UNT Theses and Dissertations - 42 Matching Results

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Dynamics of Stream Fish Metacommunities in Response to Drought and Re-connectivity

Description: This dissertation investigates the spatio-temporal dynamics of intermittent stream fish metacommunities in response drought-induced fragmentation and re-connectivity using both field and experimental approaches. A detailed field study was conducted in two streams and included pre-drought, drought, and post-drought hydrological periods. Fish assemblages and metacommunity structure responded strongly to changes in hydrological conditions with dramatic declines in species richness and abundance during prolonged drought. Return of stream flows resulted in a trend toward recovery but ultimately assemblages failed to fully recover. Differential mortality, dispersal, recruitment among species indicates species specific responses to hydrologic fragmentation, connectivity, and habitat refugia. Two manipulative experiments tested the effects of drought conditions on realistic fish assemblages. Fishes responded strongly to drought conditions in which deeper pools acted as refugia, harboring greater numbers of fish. Variability in assemblage structure and movement patterns among stream pools indicated species specific habitat preferences in response predation, resource competition, and desiccation. Connecting stream flows mediated the impacts of drought conditions and metacommunity dynamics in both experiments. Results from field and experimental studies indicate that stream fish metacommunities are influenced by changes in hydrological conditions and that the timing, duration, and magnitude of drought-induced fragmentation and reconnecting stream flows have important consequences metacommunity dynamics.
Date: August 2015
Creator: Driver, Lucas J.
Partner: UNT Libraries

Ecological Significance and Underlying Mechanisms of Body Size Differentiation in White-tailed Deer

Description: Body size varies according to nutritional availability, which is of ecological and evolutionary relevance. The purpose of this study is to test the hypothesis that differences in adult body size are realized by increasing juvenile growth rate for white-tailed deer (Odocoileus virginianus). Harvest records are used to construct growth rate estimates by empirical nonlinear curve fitting. Results are compared to those of previous models that include additional parameters. The rate of growth increases during the study period. Models that estimate multiple parameters may not work with harvest data in which estimates of these parameters are prone to error, which renders estimates from complex models too variable to detect inter-annual changes in growth rate that this simpler model captures
Date: May 2012
Creator: Barr, Brannon
Partner: UNT Libraries

The Effect of Natural Gas Well Setback Distance on Drillable Land in the City of Denton, Texas

Description: Municipalities protect human health and environmental resources from impacts of urban natural gas drilling through setback distances; the regulation of distances between well sites and residences, freshwater wells, and other protected uses. Setback distances have increased over time, having the potential to alter the amount and geographical distribution of drillable land within a municipality, thereby having implications for future land use planning and increasing the potential for future incompatible land uses. This study geographically applies a range of setback distances to protected uses and freshwater wells in the city limits of Denton, Texas to investigate the effect on the amount of land remaining for future gas well development and production. Denton lies on the edge of a productive region of the Barnett Shale geological formation, coinciding with a large concentration of drillable land in the southwestern region of the study area. This region will have the greatest potential for impacts to future municipal development and land use planning as a result of future gas well development and higher setback standards. Given the relatively high acreage of drillable land in industrially zoned subcategory IC-G and the concern regarding gas well drilling in more populated areas, future drilling in IC-G, specifically in IC-G land cover classes mowed/grazed/agriculture and herbaceous, would have the least impact on residential uses and tree cover, as well as decreasing the potential for future incompatible land uses.
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Date: May 2014
Creator: Daniel, Michael
Partner: UNT Libraries

Effect of Rancher’s Management Philosophy, Grazing Practices, and Personal Characteristics on Sustainability Indices for North Central Texas Rangeland

