Optical signatures as a diagnostic tool for tracking dynamics of sedimentary dissolved organic nitrogen, phosphorus, and sulfur in an anthropogenic bay

Tracing the anthropogenic fingerprint and potential nutrient release from sediments is crucial from ecological and economic perspectives, but the lack of effective and low-cost tracking techniques poses a significant challenge. Here, we investigate the optical properties and molecular composition of sedimentary dissolved organic matter (DOM) from surface sediments (n = 41) collected along the land-sea continuum of an industrialized and urbanized bay in China. We use optical techniques (UV–visible spectroscopy and Excitation–emission matrix fluorescence spectroscopy) and Fourier-transform ion cyclotron resonance mass spectrometry for sedimentary DOM characterization. Five fluorescent components (C1-C5) are validated by Parallel Factor analysis (PARAFAC), representing diverse sources and types of sedimentary DOM, including aromatic/terrestrial, microbial, anthropogenic, and protein-like substances. Molecular analysis further reveals 14,052 unique compounds. Distinct molecular characteristics are identified for sedimentary dissolved organic nitrogen (DON), phosphorus (DOP), and sulfur (DOS). Sedimentary DOP exhibits the highest saturation, DON the highest aromaticity, and DOS the highest molecular weight. Optical parameters (e.g. fluorescence index) correlate significantly with specific molecular formulas of sedimentary DON, DOP, and DOS, suggesting that optical signatures can serve as a diagnostic tool for exploring internal nutrient release and point source pollution in aquatic ecosystems. This linkage will allow for efficient large-scale monitoring of sedimentary heteroatomic compound cycling in aquatic systems using optical techniques with robust interpretations, which has significant implications for sustainable watershed management. © 2024 Elsevier B.V.