Modeling Phosphorus Transport in Surface Runoff

Abstract

ABSTRACT Asubmodel for estimating phosphorus loss from agricultural watersheds has been developed and incorporated into the ANSWERS watershed model. Model validation was accomplished using data from field plots. The model's usefulness as a planning tool was demonstrated on a watershed in Virginia. The model uses ANSWER'S extended sediment transport option to describe the transport of individual particle size classes. A nonequilibrium desorption equation is used to account for the desorption of phosphorus from the soil to surface runoff. Sediment-bound phosphorus is modeled as a function of the specific surface area of the soil and sediment. The equilibrium between soluble and sediment-bound phosphorus is modeled using a Langmuir isotherm.