Description: To assess sustainability of privately owned rangeland, a questionnaire was used to gathered data from ranches in Cooke, Montague, Clay, Wise, Parker, and Jack counties in North Central Texas. Information evaluated included: management philosophy, economics, grazing practices, environmental condition, quality of life, and demographics. Sustainability indices were created based on economic and land health indicator variables meeting a minimum Cronbach‘s alpha coefficient (α = 0.7). Hierarchical regression analysis was used to create models explaining variance in respondents’ indices scores. Five predictors explained 36% of the variance in rangeland economic sustainability index when respondents: 1) recognized management inaction has opportunity costs affecting economic viability; 2) considered forbs a valuable source of forage for wildlife or livestock; 3) believed governmental assistance with brush control was beneficial; 4) were not absentee landowners and did not live in an urban area in Texas, and; 5) valued profit, productivity, tax issues, family issues, neighbor issues or weather issues above that of land health. Additionally, a model identified 5 predictors which explained 30% of the variance for respondents with index scores aligning with greater land health sustainability. Predictors indicated: 1) fencing cost was not an obstacle for increasing livestock distribution; 2) land rest was a component of grazing plans; 3) the Natural Resource Conservation Service was used for management information; 4) fewer acres were covered by dense brush or woodlands, and; 5) management decisions were not influenced by friends. Finally, attempts to create an index and regression analysis explaining social sustainability was abandoned, due to the likely-hood of type one errors. These findings provide a new line of evidence in assessing rangeland sustainability, supporting scientific literature concerning rangeland sustainability based on ranch level indicators. Compared to measuring parameters on small plots, the use of indices allows for studying replicated whole- ranch units using rancher insight. Use ...
Date: December 2011
Creator: Becker, Wayne
Partner: UNT Libraries

The Effects of Air Pollution on the Intestinal Microbiota: A Novel Approach to Assess How Gut Microbe Interactions with the Environment Affect Human Health

Description: This thesis investigates how air pollution, both natural and anthropogenic, affects changes in the proximal small intestine and ileum microbiota profile, as well as intestinal barrier integrity, histological changes, and inflammation. APO-E KO mice on a high fat diet were randomly selected to be exposed by whole body inhalation to either wood smoke (WS) or mixed vehicular exhaust (MVE), with filtered air (FA) acting as the control. Intestinal integrity and histology were assessed by observing expression of well- known structural components tight junction proteins (TJPs), matrix metallopeptidase-9 (MMP-9), and gel-forming mucin (MUC2), as well known inflammatory related factors: TNF-α, IL-1β, and toll-like receptor (TLR)-4. Bacterial profiling was done using DNA analysis of microbiota within the ileum, utilizing 16S metagenomics sequencing (Illumina miSeq) technique. Overall results of this experiment suggest that air pollution, both anthropogenic and natural, cause a breach in the intestinal barrier with an increase in inflammatory factors and a decrease in beneficial bacteria. This evidence suggests the possibility of air pollution being a potential causative agent of intestinal disease as well as a possible contributing mechanism for induction of systemic inflammation.
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Date: May 2017
Creator: Fitch, Megan
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Effects of Layer Double Hydroxide Nanoclays on the Toxicity of Copper to Daphnia Magna

Description: Nanoparticles may affect secondary pollutants such as copper. Layer Double Hydroxides (LDH) are synthetically produced nanoparticles that adsorb copper via cation exchange. Pretreatment of copper test solutions with LDH nanoparticles followed by filtration removal of LDH nanoparticles demonstrated the smallest LDH aggregates removed the most copper toxicity. This was due to increased surface area for cation exchange relative to larger particle aggregates. Co-exposure tests of copper chloride and clay were run to determine if smaller clay particles increased copper uptake by D. magna. Coexposure treatments had lower LC50 values compared to the filtration tests, likely as a result of additive toxicity. LDH nanoclays do reduce copper toxicity in Daphnia magna and may serve as a remediation tool.
Date: May 2012
Creator: Blake, Deanne Renee
Partner: UNT Libraries

Effects of Macrophyte Functional Diversity on Taxonomic and Functional Diversity and Stability of Tropical Floodplain Fish Assemblages

Description: Multiple dimensions of biodiversity within and across producer and consumer guilds in the food web affect an ecosystem’s functionality and stability. Tropical and subtropical aquatic ecosystems, which are extremely diverse, have received much less attention than terrestrial ecosystems in regards to the effects of biodiversity on ecosystem functioning. We conducted a field experiment that tested for effects of macrophyte functional diversity on diversity and stability of associated fish assemblages in floodplain lakes of the Upper Paraná River floodplain, Brazil. Three levels of macrophyte functional diversity were maintained through time in five floodplain lakes and response variables included various components of fish taxonomic and functional diversity and stability. Components of functional diversity of fish assemblages were quantified using a suite of ecomorphological traits that relate to foraging and habitat use. Response variables primarily distinguished macrophyte treatments from the control. Macrophyte treatments had, on average, double the number of species and total abundance than the control treatment, but only limited effects on stability. The high diversity treatment was essentially nested within the low diversity for assemblage structure and had similar or even slightly lower levels of species richness and abundance in most cases. Gymnotiformes and young-of-year were diverse and relatively abundant in macrophyte treatments contributing to the large differences in diversity between macrophyte and control treatments. Higher fish diversity in structured habitats compared to more homogenous habitats is likely associated with increased ecomorphological diversity to exploit heterogeneous microhabitats and resources provided by the macrophytes.
Date: August 2015
Creator: Treviño, Jessica Marie
Partner: UNT Libraries

