UTSA Electronic Theses and Dissertations
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This collection contains electronic UTSA theses and dissertations (ETDs), primarily from 2005 to present. The collection is not comprehensive; search the UTSA Library Catalog for a complete list of UTSA theses and dissertations.
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Browsing UTSA Electronic Theses and Dissertations by Department "Earth and Environmental Science"
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Item Analysis of overpressure generating mechanisms in different tectonic settings(2010) Al-Najrani, FahadOverpressure occurs at depth where formation fluid pressure exceeds hydrostatic pressure. A literature review of 56 overpressured basins out of ∼600 worldwide documented various overpressure generating mechanisms. Overpressure incidences are statistically analyzed by their hosting tectonic settings. The main mechanisms cited for those overpressured basins are disequilibrium compaction (∼60%), hydrocarbon generation (∼23%), tectonic compression (∼14%) and diagenesis (∼3%). The most common tectonic setting of surveyed basins with overpressured fluid conditions is the continental passive margin setting (∼26%). Disequilibrium compaction is found to be the main overpressure generating mechanism in all tectonic settings. Basin age is an important variable to be considered because tectonic settings can change through time. The main contribution of this study is a table with percentages to be used in predicting possible overpressure generating mechanisms in a new or a reevaluated overpressured basin.Item Characterizing urban heat island phenomenon of four Texas cities using MODIS LST products(2010) Prado, DavidIn this study, MODIS's (Moderate Resolution Imaging Spectroradiometer-Earth Observing System) land surface temperature (LST) products of eight-day composite images at 10:30 am, 1:30 pm, 10:30 pm, and 1:30 am are used to study urban heat island (UHI) phenomenon over four major Texas cities (El Paso, Dallas-Ft. Worth, Houston, and San Antonio) from the Summer of 2000 to the Fall of 2008. The eight-day LST products are used to generate spatial maps characterizing the temperature distribution and UHI spatial extent for each city. The results indicate that (1) UHI can be observed in night time images in Dallas-Ft. Worth, Houston, and San Antonio all year long; the intensities of UHI are larger in night times of spring and summer seasons than those of fall and winter seasons; (2) UHI consistently appears in night time images in El Paso-Juarez and the intensities of UHI are similar in all seasons; (3) the day time images contain large amounts of cloud contamination in Dallas-Ft. Worth, Houston, and San Antonio which make the use of day time images to map UHIs in those cities difficult; and (4) from the temperature climatology maps (seasonal mean and yearly mean) of the 8 years, it is found that Aqua/MODIS LST products in the night time (1:30 am) is the best for mapping UHI for all four cities and that the spatial extent and pattern of the UHI differs from the expected HI usually centered in downtown of a city.Item Crime analysis in the San Antonio area between 2006 and 2010 using GIS applications(2012) Onwuchekwa, EzenwanyiThis study utilizes crime rate, crime density and Location Quotient to Crimes (LQCs) in mapping the most dominant crime types across different census tracts in San Antonio, Texas. In mapping dominant crime types across different census tracts in San Antonio, crime rate and density, as well as, the Location Quotient to Crimes (LQCs) are the relevant indices used in this study; however, limitations still exist when crime rate is used as an index in mapping crimes. This is evident in this work. There are also shortcomings when crime density and the LQCs are adopted in mapping crimes. Multivariable linear regression models are used to compare the strengths of the three different indices used to analyze crime in the study. The effectiveness of crime rate is confirmed together with the association with spatial disparities of crime rates across different census tracts. Variables such as vacant housing, rental homes, unemployment and female-headed households are associated highly with crime rates across census tracts. Both violent and property crimes are closely related to vacant homes and the number of rental homes in San Antonio. This is reasonable taking into account the high rate of vacant homes and high rental market today.Item Distribution and characterization of source rocks in the upper black shale facies, Green River Formation, northern Uinta Basin, Utah(2012) Wells, Stephen N.The black shale facies occurs throughout the subsurface in the Altamont-Bluebell-Cedar Rim fields of northeastern Utah. The