THE FATE OF CHROMIUM AND NICKEL IN SUB-ALPINE SOILS DERIVED FROM SERPENTINITE

Weathering of serpentinitic parent material, naturally rich in both Cr and Ni, provides soils that generally contain elevated concentrations of both metals. In this study, soil development as well as the fate o f Cr and Ni in Dystric Eutrochrepts derived from serpentinitic rock sl ide material were investigated in the Swiss Alps under subalpine clima tic conditions. Exchangeable Ni was less than or equal to 0.2 mmol kg( -1), but exchangeable Cr was always <0.01 mmol kg(-1). Linear correlat ion between dithionite-extractable Cr and Fe was positive, but negativ e between pyrophosphate extractable Cr and total soil carbon. Total Ni and Mg generally increased with depth. While most of the Cr was locat ed in refractory primary minerals (pyroxene, garnet and spinels), a mi nor part was found in secondary Fe oxides; therefore, Cr tended to acc umulate in the upper mineral part of the soil profiles and was general ly less mobile than Ni. Soil Cr was not readily available for plant up take. In some soils, exchangeable Ni reached concentrations potentiall y toxic to plants.