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The development of novel bioremediation systems has widespread benefits for human health and natural ecosystems. Optimization of such systems is only possible with a thorough understanding of the processes that drive bioremediation. This thesis developed novel understanding of carbon sources and cycling relationships for microbial communities that are integral in controlling contaminant fate in two contaminated environments. In the first case (Chapter 2), biodegradation in the soil microbial community was determined to be the primary pathway for recalcitrant petroleum pollutant removal. Microbial uptake and metabolism of petroleum hydrocarbons was conclusively demonstrated via 14C analysis of their PLFA biomarkers. This microbial community was the most 14C depleted bacterial system detected in an environmental system to date. In addition, complete mineralization of petroleum carbon was demonstrated with 14C analysis of soil COz. The second paper (Chapter 3) identified unique Phospholipid Fatty Acid (PLFA) biomarkers and stable carbon isotopic fractionation patterns for heterotrophic and autotrophic bacterial communities of an acid mine drainage (AMD) system. The characteristic isotopic fractionations observed during biosynthesis of PLF A biomarkers in autotrophic versus heterotrophic metabolic pathways provided the basis for a model capable of elucidating the relative roles of these members of the microbial community in the environment. The major implications of the knowledge developed in this thesis, are two new methods to identify microbial carbon cycling pathways and processes in contaminated environments. These advances may lead to new methods for mitigating the effects of contamination in environmental systems through better understanding of the microbial processes at the contaminated sites. / Thesis / Master of Science (MSc)

This thesis examines factors that influence the daily number of trip departures and arrivals at over 100 hubs comprising Hamilton, Ontario’s (Canada) bike share program – SoBi (Social Bicycles) Hamilton. SoBi operates all year, and during its first year of operation (April 1, 2015 to March 31, 2016), over 200,000 trips were generated on SoBi bikes. The study utilizes data from SoBi Hamilton, the 2011 Canadian Census, the 2011 Transportation Tomorrow Survey, Environment Canada, and Hamilton’s Open Source Data initiative. From these master files, daily trips, meteorological data, temporal variables, socio-demographic and built environment attributes were obtained to generate a comprehensive suite of explanatory variables to explain the daily trips at each hub. A multilevel regression approach was used to understand the associations between bike share usage at each hub and each suite of explanatory variables at two temporal scales: total daily trips at hubs and total daily trips across four time periods of the day. Findings demonstrate that weather and temporal attributes play a significant role in trip departures and arrivals. In addition, hub attributes vary in significance throughout different times of the day for trip departures and arrivals. Overall, the methodology and findings allow us to identify factors that increase SoBi usage, which can also benefit city planners and engineers who are implementing a bike share system with the goal of maximizing bike share activity in urban centers. / Thesis / Master of Science (MSc)

Cycling for transport is an increasingly popular mode of travel in Hamilton, Ontario. Between 2011 and 2016, the mode share of cycling grew from 0.6% to 1.2%. As of 2019, 46% of the planned cycling facilities network has been built, which suggests that the city is transitioning to a cycling city. However, less is known about the built environment factors that influence cycling trips or the routes travelled by people who cycle in Hamilton. Drawing on the strengths of quantitative and qualitative methods, this research explores the built environment correlates of cycling and the perceptions of people who regularly cycle. First, a spatial interaction model was developed to test the level of cycling flows against various built environment attributes using trips data from the 2016 Transportation Tomorrow Survey. A novel feature of this analysis is the use of a cycle routing algorithm to infer routes as impedance factors. The most parsimonious model suggests that the shortest-path quietest routes best explain the pattern of travel by bicycle in Hamilton. To build upon these findings, objective built environment attributes were documented along select shortest-path quietest routes using environmental audits. The qualitative phase of the study then explores how well these approximated routes match where cyclists travel in Hamilton, as well as how the built environment more broadly in a growing city is perceived and experienced, by interviewing people who regularly travel by bicycle. The interviews highlight that the built environment is not yet bicycle-oriented and that cycling infrastructure influences mobility and route choice. As a result, people who cycle seek out routes that enable them to minimize interactions with cars, by incorporating quiet streets, and that have enjoyable environments. Policy implications and recommendations specific to these findings are discussed to further support the city of Hamilton’s transition to a more bikeable city. / Thesis / Master of Public Health (MPH)