objective of this investigation was to define, delineate, and characterize the source rock potential of the basal unit within the upper black shale facies in the northern Uinta Basin. This stratigraphic interval was informally referred to as the carbonate marker unit, and is upper and lower bound by the carbonate marker and Long Point Bed, respectively. This study uses contour maps, along with applied source rock characterization of this specific interval within the upper black shale facies of the Green River Formation. In the northern Uinta Basin, depth to the carbonate marker ranges from approximately 4,500 ft in the southern Cedar Rim field to more than 13,000 ft in the northern Altamont-Bluebell field. Thickness obtains a maximum of approximately 450 ft to the north, and thins to a minimum of approximately 100 ft as you move south into the basin. The carbonate marker unit consists predominantly of source facies containing kerogen-rich calcareous shales and marlstones with present day TOC averages ranging 0.5 to 4.6 wt.%. Original, pre-maturation TOC averaged a range of 1.7 to 6.8%. As expected, both original and present-day TOC increase southward into the basin and decrease to the north. The kerogen fraction of the carbonate marker unit is dominated by type I amorphous material. An increase in proportions of herbaceous, woody and inertinitic types occurs in the southern portion of the study area. A number of direct and indirect methods were used to assess the degree of thermal maturity for the carbonate marker unit. Methods include vitrinite reflectance (Ro), Rock-Eval Tmax, Rock-Eval transformation ratio (PI), and HI-derived transformation ratio (TRHI) used to assess relative volumes of hydrocarbons generated. The carbonate marker unit is shown to be in the mature oil window throughout the majority of its extent in the northern Uinta Basin. Maximum thermal maturity occurs in a northeast-southwest trend along the interplay of depth, thickness, and source rock quality. Maturity decreases to the far north and south-southeast as this interplay becomes limited by one of these factors.Item Evaluating degradation genes in a culture obtained from a contaminated solvent bioreactor(2010) Castro, Erin YvonneThe objective of the study was to optimize the degradation of chlorinated solvents by cultivating the indigenous microbial community from in situ bioreactor (Trench 1) and to investigate which electron donors (acetate, lactate, pyruvate) would increase the degradation rate in those cultures. This investigation attempted to help optimize effectiveness and efficiency of an in situ mulch/gravel bioreactor currently implemented at Camp Stanley. This research used general microbiology, molecular biology, and analytical methods to evaluate the biodegradation in the cultures. Techniques used were polymerase chain reaction (PCR) of universal and specific Dehalococcoides dehalogenase genes (16S rDNA, DHC 16S rDNA, and tceA ) along with gas chromatography-flame ionization detector (GC-FID) to evaluate the chlorinated solvents (PCE, TCE, cis-DCE, VC) disappearance. The cultures analyzed indicated the importance of a steady concentration of electron donor and acceptor to maintain biodegradation; however if too much donor was provided it would inhibit the desired growth of the Dehalococcoides populations. The GC data suggested that biological processes may not be dominating the degradation process due to the lack of oscillation and accumulation of the solvents in the cultures. The solvents in the cultures degraded at the same rate and did not accumulate with time thus suggesting abiotic processes are more likely degrading the solvents. The geochemistry and microbiology of the mulch/gravel bioreactor technologies are more complex and dynamic than previously thought. Future research needs to examine both the abiotic and biotic processes to better understand how to optimize and maintain the degradation potential in this technology.Item Factors affecting the growth of Verbesina virginica(2008) Gagliardi, Jason W.Verbesina virginica (frost weed) is a tall, perennial, herbaceous plant that has been observed to occur in Bexar County, Texas primarily under established tree canopies such as Quercus fusiformis (scrub live oak) and Ulmus crassifolia (cedar elm). The distribution of Verbesina virginica, and possible factors affecting its distribution are not well reported. To better understand these factors, a combination of field studies, greenhouse experiments, and leaf level Li-Cor gas exchange analysis were utilized to examine species distribution, determine the species' nutrient requirements, and the plants response to various light levels, respectively. Over five transects, extending from a canopy into an adjacent open grassland, 283 total plants were