Dissertations / Theses on the topic 'Environmental science. Environmental toxicology. Ecology'

Predicting impact of oil spills on aquatic life requires a better understanding of effects on aquatic organisms, both for single hydrocarbons and for their interactions. In this study, the individual and combined effects of petroleum hydrocarbons phenanthrene (Phen) and dibenzothiophene (DBT) were assessed on the reproductive behavior of the freshwater amphipod Hyalella azteca. Following a 24-h exposure to single PAHs, or an equimolar mixture of Phen-DBT, mate-guarding behavior was assessed at the end of the exposure and during a subsequent 10 min behavioral observation period with the animals in clean water. The endpoints of the study during the behavior observation period were—time taken to initiate mate-guarding (TIMG), and proportion of time spent in amplexus (PTA). The study demonstrated that the exposure to Phen and DBT reduced the incidence of mate-guarding during the actual exposure period, but not during the observation period. However, whether or not pairs were involved in mate-guarding at the end of the exposure period did affect both TIMG and PTA during the observation period. Thus, the effects of Phen and DBT on amplexus status at the end of the exposure period indirectly affected TIMG and PTA during the observation period. The interaction between Phen and DBT with respect to their effects on mate-guarding varied among the mate-guarding measures. For the amplexus status at the end of the exposure period and for the effect on TIMG, the interaction did not deviate statistically from an additive effect. For PTA, the overall interaction was a synergistic one. This study's findings point out that assessments of hydrocarbon toxicity need to take into account that subtle reproductive behaviors (that may play an important role in population persistence) may be negatively affected. The results also show that the general assumption of additive effects among different PAHs may be an oversimplification.

The Brownsberg Nature Park (BNP) in Suriname is home to eight monkey species: Saguinus midas, Saimiri sciureus, Cebus apella, Alouatta seniculus. Pithecia pithecia, Cebus olivaceus, Chiropotes satanas (sagulatus), and Ateles paniscus. Several studies have undertaken the task to better study the feeding and behavioral ecology of these species within the park. However, studies on the black spider monkey (Ateles paniscus) have been absent. As part of my thesis, I decided to conduct a baseline feeding and behavioral ecology study of this species during the period May 2008 – July 2008. In addition, I developed a field method for determining mercury levels (in parts per million = ppm) in fecal and urine samples of wild monkeys. Since the park is under enormous pressure from illegal gold mining activities, I decided to collect baseline data on potential exposure of wild monkeys to mercury in the environment. I also collected samples from monkeys at the zoo in Paramaribo and monkeys born in captivity at Hiram College in Ohio. I collected data on the frequency of feeding, resting, and traveling by black spider monkey subgroups every 10 minutes during all day follows. Feeding ecology data consisted of identifying fruits eaten by these subgroups. For the mercury analysis I used the OSUMEX LTD. home testing kit. Results from the behavioral data show the following frequencies of activities for the entire study period: 32% feeding, 43% resting, and 25% traveling. The feeding data further justifies spider monkeys as ripe fruit frugivores: 76% of food items consisted of ripe fruit, while 22% consisted of leaves, and 2% was comprised of flowers. The mercury testing results from the Brownsberg and zoo populations ranged between 0.025 ppm to 0.1 ppm (toxic level = 0.8 ppm). The Hiram College monkeys all displayed levels at 0.000 ppm. The results from the mercury analyses indicate that 1) wild monkeys in the vicinity of gold mining activities may not be under the same threat as humans, with regards to mercury exposure through food, and 2) that wild monkeys are still relative exposed to mercury in the environment whether it be natural or anthropogenic.

