INVERTEBRATE COMMUNITY RESPONSES TO PHYSICAL AND CHEMICAL FACTORS AT THE RIVER AQUIFER INTERACTION ZONE .2. DOWNSTREAM FROM THE CITY OF LYON

Invertebrates were surveyed during November 1994 in the interstitial c ompartment (at depths of -15 and -50 cm) of six sites mainly downstrea m from the city of Lyon, along a 197km stretch of the Rhone River. Var ious physical and chemical factors (main factors and metals) were meas ured in an attempt to assess their importance in determining the struc ture of invertebrate communities and the distribution of species. The analysis revealed that the structure of these communities was related to some of the factors such as oxygen, pH and some metals (especially Fe, Ni and Cr). Contaminated sites had relatively low taxonomic richne ss and low diversity indices and the invertebrate assemblages differed from those observed at less metal-enriched sites (especially at a dep th of -15 cm). Moreover, some taxa among oligochaetes, insects and cru staceans can be defined as metal-tolerant as they were associated with sites containing sediments with high concentrations of one or more me tals. The present study and the previous one performed upstream from L yon provide a constructive basis for discussing the impact of metals o n interstitial invertebrate communities and the use of these communiti es as tools for monitoring the impact of metals on groundwater systems .