A Novel Approach Using Multiple Fluorescence Signals and Storm Event Clustering to Identify Riverine Dissolved Organic Matter Source Activation Pathways

Despite the potential of multipeak in situ fluorescence to provide better insight into solute transport pathways, most high frequency studies have focused on a single fluorescence peak (e.g., humic‐like fluorescence [HLF]). To address this gap, we analyzed two years of 15‐min fluorescence data for HLF and tryptophan‐like fluorescence (TLF) from an urban headwater in Birmingham, UK. Across 176 storms, we identified three storm types: Type 1 (low‐intensity, short‐duration), Type 2 (moderate‐intensity, long‐duration winter storms), and Type 3 (high‐intensity, short‐duration summer storms). By examining log C‐Q (concentration‐discharge) relationships within each storm type, we found that chemostatic versus chemodynamic behavior was primarily governed by intrinsic solute characteristics, with storm conditions exerting a secondary influence across storm types. HLF, owing to its recalcitrant nature and greater source availability, showed either buffered or flushing responses depending on storm type, whereas the labile nature of TLF, together with transient source availability and rapid biodegradation, led to consistently dilution dominated behavior. Comparisons between storm type and event scale log C‐Q slopes further showed that HLF responses were more predictable, whereas TLF responses were more stochastic. Analysis of synchronicity and event‐based C‐Q indices further suggested that Type 1 storms primarily mobilized in stream and near stream dissolved organic matter pools, Type 2 storms enhanced vadose zone contributions to HLF while suppressing TLF release, and Type 3 storms activated engineered headwaters and combined sewer systems. Overall, this study highlights the value of combining in situ multipeak fluorescence with storm event clustering to improve understanding of storm‐driven solute transport pathways.