Geostatistical analysis of soil contamination in the Swiss Jura

The topsoil of a 14.5 km(2) region of the Swiss Jura has been surveyed to identify the distributions of trace metals in it. The soil was sampled at 366 sites selected by combining a square grid and nesting. Concentrations of seven potentially toxic metals, namely Cd, Co, Cr, Cu, Ni, Pb and Zn, were measured. Land use and geology (stratigraphy) were also recorded. Variograms were bounded in the range from 110 m to 1500 m with contributions to the variance at all distances exceeding 6 m. The variograms of Cd, Cr, Cu and Pb are dominated by short range correlation, those of Co and Ni by correlation of long range, and Zn is intermediate. The concentrations were estimated at the nodes of a fine grid by ordinary block kriging and then contoured to produce maps. The maps of Co and Ni have a coarse patchy pattern similar to that of the geology, suggesting that these metals derive from the bedrock. This is supported by analysing the variance by geology. Copper and Pb have finer patterns of distribution, and are more likely to have been added with fertilizer or manure or domestic waste. Cadmium could originate from human activities, such as smelters or fertilizer spreading, or from specific geological deposits, such as moraine.