Proposta metodológica para a construção de índices de qualidade da água na Bacia Hidrográfica Piratini-São Gonçalo-Mangueira, RS

Abstract

The present study aims to supply the existing gaps related to the methodologies used for the construction of water quality indices, which may be adapted for any spring considering their classes and variables of a higher interest. The use of water quality indices for water bodies environmental monitoring presents fast and comprehensible results by society. In this sense, we proposed a methodology for the construction of water quality indices based on the application of multivariate statistics and the limits of a qualitative variable set by the current legislation. Therefore, we used twelve water quality monitoring points existing in ten springs located in the Piratini-São Gonçalo-Mangueira Bay, in the state of Rio Grande do Sul. To define the qualitative variables and their respective weights for each spring studied, we used the factor analysis method, and to extract these factors we used the principal component analysis procedure. To construct the curves of water quality indices, we used the CONAMA 357/2005 resolution, for fresh water spring, class 2 and reference values which were obtained in the literature review. The findings suggest that the index currently used by the Companhia Ambiental do Estado de São Paulo is not appropriate for the reality of the springs studied, since that it does not represent the reality of water quality of the water bodies. Another point relates to the fact that this index does not contemplate important variables, and does not present weights for variables with distorted data. In this way, we believe the methodology of building water quality indices is of utmost importance to a qualitative management of body resources, since that it may be adapted to the reality of any Brazilian spring.