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As a result of new concerns about subsurface drainage (networks ageing, hydraulic and hydrological operating), several methods have been developed to analyse continuously recorded field drainage experimental data. This paper presents these methods and their results, illustrated by surveys of some field drainage experiments located on various shallow temporarily waterlogged soils, three of them having been monitored during eight years. Annual and interannual hydrological performance of drainage is studied by double mass method. It highlights drainage seasons, enables a comparison between different kinds of layouts on a given soil, shows the contrasts in hydraulic behaviour between different soils and illustrates the drainage network performance particularly under tilled conditions. A statistical study of both maximum flow rates with different return periods and durations of given flow rates is conducted. This analysis of high flow rates is of practical interest for the choice of drainage design rates with different allowable surcharge duration., En réponse aux nouveaux problèmes de drainage souterrain (vieillissement des réseaux, fonctionnement hydraulique et hydrologique), plusieurs méthodes ont été développées pour analyser en continu les données expérimentales de drainage. Cet article présente ces méthodes et leurs résultats étayés par les études de certaines expériences de drainage situées sur différents sols peu profonds et temporairement détrempés, trois d'entre eux ayant été surveillés pendant huit ans. Les performances hydrologiques annuelles et interannuelles de drainage sont étudiées par la méthode de la double masse. Elles soulignent les saisons de drainage, permettent une comparaison entre différents types de configuration d'un sol donné, montrent les différences de comportement hydraulique entre les différents types de sols et illustrent les performances du réseau de drainage en particulier quand le sol est labouré. Une étude statistique des deux débit maximaux avec des périodes de retour différentes et des durées de débit données est réalisée. Cette analyse des débits élevés est intéressante sur le plan pratique pour le choix des débits théoriques de drainage d'une durée de surcharge permise différente.

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; 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.

After extrusion cooking, extrudates must be dried and are often coated by spraying with fatty materials before cooling and packaging. As a means to control the drying and coating processes of pet foods, a rapid NMR method was developed to determine water and fat contents over a large temperature range without weighing, heating or measuring the temperature of the samples. Weighing was avoided by normalizing all NMR intensities by the solid echo maximum of each sample. Formulae using estimates of the transverse relaxation time and the concentration of liquid fat protons were used to determine total fat and moisture contents without measuring the temperature of the samples. Fat content estimation had a standard deviation better than 0.2% over a large solid fat index range above 20°C. Water content was determined with a standard deviation of about 0.2% at all temperatures studied., Après cuisson-extrusion, les produits extrudés doivent être séchés et souvent enrobés par pulvérisation de matières grasses avant refroidissement et conditionnement. Afin de contrôler le séchage et l'enrobage de "pet foods", une méthode rapide RMN a été développée pour doser l'eau et la matière grasse dans une large gamme de température sans pesée, ni chauffer, ni mesurer la température des échantillons. La pesée était évitée en normalisant l'intensité des signaux RMN par le maximun de l'écho solide. Des équations utilisant des estimations du temps de relaxation et de la concentration des protons de matière grasse à l'état liquide étaient utilisées pour doser l'eau et la matière grasse sans mesurer la température des échantillons. La teneur en matière grasse était mesurée avec une erreur standard d'estimation meilleure que 0,2% dans une large gamme de taux de solide de matière grasse au dessus de 20°C. La teneur en eau était déterminée avec une erreur standard d'estimation de l'ordre de 0,2% dans toute la gamme de température étudiée.

International audience; A simple model of rainfall in time is proposed coupling the theory of renewal processes with a scale invariant representation of rain intensity. In particular, a strictly alternating renewal process mimes the sequence of wet and dry synoptic weather states, while a Fractional Noise represents the rain variability within each wet state. The rain model is adapted to Osservatorio Ximeniano (Florence) and Osservatorio di Brera (Milan) datatasets. Some rain characteristics are considered to check the agreement between model and data, namely, the annual volume of rainfall, the wet fraction of the year, the extreme values through the ""classic"" Depth-Duration-Frequency curves, and the maximum annual volume of the rainfall event. (c) 2006 Elsevier B.V. All rights reserved.

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.

The study presents the development of flood warning decision support products based on ensemble forecasts in the European Flood Alert System (EFAS). EFAS aims to extend the lead time of flood forecasts to 3–10 days in transnational river basins and complement Member States' activities on flood forecasting. Weather forecasts are used as input to a hydrological model and simulated discharges are evaluated for exceedances of flood thresholds. Products were developed in collaboration with users for a concise and useful visualization of probabilistic results. Forecasts of flood events observed in the Danube river basin in 2005 illustrate the analysis. Copyright © 2007 Royal Meteorological Society

The Jucar River Basin (Spain) harbours endemic aquatic species that are declining or going extinct at an alarming rate. After evaluating several possible stressors, flow modification is identified as the factor critically threatening one endemic cyprinid fish species Chondrostoma arrigonis. Physical habitat for this species is compared for river reaches with different flow modification histories to understand local extinctions across this species' historical range. Time-series of physical habitat, generated using PHABSIM, indicate a dramatic reduction in habitat area with flow modification. Our findings indicate that efforts to regulate and stabilize flows in the Jucar River Basin may cause the rapid extinction of the remaining populations. Copyright © 2007 John Wiley & Sons, Ltd.

International audience; Although various numerical methods were used to simulate real floods occurring in cities, the validation of the models was never accurate because of the lack of data about location and event description and about observation for validation. In order to check the capacities of our 2-dimensional shallow water equations model to simulate an urban flood, we then decided to simulate numerically an experimental event with well known characteristics and accurate flow measurements. The physical model presented in (Ishigaki T. et al., 2003) represents the flooding of the city center of Kyoto in Japan due to an overflow from the Kamo river. The 2-dimensional numerical simulation of this event was then set up and the experimental and computed data were compared. It appears that the event was calculated quite fairly in terms of flow depth and flow rates in the streets and in terms of timing. However, some discrepancies appear between the measurements and the numerical results, mostly due to some topographical local uncertainties and to the capacities of the equations to model the complex flows in the crossroads.; Bien que divers codes de calculs 2D aient déjà été utilisés afin de simuler les inondations urbaines dans des zones urbanisées, aucune validation précise de ces modèles numériques n`est disponible. La méthode de validation proposée dans cet article consiste à simuler une inondation préalablement étudiée expérimentalement par (Ishigaki T. et al., 2003) et qui représente l`inondation du centre ville de Kyoto au Japon. La simulation numérique de cet événement expérimental et la comparaison des données calculées avec les données mesurées permet en effet de vérifier les capacités du code de calcul 2D à simuler un tel événement. Il apparaît que la dynamique de l`inondation ainsi que la plupart des détails de l`écoulement sont bien reproduits numériquement, même si une incertitude subsiste concernant notamment des incertitudes topographiques locales.

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%.

Correspondance: lagache@ensam.inra.fr; International audience; Artificial stream networks play a major role in water and pollutant transfer within cultivated watersheds. Since the characteristics of these artificial stream network (e.g. width, vegetation cover, presence of sediments, etc.) are highly variable in space and in time, describing their variability appears as a prerequisite for assessing environmental risk of pollution at watershed scale. In this perspective an indicator approach is presented which includes three steps: (a) collecting properties of reach (i.e. elementary stream) along an artificial stream networks by means of a field and GIS-based approach, (b) deriving from these properties a set of quantitative indicators of hydrological and chemical processes involved in herbicide transfer, (c) classifying reaches in terms of their role in herbicide transfers on the basis of these indicators. The application of this method to three different watersheds located in France - Roujan watershed (South), La Morcille (East-Centre) and Le Cétrais (North-West) - confirms that artificial stream networks of cultivated watersheds are highly spatially variable in regard to pollutant transfer. This spatial variability includes both variations between the watersheds and variations within the watersheds. Furthermore, the study reveals that the stream network properties can also be variable in time.

