Multi-Omics Reveals the Impact of Domestic Wastewater Input on the Dissolved Organic Carbon Pool and Microbial Community in the Qiantang River Estuary

Estuarine ecosystems face intense anthropogenic pressures, yet systematic research on how domestic wastewater influences the dissolved organic carbon (DOC) pool via microbial community regulation remains limited. In this study, we conducted a microcosm experiment simulating wastewater input into the Qiantang River and integrated multi-omics (16S rRNA sequencing, metagenomics, metatranscriptomics, and FT-ICR MS) to elucidate the mechanism. Results showed that: (1) Wastewater input increased initial DOC and changed its degradation pattern: slower decay but higher removal. (2) Compared to the control, the wastewater-amended group exhibited a decreased fluorescence intensity contribution of carboxyl-rich alicyclic molecule (CRAM)-like compounds, indicating reduced chemical stability of recalcitrant DOC (RDOC). (3) Wastewater drove directional microbial succession from catabolic-dominant taxa (e.g., Comamonas, Citrobacter) to anabolic-dominant taxa (e.g., Reyranella), shifting metabolism from pollutant degradation to endogenous synthesis, thereby lowering the system’s efficiency in forming stable RDOC. (4) Multi-omics revealed a “stimulation-balance” functional response: early activation of xenobiotic degradation and signal transduction (day 2), followed by a shift to anabolic metabolism (day 28). This functional transition, driven by microbial succession, ultimately reduced RDOC stability. Our findings reveal that wastewater reshapes the microbial carbon pump, providing a theoretical basis for assessing estuarine carbon sink responses to pollution control measures.