Tracing of weathering reactions and water flowpaths: A multi-isotope approach

This chapter discusses the importance of using isotopes in a complementary manner, primarily to constrain and enrich models developed from hydrologic and chemical data. Isotopes are viewed as tools for testing rather than developing hypotheses, particularly in studies operating under tight budgetary constraints. Water isotopes are very useful tools for determining water sources in catchments. Chemical tracers are very useful for understanding the reactions along flowpaths. The potential application of Fe isotopes to catchment studies lies in the assumption that Fe mobilized inorganically from minerals under either reducing or low-pH conditions will have a different isotopic composition than microbially-reduced Fe. To the extent that certain zones or flowpaths in the catchment can be characterized by microbial cycling of labile Fe, the Fe isotopes may provide an effective tracer of contributions from these pathways. The solute isotopes, for example, strontium, carbon, and lead are as yet under-utilized in catchment research compared to the water isotopes.