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    Transport of CH₄ through open-talik lakes in discontinuous permafrost aquifers

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    Eckhardt_B_2020.pdf
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    Author
    Eckhardt, Bridget A.
    Chair
    Barnes, David L.
    Committee
    Daanen, Ronald P.
    Liljedahl, Anna K.
    Romanovsky, Vladimir E.
    Anthony, Katey Walter
    Keyword
    Greenhouse gases
    Thermokarst
    Groundwater
    Permafrost
    Methane
    Lakes
    Interior Alaska
    Metadata
    Show full item record
    URI
    http://hdl.handle.net/11122/12291
    Abstract
    As northern regions of the world experience warming climate, scientists look to permafrost, a crucial component of Arctic and subarctic ecosystems, as a source and sink of atmospheric carbon. It is well-known that the thawing of permafrost from above as a result of warming climate is a considerable source of greenhouse gases. However, few studies have considered the production of methane, a potent greenhouse gas, beneath the permafrost. A rugged permafrost bottom is proposed to favor the storage of gas in "pockets" that have been formed through permafrost thaw and degradation from below. Sub (below)-permafrost methane can migrate to reach the atmosphere when connections between the sub-permafrost and supra- permafrost open pathways from the pocket to the bottom of an open talik lake. We hypothesized that the migration of methane occurs through advection and diffusion as a dissolved gas and by movement as an immiscible fluid. Through measurement of environmental tracers in two thermokarst lakes in Goldstream Creek Basin, Fairbanks, Alaska, we found that advection was variable and was seasonally and climatically dependent demonstrating both upward and downward groundwater flow within our study lakes. Measurements of dissolved methane concentrations in the lakes demonstrated that diffusion of methane was not a significant transport mechanism in the groundwater-to-lake pathway due to the extreme temporal and spatial variability of methane concentrations. Immiscible flow of free-phase methane is likely the dominant transport mechanism but is dependent on the lake sediment composition and the formation of secondary pathways within the talik. Data obtained from this study allowed for a better understanding of methane transport and thermokarst lake dynamics.
    Description
    Thesis (M.S.) University of Alaska Fairbanks, 2020
    Table of Contents
    1 Introduction -- 1.1 Motivation -- 1.1.1 Climate Change -- 1.1.2 Groundwater hydrology and dynamics -- 1.2 Hypothesis and objectives -- 1.2.1 Advection -- 1.2.2 Diffusion -- 1.2.3 Immiscible-phase flow. 2 Literature review -- 2.1 Permafrost and taliks -- 2.2 Thermokarst lakes -- 2.3 Thermokarst lake CH₄ emissions -- 2.4 Permafrost hydrogeology -- 2.4.1 Groundwater recharge -- 2.4.2 Groundwater flow complexity -- 2.4.3 Groundwater-surface water interactions -- 2.4.4 Permafrost degradation as a result of groundwater flow -- 2.4.6 Flow direction in open taliks -- 2.5 Environmental tracers -- 2.5.1 Stable isotopes -- 2.5.2 Ionic tracers -- 2.5.3 Water temperature -- 2.5.4 Combining environmental tracers -- 2.6 Gas transport in saturated media. 3 Methods -- 3.1 Site description -- 3.1.1 Climate -- 3.1.2 Geology and permafrost features -- 3.1.3 Vegetation -- 3.1.4 Main study sites -- 3.2 Data collection locations -- 3.2.1 Lake water column samples -- 3.2.2 Lake sediment poles -- 3.2.3 Temperature loggers -- 3.2.4 Active layer drive point wells -- 3.3 Residential wells -- 3.4 Sediment core sampling -- 3.5 Water sampling procedures -- 3.5.1 In-situ pore-water sampling -- 3.5.2 Ex-situ pore-water sampling -- 3.5.3 Groundwater samples -- 3.5.4 Soil sampling for CH₄ analysis -- 3.6 Environmental tracers -- 3.6.1 Stable isotopes -- 3.6.2 Ionic tracers -- 3.6.3 Dissolved-phase CH₄ -- 3.6.4 Alkalinity -- 3.6.5 Field parameters -- 3.7 Development of soil moisture characteristic curves -- 3.7.1 Soil sampling -- 3.7.2 Sample preparations -- 3.7.3 Tempe cell tests -- 3.7.4 Pressure plate analysis -- 3.7.5 Brooks-corey model. 4 Results and discussion -- 4.1 Advection -- 4.1.1 Stable isotopes -- 4.1.2 Ionic tracers -- 4.1.3 Combining chemical tracers -- 4.1.4 Hydrostatic pressure -- 4.1.5 Temperature -- 4.2 Diffusion -- 4.3 Immiscible flow -- 4.3.1 Measurement of displacement pressures -- 4.3.2 Application of Caprock Seal Capacity theory -- 4.4 Overall transport -- 5 Future work -- Conclusion -- References -- Appendix.
    Date
    2020-08
    Type
    Thesis
    Collections
    New theses and dissertations

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