Variabilidade espacial de parâmetros de qualidade de água nas bacias do Rio Cuiabá e São Lourenço

Abstract

The basins of the Cuiabá river and São Lourenço are of utmost importance due its economic, social and cultural, as they cover the largest and most traditional cities in the state of Mato Grosso. In addition, there is also the environmental context being the main rivers that form the northern Pantanal. Despite its importance, few studies showing variations in water quality of the plateau to the floodplain, and the effects of urbanization. Thus, this study aimed to: (i) group and characterize the features excerpts with similar water quality, (ii) assess whether the number of variables analyzed were sufficient to discriminate between spatial and to check whether this number can be optimized, (iii) to identify which variables are representative of each group and if they change spatially, (iv) identify the natural features and/or the use and occupation of the basin that may be influencing spatial variations in water quality. For this, we monitored monthly 15 points, nine points in the Cuiabá river basin and six on the São Lourenço river basin. The variables analyzed were: electrical conductivity, water temperature, pH, dissolved oxygen, biochemical oxygen demand and the anions nitrate, nitrite, dissolved phosphate, sulfate, chloride and fluoride. The hierarchical cluster analysis (AHA), revealed the existence of four clusters for the Cuiabá river basin and three to the São Lourenço river basin. To evaluate the quality of clusters we performed a discriminant analysis (DA) which showed a correct classification in 81% of samples of the Cuiabá river basin and 93% for the basin São Lourenço river. Furthermore, the AD mode "stepwise forward" showed that it was not possible to reduce the number of variables collected maintaining the same effectiveness in classifying space groups. The principal component analysis (PCA) showed which were the representative variables in each group, which identified factors / sources responsible for the spatial variation of water quality in the regions identified by grouping analysis. The main sources of variations are mainly related to agricultural runoff and sediment transport (anthropogenic activities) in upland areas and in regions close to urban areas for domestic effluent releases.