Large trends in French topsoil characteristics are revealed by spatially constrained multivariate analysis

a r t i c l e i n f o Spatially constrained multivariate analysis methods (MULTISPATI-PCA) and classical principal component analysis are applied for the entire country of France to study the main soil characteristics of topsoil and to assess if their multivariate spatial pattern can provide insight on their extent and origin. The results of the MULTSPATI-PCA provided evidence of strong spatial structures attributed to different natural processes. The first axis was interpreted as an axis of global soil richness in clay content. Axis 2 reflected the influence of some parent materials on the geochemical content of K and Al. Axis 3 showed a very large gradient of relative content in coarse silt. Axis 4 was driven by gradients of maritime influence. We show that MULTISPATI-PCA allows better than classical PCA to detect and map large regional trends in the distribution of topsoil characteristics. The two first axes were expected and the maps obtained by both methods were consistent. Interestingly, the other gradients were not expected and were better shown by MULTISPATI-PCA than by classical PCA. Topsoil characteristics in temperate Western Europe mainly depend on parent material composition, geomorphology, and past and present climatic conditions. The dominant soil processes are weathering, leaching, illuviation, and, more locally, podzolisation. Among the parent materials, loess deposits are widespread in northern France, where they are locally very thick (Antoine et al., but it still unclear to what extent the silty aeolian sediments may have spatially influenced topsoil characteristics. In a recent study, Saby et al. (2009) showed that the distribution of some trace elements in French topsoil is strongly dependent on the geographical distribution of some specific parent materials. We assume that this dependence is also the case for some major elements. France has about 5500 km of coastline along the Mediterranean Sea, the Atlantic Ocean, and the Channel. Although atmospheric deposition in maritime environments is known to affect terrestrial ecosystems (Farrell, 1995) and soil (Zhang, 2003), to our present knowledge, no national systematic inventory has explored to what extent the coastal sea salt spray may have influenced the topsoil chemistry. offers an opportunity to tackle these general issues. We study the topsoil characteristics exchange capacity and exchangeable cations, and pH) to assess if their spatial distribution and correlation can provide any insight into their extent and origin. There are several statistical methods available to study the spatial covariation of variables. One …