International audience; The study presents an approach to depict the two first order moments of runoff as a function of area (and thus on a map). The focal point is the mapping of the statistical properties of runoff q=q(A,D) in space (area A) and time (time interval D). The problem is divided into two steps. Firstly the first order moment (the long term mean value) is analysed and mapped applying an interpolation procedure for river runoff. In a second step a simple random model for the river runoff process is proposed for the instantaneous point runoff normalised with respect to the long term mean. From this model theoretical expressions for the time-space variance-covariance of the inflow to the river network are developed, which then is used to predict how the second order moment vary along rivers from headwaters to the mouth. The observation data are handled in the frame of a hydrological information system HydroDem, which allows displaying the results either in the form of area dependence of moments along the river branches to the basin outlet or as a map of the variation of the moments across the basin space. The findings are demonstrated on the example of the Moselle drainage basin (French part).

We show that, when performing water-only tests in semi-static conditions with the amphipod Hyalella azteca, it is necessary to use sieves prepared as described in this paper. Feeding condition 0.1 mg/individual/working day appeared to be relevant to ensure optimal growth and reproduction. Finally, it seems that sediments do not provide extra benefit compared to prepared sieves, provided there is sufficient cover and some bacterial development.

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.

Dans cette thématique concernant le transport solide des cours d’eau, il nous semble opportun de résumer le cadre général et d’y situer notre approche. Les formules classiques du transport solide évaluent le débit en matériaux du lit (charriage et suspension) à partir de ses déformations. Elles ne permettent pas d’estimer le débit des matériaux provenant directement du lessivage des versants et qui transite sans interaction avec le lit. Dans cet article, nous considérons uniquement la phase en suspension "MES" mesurée sans distinction à priori de l’origine des grains qui la constitue : provenance directe du bassin versant (phase directe) et (ou) reprise des stocks disponibles dans le lit (phase différée). Le bassin hydrographique du Timis-Béga (Roumanie) est particulièrement bien équipé pour le suivi des débits de 28 sous bassins et le contrôle des flux de MES de douze d’entre eux. De plus, son contexte physiographique nous permet de penser que la phase directe est prépondérante. Le protocole de mesure des flux de MES prévoit, entre autres, une densification variable des observations selon l’intensité des crues liquides. Ces considérations précédentes nous permettent d’envisager une modélisation statistique des apports solides en MES des sous-bassins du Timis-Béga. Celle-ci est directement inspirée des connaissances acquises sur la modélisation statistique "QdF" des régimes hydrologiques des bassins versants. Sur l’exemple du sous-bassin du Béga à Balint, qui draine une superficie de 1064 km2, nous retiendrons deux principaux résultats issus de la transposition du concept QdF aux débits solides QMESdF : Les analyses statistiques des régimes liquide et solide montrent que les débits solides de MES ne sont pas simplement proportionnels aux débits liquides mais croissent plus rapidement. Les deux lois de distributions privilégiées, Pareto généralisée pour les MES et exponentielle pour les débits, permettent de le justifier. Le temps de montée des hydrogrammes de projet liquide ou solide est quasiment identique, autrement dit nous vérifions la quasi concomitance de leurs débits de pointe. Ce résultat n’est possible que si le débit solide de MES provient essentiellement du lessivage des versants, ce qui était supposé à priori., With respect to sediment transport, we detailed the general framework and how our approach contributes to these developments. Starting from the single traditional relation for the bed material load, specialists in river hydraulics cannot assess sediment yield of basins, when it involves the auto-suspension of fine sediments coming mainly from slope erosion (wash load). This latter estimate is needed for simulating the transfer of sediments and possible deposition in certain areas, particularly when a strong slowing down occurs. The Timis-Bega drainage basin (Romania) is fairly well equipped for the monitoring of discharge and suspended materials (sediment discharge). The hydrometric network includes 28 stations, of which 12 allow a monitoring of wash load. Moreover, its physiographic characteristics led us to think that the wash load dominates. Thus we assumed that sediment discharge was correlated with the physiographic features of the catchment area. The protocol for the measurement of the suspended sediment load was intensified during the floods. Thus, statistical modelling of the sub-basin sediment yields could be performed.The current study was directly inspired by the knowledge obtained in the domain of statistical modelling that describes hydrological regimes. The approach adopted was based on the flood-duration-frequency (QdF) analysis that takes into account the temporal variability of floods. The QdF approach analyses maximum average flows (Vd) over various durations (d), equivalent to intensity-duration-frequency (IdF) curves commonly used for rainfall analysis. The proposed model allows QdF curves V(d, T) for a given basin to be estimated using a minimum number of parameters. When the statistical law is the exponential law, this model contains only three parameters, due to observed scale invariance properties. The ∆ parameter that informs about the shape of the flood hydrograph is consequently the flood characteristic duration of the studied basin. The two parameters of the exponential maximum flood distribution for d=0 (a0 and x0) and ∆ were fitted to sample discharges (Vd). This model is called a converging QdF model because of the observed convergence of distributions towards small return periods. This model is also useful for the determination of threshold discharges (Qd). The analytical formulation of the V(d,T) model can be derived according to d, in order to obtain a Q(d,T) model. This model then permits the calculation of the hydrograph for any return period (T) and any duration (d).The regionalization of the sediment yield was achieved within the framework of the Riverlife European project, in collaboration with NIHWM (National Institute of Hydrology and Water Management of Romania). Initially, local models were built. As an example, starting from the Bega sub-basin at Balint, with a surface of 1,064 km2, our intent was to present the transposition of the discharge-duration-frequency analysis concept (or QdF) to the wash load QMES dF. The latter relates to the measurement procedure, the statistical processing of the observed data QMES (t), and to the building of the discharge hydrographs of the associated projects.The main results were:- The statistical analyses of floods and sediment discharges show that the wash loads were not simply proportional to the discharge, but rather they increased more rapidly. The selection of the appropriate distribution laws (Pareto generalised for the QMESdF model (four parameters) and exponential for the QdF model) reinforced this result.- The lag-time was the same for both hydrographs with respect to flood and sediment discharge. This result can be achieved if the sediment transport comes primarily from the scrubbing of the slopes (wash load), which was hypothesised a priori. However, falling limb of the sediment hydrograph decreases more quickly than for the discharge hydrograph (∆MES is lower than ∆).The Bega sub-basin example at Balint was a first test towards the regional modelling of the contributions to sediment discharge in the catchment area of Timis-Béga. This flood and sediment discharge regionalization is necessary for the study of the protection of the town of Timisoara against flooding.

[Departement_IRSTEA]RE [TR1_IRSTEA]RIE / TRANSFEAU; International audience; Grassed buffer strips are one way to reduce pesticide transfer by surface runoff from farmed fields to streams. Numerous experimental studies have demonstrated that this type of development is very effective in various conditions. The results are nevertheless very variable. This variability is partially explained by the multiplicity of processes and contributive factors and by the fact that the latter are dynamic in nature and site-specific. Several results also show that the intercepted products are not systematically immobilized within the strip but can move in the subsurface, thus affecting the overall effectiveness of the system. As a consequence of this complexity, the present guidelines for the sizing and siting of grassed strips are still only qualitative or are the result of empirical approaches. The present review analyses the available results and defines needs for further research. This concern several basic processes determining the pesticide interception by grassed strip and numerical models necessary to integrate the complexity of interacting processes and formulate reliable managing guidelines.

