The role of recharge and evapotranspiration as hydraulic drivers of ion concentrations in shallow groundwater on Everglades tree islands, Florida (USA)

Recently, evapotranspiration has been hypothesized to promote the secondary formation of calcium carbonate year-round on tree islands in the Everglades by influencing groundwater ions concentrations. However, the role of recharge and evapotranspiration as drivers of shallow groundwater ion accumulation has not been investigated. The goal of this study is to develop a hydrologic model that predicts the chloride concentrations of shallow tree island groundwater and to determine the influence of overlying biomass and underlying geologic material on these concentrations. Groundwater and surface water levels and chloride concentrations were monitored on eight constructed tree islands at the Loxahatchee Impoundment Landscape Assessment (LILA) from 2007 to 2010. The tree islands at LILA were constructed predominately of peat, or of peat and limestone, and were planted with saplings of native tree species in 2006 and 2007. The model predicted low shallow groundwater chloride concentrations when inputs of regional groundwater and evapotranspiration-to-recharge rates were elevated, while low evapotranspiration-to-recharge rates resulted in a substantial increase of the chloride concentrations of the shallow groundwater. Modeling results indicated that evapotranspiration typically exceeded recharge on the older tree islands and those with a limestone lithology, which resulted in greater inputs of regional groundwater. A sensitivity analysis indicated the shallow groundwater chloride concentrations were most sensitive to alterations in specific yield during the wet season and hydraulic conductivity in the dry season. In conclusion, the inputs of rainfall, underlying hydrologic properties of tree islands sediments and forest structure may explain the variation in ion concentration seen across Everglades tree islands.

Hydrological drivers of wetland vegetation community distribution within Everglades National Park, Florida

The influence of hydrological dynamics on vegetation distribution and the structuring of wetland environments is of growing interest as wetlands are modified by human action and the increasing threat from climate change. Hydrological properties have long been considered a driving force in structuring wetland communities. We link hydrological dynamics with vegetation distribution across Everglades National Park (ENP) using two publicly available datasets to study the probability structure of the frequency, duration, and depth of inundation events along with their relationship to vegetation distribution. This study is among the first to show hydrologic structuring of vegetation communities at wide spatial and temporal scales, as results indicate that the percentage of time a location is inundated and its mean depth are the principal structuring variables to which individual communities respond. For example, sawgrass, the most abundant vegetation type within the ENP, is found across a wide range of time inundated percentages and mean depths. Meanwhile, other communities like pine savanna or red mangrove scrub are more restricted in their distribution and found disproportionately at particular depths and inundations. These results, along with the probabilistic structure of hydropatterns, potentially allow for the evaluation of climate change impacts on wetland vegetation community structure and distribution.

Drivers of Innovation In Financing Transportation Infrastructure: A Systemic Investigation

Traditional methods of financing infrastructure, which include gas taxation, tax-exempt bonds, and reserve funds, have not been able to meet the growing demand for infrastructure. Innovative financing systems have emerged to close the gap that exists between the available and needed financing sources. The objective of the study presented in this paper is to assess determinants of innovative financing in the U.S. transportation infrastructure using a systemic approach. Innovation System of Systems approach is adopted for systemic assessment and a case-based research approach is utilized to explore the constituents of innovative financing for U.S. transportation infrastructure. The findings, which include constructs regarding the players, practices, and activities are used to create a model to enable understanding the dynamics of the drivers and inhibitors of innovation and, thus, to derive implications for practice. The model along with the constructs provides an analytical tool for practitioners in the U.S. transportation infrastructure.

The relationship between job structure, burnout, and coping methods among public school county bus drivers, bus aides, mechanics, and clerical workers