counted. Of those, 98.9% (280 plants) were found inside the canopy dripline. Mean soil depth along the transects was highly variable and not significantly different from one location to another. However, a light gradient was found ranging from low light beneath the canopy (207 +/- 53 mumol CO2 · m-2 · sec-1) and increasing into the open grassland (2126 +/- 71 mumol CO2 · m-2 · sec -1). Overall, dry plant mass and leaves per plant increased with increased nutrient additions however, the plants did tolerate the native low nutrient Patrick soil. Gas exchange measurements for Verbesina virginica over 19 light levels ranging from 0 to 2000 mumol · m-2 · sec-1 found its maximum rate of photosynthesis (Amax) to be 12.68 +/- 1.40 mumol CO2 · m-2 · sec-1, while its mean dark respiration (Rd) was 0.75 mumol CO2 · m-2 · sec -1. The mean light saturation point (Lsat) for V. virginica was 287.74 mumol · m-2 · sec-1, and mean light compensation point (Lcp) was 16.2 mumol · m-2 · sec-1. These results fall within established ranges reported for understory species, and together with observed field distributions suggest that Verbesina virginica is a shade species.Item Improving the quality of NEXRAD products in terms of resolution and accuracy(2009) Yu, BeibeiThe growing of economy in Central Texas area resulted in the degradation of environment. The pollutants, bacteria loading and water quality assessment is required to evaluate and predict the environment quality. Precipitation is the main source of storm discharge and runoff, which becomes a critical input to several hydrological, ecological, climatic and flood prediction models. The purpose of this study was to improve the spatial resolution as well as the accuracy of the NEXRAD MPE products. The first part of this study was to improve the resolution of the original 4km×4km NEXRAD MPE products by the means of downscaling the radar products into 1km×1km. The downscaling algorithm estimates precipitation distribution without prior knowledge of the atmospheric setting. It auto-searches precipitation spatial structures and atmospheric effects by incorporating a digital elevation model (DEM) map into precipitation maps. The downscaled precipitation fields were examined based on different time scales: hour, day and storm period. Three downscaled precipitation fields are in good agreement with the original 4 km × 4 km NEXRAD precipitation fields. However, the accuracy of the downscaled radar products has not necessarily been improved. The regression algorithm may be an efficient model in capturing the variability of spatial rainfall distribution in mountainous area, but not as efficient in flat area. Incorporating the topological information from DE M may be more effective for mountainous regions. The second part was to improve the accuracy of NEXRAD MPE products in capturing rainfall periods. The major difference between this study and precious study (Wang et al, 2008) is that the validation and correction is based on the fact that the spatial and temporal continuity of precipitation is reserved. For hydrological modeling, the continuous and spatially distributed precipitation data is recognized as a significant input. Thus, this part aimed at conducting continuous hourly spatial and temporal evaluation of the accuracy of NEXRAD and comparing 4 different interpolation methods (Bias Adjustment (BA), Simple Kriging with varying Local Means (SKlm), Kriging with External Drift (KED), and Regression Kriging (RK)) for incorporating raingauge measurements into NEXRAD MPE products. Four evaluation parameters (Percentage Bias, Mean Absolute Error, Coefficient of Determination, and Nash-Sutcliffe efficiency) were used to evaluate the performances using the observed rain gauge data as constraint. The comparison results show that the average performance of SKlm is similar to or better than the other methods. KED is a most vulnerable method and we have to use it carefully. It is worth noting that no one method can consistently outperform the other methods in terms of all evaluation coefficients, for all time steps, and at all rain gauges. In practical application of NEXRAD precipitation products, if there is plenty of time and computational resource, it is suggested to implement multiple methods to correct the original NEXRAD data, and choose the one with best performance for some specific objectives. Otherwise, SKlm is the preferable method for incorporating raingauge measurements into NEXRAD MPE products. Overall, it is clear that incorporating secondary source into the original NEXRAD MPE products can improve the resolution and accuracy of original products. To satisfy the model requirements of high quality precipitation data, combination of incorporating both DEM and rain gauge measurements can be a good