Spatial pattern of spring dissolved organic matter and microbial communities under dual anthropogenic-natural forcing...

Coastal zones serve as vital interfaces between continental and oceanic ecosystems, where anthropogenic inputs strongly influence dissolved organic matter (DOM) and associated microbial processes. However, the response of DOM-microbe interactions to various human activities remains inadequately understood. In this study, we examined physicochemical parameters, DOM optical properties, and microbial community structures in surface waters of Zhanjiang Bay, which is influenced by agricultural runoff, sewage, and industrial effluent. This pattern could be attributed to the impact of agricultural runoff and sewage input. Nutrient-rich terrestrial inputs were associated with enhanced humic-like and protein-like fluorescent DOM (FDOM) and high-molecular-weight, aromatic chromophoric DOM (CDOM), accompanied by the enrichment of Cyanobacteria and Thermoplasmatota. In contrast, in the lower bay, industrial activities, particularly effluent from a steel plant, resulted in an increased humic-like and protein-like FDOM alongside low-aromatic CDOM. Additionally, an increase in Verrucomicrobiota and humification index indicated that DOM may undergo decomposition processes in addition to in situ production. Multivariate analyses (PCA, RDA) confirmed strong correlations between physicochemical parameters, DOM properties, and microbial community composition. Collectively, these findings demonstrate that anthropogenic activities primarily shape DOM characteristics, which in turn structure microbial communities, highlighting the cascading effects of anthropogenic activities in regulating coastal biogeochemistry. This study elucidates the mechanistic pathway through which anthropogenically altered DOM composition shapes microbial community assembly, providing insights into the coupling between DOM dynamics and microbial ecology in anthropogenically impacted coastal ecosystems.