Human alterations to global riverine phosphorus fluxes to the ocean.

Rivers regulate land-ocean total phosphorus (TP) fluxes critical to ecosystem health and food security, yet global dynamics remain poorly understood due to limited observations. Here, we develop a machine learning framework integrating multimodal data and 280,000 TP measurements to reconstruct TP flux patterns over 1980-2019 across 420 major rivers. Results reveal a deceptive global equilibrium. While TP flux declines in the Northern Hemisphere, driven by dam trapping, particularly in Western Europe (-16.2%) and Eastern Asia (-8.7%), it rises in the Southern Hemisphere due to increased fertilizer use and deforestation, especially in Southern Africa (+15%) and the Malay Archipelago (+20.3%). Notably, the number of small rivers with rising TP flux is nearly double that of large rivers. This growing TP export from small rivers and Southern Hemisphere basins may intensify eutrophication, expand hypoxic zones, and threaten fishery yields. Our findings highlight a shifting global phosphorus landscape and underscore the need for more targeted, sustainable phosphorus management strategies.