Modelling rainfall-induced phosphorus loss with eroded clay and surface runoff

Phosphorus (P) loss via runoff will reduce soil fertility and cause water eutrophication. Although P is lost as both particulate phosphorus (PP) and soluble phosphorus (SP), the existing P transport models for landscapes rarely consider PP and its exchange with surface runoff. We developed an integrated P transport model which coupled both SP and PP transport mechanisms based on the Rose-Gao model and assessed it via laboratory experiments. We also introduced a temporal varying P partition coefficient K-d into the model to reveal the impacts of rapid changes in the water environment on P adsorption and desorption. Experiments using kaolinite mixed soil and montmorillonite mixed soil were conducted under artificial rainfall events. The results show that the P transport model simulates the concentrations of eroded sediment, SP, and PP in surface runoff, with good agreement with the measured values (all R-2 > 0.88). Kaolinite mixed soil had larger sediment and SP concentrations in the runoff than montmorillonite mixed soil. In addition, compared with the no K-d model (Gao model) and the constant K-d model, our model provided simulation results that most closely matched the experimental data. Considering the influence of eroded sediment and the P dynamic partitioning between sediment and water to the surface, the P transport model can provide an effective tool for P dynamics with water and sediment in surface runoff.