Dynamic exchange between particulate and dissolved matter following sequential resuspension of particles from an urban watershed under photo-irradiation

Particulate matter (PM) has long-term effects on water quality compared to dissolved matter (DM) during downstream transfer after inflows into an aquatic environment. In the present study, the characteristics, behavior, and effects of PM from an urban watershed under photo-irradiation were investigated through sequential resuspensions before being compared. Changes in the organic matter content, heavy metals (Mn, Fe, Zn, Pb), spectroscopic indices (SUVA₂₅₄, slope ratio (S_R), humidification index (HIX), fluorescence index (FI), and biological index (BIX)), excitation-emission matrix combined with parallel factor analysis components (EEM-PARAFAC), and disinfection by-product formation potential (DBPFP) were analyzed. According to our results, light enhanced the release of organic matter from PM but reduced dissolved heavy metals. The PM_U affected by urban-derived pollutants (i.e., rainfall particles, road-deposited sediment, sewer-pipeline-deposited sediment) exhibited higher quantities of terrestrial humic-like organic matter than PM_R, which contains base particles from riverines (i.e., soil, sediments). For the PM_U, the humic-like fluorescent components (C1 and C2) enhanced under light conditions with every resuspension, whereas the components decreased in the PM_R. Consistent with the PARAFAC results, the trihalomethane formation potential (THMFP) of the PM_U was enhanced by approximately 2.8 times more than that of the PM_R, and exhibited a high correlation with the fluorescent components (C1, r = 0.81, p < 0.001). The principal component analysis results also confirmed that the characteristics of dynamic exchanges between PM and DM were distinguished by PM sources and light, and the photo-released DM and their spectral characteristics displayed opposite behaviors depending on the PM sources during the sequential resuspensions.