Avaliação da Qualidade da bacia hidrográfica do rio São Pedro, sub-bacia do rio Guandu-RJ.

Abstract

Despite its importance, water has not received the value it deserves, with its quality compromised by various human activities, including industrial, commercial, domestic, and agricultural ones. To assess water quality, it is necessary to analyze several parameters; however, the complexity of the generated data complicates understanding for the lay public. In this context, the Water Quality Index (WQI) emerges as a valuable tool that synthesizes this information into a single value, facilitating interpretation and dissemination. The primary objective of this study was to evaluate the water quality of the São Pedro River, a tributary of the Guandu River, through the application of the WQI proposed by the Canadian Council of Ministers of the Environment (WQI-CCME) for the period from 2013 to 2023. Secondary data from the INEA monitoring station, SP310, on the São Pedro River were used. For this study, the quality reference for water was based on the limits set by CONAMA Resolution 357 of 2005 for freshwater class 2. A description of the monitoring data, statistical treatment, and calculation of the WQI-CCME were conducted. Data analysis identified the inappropriate use of the NSF WQI by INEA, which hindered the comparison between index results, contrary to the original intent of this index. The results showed significant improvements in the water quality of the São Pedro River over the study years (2013-2023). The application of the WQI-CCME revealed a gradual evolution, with water quality improving from "fair" to "good." A Mann-Whitney test between variables confirmed the influence of rainfall 24 hours before sampling on water quality, showing deterioration post-rainfall. The location of the monitoring point near Conservation Units and rural areas with livestock activities may explain the presence of thermotolerant coliforms in the river water. In conclusion, the WQI-CCME is an effective tool for indicating water quality, featuring a simple methodology and the advantage of allowing the incorporation of new parameters. However, its disadvantage is the need for at least four monitoring campaigns, which can be a significant limitation for inconsistent monitoring.