The Effects of Neonicotinoid Exposure on Embryonic Development and Organ Mass in Northern Bobwhite Quail

Description: Since their emergence in the early 1990s, neonicotinoid use has increased exponentially to make them the world's most prevalent insecticides. Although there is considerable research concerning the lethality of neonicotinoids, their sub-lethal and developmental effects are still being explored, especially with regards to non-mammalian species. The goal of this research was to investigate the effects of the neonicotinoid imidacloprid on the morphological and physiological development of northern bobwhite quail (Colinus virginianus). Bobwhite eggs (n = 650) were injected with imidacloprid concentrations of 0 (sham), 10, 50, 100 and 150 grams per kilogram of egg mass, which was administered at day 0 (pre-incubation), 3, 6, 9, or 12 of growth. Embryos were dissected on day 19 when they were weighed, staged, and examined for any overt structural deformities. Embryonic heart, liver, lungs and kidneys were also weighed and preserved for future use. Treated embryos exhibited increased frequency of severely deformed beaks and legs, as well as larger hearts and smaller lungs at the higher dosing concentrations. Some impacts are more pronounced in specific dosing periods, implying that there may be critical windows of development when embryos are highly susceptible to neonicotinoid exposure. This investigation suggests that imidacloprid could play a significant role in chick survival and declining quail populations in treated regions of the country.
Date: May 2016
Creator: Gobeli, Amanda
Partner: UNT Libraries

Effects of Suspended Multi-Walled Carbon Nanotubes on Daphnid Growth and Reproduction

Description: Multi-walled carbon nanotube aggregates can be suspended in the aqueous phase by natural organic matter. These aggregates are ingested by filter feeding zooplankton. Ingested aggregates result in decreased growth and decreased reproduction. These effects may be caused by reduction in energy input from normal feeding behavior. pH alters natural organic matter structure through changes in electrostatic repulsion. Altered natural organic matter structure changes multi-walled carbon nanotube aggregate size. This size variation with variation in pH is significant, but not large enough a change in size to alter toxicity, as the aggregate size range remains well within the particle size selection of the organisms.
Date: May 2010
Creator: Alloy, Matthew Michael
Partner: UNT Libraries

Evaluation of the Developmental Effects and Bioaccumulation Potential of Triclosan and Triclocarban Using the South African Clawed Frog, Xenopus Laevis

Description: Triclosan (TCS) and triclocarban (TCC) are antimicrobials found in U.S. surface waters. This dissertation assessed the effects of TCS and TCC on early development and investigated their potential to bioaccumulate using Xenopus laevis as a model. The effects of TCS on metamorphosis were also investigated. For 0-week tadpoles, LC50 values for TCS and TCC were 0.87 mg/L and 4.22 mg/L, respectively, and both compounds caused a significant stunting of growth. For 4-week tadpoles, the LC50 values for TCS and TCC were 0.22 mg/L and 0.066 mg/L; and for 8-week tadpoles, the LC50 values were 0.46 mg/L and 0.13 mg/L. Both compounds accumulated in Xenopus. For TCS, wet weight bioaccumulation factors (BAFs) for 0-, 4- and 8-week old tadpoles were 23.6x, 1350x and 143x, respectively. Lipid weight BAFs were 83.5x, 19792x and 8548x. For TCC, wet weight BAFs for 0-, 4- and 8-week old tadpoles were 23.4x, 1156x and 1310x. Lipid weight BAFs were 101x, 8639x and 20942x. For the time-to-metamorphosis study, TCS showed an increase in weight and snout-vent length in all treatments. Exposed tadpoles metamorphosed approximately 10 days sooner than control tadpoles. For the hind limb study, although there was no difference in weight, snout-vent length, or hind limb length, the highest treatment was more developed compared to the control. There were no differences in tail resorption rates between the treatments and controls. At relevant concentrations, neither TCS nor TCC were lethal to Xenopus prior to metamorphosis. Exposure to relatively high doses of both compounds resulted in stunted growth, which would most likely not be evident at lower concentrations. TCS and TCC accumulated in Xenopus, indicating that the compound has the potential to bioaccumulate through trophic levels. Although TCS may increase the rate of metamorphosis in terms of developmental stage, it did not disrupt thyroid function and metamorphosis in ...
Date: December 2010
Creator: King, Marie Kumsher
Partner: UNT Libraries

