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 longitudinal changes of richness and composition of aquatic plants have been studied from headwaters to the fifth stream order in three rivers in western Brittany (France), the Orne, Sélune and Rance. All rivers are regulated by dams along their lower reaches. The total macrophyte richness differed between the rivers (61 to 150 taxa); it was lowest in the Sélune, which flows over a granite substratum throughout its basin. Absolute richness per site varied greatly between rivers, and between groups of sites either upstream or downstream of the dams, though consistently higher values were observed downstream. In contrast, the relative richness at the river basin scale was similar for the group of upstream (average 20 taxa) and downstream sites (average 28) of all rivers. At the site level, richness increased along all there rivers. Several sites below the dams had the highest richness per site, with more than 40 taxa. A shifting evolution of the macrophyte richness was revealed along the river axis, related to habitat heterogeneity and geological changes.Of the 27 abiotic variables initially considered for canonical correspondence analysis, only five to six per river were retained by a forward selection procedure. The eigenvalues of the first two canonical axes explained 16.1 to 22.4% of the total biological variability and 53.9 to 67.7% of the species-environment relationships. The macrophyte distribution was mainly determined by the stream hierarchy, expressed by the distance to source and slope, and showed also the influence of regulation, i.e. the position of the site in relation to the dam. Other physical variables significantly contributed to plant distribution, namely particular habitat types, depth and geological substratum. Nutrient enrichment and organic pollution influences were the main secondary gradients for the Orne and Rance rivers.

Key-words:remote sensing, riparian vegetation, UAV, LiDAR, radar Riparian vegetation restoration projects require appropriate tools to monitor actions efficiency. On a large scale remote sensing approaches can provide continuous and detailed data to describe riparian vegetation. In this paper, we illustrated recent developments and perspectives for riparian vegetation monitoring purposes through three examples of image sources: Light Detection And Ranging (LiDAR), radar and Unmanned Aerial Vehicule (UAV) images. We notably focused on the potential of such images to provide 3D information for narrow strips of riparian vegetation with high temporal resolution to allow fine monitoring following restoration program. LiDAR data allows canopy structure identification with a high accuracy level and automatic classifications for heterogeneous riparian corridors. Radar images allow a good identification of riparian vegetation but also of the structure and phenology of vegetation through time with an analysis of the Shannon entropy of the signal. The UAV system used here is a very flexible approach that can easily provide RGB mosaic but also a local digital surface model with very high spatial resolution. Lastly, we discuss the advantages and limitations of each approach from an applied perspective, in terms of flexibility, resolution and technicality. RÉSUMÉSuivre la restauration de la végétation riveraine : comment les développements récents de la télédétection peuvent-ils aider ? Mots-clés : télédétection, végétation riveraine, UAV, LiDAR, radarLe suivi des projets de restauration de la ripisylve nécessite des outils spécifiques. Dans cet article, nous illustrons et discutons comment les développements ré-cents dans le domaine de la télédétection permettent une description détaillée, continue et à large échelle des ripisylves restaurées à partir de trois exemples d'images : laser (LiDAR), radar et drone. Nous analysons notamment la capacité et le potentiel de ces images à fournir une information volumétrique de ripisylves étroites avec une forte résolution temporelle afin de permettre un suivi fin des actions de restauration. Les données LiDAR permettent une description de la structure de la canopée avec une très bonne précision ainsi qu'une classification automatique des ripisylves hétérogènes. Les images radar permettent une bonne identification non seulement de la végétation riveraine mais aussi de sa structure et de sa phénologie par analyse de l'entropie du signal. La technologie drone dé-ployée ici est très flexible et facile à mettre en oeuvre ; elle donne accès à des mosaïques de photographie à très haute résolution spatiale et à faible résolution