To characterise different abandoned river channels, a simple index of the surface sediment was developed i.e. the content of organic matter (expressed as C x N ) plotted in relation to that of CaCO,. The age of the channels studied ranges from 20 to 300 years. Some of them still contain water; others are silted up. Two types are distinguished. The ecosystems of the first one are closed and show a slow rate of development governed by autogenous processes. Those of the second type are more open and show a fast rate of development mainly controlled by allogenous processes. These distinctions are used in a diagrammatic model of the dynamics of Rh8ne River alluvial plain to be used in fundamental or applied future research.

SUMMARY1. Aquatic oligochaetes appear to be pre-adapted to live in the subterranean environment. However, in the absence of genuine troglomorphic characters, the stygobiotic status of groundwater oligochaetes can currently be inferred only from their exclusive presence in the subterranean environment. 2. Aquatic oligochaetes constitute a diverse and mostly endemic fauna. Of the more than 100 species currently considered to be stygobionts, 60% are known only from their type locality. In the Rhône-Alpes region of France, about 93% of samples taken from caves and galleries were found to contain oligochaetes of which 13 species are classified as stygobionts. 3. Oligochaete biodiversity in aquatic subterranean environments probably originated by both preservation of relict forms and speciation in situ, possibly followed by radiations favoured by heterogeneous and fragmented habitats. Close phylogenetic affinities between some tubificid species from continental waters and the deep sea suggest a marine origin of part of the subterranean oligochaetes. 4. Oligochaetes are well known to promote bioturbation in surface habitats. Similar information on subterranean oligochaetes is scarce, but some evidence suggests notable bioturbation activity also of hypogean species, and they may also play other ecological roles (e.g. as prey and consumers) where present in high densities. 5. Valuable studies to enhance knowledge of subterranean aquatic oligochaetes include continued exploration of a variety of groundwater habitats, phylogeographic surveys that take advantage of molecular methods, analyses of species traits of both stygobiotic and epigean oligochaetes in subterranean environments, and laboratory studies to describe life histories and resolve other aspects of oligochaete biology and ecology.

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1. This paper summarizes twenty years of ecological research on aquatic oligochaetes of the Upper Rhone River and its alluvial floodplain (France). Species traits of fifty species of the ninety taxa recorded from two areas Qons and Brdgnier-Cordon) were used to examine the relationships among species traits, habitat utilization of these species, whether a relationship exists between species traits and habitat utilization, and the applicability of predictions from the river habitat templet and the patch dynamics concept in the framework of spatial and temporal habitat variability. We used fourteen habitat types and sixteen species traits in this analysis. 2. When examined by correspondence analysis, species traits separate the Naididae (with a higher potential for reproduction, small size, high mobility, and opportunistic diet) from all other families. 3. Habitat utilization by oligochaetes demonstrates two gradients: a vertical gradient that arranges species by their affinity for interstitial habitats (stygophily) and a transversal gradient that arranges them by their affinity for main channel habitats (rheophily). 4. No significant relationship was found between species traits and habitat utilization in a co-inertia analysis. 5. Trends observed for species traits within the framework of spatial-temporal habitat variability show only minor agreement with predictions of the river habitat templet. 6. Species richness is generally higher in superficial and interstitial habitats that are permanently connected with the main channel, and peaks in the superficial parapotamons (backwaters that are permanently connected with the main channel) characterized by intermediate levels of spatial as well as temporal variability; this pattern only partially fits with predictions of the patch dynamics concept.