Avaliação da qualidade da água e influência do uso e ocupação do solo em microbacias do Lajeado Três Passos no noroeste do Rio Grande do Sul

Abstract

The water quality of watercourses is impacted by anthropic activities, mainly due to the development of urban areas and agriculture. Thus, the present study aimed to evaluate the water quality and the influence of land use and occupation in three watersheds (A, B and C) of Lajeado Três Passos, in the municipality of Três Passos, Rio Grande do Sul. The water collections were performed in eight different points distributed along the three watersheds. Two water collections campaigns were carried out, the first in September, and the second in November 2022. In general, the parameters analyzed are in accordance with the maximum values allowed by the CONAMA Resolution No. 357/2005, for class 2 freshwater, except for the variables nitrate, phosphorus and E. coli which, in some points exceeded the limits established in the legislation. These results indicate that the land use and occupation around the watersheds may be contributing to the worsening of the water quality, due to the urban influence with the discharge of domestic and industrial effluents and the possible carriage of nutrients from agricultural activities to the water body. According to the Trophic State Index (TSI), the aquatic environment was classified as hypereutrophic for all points in both collection campaigns, except for P6, which presented the supereutrophic level in the second campaign, raising an alert for the water quality in the Lajeado.The results of the analyses obtained in watershed C demonstrate that it remains in a better state of preservation, due to the larger area of forest formation around it and the longer distance from the urban área.