The effects of chromium in a zooplanktonic community of freshwater

The effects of chromium in the zooplankton structure, was evaluated using experimental tanks of 150 liters, during 5 weeks, in a control and 4 treatments (2 discharges of 0.1, 0.4, 0.7) and 1.0 mg.l super(-1) K sub(2)Cr sub(2)O sub(7), all replicated. Diversity, species richness, zooplankton density were evaluated with repeated measures of ANOVA. Temperature, pH, conductivity, dissolved oxygen, total Cr and Cr (VI) were also measured. Cr had an important negative effect on zooplankton. Density, species richness and diversity diminished significatively with the increment in Cr concentration. Community recovery was only possible in the tank with the lowest Cr concentration. The adaptative advantages of organisms with sexual reproduction, the possible action of Cr via ingestion and its effect on the community sizes structure are discussed. The relevance of research on the effects of low levels of Cr on assemblages of stressed ecosystems is pointed out.