Vadose-zone geochemistry of playa wetlands, High Plains, Texas

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dc.contributor.advisorBennett, Philip C. (Philip Charles), 1959-
dc.creatorRomanak, Katherine Duncker
dc.date.accessioned2018-01-29T21:26:55Z
dc.date.available2018-01-29T21:26:55Z
dc.date.issued1997
dc.description.abstractSoil-gas beneath 3 playa wetlands was monitored June 1992-May 1995 and sampled from as deep as 45 feet within the >2OO-ft unsaturated zone. Playa soils, surface water, rainwater, and groundwater were also analyzed, along with subsurface temperature and pressure. The objective was to assess factors controlling vadose zone geochemistry in the playa basin slope, playa lake annulus (shoreline), and playa floor. CO₂ as high as 17%, CH₄ as high as 2.2%, and O₂ from 0 to 21% were measured during the study and indicate the playa subsurface is microbially active. Microbial CO₂ gas production is highest in the playa floor and in the annulus during high water levels where high water flux (indicated by low soil carbonate and chloride contents) and high soil organic carbon exist. Methanogensis occurs locally on the playa floor in the "transition zone" and may result from locally high carbon flux and subsequent increased oxygen demand that exceeds oxygen replenishment to the subsurface. Soil-gas CO₂ is distributed throughout the subsurface via dissolution in infiltrating water and through gas transport. Floor and annulus areas have high PCO₂s (> 2.5%) that react with soil carbonate to cause extensive CO₂ and calcite dissolution as indicated by CO₂:0₂ mole ratios < 1 and N₂ > 78%. Soil breathing also lowers subsurface CO₂ concentrations but supplies O₂ to subsurface microbes. Temporary increases in CO₂ and decreases in O₂ result from standing water in playas and wetting fronts produced by rainfall events. Subsurface pressure measurements indicate that infiltrating water lowers gas permeability and inhibits mixing of subsurface and atmospheric gases. Barriers to vertical atmospheric mixing and pressure gradients produced by CO₂ dissolution in the playa center also drive lateral gas transport back and forth between the playa slope and playa floor. These flux potentials are as large as diffusive flux potentials but at times act in different directions. Direction of advective transport fluctuate with changes in barometric pressure favoring transport from the slope into the playa during high barometric pressures and transport out of the playa toward the slope during low barometric pressures.en_US
dc.description.departmentEarth and Planetary Sciencesen_US
dc.format.mediumelectronicen
dc.identifierdoi:10.15781/T20G3HF3H
dc.identifier.urihttp://hdl.handle.net/2152/63279
dc.language.isoengen_US
dc.relation.ispartofUT Electronic Theses and Dissertationsen_US
dc.rightsCopyright © is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en
dc.rights.restrictionOpenen_US
dc.subject.lcshWetland ecology--Texas
dc.subject.lcshWetland ecology--High Plains (U.S.)
dc.subject.lcshPlayas--Texas
dc.subject.lcshPlayas--High Plains (U.S.)
dc.subject.lcshGeochemistry--Texas
dc.subject.lcshGeochemistry--High Plains (U.S.)
dc.subject.lcshZone of aeration--Texas
dc.subject.lcshZone of aeration--High Plains (U.S.)
dc.titleVadose-zone geochemistry of playa wetlands, High Plains, Texasen_US
dc.typeThesisen_US
dc.type.genreThesisen
thesis.degree.departmentGeological Sciencesen_US
thesis.degree.disciplineGeological Sciencesen_US
thesis.degree.grantorUniversity of Texas at Austinen
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US

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