Hydraulic Properties of a Desert Soil Chronosequence in the Mojave Desert, USA

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Desert pavements are prominent features in arid environments and consist of a surface layer of closely packed gravel that overlies a thin, gravel-poor, vesicular A (Av) soil horizon. Well-developed Av horizons form distinct and highly structured columnar peds. These structures, along with their silt- and clay-rich texture, are hypothesized as controlling infiltration and hence the overall hydrologic conditions in the soil profile. The objectives of this study were to (i) evaluate how pedological development in near-surface soil horizons in an arid alluvial fan complex affects the soil hydraulic characteristics, and (ii) to compare the use of Wooding's equation and inverse modeling for evaluating hydraulic conductivity in highly layered, near-surface soils. These objectives were approached through field tension infiltrometer studies, soil sampling, and laboratory analyses of soil texture, water content, and soluble salt concentrations. Soils at five sites were studied at the Mojave National Preserve, California, representing a soil chronosequence (50–100000 yr) with varying degrees of desert pavement development. Results indicated 100-fold and threefold declines, respectively, in saturated hydraulic conductivity (K s) with both analytical methods, and αw using Wooding's method, as the soils aged. No clear trends in K s or αw were detected in the underlying horizon, indicating that the controlling feature at these sites, in terms of water entry, was the K s of the surface (Av) horizon. Soluble salt concentrations within the profile indicated reduced infiltration with increased pavement development. Results showed that surface age can be used as an excellent predictor of saturated hydraulic conductivity (r 2 = 0.9254). Further, results suggest that Av horizon development represents a key process controlling water cycling, potentially influencing ecosystem function in arid lands.