Modeling soil solute release into runoff with infiltration

SummaryDespite empirical evidence that infiltration plays an important role in controlling the transfer of chemicals from soil to surface runoff, few mechanistic models have been tested under both infiltrating and non-infiltrating conditions. We used previously published experimental data to test a physically-based, solute transport model. The model’s underlying conceptual basis is that near-surface soil chemicals are ejected into runoff by raindrop impact and chemicals deeper in the soil diffuse into this near-surface raindrop “exchange-layer.” The experiments consisted of three soil types (clay, loam, and fine sandy loam) subjected to three infiltration conditions (none, full drainage, and reduced infiltration). Model parameters that could not be directly determined from the descriptions of the experiments were determined from previously published information or otherwise internally constrained. The model’s governing equations were solved numerically and the results agreed well with measured solute concentrations in both runoff and soil-water for all the experiments. The results emphasize the potentially important role of saturated, poorly draining parts of the landscape in contributing solutes to streams and lakes via overland flow.