The purpose of this study was to examine the relationship between the structure of jobs and burnout, and to assess to what extent, if any this relationship was moderated by individual coping methods. This study was supported by the Karasek's (1998) Job Demand-Control-Support theory of work stress as well as Maslach and Leiter's (1993) theory of burnout. Coping was examined as a moderator based on the conceptualization of Lazarus and Folkman (1984). ^ Two overall overarching questions framed this study: (a) what is the relationship between job structure, as operationalized by job title, and burnout across different occupations in support services in a large municipal school district? and (b) To what extent do individual differences in coping methods moderate this relationship? ^ This study was a cross-sectional study of county public school bus drivers, bus aides, mechanics, and clerical workers (N = 253) at three bus depot locations within the same district using validated survey instruments for data collection. Hypotheses were tested using simultaneous regression analyses. ^ Findings indicated that there were statistically significant and relevant relationships among the variables of interest; job demands, job control, burnout, and ways of coping. There was a relationship between job title and physical job demands. There was no evidence to support a relationship between job title and psychological demands. Furthermore, there was a relationship between physical demands, emotional exhaustion and personal accomplishment; key indicators of burnout. ^ Results showed significant correlations between individual ways of coping as a moderator between job structure, operationalized by job title, and individual employee burnout adding empirical evidence to the occupational stress literature. Based on the findings, there are implications for theory, research, and practice. For theory and research, the findings suggest the importance of incorporating transactional models in the study of occupational stress. In the area of practice, the findings highlight the importance of enriching jobs, increasing job control, and providing individual-level training related to stress reduction.^

Drivers of Decadal-Scale Change in Southern Everglades Wetland Macrophyte Communities of the Coastal Ecotone

Understanding the relationships between hydrology and salinity and plant community structure and production is critical to allow predictions of wetland responses to altered water management, changing precipitation patterns and rising sea-level. We addressed how salinity, water depth, hydroperiod, canal inflows, and local precipitation control marsh macrophyte aboveground net primary production (ANPP) and structure in the coastal ecotone of the southern Everglades. We contrasted responses in two watersheds - Taylor Slough (TS) and C-111 - systems that have and will continue to experience changes in water management. Based on long-term trajectories in plant responses, we found continued evidence of increasing water levels and length of inundation in the C-111 watershed south of the C-111 canal. We also found strong differentiation among sites in upper TS that was dependent on hydrology. Finally, salinity, local precipitation and freshwater discharge from upstream explained over 80 % of the variance in Cladium ANPP at a brackish water site in TS. Moreover, our study showed that, while highly managed, the TS and C-111 watersheds maintain legacies in spatial pattern that would facilitate hydrologic restoration. Based on the trajectories in Cladium and Eleocharis, shifts in plant community structure could occur within 5–10 years of sustained water management change.

The Role of Recharge and Evapotranspiration as Hydraulic Drivers of Ion Concentrations in Shallow Groundwater on Everglades Tree Islands, Florida (USA)

Recently, evapotranspiration has been hypothesized to promote the secondary formation of calcium carbonate year-round on tree islands in the Everglades by influencing groundwater ions concentrations. However, the role of recharge and evapotranspiration as drivers of shallow groundwater ion accumulation has not been investigated. The goal of this study is to develop a hydrologic model that predicts the chloride concentrations of shallow tree island groundwater and to determine the influence of overlying biomass and underlying geologic material on these concentrations. Groundwater and surface water levels and chloride concentrations were monitored on eight constructed tree islands at the Loxahatchee Impoundment Landscape Assessment (LILA) from 2007 to 2010. The tree islands at LILA were constructed predominately of peat, or of peat and limestone, and were planted with saplings of native tree species in 2006 and 2007. The model predicted low shallow groundwater chloride concentrations when inputs of regional groundwater and evapotranspiration-to-recharge rates were elevated, while low evapotranspiration-to-recharge rates resulted in a substantial increase of the chloride concentrations of the shallow groundwater. Modeling results indicated that evapotranspiration typically exceeded recharge on the older tree islands and those with a limestone lithology, which resulted in greater inputs of regional groundwater. A sensitivity analysis indicated the shallow groundwater chloride concentrations were most sensitive to alterations in specific yield during the wet season and hydraulic conductivity in the dry season. In conclusion, the inputs of rainfall, underlying hydrologic properties of tree islands sediments and forest structure may explain the variation in ion concentration seen across Everglades tree islands.

