Pollution of a river basin and its evolution with time studied by multivariate statistical analysis

A set of quantitative analytical data for 13 rivers belonging to the basin of the Tanaro (Piedmont region, north-western Italy) has been processed by multivariate statistical techniques. The original matrix, which refers to the year 1990, consisted of 20 chemical and physico-chemical variables, determined at 44 sampling sites. The following methods have been used for the treatment of the data: cluster analysis (unsupervised pattern recognition), factor analysis, variable selection by Fisher weights. A comparison has also been made between the data referring to 1990 and to 1978 in order to investigate the evolution of the environmental situation for the Tanaro basin after such a lapse of time. This comparison has been carried out by processing the 3-D matrix which collects the data of the two different periods.