IMPACT OF HEAVY-METALS ON BENTHIC OLIGOCHAETE COMMUNITIES IN THE RIVER ILL AND ITS TRIBUTARIES

The aim of this research is to describe the impact of heavy metals contaminating sediments on oligochaete communities Sediments were collected three times (June, August, October 1991) for chemical and biological analyses in 15 sites situated in the river Ill and its tributaries (Rhine Basin, France). The sediments are characterized by high contents of heavy metals, mainly Hg, Cu, Cr, Pb, Zn from below the city of Mulhouse. The majority of sediments are heavily loaded with organic matter and organic micropollutants are also present Oligochaete communities are rich in species. However five species only, considered as pollution-tolerant or opportunist, are significantly present and abundant. The percentages of Tubificidae without hair setae are positively related to heavy metal contents of the sediments, and the percentages of Tubificidae with hair setae are negatively related. Several species such as N. communis, N. barbata, D. digitata and Bothrioneurum sp. are considered as tolerant to heavy metals; on the contrary L. claparedeanus, L. udekemianus, Stylodrilus sp. and S. josinae are considered as intolerant. The reproductive strategy of oligochaetes in contaminated areas and the role of organic matter are discussed. Several recommendations are given for the rehabilitation of the investigated sites.