Managing small-scale commercial fisheries for adaptive capacity: Insights from dynamic social-ecological drivers of change in Monterey Bay

Globally, small-scale fisheries (SSFs) are driven by climate, governance, and market factors of social-ecological change, presenting both challenges and opportunities. The ability of small-scale fishermen and buyers to adapt to changing conditions allows participants to survive economic or environmental disturbances and to benefit from optimal conditions. This study presented here identifies key large-scale factors that drive SSFs in California to shift focus among targets and that dictate long-term trends in landings. We use Elinor Ostrom’s Social-Ecological System (SES) framework to apply an interdisciplinary approach when identifying potential factors and when understanding the complex dynamics of these fisheries. We analyzed the interactions among Monterey Bay SSFs over the past four decades since the passage of the Magnuson Stevens Fisheries Conservation and Management Act of 1976. In this region, the Pacific sardine (Sardinops sagax), northern anchovy (Engraulis mordax), and market squid (Loligo opalescens) fisheries comprise a tightly linked system where shifting focus among fisheries is a key element to adaptive capacity and reduced social and ecological vulnerability. Using a cluster analysis of landings, we identified four modes from 1974 to 2012 that were dominated by squid, sardine, anchovy, or lacked any dominance, enabling us to identify external drivers attributed to a change in fishery dominance during seven distinct transition points. Overall, we show that market and climate factors drive the transitions among dominance modes. Governance phases most dictated long-term trends in landings and are best viewed as a response to changes in perceived biomass and thus a proxy for biomass. Our findings suggest that globally, small-scale fishery managers should consider enabling shifts in effort among fisheries and retaining existing flexibility, as adaptive capacity is a critical determinant for social and ecological resilience.

Environmental and biological drivers of feeding and spatial dynamics in the green sea urchin, Strongylocentrotus droebachiensis

In eastern Canada, the destruction of foundational kelp beds by dense aggregations (fronts) of the omnivorous green sea urchin, Strongylocentrotus droebachiensis, is a key determinant of the structure and dynamics of shallow reef communities. Current knowledge about factors affecting the ability of S. droebachiensis to exert top-down community control is based largely on observational studies of patterns in natural habitats, yielding fragmentary, and sometimes contradictory, results. The present research incorporated laboratory microcosm experiments and surveys of urchins in natural habitats to test the effects of abiotic (wave action, water temperature) and biotic (body size, population density) factors on: (1) individual and aggregative feeding on the winged kelp, Alaria esculenta; and (2) displacement, microhabitat use, distribution, and aggregation in food-depleted habitats. Wave action, water temperature, and body size strongly affected the ability of urchins to consume kelp: individual feeding increased with increasing body size and temperature, while aggregative feeding decreased with increasing wave action. Yet, feeding in large urchins dropped by two orders of magnitude between 12 and 18°C. Increasing wave action triggered shifts in urchin displacement, microhabitat use, distribution, and aggregation: urchins reduced displacement and abandoned flat surfaces in favour of crevices. They increasingly formed two-dimensional aggregations at densities ≥110 individuals m⁻². Collectively, results provide a foundational understanding of some of the drivers of feeding and spatial dynamics of S. droebachiensis and potential impacts on the formation of grazing fronts.

Seasonal water storage and delayed evapotranspiration across continents: patterns and drivers

Non peer reviewed

Drivers of atmospheric methane uptake by montane forest soils in the southern Peruvian Andes

Acknowledgements. This study is a product of the Andes Biodiversity and Ecosystem Research Group consortium (http://www.andesconservation.org/). The authors would like to acknowledge the agencies that funded this research; the UK Natural Environment Research Council (NERC; joint grant references NE/G018278/1, NE/H006583, NE/H007849 and NE/H006753) and the Norwegian Agency for Development Cooperation (Norad; via a sub-contract to Yit Arn Teh managed by the Amazon Conservation Association). Patrick Meir was also supported by an Australian Research Council Fellowship (FT110100457). Javier Eduardo Silva Espejo, Walter Huaraca Huasco and the ABIDA NGO provided critical fieldwork and logistical support. Angus Calder, Michael Mcgibbon, Vicky Munro and Nick Morley provided invaluable laboratory support. Thanks to Adrian Tejedor and the Amazon Conservation Association (http://www.amazonconservation.org/), who provided assistance with access and plot selection at Hacienda Villa Carmen. This publication is a contribution from the Scottish Alliance for Geoscience, Environment and Society (http://www.sages.ac.uk). Edited by: E. Veldkamp

Harness race drivers

General note: Title and date provided by Bettye Lane.

