Microbial communities in an oligotrophic reservoir influenced by high levels of ionizing radiation

¹ Poços de Caldas Laboratory, Brazilian Nuclear Energy Commission, Poços de Caldas – Andradas Road, Km 13, 37701-970 Poços de Caldas, MG - Brazil
² Department of Ecology and Evolutionary Biology, Federal University of São Carlos, Washington Luis Road, (SP 310) Km 235, 13565-905 São Carlos, SP - Brazil
³ Department of Exact Sciences, “Luiz de Queiroz” College of Agriculture, São Paulo University, Pádua Dias Avenue, 11, 13418-900 Piracicaba, SP - Brazil

Abstract

In this study, we investigated the microbial community (bacteria and protozooplankton) of a Brazilian reservoir that receives neutralized acid mine drainage flowing from piles of earth produced during uranium extraction. Thus, this research represents an attempt to fill a gap in the information on the ecology of freshwater microorganisms in tropical oligotrophic habitats, in particular in systems affected by high levels of the uranium. During the study, we observed very low chlorophyll a contents and protozooplankton cell densities and biomass. These cell densities were between 0 and 89 cells L⁻¹ and were lower than those frequently reported for oligotrophic freshwater lakes. In contrast, bacterial densities were normal or even slightly high, between 1.85 to 6.0 × 10⁹ cells L⁻¹. The present study has demonstrated very low protozooplankton cell densities and biomass in oligotrophic reservoir under the influence of acidic mining effuents and of high levels of ionizing radiation. It is likely that the ciliate cell densities and biomasses recorded in this study, which fall significantly below the previously published values, can be explained by the chronic fractionated exposure of these protozoa to the high levels of uranium to this system.