Qualidade da água e classificação trófica do reservatório da usina hidrelétrica do Funil em Ijaci - MG

Abstract

The artificial reservoirs, intended to produce hydroelectric energy, significantly alter the landscapes of the municipalities in which an area is flooded. Areas previously used for pasture or crops become tourist attractions for the practice of various activities, such as boat trips and water sports. The real estate of urban land subdivisions that develop in the surrounding areas also increases in value, as in Ijaci-MG. Thus, monitoring the water quality in the reservoir is essential to maintain good water conditions and support public policies aimed at overseeing the sustainable use of water and areas surrounding the reservoir, as well as protecting aquatic life. Thus, this study aimed to verify the framework of the monitored section according to the class assigned to it and the parameters established in the National Council for the Environment (CONAMA) Resolution nº 357/2005 to analyze the quality through the CETESB Water Quality Index and Trophic State Index (TSI). The study also aimed to identify the uses for which water is indicated. Water samples were collected at three points in a 5 km stretch in Ijaci. PI is the point where bathing is practiced; PII is the location of possible future water capture for human supply; and PIII is the end of the urbanized area. Monitoring was done in four campaigns in November 2021 and February, May, and August 2022. Data analyses showed that all points presented water unsuited for bathing, according to Resolution CONAMA 274/2000, outside the parameters for Class 2 waters according to CONAMA Resolution 357/2005. As for the indices, the average TSI was classified as Eutrophic at all points, according to the methodology for rivers and Mesotrophic. Higher concentrations of Chlorophyll-a were observed for the reservoir’s methodology in the warmer months due to greater solar incidence in the water mirror and a higher supply of nitrogen in the months with higher rainfall, which can lead to a greater bloom of cyanobacteria not catalyzing atmospheric nitrogen. The average Water Quality Index (WQI) was good at all points, with the variable Thermotolerant Coliforms being the primary factor responsible for the decline in the index. A significant increase in Thermotolerant Coliforms was also observed in November 2021 and February 2022, with higher rainfall rates, which can be associated with the increased transport of animal waste in the surrounding area and greater flow of domestic effluents due to the possibility of an increase in the floating population during this period. Therefore, despite the average water WQI being classified as good, it does not meet the established parameters according to the required uses, demanding the disclosure of complementary information to the population, such as compliance with bathing standards and eutrophication status, and the adoption of public policies aimed at monitoring and controlling polluting sources to ensure compliance with established standards, according to the purpose of using the resource and framing the section.