A MULTIVARIATE STATISTICAL ANALYSIS OF WATER CHEMISTRY – THE ANKOBRA BASIN, GHANA

Hierarchical Cluster and Factor analysis were simultaneously applied to surface water hydrochemical data from three different locations, along the Ankobra basin, Ghana, to extract principal factors corresponding to the different sources of variation in the hydrochemistry, with the objective of defining the main controls on the hydrochemistry at the basin scale. Spatial variations in the hydrochemistry along the basin were elucidated and the different chemical components related using dendrograms and factor tree plots. The application of varimax rotation ensured clear definition of the main sources of variation in the hydrochemistry. Using the Kaiser criterion, principal factors were extracted from the data for each location. A total variance criterion of 80% was further applied to ward off factors, which do not constitute unique sources of variation in the hydrochemistry. The analysis reveals that precipitation, weathering/dissolution of the underlying rock mediated by anthropogenic activities, and organic matter decomposition are the probable agents influencing the hydrochemistry of the basin. Precipitation and silicate mineral weathering have been determined to be the principal factors influencing the hydrochemistry at all three locations. The major cations appear to be controlled by silicate mineral weathering and precipitation, whilst sulfide oxidation, organic matter decay, and precipitation show high tendencies to enrich anionic concentrations in the water. These interpretations are within the limits of the uncertainties associated with multivariate statistical analysis. Detailed field geochemical and chemical relationships are required to constrain the origins of the different chemical agents.