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National audience; L’étude de la faune aquatique vivant dans les systèmes karstiques proches des gorges de la Cèze a été menée dans deux habitats (6 cavités et 4 sources) en complément de celle de la faune hyporhéique de la rivière (faune vivant dans les interstices des sédiments du lit). La faune du karst s’est révélée peu diversifiée, mais sans doute sous-évaluée. Sa distribution spatiale est fortement hétérogène, aussi bien entre cavités qu’entre habitats (cavités versus sources) ou entre micro-habitats au sein d’une même cavité. À l’échelle du micro-habitat, les zones riches en argile sont les plus peuplées, sans doute parce que l’argile représente à la fois un lieu de vie pour les organismes fouisseurs et une ressource alimentaire. Les échanges faunistiques entre les cavités et les sources sont faibles et seules quelques espèces karstiques dérivent vers le milieu hyporhéique de la rivière. Ces dernières peuvent nous renseigner sur l’origine de l’eau interstitielle et ainsi guider certains choix de gestion.

International audience

International audience

International audience; Managing groundwater for a given territory from a quantitative standpoint should be based on a precise estimation of the available resource. Quantifying groundwater resource is necessary in order to see if it can supply the water demand of the territory dependent on it. For some systems, such as karstic aquifers, the resource estimation can represent a huge challenge due to the limited knowledge in terms of geometry and structure. One way to provide water managers with an operational assessment method is to estimate the renewable water resource corresponding to the recharge by precipitation. While such approach may, in some cases, under-estimate the actual renewable resource (for example by neglecting river flows infiltration), it allows comparing situations of contrasted systems and assessing the impact of future climate on groundwater resources availability, in a broad context of a higher water scarcity. A multi-method recharge estimation tool, combining several analytical recharge estimation methods based on climate data, discharges or piezometric levels depending on the method, has been built and applied to four contrasted karstic aquifers in France. These aquifers are: Fontaine de Vaucluse, Loue-Lison, Gillardes and Lez karstic systems subjected to variable climatic and pumping conditions. This study presents a comparative assessment of the results and discusses the issues of uncertainty linked to the estimation method and usefulness of the proposed tool.

International audience; Karst systems constitute aquifers in which infiltration and groundwater flows are generally complex processes and are characterized by limited knowledge in terms of geometry and structure. Nonetheless, they often represent interesting groundwater resources, some of them being subjected to intensive exploitation and others non exploited due to their poor understanding. In the future, it is likely that climate change impact on water resources will increase the interest for such a kind of aquifers due to their strong infiltration and storage capacity, in a broad context of higher water scarcity.The Lez and the Lison karst systems in Southern and Eastern France, respectively, provide 2 examples of such systems of several km² under two contrasted climate conditions, the first one being heavily exploited. This study presents a comparative climate change assessment onboth karst systems. Nine climate scenarios corresponding to the Fourth assessment report of the IPCC (SRES A1B scenario), downscaled using weather-type methods by the CERFACS, have been applied to various recharge modelling approaches, as standard analytical solutions of recharge estimation and soil-water balance models. Results are compared and discussed in order to assess the influence on climate change impacts of i) the climate conditions(geographic location), ii) the groundwater exploitation and iii) the modelling approach.