AIM: The Taquari River, a tributary of Guaíba Lake, is a major economic and environmental source for Rio Grande do Sul, a state located in the far south of Brazil; METHODS: This study evaluated the interference of sediment from this river in the reproduction and survival of 320 microcrustaceans (80 organisms per site) of the Daphnia magna species. Four sites between the middle course and the river mouth were monitored using eight samples from each site, between June/06 and April/10. Mortality higher than 20% suggested the acute action of the sample on the daphniids, while low reproduction indicated the presence of chronic toxicity. Sometimes an effect on survival was noted, but the number of individuals generated was always low. Semi-static chronic assays (21 day) were developed in 50 mL beakers using sediment and M4 culture medium at a ratio of 1:4 (v:v). Each beakers received a microcrustacean born from lots presenting LC50-24 hours = 0.98 mg K2Cr2O7 ± 0.04 mg totaling ten replicas per sample. The assays were developed under controlled light (16 hours light/day) and temperature (20 ºC ± 2 ºC) conditions; RESULTS: Duncan test showed a variation in reproduction (p < 0.05) with the presence of chronic toxicity. There was less reproductive activity in 91% of the samples, while for survival the reduction attained 9%. Spearman correlation identified the dependence between the rainfall index and reproduction in one of the samples and was absent when the rainfall index was compared to survival; CONCLUSIONS: Taquari River presented episodes of toxicity, and it is necessary to continue studies in the area and to inspect local sources of pollution, as already has been done. Chronic bioassays should be maintained when the purpose is to evaluate environmental quality, since reproduction proved more sensitive than survival.
bioassays; reproduction; survival; cladocerans; sediments
