Environmental Fingerprints of Nonoxygen Heteroatomic Molecules in Aquatic Dissolved Organic Matter Elucidated by Ultra-High-Resolution Mass Spectrometry

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The quality and chemodiversity of aquatic dissolved organic matter (DOM), crucial to global carbon cycling and aquatic ecological functions, are affected by microbial and anthropogenic activities. In this study, molecular characteristics of DOM collected from 14 field water samples were compared with three standard samples from the International Humic Substances Society using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Results indicated that microbially and terrestrially derived DOM contributed to the surface water and groundwater DOM pool, with higher DOM molecular lability (higher H/C_iw) in field water than IHSS standards, which was related to the overall impact of diverse biogeochemical processes and anthropogenic factors. The microbial and anthropogenic perturbations contribute more nonoxygen heteroatomic (N, S, and Cl atoms) molecules in the field water, and organic pollutants (surfactants and sucralose) had significant DOM signatures in waters affected by intensive anthropogenic emissions. A strong correlation among microbial indicators, nutrients, and DOM molecular characteristics indicated that the synthetic results of microbial and anthropogenic activities within the basin contributed more nonoxygen heteroatoms and increased the DOM molecular diversity. This study has highlighted the environmental molecular signatures of nonoxygen heteroatoms in reflecting the microbial and anthropogenic factors, shedding new insights into freshwater health.