International audience; Numerical models simulating changes in soil water content with time rely on accurate estimation of root water uptake. This paper considers two root water uptake modules that have a compensation mechanism allowing for increase root uptake under conditions of water stress. These models, proposed by Lai and Katul (2000) and Li et al. (2001) use a potential transpiration weighted, for each soil layer, by a water stress and a compensation function in order to estimate actual transpiration. The first objective of the paper was to assess the accuracy of the proposed root extraction models against two existing data sets, acquired under dry conditions for a winter wheat and a soybean crop. In order to perform a fair comparison, both modules were included as possible root water extraction modules within the Simple Soil Plant Atmosphere Transfer (SiSPAT) model. In this first set of simulations, actual transpiration was calculated using the solution of the surface energy budget as implemented in the SiSPAT model. Under such conditions, both root extraction modules were able to reproduce accurately the time evolution of soil moisture at various depths, soil water storage and daily evaporation. Results were generally improved when we activated the compensation mechanisms.When water balance models are run at larger scales or on areas with scarce data, actual transpiration is often calculated using models based on potential transpiration without solving the surface energy balance. The second objective of the paper was to assess the loss of accuracy in such conditions for the Lai and Katul (2000) and Li et al. (2001) models. For this purpose we compared results from the SiSPAT model solving the surface energy balance with those of a degraded version where only potential evapotranspiration was imposed as input data. We found that actual transpiration and evapotranspiration were in general underestimated, especially for the Lai and Katul (2000) model, when we used the potential evapotranspiration as calculated from FAO standards. The use of crop coefficients improved the simulation although standard values proposed by the FAO were too small. The definition of the potential evapotranspiration was the major source of error in simulating soil moisture and daily evaporation rather than the choice of the root extraction models or the inclusion of a compensation mechanism. When used for water management studies, a sensitivity to the definition of potential evapotranspiration used to run the models is therefore advisable.; Les modèles numériques simulant les variations du contenu en eau des sols dépendent d`une estimation précise de l`extraction racinaire. Cet article considère deux modules d`extraction racinaire, comprenant un mécanisme de compensation permettant une extraction racinaire accrue en cas de stress hydrique. Ces modèles, proposés par Lai and Katul (Adv. Wat. Res., 23, 2000) and Li et al. (J. Hydrol., 252, 2001) utilisent une évapotranspiration potentielle, pondérée, pour chaque couche, par une function de stress et une fonction de compensation, afin d`estimer la transpiration réelle. Le premier objectif de cet article était d`évaluer la précision de ces modules d`extraction racinaire par comparaison avec deux jeux de données, acquis dans des conditions de stress hydrique pour un blé d`hiver et un champ de soja. Afin de les comparer dans les mêmes conditions, les deux modules ont été introduits comme modules d`extraction racinaire dans le modèle SiSPAT. Dans ce premier jeu de simulations, la transpiration réelle était calculée à partir de la résolution du bilan d`énergie de surface. Dans ces conditions, les deux modules se sont montrés capables de reproduire avec précision les évolutions temporelles de la teneur en eau des sols à différentes profondeurs, le stock d`eau dans le sol et l`évaporation journalière. Les résultats étaient en général meilleurs quand on prenait en compte le mécanisme de compensation. Quand les modèles de bilan hydrique sont utilisés à grande échelle ou sur des zones avec peu de données, la transpiration réelle est souvent estimée à partir d`une transpiration potentielle, sans résoudre le bilan d`énergie. Le second objectif de cet article était de quantifier la perte de précision dans de telles conditions pour les modules de Lai et Katul (2000) et Li et al. (2001). Pour cela, nous avons comparé les résultats de SiSPAT, résolvant le bilan d`énergie, avec ceux d`une version dégradée où on ne considérait qu`une transpiration potentielle en entrée des modules d`extraction racinaire. Nous avons obtenu une sous-estimation de la transpiration réelle, plus particulièrement pour le modèle de Lai et Katul (2000), lorsque nous utilisions une evapotranspiration potentielle calculée selon la méthode de la FAO. L`utilisation de coefficients culturaux permet d`améliorer les résultats, même si les valeurs standard proposées par la FAO étaient trop faibles. La définition de l`évapotranspiration potentielle apparaît donc comme la source majeure d`incertitude pour la simulation de l`évolution du contenu en eau du sol et de l`évapotranspiration journalière, par rapport au choix du module d`extraction racinaire ou d`un mécanisme de compensation. Quand l`évapotranspiration potentielle est utilisée pour des études de bilan en eau, une étude de sensibilité à sa valeur de est donc recommandée.

International audience; This work is part of a research activity aiming to improve and to optimise air-distribution systems in refrigerated vehicles in order to decrease the temperature differences throughout palletised cargos. This condition is essential in order to preserve the quality, safety and shelf life of perishable products. The present study reports on the numerical and experimental characterization of airflow within a semi-trailer enclosure loaded with pallets. The experiments were carried out on a reduced-scale (1:3.3) model of a refrigerated-vehicle trailer. The performance of ventilation and temperature homogeneity were characterized with and without supply air duct systems. Both configurations are extensively used in refrigerated transport. The numerical modelling of airflow was performed using the Computational Fluid Dynamics (CFD) code Fluent and a second-moment closure, the Reynolds stress model (RSM). The results obtained using the RSM model showed good agreement with the experimental data. Numerical and experimental results clearly show the importance of air ducts in decreasing temperature differences throughout the cargo.

[Departement_IRSTEA]EA [TR1_IRSTEA]TEPSA / ENERFRI; International audience; Many studies have been carried out on two-phase flow heat transfer in channels with hydraulic diameter bigger than 6 mm, but relatively little work has been done for small diameter channels in the meso and compact range (diameter from 0.1 to 3 mm). The use of exchangers with small channels in refrigeration units, which are very numerous besides, could bring a significant reduction of the internal volume of the exchanger, and therefore diminish the refrigerant charge of the whole refrigerating system. One can imagine the interest to widen knowledge on the flow and the heat transfer in small-diameter tubes. This paper examine the thermal behavior of refrigerants boiling in small pipes. The correlations available for in-tube evaporation heat transfer coefficient are discussed and evaluated, when possible, and new research areas of relevance than can contribute to expand the use of small-diameter channels evaporators in refrigeration units are suggested.

The method to build a numerical model intended to predict the formation and the change of sediment deposits upstream from a dam is presented. From information about the inputs of water and sediments coming from the catchment supported by a QdF type hydrological analysis, a horizontal 2-D hydraulic model which couples shallow water equations and one equation for advection and diffusion of sediment concentration is used. Applying this model to Zardezas reservoir in Skikda (Algeria) region shows, on the one hand, the practical difficulties met on such case and, on the other hand, the potentialities of such a method for the management of Algerian reservoirs., La construction d`un modèle numérique destiné à prédire la formation et l`évolution de dépôts de sédiments à l`amont d`un barrage est présentée. A partir d'informations sur les apports en eau et en sédiments en provenance du bassin versant consolidées par une analyse hydrologique en QdF, un modèle hydraulique bidimensionnel horizontal couplant équations de Saint Venant et une équation de convection - diffusion est mis en oeuvre. L'application de ce modèle sur la retenue de Zardezas de la région de Skikda (Algérie) montre, à la fois, les difficultés pratiques rencontrées dans la mise en oeuvre et l'apport possible d'une telle méthode pour la gestion des retenues algériennes.

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.

