Alumni Dissertations

 

Alumni Dissertations

Filter Dissertations By:

 
 
  • Cryospheric Teleconnections: The Response of Northern Hemisphere Snow to the Atmospheric and Arctic Sea Ice Variations

    Author:
    Debjani Ghatak
    Year of Dissertation:
    2011
    Program:
    Earth & Environmental Sciences
    Advisor:
    Allan Frei
    Abstract:

    The primary focus of this dissertation is the land-surface snow cover, which plays a significant role in modulating the earth's surface energy balance. It is an indicator of climatic variations as well as a part of the earth's system of feedback mechanisms that control the climate. The main goal of the thesis is to contribute to our understanding of the factors causing variations in snow. In order to fulfill this goal, specific objectives are formulated with a particular focus on an under-utilized snow pack metric, i.e. the snow depth. These objectives include the spatially robust explanation of climate-driven North American snow depth variability as well as the investigation of any evidence of a climate change signal and/or Arctic sea ice loss signal in the Northern Hemisphere snow cover record. This thesis identifies major winter climate teleconnection modes i.e. the North Atlantic Oscillation (NAO) and the Pacific-North American pattern (PNA) as the two main drivers of the snow depth variations over North America. Furthermore, the distinct mechanistic pathways linking circulation patterns to snow variations are also determined. These involve regional winter circulation patterns and hydrologic fluxes. Next, analyses of observational datasets show increased snow over Siberia during fall and early winter, which may be related to the loss of summer Arctic sea ice. Historic and future simulations of Community Climate System Model version3 (CCSM3) indicate the emergence of a similar signal during the last half of the 21st century. Finally, a suite of Community Atmosphere Model Version 3 (CAM3) experiments is analyzed, which suggests a key role played by the high-latitude surface forcings due to the SST and sea ice in generating the snow signal over the Eurasian landmasses as emerges in observations. This thesis contributes to the state of the knowledge of snow - climate interactions by focusing on the snow depth - climate interaction. Furthermore, the identification of a snow response to the recent climatic changes including the loss of Arctic sea ice is another original contribution. Thus, this work may enhance the prediction capabilities of the future hydro-climatic changes over the high latitude regions.

  • Mapping Forest Canopy Structure with On-Demand Fusion of Remotely Sensed Data

    Author:
    Gordon Green
    Year of Dissertation:
    2014
    Program:
    Earth & Environmental Sciences
    Advisor:
    Sean Ahearn
    Abstract:

    Current methods of mapping forest canopy structure often result in data products that are limited in resolution, coverage, or ease of access. On-demand processing introduces several new ways in which existing data products can be combined and re-purposed, mitigating some of these limitations. In this research, we investigate several methods of extending the spatial and temporal resolution, coverage, and accessibility of existing forest canopy datasets by processing them on demand. These methods include downscaling coarse-resolution canopy height data dynamically to estimate height at 30 m and 1 m resolution for any location within the contiguous United States. A related method involves sampling individual trees from field measurements on demand to estimate local forest canopy characteristics, using globally-available remotely sensed data and field data from across the United States. Canopy height profiles, which are highly sensitive to horizontal canopy variability, are generated on demand for any location within North America using new methods that account for this variability. Trends in canopy coverage and above-ground biomass are generated for any location globally using methods sensitive to local conditions. Each of the techniques developed as part of this research extends the resolution, coverage, or ease-of-access of existing remote sensing datasets, by combining multiple existing resources on demand.

  • Tiebout Sorting and Jurisdictional Homogeneity: Empirical Validity and Ethical Implications

    Author:
    Lee Hachadoorian
    Year of Dissertation:
    2011
    Program:
    Earth & Environmental Sciences
    Advisor:
    Jochen Albrecht
    Abstract:

