Combining Fluorescent Organic Substances, Ions, and Oxygen-18 to Trace Diverse Water Sources of River Flow in a Hilly Catchment

Reliable identification of river hydrograph separation is crucial for prioritizing water source areas to be protected from pollution. A field study was carried out in a hilly catchment with diverse land uses, located in Southwest China. A novel water-tracing method, combining the ratio of two conservative fluorescent components of dissolved organic matter, two ion ratios, and oxygen-18, was proposed for river hydrograph separation with MixSIAR. During a rain event with the longest preceding no-rain period, a set of four tracers were found to be applicable to drainage areas with diverse land uses. Notably, a drier antecedent soil moisture condition could favor the occurrence of more tracers qualified for distinguishing multiple water sources of river flow.