Habitat Fragmentation by Land-Use Change: One-Horned Rhinoceros in Nepal and Red-Cockaded Woodpecker in Texas

Description: This research focuses on the spatial analysis of the habitat of two vulnerable species, the one-horn rhinoceros in the grasslands of southern Nepal, and the red-cockaded woodpecker in the Piney woods of southeast Texas, in the USA. A study sites relevant for biodiversity conservation was selected in each country: Chitwan National Park in Nepal, and areas near the Big Thicket National Preserve in Texas. Land-use differs in the two study areas: the first is still undergoing agrarian development while the second is in a technological phase and undergoing urbanization processes. Satellite remote sensing images were used to derive land-cover maps by supervised classification. These maps were then processed by Geographic Information Systems methods to apply habitat models based on basic resources (food and cover) and obtain habitat suitability maps. Several landscape metrics were computed to quantify the habitat characteristics especially the composition and configuration of suitable habitat patches. Sensitivity analyses were performed as the nominal values of some of the model parameters were arbitrary. Development potential probability models were used to hypothesize changes in land-use of the second study site. Various scenarios were employed to examine the impact of development on the habitat of red-cockaded woodpecker. The method derived in this study would prove beneficial to guide management and conservation of wildlife habitats.
Date: December 2010
Creator: Thapa, Vivek
Partner: UNT Libraries

Hepatotoxicity of Mercury to Fish

Description: Tissue samples from spotted gar (Lepisosteus oculatus) and largemouth bass (Micropterus salmoides) were collected from Caddo Lake. Gar and bass livers were subjected to histological investigation and color analysis. Liver color (as abs at 400 nm) was significantly correlated with total mercury in the liver (r2 = 0.57, p = 0.02) and muscle (r2 = 0.58, p = 0.01) of gar. Evidence of liver damage as lipofuscin and discoloration was found in both species but only correlated with liver mercury concentration in spotted gar. Inorganic mercury was the predominant form in gar livers. In order to determine the role of mercury speciation in fish liver damage, a laboratory feeding study was employed. Zebrafish (Danio rerio) were fed either a control (0.12 ± 0.002 µg Hg.g-1 dry wt), inorganic mercury (5.03 ± 0.309 µg Hg.g-1 dry wt), or methylmercury (4.11 ± 0.146 µg Hg.g-1 dry wt) diet. After 78 days of feeding, total mercury was highest in the carcass of zebrafish fed methylmercury (12.49 ± 0.369 µg Hg.g-1 dry wt), intermediate in those fed inorganic mercury (1.09 ± 0.117 µg Hg.g-1 dry wt), and lowest in fish fed the control diet (0.48 ± 0.038 µg Hg.g-1 dry wt). Total mercury was highest in the viscera of methylmercury fed zebrafish (11.6 ± 1.86 µg Hg.g-1 dry wt), intermediate in those fed inorganic diets (4.3 ± 1.08 µg Hg.g-1 dry wt), and lowest in the control fish (below limit of detection). Total mercury was negatively associated with fish length and weight in methylmercury fed fish. Condition factor was not associated with total mercury and might not be the best measure of fitness for these fish. No liver pathologies were observed in zebrafish from any treatment.
Date: August 2010
Creator: Barst, Benjamin Daniel
Partner: UNT Libraries

The Influence of Urban Green Spaces on Declining Bumble Bees (Hymenoptera: Apidae)

Description: Bumble bees (Bombus spp.) are adept pollinators of countless cultivated and wild flowering plants, but many species have experienced declines in recent decades. Though urban sprawl has been implicated as a driving force of such losses, urban green spaces hold the potential to serve as habitat islands for bumble bees. As human populations continue to grow and metropolitan areas become larger, the survival of many bumble bee species will hinge on the identification and implementation of appropriate conservation measures at regional and finer scales. North Texas is home to some the fastest-growing urban areas in the country, including Denton County, as well as at least two declining bumble bee species (B. pensylvanicus and B. fraternus). Using a combination of field , molevular DNA and GIS methods I evaluated the persistence of historic bumble bee species in Denton County, and investigated the genetic structure and connectivity of the populations in these spaces. Field sampling resulted in the discovery of both B. pensylvanicus and B. fraternus in Denton County's urban green spaces. While the relative abundance of B. fraternus in these spaces was significantly lower than historic levels gleaned from museum recors, that of B. pensylvanicus was significantly higher. Statistical analyses found that both bare ground and tree cover surrounding sample sites were negatively associated with numbers of bumble bee individuals and hives detected in these green spaces. Additionally, limited genetic structuring of bumble bee populations was detected, leading to the conclusion that extensive gene flow is occurring across populations in Denton County.
Date: May 2016
Creator: Beckham, Jessica Lorene
Partner: UNT Libraries

