TOLERANCE INDUCTION AND SUCCESSION IN MICROALGAE COMMUNITIES EXPOSED TO COPPER AND ATRAZINE

A major need in ecotoxicology is the development of sensitive and robust ecotoxicological methods to detect the effects of toxic substances in complex aquatic ecosystems. In this study, we investigated how copper and atrazine affect the tolerance of microalgal communities and the succession of species. The effects of atrazine and copper on microalgal communities in large freshwater enclosures were investigated for a 20-day period. The community's tolerance of copper and atrazine was determined by short-term photosynthesis tests. Species composition was evaluated using a similarity index and multivariant analysis. In enclosures exposed to copper, tolerance gradually increased during the experiment. In the enclosures exposed to the highest copper concentration (0.24 mu M), an increased tolerance of copper was found in phytoplankton communities even after 2 days, and in the enclosure exposed to the lowest copper concentration (0.016 mu M), increased tolerance was found after 12 days. In accordance with the PICT (pollution-induced community tolerance) concept, the added copper was sufficient to affect the phytoplankton community, as was confirmed by changes in species composition. Communities exposed to increased copper concentrations also showed increased tolerance for zinc, indicating common tolerance mechanisms for copper and zinc. The effects of atrazine in the enclosures were small and did not induce changes in community tolerance for atrazine or diuron, although the same concentration was high enough to reduce photosynthesis activity by 20% in the short-term test and cause minor changes in species composition. Tolerance levels in phytoplankton and periphyton communities were compared. Neither copper nor atrazine induced changes in the tolerance of the periphyton communities. The short-term EC(50) values for atrazine were very similar in periphyton and phytoplankton communities, but for copper, EC(50) values for periphyton were about ten times higher than for phytoplankton.