Monitoramento da qualidade microbiológica das águas do arroio clarimundo, Município de Cerro Largo(RS)

Abstract

Water quality is a topic of constant concern, due to both its importance for ecosystem functioning and its scarce availability for human use. A major problem related to water quality deterioration in urban environments is the contamination of water resources by organic wastes and domestic sewage, which might contain, among others, pathogenic microorganisms. Coliform bacteria are usually employed as indicators of microbiological quality of water; also, heterotrophic bacteria could be utilized as complementary indicators. In this context, this work aimed to evaluate the microbiological quality of waters from the Clarimundo stream, which runs through the city of Cerro Largo/RS, in three distinct points: Point 1 (P1), in an area near the stream spring; Point 2 (P2), prior to the stream cross through the city; Point 3 (P3), after the stream crossed through the urban area. From water samples, collected during the summer, autumn, winter and spring seasons of the year 2016, the densities of total and thermotolerant coliforms were determined using the Most Probable Number (MPN) technique, and total heterotrophic bacteria were quantified through plate counting technique. The average density of total coliforms at P1 was 2,715 NMPN/100 mL, 6,800 MPN/100 mL at P2, and 166,500 MPN/100 mL at P3. Regarding thermotolerant coliforms, P1 displayed average density of 693 MPN/100 mL, P2 of 3,455 MPN/100 mL, and the average density at P3 was 62,250 MPN/100 mL. Counts of heterotrophic bacteria were also higher at P3, reaching an average value of 1.49 × 10 5 Colony Forming Units (CFU)/mL in comparison to the counts reached at P1 and P2, which were 2.96 × 10 3 CFU/mL and 6.77 × 10 3 CFU/mL, respectively. Therefore, as the watercourse crossed the urban area (specially at P3), an increment in the coliform numbers was observed when compared to the coliform densities detected at P1. Considering the short extension of the Clarimundo stream, the abrupt increases in the coliform densities at P3 might indicate a possible water contamination by material of fecal origin. The increased number of heterotrophic bacteria at P3 suggests that, at this point, the Clarimundo stream presents a higher concentration of organic matter, which might originate from human activities. Water monitoring could be useful for the management and planning of water and soil uses, aiming to diminish the risks related to public and environmental health. In this sense, implementation of efficient systems (individual and/ou collective) for collection and treatment of wastes and sewage might be beneficial to the water quality of Clarimundo stream.