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Some limnological aspects of Lake Massacará (adjoining the Paraopeba River, São Francisco River Basin) were studied during two periods of the hydrological cycle. Water transparency was equally low during both the periods. During high water, thermal stratification was recorded, with a clinograde oxygen profile; pH was slightly acid, and conductivity was higher near the bottom. Concentrations of inorganic carbon and ammonia, and rates of primary production were higher than during the low water period. During the latter period, complete mixing occurred, with a clinograde oxygen profile; pH was slightly acid, and conductivity unvarying with depth. Higher concentrations of nitrate were found than during high water. With regard to the zooplankton communities, higher density and species richness of organisms occurred during high water. Copepods and rotifers were most numerous during both periods. The taxa identified consisted of 17 rotifers, four copepods, six cladocerans, five protozoans, and two macroinvertebrates. The most abundant species were Thermocyclops minutus, Keratella cochlearis, K. lenzi, and Trichocerca capucina during high water, and Thermocyclops minutus and Conochilus unicornis during low water. Lagoa Massacará (marginal ao Rio Paraopeba-MG, Bacia do Rio São Francisco) foi estudada do ponto de vista de alguns aspectos limnológicos durante dois períodos do ciclo hidrológico (cheia e seca). A transparência da água foi baixa e semelhante nos dois períodos. No período de cheia ocorreu estratificação, perfil de oxigênio clinógrado com camadas inferiores anóxicas, pH ligeiramente ácido, alta condutividade elétrica no fundo, com maiores concentrações de CO2 inorgânico, de íons amônio e taxa de produção primária que na época seca. No período de seca ocorreu desestratificação, perfil de oxigênio clinógrado com camadas inferiores não anóxicas, pH ligeiramente ácido, condutividade elétrica constantes, com maiores concentrações de nitrato que na época cheia. A composição e abundância da comunidade zooplanctônica não demonstrou grandes flutuações nas duas épocas estudadas. A maior densidade e riquesa de organismos foi detectada na pós-cheia. Copépodas e rotíferos detiveram a maior representatividade numérica em ambos os períodos, não havendo contudo espécies dominantes. Foram identificados um total de 17 taxa de rotiferos, 6 de cladóceros, 4 de copépodas, 4 de protozoários, e 2 de macroinvertebrados. As espécies mais abundantes encontradas na cheia foram: Thermocyclops minutus, Keratella cochleares, Keratella lenzi, e Trichocerca capucina, e na seca Thermocyclops minutus, e Conochilus unicornis

brazilian archives of biology and technology

Zooplankton community composition and some limnological aspects of an oxbow lake of the Paraopeba River, São Francisco River Basin, Minas Gerais, Brazil