Using the pollutant load concept to assess water quality in an urban river: the case of Carahá River (Lages, Brazil)

The objective of this study was to evaluate the water quality of Caraha River in Lages (Brazil), using the concept of pollutant load and comparing the results with the water quality index. Thirteen points along the river were selected and eight collections were carried out over a period of 16 months. The parameters analysed were those required for the calculation of the water quality index (WQI). Flow measurements were also carried out, which enabled the calculation of the polluting load. The results showed that the WQI score ranges between 24.95 at the source and peaks at 40 at the outlet. The water classification, therefore, ranges from “very bad” to “bad”. The calculation of the pollutant load showed a constant disposal of contaminants into the river, which demonstrates that the quality of the water is continuously degraded. This information could not be obtained by analysing only the WQI, which presented a nearly constant quality at point 4 and beyond. The use of the calculation of pollutant load for Caraha River is, therefore, a tool for assessment of pollution that can provide more appropriate information for the water resources management.