Sediments were collected in three small water courses upstream and downstream a water treatment plant discharge, in one highly fertilized eutrophic pond, and from one oligotrophic brook. They were analysed for ammonium oxidation activity, for nitrite oxidation activity and for their respective nitrifying community size. The relationships between variables was investigated by a principal components analysis of the physicochemical and biological data. Upstream sites of treatment plant discharges looked similar to an oligotrophic river, but the downstream sites have certain similarities with a highly eutrophic pond. Globally, whatever the hydrosystem, the organic carbon and organic nitrogen content of the sediments were highly correlated with nitrifying activity and nitrifiers number (significance level α = 0.001), but there was no significant correlation between the nitrifiers number and the related activity. The hypothesis of a role of the grain size on the nitrification communities was tested. A Mann-Withney U test (α = 0.05) indicated that, whatever the sediment, the two fractions of sand (500–200 μm and 200–50 μm) were non significantly different for nitrification. Conversely, the silt-clay fraction was significantly different from sands for all the nitrification's parameters. This silt-clay fraction exhibited the highest functional nitrifying community per mass unit indicating that the silt fraction is a main contributor to the nitrification process in river sediment. Finally, for each river, there were significant differences (at α = 0.05) between the nitrifiying communities in downstream and upstream sediments. In the 3 studied rivers, upstream sites were significantly higher in terms of activity and in terms of number of nitrifying bacteria. The effect of wastewater effluents discharge seems to be site specific.

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.

Corbicula fluminea populations were sampled annually from 1997 to 2000 at the beginning of the autumn, i.e. at the end of the reproduction period, at 14 sites along the Saône and Rhône rivers. Recruitement in the upper reach of these rivers was generally high. Conversely, the observation of other sectors revealed generally low or no production of juveniles, missing cohorts and major year to year variations in population structure. Nevertheless, no dramatic fall in population density was observed during the surveyed four years. This suggests that the longevity of the Corbicula populations of the Saône and Rhône rivers is ensured to a great extent by the drifting of individuals from the upper course of these rivers and their tributaries. Two possible causes are put forward to explain the low recruitment observed: low production of phytoplankton that prevents adults from development of phytoplankton and it is lethal for pediveligers., Les populations de Corbicula fluminea ont été échantillonnées annuellement en début d'automne, c'est-à-dire en fin de période de reproduction, de 1997 à 2000 sur 14 sites jalonnant la Saône et le Rhône. Dans le cours supérieur de ces cours d'eau, le recrutement est généralement important. En revanche, dans les autres secteurs on observe une production de juvéniles généralement faible ou nulle, des cohortes manquantes et d'importantes variations de la structure des populations d'une année sur l'autre. Néanmoins, on ne constate pas au cours de ces quatre années de chute dramatique de la densité des populations. Ceci suggèrent que la pérennité des populations de Corbicula de la Saône et du Rhône est largement assurée par la dérive d'individus provenant du cours supérieur de ces cours d'eau et de leurs affluents. Deux causes sont proposées pour expliquer les faibles recrutements observés : - la faible production de phytoplancton ne permettrait pas aux adultes de constituer les réserves énergétiques nécessaires aux complet développement des larves ; - la contamination toxique inhibitrice du développement phytoplanctonique serait létale pour les pediveligers.

The Simplex method has been used to determine the value of process parameters, mixing duration and mixer rotation speed, that lead to a product with desired sensory characteristics at the end of the chopping step during the manufacture of meat emulsion. These characteristics are evaluated as a global index called chopping degree (CD). It is calculated using the theory of fuzzy sets on the basis of a temperature measurement and four sensory evaluations made close to the line by operators. CD value should be as close as possible to 5. The results have allowed the optimisation of intermediary sensory quality by obtaining a maximum point where CD equals 4.8. The processing conditions established at the end of the Simplex algorithm are 3 min and 2000 rpm., La méthode du Simplex a été utilisée pour déterminer la valeur des paramètres du procédé, vitesse et durée d'émulsification, qui conduisent à un produit avec des caractéristiques sensorielles souhaitées à la fin de l'étape de cutterage durant la fabrication des émulsions de viande. Ces caractéristiques sont évaluées sous la forme d'un indice global appelé degré de cutterage (CD). Il est calculé en employant la théorie des sous-ensembles flous sur la base d'une mesure de température et quatre évaluations sensorielles réalisées près de la ligne par les opérateurs. CD doit être aussi proche que possible de 5. Les résultats ont permis l'optimisation de la qualité sensorielle intermédiaire en obtenant un point maximum où CD est égal à 4.8. Les conditions procédé correspondent à une durée de 3 min et une vitesse de 2000 tr/min.

International audience; During the second phase of the EFEDA experiment (ECHIVAL Field Experiment in a Desertification Threatened Area), the spatial variability of the soil water retention and hydraulic conductivity characteristics of layers 2-12 and 17-27 cm depth was characterized. A simplified method, based on particle size distribution and simple infiltration tests was used. It provided these characteristics at the nodes of a 1 km grid over 10x10 km2 around the town of Tomelloso (Castilla- La Mancha, Spain). A total number of 78 sample points were used to address the problem of soil surface properties variability and its consequences on the monthly and annual water balance. The SiSPAT (Simple Soil Plant Atmosphere Transfer model) 1-D Soil-Vegetation-Atmosphere Transfer (SVAT) model was run with a one-year climatic forcing for the 78 soil profiles until equilibrium was reached. As no runoff was generated, the spatial variability of the water budget components only concerned soil evaporation, transpiration and deep drainage. It was found that i) the choice of the type of boundary condition at the bottom of the soil profile was greatly influencing the final variability, ii) the variability of transpiration was the largest in situations of water stress for the vegetation, iii) soil evaporation was the most sensitive component when plants were well supplied with water. Various aggregation methods of soil surface parameters (use of the arithmetic mean, median of the parameters or parameters associated to the average soil texture of the Clapp and Hornberger (1978) classification) were assessed. The use of median parameters in a single 1-D simulation was found to provide the best agreement with the average of the 78 simulations performed for each grid cell using locally measured soil properties. The use of average soil texture parameters led to a significant bias, especially in the case of water stress.; Durant la seconde phase du Projet Européen EFEDA (ECHIVAL Field Experiment in a Desertification Threatened Area), la variabilité spatiale des courbes de rétention et de conductivité hydraulique des couches 2-12 et 17-27 cm de profondeur a été caractérisée. Une méthode simplifiée, s'appuyant sur la distribution granulométrique du sol et des essais simples d'infiltration a été utilisée. Elle fournit ces propriétés hydrodynamiques sur une grille de 1 km de résolution sur une surface de 100x100 km2 autour de la ville de Tomelloso (Castilla La Mancha, Espagne). Un nombre total de 78 échantillons ont été utilisés pour étudier le problème de la variabilité spatiale des propriétés de la surface du sol et de sa conséquence sur le bilan hydrique annuel et mensuel. On a fait tourner le modèle 1D de Transfert Sol-Végétation-Atmosphère (TSVA) SiSPAT (Simple Soil-Plant-Atmosphere Transfer model) avec un forçage climatique d'une année pour les 78 profils de sol, jusqu'à ce que l'équilibre soit atteint. Comme on ne générait pas de ruissellement, la variabilité spatiale du bilan hydrique concernait uniquement l'évaporation du sol, la transpiration et le drainage profond. On a obtenu que (i) le choix du type de condition à la limite au bas de la colonne de sol influençait beaucoup la variabilité finale, (ii) la variabilité spatiale de la transpiration était la plus grande en cas de stress hydrique pour la végétation et (iii) l'évaporation du sol était la composante la plus sensible quand les plantes étaient bien alimentées en eau. Différentes méthodes d'agrégation des paramètres de surface (utilisation de la moyenne arithmétique, de la médiane des paramètres ou paramètres associés à la texture moyenne selon la classification de Clapp et Hornberger) ont été évaluées. L'utilisation de la médiane des paramètres dans une seule simulation 1D conduit au meilleur accord avec la moyenne des 78 simulations réalisées pour chaque point de grille à l'aide des mesures locales des propriétés du sol. L'utilisation de paramètres issus de la texture moyenne conduisait à un biais significatif, surtout en cas de stress hydrique.