    In a seminal paper, Tiebout (1956) argues that a large number of small local governments will function as a market in local services, leading to efficient allocation of local public goods. This result only obtains if households actually move in response to local fiscal differences. Spatial dependence of socioeconomic variables confounds attempts to infer Tiebout-motivated residential choice from observed socioeconomic homogeneity. I correct for this by focusing on socioeconomic difference across local government borders. In an investigation of socioeconomic sorting in Queens and Nassau Counties, NY, I find strong evidence of income sorting at the level of small suburban municipalities and of racial sorting across school districts. There is no evidence of income sorting across school districts, which I attribute to NYS school districts' lack of control over zoning. This study design exploits the incongruent boundaries of municipalities and school districts in New York State. In neighboring New Jersey, school districts are by law coterminous with municipalities. I hypothesize that, where boundaries are coterminous, sorting by school district and municipality will be mutually reinforcing. This hypothesis is tested in a comparison of income and racial heterogeneity in Nassau County, NY, with Bergen County, NJ, both suburban commuter counties within the New York MSA. Sorting is not found to be higher in Bergen than in Nassau. These negative results imply that the argued advantages of coterminous boundaries in terms of citizen oversight (Schwartz 2001) need not be traded off against increased segregation. I conclude with a discussion of the scope of public services that may be allocated via the Tiebout mechanism. Education is a primary good of such importance to well-being and to democracy that a pure system of local finance violates Rawlsian principles of justice (Rawls 1971). If good reasons exist, in terms of efficiency and/or democratic participation, for supporting local control in public goods with such significant distributive impacts, equalizing transfers are necessary to achieve just outcomes. This policy of equalizing transfers is consistent both with a spatialized Rawlsian theory of justice, as well as with the welfare economist's concept of efficiency (Schwab, Oates 1991).

  • Paleoecology of Late Cretaceous methane cold-seeps of the Pierre Shale, South Dakota

    Author:
    Kimberly Handle
    Year of Dissertation:
    2014
    Program:
    Earth & Environmental Sciences
    Advisor:
    Neil Landman
    Abstract:

    Most investigations of ancient methane seeps focus on either the geologic or paleontological aspects of these extreme environments. In contrast, this thesis encompasses both disciplines to evaluate the paleoecology of these systems with greater detail than previously published either within the Western Interior Basin or elsewhere. This thesis addresses the following questions: 1) Are the changes in mineralogy of a seep discernable and predictable as a seep shifts from a clay-based environment to a carbonate-based environment? 2) What are the foundation organism(s) of Late Cretaceous methane cold-seeps? 3) Is there a correlation to the mineralogic changes and shifts in community structure? 4) What is the mediating factor of these shifts? and 5) Are there any spatial trends in seep formation and persistence? To help resolve these queries, seep cement material and fossils were collected from 25 locations from the Baculites scotti - Didymoceras nebrascense, Didymoceras cheyennense, and Baculites compressus zones spanning ~2 million years in the Campanian of the Pierre Shale in South Dakota. The mineralogy of cements was determined through microprobe and electron dispersive spectroscopy. These data was spatially analyzed and suggest that there is a potential shift in mineralogy due to relative fluid flow rates over space and time: Baculites scotti - Didymoceras nebrascense Zone was of consistent moderate flow rates, Didymoceras cheyennense Zone was dominated by low fluid flow rates, and Baculites compressus Zone contained an unusually large number of high fluid flow seep assemblages compared to other biostratigraphic zones. Over 8000 individual organisms were counted and identified to the genus or species level (where possible) and these data were then processed with a series of diversity indices. A faunal pattern was found and shows that the foundation organisms, baculites, inoceramids, and lucinids, always dominate these seep assemblages, unlike the foundation organisms in modern methane cold-seep analogs. These fossil data were then paired up with each location's mineral data and a correlation was found between shifts in mineralogy and basic seep structure (general flow rate) and shifts in faunal compositions. Furthermore, specific fauna patterns and flow rates may indicate changes in oxygen or food availability. However, Akaike modeling techniques implemented found that the shifts in community composition within the cold-seeps of the Pierre Shale of South Dakota are most likely a reflection of sulfur availability according to the data.

