a large river basin like the Rhone, at mid- or downstream sites the various upstream sources are mixed. We applied two different factor analysis techniques in order to characterize source profiles and their relative contribution to total PCB content in each sediment sample. These results will be discussed in relation to the hydrology, geography, and water management of the area.

Bottom sediments may impair the functioning of equipments such as locks, increase the risk of flooding, or disturb habitats of aquatic species and related ecosystems functions. When dredged and accordingly abstracted from the water compartment, sediments become wastes, and are submitted regulations. Both aspects are related to the management of risks (to ecosystem functions or uses) and to their assessment. Sediment characterization entail chemical or biological approaches. Based on results obtained from these approaches, hazard characterization may be performed by means of classification methods or sediment quality standards., Pourquoi s'intéresser aux sédiments ? Leur présence a des implications pour la gestion des ouvrages, les crues, le fonctionnement des milieux (habitat important et donc déterminant pour ressources trophiques, frayères etc.) ; s'ils sont dragués, donc extraits des cours d'eau, ils entrent dans la réglementation « déchets ». Ces deux notions renvoient plus largement à la question des risques pour des fonctions de l'écosystème ou des usages, et de l'évaluation de ces risques. La caractérisation des sédiments fait appel à des méthodes chimiques et biologiques (biotests). La caractérisation du danger se base sur ces résultats, et fait appel notamment à des procédures de classification, ou des "normes de qualité environnementales".