Surface water quality assessment of the main tributaries in the lower São Francisco River, Sergipe

ABSTRACT Contamination of water body by diffuse and point sources in springs has caused concerns mainly due to restrictions on its quality. The problem becomes more serious when contamination affects water for human consumption, as occurs in the river São Francisco, which supplies several municipalities of Sergipe. In this sense, the objective of the study was to evaluate water quality in eleven tributaries of the São Francisco river in its low course in the period from 2013 to 2014, in order to subsidize decision making by public management bodies operating in the region. For this purpose, it was used the Water Quality Index (WQI) and the Trophic State Index (TSI), as well the hierarchical grouping techniques associated to the samples to compare the different causes of contamination of each source. The lowest WQI values were observed in the rivers Betume and Jacaré and they were associated with high concentrations of coliforms related to the disposal of domestic effluents from the riverside cities. It was observed a tendency to eutrophication in the Jacaré stream, Santo Antônio, Pilões, Papagaio and Capivara rivers demonstrated by the high TSI in the rainy season. The results of the cluster analysis were close to their Euclidean distance, and showed that there were similarity relationships between the different water sources related to their parameters of water quality. In this piece of work, we also used the Factor Analysis resulted in the selection of five factors of water quality indicators which are mainly related to mineral content, organic matter, surface runoff and the level of pollution. Thus, it is concluded that the water quality of the São Francisco river tributaries is at a strong tendency towards contamination and that its tributaries need a constant monitoring for the environmental management decisions to be the most adequate for the sustainable survival of the riverside communities.