Multivariate Analysis to Summarize Qualitative-Quantitative Variables of the Water Resources in a Sub-basin of the Rio Piratini/RS, Brazil

The water quality monitoring is one of the most important tools to synthesizing data for easier interpretation about pollution and multiple uses of the water body. Therefore, it can be used the multivariate statistical techniques, such as the principal component analysis, used to analyze interrelations between many variables and to explain them in terms of their common factors. Thus, the objective of the present study was to determine water quality variables using multivariate analysis techniques in the sub-basin of the Passo das Pedras stream, located in the Piratini/RS river basin. The study was carried out at three sub-basin sampling points (sector 1, sector 2 and sector 3), for which fifteen water samples were collected in precipitation events from November/2013 to Oct/2014. The values of temperature, dissolved oxygen (OD), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (STD), total suspended solids (STS), pH, electrical conductivity, turbidity, color, iron, manganese, calcium and magnesium, total kjeldahl nitrogen (NTK), total phosphorus, fecal coliforms, total coliforms, Escherichia coli, magnesium. From the results of the multivariate analysis, considering the two factors, whose variations explain between 50.74% and 60.37% of the total variance for sectors 1, 2 and 3, it can be classified as the indicators of each factor as pollution diffuse by aggregating physical-chemical variables common to the agricultural runoff. Thus, the variables with greater variance explained by the data and present in the first factor of each sector are: precipitation, drained volume and peak flow. These variables are also identified in the secondary factor, for the third collection sector, where the highest portion of the river basin is located.