CHANGES AND INTERACTIONS IN THE PELAGIC COMMUNITY IN ACIDIFIED LAKES IN SWEDEN

The pelagial communities of lakes undergo dramatic changes during the course of acidification and all major groups of organisms; algae, roti fers and crustaceans showing a reduction in number of species. Calanoi d copepods, Eudiaptomus gracilis in particular, increase in relative i mportance, cladocerans become less important, and daphnids are lost. T he decrease in diversity in the plankton community is more apparent in clear-water lakes than in humic lakes. Invertebrate zooplanktivores, especially, increase in importance after the loss of fish species. The increase in concentration of hydrogen ion and metals have had a direc t impact on reproduction and survival of both algae and invertebrates. Indirect effects contributing to reduced diversity are altered specie s structure via predatory and competitive changes, and impact on pathw ays and rates for nutrient cycling.