Informing Conservation Management Using Genetic Approaches: Greater Sage-grouse and Galápagos Short-eared Owls as Case Studies

Description: Small isolated populations are of particular conservation interest due to their increased extinction risk. This dissertation investigates two small wild bird populations using genetic approaches to inform their conservation. Specifically, one case study investigated a Greater Sage-grouse (Centrocercus urophasianus) population located in northwest Wyoming near Jackson Hole and Grand Teton National Park. Microsatellite data showed that the Jackson sage-grouse population possessed significantly reduced levels of neutral genetic diversity and was isolated from other Wyoming populations. Analysis with single nucleotide polymorphisms (SNPs) and microsatellite data provided further evidence that the population's timing of isolation was relatively recent and most likely due to recent anthropogenic habitat changes. Conservation recommendations include maintaining or increasing the population's current size and reestablishing gene flow with the nearest large population. The second case study investigated the genetic distinctiveness of the Floreana island population of the Galápagos Short-eared Owl (Asio flammeus galapagoensis). Mitochondrial DNA sequence data did not detect differences across nine island populations, yet microsatellite and morphometric data indicated that limited gene flow existed with the population and surrounding island populations, which appeared asymmetric in direction from Floreana to Santa Cruz with no indication of gene flow into Floreana. These results have important conservation implications and recommend that the Floreana Short-eared Owl population be held in captivity during the rodenticide application planned for an ecosystem restoration project in 2018. The population is less likely to receive immigrants from surrounding island populations if negatively effected by feeding on poisoned rodents.
Date: May 2016
Creator: Schulwitz, Sarah E
Partner: UNT Libraries

Integrating Selective Herbicide and Native Plant Restoration to Control Alternanthera philoxeroides (Alligator Weed)

Description: Exotic invasive aquatic weeds such as alligator weed (Alternanthera philoxeroides) threaten native ecosystems by interfering with native plant communities, disrupting hydrology, and diminishing water quality. Development of new tools to combat invaders is important for the well being of these sensitive areas. Integrated pest management offers managers an approach that combines multiple control methods for better control than any one method used exclusively. In a greenhouse and field study, we tested the effects of selective herbicide application frequency, native competitor plant introduction, and their integration on alligator weed. In the greenhouse study, alligator weed shoot, root, and total biomass were reduced with one herbicide application, and further reduced with two. Alligator weed cumulative stem length and shoot/root ratio was only reduced after two applications. In the greenhouse, introduction of competitors did not affect alligator weed biomass, but did affect shoot/root ratio. The interaction of competitor introduction and herbicide did not significantly influence alligator weed growth in the greenhouse study. In the field, alligator weed cover was reduced after one herbicide application, but not significantly more after a second. Introduction of competitor species had no effect on alligator weed cover, nor did the interaction of competitor species and herbicide application. This study demonstrates that triclopyr amine herbicide can reduce alligator weed biomass and cover, and that two applications are more effective than one. To integrate selective herbicides and native plant introduction successfully for alligator weed control, more research is needed on the influence competition can potentially have on alligator weed growth, and the timing of herbicide application and subsequent introduction of plants.
Date: December 2011
Creator: Adams, Justin
Partner: UNT Libraries

Macroinvertebrate Colonization and Assemblages Associated with Aquatic Macrophytes in a Newly Created Urban Floodway Ecosystem, Dallas, Tx