Interdisciplinary frameworks for studying natural hazards and their temporal trends have an important potential in data generation for risk assessment, land use planning, and therefore the sustainable management of resources. This paper focuses on the adjustments required because of the wide variety of scientific fields involved in the reconstruction and characterisation of flood events for the past 1000 years. The aim of this paper is to describe various methodological aspects of the study of flood events in their historical dimension, including the critical evaluation of old documentary and instrumental sources, flood-event classification and hydraulic modelling, and homogeneity and quality control tests. Standardized criteria for flood classification have been defined and applied to the Isère and Drac floods in France, from 1600 to 1950, and to the Ter, the Llobregat and the Segre floods, in Spain, from 1300 to 1980. The analysis on the Drac and Isère data series from 1600 to the present day showed that extraordinary and catastrophic floods were not distributed uniformly in time. However, the largest floods (general catastrophic floods) were homogeneously distributed in time within the period 1600-1900. No major flood occurred during the 20th century in these rivers. From 1300 to the present day, no homogeneous behaviour was observed for extraordinary floods in the Spanish rivers. The largest floods were uniformly distributed in time within the period 1300-1900, for the Segre and Ter rivers., Une approche interdisciplinaire sur l`étude des phénomènes climatiques et de leur variabilité temporelle présente un intérêt certain pour l`analyse des risques naturels, de l`aménagement du territoire et de la gestion durable des ressources en eau. Cet article traite des aspects méthodologiques liés à la reconstitution et l`analyse d`événements de crue sur le dernier millénaire. Il aborde les questions de la critique des sources documentaires historiques, de la classification des crues et de la modélisation hydraulique des crues anciennes, des tests statistiques sur l`homogénéité des valeurs. Une échelle standardisée de classification des crues a été définie et appliquée aux crues de l`Isère et du Drac en France, de 1600 à 1950, et du Ter, du Llobregat et du Segre en Espagne, de 1300 à 1980.L`analyse des séries chronologiques du Drac et de l`Isère, de 1600 à aujourd`hui, montre que les crues fortes à exceptionnelles ne sont pas réparties de façon homogène dans le temps. Aucune tendance n`est décelable pour les crues exceptionnelles de 1600 à 1900. Aucune crue majeure de ce type n`a été observé sur ces deux rivières au cours du XXe siècle. En Espagne, de 1300 à aujourd`hui, l`occurrence des crues n`est pas stationnaire pour les crues fortes à exceptionnelles. Les crues exceptionnelles, de 1300 à 1900, sont par contre réparties de façon homogène pour le Segre et le Ter.

Boosting is a classification method used to assign an object to a predetermined class, according to the values obtained for several variables. It is a very general method, whieh can be used fbr a avide range of applications (economics, agronomy, sociology, geography, pedology, epidemiology, remote sensing, etc), particularly those in which the object is geographical space. The method is vert' powerful, and can discriminate between groups where other techniques such as linear methods would fail. However, it calls for considerable caution and a watchful eye on certain criteria such as the weight of observations. Lastly, it is easily integrated into geographical information systems., Le boosting est une méthode de classification gui permet d'affecter un objet dans une classe définie a priori en fonction des valeurs prises par plusieurs variables. De caractère très général, cette méthode est susceptible d'être utilisée dans de nombreux domaines d'application (économie, agronomie, sociologie, géographie, pédologie, épidémiologie, télédétection...) et notamment dans ceux gui ont pour cadre l'espace géographique. Très puissante, cette méthode arrive à discriminer des groupes là où d'autres méthodes, comme les méthodes linéaires, échouent. En contrepartie, elle demande une grande prudence et l'examen attentif de certains critères comme l'évolution du poids des observations. Enfin, elle est très facile à intégrer dans les systèmes d'information géographiques.

International audience; We use data from the French national butterfly atlas to compare the potential of direct geographical and neighbourhood models to account for numbers of species and incidence of species in French departements. Direct geographical models use data on latitude, longitude and altitude, whereas neighbourhood models use information from adjacent areas. Both geographical models and neighbourhood models account for a large proportion of the variance in species richness (68-78%). However, neighbourhood models are more successful than models based solely on simple geographical variables. A large number of individual species distributions are accounted for by logistic and autologistic regression models (222 of 246 species, 90.2%). The autologistic models incorporate information on neighbouring areas. The exceptions are rare species, five of six of which occur in a single administrative unit only (2.4%), or virtually ubiquitous species found in > 90% of units (7.3%). Autologistic models dominate logistic models in accounting for species incidences using stepwise logit regressions, neighbourhood variables appearing in 64.5% of successful species models (absent in 22.8%) and then always entering first. A simple neighbourhood (distance-unweighted) measure (C-2) dominates more models (89 of 246 species, 36.2%) than a distance-weighted neighbourhood measure (C-1; 77 of 246 species, 31.3%). The models are here demonstrated to be potentially valuable for identifying under-recording and losses from regional extinction and for filling gaps in recording. The findings reveal substantial, apparent, losses of species in western and northern France as well as substantial discrepancies (differences) in numbers of species, for some administrative units (departements) and for both post-1970 and total records, compared with numbers predicted to occur. We use two distinct approaches on total species and individual species to provide comparative estimates of the numbers of species expected within spatial units and we present the number of additional units in which species are expected to occur. The probabilities for these species in French departements are available on Web site: http://www.brookes.ac.uk/schools/bms/research/data/ecology/butterfly.html.

International audience; This paper describes an easy-to-use and accurate method to calculate some of the thermophysical properties of aqueous solutions which are used as secondary refrigerants. This method is based on the correction of the ideal behaviour of aqueous solutions by excess functions. This method allows to determine the following properties: freezing points, densities, heat capacities, thermal conductivities and dynamic viscosities. As an illustration, it is applied to aqueous solutions of (i) ethyl alcohol, (ii) ammonia, (iii) sodium chloride, (iv) ethylene glycol and (iii) propylene glycol.; Cet article présente une méthode facile à mettre en oeuvre et précise du calcul des propriétés thermophysiques des solutions aqueuses utilisées comme fluides frigoporteurs monophasiques. Cette méthode est basée sur la correction du comportement idéal des solutions aqueuses en utilisant des fonctions d'excès. Elle est utilisée pour déterminer les propriétés suivantes : températures de cristallisation commençante, masses volumiques, chaleurs spécifiques, conductivités thermiques et viscosités dynamiques. A titre d'illustration, le modèle proprosé est appliqué aux solutions aqueuses de (i) éthanol, (ii) ammoniaque, (iii) chlorure de sodium, (iv) éthylène glycol et (iii) propylène glycol.

International audience; Finished food products must meet specific sensory, sanitary, technological requirements. Among these requirements, sensory properties are essential because they condition the choice and the preferences of consumers. We propose an approach based on the theory of fuzzy sets to reproduce, with the help of a camera, the evaluation of sensory properties, made close to the manufacturing line (at-line), by a single expert:the operator. Our study is applied to the assessment of a sausage defect: the crusting. By means of a camera and an adapted image processing, the human evaluation of crusting is reproduced. Good results have been obtained from a data base of 76 images.; Les produits finis alimentaires doivent respecter des propriétés sensorielles, sanitaires et technologiques définies dans le cahier des charges. Parmi ces propriétés, les propriétés sensorielles sont essentielles car elles conditionnent le choix et préférences des consommateurs. Nous proposons une approche basée sur la théorie des ensembles flous pour reproduire, avec l'aide d'une caméra, l'évaluation des propriétés sensorielles, faite près de la ligne par un seul expert : l'opérateur. Notre étude est appliquée à l'évaluation d'un défaut du saucisson : le croûtage. Par une caméra et un traitement d'images adapté, l'évaluation humaine du croûtage est reproduite. De bons résultats sont obtenus sur une base de données de 76 images.

