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Description
Growth of the Phoenix metropolitan area led to exposures of the internal bedrock structure of surrounding semi-arid mountain ranges as housing platforms or road cuts. Such exposures in the Sonoran and Mojave deserts reveal the presence of sedimentary calcium carbonate infilling the pre-existing fracture matrix of the bedrock. Field surveys

Growth of the Phoenix metropolitan area led to exposures of the internal bedrock structure of surrounding semi-arid mountain ranges as housing platforms or road cuts. Such exposures in the Sonoran and Mojave deserts reveal the presence of sedimentary calcium carbonate infilling the pre-existing fracture matrix of the bedrock. Field surveys of bedrock fractures filled with carbonate (BFFC) reveal an average of 0.079 +/- 0.024 mT C/m2 stored in the upper 2 m of analyzed bedrock exposures. Back-scattered electron microscopy images indicate the presence of carbonate at the micron scale, not included in this estimation. Analysis of the spatial extent of bedrock landforms in arid and semi-arid regions worldwide suggests that ~1485 GtC could potentially be stored in the upper 2 m horizon of BFFCs. Radiocarbon dating obtained at one of the sites indicates it is likely that some of the carbonate was flushed into the bedrock system during glacial wet pulses, and is stored on Pleistocene timescales or longer. Strontium isotope analysis at the same site suggest the potential for a substantial cation contribution from weathering of the local bedrock, indicating the potential exists for sequestration of atmospheric carbon in BFFCs. Rates of carbon release from BFFCs are tied to rates of erosion of bedrock ranges in desert climates.
ContributorsHarrison, Emma (Author) / Dorn, Ronald (Thesis advisor) / Reynolds, Stephen (Committee member) / Schmeeckle, Mark (Committee member) / Arizona State University (Publisher)
Created2013
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Description
Increasing concentrations of carbon dioxide in the atmosphere will inevitably lead to long-term changes in climate that can have serious consequences. Controlling anthropogenic emission of carbon dioxide into the atmosphere, however, represents a significant technological challenge. Various chemical approaches have been suggested, perhaps the most promising of these is based

Increasing concentrations of carbon dioxide in the atmosphere will inevitably lead to long-term changes in climate that can have serious consequences. Controlling anthropogenic emission of carbon dioxide into the atmosphere, however, represents a significant technological challenge. Various chemical approaches have been suggested, perhaps the most promising of these is based on electrochemical trapping of carbon dioxide using pyridine and derivatives. Optimization of this process requires a detailed understanding of the mechanisms of the reactions of reduced pyridines with carbon dioxide, which are not currently well known. This thesis describes a detailed mechanistic study of the nucleophilic and Bronsted basic properties of the radical anion of bipyridine as a model pyridine derivative, formed by one-electron reduction, with particular emphasis on the reactions with carbon dioxide. A time-resolved spectroscopic method was used to characterize the key intermediates and determine the kinetics of the reactions of the radical anion and its protonated radical form. Using a pulsed nanosecond laser, the bipyridine radical anion could be generated in-situ in less than 100 ns, which allows fast reactions to be monitored in real time. The bipyridine radical anion was found to be a very powerful one-electron donor, Bronsted base and nucleophile. It reacts by addition to the C=O bonds of ketones with a bimolecular rate constant around 1* 107 M-1 s-1. These are among the fastest nucleophilic additions that have been reported in literature. Temperature dependence studies demonstrate very low activation energies and large Arrhenius pre-exponential parameters, consistent with very high reactivity. The kinetics of E2 elimination, where the radical anion acts as a base, and SN2 substitution, where the radical anion acts as a nucleophile, are also characterized by large bimolecular rate constants in the range ca. 106 - 107 M-1 s-1. The pKa of the bipyridine radical anion was measured using a kinetic method and analysis of the data using a Marcus theory model for proton transfer. The bipyridine radical anion is found to have a pKa of 40±5 in DMSO. The reorganization energy for the proton transfer reaction was found to be 70±5 kJ/mol. The bipyridine radical anion was found to react very rapidly with carbon dioxide, with a bimolecular rate constant of 1* 108 M-1 s-1 and a small activation energy, whereas the protonated radical reacted with carbon dioxide with a rate constant that was too small to measure. The kinetic and thermodynamic data obtained in this work can be used to understand the mechanisms of the reactions of pyridines with carbon dioxide under reducing conditions.
ContributorsRanjan, Rajeev (Author) / Gould, Ian R (Thesis advisor) / Buttry, Daniel A (Thesis advisor) / Yarger, Jeff (Committee member) / Seo, Dong-Kyun (Committee member) / Arizona State University (Publisher)
Created2015
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Description
Coastal dunes are dynamic landforms that provide the first defense for sea-level rise and coastal flooding. Coastal dunes depend on vegetation to trap and store sediment, which alters beach-dune sediment budgets and foredune morphology. Invasive vegetation species change these patterns and alter how the system responds to both littoral and

Coastal dunes are dynamic landforms that provide the first defense for sea-level rise and coastal flooding. Coastal dunes depend on vegetation to trap and store sediment, which alters beach-dune sediment budgets and foredune morphology. Invasive vegetation species change these patterns and alter how the system responds to both littoral and aeolian processes. Dynamic restoration is a growing practice whereby plant communities are modified to enhance aeolian processes and help return coastal dune ecosystems to a more ‘natural’ state of ecosystem structure and function. A portion of the foredune system at the Lanphere Dunes in the Humboldt Bay National Wildlife Refuge (HBNWR), near Arcata in northern California was targeted for dynamic restoration. The invasive plant species Ammophila arenaria (European beach grass) was removed in August 2015, while native vegetation treatments consisting of combinations of a dune mat forb assemblage and the dune grass Elymus mollis (Sea Lyme-grass) were planted over the summer and over the winter of 2016-17. Four different vegetation regimes were studied consisting of a control plot of A. arenaria two plots of exclusively Dune mat and E. mollis, and then a plot that is the combination if Dune mat and E. mollis. This restoration presented the opportunity to study the patterns of vegetation re-establishment and the related responses in sedimentation and morphological adjustment of the foredune system at both the landform and vegetation plot scales. Bi-annual terrestrial laser scanning surveys and cross-shore transects were used to calculate volumes of sediment change, distinguish patterns of sediment erosion/deposition and discern geomorphic change within different plant cover types. Results suggest that the Dune mat-E. mollis assemblage was most effective a trapping sediment with 96.9% of the plot experiencing deposition over the 17-month observation period, to a spatially averaged depth of +0.16m. During the study, the Dune mat treatment site experienced a landward flattening of its crest and considerable erosion of up to -0.5m around the plants, resulting in a normalized volumetric change of -0.139 m3 m-2. The E. mollis site experienced considerable sediment bypassing on the stoss slope and deposition on the lee slope of the foredune, resulting in accumulation at the toe of the lee slope of +0.6m while base of the lee slope moved 4m landwards. Site morphodynamics and sediment budgets were also influenced by changes in vegetation density and recovery from storm erosion. Longer terms studies could be conducted to investigate responses to vegetation disturbances over a longer temporal scale.
ContributorsHuck, Rosemary Alice (Author) / Walker, Ian (Thesis director) / Dorn, Ronald (Committee member) / Historical, Philosophical & Religious Studies (Contributor) / School of Geographical Sciences and Urban Planning (Contributor, Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05