Applications of cosmogenic ³⁵S in hydrological cycle studies

As global climate change intensifies and demands for water resource management increase, scientific understanding of water cycle processes has become critical. The concentration of the radioactive sulfur isotope (³⁵S, t_1/2 = 87.4 days) varies considerably among water cycle components, and this isotope has conservative chemical properties and a moderate half-life; it thus has unique advantages in short-term hydrological tracing studies. This paper reviews recent advances in the application of ³⁵S in hydrological research, encompassing research on its transport processes in precipitation, the key factors influencing its activity levels, and its utility in tracing hydrological processes, such as runoff partitioning and groundwater residence time estimation. Barriers to this research include insufficient monitoring networks and incomplete input function models. In future work, scholars should (1) establish a systematic ³⁵S field monitoring network, (2) optimize ³⁵S input function models, and (3) improve pretreatment methods for aqueous samples and reduce detection costs and pretreatment cycles. This review provides theoretical insights and methodological support to advance the application of ³⁵S in hydrogeology and the environmental sciences.