In running water, the main natural factor of disturbance is hydraulic. Investigation of its biological impact is currently complicated by the increase of anthropogenic disturbances which tend to mask the natural functioning of rivers. Monitoring of the impacts of the artificial alterations undergone by the Middle Rhone River for some decades took place in the mid-1980s. Discharge and temperature could constitute the major events controlling the biological dynamics in terms of variations in species richness, diversity, and abundance. The between-years changes of the structure and diversity of macroinvertebrate communities were connected with the amplitude of discharge fluctuations. This was in accordance with the disturbance-diversity concept and it seems to confirm the intermediate disturbance hypothesis. The fish community mainly depended on hydroclimatic factors that influenced breeding success. Variations in nutrient input played a secondary role in controlling changes in some communities (particularly the periphyton). Therefore it appears that the study of long-term changes in river systems, including the dynamics of their biological communities, requires continuous observations and data collection that only medium- to long-term studies can provide, implying the setting up of ecological monitoring centres for the natural environment such as the Long Term Ecological Research (LTER) sites in United.

1. The importance of microhabitat characteristics for macroinvertebrate microdistribution was studied within a reach of themain channel of the Upper Rhône River (France). 9 locations (3 on the left hand side, 3 across the middle, and 3 on the righthand side) were sampled twice on two dates (as duplicates in June and July 1982). From 19 variables, including substratum andhydraulic parameters, 14 were selected to describe the physical habitat of each location. 47 macroinvertebrate species were collectedby means of dredging with a modified Rallier du Baty dredge. The habitat-fauna co-structure was studied using co-inertiaanalysis.2. The river reach was transversally asymmetrical : shallow on one side (up to 2.80 m) with coarse sediments rich in periphyton,and much deeper on the other side (up to 4.80 m) with a gravel bottom rich in organic particles. In the middle of thechannel these conditions were intermediate, but the current was stronger. Velocity and the other hydraulic parameters variedindependently of the substratum characteristics. This independence is a consequence of old man-made impoundments (inheritedstructures) and perhaps of present paving of the substratum also.3. The macroinvertebrate fauna was closely linked to this transverse asymmetry of the reach, with the highest richness andabundance to the shallow side of the channel and the lowest species richness in the rapid central part. The most significant faunisticdifferences were linked i) to water depth, acting on both hydraulic parameters and periphyton (by light transmission), ii)to the inherited old bottom substratum, and iii) to a lesser extent, to the present current velocity.

Le site de l'Ile du Grand Gravier constitue un champ captant pour l'alimentation en eau potable de 80 000 équivalent-habitants. Sa situation dans le fleuve Rhône, à l'aval immédiat de l'agglomération lyonnaise et du couloir de la chimie, pose le problème de la vulnérabilité de la ressource en eau à une pollution du fleuve. Le site a fait l'objet de recherches hydrauliques et biologiques au niveau d'une parcelle expérimentale.L'étude des oligochètes a permis de dresser le diagnostic d'un état de pollution important du fleuve sur le secteur envisagé. Il apparaît de plus que certains taxons d'oligochètes, en particulier le genre Phallodrilus, décrivent une augmentation des échanges nappe-cours d'eau.L'ensemble de ces données souligne la vulnérabilité du site à une pollution transitant par le Rhône.Les résultats de cette première approche sont discutés. Il s'avère notamment que les aspects saisonniers n'ont pas été pris en considération. Le développement de la méthodologie est envisagé par l'étude complète de plusieurs autres parcelles.

One new species of the family Niphargidae (Amphipoda, Gammaridea), Niphargus renei n. sp. is described from the subterranean waters of Rhône river near Lyon, France. This species is closely allied to the Niphargus orcinus - group of species.