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Item Tracing interactions of hydrogeology and land use in two Montana watersheds(Montana State University - Bozeman, College of Agriculture, 2024) Keeshin, Skye Ilan; Chairperson, Graduate Committee: Stephanie A. EwingHydrogeologic systems dictate the introduction, transport, processing, and mixing of groundwaters, with implications for both groundwater and surface water quality. Land use can transform hydrogeologic processes and water quality through contributions of human amendments, alteration of soil and aquifer materials, and redistribution and consumption of water resources. Groundwater transit times are also orders of magnitude longer than those of surface water systems, resulting in lag times in water quality changes. In this thesis, I examine water quality consequences of land use in Montana at two headwater sites using geochemical tracers in groundwater and surface water. The first is within the Powder River Basin, the largest coal producing region in the US, where manmade aquifers composed of spoils from mine overburden replace existing unconsolidated and bedrock aquifers with salinity effects on downgradient waters. In a reclaimed coulee supplying groundwater to Rosebud Creek, a tributary of the Yellowstone River, geochemical and isotopic tracers reveal lateral contributions that contribute to dilution of high salinity mine-derived waters. These contributions include local inputs from shallow unconsolidated and bedrock aquifers and inputs of water on the order of 10,000 years from regional bedrock systems. The second site is the Gallatin Valley, a rapidly urbanizing intermountain basin in the Upper Missouri headwaters, where groundwater and surface water transects reveal mixing of water with a range of ages from a few years to 100,000 years. While not associated with spatial variation in nitrate concentration, these contributions likely attenuate rising nitrate concentrations in the valley aquifer as a whole over time, reflecting spatially variable loading from a legacy of agricultural fertilization and increasingly prevalent septic wastewater systems. A large component of the Gallatin Valley aquifer is decades old water sourced from higher elevation precipitation, consistent with long travelled mountain front stream losses. This component may diminish over time with an increasingly limited snowpack. Overall, hydrogeologic systems in these two land use regimes limit but do not eliminate effects of human-derived water quality concerns, and documenting them will improve water quality forecasting with impending changes in snowpack and precipitation.Item Rock powered life in the Samail ophiolite: an analog for early Earth(Montana State University - Bozeman, College of Agriculture, 2021) Fones, Elizabeth Marie; Chairperson, Graduate Committee: Eric Boyd; Daniel R. Colman, Emily A. Kraus, Daniel B. Nothaft, Saroj Poudel, Kaitlin R. Rempfert, John R. Spear, Alexis S. Templeton and Eric S. Boyd were co-authors of the article, 'Physiological adaptations to serpentinization in the Samail ophiolite, Oman' in the journal 'The International Society for Microbial Ecology journal' which is contained within this dissertation.; Daniel R. Colman, Emily A. Kraus, Ramunas Stepanauskas, Alexis S. Templeton, John R. Spear and Eric S. Boyd were co-authors of the article, 'Diversification of methanogens into hyperalkaline serpentinizing environments through adaptations to minimize oxidant limitation' in the journal 'The International Society for Microbial Ecology journal' which is contained within this dissertation.; David W. Mogk, Alexis S. Templeton and Eric S. Boyd were co-authors of the article, 'Endolithic microbial carbon cycling activities in subsurface mafic and ultramafic igneous rock' which is contained within this dissertation.Serpentinization is a geochemical process wherein the oxidation of Fe(II)-bearing minerals in ultramafic rock couples with the reduction of water to generate H 2, which in turn can reduce inorganic carbon to biologically useful substrates such as carbon monoxide and formate. Serpentinization has been proposed to fuel a subsurface biosphere and may have promoted life's emergence on early Earth. However, highly reacted waters exhibit high pH and low concentrations of potential electron acceptors for microbial metabolism, including CO 2. To characterize how serpentinization shapes the distribution and diversity of microbial life, direct cell counts, microcosm-based activity assays, and genomic inferences were performed on environmental rock and water samples from the Samail Ophiolite, Oman. Microbial communities were shaped by water type with cell densities and activities generally declining with increasing pH. However, cells inhabiting highly reacted waters exhibited adaptations enabling them to minimize stresses imposed by serpentinization, including preferentially assimilating carbon substrates for biomolecule synthesis rather than dissimilating them for energy generation, maintaining small genomes, and synthesizing proteins comprised of more reduced amino acids to minimize energetic costs and maximize protein stability in highly reducing waters. Two distinct lineages of a genus of methanogens, Methanobacterium, were recovered from subsurface waters. One lineage was most abundant in high pH waters exhibiting millimolar concentrations of H2, yet lacked two key oxidative [NiFe]-hydrogenases whose functions were presumably replaced by formate dehydrogenases that oxidize formate to yield reductant and CO 2. This allows cells to overcome CO 2/oxidant limitation in high pH waters via a pathway that is unique among characterized Methanobacteria. Finally, gabbro cores from the Stillwater Mine (Montana, U.S.A) were used to develop methods for detecting the activities of cells inhabiting mafic to ultramafic igneous rocks while controlling for potential contaminants. Optimized protocols were applied to rock cores from the Samail Ophiolite, where rates of biological formate and acetate metabolism were higher in rocks interfacing less reacted waters as compared with more extensively reacted waters, and in some cases may greatly exceed activities previously measured in fracture waters. This dissertation provides new insights into the distribution, activities, and adaptations exhibited by life in a modern serpentinizing environment.