International audience; Almost all of the many technical papers on the quantification of advective flow rates through composite liners focus on uniform interface transmissivity and mathematical modelling. Few papers have addressed situations where the transmissivity is non-uniform or experimental validation of previously developed analytical or empirical equations. This paper therefore attempts to present both the results of a numerical survey based on previously developed equations addressing the case of non-uniform hydraulic transmissivity at the liner interface and an experimental survey conducted on large-scale tests. Even if the two aspects of this study are based on different assumptions-two-dimensional geometry, steady-state flow, saturated soil and interface for the numerical study and axi-symmetric geometry, transient flow and unsaturated soil and interface for the experimental study both tend to show that the advective flow rate through the composite liner is greatly influenced by the position of a hole in a geomembrane in relation to the spatial distribution of transmissivities at the composite liner interface. It is also shown that the existence of two fluids in the interface, air and water or leachate for instance, will have an influence on the wetted area.; La plupart des articles relatifs à la quantification des transferts advectifs dans les étanchéités composites traitent de modélisation mathématique et de transmissivité d'interface uniforme. Peu d'articles se sont intéressés à des cas de figure où la transmissivité d'interface est non uniforme, ou bien à des validations expérimentales des équations empiriques ou des solutions analytiques existantes. Par conséquent l'objectif de cet article est de présenter à la fois les résultats d'une étude paramétrique utilisant des solutions analytiques existantes pour le cas d'une transmissivité d'interface non uniforme à l'interface d'une étanchéité composite, et les résultats expérimentaux obtenus sur des planches d'essai de grandes dimensions. Bien que les deux aspects de cette étude soient basés sur des corps d'hypothèses différents (géométrie bidimensionnelle, régime permanent, sol et interface saturés pour l'étude numérique et géométrie axisymétrique, régime transitoire et sol et interface non saturés pour l'expérimentation) tous deux tendent à montrer que les transferts advectifs à travers une étanchéité composite sont grandement influencés par la position d'un défaut dans la géomembrane en relation avec la distribution spatiale de transmissivités dans l'interface de l'étanchéité composite. On montre également que la coexistence d'air et d'eau à l'interface aura une influence sur l'allure de la surface d'infiltration aux échelles de temps considérées.

International audience; A survey was carried out in France from April to June 1999. Temperatures were recorded at three levels (top, middle and bottom) of the refrigerator compartment using a data logger. A questionnaire was filled in, enabling the following information to be obtained: characteristics of the family, characteristics of the refrigerator and the use conditions. One hundred and forty-three domestic refrigerators were surveyed, but due to various technical problems, only 119 sets of recorded temperatures were exploitable. The temperatures of the surveyed refrigerators were: average 6.6 °C, minimum 0.9 °C and maximum 11.4 °C. Statistical analysis such as clustering and segmentation were used. It was found that the heterogeneousness of temperature inside each refrigerator seems to be dependent on the type. This study shows the influence of the use conditions on the temperature. No one factor exerts a single direct effect; a combination of the effects of all factors is observed.; Une enquête a été réalisée en France durant les mois d'Avril et Juin 1999. Des températures ont été enregistrées à trois niveaux (haut, milieu et bas) du compartiment du réfrigérateur en utilisant un enregistreur de températures. A l'aide d'un questionnaire, les informations suivantes ont pu être obtenues : caractéristiques de la famille, caractéristiques du réfrigérateur et conditions d'utilisation. L'enquête a porté sur cent quarante quatre réfrigérateurs ménagers, mais pour divers problèmes techniques, seul 119 fichiers de températures ont pu être exploités. La température moyenne des réfrigérateurs est de 6,6 °C (minimum 0.9 °C et maximum 11.4 °C). Des analyses statistiques telles que l'arbre de classification et de segmentation ont été utilisées. L'étude a montré que l'hétérogénéité de température dans le compartiment d'un réfrigérateur dépend du type de réfrigérateur. L'influence des conditions d'utilisation est mise en évidence. Le niveau de température des réfrigérateurs est le résultat de nombreuses interactions entre les différents paramètres et non d'un seul des paramètres en particulier.

International audience; A laboratory scale aeration treatment system was built to study the fate of nitrogen during aeration of pig slurry. For each run evaluated, the nitrogen mass balance was determined including measurement of the nitrous oxide gas Emissions. Intermittent aeration led to a nitrogen removal about 53% of the total nitrogen content of the raw slurry. About 18% of the total nitrogen content of the raw slurry was emitted as N2O during aeration with an aerobic to anoxic ration equal to 0.625. In contrast, the extension of the anoxic period (aerobic to anoxic ratio = 0.375) allowed complete denitrification and avoided N2O emissions.; Un pilote de laboratoire a été développé pour étudier les transformations de l'azote au cours de l'aération du lisier. Pour chaque essai, un bilan azoté a été effectué incluant la mesure des émissions gazeuses de protoxyde d'azote. L'aération séquentielle a conduit à une élimination d'azote d'environ 53% de l'azote total du lisier brut. Environ 18% de l'azote total du lisier brut était émis sous forme de N2O au cours de l'aération avec un ratio aérobie sur anoxie de 0.625. L'augmentation de la période d'anoxie (ratio aérobie sur anoxie de 0.375) a permis une dénitrification complète sans émission de N2O.

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; This work reports on the use of insulated pallet covers to provide thermal protection for heat-sensitive foodstuffs, in particular during logistic operations carried out in an uncontrolled temperature atmosphere. The effectiveness of these insulating devices in reducing the rate of temperature changes allows the products to be transported in a semitrailer without refrigeration or to be stored temporarily on unrefrigerated docks. Consequently, logistic operations can be managed with more flexibility. To evaluate the performance of the insulating device, temperature rises within covered pallets were investigated numerically and experimentally. The experiments were carried out on an individual pallet and on a whole load. All experiments were performed in a temperature-controlled test room. A three-dimensional (3-D) finite-volume heat transfer model was developed using the computational fluid dynamics (CFD) code Phoenics. The model took into account the thermal characteristics of products and insulating covers, the arrangement of the pallets in the vehicle and the external conditions of ambient temperature and solar exposure. The good agreement obtained between experimental and numerical results shows that the model can be used to estimate the average transportation or storage duration for heat-sensitive products under given ambient conditions.; Le travail porte sur l'utilisation des housses isolantes pour assurer la protection thermique de palettes de produits thermo-sensibles transportés lors d'opérations logistiques effectuées dans des conditions ambiantes à température non maîtrisée. La réduction des remontées en température apportée par les housses permet d'envisager le transport de ces produits dans une semi-remorque bâchée non munie de groupes frigorifiques ainsi que leur stockage provisoire sur des quais non réfrigérés. Afin d'évaluer les performances thermiques des housses, les évolutions de température au sein des palettes protégées ont été caractérisées numériquement et expérimentalement. Les expériences ont été effectuées sur une palette individuelle et sur un chargement de palettes dans des conditions à température maîtrisée. Une approche tridimensionnelle a été élaborée avec la méthode des volumes finis sur le code Phoenics. Le modèle prend en considération les caractéristiques thermophysiques des produits, des housses, la disposition des palettes, les conditions ambiantes et le flux solaire. Un bon accord a été observé entre les données numériques et expérimentales et montre que le modèle peut être utilisé pour estimer les temps de séjour qu'il convient de respecter lors de transport des produits sensibles dans des conditions ambiantes.

