Mechanisms Governing Phosphorus Dynamics in the Yellow River: The Role of Damming and the Water‐Sediment Regulation Scheme

Abstract Phosphorus is a critical nutrient for freshwater ecosystem health, yet the interactive effects of dam operation and anthropogenic pollution on water‐sediment‐phosphorus dynamics in sediment‐rich river systems remain poorly characterized. This study analyzes the spatiotemporal heterogeneity of total phosphorus (TP) concentration (TPC) and flux (TPF) across the Yellow River during 2006–2022, to investigate the mechanisms by which damming and Water‐Sediment Regulation Scheme (WSRS) reshape water‐sediment‐phosphorus dynamics. Our findings reveal that damming reduced the phosphorus transport capacity by ∼60% compared with non‐dam‐influenced reaches during 2006–2015. As reservoir sedimentation progressed and the WSRS was implemented, the TP in the middle reach gradually recovered, leading to a substantial increase in TPC during 2016–2022. The Xiaolangdi mega‐reservoir substantially disrupts the synchronization of water‐sediment‐phosphorus relationship due to large storage capacity, extended hydraulic retention time, and complex WSRS. We suspect that damming induces an approximately 6‐year time lag effect between the cumulative pollution source input and the net TPF. The study emphasizes that global management of dammed rivers should shift from simple source control and water‐sediment regulation toward an integrated strategy encompassing legacy phosphorus management and multi‐objective reservoir operation.