Statistical treatment of water quality parameters measured at the upper course of the rio das velhas basin.

Water quality was monitored at the upper course of the Rio das Velhas, a major tributary of the Sao Francisco basin located in the state of Minas Gerais, over an extension of 108 km from its source up to the limits with the Sahara district. Monitoring was done at 37 different sites over a period of 2 years (2003-2004) for 39 parameters. Multivariate statistical techniques were applied to interpret the large water-quality data set and to establish an optimal long-term monitoring network. Cluster analysis separated the sampling sites into groups of similarity, and also indicated the stations investigated for correlation and recommended to be removed from the monitoring network. Principal component analysis identified four components, which are responsible for the data structure explaining 80% of the total variance of the data. The principal parameters are characterized as due to mining activities and domestic sewage. Significant data reduction was achieved.