Evaluation and comparison of the water quality between São Gonçalo channel and Mirim Lagoon

Abstract

Water resources play a large role in population development. This is due to the fact that urban centres have developed, historically, around rivers and lakes. With the increase in water resources degradation, there was a greater need to assess water quality. The Water Quality Index (IQA) was developed by the National Sanitation Foundation (NSF) in the United States in 1970 to compare and monitor changes in water quality of water bodies. The objective of this study was to evaluate and compare the water quality between the Sao Gonçalo Channel and the Mirim Lagoon by means of the monitoring of these water resources, as well as to identify the points that presented better or worse quality index, by calculating the Index of Quality of Waters adapted by the Environmental Company of the State of São Paulo. The IQA proved to be a strong monitoring tool for the Mirim Lagoon and the Sao Gonçalo Channel since there was a considerable difference between the points of collection of the water bodies studied. It can be verified that the LM7 point was the one that presented the best IQA result, and in November 2017 it was 91, a number considered excellent by the National Water Agency, and consequently presented a smaller quantity of coliforms and a larger amount of Dissolved Oxygen. On the other hand, point SG4 presented the worst IQA and the ratio of coliforms and dissolved oxygen was inversely proportional to that presented in LM7. Multivariate statistical methods were used as a strong tool to monitor the quality of water resources, corroborating, for this study, the division of the monitoring points used, as well as allowing the grouping of these points into separate components for better monitoring of their quality.