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Bacteriological indicators of fecal contamination in the rivers of Cuenca, Ecuador

Abstract:

Given the necessity to reliably control the microbiological condition of water, it is recommended to select indicators of fecal contamination sensitive to changes in quality. In this research, the contamination of the rivers Tomebamba, Tarqui, Yanuncay, and Machángara of the city of Cuenca was analyzed, using the traditional bacterial indicators Total Coliforms and Fecal Coliforms. In parallel, the bacterial indicators Fecal Streptococci and Enterococci were used as alternative and/or complementary indicators, given their evidence shown in several water quality studies. All these organisms come from the gastrointestinal tract of man and warm-blooded animals and are excreted through the feces. Three monitoring campaigns were conducted in each river during representative hydrological flow conditions, respectively of high, medium, and low flow. A total of 78 samples was collected, and the Multiple Tubes technique, expressed as MPN/100 ml, was used for the quantification of the indicators. The results showed significant differences in quality between the sections of the 4 rivers and suggest that Fecal Streptococci and Enterococci perform satisfactory as indicators of fecal contamination. They provide accurate and reliable information with respect to the safe uses of the water resource and complement the diagnosis obtained by the traditional indicators. The relationships between the indicators permitted to identify possible sources of contamination. Furthermore, the comprehensive evaluation of the microbiological water quality of the examined rivers suggests that the use of traditional and alternative indicators, especially in peculiar environments, permits to define the most appropriate corrective measures to control the contamination.