Samples of aquatic macroinvertebrates were taken from abandoned beds of the river RhBne in the Brkgnier-Cordon area. This sector of the French Upper Rh6ne is particularly rich in old beds or'l6nes' which vary in age and morphological type and have more or less direct connections with the river.Samples were collected using a hand net in eight different '16nes'. The results concerned five groups of fauna: Mollusca, Crustacea, Ephemeroptera, Coleoptera, Trichoptera. The study revealed a wide range of fauna, and the fact that group of taxa can be used to describe types of Wnes' defined by morphological and hydrological characteristics. This kind of research adds to our understanding of how such aquatic ecosystems evolve, and may be applied in a more general way to other important river systems.

The study examines the relationship between floodplain aquatic macroinvertebrates and sector-scale parameters such as geomorphology and history of regulation. The assemblages of six groups of invertebrates (Molluscs, Crustaceans, Ephemeroptera, Odonata, Trichoptera, and Coleoptera) were compared in various types of former channels from two contrasting but adjacent floodplain sectors: (1) the Jons sector of the RhBne River where successive meandering and braiding phases has left diversified fluvial forms in the landscape but where the main river is now embanked, and (2) the unregulated Ain River sector where the river is still actively meandering, although this process is being slowed by incision. The results demonstrate little difference in faunal composition between the two sectors but a significant difference in faunal structure. In the Rhbne floodplain, there was a clear distinction between the faunal assemblages together with a high taxa richness at the scale of the sector (dominance of the beta diversity). In the Ain floodplain, the faunal assemblages were overlapping and the taxa richness was high at the sample scale (alpha diversity). Sector-scale spatial patterns of the faunal assemblages along former channels were also distinct: between-channel heterogeneity dominated in the Rhbne, whereas within-channel heterogeneity dominated on the Ain. These results stress the influence of geomorphological and historical determinants on the floodplain communities and, conversely, the relevance of macroinvertebrate assemblages for the assessment, at the landscape scale, of aquatic systems within the floodplains.

Structure and functioning manner of the ecosystems in the upper French Rhdne. VII. The hydrographic complex of the 'L6ne des P~cheurs" a former bed of the Rh~neThe hydrological analysis of one of the old meanders of the french upper Rh6ne, called the 'L6ne des PScheurs', is carried out from September 1976 to November 1977. The principal components analysis of the physico-chemical characteristics of the water shows an ecological tripartition along the longitudinal axe of the '16ne', according to the mixing processus of two types of waters, the one influenced by the lateral underflow, the other flowing in from the Rh6ne, and related with the overflow. Partitional analogies are also noted between the structure of phytoplanctonic community and the hydrological environment.

This paper deals with the results of an extensive sampling of eight former channels of the Rhǒne and eight of its tributary, the Ain River, France, designed to assess the value of molluscs as ‚describers’ of ecosystem dynamics. The sampling was stratified on the distribution of aquatic macrophytes. The distribution of molluscs species is shown to provide information on the rate of eutrophication, the groundwater supply and the succession of the abandonned river channels toward semi-aquatic and terrestrial conditions. Molluscs, together with other macroinvertebrates, not only describe the present stage of these ecosystems but also provide some predictive information on their successional pattern for assistance in the management of the alluvial plain