ABSTRACT
Stable isotopes are used in two ways in environmental investigations: (1) they are introduced as tracers to map the ow of mass through a system, or (2) the stable isotope compositions of materials are measured to infer the processes responsible for isotope distribution patterns at the natural abundance level. The latter usage requires some fundamental knowledge about the factors that inuence stable isotope partitioning in nature. Much of this information has been gathered over the last half century for the biologically active elements, hydrogen (H), carbon (C), nitrogen (N), oxygen (O), and sulfur (S). The mass difference between the rare and most common isotope is relatively large for these elements, which results in isotope fractionation during physicochemical and biological reactions and permits distinctions to be made concerning the origin and modication of materials over time.
