Isotope-Based Methods for Tracing Biogeochemical Processes in Natural Environments

Abstract

Isotopes provide a powerful and increasingly accessible means of following the movement and transformation of elements through air, water, soil, sediments and living organisms. Because physical, chemical and biological processes discriminate subtly between light and heavy isotopes, the isotopic composition of a compound carries a record of its origin and history. This article reviews the principles, analytical foundations and applications of isotope-based methods for tracing biogeochemical processes in natural environments. It discusses isotope fractionation, mass spectrometric measurement and reference standards, and then examines carbon, nitrogen, sulfur, hydrogen, oxygen and selected non-traditional isotope systems. Mixing models used for source apportionment are explained, together with their uncertainties. Finally, current challenges such as analytical standardization, process overlap, spatial and temporal scaling and data accessibility are considered, along with emerging directions including compound-specific, clumped and multi-isotope approaches. The review emphasizes that isotopes are most informative when combined with hydrological, chemical and microbiological evidence.