AN IMPROVED INDEX OF ENVIRONMENTAL-QUALITY FOR SWISS RIVERS BASED ON BENTHIC INVERTEBRATES

A total of 1424 samples of benthic invertebrates, collected in 56 rive rs of western Switzerland (canton of Vaud), was used to improve the RI VAUD (Rivers of Vaud) index of environmental quality. This index, desc ribed for the first time in 1989, was based on total number of taxa an d on number of taxa intolerant of pollution (Plecoptera, Heptageniidae , and Trichoptera with a case). The 1995 version of RIVAUD, called RIV AUD 95, presented a larger range of values (0-20) than the previous on e (0-10), to describe more precisely the variations of environmental q uality. According to RIVAUD 95, the environmental quality of Swiss riv ers increased with the altitude of sampling sites because anthropogeni c impacts decreased along the same gradient. This altitudinal pattern was used to define classes of environmental quality which can be adapt ed to the rivers of other regions.