Description: A study of macroinvertebrate colonization and assemblages, including secondary productivity of the familiar bluet damselfly or Enallagma civile Hagen (Odonata: Coenagrionidae), associated with the aquatic macrophytes Heteranthera dubia (Jacq.) MacMill. (water stargrass) and Potamogeton nodosus Poir. (American pondweed) was conducted at the Dallas Floodway Extension Trinity River Project (DFE) Lower Chain of Wetlands (LCOW), Dallas, TX, from September 2010 through November 2011. Macroinvertebrate abundance, taxa richness, Simpson's index of diversity, and Simpson's evenness from the two macrophytes and from three different wetland cells of varying construction completion dates, water sources, and native aquatic vegetation establishment were analyzed along with basic water quality metrics (temperature °C, pH, dissolved oxygen mg/L, and conductivity µs/cm). E. civile nymphs were separated into five developmental classes for secondary productivity estimations between macrophytes and wetland cell types. Mean annual secondary productivity in the DFE LCOW among two macrophytes of E. civile was 1392.90 ash-free dry weight mg/m²/yr, standing stock biomass was 136.77 AFDW mg/m2/yr, cohort production / biomass (P/B) ratio was calculated to be 4.30 / yr and the annual production / biomass (P/B) ratio was 10.18 /yr.
Date: August 2013
Creator: Schad, Aaron Neale
Partner: UNT Libraries

Measuring Atmospheric Ozone and Nitrogen Dioxide Concentration by Differential Optical Absorption Spectroscopy

Description: The main objective was to develop a procedure based on differential optical absorption spectroscopy (DOAS) to measure atmospheric total column of ozone, using the automated instrument developed at the University of North Texas (UNT) by Nebgen in 2006. This project also explored the ability of this instrument to provide measurements of atmospheric total column nitrogen dioxide. The instrument is located on top of UNT’s Environmental Education, Science and Technology Building. It employs a low cost spectrometer coupled with fiber optics, which are aimed at the sun to collect solar radiation. Measurements taken throughout the day with this instrument exhibited a large variability. The DOAS procedure derives total column ozone from the analysis of daily DOAS Langley plots. This plot relates the measured differential column to the airmass factor. The use of such plots is conditioned by the time the concentration of ozone remains constant. Observations of ozone are typically conducted throughout the day. Observations of total column ozone were conducted for 5 months. Values were derived from both DOAS and Nebgen’s procedure and compared to satellite data. Although differences observed from both procedures to satellite data were similar, the variability found in measurements was reduced from 70 Dobson units, with Nebgen’s procedure, to 4 Dobson units, with the DOAS procedure.A methodology to measure atmospheric nitrogen dioxide using DOAS was also investigated. Although a similar approach to ozone measurements could be applied, it was found that such measurements were limited by the amount of solar radiation collected by the instrument. Observations of nitrogen dioxide are typically conducted near sunrise or sunset, when solar radiation experiences most of the atmospheric absorption.
Date: December 2011
Creator: Jerez, Carlos J.
Partner: UNT Libraries

Modeling the Effects of Chronic Toxicity of Pharmaceutical Chemicals on the Life History Strategies of Ceriodaphnia Dubia: a Multigenerational Study

Description: Trace quantities of pharmaceuticals (including carbamazepine and sertraline) are continuously discharged into the environment, which causes concern among scientists and regulators regarding their potential long-term impacts on aquatic ecosystems. These compounds and their metabolites are continuously interacting with the orgranisms in various life stages, and may differentially influence development of embryo, larvae, juvenile, and adult stages. To fully understand the potential ecological risks of two candidate pharmaceutical chemicals (carbamazepine (CBZ) and sertraline (SERT)) exposure on survival, growth and reproduction of Ceriodaphnia dubia in three sucessive generations under static renewal toxicity test, a multigenerational approach was taken. Results indicate that SERT exposure showed higher sensitivity to chronic exposure to C. dubia growth and reproduction than CBZ exposure. The lowest concentration to affect fecundity and growth was at 50 µg L-1 SERT in the first two generations. These parameters become more sensitive during the third generation where the LOEC was 4.8 µg L-1. The effective concentrations (EC50) for the number of offspring per female, offspring body size, and dry weight were 17.2, 21.2, and 26.2 µg SERT L-1, respectively. Endpoints measured in this study demonstrate that chronic exposure of C. dubia to SERT leads to effects that occur at concentrations an order of magnitude higher than predicted environmental concentrations indicating potential transgenerationals effects. Additionally, a process-based dynamic energy budget (DEB) model is implemented to predict the simulated effects of chronic toxicity of SERT and CBZ to C. dubia individual behavior at laboratory condition. The model‘s output indicates the ecotoxicological mode of action of SERT exposure, which acts on feeding or assimilation with an effect that rapidly saturates at higher concentrations. Offspring size decreases with the toxic effects on feeding, and offspring number is thus less affected than total investment in reproduction. Consequently, CBZ affects direclty in reproduction which are captured by DEBtox ...
Date: December 2013
Creator: Lamichhane, Kiran
Partner: UNT Libraries

