The Yellow River Wetland (YRW) serves as a critical zone for groundwater transport of dissolved substances to the Bohai Sea. Geo-engineering such as the Water-Sediment Regulation Scheme (WSRS) along the Yellow River strongly influence water fluxes both within the Yellow River and the YRW. Quantifying the impacts of WSRS on groundwater biogeochemical cycles requires field surveys that not only cover high-spatial resolution but also concurrently investigate both the dissolved and solid phases within the groundwater system. In this study, we present vertical distributions and spatiotemporal evolution of dissolved nutrients, major ions, metal elements and dissolved organic matter (DOC), and sediment mineral compositions from long sediment cores (up to 3.5 m long) retrieved from three sites along a river-to-sea transect collected before, during, and after the WSRS in 2024. Our results showed that the mobility of metal elements is strongly dependent on groundwater redox states, in line with earlier studies. Specifically, much higher concentrations of groundwater ferrous iron (Fe (II)) and manganese were observed at both the riparian and tidal site after the WSRS, suggesting that the WSRS significantly enhanced reducing conditions within the wetlands. Strengthened reducing conditions resulted in lower levels of groundwater DOC, uranium, nickel, and zinc, yet elevated concentrations of arsenic. Conversely, elemental distributions at each site displayed strong heterogeneity, demonstrating that lateral migration of metal elements within the aquifer is severely restricted by the low permeability and high adsorption capacity of the wetland soils (dominated by silt and clay). Our new data demonstrated that the WSRS has profoundly impact groundwater geochemical cycling within the wetlands, yet its contribution to metal exports to the near-shore environment is likely limited and largely regulated by local hydrogeomorphic settings.

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