approach. SKlm is generally a good method in precipitation interpolation, since it is easy to implement and achieve desire results.Item Insights to progradational development of the northwest Delaware Basin margin from Patterson Hills outcrops (Guadalupe Mountains National Park), West Texas(2011) Hughes, Joshua NeilThe resolution of the northwest Delaware Basin margin in the Patterson Hills is much lower than in the Guadalupe Mountains. This study examined the positional details and timing of progradation of the Capitan Reef into the Delaware Basin within the Patterson Hills, and created a more concise picture of spatial and temporal aspects of progradation. Patterson Hills outcrops were examined, and the contact between the reef and the basinal limestone member it was prograding over was mapped in more detail than ever before. Previous work showing the direction of basin progradation at various times was analyzed, and corrections are suggested using evidence from the field. Results include a map showing the contact between the Capitan Reef and the Rader Limestone Member of the Bell Canyon Formation, where only the general Bell Canyon Formation was shown to be present before. This result, paired with positions of the reef prograding over older limestone members, gives an idea about how the reef progradation changed over time. Improvements to the generally accepted limestone member location and progradation directions first proposed by P. B. King in 1948 are presented, showing a more eastward movement than previously believed.Item Intercomparisons of sea ice thickness and concentration from visual observation, EM-31 measurements, and video imagery(2009) Wagner, PenelopeAntarctic sea ice dynamics are largely affected by ocean and wind forcing because it is surrounded by the open ocean, whereas Arctic sea ice is surrounded by a land mass. Opportunities to study the variations in sea ice conditions are infrequent due to the remote location and relative expense. For that reason, it is necessary to develop methods that will allow efficient and effective collection of sea ice measurements for integration with large-scale models and validation schemes for satellite products. The use of automated devices will improve estimates on sea ice trends for the Antarctic region. Collecting ice thickness distribution trends from drilling transects can be a cumbersome ordeal and provides very little data over a large area. Therefore, it is necessary to consider using automated devices to assist in further data collection for future cruises. The first part of this study focused on compiling various datasets from the SIMBA cruise (Sea Ice Mass Balance in the Antarctic) which included ship-based sea ice observations, an electromagnetic induction device (EM-31), and video imagery (Evaluative Imagery Support Camera (EIS Cam 1)) to evaluate which automated device provided the best method to measure the sea ice thickness distribution. Remote sensing applications were used for image analysis with data from EIS Cam 1 to measure thickness of overturned ice that was being broken by the ship's hull. The thickness distribution of EIS Cam 1 and the EM-31 were then compared with the ASPeCt (Antarctic Sea Ice Processes and Climate) ship-based observations to evaluate how well each device performs. Since the footprints of three datasets were different from each other, only the frequency of the ice thickness distribution was gauged and compared. The EM-31 data overall performed better than the video imagery, for the reason that it was measuring ice conditions far enough from the ship's base, where it was capable of measuring ridged and deformation features not present in the video footprint. The study also shows potential good results for level ice up to 2.50m, although the ship's track will be biased toward thinner ice and may cause the EM-31 to oversample thin ice compared to the thicker ice surrounding the narrow track. However, under those conditions the EM-31 will act as an appropriate supplement for ASPeCt visual observations taken hourly from the ship's bridge. The second part of this study evaluated sea ice concentration data recorded with the use of video imagery (EIS Cam 2) compared with ship-based ice observations. Images from the inbound and outbound transects were classified using techniques provided by Weissling et al. (2009) to ascertain the amount of error between camera measurements and ship-based observations. Analysis of these comparisons found poor correlations during evening conditions due to highlights and shadows generated by ridging, deformation features on the sea ice, and darker lighting conditions, in which EIS Cam 2 either underestimated concentration values up to 30% when the ASPeCt ice concentration was over 80% or overestimated ice