Scholarship & Research
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Item Glacial effects on stream water nitrate: an examination of paired catchments in southern Montana(Montana State University - Bozeman, College of Letters & Science, 2019) Allen, Jordan Jon; Chairperson, Graduate Committee: Mark L. Skidmore and Jean Dixon (co-chair)Nitrogen is frequently a limiting nutrient in biologic systems. Previous research on alpine streams and lakes in the Beartooth Mountains, Montana/Wyoming has demonstrated nitrate concentrations in waters draining glaciated catchments that are up to ten times greater than comparable adjacent non-glaciated catchments. The enhanced nitrate concentrations in the glacial fed lakes have been associated with increased diatom abundance relative to the snow fed-lakes. However, the source of the enhanced nitrate input remained undetermined, as well as how nitrate concentrations vary temporally during summer melt. This study measured concentrations of nitrate and ammonium and the isotopic composition of nitrate over the 2016 melt-season in a paired catchment system, in the Beartooth Mountains, Montana. The two catchments have similar elevations, atmospheric inputs, bedrock geology, area, and contain lakes, however, one catchment contains a glacier, the other does not. The stream waters in the glaciated catchment showed significantly elevated nitrate concentrations relative to those in the non-glaciated catchment and to catchment atmospheric input, as determined by snowpack nitrate concentrations. Nitrate concentrations in the glacial stream were observed to increase both temporally as the melt-season progressed, and spatially, with distance downstream from the glacier terminus. Ammonium concentrations in the glacial stream were highest close to the glacier terminus, declining with distance downstream, but also increasing during the melt season. Nitrate isotopic values distinguish the stream waters from atmospheric inputs indicating additional nitrate sources in the catchment. Potential additional sources include inorganic nitrogen released from bedrock sources and microbially fixed nitrogen. Abiotic laboratory weathering experiments simulating subglacial conditions reacted deionized water with finely milled bedrock at 4°C, and a modest quantity of ammonium was released. Potassium is often replaced by ammonium in minerals. Rocks from the study area contained ~3% potassium by weight. Ammonium could then be converted to nitrate through microbial processes within the proglacial environment adding to the atmospheric nitrate input to the stream nitrate budget. However, estimated rates of sediment production, and by inference ammonium production, cannot account for the observed nitrate concentrations and flux, indicating an additional nitrate source, which is most likely ultimately derived from microbial nitrogen fixation.Item Impacts of low summer streamflows on water resources in the Jefferson Valley : historical responses and future challenges(Montana State University - Bozeman, College of Letters & Science, 2016) Leone, Alex Michael; Chairperson, Graduate Committee: Julia Hobson HaggertyIn an attempt to understand the complex interrelationships between climate, water infrastructure regimes, and water governance this thesis examines relationships between drought and water use in the Jefferson River Basin in southwest Montana. The Jefferson River is one of the three great headwater streams of the Missouri River and is itself comprised of the Beaverhead, Big Hole and Ruby Rivers, encompassing a substantial drainage basin of 9,532 sq. miles. The Jefferson's unique hydrological position inherently situates the basin "at the end of the line" of water users and flows at its confluence have plummeted to 200 cubic feet per second (cfs) during extreme drought periods, leaving little water in the river to appease appropriators along the river's remaining 80 miles. The Jefferson River (and all of its important tributaries) is highly utilized for agriculture, resulting in chronic dewatering during peak irrigation demand (typically July through mid-September). Persistent water scarcities over the last 15 years have tested the Basin's ability to sustain historic levels of agricultural production and maintain a commercial sports fishery. This thesis provides a resilience assessment of water resources in Jefferson Basin. RA's attempt to conceptualize dynamic interactions between linked social and ecological systems (SES's). Analysis of complex human use systems (SES's) is inherently interdisciplinary and necessitates a mixed methods approach. The RA completed for this thesis integrated physical analyses of the water use system (utilizing GIS, hydrology, climate and demographic data) with a qualitative survey of water stakeholders with the goal of understanding the processes that drive the Jefferson SES and identifying weaknesses that reduce resilience. Over the last 30 years the Jefferson Basin has benefited from a unique subset of water users and natural resource managers that have successfully worked to improve conditions in the face of extreme environmental challenges. This RA found that although it is highly likely that the Jefferson will be challenged by extreme conditions in the future (related to a changing climate), it is also evident that there is potential for the basin to transition into alternate and more resilient regimes.