Multi-approach framework to estimate the mass flux at the sediment-water interface based on the effective diffusivity coefficient: A case study of the largest lake in North China

Study region: Baiyangdian Lake, the largest freshwater lake on the North China Plain, is located in Xiong'an New Area of Hebei Province.Study focus: Physical, chemical, and biological reactions are active at the sediment-water interface and have a complex impact on the interfacial transport process. Based on the theory of the effective diffusion coefficient, combined with the analysis of sediment, in-situ observations, and a hydrodynamic model, we built a multi-approach framework to accurately estimate the interfacial mass flux and its temporal and spatial variations.New hydrological insights for the region: The results showed that the NH4+-N release flux across the interface varies between 6.12 and 62.30 mg m ? 2 d-1. The transport processes in the Nanliuzhuang and Mapeng regions were dominated by the dispersive regime, whereas those in the remaining regions were dominated by the molecular regime. Under extreme weather conditions, such as typhoons, the mass flux is more than five times that under windless conditions. At this time, the framework to estimate the interfacial mass flux based on the effective diffusivity coefficient (FEIMF-EDC) can better reflect the sudden increase in mass flux caused by short-term strong hydrodynamic disturbances. This framework has a good application effect in shallow lakes with obvious spatiotemporal heterogeneity of sediment and hydrodynamics and can provide a basis for accurately formulating plans for water environment monitoring and management.