East China Sea (ECS) is a highly dynamic hotspot of dissolved organic matter (DOM) production, transformation, degradation, and transport. Optical and ultrahigh-resolution mass spectrometry techniques have been well applied in characterizing the sources, degradation and transformation of DOM. However, further studies are still needed to clarify the environmental controlling factors of DOM degradation in highly dynamic coastal oceans, which is imperative for advancing our understanding of the DOM biogeochemical cycles. In this study, seasonal field investigations were conducted in 2023 in the Changjiang Estuary and its adjacent ECS. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and optical techniques were combined to characterize the composition and degradation state of DOM. The relations between bacterial community composition, environmental factors and DOM components were analyzed to interpret the controlling factors of DOM degradation and the DOM-microbial interactions. The differences and linkages between optical and molecular parameters in interpreting the DOM behaviors were also discussed. The results provide new perspectives for the biogeochemical cycles of DOM in dynamic coastal oceans.

FT-ICR MS,CDOM,DOM,microbial degradation