STRONTIUM ISOTOPES AS TRACERS OF ECOSYSTEM PROCESSES - THEORY AND METHODS

The strontium (Sr) isotope method can be a powerful tool in studies of chemical weathering and soil genesis, cation provenance and mobility, and the chronostratigrahic correlation of marine sediments. It is a s ensitive geochemical tracer, applicable to large-scale ecosystem studi es as well as to centimeter-scaled examination of cation mobility with in a soil profile. The Sr-87/Sr-86 ratios of natural materials reflect the sources of strontium available during their formation. Isotopical ly distinct inputs from precipitation, dryfall, soil parent material, and surface or groundwater allow determination of the relative proport ions of those materials entering or leaving an ecosystem. The isotopic compositions of labile (soil exchange complex and soil solution) stro ntium and Sr in vegetation reflect the sources of cations available to plants. Strontium isotopes can be used to track the biogeochemical cy cling of nutrient cations such as calcium. The extent of cation contri butions from in situ weathering and external additions to soil from du st and rain can also be resolved with this method. In this paper, we r eview the geochemistry and isotopic systematics of strontium, and disc uss the use of this method as a tracer of earth surface processes. (C) 1998 Elsevier Science B.V.