concentration up to 60% when ASPeCt ice concentration was less than 80%. Large over- or under-estimation from ASPeCt observers was also possible due to the night condition, which was seasonally dependant. However, there was an overall good agreement between both datasets during the day time where EIS Cam 2 and ASPeCt differed approximately ∼5% (inbound track) or 10% (outbound track). The errors with the datasets were related to the coarse resolution of ASPeCt parameters and the inability for the EIS Cam 2 to distinguish shadows (from ridges or the ship) and/or very thin ice types from open water when the unsupervised classification method was applied. However overall, EIS Cam 2 is advantageous in providing a constant record of sea ice concentration for a large field of view that can be used to support quality assurance purposes for ASPeCt records or supplement future cruises without an observer.Item Mapping zones of aquifer recharge and discharge based on correlation of naturally occurring hydrologic features, Central Texas(2009) Lupton, Daniel M.Defining vertical flow of groundwater is important for developing conceptual hydrologic/hydrogeologic models and water budgets. Defining vertical flow components can be difficult with sparse well data. This concept is of particular interest when attempting to predict the flow path (local-, intermediate- or regional-scale) that additional recharging surface water will take when phreatophytes (water intensive species) are removed in support of landscape restoration. A GIS-based analysis of dynamic pressure increments (DPI) and proximity of wells to streams of different Strahler order maximizes the use of sparse data to map upward- and downward-directed flow. The method was tested in a part of the Pedernales River watershed in Central Texas to study recharge and discharge and movement of groundwater between the Trinity Hill Country and the Llano Uplift aquifers. A dynamic pressure increment (DPI) as defined by Tóth measures departure from hydrostatic and indicates where groundwater flow is directed upward (+DPI; discharge) or downward (-DPI; recharge). Posting DPI on a GIS-based topographic map showed an obvious correlation--positive values in tributary valleys and negative values in upland settings. Correlation of DPI and well distance is statistically significant for 2nd - to 5th-Strahler order streams. Recharge and discharge areas for individual streams were mapped as a function of distance from each stream and considered the linear regression's prediction interval. In an attempt to further understand the link between stream order and local-, intermediate- and regional-scale flow paths, an elevation-depth-DPI plot was made of all wells within the study area. Patterns showed a regional hydrostatic (DPI = 0) divide between recharging (downward vertical component) and discharging (upward vertical component) at an elevation of approximately 1450 ft. Intermediate-scale systems of groundwater flow were identified by the occurrence of hydrostatic (DPI = 0) conditions as subsets of the regional system.Item Oxygen isotopes, trace elements, and sedimentology of the Cretaceous-aged Hensel Paleosol indicate aridity and rising temperatures in Central Texas(2009) White, Lee A.An Early Aptian to Late Albian Cretaceous aged paleosol (~112 MA) in the Hensel Formation in Kimble County, Texas, was used as a climate proxy. Abundant, downward tapering rhizoliths, along with columnar peds and carbonate nodules, are dominant macroscopic features. Petrographic analyses reveal primary soil features such as dense microspar plasmic fabric with quartz and calcite filled root traces. Stable oxygen isotope ratios (δ18O) in the carbonate material within the paleosol were used as a proxy to determine the Mean Annual Temperature (MAT). Isotopic analyses of 36 samples from the Hensel Paleosol were performed with a DeltaPlus XP Isotope Ratio Mass Spectrometer. The δ18OVPDB values increase, becoming heavier, up section and range -5.21 to -4.01 %o. Temperature was estimated using an equation which relates the MAT with the measured δ18O in the pedogenic calcite. The MAT for the Hensel Paleosol ranges from 17-22 ºC increasing from bottom to top. Hensel Paleosol samples were analyzed by X-Ray Fluorescence to determine major element composition and Mean Annual Precipitation (MAP). The Hensel Paleosol data suggest warm, arid subaerial conditions existed during the mid-Cretaceous in Central Texas. The warming trend apparent from the Hensel Paleosol section is in agreement with global warming conditions noted from Sea Surface Temperatures during this period. The MAP estimate for the Hensel Paleosol data suggest arid conditions at the Aptian/Albian boundary in Central Texas which corresponds to the arid belt at the paleolatitude at 