Modeling the Relationship Between Golden Algae Blooms in Lake Texoma, Usa, Versus Nearby Land Use and Other Physical Variables

Description: Pyrmnesium parvum, commonly known as golden algae, is an algal species that under certain circumstances releases toxins which can lead to fish kills and the death of other economically and ecologically important organisms. One of the major objectives of the study was to investigate whether a relationship exists between land use and Prymnesium parvum abundance in littoral sites of Lake Texoma, USA. Another objective was to investigate whether a relationship exists between other physical variables and counts of P. parvum. Lastly, developing a valid model that predicts P. parvum abundance was an objective of the study. Through stepwise regression, a small but highly significant amount of the variation in P. parvum counts was found to be explained by wetlands, soil erodibility and lake elevation. The developed model provides insight for potential golden algae management plans, such as maintaining wetlands and teaching land owners the relationship between soil erosivity and golden algae blooms.
Date: August 2012
Creator: Ware, Trudy M.
Partner: UNT Libraries

Optimizing Scientific and Social Attributes of Pharmaceutical Take Back Programs to Improve Public and Environmental Health

Description: Research continues to show that pharmaceutical environmental contamination has caused adverse environmental effects, with one of the most studied effects being feminization of fish exposed to pharmaceutical endocrine disruptors. Additionally, there are also public health risks associated with pharmaceuticals because in-home reserves of medications provide opportunities for accidental poisoning and intentional medication abuse. Pharmaceutical take back programs have been seen as a remedy to these concerns; however a thorough review of peer-reviewed literature and publicly available information on these programs indicates limited research has been conducted to validate these programs as a purported solution. Furthermore, there are significant data gaps on key factors relating to take back program participants. The purpose of this dissertation was therefore to address these gaps in knowledge and ultimately determine if take back programs could actually improve public and environmental health. This was accomplished by conducting social and scientific research on a take back program called Denton Drug Disposal Day (D4). Socioeconomic, demographic, and geographic characteristics of D4 participants were investigated using surveys and geographic analysis. Impacts on public health were determined by comparing medications collected at D4 events with medications reported to the North Texas Poison Center as causing adverse drug exposures in Denton County. Impacts to environmental health were determined by monitoring hydrocodone concentrations in wastewater effluent released from Denton’s wastewater treatment plant before and after D4 events. Data collected and analyzed from the D4 events and the wastewater monitoring suggests D4 events were successful in contributing to improvements in public and environmental health; however there was insufficient evidence to prove that D4 events were exclusively responsible for these improvements. An additional interesting finding was that willingness to travel to participate in D4 events was limited to a five to six mile threshold. This geographic information, combined with other findings related to socioeconomic, ...
Date: August 2012
Creator: Stoddard, Kati Ireland
Partner: UNT Libraries

Photo-induced Toxicity of Deepwater Horizon Spill Oil to Four Native Gulf of Mexico Species

Description: The 2010 Deepwater Horizon oil spill resulted in the accidental release of millions of barrels of crude oil into the Gulf of Mexico (GoM). Photo-induced toxicity following co-exposure to ultraviolet (UV) radiation is one mechanism by which polycyclic aromatic hydrocarbons (PAHs) from oil spills may exert toxicity. Blue crab (Callinectes sapidus) are an important commercial and ecological resource in the Gulf of Mexico and their largely transparent larvae may make them sensitive to PAH photo-induced toxicity. Mahi-mahi (Coryphaena hippurus), an important fishery resource, have positively buoyant, transparent eggs. These characteristics may result in mahi-mahi embryos being at particular risk from photo-induced toxicity. Red drum (Sciaenops ocellatus) and speckled seatrout (Cynoscion nebulosus) are both important fishery resources in the GoM. They spawn near-shore and produce positively buoyant embryos that hatch into larvae in about 24 h. The goal of this body of work was to determine whether exposure to UV as natural sunlight enhances the toxicity of crude oil to early lifestage GoM species. Larval and embryonic organisms were exposed to several dilutions of water accommodated fractions (WAF) from several different oils collected in the field under chain of custody during the 2010 spill and two to three gradations of natural sunlight in a factorial design. Here, we report that co-exposure to natural sunlight and oil significantly reduced larval survival and embryo hatch compared to exposure to oil alone.
Date: December 2015
Creator: Alloy, Matthew Michael
Partner: UNT Libraries