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Although cycling offers many health and environmental benefits, it is not an activity free of injury risk. Increases in cycling popularity in the United States over the past 15 years have been paralleled by a 120% growth in cycling-related hospital admissions, with injuries to the head among the most common and debilitating injuries. Bicycle helmets can reduce head injury risk and are presently required to meet safety standard certification criteria specifying a minimal level of acceptable impact protection. However, the conditions surrounding cyclist head impacts are thought to be much more complex than the test conditions prescribed in standards and have important implications related to mechanisms of injury. The overarching aim of this dissertation was thus to investigate the protective capabilities of bicycle helmets in the context of real-world impact conditions and relevant head injury mechanisms. This aim was achieved through a series of studies, the objectives of which were to: compare helmet impact performance across standards impact testing and more realistic, oblique impact testing; to probe how changing boundary conditions of oblique impact testing may influence helmet test outcomes; to use this knowledge to inform the development of an objective helmet evaluation protocol reflective of realistic impact conditions and related head injury risks; and finally, to enhance the body of knowledge pertaining to cyclist head impact conditions via advanced helmet damage reconstruction techniques. The compilation of results across these studies serves to enhance cyclist safety by stimulating improved helmet evaluation and design while simultaneously providing objective, biomechanical data to consumers, enabling them to make safety-based purchasing decisions. / Doctor of Philosophy / Although cycling offers many health and environmental benefits and is increasing in popularity in the United States, it is not always a perfectly safe activity. The number of cycling-related hospital admissions in the US has been increasing over the past 15 years. Cyclists often sustain head injuries from crashes, which can be particularly debilitating. Fortunately, wearing a helmet can protect against head injuries during a crash. Bicycle helmets are presently designed around safety standards that drop a helmeted dummy head onto a horizontal anvil and require the helmet to limit the force on the head to acceptable levels. However, standards tests overly simplify how cyclists actually hit their head during a crash and are consequently unable to assess how well helmets protect against common brain injuries like concussion. The overarching goal of this research was to evaluate how effectively bicycle helmets protect cyclists from concussion in realistic impact scenarios. Several studies were conducted to achieve this goal. Their individual objectives were to: compare how bicycle helmets reduce impact forces associated with standards tests versus more realistic, angled impact tests; to understand how changing constraints of an angled impact setup influences helmet effectiveness; to develop an unbiased evaluation protocol for bicycle helmets based on realistic cyclist crash scenarios and concussion risk assessment; and finally, to further explore how cyclists impact their head in real-world crashes using advanced techniques for reconstructing bicycle helmet damage from actual accidents. All of these studies lead to improved cyclist safety by stimulating improved helmet evaluation and design, while also providing consumers with information on how protective their helmets are.

Thesis advisor: Jeremy Shakun / Thesis advisor: Tony Wang / To better understand ice sheet and nutrient cycling dynamics in the North Atlantic, three geochemical paleo-proxies have been analyzed in Pleistocene marine sediments: cosmogenic nuclides (10Be and 26Al) in ice-rafted debris (IRD), 40Ar/39Ar in IRD, and foraminifera-bound nitrogen isotopes (FB-δ15N). For Chapter 1, we analyzed 10Be and 26Al concentrations in quartz separates of IRD from last-glacial North Atlantic sediments and used these data to constrain the history of Laurentide Ice Sheet (LIS) cover over Canada during the Pleistocene. While LIS history is well constrained since the Last Glacial Maximum (LGM) (~20,000 years ago), there is little evidence available from earlier times. 26Al/10Be ratios are depressed in these samples, the result of long-term decay under cover, which we suggest is best explained by a persistent LIS over much of the last million years. This finding implies that the LIS did not fully disappear during many Pleistocene interglacials, making the current ice-free Holocene interglacial relatively unique. For Chapter 2, we synthesized 3,762 40Ar/39Ar ages from North Atlantic IRD, including 670 new analyses. 595 of these single-grain analyses come from some of the same sample intervals as Chapter 1. These 40Ar/39Ar ages in IRD, a tracer of IRD provenance, clarify changes in North Atlantic ice sheet extent during the past few glacial cycles. Comparison of 40Ar/39Ar ages with hypothesized ice margins and cosmogenic nuclide data (from Chapter 1) aid in our interpretations. For last-glacial samples, results suggest ice sheets around the basin may have been in a retracted state during Marine Isotope Stage (MIS) 3 (~29-57 ka), an interval of debated ice extent for the LIS. Our synthesis also allows us to present the first complete records 40Ar/39Ar ages in IRD during Heinrich intervals – times when the LIS exhibited iceberg discharge events. These results support the suggestion made by previous work that Heinrich events 3 and 6 are anomalous relative to other intervals. 