Numerical Simulations of Salt Accumulation In a Hyper-Arid Soil Chronosequence In the Sonoran Desert

Soil morphological features, including desert pavement, vesicular (Av) horizon and subsoil horizonation, are known to effect infiltration and redistribution processes and thus regulate the soil water balance. Soils of arid environments (PET>>ET) accumulate material both dust and salts through geologic time. For this study, a combination of field measurements, soil profiles, geomorphic and vegetation mapping, continuous soil moisture monitoring, and numerical modeling was used to evaluate numerical simulations of the soil moisture regime across a soil chronosequence (i.e. the substitution of space for time) ranging in age from 3 ka to >200 ka. The monitored soil microclimate (matric potential and temperature) were evaluated over a 4-year period and used to benchmark numerical simulations using Hydrus.

Results indicate a 10-fold decrease in the saturated conductivity (K_s) due to the presence of the Av horizon regardless of surface age (0.7 ± 0.1 cm h^-1). Measured B-horizon K_s were significantly higher (30 ± 12 cm h^-1) with a sharp textural contact between the B and overlying Av horizons. Av horizon thickness increased with surface age with concomitant increase in salt accumulation in the profile. Data and numerical results further illustrate the role of pedologic soil development on the resulting salt distributions within a heterogeneous alluvial fan sequence.