ANÁLISE ESPAÇO-TEMPORAL DA QUALIDADE DA ÁGUA NA PARTE ALTA DA BACIA DO RIO SALGADO, CEARÁ

Abstract

The aim of this research was to investigate the similarity of water quality in space and time in the upland of Salgado watershed, Ceará, Brazil. Multivariate analysis/Cluster Analysis was used for this investigation. Water samples were took in nine stations, spread out along the rivers during March, May, July, August and September, 2005, totalizing 45 samples. The water quality attributes analyzed were: electrical conductivity (EC), chloride (Cl-), sulphate (SO4-2), soluble orthophosphate (OPS), nitrate (NO3-), dissolved oxygen (DO), bicarbonate alkalinity (BA), total coliforms (TC) and turbidity (T). Four homogeneous groups were identified. The water samples collected at rainfall season defined the dissimilarity of group 1 in relation to the others. This group showed the best water quality due to the dilution of salts. Water samples collected during the end of rain-fall season and began of dry season formed group 2. Waters sampled at dry season in stations located down of discharge point of effluents defined group 3. These stations presented the highest concentrations of Cl-, EC, SO4-2 and TC. The values of NO3- and TC defined the similarity of group 4. Although Cl-, SO4-2, DO, and TC influenced the cluster definition, the most important variables were EC and NO3-. The water quality similarity was defined by two factors: punctual pollution and climatic seasonality.