  • BIODEGRADATION OF FUEL OXYGENATES IN NORTHEASTERN UNITED STATES AQUIFERS WITH AN ANALYSIS OF UNDERGROUND STORAGE TANK LEAKS

    Author:
    Gordon Hinshalwood
    Year of Dissertation:
    2009
    Program:
    Earth & Environmental Sciences
    Advisor:
    David Locke
    Abstract:

    Abstract BIODEGRADATION OF FUEL OXYGENATES (MTBE) IN GROUND WATER AQUIFERS OF THE NORTHEASTERN UNITED STATES/LEAKING UNDERGROUND STORAGE TANK CAUSATION ANALYSIS by Gordon Hinshalwood Adviser: Professor David Locke During the past decade the application of monitored natural attenuation has become one of the predominant technologies used in the remediation of gasoline spills impacting subsurface soils and groundwater. The success of this method has depended, for the most part, on the biodegradation of those gasoline constituents that dissolve into groundwater and transport with the groundwater most readily. One of the most mobile components of gasoline formulations during the past 20 years has been methyl tertiary butyl ether (MTBE), which has traditionally been viewed in both the scientific and the regulatory communities as relatively recalcitrant to biodegradation. However, cases of both in and ex situ MTBE biodegradation have recently been documented. In order to better understand and perhaps enhance the process of in situ MTBE biodegradation, a fundamental understanding of where, when and under what hydrogeological conditions MTBE biodegradation occurs is needed. To this end, the northeastern United States offers a wide range of lithologies to study. This study examines which subsurface conditions are most conducive to MTBE biodegradation. Retail gasoline service stations with leaking underground storage tank (LUST) releases located within a variety of hydrogeological conditions in the northeastern United States were screened for lithology, MTBE concentration in ground water, monitoring well network location, and MTBE concentration trends. Ground water samples were collected from those sites that passed this initial screening phase. MTBE from the samples collected were analyzed using stable carbon isotope ratio analysis (SCIRA) to determine where biodegradation is occurring. Geochemistry in each well was also examined to determine which hydrogeological conditions are most conducive to MTBE biodegradation. MTBE biodegradation under a variety of subsurface conditions was observed in this study. Loose soil conditions combined with reduced aquifer redox potential exhibited the greatest MTBE biodegradation frequency. Although statistically significant correlations were not found with respect to MTBE biodegradation and aquifer geochemistry, scatter plots showed notable trends with respect to pH, dissolved oxygen, and methane concentration correlated with MTBE biodegradation. Increased biodegradation frequency in the presence of increasing methane concentrations under varied aquifer redox and lithological conditions was observed.

  • BIODEGRADATION OF FUEL OXYGENATES IN NORTHEASTERN UNITED STATES AQUIFERS WITH AN ANALYSIS OF UNDERGROUND STORAGE TANK LEAKS

    Author:
    Gordon Hinshalwood
    Year of Dissertation:
    2009
    Program:
    Earth & Environmental Sciences
    Advisor:
    David Locke
    Abstract:

    Abstract BIODEGRADATION OF FUEL OXYGENATES (MTBE) IN GROUND WATER AQUIFERS OF THE NORTHEASTERN UNITED STATES/LEAKING UNDERGROUND STORAGE TANK CAUSATION ANALYSIS by Gordon Hinshalwood Adviser: Professor David Locke During the past decade the application of monitored natural attenuation has become one of the predominant technologies used in the remediation of gasoline spills impacting subsurface soils and groundwater. The success of this method has depended, for the most part, on the biodegradation of those gasoline constituents that dissolve into groundwater and transport with the groundwater most readily. One of the most mobile components of gasoline formulations during the past 20 years has been methyl tertiary butyl ether (MTBE), which has traditionally been viewed in both the scientific and the regulatory communities as relatively recalcitrant to biodegradation. However, cases of both in and ex situ MTBE biodegradation have recently been documented. In order to better understand and perhaps enhance the process of in situ MTBE biodegradation, a fundamental understanding of where, when and under what hydrogeological conditions MTBE biodegradation occurs is needed. To this end, the northeastern United States offers a wide range of lithologies to study. This study examines which subsurface conditions are most conducive to MTBE biodegradation. Retail gasoline service stations with leaking underground storage tank (LUST) releases located within a variety of hydrogeological conditions in the northeastern United States were screened for lithology, MTBE concentration in ground water, monitoring well network location, and MTBE concentration trends. Ground water samples were collected from those sites that passed this initial screening phase. MTBE from the samples collected were analyzed using stable carbon isotope ratio analysis (SCIRA) to determine where biodegradation is occurring. Geochemistry in each well was also examined to determine which hydrogeological conditions are most conducive to MTBE biodegradation. MTBE biodegradation under a variety of subsurface conditions was observed in this study. Loose soil conditions combined with reduced aquifer redox potential exhibited the greatest MTBE biodegradation frequency. Although statistically significant correlations were not found with respect to MTBE biodegradation and aquifer geochemistry, scatter plots showed notable trends with respect to pH, dissolved oxygen, and methane concentration correlated with MTBE biodegradation. Increased biodegradation frequency in the presence of increasing methane concentrations under varied aquifer redox and lithological conditions was observed.