25°N. The deep root system and abundance of calcareous nodules is indicative of a dry climate.Item Resource mediated competition of two Texas natives: Acacia berlandieri, a C3 shrub, and Trichloris pluriflora, a C4 grass(2009) Roach, Sara J.Acacia berlandieri, an early successional C3woody shrub, and Trichloris pluriflora, a late successional/climax C4 tall grass, reside in similar habitats and have both been documented in Texas for over 150 years. This study examines resource mediated above and below ground competition within and between these species, which may illuminate some of the variables involved in the expansion of woody shrub species into the former grasslands. These species were started from seed and grown outdoors (five replicates/treatment) using sandy clay loam soil in plastic lined 15×15 cm pots for 155 days and watered daily. Half of these pots received 12.5% Hoagland's solution as a nutrient source. Using a factorial design, growth measurements were taken 3 times, spaced evenly apart, after a 72 day establishment period. The plants were then harvested intact, rinsed with water to remove the soil, and dried at 60°C. The above and below ground dry masses were separated, and the roots were ashed at 650°C to remove all foreign organic debris. Measurements were then taken for the above and below ground biomass. Then by utilizing the ANOVA, the effects of the growth and harvest parameters on each species was determined for both intraspecific and interspecific competition. The addition of nutrients had little or no effect on the intra- or interspecific competition for either species growth or harvest. However, nutrients did appear to have a negative effect on Acacia berlandieri for harvested intraspecific competition. Although this legume is not known for nodulation, the possibility of N2 fixation occurring in the root system must be considered because of this negative response. The variable of density appeared to be the driving force for the intra- and interspecific competition of these two species for both growth and harvest. Although grassland and woody shrub interactions should be mediated by resource availability, nutrients did not mediate the intra or interspecific competition of Acacia berlandieri and Trichloris pluriflora in this study. Clearly, density is an important variable involved in the disappearance of the grasslands.Item The effects of carbon dioxide on three species of milkweed (Asclepiadaceae) and monarch butterfly (Danaus plexippus) larva feeding preference(2009) Matiella, Terri JeneeThis research evaluated the effect of three levels of carbon dioxide (280 ppm = subambient, 363 ppm = ambient, and 457 ppm = elevated) on the growth of three species of Asclepiadaceae, which were Asclepias asperula (antelope horn milkweed), A. syriaca (common milkweed), and A. tuberosa (butterfly weed). Number of leaves, plant length, number of branches, color, aboveground dry mass, and belowground dry mass of the plants were measured after exposure to carbon dioxide treatment for fourteen weeks. Danaus plexippus larvae were offered fresh leaf material from plants from each CO2 treatment level, and were monitored for feeding preference. There was a significant difference in plant growth parameters across the three milkweed species. For dry mass, A. asperula had a significantly lower above-, belowground and total dry mass than the other two species. There was no significant difference in most plant growth parameters for the three species across the carbon dioxide treatments. There was a significant difference seen in A. syriaca mean leaf number and number of branches across carbon dioxide treatments. For number of branches, a significant interaction was found between carbon dioxide treatments and species, indicating that the response to CO2 was dependant on the species examined. There was a significant difference in the Danaus plexippus larval feeding preference to leaf tissue from the three Asclepiadaceae species among the species, with the larvae preferring A. asperula and A. syriaca over A. tuberosa; but no significant difference in feeding preference within a species across carbon dioxide treatments.Item The effects of repetitive grazing on Schizachyrium scoparium and the role it plays in woody plant encroachment of Texas grasslands(2012) Baldwin, Andrew RossThe composition and structure of the semiarid grasslands of Central Texas have been changing over the past 200 years. Selective grazing of domesticated animals is thought to be one of the main causes of these changes; however there are many factors that contribute to the encroachment of woody plants, such as global warming and underground root herbivory. This Thesis research, which built on a previous experiment, analyzed the direct effect of aboveground grazing on Schizachyrium scoparium (little bluestem) a naturally occurring grass all over Texas, at different rates of grazing for five weeks. The previous experiment tested dry biomass of little bluestem vs. Prosopis glandulosa (honey mesquite) in grazed vs. ungrazed scenarios. In the second experiment, 60 pots (15 cm X 15 cm) were filled with a thin layer of crushed limestone at the bottom with soil collected from the University of Texas at San Antonio 1604 campus. Two hundred seeds were sown into each of the 60 pots and given 3 days to germinate in a greenhouse. After germination each pot was watered as needed for one month while they had time to establish some structure. 