Factor analysis for the study of water resources contamination due to the use of livestock slurries as fertilizer

We investigated the effects of slurry application on water quality in wells, pasture-drainage conduits and rivers. The parameters determined were electrical conductivity, dry residue, pH, dissolved O2, NO3−, NO2−, Cl−, Na, PO43− organic matter content, COD, suspended solids, turbidity, colour, Fe, Mn, Cu and Zn. The data were analysed by principal components analysis and cluster analysis. The first axis extracted by principal components analysis of the samples-by-variables matrix represented the degree of dilution of the water strongly related with saline content; the second axis represented redox conditions, affecting organometallic component. In general, the positions of the samples in this factor space reflected the major contamination processes affecting water resources of that type (wells, conduits or rivers). In the case of river-water samples, cluster analysis showed that month of sampling had a clear effect, reflecting the importance of rainfall. Finally, in all three water resource types, contamination was most severe in the area of highest livestock density and highest frequency of slurry application.