<p>Eutrophication-induced hypoxia suppresses reactive oxygen species (ROS) formation at the sediment-water interface, impairing nutrient transformations. Here, we show that a nitrate-intercalated layered double hydroxide (CuFe/NO₃-LDH) reconstructs a ROS-active interface in eutrophic sediments. In sediment-column simulations with natural sediments and overlying water, CuFe/NO₃-LDH increased dissolved oxygen by 2.4-fold and raised peak H₂O₂, ·O₂⁻ and ·OH concentrations by 191%, 114% and 181%, respectively. Enhanced ROS accelerated dissolved organic matter turnover and bioavailability, enriching microorganisms involved in denitrification and phosphorus transformation and increasing the abundance of related functional genes. Coupled with phosphate immobilization by CuFe/NO₃-LDH and microbially mediated phosphorus mineralization, these processes reduced sediment total phosphorus by 28.5%. Meanwhile, CuFe/NO₃-LDH increased microbial electron transport chain activity by 74.6%, supporting denitrification and lowering sediment total nitrogen by 30.6%. These findings provide a mechanistic basis for sustainable in situ remediation of eutrophic sediments through ROS-mediated reconstruction of sediment redox and nutrient-cycling functions.</p><p></p>