Coupled water flow, heat transport, and solute transport in a seasonally frozen rangeland soil
T. J. Kelleners
Abstract
Abstract Soil water flow, heat transport, and solute transport in cold regions exhibit complex interactions that are difficult to quantify with measurements alone. For example, dissolved ions will lower the freezing point of soil water, while frozen soil will limit solute transport. In this study, a vertical one‐dimensional numerical model for coupled water flow, heat transport, and solute transport was combined with 8 years of Hydra impedance sensor monitoring data to estimate solute transport parameters in a high elevation, cool, semi‐arid mixed‐grass rangeland near Laramie, WY. Model calibration focused on the linear adsorption coefficient and the dispersivity in the solute transport equation. The brute force method was used to examine the complete parameter space using bulk soil electrical conductivity (σ b ) alone, and σ b divided by tortuosity (τ) in the objective function. The use of σ b yielded positive Modeling Efficiency (ME) for three out of five sensor depths (ME ≤ 0.49), while use of σ b τ −1 yielded negative ME ≤ −0.01 for all depths. The low ME for σ b τ −1 was expected as this ratio serves as a proxy for solute storage, which is expected to fluctuate relatively little with time for most terrestrial ecosystems. Reliable adsorption and dispersion coefficients could be determined for the 0–10 cm depth, and to a lesser extent, the 10–30 cm depth. At deeper depths, solute transport was only sensitive to the adsorption coefficient, so that reliable values for dispersivity could not be determined.