Avaliação preliminar da qualidade da água na bacia de captação de água de abastecimento da cidade de Erechim-RS

Abstract

Water is an important resource for life maintenance on Earth. Although it is a renewable resource, the degradation process of its quality and quantity is a major issue in Brazil. Water uses are also related to agriculture, industry and domestic needs, thereby characterizing its importance to the country's economy. The city of Erechim has two main rivers, which are the sources for public water supply. The Ligeirinho and Leãozinho rivers contributes to a reservoir, which is managed by the Sanitation Company of Rio Grande do Sul (CORSAN). Thus, the aim of this study was to evaluate the water quality of the Ligeirinho River and Leãozinho River by means of monitoring water quality at three locations: the two rivers outlet near the water reservoir (R1 and R2) and near the reservoir dam (R3). Water Quality Index (WQI) and toxicological tests using the micro-crustacean Daphnia magna were used to evaluate the water quality. The Water Quality Index (WQI) was estimated through the evaluation of the following parameters: pH, Temperature, Oxygen Dissolved (DO), Turbidity, Total Solids, Thermotolerant Coliforms, Biochemical Oxygen Demand (BOD), Nitrate, Nitrite, Ammonical Nitrogen and Total Phosphorus. In addition, toxicological tests were carried out, as follows: acute toxicity (in all the samples) and chronic toxicity (reservoir samples). A WQI considered good was registered for all the samples using CETESB-SP as reference, and a Medium WQI for the sample R2 and a Medium to Good WQI for samples R1 and R3 using FEAM-MG as reference was registered. Despite the Good quality registered in WQA, it was verified that there were some parameters in discordance with the resolution CONAMA 357/2005, which are as follows: Fecal Coliforms, BOD, Nitrate, Total Phosphorus, pH and DO. Regarding acute toxicity test, it was verified the absence of acute toxicity for all samples. Similarly, it was not recorded any chronic toxicity in the water of the reservoir. Considering the results of the assessed parameters in this study, the results obtained are of concern, once the rivers are used for the public water supply of the city of Erechim.