Water Quality Index - IQA of the Tanque Grande Reservoir, guarulhos, São Paulo State, Brazil: 1990 - 2006.

Abstract

The main objective of this research was to evaluate water quality of the Tanque Grande Reservoir, located in the city of Guarulhos, State of São Paulo, Brazil, in the period between the years of 1990 and 2006, in relation to the population grwoth in its surrounding areas, as well as to the diversification of land use and occupation of its region. The physical, chemical and biological parameters data provided by CESTESB and used for the determination of Index of Water Quality (IQA) were: Thermotolerant coliforms, Biochemical Oxygen Demand (BOD 5,20), Total Phosphorus, Total Nitrogen, Total Dissolved Oxygen, pH, Total Solid Residues, Water Temperature and Turbidity. As support to the interpretation of these parameters, a Person statistical correlation and multiple regression analyses, a general survey of physical, biotical and social-economic of the region and its surrounding were performed. The results indicate that the urban expansion in the Guarulhos region, starting in the 1970´s, has reached the areas surrounding the reservoir, and affected partially its surface hydric resources. In the past the reservoir was classified by CETESB as belonging to the category Special Class, defined as containing water appropriate for human consumption, without the need of disinfection. However, presently, the classification that best suits the reservoir is Class 1, according to the CONAMA 357/2005 resolution for it requires a simplified treatment before distribution to the population of Guarulhos. The Person correlation and multiple regression analyses reveal that among the nine parameters employed in the IQA determination, only four have shown to influence significantly in the calculated Index for the Tanque Grande Reservoir (n = 84, p<0,05): Thermotolerant coliforms (r2= 0,50), Turbidity (r2=0,21), Dissolved Oxygen (r2=0,14) and Total Solids (r2=0,08). The results show that the majority of low IQA occurred during the rainy months, synchronously with an increase in the thermotolerant coliforms concentrations. Animal farms located in the headwaters of the studied basin, and recreational activities in the reservoir could function as sources of thermotolerant coliforms in this aquatic system.