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.摘要：泉眼水体遭受面源污染与点源污染，其水质受到影响，该问题已因水质达标受限而引发广泛担忧。当污染波及饮用水源时，问题会更为严峻，巴西塞尔希培州多个市镇的供水水源圣弗朗西斯科河便存在此类问题。有鉴于此，本研究旨在评估2013至2014年间圣弗朗西斯科河下游11条支流的水质，以期为该区域内公共管理机构的决策提供支撑。为此，本研究采用了水质指数（Water Quality Index, WQI）和营养状态指数（Trophic State Index, TSI），并结合样本分层聚类技术，以对比各水源的不同污染成因。贝图梅河（Betume）与雅卡雷河（Jacaré）的WQI值最低，其高浓度大肠菌群与沿岸城镇生活污水排放直接相关。雅卡雷溪、圣安东尼奥河、皮洛埃斯河、鹦鹉河与卡皮瓦拉河在雨季的TSI值偏高，表明这些水体呈现富营养化趋势。聚类分析结果与欧氏距离（Euclidean distance）的测度结果高度吻合，表明不同水源的水质参数存在相似性关联。本研究同时采用因子分析（Factor Analysis），最终筛选出五类水质指标因子，其主要关联要素涵盖矿物含量、有机质、地表径流及污染程度。综上，本研究得出结论：圣弗朗西斯科河支流的水质已呈现显著污染趋势，需对其支流开展常态化监测，以便为沿岸社区的可持续存续制定最适配的环境管理决策。