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

Abstract

packed gravel that overlies a thin (3-10 cm), fine-grained, gravel-poor, vesicular A (Av) soil horizon. 1 Desert pave-Desert pavements are prominent features in arid environments ments are prominent features in arid environments and and consist of a surface layer of closely packed gravel that overlies a thin, gravel-poor, vesicular A (Av) soil horizon. Well-developed Av can be found on a variety of landforms of significantly horizons form distinct and highly structured columnar peds. These diverse ages ranging from Holocene to Tertiary (Bull, structures, along with their silt-and clay-rich texture, are hypothesized 1991; Cooke et al., 1993). Pavements have been used in as controlling infiltration and hence the overall hydrologic conditions subdividing and correlating Quaternary alluvial fans for in the soil profile. The objectives of this study were to (i) evaluate studying neotectonics and Quaternary climate change how pedological development in near-surface soil horizons in an arid (McFadden et al., 1998; Bull, 1991; McDonald et al., alluvial fan complex affects the soil hydraulic characteristics, and (ii) 2003). Other research has shown that age is an important to compare the use of Wooding's equation and inverse modeling for consideration in development of desert pavements, esevaluating hydraulic conductivity in highly layered, near-surface soils. pecially in areas downwind of source zones for aeolian These objectives were approached through field tension infiltrometer deposited material (McDonald, 1994; McDonald et al., studies, soil sampling, and laboratory analyses of soil texture, water content, and soluble salt concentrations. Soils at five sites were studied 1996; McFadden et al., 1998). Pavements tend to be more at the Mojave National Preserve, California, representing a soil chro-prevalent and more strongly developed on older surnosequence (50-100 000 yr) with varying degrees of desert pavement faces where aerosolic clay-and silt-sized particles are development. Results indicated 100-fold and threefold declines, redeposited on the surface and are subsequently transspectively, in saturated hydraulic conductivity (K s ) with both analytical located downward into the soil profile. Increasing accumethods, and ␣ w using Wooding's method, as the soils aged. No clear mulation of aerosolic fines with time enhances the develtrends in K s or ␣ w were detected in the underlying horizon, indicating opment of a highly structured Av horizon consisting of that the controlling feature at these sites, in terms of water entry, was distinct columnar-shaped peds, ranging in diameter from the K s of the surface (Av) horizon. Soluble salt concentrations within about 3 to 8 cm, that part to platy peds, ranging in thickthe profile indicated reduced infiltration with increased pavement ness from 0.2 to 1 cm. The formation of desert pavement development. Results showed that surface age can be used as an excellent predictor of saturated hydraulic conductivity (r 2 ϭ 0.9254).and the Av horizon is extremely slow and can take from...

Runoff Generation, Overland Flow and Erosion on Hillslopes

“…The difficulty plant roots have in penetrating these horizons -most likely because of feedbacks with soil-water chemistry -is often a significant feedback on the ability of desert plants to maintain themselves (Cunningham and Burk, 1973;McAuliffe, 1994;Escoto-Rodríguez and Bullock, 2002;Gibbens and Lenz, 2001). Other developments of soil horizonisation, either at the surface (Abrahams and Parsons, 1991a;Young et al, 2004) or in the subsurface (Hamerlynck, McAuliffe and Smith, 2000;Hamerlynck et al, 2002), have been noted as having significant effects on reducing infiltration rates.…”

Pavements and Stone Mantles

“…The establishment of a mature desert pavement may take 4000-10 000 years or longer. After Young et al, 2004. hypothesis that pavement clasts have been continuously exposed since their formation (Liu and Broecker, 2008).…”

“…In some, but not all, regions, vesicular horizons show a pronounced columnar structure, caused by the alternating shrinking and swelling of clays in the increasingly clay-enriched Av-horizon, and a platy soil structure (McFadden, Wells and Jercinovich, 1987;Anderson, Wells and Graham, 2002;Young et al, 2004). Fine sand, silt and solutes are transported below the surface through the polygonal cracks by rain splash, surface wash and translocation, and the walls of the peds are coated with loose silt.…”

“…These properties diminish with time. The introduction of fines and salts into the soil profile retards the infiltration of water (Sena et al, 1994;Young et al, 2004). As a result, stone pavement surfaces with mature soils, embedded fragments and a well-knit surface texture tend to have very low infiltration rates, with little absorption of rain (Wells et al, 1985;Amit and Gerson, 1986;Valentin, 1994;Wood, Graham and Wells, 2005).…”

Desert Soils

“…Scattered patches of grass can be seen, marking locations where the pavement is less complete, and where water infiltration is possible. vesicular horizons develop includes progressive changes to infiltrability and surface water partitioning (Young et al, 2004). The development and significance of stone mantles are considered more fully in Chapter 9, and we will not consider them further here.…”