Temporal dynamics of water quality in an urban stream

ABSTRACT

Urbanization leads to the addition of areas of low permeability in watersheds, which results in an increase in the volume of rainwater drained superficially and, consequently, in the expansion of pollutants carried to the receiving watercourses, which may impair the quality of their waters. The main objective of this research was to analyze the variation in water quality throughout the day in a stream impacted by urban areas through the water quality index (WQI_CETESB) and the parameters involved in its calculation. Sample collection was performed once a month, for a period of seven months, at the following times: 8:00 am, 2:00 pm, and 7:00 pm. In general, low concentrations of dissolved oxygen and high levels of organic matter and nutrients were found in the stream evaluated. Sampling at different times of the day was efficient in terms of understanding the anthropic processes that take place in the studied sub-basin (e.g., the release of fresh domestic sewage and intense phosphorus input in the morning). In addition, a significant fluctuation in the value of the WQI_CETESB was observed between the three periods of the day, as in June 2018: 52 (morning) and 23 (night). Thus, the evaluation of the WQI_CETESB conducted in only one hour of the day can pass on essential information for environmental managers, resulting in an erroneous view of the problem.

Keywords:
water quality index; nonpoint pollution; environmental degradation