Photoinduced Toxicity in Early Lifestage Fiddler Crab (Uca longisignalis) Following Exposure to Deepwater Horizon Spill Oil

Description: The 2010 Deepwater Horizon (DWH) oil spill resulted in a large release of polycyclic aromatic hydrocarbons (PAH) into the Gulf of Mexico. PAH can interact with ultraviolet radiation (UV) resulting in increased toxicity, particularly to early lifestage organisms. The goal of this research was to determine the sensitivity of fiddler crab larvae (Uca longisignalis) to photo-induced toxicity following exposure to Deepwater Horizon spill oil in support of the DWH Natural Resource Damage Assessment. Five replicate dishes each containing 20 larvae, were exposed to one of three UV treatments (10%, 50%, and 100% ambient natural sunlight) and one of five dilutions of water accommodated fractions of two naturally weathered source oils. A dose dependent effect of PAH and UV on larval mortality was observed. Mortality was markedly higher in PAH treatments that included co-exposure to more intense UV light. PAH treatments under low intensity sunlight had relatively high survival. These data demonstrate the importance of considering combined effects of non-chemical (i.e. UV exposure) and chemical stressors and the potential for photo-induced effects after exposure to PAH following the Deepwater Horizon spill.
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Date: December 2015
Creator: Taylor, Leigh M.
Partner: UNT Libraries

Population Dynamics of Zebra Mussels (Dreissena Polymorpha) in a North Texas Reservoir: Implications for Invasions in the Southern United States

Description: This dissertation has two main objectives: first, quantify the effects of environmental conditions on spatio-temporal spawning and larval dynamics of zebra mussels (Dreissena polymorpha [Pallas 1771]) in Lake Texoma, and second, quantify the effects of environmental conditions on survival, growth, and reproduction of young of the year (YOY) juvenile zebra mussels. These biological responses directly influence population establishment success and invasive spread dynamics. Reproductive output of the zebra mussel population in Lake Texoma was significantly related to water temperature and lake elevation. Annual maximum larval (veliger) density decreased significantly indicating a population crash, which was likely caused by thermal stress and variability of lake elevation. In 2011, temperatures peaked at 34.3°C and lake elevation decreased to the lowest level recorded during the previous 18 years, which desiccated a substantial number of settled mussels in littoral zones. Estimated mean date of first spawn in Lake Texoma was observed approximately 1.5 months earlier than in Lake Erie, and peak veliger densities were observed two months earlier. Veligers were observed in the deepest oxygenated water after lake stratification. During a 69-day in situ experiment during summer in Lake Texoma, age-specific mortality of zebra mussels was generally high until temperatures decreased to approximately 28°C, which was observed after lake turnover in late summer. No study organism died after temperatures decreased to less than 26°C, which indicates individuals that survive high summer temperatures are likely to persist into autumn/winter. Shell length growth and soft tissue growth rates were related to temperature and chlorophyll-a concentration, respectively. Growth rates of study organisms were among the highest ever reported for D. polymorpha. Water temperature and body size influenced reproduction of YOY zebra mussels in Lake Texoma. Fecundity of females were positively related to temperature; however, sperm production was negatively related to temperature, which indicates males could be more ...
Date: December 2013
Creator: Churchill, Christopher J.
Partner: UNT Libraries

Quantifying Forest Vertical Structure to Determine Bird Habitat Quality in the Greenbelt Corridor, Denton, Tx

Description: This study presents the integration of light detection and range (LiDAR) and hyperspectral remote sensing to create a three-dimensional bird habitat map in the Greenbelt Corridor of the Elm Fork of the Trinity River. This map permits to examine the relationship between forest stand structure, landscape heterogeneity, and bird community composition. A biannual bird census was conducted at this site during the breeding seasons of 2009 and 2010. Census data combined with the three-dimensional map suggest that local breeding bird abundance, community structure, and spatial distribution patterns are highly influenced by vertical heterogeneity of vegetation surface. For local breeding birds, vertical heterogeneity of canopy surface within stands, connectivity to adjacent forest patches, largest forest patch index, and habitat (vegetation) types proved to be the most influential factors to determine bird community assemblages. Results also highlight the critical role of secondary forests to increase functional connectivity of forest patches. Overall, three-dimensional habitat descriptions derived from integrated LiDAR and hyperspectral data serve as a powerful bird conservation tool that shows how the distribution of bird species relates to forest composition and structure at various scales.
Date: August 2013
Creator: Matsubayashi, Shiho
Partner: UNT Libraries