Coregionalization of trace metals in the soil in the Swiss Jura

Abstract

SummaryThe provenance of trace metals in soil, whether from the parent material or from pollution, is rarely known with certainty, and the metals' history must usually be pieced together from fragmentary statistical information. This is particularly true in the Swiss Jura where the concentrations of several heavy metals around La Chaux de Fonds exceed the statutory recommended thresholds for safety.The topsoil of the 14.5‐km2 region was sampled on a square grid at 250‐m intervals with additional nesting with distances of 100 m, 40 m, 16 m and 6 m. The concentrations of seven potentially toxic metals, namely Cd, Co, Cr, Cu, Ni, Pb and Zn, were measured. Their coregionalization could be represented by a linear model consisting of a nugget component plus two spherical structures with ranges of 0.2 km and 1.3 km. The short‐range component dominated the variograms of Cd, Cr, Cu and Pb; the long‐range component dominated those of Co and Ni; the variogram of Zn combined the two in approximately equal proportions. The coregionalization matrices contain moderate correlation among the nugget and the short‐range components, notably between Cu and Pb, between Cd and Zn, and between Cr, Ni and Zn. The strongest correlations are at the long range between Co, Cr and Ni, and to a somewhat smaller degree between Zn and Co. Analysis of variance showed Co and Ni to be related to geology, and to the Argovian formation in particular. The indicator variogram of this formation has also a short‐range component. The analysis also showed Cr and Cu to be related to land use (in different ways). Copper and Pb are strongly correlated to one another and distinct from the five other metals. The long‐range structure is almost certainly a geological effect, whereas the one of short range probably results from both the geology and human activities.