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, topsoils, 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 lithosphere, local soils and sediments. Topsoils of different ages and soil profiles are most clearly differentiated by the degree of leaching of Ca, Mg and some minor elements with respect to less mobile Si and Ti. Clay translocation within soil profiles of older terraces leads to accumulation of Al and associated elements in deeper horizons and accumulation 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 strongly in oak bark than in grasses, and the relative accumulation is greater 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 terraces 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 rapid appraisal of long-term landscape processes, such as erosion/ sedimentation, weathering and preferential plant uptake.