The paper deals with the automatic control of a dam-river system, where the action variable is the upstream discharge and the controlled variable the downstream discharge. The system is a cascade of single intput-single output (SISO) systems, and can be considered as a single output-multiple output (SIMO) systel, since there multiple outputs given by intermediate measurement points distributed along the river. A generic robust design synthesis based on internal model controller (IMC) design is developed for internal model based controllers. The robustness is estimated with the use of a bound on multiplicative uncertainty taking into account the model errors, due to the nonlinear dynamics of the system. Simulations are carried out on a nonlinear model of the river., L'article traite de la commande automatique d'un système barrage-rivière, où la variable de commande est le débit amont lâché par le barrage et la variable contrôlée est le débit aval de la rivière. Le système est une cascade de systèmes monovariables (SISO) et peut être considéré comme un système à plusieurs sorties et une seule entrée (SIMO), avec les sorties intermédiaires données par les mesures de débit le long de la rivière. Une méthode générique de synthèse d'un contrôleur robuste est développée pour une architecture à modèle interne. La robustesse est évaluée à l'aide d'une borne sur l'incertitude multiplicative qui prend en compte les erreurs de modèle dues à la dynamique non linéaire du système. Les simulations sont effectuées sur un modèle non linéaire de la rivière.

The conventional analysis of bioassays does not account for biological significance. However, mathematical models do exist that are realistic from a biological point of view and describe toxicokinetics and effects on test organisms of chemical compounds. Here we studied a biology-based model (DEBtox) which provides an estimate of a no-effect concentration (NEC) and we demonstrated the ability of such a model to adapt to different situations. We showed the basic model can be extended to deal with problems usually faced during bioassays like time-varying concentrations or unsuitable choices of initial concentrations. To reach this goal we report experimental data from Daphnia magna exposed to zinc. These data also showed the potential benefit of the model in understanding the influence of food on toxicity. We finally make some recommendations about the choice of initial concentrations and we propose a test with a depuration period to check the relevance and the predictive capacity of the DEBtox model. In our experiments, the model performed well and proved its usefulness as a tool in risk assessment., L'analyse conventionnelle des bioessais ne prend pas en compte la pertinence biologique. Cependant, des modèles biologiques existent, réalistes d'un point de vue biologique, qui décrivent la cinétique et les effets des produits chimiques sur les organismes tests. Nous nous sommes intéressés ici à un modèle à fondement biologique (DEBtox) qui fournit une estimation d'une concentration sans effet (NEC) et nous avons démontré la capacité d'adaption d'un tel modèle. Nous avons ainsi montré que le modèle de base peut être étendu pour traiter des problèmes rencontrés souvent au cours des bioessais comme des variations des concentrations d'exposition ou un mauvais choix des concentrations de départ. Pour cela, nous avons réalisé un test avec des daphnies (Daphnia magna) exposées au zinc. Ces données ont aussi montré l'intérêt du modèle pour comprendre l'influence de la nourriture sur la toxicité. Nous faisons, pour finir, quelques recommendations sur le choix des concentrations d'exposition et nous proposons un test avec une phase de dépuration pour vérifier la pertinence et la capacité prédictive du modèle DEBtox. Au cours de nos expérimentations, le modèle a passé ce test avec succès, démontré son utilité comme outil pour l'analyse du risque.

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.

[Departement_IRSTEA]DS [TR1_IRSTEA]51 - METHODO / MAGESTYC; International audience; We present a model of opinion dynamics in which agents adjust continuous opinions as a result of random binary encounters whenever their difference in opinion is below a given threshold. High thresholds yield convergence of opinions toward an average opinion, whereas low thresholds result in several opinion clusters. The model is further generalized to network interactions, theshold heterogeneity, adaptive thresholds, and binary strings of opinions.; Nous présentons un modèle de dynamique d'opinions dans lequel les agents ajustent des opinions continues suite à des rencontres binaires aléatoires quand la différence d'opinion est en dessous d'un seuil fixé. Des seuils importants conduisent à une convergence des opinions vers une opinion moyenne, alors que des seuils plus faibles résultent en plusieurs clusters d'opinions. Le modèle est ensuite généralisé à des interactions sur réseau, des seuils hétérogènes, des seuils adaptatifs et des chaines binaires d'opinions.

International audience; The impact of forest cover on streamflow has been studied in sub-Mediterranean mountain watersheds using the daily time step conceptual rainfall/runoff model GRHUM. Certain characteristics (pertaining to the soil, vegetation or atmosphere) are used to compute model parameters that describe the behaviour of the various interfaces with respect to water exchange by evapotranspiration. This model enables the simulation of runoff and soil water content evolution. A snow function has been added to the initial version of the model to simulate the hydrological behaviour during the snow melt periods. This model has been applied to the Mont-Lozere experimental watersheds, for which hydro-meteorological data have been available since 1981. A site where a gradual felling of the forest was prescribed between 1987 and 1989 (the Latte watershed) is compared to an unexploited forest site (the Sapine watershed), used as reference. The period covered by the study of the Latte site has been divided into three parts, on the basis of changes in land cover. For both watersheds, the model produced good results over all three periods. It is also possible to identify the role of forests on hydrological behaviour by simulating discharge from the Latte watershed during the felling period using adjusted pre- and post-felling model parameters. This exercise has shown that felling induces a significant increase in high flow rates. A similar approach conducted for the Sapine reference watershed made it possible to evaluate the validity of our model predictions (accurate to within 10% of true values) , the model bias being mostly due to climatic differences between the three simulation periods. Taking into account this model bias, results suggest that felling may increase runoff by 10%.

In the framework of the cooperating research GEWEX-Rhone project, runoff mapping was examined. Two versions of a mesoscale hydrological model were tested and interpolation procedures provide objective basis for comparison between observed and simulated discharge data at regional scale. Specific algorithms based on kriging were developed to map mean annual and monthly streamflows within the French part of the Rhone basin. Mean annual runoff values are calculated involving a spatial disaggregation of the annual volume generated by the area under study. Monthly discharges are deduced from the map of the mean annual runoff and are estimated with respect to the autocorrelation between successive months and the links to the river network., Dans le cadre du projet GEWEX-Rhône de modélisation du fonctionnement hydrologique d'un grand bassin versant, une réflexion sur les méthodes d'interpolation des débits a été engagée. Deux nouvelles méthodes dédiées aux écoulements annuels et mensuels moyens interannuels ont ainsi été développées, répondant au besoin de validation des sorties de deux modèles hydrologiques testés dans ce projet fonctionnant à méso-échelle. La première vise la cartographie des écoulements interannuels par désagrégation spatiale du volume généré par la zone étudiée sur une partition de cette zone ; la seconde concerne les débits mensuels interannuels et exploite les résultats de l'interpolation des débits interannuels pour réaliser une répartition temporelle au pas de temps mensuels en respectant l'autocorrélation entre les termes mensuels successifs et en s'appuyant sur des descripteurs des bassins versants.

International audience; Pyrene biodegradation in a freshwater sediment without fungi supply, or inoculated with two sediment Micromycetes, Mucor racemosus var. sphaerosporus and Phialophora alba was studied after 0, 5, 13, 28, 60 and 90 days. The influence of glucose addition was estimated, and a liquid chromatographic method for simultaneous quantitative determination of residual anthracene, fluoranthene and pyrene in the sediment was developed. Samples with PAHs were extracted in Soxhlet with ethyl acetate, and LC analysis was performed on a 5µm Supelcosil(TM) column (150×4.6mmI.D.) with gradient elution (2 ml min1) of acetonitrile-water and UV detection at 254 nm. Recoveries of anthracene, fluoranthene and pyrene were 90.3%±1.1%,93.2%±0.9% and 90.42%±1.9%, respectively, without interference. The native sediment microorganisms (with or without glucose added) have shown35% pyrene degradation and sediment with glucose inoculated by the strains revealed 40%.; Etude de la dégradation du pyrène par 2 micromycètes en sédiment d'eau douce.

