Abstract
SUMMARY1. In Lake Geneva (Switzerland), total phosphorus concentrations have decreased from 90 mg m−3 in 1979 to 55 mg m−3 in 1990.2. To assess the effects of this improvement, tubificid and lumbriculid communities were sampled in 1982 and in 1991 in the same areas, at a depth of 40 m.3. Abundance of mesotrophic species (mostly Potamothrix vejdovskyi) and of eutrophic species (mostly Potamothrix hammoniensis) was lower in 1991 than in 1982; in contrast, oligotrophic species (mostly Peloscolex velutinus) were more abundant in 1991 than in 1982.4. The changes recorded in 1991 were the same as those associated with a decrease of organic sedimentation.5. Mean relative abundance of oligotrophic species increased from 17% in 1982 to 41% in 1991. According to these values, Lake Geneva was mesoeutrophic in 1982, but mesotrophic in 1991.
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