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Accueil du site → Doctorat → États-Unis → 2008 → Surface processes, pedology, and soil-landscape modeling of the southern Fry Mountain bolson, Mojave Desert, California

University of California, Riverside (2008)

Surface processes, pedology, and soil-landscape modeling of the southern Fry Mountain bolson, Mojave Desert, California

Hirmas, Daniel Richard

Titre : Surface processes, pedology, and soil-landscape modeling of the southern Fry Mountain bolson, Mojave Desert, California

Auteur : Hirmas, Daniel Richard

Université de soutenance : University of California, Riverside

Grade : Doctor of Philosophy (PhD) 2008

Résumé
Previous research studying desert pedogenic and soil-geomorphic processes have concentrated on relatively subdued landforms of the piedmont. In so doing, these studies have neglected the contribution of and mountains to these processes. In addition, quantitative modeling approaches to understand soil inorganic carbon (SIC) have ignored topographic and soil effects on landscape water redistribution. The objectives of this work were to elucidate soil-geomorphic processes of arid mountains and to develop and test the application of a process-based model of SIC that accounts for landscape water redistribution. Sixty-five soils pits were sampled across a "complete" arid landscape in the southern Fry Mountains, Mojave Desert. At each location, a suite of land surface characteristic (LSC) variables were measured. These variables were used to discriminate and refine a classification system developed in this study for mountain landforms. The results distinguished four major landforms : mountaintop and bench, mountainflat, mountainflank, and mountainbase. Subsurface properties reflect the interaction of the mountains with dust and water at two scales. At the landscape-scale, the mountains are a topographic wind baffle encouraging the deposition of dust on windward sides. As a result, these mountains are a sink for considerable quantities of silicate dust (41 kg m−2), soluble salts (172 g m–2), NO3−-N (3.3 g m−2), and CaCO3 (79 kg m−2 ). At the landform-scale the distributions of these constituents are controlled by LSC variables and account for differences in soil morphology across the range. A cyclic process is proposed where water transports sediment to the piedmont and wind carries dust, salts, nitrate, and carbonate to the mountains where they are retained as long-term storage. The incorporation of two parameters (the precipitation and topographic index thresholds) into the SIC model allowed the average runoff-event recurrence interval to be estimated at 2.63 yr over the simulation period. Applying the model to the piedmont under an elevated atmospheric CO2 scenario resulted in the prediction of a consistent loss of CaCO3 from the upper 10 cm soil depth and a gain below 10 cm. The translocation of CaCO3 to deeper depths may stabilize SIC in landforms susceptible to wind erosion.

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