Increasing phosphorus loss despite widespread concentration decline in US rivers

Chaopeng Shen

Abstract: Phosphorus (P) reserves in Earth’s rocks are finite. P loss from land to rivers threatens not only food production but also aquatic ecosystem health. Long-term trend analysis of P loss has historically been challenged by sparse data. Here, we overcome this limitation by leveraging weather and earth characteristics data and building a multitask deep learning model for daily concentrations and fluxes (1980–2019) in 430 rivers at the Contiguous United States. Trend analysis shows widespread declines in concentrations, particularly in urban rivers. Concentrations in agricultural rivers, however, have mostly increased, suggesting not-as-effective controls of nonpoint sources. Despite declining concentrations, riverine P loss (fluxes) has significantly increased, driven largely by increasing streamflow in a changing climate.