Limnological and microbiological parameters of Machado river and afluents near the city of Presidente Médici, Rondônia, Brazil

Abstract

The rapid growth of the urban population and industrialization puts water resources under severe pressure. In addition, the Machado River receives untreated sewage from populations along the river basin. Therefore, the aimed of this study was to evaluate the limnological and microbiological parameters of the water of the Machado river and of three streams in the vicinity of the city of Presidente Médici, Rondônia-Brazil. The seven collection points were established from the course of the Machado River and tributaries, based on ease of access. The results obtained were submitted to ANOVA and the comparison between the averages by the Tukey test (a = 0.05) to verify the less preserved areas. For the assessment of water quality in different hydrological periods (full and dry), the data obtained were submitted to Student's T test (a = 0.05). Occasional changes were observed in some limnological parameters. However, in general, they were within the limits of variation of the current regulations. Seasonality directly influenced pH, temperature, dissolved oxygen concentration, transparency and ammonia concentration. In relation to pH, ~ 4% of the samples were below what was stipulated by CONAMA resolution 357/2005 for freshwater class 2. For dissolved oxygen, only one sample presented below that established by the same legislation. The limnological and microbiological parameters of the points closest to the urban area, presented more alarming results, most likely due to diffuse pollution. The levels of total and thermotolerant coliforms were below the limit of the legislation in all analyzed points. The study indicates that there is a need to generate information on the quality of the water in rivers and streams in the state of Rondônia, above all, in watercourses close to urban areas. Because they are important information for health and public supply, as well as environmental health.