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Ecological qualité assessment of lakes based on marcrohytes communities: firts results of the development of a french index in the context of the water framework directive WFD)

Evaluation de la qualité écologique des plans d'eau à l'aide des communautés de macrophytes : premiers résultats du développement d'un indice de bioindication «Macrophytes en plans d'eau» dans le contexte de la Directive Cadre Européenne sur l'Eau (DCE) en métropole

Abstract : Aquatic macrophytes are part of the biological quality elements selected by the WFD for the ecological quality assessment of about 260 lakes and ponds in France. After having developed a standardized sampling protocol and database tools as preliminary steps for routine application by several French operators, our team is now in charge of the development of a macrophyte-based index for lakes. Descriptive metrics proposed by other European member states were tested and didn't give satisfying results. Indeed, the adaptation of these metrics to the French context as well as problems in defining reference conditions and ecological profiles of macrophytes taxa were the main limits for the use of these indices in France. In the meantime, we adapted the French Macrophytes Index for Rivers (IBMR) to lakes and ponds, leading to more relevant results. This index constitutes a good basis for the proposal of a functional index for lakes. Different metrics were developed from standardized data collected at national scale as relative proportion of helophytes and hydrophytes, maximum colonization depth or the abundances of type specific taxa. Here we present the main results of these metrics and the improvement of indicative values of contributory taxa, aimed to a better monitoring of the trophic pression and the hydromorphology changes.