A convective-dispersive-adsorptive flow model for solute transport in soils. II. Evaluation of single and two-component adsorption models for phosphate movement in soils

Abstract

Comparisons have been made between experimental breakthrough curves for phosphate ions in soil columns and computer simulations of solute transport based on a number of different adsorption models. These include single component linear and non-linear, instantaneous and dynamic adsorption models; as well as the model incorporating a combination of instantaneous and time-dependent components suggested in Part I. While certain portions of the complete breakthrough curves for phosphate could be reasonably approximated using simple one-component models, these generally failed badly to describe the shape and position of the experimental data over the complete range of the breakthrough curve. This was even more evident when both adsorption and desorption phases were considered. On the other hand, the model described in Part I combining instantaneous linear and a simultaneous time-dependent (dynamic) Freundlich-type adsorption components provided a good simulation of the experimental data over the full range of the breakthrough curves for both adsorption and desorption phases. Of particular significance is the ability of the model to handle successive experimental breakthrough curves with different amounts of residual adsorption. A method for 'normalizing' the solute transport equations to facilitate computer simulations is presented.