Temporal moments analysis of preferential solute transport in soils

Temporal moments analysis of solute breakthrough curves is used to investig ate the preferential leaching of chloride, nitrate and phosphate trough an Australian soil. Recent studies have shown that current models and methods do not adequately describe the leaching of nutrients through soil, often un derestimating the risk of groundwater contamination by surface-applied chem icals, and overestimating the concentration of resident solutes. This inacc uracy results primarily from ignoring soil structure and nun-equilibrium be tween soil constituents, watts and solutes. Therefore simple models are req uired to accurately characterise solute transport in natural and agricultur al soils under non-equilibrium conditions. A multiple sample percolation sy stem, consisting of 25 individual collection wells was constructed to study . the effects of localised soil heterogeneities on the transport of nutrien ts (NO3-, Cl-, PO43-) in the vadose zone of an agricultural soil predominan tly dominated by clay. Using data collected from the multiple sample percol ation experiments, this paper compares and contrasts the performance of tem poral moments analysis with two mathematical models for predicting solute t ransport: the advective-dispersion model with a reaction term (ADR) and a t wo-region preferential flow model (TRM) suitable for modelling preferential transport. The values for solute transport parameters predicted by tempora l moments analysis were in excellent agreement with experimental data and r esults from ADR and TRM. It is concluded that temporal moments analysis whe n applied with other physical models such as the ADR and TRM, provide an ex cellent means of obtaining values for important solute transport parameters and gaining insight of preferential flow. These results have significant r amifications for modelling solute transport and predicting nutrient loading s.