The influence of geology and land use on the geochemical baselines of the East River basin, China

A geochemical baseline refers to the concentration of an element or any chemical property of a naturally occurring substance in the earth's near-surface materials, originating from both natural and non-natural sources. In this study, the Tukey boxplot approach was adopted to develop geochemical baselines for 42 analytes in the East River basin, South China. Data subset analyses, change ratios and factor analyses were used to explore the anthropogenic effects and the influence of land use and geology on the spatial distribution of the geochemical baselines. The sample medium was active, fine-grained (< 63 μm) fluvial bed sediment collected during 2007–2009 at an average spatial density of one sample per 200 km2 (n = 137). Although considerable variation in elemental concentration was exhibited by the dataset, the geochemistry of the study basin was generally consistent with the upper crustal abundance for China and with world average fluvial suspended matter concentrations. Median concentrations of the heavy metals lay within the limits of sediment quality guidelines and the bed sediment of this macro-scale basin was relatively unpolluted. The results revealed that whilst base cations were depleted, background levels of As, Pb, W and some rare earth elements were elevated relative to the crustal values. Subset analysis and factor analysis indicated that As, Pb and W were associated with anthropogenic activities, whereas rare earth elements were affiliated with the igneous geology in the study basin.

► Geochemical baselines of a sub-tropical macro-scale drainage basin were developed.
► Elements As, Pb, W and some rare earths were elevated relative to crustal values.
► Spatial distribution of these elements is related to anthropogenic activities and igneous geology.
► Pollution of the study basin, although detectable, is limited to a local scale.