Internal Capital, External Knowledge, and Random Draws: Three Drivers of Organizational Structure

This dissertation explores the complex interactions between organizational structure and the environment. In Chapter 1, I investigate the effect of financial development on the formation of European corporate groups. Since cross-country regressions are hard to interpret in a causal sense, we exploit exogenous industry measures to investigate a specific channel through which financial development may affect group affiliation: internal capital markets. Using a comprehensive firm-level dataset on European corporate groups in 15 countries, we find that countries

with less developed financial markets have a higher percentage of group affiliates in more capital intensive industries. This relationship is more pronounced for young and small firms and for affiliates of large and diversified groups. Our findings are consistent with the view that internal capital markets may, under some conditions, be more efficient than prevailing external markets, and that this may drive group affiliation even in developed economies. In Chapter 2, I bridge current streams of innovation research to explore the interplay between R&D, external knowledge, and organizational structure–three elements of a firm’s innovation strategy which we argue should logically be studied together. Using within-firm patent assignment patterns,

we develop a novel measure of structure for a large sample of American firms. We find that centralized firms invest more in research and patent more per R&D dollar than decentralized firms. Both types access technology via mergers and acquisitions, but their acquisitions differ in terms of frequency, size, and i\ntegration. Consistent with our framework, their sources of value creation differ: while centralized firms derive more value from internal R&D, decentralized firms rely more on external knowledge. We discuss how these findings should stimulate more integrative work on theories of innovation. In Chapter 3, I use novel data on 1,265 newly-public firms to show that innovative firms exposed to environments with lower M&A activity just after their initial public offering (IPO) adapt by engaging in fewer technological acquisitions and

more internal research. However, this adaptive response becomes inertial shortly after IPO and persists well into maturity. This study advances our understanding of how the environment shapes heterogeneity and capabilities through its impact on firm structure. I discuss how my results can help bridge inertial versus adaptive perspectives in the study of organizations, by

documenting an instance when the two interact.

Investigating the Intrinsic and Extrinsic Drivers of Primate Heterothermy

Seasonal heterothermy—an orchestrated set of extreme physiological responses—is directly responsible for the over-winter survival of many mammalian groups living in seasonal environments. Historically, it was thought that the use of seasonal heterothermy (i.e. daily torpor and hibernation) was restricted to cold-adapted species; it is now known that such thermoregulatory strategies are used by more species than previously appreciated, including many tropical species. The dwarf and mouse lemurs (family Cheirogaleidae) are among the few primates known to use seasonal heterothermy to avoid Madagascar’s harsh and unpredictable environments. These primates provide an ideal study system for investigating a common mechanism of mammalian seasonal heterothermy. The overarching theme of this dissertation is to understand both the intrinsic and extrinsic drivers of heterothermy in three species of the family Cheirogaleidae. By using transcriptome sequencing to characterize gene expression in both captive and natural settings, we identify unique patterns of differential gene expression that are correlated with extreme changes in physiology in two species of dwarf lemurs: C. medius under captive conditions at the Duke Lemur Center and C. crossleyi studied under field conditions in Madagascar. Genes that are differentially expressed appear to be critical for maintaining the health of these animals when they undergo prolonged periods of metabolic depression concurrent with the hibernation phenotype. Further, a comparative analysis of previously studied mammalian heterotherms identifies shared genetic mechanisms underlying the hibernation phenotype across the phylogeny of mammals. Lastly, conducting a diet manipulation study with a captive colony of mouse lemurs (Microcebus murinus) at the Duke Lemur Center, we investigated the degree to which dietary effects influence torpor patterns. We find that tropical primate heterotherms may be exempt from the traditional paradigms governing cold-adapted heterothermy, having evolved different dietary strategies to tolerate circadian changes in body temperature.