Over the last several decades declines in pollinator populations, especially those of wild bees and other insects, have raised awareness of the economic impact pollination services have for crop production. This awareness and concern was heightened by an ongoing loss of millions of managed honey bee colonies since the early 1950s. Colonies are used predominantly for pollination services in fruit and vegetable crops. During 2007, an unusually large overwintering loss in colonies that was not characterized by the presence of dead bees was termed colony collapse disorder (CCD), a syndrome in which hives lacked sufficient worker caste bees to maintain the queen and brood. Potential factors hypothesized to be associated with CCD include parasite infestations (e.g., Varroa mite) and pathogen infections (Nosema spp. fungus and viruses), insecticide exposure (especially to the neonicotinoid class), and poor nutrition owing to a reduction in landscape areas containing high quality floral resources. Although no one stressor has been definitively associated with CCD, possible interactions among them have only recently been studied. Of particular interest are possible interactions of Nosema spp. with neonicotinoid insecticide exposure. The main objective of this dissertation was an examination of these potential interactions using a combination of literature analysis, empirical study of Nosema infection prevalence in adult bees, and simulation modeling of the combined effects of several stressors on worker population abundance. After the introduction, the dissertation is divided into four chapters addressing the following objectives: (1) Comparison of regulatory procedures for risk assessment of insecticides potentially impacting honey bees in the United States and in the European Union; (2) Analysis of published literature that document potential interactions between bee pathogens, parasites, and neonicotinoid insecticide residues; (3) Analysis of field-collected apiary bees for prevalence of Nosema spores in association with land uses and the presence of neonicotinoid residues; (4) Use of the honey bee colony model BEEHAVE to predict colony collapse in the presence of pathogens and insecticide-induced mortality. Results of the various analyses suggest a need for modifying risk assessment procedures to include the interaction of pesticide residues with parasite/pathogen stressors.

Mining is widespread and an economically important industry. Unfortunately, acid mine drainage (AMD) can pollute ecosystems with a cocktail of contaminants too complex for accurately forecasting its health consequences. However, through quantification of fundamental toxic events, the effects of complex mixtures can be observed. This project explored two potentially insightful and convenient endpoints. First, oxygen consumption (MO₂), a well-established and sensitive indicator of respiratory impairment was utilized. Second, protein carbonyl content (PCC), an experimental ecological biomarker widely lauded in biomedical circles as a highly conserved indicator of health status was assessed for its utility in a metal tolerant aquatic macroinvertebrate, Arctopsyche grandis. A. grandis were exposed to eight environmentally relevant target concentrations (in duplicate) of AMD for eight days at a temperature controlled greenhouse containing artificial flow-through streams. As expected, MO₂ was inversely related to treatment concentration (R ²=0.35, p=0.015). Protein carbonyl content, however, diverged from predictions. Protein carbonyl content analysis detected significantly more oxidative protein injury in control treatments than in metal-rich AMD treatments (p<0.001). Moreover, there was not a significant difference in PCC between different AMD concentrations. Protein carbonyl content’s departure from anticipated results likely is the consequence of dynamic interactions between direct and indirect effects at the chemical, biochemical, physiologic and behavioral levels. The results of this project illustrate flaws of utilizing a single biochemical marker to observe effects of a toxic mixture. Rather, a broad suite of biomarkers should be assayed to determine sublethal toxicity. These results also illustrates how multiple stressors can yield unanticipated outcomes.

Sediment bioturbators play an important ecological role and may both be affected by contaminants in the sediment and affect the fate and distribution of these contaminants. This is especially important for the many contaminants, like lead, for which sediments serve as a sink upon the contaminants’ release into the environment. In this study, I investigated the toxicity of sediment Pb to a freshwater bioturbator, the effect of bioturbation on the environmental distribution of the Pb, the effect of sediment characteristics on the bioturbation-mediated transfer of Pb from the sediment to the water column, and this transfer’s toxicological consequences for planktonic organisms. Experiments were conducted in microcosms with control sediment or Pb-spiked sediment, the freshwater oligochaete Lumbriculus variegatus served as the model bioturbator, and the water flea Daphnia magna served as the model planktonic organism. The rate of bioturbation of the oligochaete was quantified using luminophores.

The bioturbation resulted in the transfer of Pb from the sediment to the water column. However, it did not affect Pb levels in the worm tissue or in the sediment. The environmental distribution of Pb among water column, biota, and sediment in the presence of the bioturbator was dependent on sediment characteristic like organic content, silt/clay content, and the pH of the sediment. Bioturbation by L. variegatus increased bioaccumulation of Pb in D. magna; however, this Pb had no toxic effect on survival, reproduction, and biomass of D. magna under the specific conditions used here. Quantification of the bioturbation rates of L. variegatus showed that the intensity of the bioturbation was enhanced at higher densities of the oligochaete but reduced at high sedimentary Pb concentrations. Overall this study demonstrated that bioturbation by L. variegatus can transfer Pb from the sediment to the water column, and that this transfer is dependent on sediment characteristics. The Pb transferred as a result of the bioturbation can enhance Pb availability to organisms in the water column, and potentially cause toxic effects in these organisms.

