COREGIONALIZATION OF TRACE-METALS IN THE SOIL IN THE SWISS JURA

The provenance of trace metals in soil, whether from the parent materi al or from pollution, is rarely known with certainty, and the metals' history must usually be pieced together from fragmentary statistical i nformation. This is particularly true in the Swiss Jura where the conc entrations of several heavy metals around La Chaux de Fonds exceed die statutory recommended thresholds for safety. The topsoil of the 14.5- km2 region was sampled on a square grid at 250-m intervals with additi onal nesting with distances of 100 m, 40 m, 16 m and 6 m. The concentr ations of seven potentially toxic metals, namely Cd, Co, Cr, Cu, Ni, P b 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 compone nt dominated those of Co and Ni; the variogram of Zn combined the two in approximately equal proportions. The coregionalization matrices con tain moderate correlation among the nugget and the short-range compone nts, 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, C r 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 Arg ovian formation in particular. The indicator variogram of this formati on has also a short-range component. The analysis also showed Cr and C u to be related to land use (in different ways). Copper and Pb are str ongly correlated to one another and distinct from the five other metal s. The long-range structure is almost certainly a geological effect, w hereas the one of short range probably results from both the geology a nd human activities.