The paper introduces the Ecological State Macrophyte Index (ESMI), a method compliant with the Water Framework Directive (2000/60/EC) for assessing the ecological status of lakes based on macrophytes. A description of the elaboration of macrophyte metrics, relevant reference conditions and a classification system for two types of high-alkalinity lowland lakes (stratified and polymictic), and a customised field survey procedure based on belt transects are presented. The ESMI evaluates two aspects of macrophyte community: taxonomic composition (index of evenness J) and abundance (colonisation index Z), which are combined into one multimetric. ESMI values range from 0 to 1, where 1 denotes pristine conditions and 0, highly degraded habitats. The high/good class boundary (H/G) was set at the first quartile of ESMI values of reference lakes. For the other classes, boundaries were set by dividing the range of ESMI values between the H/G boundary and the minimum value recorded in the dataset in a logarithmic scale into four. The ESMI correlated best with water transparency (Pearson’s R = 0.62 in stratified lakes and 0.79 in polymictic ones), whereas the correlations with phosphorus and nitrogen concentrations were somewhat weaker (R = −0.48 to −0.57). Based on the results of international intercalibration, the original class boundaries were modified (merged for stratified and polymictic lakes, the good/moderate boundary tightened to approximately 20 %), to make ESMI-based assessment results comparable with the outcomes of other European methods.Electronic supplementary materialThe online version of this article (doi:10.1007/s10661-014-3799-1) contains supplementary material, which is available to authorized users.

Key-words: macrophytes, lakes, rivers, plant ecology, ecological assessmentWe analysed macrophyte species composition and abundance, water chemistry and hydromorphological parameters of all major river stretches and lakes in the catchment of the lowland river Wel, Poland. We studied (i) which hydromorphological and physico-chemical factors best explained macrophyte species composition, (ii) if environmental factors structuring macrophyte communities were different between rivers and lakes; and (iii) if macrophyte indices developed to indicate eutrophication correlated with nutrient concentrations. Based on two-way indicator species analysis, correlation analysis and canonical correspondence analysis, we found that river substrate was most important in structuring macrophyte species composition and abundance in rivers, while water quality parameters were most important in lakes; species richness and diversity were correlated with river size and substrate type in rivers, but not in lakes; the relative abundance of macrophyte growth forms was best explained by total organic carbon and Secchi depth in lakes, but it was not correlated with any of the water chemical or hydromorphological parameters in rivers. Irrespective of which factors best explained macrophyte community composition, macrophyte metrics developed to indicate ecological status responded most strongly to total phosphorus concentrations, both in rivers and lakes. We conclude that macrophyte metrics are valuable tools for ecological status assessment also in ecosystems where parameters other than nutrients shape macrophyte community composition. RÉSUMÉParamètres structurant les communautés de macrophytes dans les rivières et les lacsrésultats d'une étude de cas dans le Centre-Nord de la Pologne Mots-clés :macrophytes, lacs, rivières, Nous avons analysé la composition spécifique et l'abondance de macrophytes, la chimie de l'eau et les paramètres hydromorphologiques de tous les principaux tronçons des rivières et les lacs du bassin versant de la rivière de plaine Wel, en Pologne. Nous avons étudié, (i) les facteurs hydromorphologiques et physicochimiques qui expliquent le mieux la composition des espèces de macrophytes, (ii) si les facteurs environnementaux structurant les communautés de macrophytes étaient différents entre les rivières et les lacs, et (iii) si les indices macrophytiques développés pour indiquer l'eutrophisation sont corrélés avec les concentrations de nutriments. Basée sur l'analyse des espèces indicatrices, l'analyse de corrélation et l'analyse de correspondance canonique, nous avons trouvé que le substrat de la rivière était plus important dans la structuration de la composition des espèces de macrophytes et leur abondance dans les rivières, tandis que les paramètres de qualité de l'eau étaient les plus importants dans les lacs ; la richesse en espèces et la diversité sont corrélées avec la taille de la rivière et le type de substrat dans les rivières, mais pas dans les lacs ; l'abondance relative des formes de croissance de m...

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