International audience; The one-dimensional pressure head profile above a fixed water-table was studied for different steady infiltration rates. As shown in previous studies, when the infiltration rate (qin) is less than the soil saturated hydraulic conductivity (Ks), this profile can be divided into two parts: (1) from the water-table surface (z0) to an elevation z, the pressure head varies from 0 to a value h such as K(h)=-qin; (2) above the elevation z the pressure head is constant and equal to h. Above the water-table the zone where the pressure head is variable has been called `transition zone'. Its height is shown to be highly variable and to depend on soil properties as well as on the infiltration rate. This transition zone is not the `capillary fringe' as defined by Gillham (Gillham R.W., 1984. The capillary fringe and its effect on water-table response. J. Hydrol. 67, 307-324). Numerical experiments performed with HYDRUS-2D(r) for the case of a water-table drained by parallel ditches have shown that the height of the transition zone is similar in the one-dimensional profile and in the two-dimensional system as long as the local slope of the water-table is small. This result is important since in a two-dimensional system, the transition zone is the place where all the horizontal component of the unsaturated flow occurs. The ratio of the horizontal component of the unsaturated flow vs the total horizontal flow in both the unsaturated and saturated zones has been computed. For a given soil, this ratio decreases as the infiltration rate increases; for a given infiltration rate, the soil with the thinnest transition zone transfers the largest amount of water above the water-table.; Le profil vertical de pression au dessus d'une nappe de niveau fixé a été étudié pour différents régimes d'infiltration. Comme l'ont montré de précédents travaux, quand le taux d'infiltration (qin) est plus faible que la conductivité à saturation (Ks), le profil peut être décomposé en deux parties : (1) entre le toit de la nappe et une côte (z0), la pression varie entre 0 et une valeur h, telle que K(h)=-qin; (2) au dessus de la côte z, la pression est constante et égale à h. Au dessus de la nappe, la zone de pression variable a été appelée "zone de transition". Nous avons montré que l'extension verticale de cette zone est variable et dépend aussi bien des propriétés du sol que du régime d'infiltration. Cette zone de transition n'est pas assimilable à la "frange capillaire" telle que définie par GILLHAM (1984). Des expérimentations numériques réalisées avec HYDRUS 2D dans le cas d'une nappe drainée par des fossés parallèles ont montré que la hauteur de la zone de transition était identique au cas monodimensionnel, tant que la pente de la nappe est faible. Ce résultat est important dans la mesure où dans le système 2D la zone de transition est la zone où peuvent exister des écoulements non saturés à composante horizontale. Le rapport entre cette composante horizontale et le flux horizontal total a été calculé. Pour un sol donné, ce rapport décroît alors que le taux d'infiltration augmente ; pour un taux d'infiltration donné, le sol avec la zone de transition la plus fine transfère le plus d'eau dans la zone non saturée au dessus de la nappe.

International audience; The authors have developed a model of coupled heat and mass transport within porous medium (sheet) saturated with an aqueous solution of initial non-zero solute concentration. The novel contribution of the present work is the resolution of the equations for simultaneous heat and mass flows at one of the interfaces for a wide range of temperatures and concentrations. Good agreement was noted between simulated and experimental data. The results presented also underline the fact that this knowledge model helps to clarify our understanding of the interaction mechanisms between heat and mass transport during the immersion freezing process.; Les auteurs ont développé un model de transport couplant la chaleur et la masse dans un milieu poreux saturé avec une solution aqueuse avec une concentration initiale non égale à zéro en soluté. Les travaux présents apportent une nouvelle résolution des équations pour les écoulements simultanés de chaleur et de masse à un des interfaces pour diverses températures et concentrations. Les données simulées et expérimentales concordent. Les résultats présentés soulignent aussi le fait ce modèle de savoir aide à la compréhension des mécanismes d'interaction entre le transport de chaleur et de masse pendant le processus d'immersion réfrigérante.

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; Nitrate concentrations monitored for 2.5 a in the stream water and groundwater of a small catchment, 86.5% of which is devoted to intensive agriculture, show temporal variations with a maximum during winter (as much as 200 mg l-1 in groundwater and 100 mg l-1 in stream water) and a minimum at the end of summer/beginning of autumn. Variations were also observed in the stream water and shallow groundwater after rainfall. The processes involved to explain these variations, determined mainly from NO3-, Cl-, SO42-, piezometric and streamflow data, are : (a) variability of the relative contributions to stream water and shallow groundwater by upward fluxes of deeper groundwater which, as demonstrated previously, is denitrified mainly as a result of reaction with pyrite (b) Denitrification of shallow groundwater during summer with organic matter acting as the electron donor (c) Dilution by rain water. Nitrate concentrations in both stream water and shallow groundwater depend on the amount precipitation, with an increased contribution from deep denitrified groundwater during dry periods. The temporal variations in NO3- concentration observed several metres below the water table are related to the preferential and rapid movement of NO3- - polluted water through fractures and large fissures, which has been estimated at 1 m day-1. Nitrate pollution in the catchment, because of the interaction with pyrite, also increases the net chemical weathering rate to values exceeding the world average.; Les concentrations en nitrates suivies pendant plus de 2 ans sur des eaux de surface et d'aquifères d'un petit bassin versant (dont 86,5% de la surface est de type agriculture intensive) témoignent de variations saisonnières avec un maximum au cours de l'hiver (au delà de 200 mg.l-1 sur les eaux d'aquifères et 100 mg.l-1 sur les eaux de surface) et un minimum à la fin de l'été/début de l'automne. Les processus évoqués pour expliquer ces variations, issus de données sur les teneurs en NO3-, Cl-, SO42-, sont : (a) variabilité de la contribution relative vers les eaux de surface et les nappes peu profondes de flux ascendants, de nappes profondes qui ont été dénitrifiées via une réaction avec des pyrites (b) dénitrification des eaux de nappes peu profondes au cours de l'été via l'apport de matière organique agissant en tant que donneurs d'électrons, (c) dilution avec eaux de pluie.

Spatial heterogeneity is a characteristic of most natural ecosystems which is difficult to handle analytically, particularly in the absence of knowledge about the exogenous factors responsible for this heterogeneity. While classical methods for analysis of spatial point patterns usually require the hypothesis of homogeneity, we present a practical approach for partitioning heterogeneous vegetation plots into homogeneous subplots in simple cases of heterogeneity without drastically reducing the data. It is based on the detection of endogenous variations of the pattern using local density and second-order local neighbour density functions that allow delineation of irregularly shaped subplots that could be considered as internally homogeneous. Spatial statistics, such as Ripley's K-function adapted to analyse plots of irregular shape, can then be computed for each homogeneous subplots. Two applications to forest ecological field data demonstrate that the method, addressed to ecologists, can avoid misinterpretations of the spatial structure of heterogeneous vegetation stands., L'hétérogénéité spatiale est une caractéristique de la plupart des écosystèmes qu'il est difficile de prendre en compte analytiquement, en particulier lorsque les facteurs exogènes responsables de cette hétérogénéité sont inconnus. Alors que la plupart des méthodes d'analyse de la structure spatiale nécessitent l'hypothèse d'homogénéité, nous présentons un approche pratique pour définir des zones homogènes à l'intérieur d'une placette hétérogène, sans diminuer excessivement les données disponibles, dans des cas simples d'hétérogénéité de la végétation. Le principe de cette approche est de détecter des variations de densité locale ou des fonctions de voisinage à l'intérieur de la placette, afin de délimiter des zones de formes irrégulières qui peuvent être considérées comme homogènes. Des outils d'analyse de la structure spatiale, comme la fonction K(r) de Ripley, une fois adaptés à ces zones de formes irrégulières, peuvent être utilisés dans chaque zone homogène. Nous montrons sur deux exemples d'application, sur des données forestières, comment cette approche permet d'éviter des erreurs d'interprétation de la structure spatiale dans le cas de végétation hétérogène.