Development and application of laboratory and geophysical methods for the determination of hydraulic properties on desert pavements in the Mojave Desert

Interactions between pedologic development and hydrology have important implications for arid ecosystems and landscape evolution. The ability to rapidly evaluate hydraulic properties of a soil would greatly enhance our ability to study these relationships. The purpose of this work was (1) to develop a method for determining the hydraulic properties of structured soil peds; (2) to use the method to investigate the impact of surface age on the hydraulic properties; and (3) to investigate the efficacy of noninvasive geophysical methods for estimation of clay content and hydraulic properties of surface soils in arid environments. This work was conducted on multiple aged desert pavements in the Mojave National Preserve, California. To more fully investigate the mechanism of infiltration on desert pavements, we first ran a tension infiltrometer experiment on a well-developed pavement to determine the field hydraulic properties. The area directly underneath the disc was then excavated and brought to the laboratory. The peds that comprised the disc area were individually sampled using the newly developed method, which is a combination of the traditional evaporation experiment and parameter estimation. Hydraulic properties of the individual peds were then areally averaged and compared with the field-determined values. A comparison of the two methods provides an indication of the impact of the interped region on the hydraulic properties because the laboratory method sampled only the peds, whereas the field method sampled both peds and the interped cracks that separate them in the field. This method was then used on three different pavements of varying age (10 ka, 100 ka, and ∼600 ka), with triplicate measurements on each surface. Although the 600 ka is the oldest surface, the Av horizon and desert pavement mantling this surface is similar in age to the 10 ka because the original soil has been stripped and the horizon re-formed, making the Qf3 the oldest surface soil. Average field-determined hydraulic properties were compared to the average laboratory-determined values for each surface. Laboratory-determined values of KS and alpha showed a progressive decrease with age. This is in agreement with the aggradation model of desert pavement formation, where an influx of fine-grained eolian material causes the surficial soil horizon to grow and structurally develop. Field-determined values showed a similar decrease in KS and alpha from the Qf5 to the Qf3. However, these values both increased from the Qf3 to the Qf2, which supports the age data that suggests the Qf5 and Qf2 are similar in age at about 10 ka. (Abstract shortened by UMI.)...