Endocrine disrupting chemicals are a group of exogenous compounds which disrupt the endocrine functions of human and wildlife. This disruption might be in the synthesis, storage, release, and actions of specific hormones. Endocrine disrupting chemicals encompass a variety of chemical classes including drugs, compounds used in plastic consumer products manufacturing, pollutants, insecticides, herbicides, and even naturally-occurring botanical products like phytoestrogens. Most of these disrupters produce estrogenic properties because of having structural similarity to endogenous 17 beta estradiol. Mimicking estradiol, they can interfere with its actions resulting in the development of several diseases, such as nervous system, diabetes, obesity, breast cancers, and reproductive impairments. One of the endocrine disrupting chemicals of most interest is bisphenol A.

Bisphenol A is a carbon-based synthetic compound and it is used in epoxy resins, polycarbonate plastics, fungicides, antioxidants, stabilizers in rubber, and as a component of dental sealants. Numerous studies have found that bisphenol A may accidentally leak into canned foods or plastic bottled drinks ingested by humans. Studies indicate that bisphenol A effects are due to its estrogenic activity and the ability to bind and activate the estrogen receptor specifically. A growing number of studies have indicated that bisphenol A might be responsible for reduction in sperm count, spermatogenesis, aromatase, seminal fluid, 17 beta hydroxysteroid dehydrogenase activity, and testosterone biosynthesis. The primary objective of this capstone project is to review the available literature in order to determine the mechanism of bisphenol A action on testosterone biosynthesis. The working hypothesis was that bisphenol A-induced reduction in testosterone production may be due predominantly to inhibition of 17 beta beta hydroxysteroid dehydrogenase rather than an increase in aromatase enzyme activity. This study had the following specific aims: 1) review the sex steroid biosynthesis pathway, 2) review the endocrine disrupting chemicals; 3) determine a mechanism by which bisphenol A mimics estrogen and affects testosterone synthesis. Literature review was conducted using the databases PubMed, Ovid Medline, CINAHL Plus, as well as the search engine Google Scholar for the period 1940 to present. The keywords used: bisphenol A, testosterone, luteinizing hormone, 17 beta hydroxysteriod dehydrogenase enzymes. It was found that human studies were limited to urine measurements in which increased bisphenol A correlated with decreased sperm account and seminal fluid volume. In animal studies, bisphenol A reduced testosterone production by direct action on the leydig cells. In the ovarian granulosa cells, bisphenol A reduced aromatase enzyme activity but unlikely to be the method, in the testes as, a decrease in aromatase activity would cause an increase in testosterone level. Since bisphenol A causes significant decrease in testosterone biosynthesis, this suggests that the inhibition of 17 beta hydroxysteroid dehydrogenase, the enzyme that converts androstenedione to testosterone, is probably the principal target for bisphenol A. In conclusion, the literature supports a strong threat from bisphenol A on male reproductive function and every action must be taken seriously to reduce the exposure of male to this endocrine disrupting chemical.

Russian olive is an exotic actinorhizal tree intentionally introduced to the U.S. in the early 1900’s. It has become a dominant component of riparian ecosystems throughout the western U.S. Unlike most other riparian trees in the semi-arid west, Russian olive germinates and grows both in the open and in the understory of mature cottonwood stands. As an actinorhizal species, it forms an endosymbiosis with soil actinobacteria in the genus Frankia that allows for atmospheric N₂-fixation. This leads to higher soil N concentrations and mineralization rates underneath the tree’s canopy than outside. Russian olive’s high abundance and impact on soil N suggest it may alter plant communities, but these impacts have not been previously demonstrated. I investigated the impacts of Russian olive on shading, soil N availability, and plant communities and documented how those impacts varied across a semi-arid riparian ecosystem along the South Fork of the Republican River in eastern Colorado. Of the suite of environmental variables I measured, presence or absence of cottonwood canopy had the largest effect on Russian olive impacts. Russian olive increased shading, soil N availability, and proportion exotic plant and forb cover more in the open than underneath a cottonwood overstory.

Actinorhizal endosymbioses provides an important N source in terrestrial ecosystems, but N₂-fixation rates decrease due to high exogenous N and low photosynthetically active radiation (PAR). The amount that these environmental variables reduce N₂-fixation in host-Frankia symbiosis types dictates the strength and duration of those symbioses’ impacts on ecosystems. To understand how the two main types of endosymbioses (Alnus- and Elaeagnus-Frankia) differ in their response to environmental variability, I conducted a greenhouse experiment comparing growth and nodulation between two genera of actinorhizal species, Elaeagnus and Alnus, across exogenous N and PAR levels. Overall, Elaeagnus species had higher nodulation rates and tissue % N than Alnus species. Nodulation rate and growth response to nodulation were both lower at low PAR than high PAR for both genera. The reduction in the growth response to nodulation at high exogenous N was lower in Elaeagnus-Frankia symbiosis than Alnus-Frankia symbiosis. These results suggest that Elaeagnus species are more likely to cause a greater and longer-lasting increase in soil N than Alnus species.

