Reversal of eutrophication in four Swiss lakes: Evidence from oligochaete communities

Following the Limitation of phosphorus inputs, total phosphorus concentrations decreased substantially between 1980 and 1990 in four lakes of western Switzerland. Tubificid and lumbriculid communities of Lakes Geneva and Neuchatel responded clearly to this decrease. Indeed, mean relative abundance of species typical of oligotrophic conditions (mostly Stylodrilus heringianus and Spirosperma velutinus) doubled in oligochaete communities of both these deep lakes (> 40 m). These changes indicated that both lakes were meso-eutrophic around 1980, but mesotrophic since 1990. In contrast, oligochaete communities of Lakes Morat and Joux, which consisted mostly of tolerant species (Tubifex: tubifex, Potamothrix hammoniensis, and Limnodrilus hoffmeisteri), did not indicate an improvement of environmental conditions between 1980 and 1990. In Lake Joux the ratio of chironomid to oligochaete biomass was a more simple indicator of change than the species present in oligochaete communities.