Response of greenhouse gas emissions to synergistic effects of terrigenous organic matter input and salinity dynamics in estuary

Abstract Estuarine regions experience significant accumulation of multi-source dissolved organic matter (DOM), which is associated with the greenhouse gas (GHGs) emission. However, the heterogeneous origins of DOM and its dynamic interplay with microbial processes complicate the understanding of its precise role in GHGs production, warranting further investigation. Here, we assessed the potential association between the composition of DOM and GHGs across three seagoing rivers in the estuary. Results showed that terrestrial-derived inputs predominate as the primary source of DOM in these inflowing rivers. Lignin constituted the principal component of riverine DOM, comprising 68.2% to 75.3% of the total, with its proportion demonstrably diminishing from upstream to downstream. The composition of DOM significantly influences the structure of microbial communities, with Proteobacteria emerging as the predominant microbial group in this region. Overall, the basin exhibited net GHGs emissions, particularly CH 4 , with recorded average fluxes in the three rivers measuring 11.5, 7.74, and 11.6 μg/m 2 ·min, respectively. GHGs emission reflect the distribution pattern of DOM, with emission fluxes and terrestrial DOM components gradually decreasing from upstream and downstream. This pattern was primarily driven by stronger terrestrial DOM inputs from surface runoff in upstream areas and the associated enhancement of microbial activity. Salinity was negatively correlated with GHGs emissions, particularly N 2 O, reflecting a suppressive effect of salinity on GHGs production in this estuarine region. These findings advance our understanding of DOM sources and clarify their influence on GHGs emission, providing a theoretical basis for more accurate assessment of GHGs dynamic in estuarine environments. Graphical Abstract