Influence of relative surface age on hydraulic properties and infiltration on soils associated with desert pavements

Av horizons found in desert pavement environments are known to evolve pedogenically over geologic time. This study was conducted to determine whether increased pedogenic development of the Av (vesicular) horizon over relative time impacts the hydraulic properties of individual soil peds and the mechanism of infiltration as inferred by dye patterns. We examined peds from the Av horizons associated with desert pavements that mantled three different alluvial deposits with different relative surface ages (Qf5 (∼ 10 ka), Qf3 (∼ 50–100 ka), and Qf2 (∼ 10–50 ka)) and included an additional surface (Qf6 (∼ 4 ka)) for the dye studies. We hypothesized that increases in the development of the Av over time would lead to a more structured soil surface with greater potential flow between soil peds and lower hydraulic conductivity of the soil peds themselves. Results showed that average Ks and α of the Qf5 peds were significantly greater than estimated for the Qf2 and Qf3 peds. Although Ks was greater for the Qf5 peds, the steady-state infiltration rate was equal for the Qf3, Qf2, and Qf5 surfaces, perhaps indicating a reduction in matrix flow through soil peds and an increase in interped flow between soil peds.Studies were also conducted using dyed water and a tension disc infiltrometer, set to saturation. Following the tests the soil was excavated in 2-cm increments and photographed. The dye patterns for the Qf6 indicated that the water moved rapidly through the soil matrix into deeper soil, and without any preferential flow around peds. The Qf5 exhibited more dye-stained soil at depth than seen in the Qf2 and Qf3, perhaps due to higher ped conductivity. Qualitative observations on the Qf2 and Qf3 suggest that water flowed primarily along the ped faces and then toward the ped interiors. The results suggest that infiltration through Av horizons evolves from a matrix-dominated process on the younger soils to a preferential flow-dominated process on older surfaces.