Avaliação do índice de qualidade das águas na área urbana da bacia hidrográfica do Rio Mourão, Paraná

Abstract

The objective of this research was to statistically analyse the Water Quality Index (WQI) in the urban area of the Mourao River watershed. In order to evaluate the WQI, it was determined and analysed the parameters temperature, potential hydrogen (pH), turbidity, biochemical oxygen demand (BOD5,20), dissolved oxygen (DO), total nitrogen, total phosphorus, total solids and fecal coliforms from 4 preselected sampling sites, during 12 months. The results obtained for the WQI revealed that the sampling site #3 was the one that obtained the less satisfactory classification, having the water quality classified as moderate for all the samples. In the sampling site #1, it was obtained the best results, with the water quality classified as good for 58,33% of samples. Aiming to have a more detailed evaluation, each of the parameters was analysed individually, which allowed to observe that, on at least one sampling site, the parameters fecal coliforms, pH, DBO5,20 and total phosphorus did not fit the water quality standards of the CONAMA 357 resolution. Except for the total phosphorus, all the parameters that did not meet the resolution standards indicated less satisfactory results for the site #3, followed by the site #4. It is explained due to the fact that both of them are located downstream from Campo Mourão urban area, having then, more anthropic influence. From the principal components analysis (PCA), it can be highlighted, related to the WQI, the samplings #4 and #8 from the site #3, with a positive score for the principal component 1 (PC1) and the sampling #3 from the sites #1 and #2 with a negative score for the principal component 3 (PC3). Through the analysis of variance (ANOVA), it was found that the data obtained from the WQI analysis are statistically significant; requiring the execution of a means comparison test in order to determine which mean is considered different from the others. This way, through the Tukey’s test, it was concluded that the sites #1 and #3 are considered statically different, which can be explained due to the fact that the site #3 obtained the smaller score for the WQI, while the site #1 was considered to be the one with the best water quality.