Drivers of Dengue Within-Host Dynamics and Virulence Evolution

Dengue is an important vector-borne virus that infects on the order of 400 million individuals per year. Infection with one of the virus's four serotypes (denoted DENV-1 to 4) may be silent, result in symptomatic dengue 'breakbone' fever, or develop into the more severe dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Extensive research has therefore focused on identifying factors that influence dengue infection outcomes. It has been well-documented through epidemiological studies that DHF is most likely to result from a secondary heterologous infection, and that individuals experiencing a DENV-2 or DENV-3 infection typically are more likely to present with more severe dengue disease than those individuals experiencing a DENV-1 or DENV-4 infection. However, a mechanistic understanding of how these risk factors affect disease outcomes, and further, how the virus's ability to evolve these mechanisms will affect disease severity patterns over time, is lacking. In the second chapter of my dissertation, I formulate mechanistic mathematical models of primary and secondary dengue infections that describe how the dengue virus interacts with the immune response and the results of this interaction on the risk of developing severe dengue disease. I show that only the innate immune response is needed to reproduce characteristic features of a primary infection whereas the adaptive immune response is needed to reproduce characteristic features of a secondary dengue infection. I then add to these models a quantitative measure of disease severity that assumes immunopathology, and analyze the effectiveness of virological indicators of disease severity. In the third chapter of my dissertation, I then statistically fit these mathematical models to viral load data of dengue patients to understand the mechanisms that drive variation in viral load. I specifically consider the roles that immune status, clinical disease manifestation, and serotype may play in explaining viral load variation observed across the patients. With this analysis, I show that there is statistical support for the theory of antibody dependent enhancement in the development of severe disease in secondary dengue infections and that there is statistical support for serotype-specific differences in viral infectivity rates, with infectivity rates of DENV-2 and DENV-3 exceeding those of DENV-1. In the fourth chapter of my dissertation, I integrate these within-host models with a vector-borne epidemiological model to understand the potential for virulence evolution in dengue. Critically, I show that dengue is expected to evolve towards intermediate virulence, and that the optimal virulence of the virus depends strongly on the number of serotypes that co-circulate. Together, these dissertation chapters show that dengue viral load dynamics provide insight into the within-host mechanisms driving differences in dengue disease patterns and that these mechanisms have important implications for dengue virulence evolution.

Characterizing Genetic Drivers of Lymphoma through High-Throughput Sequencing

The advent of next-generation sequencing, now nearing a decade in age, has enabled, among other capabilities, measurement of genome-wide sequence features at unprecedented scale and resolution.

In this dissertation, I describe work to understand the genetic underpinnings of non-Hodgkin’s lymphoma through exploration of the epigenetics of its cell of origin, initial characterization and interpretation of driver mutations, and finally, a larger-scale, population-level study that incorporates mutation interpretation with clinical outcome.

In the first research chapter, I describe genomic characteristics of lymphomas through the lens of their cells of origin. Just as many other cancers, such as breast cancer or lung cancer, are categorized based on their cell of origin, lymphoma subtypes can be examined through the context of their normal B Cells of origin, Naïve, Germinal Center, and post-Germinal Center. By applying integrative analysis of the epigenetics of normal B Cells of origin through chromatin-immunoprecipitation sequencing, we find that differences in normal B Cell subtypes are reflected in the mutational landscapes of the cancers that arise from them, namely Mantle Cell, Burkitt, and Diffuse Large B-Cell Lymphoma.

In the next research chapter, I describe our first endeavor into understanding the genetic heterogeneity of Diffuse Large B Cell Lymphoma, the most common form of non-Hodgkin’s lymphoma, which affects 100,000 patients in the world. Through whole-genome sequencing of 1 case as well as whole-exome sequencing of 94 cases, we characterize the most recurrent genetic features of DLBCL and lay the groundwork for a larger study.

In the last research chapter, I describe work to characterize and interpret the whole exomes of 1001 cases of DLBCL in the largest single-cancer study to date. This highly-powered study enabled sub-gene, gene-level, and gene-network level understanding of driver mutations within DLBCL. Moreover, matched genomic and clinical data enabled the connection of these driver mutations to clinical features such as treatment response or overall survival. As sequencing costs continue to drop, whole-exome sequencing will become a routine clinical assay, and another diagnostic dimension in addition to existing methods such as histology. However, to unlock the full utility of sequencing data, we must be able to interpret it. This study undertakes a first step in developing the understanding necessary to uncover the genomic signals of DLBCL hidden within its exomes. However, beyond the scope of this one disease, the experimental and analytical methods can be readily applied to other cancer sequencing studies.

Thus, this dissertation leverages next-generation sequencing analysis to understand the genetic underpinnings of lymphoma, both by examining its normal cells of origin as well as through a large-scale study to sensitively identify recurrently mutated genes and their relationship to clinical outcome.