  • The Work of the Urban Commons: Limited-Equity Cooperatives in Washington, D.C.

    Author:
    Amanda Huron
    Year of Dissertation:
    2012
    Program:
    Earth & Environmental Sciences
    Advisor:
    Marianna Pavlovskaya
    Abstract:

    This research theorizes the work of the urban commons through close examination of a group of ten limited-equity housing cooperatives in Washington, D.C. Limited-equity co-ops, or LECs, are a noncommodified resource that is collectively owned and maintained by their members. I argue that LECs are a manifestation of the commons, and that they represent a specific form of the commons - the urban commons. In this research, I ask: how does the urban commons - as manifested in this case by limited-equity housing cooperatives - function? The commons, as I theorize it, is a space that both provides a basis for life outside of (or at least less dictated by) capitalism, and that requires collective work to build and maintain. The commons, Peter Linebaugh (2008) argues, is constituted through commoning - the many overlapping practices of being-in-common that allow for a collective approach to life. The urban commons, I argue, is constituted through work, and future theorizing and action around the commons needs to take work seriously.

  • SYSTEMATICS ON VIAPHACOPS MAXIMOVA, 1972 FROM BOLIVIA AND PALEOBIOGEOGRAPHY OF THE SUBFAMILY PHACOPINAE HAWLE & CORDA, 1847 FOR THE LOWER AND MIDDLE DEVONIAN, WITH A PARTICULAR EMPHASIS ON THE GENUS PACIPHACOPS MAXIMOVA, 1972

    Author:
    Yumiko Iwasaki
    Year of Dissertation:
    2010
    Program:
    Earth & Environmental Sciences
    Advisor:
    Niles Eldredge
    Abstract:

    The Subfamily Phacopinae Hawle & Corda, 1847 occurs stratigraphically from the Upper Ordovician to the end of the Devonian, spanning an approximately 85 million year interval. Its global distribution allowed extensive studies and a number of monographs have been published since the mid-1800s. The first chapter analyzes Viaphacops Maximova, 1972 which is one of the genera occurring in the Lower to Middle Devonian. New material from Bolivia enabled three new species (Viaphacops spinoedgecombei, V. newelli, and V. pirovanoi) and two in open nomenclature to be described here, in addition to the four described previously. With the examination of these species, the generic diagnosis of Viaphacops is revised. Cladistic analysis was conducted for the Bolivian Viaphacops together with 8 North American species to test their monophyletic relationship. It is found that two geographically separate groups Viaphacops, those from North America and those from the Malvinokaffric Realm in Bolivia, are non-monophyletic (Bolivian species either being a basal grade or nesting in otherwise North American clades), and that the difference in environmental settings for these regions did not seem to have affected the developmental constraints of the species. The second chapter treats the phacopid biogeography for the Lower and Middle Devonian, and follows the model of rugose coral biogeography of Pedder and Oliver (1990). More than 300 species belonging to 32 established genera were analyzed. Otsuka, Dice, and Jaccard Coefficient faunal similarity indices at the generic level were used for the 15 phacopid biogeographic units. Together with an area cladogram of Paciphacops, Maximova, 1972, strong connection was established between southeastern Australia and Bolivia-Argentina by the circumpolar circulation within southern Panthalassa. The position of Kazakhstan is still unresolved, however, both Otsuka Coefficients and the Paciphacops area cladogram show its connection with Australia and South America.

