SOURCE INPUT ELUCIDATION IN AQUATIC SYSTEMS BY FACTOR AND PRINCIPAL COMPONENT ANALYSIS OF MOLECULAR MARKER DATA

The usefulness of principal component analysis (PCA) and factor analys is (FA) for source input elucidation in environmental studies using mo lecular markers for sample description was evaluated. A case study inv olving the determination of aliphatic and chlorinated hydrocarbons, fa tty acids, alcohols, chlorophylls and some detergent indicators in wat er particulates from a deltaic system was selected as a representative testing dataset. PCA afforded useful results to differentiate between major groups of samples but not between geochemical sources. In contr ast, FA provided a direct correspondence between factor loadings and m arker groups defining geochemically consistent organic matter contribu tions. For autochthonous compounds, FA has allowed an even more precis e characterization of input sources than that obtained by the common ' 'qualitative'' molecular marker approach. These results were obtained despite the unsuitable dimensions of the dataset describing the system [102 compounds (variables) X 40 samples). No improved results were ob tained from the application of FA or PCA to subgroups of the data invo lving smaller number of compounds. This is consistent with the hypothe sis that a limited number of sources is responsible for the occurrence of these lipid markers in the delta waters.