Dissolved organic matter (DOM) entering river networks originates from a heterogeneous mixture of terrestrial, biological, and anthropogenic sources, yet resolving individual source contributions remains challenging due to overlapping chemical signatures. Here, we characterize the fluorescence signatures of eight major potential DOM sources in the Jiseok Stream, an agricultural tributary of the Yeongsan River, Korea, using excitation-emission matrix (EEM) fluorescence and optical indices (HIX, BIX, FI, SUVA₂₅₄). Sources included soils, vegetation, algae, composted manure, wastewater effluent, agricultural runoff, groundwater, and fertilizers (n= 58 total).
Terrestrial sources showed long-wavelength, humic-like fluorescence with high HIX (4-20) and low BIX/FI (<1.0), reflecting aromatic, refractory material. Biologically and anthropogenically derived sources showed blue-shifted, protein-like fluorescence, low HIX (<5), and elevated BIX/FI (>0.7, 1.3–1.7), reflecting labile, reworked material. Groundwater displayed a distinct low-aromaticity, high-FI signature (1.6-1.8). Across sources, HIX increased with terrestrial contribution while BIX and FI increased with microbial and anthropogenic input, forming a coherent spectral continuum. These results establish EEM-derived optical fingerprints as a rapid, transferable diagnostic tool for pollution-source tracing in agriculturally influenced watersheds.