Modeling of rainfall induced phosphorus transport from soil to runoff with consideration of phosphorus-sediment interactions

Abstract

Phosphorus (P) transport from soil to surface runoff is of great concern for the accurate prediction of P transport within the watershed, while the interaction between P and sediments has rarely been considered in conventional soil solute transport models. This study develops a novel P transport model that couples the processes of selective soil erosion and dynamic partitioning of P at the particle-water interface. The model assumes that the gradation of soil/sediment particles strongly affects the maximum amount of adsorption and therefore, affects P partitioning, while changes in the water environment also influence the partition coefficient. The novel model was then validated by four laboratory experimental runs. The R2 and RMSE values show that the simulated results are in good agreement with the measured data, indicating that the model is capable of effectively simulating rainfall induced P transport from soil to runoff. The modelled results indicate that an increase in the coarseness of sediment particles resulted in a sharp decrease in particle P adsorption (Csd) during erosion. Therefore, if the change in particle size was not accounted for in the model (Ked=Kp), the concentrations of soluble phosphorus (SP) and particulate phosphorus (PP) would be significantly underestimated. This highlights the importance of including selective erosion and P-sediment interactions in models of P transport from soils to surface runoff.