Avaliação das características quanti-qualitativas dos recursos hídricos em uma sub-bacia do Rio Piratini/RS.

Abstract

Water consists in a vital resource, being considered public domain property and endowed with economic value. Due to the development of anthropogenic activities, it has been observed a significant increase in the demand for the resource, besides a constant degradation of its quality, which ends up compromising, beyond the maintenance of natural ecosystems, its use for multiple purposes. In this context, the aim of this study was to determine the variables of water quality, as well as to estimate the maximum discharge and runoff volume in the subbasin of the stream Passo das Pedras, inserted in the drainage basin of the Piratini/RS river. The study was accomplished in three sampling points of the subbasin (sector 1, sector 2 and sector 3), for which fifteen water samples were collected, in rainfall events, in the period of November/2013 to December/2014. As quantitative variables, rainfall, runoff volume and peak discharge were evaluated, while for determination of water quality were monitored temperature, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), Total Kjeldahl Nitrogen (TKN), total phosphorus, fecal coliform, total coliform, Escherichia coli, total dissolved solids (TDS), total suspended solids (TSS), pH, electric conductivity, turbidity, color, iron, manganese, calcium e magnesium. For analysis of quantitative and qualitative variables were applied multivariate exploratory techniques of principal component analysis and common factors. By the criterion of the variance percentage, it was decided to extract two factors for each researched sector, whose variations explain between 50,74% and 60,37% of total variance, indicating a substantial degree of conservation of information. Inside each factor, variables that contributed significantly to water quality in the drainage basin were identified. Between these, besides the quantitative variables, physicochemical and biological variables, both related to diffuse pollution from agricultural areas and domestic sewage. Despite the specificities of each sector, it is observed that water quality in the three sectors of the basin is influenced by a common set of variables.