Soil Solute Concentration Distributions for Spatially Varying Pore Water Velocities and Apparent Diffusion Coefficients1

Water-carried constituents through soils are of great concern for maintaining a productive agriculture and a healthy environment. Soil water properties and salt concentrations are highly variable in natural soils. A Monte Carlo simulation is performed to obtain solute concentration and solute movement properties as affected by the variability of pore water velocity, v, and apparent diffusion coefficient, D. Normal distributions of ln v, ln D, and water-filled porosity were used to calculate 2,000 values of c/co using the solute flow equation with no soil-solute interaction. Both "step" and "pulse" inputs of salt water were simulated. For the pulse, both equal depths and equal infiltration time were investigated. The results indicate sharp differences between the solute profile when deterministic value of v is used as compared to average salt profile for 2,000 random values of v. The results also indicate that the variability of D is much less important than for v, particularly for deeper depths. For the pulse input, more salt is present in the upper part of the profile when 7.5 cm of salt water infiltrate at each point in the field as compared to the situation where 7.5 cm is the average infiltration depth for the whole area.