ELEMENT PARTITIONING IN SEDIMENT, SOIL AND VEGETATION IN AN ALLUVIAL TERRACE CHRONOSEQUENCE, LIMAGNE RIFT-VALLEY, FRANCE - A LANDSCAPE GEOCHEMICAL STUDY

The geochemical behaviour of specific elements in fluvial sediments, t opsoils, soil profiles and plant material on a sequence of Quaternary alluvial terraces was reconstructed semi-quantitatively using indices of accumulation or depletion with respect to abundance in the lithosph ere, local soils and sediments. Topsoils of different ages and soil pr ofiles are most clearly differentiated by the degree of leaching of Ca , Mg and some minor elements with respect to less mobile Si and Ti. Cl ay translocation within soil profiles of older terraces leads to accum ulation of Al and associated elements in deeper horizons and accumulat ion of Fe and Mn in pseudogley horizons in the upper part of the clay accumulation layers. P, K, Ca, Mn and Zn are strongly concentrated in plant materials relative to the topsoils. Ca is accumulated more stron gly in oak bark than in grasses, and the relative accumulation is grea ter on the older terraces due to the low Ca content in their topsoils. Mn contents of both grasses and oak bark are greater on the older ter races than the younger. For most elements, topsoil and plant material contents show little correlation, probably because plant requirements exert a greater control on element uptake than does availability. The results illustrate that landscape geochemical analysis is useful for r apid appraisal of long-term landscape processes, such as erosion/sedim entation, weathering and preferential plant uptake. (C) 1997 Elsevier Science B.V.