  • SYSTEMATICS ON VIAPHACOPS MAXIMOVA, 1972 FROM BOLIVIA AND PALEOBIOGEOGRAPHY OF THE SUBFAMILY PHACOPINAE HAWLE & CORDA, 1847 FOR THE LOWER AND MIDDLE DEVONIAN, WITH A PARTICULAR EMPHASIS ON THE GENUS PACIPHACOPS MAXIMOVA, 1972

    Author:
    Yumiko Iwasaki
    Year of Dissertation:
    2010
    Program:
    Earth & Environmental Sciences
    Advisor:
    Niles Eldredge
    Abstract:

    The Subfamily Phacopinae Hawle & Corda, 1847 occurs stratigraphically from the Upper Ordovician to the end of the Devonian, spanning an approximately 85 million year interval. Its global distribution allowed extensive studies and a number of monographs have been published since the mid-1800s. The first chapter analyzes Viaphacops Maximova, 1972 which is one of the genera occurring in the Lower to Middle Devonian. New material from Bolivia enabled three new species (Viaphacops spinoedgecombei, V. newelli, and V. pirovanoi) and two in open nomenclature to be described here, in addition to the four described previously. With the examination of these species, the generic diagnosis of Viaphacops is revised. Cladistic analysis was conducted for the Bolivian Viaphacops together with 8 North American species to test their monophyletic relationship. It is found that two geographically separate groups Viaphacops, those from North America and those from the Malvinokaffric Realm in Bolivia, are non-monophyletic (Bolivian species either being a basal grade or nesting in otherwise North American clades), and that the difference in environmental settings for these regions did not seem to have affected the developmental constraints of the species. The second chapter treats the phacopid biogeography for the Lower and Middle Devonian, and follows the model of rugose coral biogeography of Pedder and Oliver (1990). More than 300 species belonging to 32 established genera were analyzed. Otsuka, Dice, and Jaccard Coefficient faunal similarity indices at the generic level were used for the 15 phacopid biogeographic units. Together with an area cladogram of Paciphacops, Maximova, 1972, strong connection was established between southeastern Australia and Bolivia-Argentina by the circumpolar circulation within southern Panthalassa. The position of Kazakhstan is still unresolved, however, both Otsuka Coefficients and the Paciphacops area cladogram show its connection with Australia and South America.

  • Fate, Reaction and Transport of Groundwater Arsenic during Discharge to Waquoit Bay, USA and Meghna River, Bangladesh

    Author:
    Hun Bok Jung
    Year of Dissertation:
    2009
    Program:
    Earth & Environmental Sciences
    Advisor:
    Yan Zheng
    Abstract:

    A field, laboratory, and modeling study of As in groundwater discharging to Waquoit Bay, MA, shed light on coupled control of chemistry and hydrology on reactive transport of As in a coastal aquifer. Precipitation of Fe(III) oxides, along with oxidation and adsorption of As occur at the redox interfaces above or below the reducing plume migrating toward the bay. Batch adsorption of As(III) onto orange, brown and gray sediments follows Langmuir isotherms, and can be fitted by a surface complexation model (SCM) assuming a diffuse double layer for ferrihydrite. The SCM simulated the observed dissolved As concentration better than a parametric approach based on Kd. Shallow groundwaters in the Ganges-Brahmaputra-Meghna Delta (GBMD) are frequently elevated in Fe and As, and discharge to rivers during dry season. Sediment As enrichment up to hundreds to thousands mg/kg in the shallow subsurface along the Meghna Riverbank suggests a plausible mechanism of trapping of As by a natural reactive barrier consisting of oxidatively precipitated Fe(III) oxyhydroxides formed at the redox boundary between reducing groundwater and oxic river water during discharge. Depth profiles of sediment Fe(II)/Fe(II+III) ratios and pore water dissolved oxygen and Fe concentrations indicate that there is a redox transition zone from anoxic to suboxic from ~2 m depth to the surface, which closely associated with sediment As enrichment. Ferrihydrite is the dominant Fe mineral in As enriched Meghna Riverbank sediment by X-ray absorption spectroscopy. To study the processes relevant to sorption and desorption of groundwater As in GBMD aquifer, brown and gray sandy sediment collected from suboxic and anoxic zones in Meghna Riverbank were subject to batch sorption and desorption experiments. Sorption experimental data were well fitted to Langmuir isotherm, resulting in Kd of 1~2 L kg-1 for reducing riverbank sediments, while ~7 L kg-1 for a suboxic sediment at equilibrium with 100 mg L-1 As(III) or As(V). Amendment with 1 mM lactate greatly enhanced As release from a As enriched sediment, mobilizing ~70% of initial sediment As, while no further mobilization of As occurred for 1 month after rapid desorption of ~3 mg kg-1 As within 2 days without lactate.