Scale of spatial dependence between chemical properties of topsoil and subsoil over a geologically contrasted area (Massif central, France)

This study investigates scale spatial specific dependence of some major and trace element contents in topsoil horizons and in alterite type horizons (subsoil horizons) over a weakly contaminated area. The study seeks also to compare the spatial distributions of chemical elements at both depths to the spatial variability of the alterite type in order to examine the effect of the parent material. The probability of occurrence of afterite type was estimated using indicator kriging (IK). Factorial kriging analysis (FKA) was used to analyze spatial variability in some soil chemical properties (Ca, Mg, K, Fe, Cr and Co) measured at two depths over a geologically contrasted area of 10 ha in central of France. The coefficients of the coregionalization matrix at different spatial scales reveal the dominant long-range autocorrelation and cross-correlation in all chemical elements in both depths except for trace elements (Co and Cr) where the short-range structure dominates the cross-correlation. The resulting structural correlation coefficients showed strong correlations between variables changing as a function of spatial scale. These relationships between chemical properties at different spatial scales were not revealed by the linear correlation coefficients. A principal component analysis was performed on the coregionalization matrices at each depth to summarize the relationships among the variables at the different spatial scales. Cokriging allowed mapping each spatial component for both depths. These maps were then compared with the probability map of alterite type estimated using indicator kriging. This comparison revealed that the spatial pattern of chemical elements in the subsoil horizons is almost certainly due to the alterite type effect, whereas the afterite type effect on the spatial pattern of chemical properties in the topsoil horizons was partly hidden by human activities and erosion. (C) 2002 Elsevier Science B.V. All rights reserved.