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Item Geochemical characterization of shallow sediments from the grounding zone of the Whillans Ice Stream(Montana State University - Bozeman, College of Agriculture, 2019) Roush, Kimberly Anne; Chairperson, Graduate Committee: John C. Priscu and John Dore (co-chair); John Priscu, Mark Skidmore, Alex Michaud and the WISSARD Science Team were co-authors of the article, 'Signatures of subglacial water in shallow sediments of the Whillans grounding zone and overlying water column' which is contained within this thesis.; John Priscu, John Dore, Wei Li, Tristy Vick-Majors and the WISSARD Science Team were co-authors of the article, 'Sediment porewater organic matter content' which is contained within this thesis.The research presented in this thesis focused on subglacial flow beneath the West Antarctic Ice Sheet (WAIS) and its potential influence near the grounding zone. Antarctic grounding zones are of specific scientific interest because they can impact the stability of the continental ice sheet and its breakup, potentially resulting in significant sea level rise. My major objective was to determine whether there was influence of subglacial water at the Whillans Grounding Zone (WGZ) on the Siple Coast of the WAIS. A gravity corer was used to collect a 70 cm sediment core through 780 m of ice borehole drilled using a hot water clean access drilling system. The core was collected in a marine embayment adjacent to the WGZ beneath a 10 m water column. I used a combination of geochemical, isotopic and organic matter analyses to characterize the benthic sediments, porewater and water column. The geochemical and isotopic data showed the influence of subglacial freshwater on sediment porewater at specific depths in the 70 cm core. Vertical gradients of chloride and sulfate between surficial sediment and the overlying water column indicated ion diffusion from porewater to the column water. Dissolved organic matter concentration of sediment porewater and the overlying water column also indicated upward diffusion occurs from porewater to the overlying seawater. Sediment particulate carbon and nitrogen data showed that benthic sediments were more depleted in nitrogen than the overlying seawater. Sediment particulate carbon and nitrogen data showed that benthic sediments were more depleted in nitrogen than the overlying seawater. Geochemical, isotopic and organic matter data supports the influence of subglacial freshwater at the WGZ.Item Thermal insulation versus capacitance: a comparison of shading and hyporheic exchange on daily and annual stream temperature patterns(Montana State University - Bozeman, College of Agriculture, 2017) Fogg, Sarah Kathleen; Chairperson, Graduate Committee: Geoffrey Poole; Geoffrey C. Poole, AnnMarie Reinhold and Scott J. O'Daniel were co-authors of the article, 'Thermal insulation versus capacitance: a comparison of shade and hyporheic exchange on daily and annual stream temperature cycles' submitted to the journal 'Water resources research' which is contained within this thesis.Channel shading and hyporheic exchange both effect daily and annual stream temperature cycles. In streams with thermal regimes that are too warm to support native biota, increasing shading or hyporheic exchange have largely been thought of as interchangeable management strategies because they influence summertime stream channel temperatures in similar ways. But, shading and hyporheic exchange operate via different mechanisms and influence stream temperature differently at differently times of the year. To understand daily and seasonal differences of shading and hyporheic exchange on stream channel temperature we used a process-based heat-budget model of channel temperature. Our model incorporates stream channel-atmospheric energy exchanges and a novel channel-subsurface heat exchange model that more appropriately represents the effects of hyporheic residence time distributions. We used our model to conduct an in silico experiment where we vary shading and hyporheic exchange on the same stream reach. In summer, the cooling and damping of channel temperatures associated with an expansive, coarse-grained hyporheic zone were similar to shading effects. However, the differences between shading and hyporheic exchange effects were most pronounced in the winter when channel warming associated with hyporheic exchange was substantially greater than warming associated with shade. By interpreting the changes in heat fluxes between shading a stream and adding hyporheic exchange, we find that shading acts as a thermal insulator and hyporheic exchange acts as a thermal capacitor. Our results show that shading and hyporheic exchange can have similar and differently effects on stream channel temperatures depending on what part of the year the effects are investigated, which has important management and modeling implications. Geography and geomorphic context of a stream are important considerations when choosing shading or hyporheic exchange for thermal restoration. In bedrock-confined streams that historically had closed canopies, shading has the greatest potential to reduce summer temperatures while restoration of hyporheic restoration is impractical in these systems. In contrast, in large, coarse-grained alluvial stream reaches, where riparian vegetation is historically sparse, restoring hyporheic influences has the greatest potential for reducing summer temperatures while increasing streamside shading is likely unattainable.