LIMNOLOGICAL FEATURES OF DIFFERENT ACIDIC DRINKING-WATER RESERVOIRS IN THE ERZGEBIRGE (GERMANY)

The biological and chemical investigations of three drinking water res ervoirs differing in their acidic and trophic conditions (neutral/meso -eutrophic; circumneutral/oligotrophic; acid/oligomesotrophic) and of some of their tributaries in the Erzgebirge (Germany) are presented. I t is shown that the chemistry of acidic waters is very different from circumneutral ones, particularly with respect to hardness, acid neutra lizing capacity; pH and aluminium. As acidity in running and stagnant waters increases, the filtrable aluminium concentration also rises. A consequence of the changed chemical and biological conditions and thei r direct and indirect effects on the organisms is an overall decrease in the number of species (despite the fact that also some species newl y appear in the acidified waters). Furthermore, a loss of food web com plexity is observed and the trophic structure changes, e.g. fish have disappeared and invertebrate predators have become more numerous. In t he acidic reservoir, species well adapted to waters low in pH and hard ness (e.g. Synura sphagnicola) are more abundant and commonly benthic animals (e.g. Chydorus sphaericus) are able to extend their habitat to the open waters.