A main objective of exotic species management is to increase native plant cover. However, few studies monitor plant community response to exotic species management, and the few that have suggest secondary invasion is likely, particularly when effects of the target invasive persists and management efforts cause disturbance. To measure the role of these two factors in plant community response to Russian olive removal, I monitored soil N availability and plant communities along the South Fork of the Republican River two years before and three years after the tree’s removal. Russian olive’s impact on soil N availability persisted, with levels staying high around removed Russian olive stems three years after removal. The plant community around removed Russian olive also had no increase in native plant cover but a dramatic increase in kochia ( Bassia scoparia) cover following removal. My research demonstrates that Russian olive increases exotic plant cover in areas it invades and simply removing the tree does not promote native species recovery.

The practice of restoration has been called the acid test for ecological theories, as theoretical outcomes may or may not occur in real life scenarios. Regardless, the need for increased communication between theory and practice is necessary to mutually benefit both disciplines. My dissertation research used several major ecological theories to formulate questions regarding environmental constraints on the establishment and expansion of several species of freshwater tidal macrophytes (Schoenoplectus acutus, Schoenoplectus californicus, and to a lesser extent, Typha latifolia). I investigated the response of these species at different life-history stages to various environmental stressors (i.e., degree of soil compaction, flooding duration, and nutrient availability) in both field and controlled greenhouse settings. These studies revealed that adult individuals are more tolerant to environmental stressors than their rhizome or seedling counterparts. Schoenoplectus californicus exhibited superior performance than S. acutus or T. latifolia in when subjected to extreme flooding and stressful abiotic conditions. My research regarding silicon and nitrogen nutrient availability emphasizes the role that Si plays in sustaining Schoenoplectus spp., especially in the presence of high nitrogen concentrations. Finally, my research showed that the species of concern are powerful ecosystem engineers and are capable of ameliorating their abiotic conditions over time. The information presented in my dissertation research provides specific, useful information for freshwater tidal marsh restoration managers and emphasizes the utility of incorporating theory to improve our understanding and stewardship of ecosystems.

During and following the Deepwater Horizon (DWH) accident in 2010, concerns about air and seafood quality were paramount. Though individual perceptions varied, many people in coastal communities in southeast Louisiana felt they had been exposed to oil- and dispersant-related compounds. We hypothesized that implementation of a Community-based Participatory Research (CBPR) project would promote a more transparent and mutually beneficial relationship between researchers and the community. We conducted both in-home and community-based assessments (n=198) in culturally diverse populations most impacted by the DWH event, including the Vietnamese in New Orleans East and the residents of the Bayou communities. Levels of volatile organic compounds (VOCs) in paired indoor/outdoor air samples and polycyclic aromatic hydrocarbons (PAHs) in seafood samples were determined with chemical analysis. Data were collected from multiple self-administered surveys regarding environmental awareness and impact of the DWH event, access to, and trusted sources of, information, perceptions about safety, and selected behavioral and socio-demographic variables. In an effort to enhance public understanding of the interconnectedness of their health with the Gulf ecosystem, we disseminated the information directly to the participants as well as the larger communities at risk. Through post-dissemination follow-up surveys, we explored the effectiveness of our environmental CBPR research strategy with our primary goals being to improve risk communication and promote informed decision-making among our coastal populations.

The island apple snail, Pomacea maculata, family Ampullariidae, is a large freshwater gastropod native to South America. P. maculata is known as a heavy consumer of aquatic plants. P. maculata was introduced to Florida in the 1990s and has rapidly spread throughout natural and man-made wetlands and waterways in the southeastern United States. Negative ecosystem impacts associated with P. maculata invasion include destruction of macrophyte communities via overgrazing, competitive exclusion of the native Florida apple snail Pomacea paludosa, and the potential transmission of toxins and parasites to predators.

