Insight into the pollution potential of different ecological types of lakes from the perspective of dissolved organic matter characteristics: Field and experimental evidence

The changes in dissolved organic matter (DOM) in freshwater lakes are crucial for understanding water quality dynamics and the carbon cycle, yet the mechanisms driving these changes remain unclear. In this study, six freshwater lakes were categorized into two ecological types: algae-dominated and hydrophyte-dominated. The characteristics of their DOM were found to be significantly different. Algae-dominated lakes exhibited a higher distribution ratio of C4 (tyrosine-like) fluorescence component. Notably, the emission fluxes of methane (CH₄) and carbon dioxide (CO₂) were significantly correlated with tyrosine-like substances the in algae-dominated lakes. Simultaneously, microcosms simulating algae and hydrophyte decomposition were cultured to represent these distinct ecological types. The characteristics of the DOM components aligned with the field survey results, and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) indicated that the algae-dominated microcosms contained higher protein content and greater variation. The relative abundance of Bacteroidetes was consistently higher in algae-dominated microcosms. Furthermore, this study identified that the high concentration of proteins produced by algae decomposition played a key role in promoting water quality deterioration. These findings illuminate the differences in DOM characteristics during hydrophyte and algae decomposition across various lake types, providing valuable insights for effective lake management.