Simulating Bromide Transport from Soil to Overland Flow: Application and Evaluation of Interfacial Diffusion-Controlled Model

The interfacial diffusion-controlled models of chemical transport across the interface of the soil surface and overland flow are physically based and can be easily expanded to include other functional modules to predict chemical loads from soil to overland flow. The efficiency of the model predictions and the veracity of the parameters are critical for accurate estimation of the chemical loads. In this study, the interfacial diffusion-controlled model was employed to simulate the transport process of a dissolved chemical (bromide, ${\mathrm{Br}}^{-}$) from saturated soil to overland flow. The model parameters were optimized by fitting the analytical solution of the model with experimental data. Comparison between model simulations and experimental observations showed that the model is efficient for predicting (${\mathrm{Br}}^{-}$) transport in the soil and overland system. It predicted runoff-concentration data very well and predicted the short-term change in the upper soil profile better than the long-term change in the lower profile. When the mass transfer coefficient estimated by the existing equation was applied in the model, the model underestimated the chemical loads in overland flow by a relative error of 21.5% in this study, which was attributed to the neglect of rainfall impact on the solute transfer from the soil surface to overland flow.