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

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The distribution of Characeae vegetation from the Pays-de-la-Loire region was studied in ponds and standing waters (e.g. gravel pits, quarries, oxbows) in relation to water quality, other existing algae or macrophyte competition, and human activities. The potential of using stoneworts to characterise the type of biotope is presented and stoneworts show some possibility for use as general bioindicators of trophic quality in ponds and other still waters.

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Les relations spatiales et les évolutions entre les groupements végétaux d'un étang soumis à de fortes variations de niveau ont été étudiées par des croisements manuels des relevés et par Analyse Factorielle des Correspondances. Les résultats des deux ap-, proches concordent partiellement. Deux schémas évolutifs distincts sont mis en évidence, dans la zone principale et dans la queue d'étang. De fortes disparités apparaissent en fonction d'une part, de la morphologie des rives et, d'autre part, des variations interannuelles des niveaux d'eau. Des recommandations pour une gestion patrimoniale sont présentées. Spatio-temporal variability of plant communities from a pond Anjou (France)Keywords : pond, macrophyte, Maine-et-Loire, Factorial Correspondence Analysis, Hierarchical Cluster Analysis, dynamics.Spatial relationships and development in plant communities from a pond subjected to marked water level variations have been studied, using manual crossings of relevés and Factorial Correspondence Analysis. The results of these two approaches agree partially. Two distinct development schemes are presented, in the main area and in the tail-end of the pond. Large disparities appear related to the shape of the shores and to the interannual variations of water level. Advices for a natural heritage approach to management are proposed.