Biogeochemical reactions and vadose zone transport, in particular gas phasetransport, are inherently coupled processes. To explore feedback mechanisms between these processes in a quantitative manner, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described based on the Dusty Gas Model, which provides the most generally applicable description for gas diffusion.Gas advection is described by Darcy's Law, which in the current formulation, is directly substituted into the transport equations. The model is used to investigate the interactions between geochemical reactions and transport processes with an emphasis to quantify reaction-induced gas migration in the vadose zone. Simulations of pyrite oxidation in mine tailings, gas attenuation in partially saturated landfill soil covers, and methane production and oxidation in aquifers contaminated by organic compounds demonstrate how biogeochemical reactions drive diffusive and advective transport of reactive and non-reactive gases. Pyrite oxidation in mine tailings causes a pressure reduction in the reaction zone and drives advective gas flow into the sediment column, enhancing the oxidation process. Release of carbondioxide by carbonate mineral dissolution partly offsets pressure reduction, and illustrates the role of water-rock interaction on gas transport. Microbially mediated methane oxidation in landfill covers reduces the existing upward pressure gradient, there by decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, both generation of CH⁴ in the methanogenic zone and oxidation of CH⁴ in the methanotrophic zone contribute to drive advective and diffusive fluxes. The model confirmed that non-reactive gases tend to accumulate in zones of gas consumption and become depleted in zones of gas production. In most cases, the model was able to quantify existing conceptual models, but also proved useful to identify data gaps, sensitivity, and inconsistencies in conceptual models. The formulation of the model is general and can be applied to other vadose zone systems in which reaction-induced gas transport is of importance.

Thesis (M.S.)--University of Wisconsin--Madison, 1961. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 63-65).

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 167-178). Available also in a digital version from Dissertation Abstracts.

Thesis (MMedVet. (Production Animal and Community Health, Veterinary Science))--University of Pretoria, 2000. / Also available in print format.

Afhandling--Kgl. Veterinaer- og Landbohøjskole, Copenhagen. / Summaries in Danish and German. Includes bibliographies.

Thesis (M.S.)--West Virginia University, 2010. / Title from document title page. Document formatted into pages; contains ix, 49 p. : ill. (some col.), col. maps. Includes abstract. Includes bibliographical references (p. 47-49).

Inaug.-diss.-Bern. / "Literaturverzeichnis": p. [61]-64.

Thèse (M.Sc.) -- Université Laval, 1998. / Bibliogr.: f. 29-32. Publié aussi en version électronique.

Thesis (M. Sc.)--University of Hong Kong, 2006.

AN ABSTRACT OF THE THESIS OF Mana-anya Iemsam-arng, for the Master's degree in Agribusiness Economics, presented on November 9, 2010, at Southern Illinois University Carbondale. TITLE: Contamination Events and Linkages in World Rice Markets MAJOR PROFESSOR: Dr. Dwight Sanders In August of 2006, genetically modified LibertyLink rice contaminated the supply of non-GMO rice in the United States, causing damage to the U.S. rice production sector's credibility in their export market. The damage to the United States' credibility included doubt as to whether or not they had the ability to separate GMO and non-GMO rice strains during planting and/or production. This caused a short-term decline in the price of U.S. rice. The purpose of this paper is to examine rice price relationships from August 1997 to February 2010 among the four major rice exporting countries (Thailand, Vietnam, the United States, and India) before and after the genetically modified rice contamination event. Using unit root tests and cointegration tests, the results show that international rice export prices are independent from each other, yet the U.S., Thailand, and Vietnam 5 percent broken DWP rice prices tended to change in the same direction. The fact that the change in rice prices occurred right after the U.S. GMO contamination event of August 2006 is statistically significant. However, the results of this study cannot be proven to indicate that the contamination event's impact caused this change in rice export prices. Keywords: Rice prices, Contamination Events