Award Date

1-1-2004

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geoscience

First Committee Member

Zhongbo Yu

Number of Pages

169

Abstract

Thick vadose zones in arid regions recorded past climate changes up to 100 ka, so they are unique archives for continental paleoclimate change and groundwater recharge during the late Quaternary. Despite extensive research on flow and transport in arid regions, the transport properties and general response of arid vadose zones to climate regimes are still not well understood. Some of these issues are addressed with four distinct studies in this dissertation. The first study investigates effects of soil texture, vegetation coverage, and macropores on soil moisture variation at Nevada Test Site (NTS). The simulations show that bare soils have higher soil water content than vegetated soils. Effects of macropore flow on soil water content are insignificant; The second study evaluates the impacts of climate change on solute transport in arid vadose zones. Undisturbed soil cores were collected at ground surface, directly below where tension infiltrometer measurements were made. The water fluxes and Br dispersion coefficients at investigated matric heads were very high due to the coarseness of the soils and possibly due to preferential flow pathways. These high water fluxes are more likely to occur in ephemeral washes. However, higher fluxes through the surface soil would be more likely during wetter climates; The third study simulates paleolake extent in Owens Valley in the last 18 ka. A coupled catchment-lake model is developed in this study, and used to reconstruct the observed paleolake levels for Owens Lake and Searles Lake. Finally, a quantitative time-series of paleoclimate information was obtained; The fourth study models the actual measured chloride profile in Amargosa Desert Research Site (ADRS) with the modified version of the HYDRUS-1D computer code by using variable boundary conditions. The paleoinformation estimated from the third study, and chloride concentration in Greenland ice core (GISP2) are used to prepare the atmospheric boundary file. The simulated chloride profile is in agreement with the measured chloride profile, and simulated water flux at ADRS is ∼0.016 mm/year upward at the base of the profile; Transport properties and general response of vadose zones to climate regimes are addressed by these four independent studies.

Keywords

Basin; Chloride; Chloride; Extraction; Great; Great Basin; Paleoclimate; Paleohydrology; Paleolake; Proxies; Records; Southwestern; Vadose; Zones

Controlled Subject

Geology; Hydrology; Geochemistry

File Format

pdf

File Size

3553.28 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Permissions

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Identifier

https://doi.org/10.25669/z7m5-pt8n


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