40Ar/39Ar analyses from earlier glacial periods – the first yet published – highlight that IRD provenance data may be reflecting iceberg survivability in addition to changes in ice extent. Lastly, analyzing cosmogenic nuclides and 40Ar/39Ar ages in IRD from the same sample intervals indicates that both proxies may be used to infer changes in ice sheet provenance; this is the first time cosmogenic nuclides in IRD have been considered in this way. For Chapter 3, we analyzed FB-δ15N at Site U1313 in North Atlantic samples during the Plio-Pleistocene to reconstruct marine nutrient cycling. In the North Atlantic, nutrient cycling is known to play an important role in regulating surface ocean productivity and CO2 drawdown via photosynthesis. We nevertheless lack a complete understanding of nutrient cycling evolution for the Plio-Pleistocene, during which Northern Hemisphere ice sheets and climate exhibited dramatic fluctuations. We find increasing FB-δ15N values at the transition from the Pliocene to the Pleistocene. Additionally, FB-δ15N values are generally higher during glacials compared to interglacials. We suggest these observations can best be explained by an expansion or increase of N2 fixation in the North Atlantic during warmer intervals (interglacials, Pliocene) and a retraction or decrease of N2 fixation during cold intervals (Pleistocene glacials). Considered alongside previously published paleo-proxy data from Site U1313 we suggest these changes in nutrient cycling reflect climate-driven migrations of the North Atlantic Current. In Chapter 4, I reflect upon how I have worked to integrate broader impacts into my Ph.D. work. Using a combined approach, I focused on fostering an inclusive environment within paleoclimate research spaces as well as engaging non-scientists in paleoclimate-and Earth science-related activities. These approaches ranged from K-12 partnership activities to mentoring students to more experimental avenues, such as a collaborative art project. I have evaluated the success of this work using a combination of quantitative metrics and subjective assessments. Participating in these efforts was also crucial for reminding me of the importance of making science accessible to everyone as well as for helping me hone my mentorship and science communication skills. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Arsenic (As) in drinking water poses a critical threat to public health. More than 150 million people worldwide are at risk of developing diseases from unsafe concentrations of As in groundwater. Arsenic occurs naturally in rocks, soils, and sediments and generally remains associated with solid phases. However, changes in aquifer geochemistry can mobilize As into groundwater, contaminating drinking water sources. This dissertation investigates As cycling in an aquifer contaminated by petroleum hydrocarbons near Bemidji, Minnesota, where As is mobilized into groundwater due to biodegradation of hydrocarbons coupled to reduction of ferric oxides. The first project describes how aquifer sediments act as both sources and sinks for As in groundwater, depending on the prevailing redox conditions. Results show that As is released to groundwater near the hydrocarbon source but is removed near the hydrocarbon plume's leading edge. Comparison of data from 1993 to 2016 shows that As has been redistributed in aquifer sediment as the plume has expanded over time. The second project presents a mass balance for As, which shows that despite elevated As in groundwater (up to 230 μg/L), >99.7% of As mass in the aquifer is in sediments. Calculations demonstrate that As in sediment can be 22x less than the method detection limit and still cause unsafe concentrations in groundwater, suggesting that the use of standard methods limits our ability to predict where naturally occurring As poses a threat to groundwater. In the third project, a reactive transport model simulates As cycling for 400 years. Results show that sorption of As to ferrihydrite limits As transport within 300 m of the hydrocarbon source. Modeling predicts that over the plume's lifespan, more groundwater will be contaminated by As than benzene, the primary contaminant of concern in hydrocarbon plumes. Combined, these studies suggest that many aquifers are vulnerable to unsafe As concentrations due to mobilization of natural As if bioavailable organic carbon is introduced. Although aquifers can attenuate As, it may take centuries for As to be fully removed from groundwater, suggesting it is prudent to account for natural contaminants like As when developing remediation strategies at petroleum spill sites. / Ph. D. / Arsenic (As) in groundwater used for drinking water is a risk to public health. More than 150 million people worldwide are at risk of developing diseases and cancer from unsafe levels of As in groundwater. Arsenic occurs naturally in rocks, soils, and sediments. However, changes in aquifer chemistry can release As from these solid materials into groundwater, contaminating drinking water sources. This dissertation investigates As cycling in a petroleum-contaminated aquifer near Bemidji, Minnesota, where As is released into groundwater due to the breakdown of petroleum by microorganisms under zero-oxygen conditions. The first project describes how sediments release As to, and remove As from, groundwater. Results show that As in groundwater is removed by sediments under medium-to-high-oxygen conditions. Analyses of sediment collected in 1993 showed that in the past, similar processes affecting As in groundwater were occurring closer to the petroleum release site. Over time, the zero-oxygen conditions that allow As to be released into groundwater spread, causing a more widespread As release. The second project presents a mass balance for As, which shows that despite high As in groundwater (up to 230 μg/L), >99.7% of As is associated with sediments. Calculations demonstrate that the analytical methods used to detect As in sediment are not sensitive enough to predict where natural As poses a threat to groundwater. In the third project, a numerical model shows that the presence of iron oxide minerals limit As transport in groundwater. Modeling simulations suggest that in the future, more groundwater will be contaminated by As than benzene, the primary contaminant of concern in petroleum plumes. Combined, these studies suggest that many aquifers are vulnerable to the release of unsafe levels of As from naturally occurring sources if organic carbon is introduced. Although aquifers can naturally remove As from groundwater, it may take centuries for As to be fully removed, suggesting it is prudent to account for natural contaminants like As when developing clean-up plans at oil spill sites.