DETERMINATION OF INTERPED FLOW AND SURFACE SEALING THROUGH INFILTRATION EXPERIMENTS ON A 100 KA DESERT PAVEMENT

Desert pavements are common surficial features in arid and semiarid regions worldwide. Pavements consist of a layer of varnished clasts at the surface, partially embedded within the underlying vesicular A (Av) soil horizon. The Av horizon is comprised of interconnected prismatic soil peds each with a platy internal structure as well as abundant vesicles. The highly structured, fine-grained nature of the Av horizon (typically 1-10 cm thick) has important ecological consequences in these water limited environments. Observational evidence indicates that the soil water content of material beneath the Av horizon is elevated, suggesting that the clast and horizon layers act as a mulch, which prevents water loss from the high evaporative demand. However, the mechanism by which moisture flows through the surficial layer, in both directions, is poorly understood. Recent work indicates that significant flow occurs through minute interped cracks. To investigate this hypothesis more fully, we conducted multiple tension infiltrometer experiments on a 100 kA desert pavement in the Mojave National Preserve, CA. Experiments were run for 1 hour at 0 cm of tension using dyed water. The area underneath the infiltrometers was then excavated at 2 cm depth increments with each depth being photographed. It has also been observed that a reduction in hydraulic conductivity caused by swelling clays could seriously affect the conditions under which moisture percolates through the Av horizon. To test this hypothesis, infiltrometer tests were also conducted at 0 cm tension on initially dry soil. Approximately 24 hours later, tests were repeated at the same locations to investigate the impact of antecedent moisture content on saturated hydraulic conductivity. Preliminary results of this study indicate that moisture preferentially moves through the interped areas, but that surface sealing does not significantly reduce the hydraulic conductivity of the Av horizon.