Pattern recognition on X-ray fluorescence records from Copenhagen lake sediments using principal component analysis

Principle Component Analysis (PCA) was performed on chemical data of two sediment cores from an urban fresh-water lake in Copenhagen, Denmark. X-ray fluorescence (XRF) core scanning provided the underlying datasets on 13 variables (Si, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Cd, Pb). Principle Component Analysis helped to trace geochemical patterns and temporal trends in lake sedimentation. The PCA models explained more than 80 % of the original variation in the datasets using only 2 or 3 principle components. The first principle component (PC1) was mostly associated with geogenic elements (Si, K, Fe, Rb) and characterized the content of minerogenic material in the sediment. In case of both cores, PC2 was a good descriptor emphasized as the contamination component. It showed strong linkages with heavy metals (Cu, Zn, Pb), disclosing changing heavy-metal contamination trends across different depths. The sediments featured a temporal association with contaminant dominance. Lead contamination was superseded by zinc within the compound pattern which was linked to changing contamination sources over time. Principle Component Analysis was useful to visualize and interpret geochemical XRF data while being a straightforward method to extract contamination patterns in the data associated with temporal elemental trends in lake sediments.