Populations of P. maculata have been documented in freshwater tributaries of estuaries such as Mobile Bay, Alabama and the Caloosahatchee Estuary, Florida, and the snails may be moving into the estuaries themselves. The objectives of this study were: 1) to evaluate P. maculata's potential to harm macrophytes like tapegrass, Vallisneria americana, in low-salinity estuarine environments, 2) to determine how the grazer's destructiveness might by moderated by environmental context (salinity, temperature, and the presence of other macrophyte species), and 3) to identify management and restoration strategies for V. americana to minimize the harm done by P. maculata. We accomplished these objectives with feeding trials and mesocosm experiments conducted under varying conditions of salinity, temperature, and macrophyte community composition.

We found that increasing salinity lowered P. maculata grazing pressure on V. americana but increasing temperature increased grazing pressure. Herbivory on V. americana was not reduced and was sometimes intensified when other aquatic plant species were present. The results of two mesocosm experiments suggested that salinity and snail presence have a nonadditive, antagonistic, effect on V. americana. I.e., in the absence of snails the plant performed best at 0 psu, whereas when snails were present the plant did best at 5-10 psu due to reduced snail grazing. Due to the significant sub-lethal impacts of salinity on P. maculata's grazing and health it is unlikely that the snail's invasion will proceed beyond the lowest salinity portions of estuaries. These estuarine regions can therefore serve as a valuable refuge for V. americana populations, providing that effective water management keeps salinity below the approximately 10 psu threshold where significant direct harm occurs to the plants.

Climate change is arguably the biggest challenge facing humanity. Successful mitigation and adaption planning vitally requires more science in regard to its impacts on ecological systems. To address knowledge gaps regarding climate change impacts within the regional level, I performed a series of analyses on an "early responder" species in the Greater Yellowstone Ecosystem and examine how its distribution may be impacted by biotic and abiotic factors. My research aids in decision making processes for regional land managers that must address climate change in their policy decisions and increases ecological understanding at a landscape level.

This manuscript includes a detailed analysis of past, present, and projected climate in the Greater Yellowstone Ecosystem. I addressed the expected impacts of present and future climate shifts on the distribution of the sub-alpine tree species, whitebark pine (Pinus albicaulis) and its main disturbance agent, mountain pine beetle (Dendroctonus ponderosae). This research found a major reduction of suitable climate habitat for P.albicaulis within the Greater Yellowstone Ecosystem under multiple Global Circulation Models and Representative Concentration Pathway futures. Finally, this research determined that the recent D.ponderosae outbreak driven by climate effects in 2000–2010, that resulted in an unprecedented mortality event on P.albicaulis was more than double the risk area size of any previous outbreak since 1951. Although more studies are necessary to reduce uncertainty and make assertive recommendations for management actions, this research suggests that future sub-alpine stand structure and composition may be radically different than anything in recent history due to range shifts of suitable climate habitat and disturbance agents, and advocates for land managers to apply a multifaceted approach of competitor thinning and controlled burning to ensure the resilience and persistence of P.albicaulis.

Bird migration is the regular seasonal movements between breeding and nonbreeding grounds. In general, birds that breed in the Northern Hemisphere tend to migrate northward in the spring to take advantage of increasing insect populations and lower predation pressures and fly south when food availability and weather conditions decline. Embarking on a journey that can stretch a thousand miles round trip is a dangerous and arduous undertaking. While en route migrants must stop and feed to replenish their depleted energy reserves, often in unfamiliar locations with unknown predation pressures. They also must react to weather conditions during flight and while on the ground. Additionally, areas of high quality habitats where birds can refuel efficiently and safely may be few and far between. Therefore, it's not surprising that mortality rates can be higher during migration than at any other period of the year. Behavioral decisions such as where and where to stop, how long to stay, and when to leave all involve costs and benefits with an ultimate goal to balance the costs and benefits on order to achieve a successful and efficient migration. Optimal migration theory, aims to explain how migrants balance behavioral and physiological parameters of migration that minimize total time spent on migration, total energy expended, or mortality risk. The eventual result of these optimization pressures is thought to be a gradient of behavioral strategies that optimize different combinations of the three currencies: time, energy, and risk. I investigated how migratory behaviors of North American songbirds in the autumn balance the three currencies. More specifically I 1) explored how stopover site selection varies across migratory strategies at the landscape (Chapter 2) and habitat-patch (Chapter 3) scale; 2) investigated the importance of wind for the evolution and maintenance of migratory routes (Chapter 4); and 3) explored how selection of wind conditions for migratory departure affects overall behavioral strategies (Chapter 5). With this research, I hope to further our predictive abilities of migratory behaviors under various environmental and geographic situations using an optimal migration framework.