Water quality indicators are important tools for the summary and generation of solid
foundations about water resources degradation. The Water Quality Index of the
Environmental Company of the State of São Paulo (WQI-CETESB) is the main water
quality index used in Brazil. In relation between water quality and degradation in
drainage basins, it is common to associate multiple uses of soil and water. This research
correlates the WQI-CETESB to multiple uses of water and soil at three collection sites
in the Prata catchment, located in the municipality of Capitão Poço / PA, about 154 km
east of Belém / PA. It is a rural area in northeast Pará with intense agricultural activities.
It was carried out eighteen campaigns with twenty-three collections, being that are
twelve ones in the rainy season and eleven ones in the less rainy season. The index was
calculated from the analysis of its nine parameters: turbidity, dissolved oxygen (DO),
biochemical oxygen demand (BOD), total nitrogen, total phosphorus, total solids, pH,
temperature and thermotolerant coliforms. The descriptive statistics was applied to
synthesize the obtained data. The morphometry of the drainage areas of the collection
sites was analyzed in order to understand the influence of these physical characteristics
on the water quantity and quality. Soil use and coverage were mapped using
georeferencing tools. The association between WQI-CETESB results and multiple uses
was verified by checking the variables with the greatest influence on the value obtained
for the index. Based on the WQI-CETESB, the water quality in the Prata catchment
ranges between the categories Fair and Good. The values obtained in the majority did
not present significant variations for the different periods (rainy and less rainy). The
descriptive statistics proved to be efficient for the analysis of the results obtained from
WQI-CETESB. The morphometric analysis of the drainage areas showed that the shape
and the topography are not factors that impact the water quantity and quality in the
catchment. The mapping of soil use and coverage and activities related to multiple uses
of water, showed to be efficient as an aid in the visualization of local dynamics. The
variables that most influenced the results were thermotolerant coliforms, pH, DO, BOD
and total phosphorus, with representativeness associated to the three collection sites
studied. The main sources of pollution raised by the mapping are strongly related to the
results obtained. Targets for quality improvement and mitigation measures should be
established with the aim of reducing local water degradation.
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