Qualidade da água e dimensionamento amostral da microbacia Lajeado do Pardo em Frederico Westphalen

Abstract

The studied area is called Lajeado do Pardo, located in the municipality of Frederico Westphalen. The municipality has characteristics of rural and urban use, and due to the current concern with the problem of scarcity of natural resources, mainly the water resource, this approach was chosen, which may contribute to the standardization of the method to determine the water quality index. (IQA), facilitating discussions concerning environmental problems. In this sense, 102 strategic points of water collection were determined, from the source to the water capture point of the municipality, where measurements were taken, through a multiparameter probe, and physical, chemical and microbiological analyzes were carried out, for the purpose of comparing the values maximum limit established by CONAMA RESOLUTION 357. Statistical analyzes were performed with the aid of the R program (R Development Core Team, 2021) and the Microsoft Office Excel® application. The objective of this work was to determine the sample size necessary to estimate the average of variables related to water quality parameters, using T Student distribution methods and Resampling at precision levels. In addition, to evaluate the gain of precision in the estimation of measures of central tendency and of variability in variables of parameters of water quality in water courses. From the data obtained, it was found that the levels of thermotolerant coliforms and total phosphorus are outside the standards for class II waters. A larger sample size is required in the evaluation of N-NH3 and NH3 and a smaller sample size is required for the determination of temperature, redox potential, among others. The estimation error made when using 102 sampling points ranged between 1.20% and 56.14% of the average for variables that require a larger sample size. Accuracy gain is faster for estimating mean than standard deviation and coefficient of variation.