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 of Cr and Ni in Dystric Eutrochrepts derived from serpentinitic rock slide material were investigated in the Swiss Alps under subalpine climatic 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 correlation between dithionite-extractable Cr and Fe was positive, but negative between pyrophosphate extractable Cr and total soil carbon. Total Ni and Mg generally increased with depth. While most of the Cr was located in refractory primary minerals (pyroxene, garnet and spinels), a minor part was found in secondary Fe oxides; therefore, Cr tended to accumulate in the upper mineral part of the soil profiles and was generally less mobile than Ni. Soil Cr was not readily available for plant uptake. In some soils, exchangeable Ni reached concentrations potentially toxic to plants.