Qualidade da água do rio Itanhém entre os municípios de Medeiros Neto e Teixeira de Freitas, Bahia.

Abstract

The Itanhém river basin in the far south of Bahia is responsible for water supply in the counties of Medeiros Neto and Teixeira de Freitas and receives daily loads of domestic and industrial effluents, which compromise the quality of its waters. In this context, the objective of this study was to evaluate the water quality and identify the pollution or contamination groups present in the Itanhém River based on the physical, chemical and microbiological parameters, in the river stretches between Teixeira de Freitas and Medeiros Neto, from August of 2018 to July of 2019, and compare with the parameters set by the CONAMA resolution 357/2005. Twelve collects were performed at eight different points located within the urban perimeters and outside these nuclei, in order to verify the interference level in each location. The data on Dissolved Oxygen (DO), hydrogen potential (pH), oxi-reduction potential (ORP), salinity (PSU), electrical conductivity (CM), total dissolved solids (TDS), and temperature (TEMP) were obtained. HI 9829 HANNA Instruments® multiparameter probe with readings taken on the spot. In addition to these parameters, laboratory analyzes were performed to obtain Ammonia, Nitrite and Nitrate, BOD and Thermotolerant Coliforms. All analyzed parameters were used to measure the water quality of the Itanhem river, both at the points closest to urban agglomerations, where effluent discharges with high loads of organic matter were found, which compromise the water quality, as well as in the most distant areas, which are therefore further from the effluent discharge points. In order to assess the impacts generated by economic activities developed around the river, a study was also carried out through ArcGis®, to verify the crops developed within the river basin under study. This procedure was performed in order to obtain comparative data between points near the effluent discharges and others more distant from them. The data were analyzed using descriptive statistics, Shapiro-Wilks test, Kruskal-Wallis nonparametric test, analysis of variance, Tukey test (parametric) or Wilcoxon test (nonparametric). Pearson correlation analysis (parametric) or Spearman correlation (nonparametric) was also performed. All analyzes were performed at the 5% probability level (P <0.05). Principal component analysis was performed in order to reduce the dimensionality of the data and generate an index with the studied parameters. It was observed that, at the points closest to urban agglomerations, water could be considered bad, as it presents different parameters that do not comply with CONAMA Resolution 357/2005, and as the collection points moved away from cities, water quality presented values, for the same parameters, within the recommended by the referred resolution, which indicates the occurrence of the self-purification phenomenon in the Itanhém river. The occurrence of this phenomenon does not exclude the care required by this watercourse, so it is still necessary to monitor and reduce the direct discharge of untreated effluents, at Medeiros Neto and at its district Nova Lídice as well, and near the city of Teixeira de Freitas, besides several agricultural and livestock activities developed in the river basin, which has as an aggravating factor the absence of riparian forests in several points of the river stretch