Influências da eutrofização e das variáveis climatológicas sobe a mortandade de peixes e a composição e abundância da comunidade zooplanctônica no reservatório de Furnas e experimentos de toxicidade com Ceriodaphnia silvestrii (Cladocera: Daphnidae)

Abstract

Anthropic activities always impact nature and natural resources. On hydric resources, the burden is seen on the prevalence of eutrophication processes, of fish die-offs, of toxicity of waters and depletion of aquatic species. This work aimed at tackling the effect of eutrophication, sewage disposal and fish production on zooplankton community and to correlate physical and chemical with biological aspects factoring in two episodes of fish die-off. On the analysis of the zooplankton community found on 2 fish die-off events, the prevalence of Rotifera organisms and the presence of Cyclopoida such as Thermocyclops decipiens attest to the previously deteriorated water quality, in where a worsening event, dropping the dissolved oxygen, led to the fish die-off. This work also aimed at analyzing the effects of compounds commonly found in aquatic systems, through sewage disposal and through lixiviation, studying the acute and chronic toxicity of 3 compounds – cloprostenol, 17α-ethynilestradiol and estrone – on reproduction, survival and filtering behavior aspects of a well-known water pollution indicator, Ceriodaphnia silvestrii. EC50 (48 hours) acute toxicity test for cloprostenol, using the concentrations 0; 0.25; 0.5; 1.0; 2.0 and 4.0 mg.L-1, was 0.41 ± 0.08 mg.L -1 , and EC50 for the chronic test, with the concentrations 0; 0.2; 0.4; 0.7, 1.0, 1.5 mg.L -1 was of 0.618 ± 0.05 mg.L-1 . Specimens exposed to Cloprostenol yielded lower numbers of neonates on 48 hours exposition to 1.5 mg.L-1 . EC50 acute toxicity test for 17α-ethynilestradiol, with the concentrations 0; 0.05; 0.1; 0.2; 0.5; 1; 2; 3 was 0.23 ± 0.03 mg.L-1 , and chronic toxicity with the concentrations 0; 0.05; 0.1; 0.2; 0.5; 1; 2; 4 mg.L-1 was of 0.89 ± 0.26 mg.L-1 . Estrone CE50 acute toxicity, with the concentrations 0; 0.16; 0.31; 0.63; 1.59; 3.18 mg.L-1 was 0.71 ± 0.07 mg.L-1 , and chronic toxicity with the concentrations 0; 0.09; 0.19; 0.38; 1,908 mg.L-1 was 0.543 ± 0.17 mg.L-1 . Filtering rates of specimens after acute toxicity exposure (48 hours) to cloprostenol increased, and neonates derived from specimens exposed chronically to cloprostenol (7 days) showed no differences in filtering rates. When directly exposed, filtering rates increased with estrone, decreased with cloprostenol and were non-significant for 17α-ethynilestradiol. Hormones that can be found at sewage release sites impact survival and reproduction of the cladoceran C. silvestrii and thus can affect the aquatic ecosystem, disrupting the community structure and changing clearance rates and therefore energy transference.