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Item Biogeochemical gradients and energetics in geothermal systems of Yellowstone National Park(Montana State University - Bozeman, College of Agriculture, 2006) Ackerman, Galena Gene; Chairperson, Graduate Committee: William P. Inskeep.The fate and behavior of redox-active chemical species in geothermal systems is linked with the metabolic processes of chemotrophic thermophilic microorganisms. The major goal of the current work was to perform a thorough geochemical analysis of redox active species in geothermal outflow channels, and utilize these measurements to quantify the Gibbs free energy (?Grxn) values for numerous oxidation-reduction reactions that represent potential chemolithotrophic metabolisms. Insights gained from energetic analyses can be used to structure hypotheses regarding novel microbial metabolisms and to guide cultivation strategies for isolating relevant microorganisms. A comprehensive suite of geochemical parameters, including major ions, trace elements, redox-active species and dissolved gases, were analyzed and monitored in vertical transects of 11 geothermal outflow channels in Yellowstone National Park from 2003-2005. The geothermal springs chosen for this study contained strikingly different aqueous and solid-phase geochemistry. These systems exhibited a wide range of conditions, including ranges in pH (2.7 to 7.0), temperature (60 oC to 92 oC), Cl- (0.01 to 23 mM)), SO42- (0.4 to 7.5 mM), NH4+ (0.02 to 5.7 mM), CO2 (aq) (0.1 to 4.5 mM), Fe (0.2 to 230 uM), and As (0.03 to 130 uM)