60 pots of S. scoparium were trimmed with scissors once a week at various repetitions; simulating high intensity grazing for the next five weeks. It was predicted that the S. scoparium pots with greater intensities of grazing would have a significantly lower total dry biomass. Therefore, with correct land management, grasslands and ranchlands can be preserved and prevent the woody plant encroachment. Results will indicate the most abundant dry biomass, and the intensity of grazing scenario with this biomass. The results can be used to create the most effective way to manage a grassland/ranchland for maximum growth to keep woody plants from encroaching. Thus, controlled herbivory of grasslands and ranchlands by domesticated animals could play a positive role in preventing woody plant encroachment.Item The observed feeding preference of Cantareus aspersus (ex-Helix aspersa) (brown garden snail) between different plant species(2012) Valdez, JessicaPlants have developed many different mechanisms to defend themselves against natural enemies. Defense mechanisms can be structural and/or chemical and can be either inducible or constitutive. The phytohormone jasmonic acid plays an important role in the regulation of inducible plant defense responses in herbivory. The gastropod Cantareus aspersus (ex-Helix aspersa), or more commonly known as the brown garden snail, is a generalist herbivore and will consume almost any plant. Cantareus aspersus can cause excessive damage feeding on leaves, fruit and young tree bark and is a pest in California and Florida. The brown garden snail is not known to be deterred in feeding behavior by specific secondary metabolites, and currently the most effective pesticide used for snails contains an active an ingredient that is not permitted in US food crops. The biology of the snail has been studied, but not much is known as to their feeding preference with plants in their natural state. In this study we used Brassica oleracea var. italica (broccoli), Brassica rapa L. (chinese cabbage), Triticum aestivum L. (winter wheat), Medicago sativa L. (alfalfa) and Arabidopsis thaliana to determine the feeding preference of C. aspersus. More specifically, we used Arabidopsis thaliana ecotype Columbia (Col), Landsberg erecta (L er), Wassilewskija (Ws), Arabidopsis thaliana 12-oxophytodienoate reductase 3 (opr3) mutant (background Ws), the ethylene resistant (etr1 ) mutant (background Col), and transport inhibitor response (tir3) mutant (background Col). Observational and juvenile weight gain studies were performed with snails being given a choice between different plant species or types. Additionally, jasmonic acid (JA)-treated plants were tested against an untreated control of the same species. Observations of the feeding preference assays with C. aspersus determined that there was no difference in feeding preference when given a choice between JA-treated and control plants, possibly due to plants responding to neighboring plant volatiles. Observations of the feeding preference assays determined C. aspersus preferred alfalfa> chinese cabbage> broccoli= wheat possibly due to varying glucosinolates levels between these plants. Observations also determined that C. aspersus preferred to consume opr3> Ws> Ler> Col> etr1> tir3. However the weight gain studies indicated that there was no significant difference when compared with each respective wild-type, possibly due to small sampling size and the small number of trials. The combination of Arabidopsis thaliana and a juvenile weight study seems to be a good indicator for C. aspersus feeding preference. Further research is necessary to characterize what secondary metabolites and defense mechanisms snails find attractive or unattractive.Item Transcriptional analysis of distant signaling induced by insect elicitors and mechanical wounding in Zea mays(2011) Contreras, Claudia FabiolaTo characterize distant signaling in Zea mays we performed a transcriptional analysis in various regions of a corn seedling after treatment with insect elicitor (IE) and mechanical wounding (MW). The genes tested for accumulation were selected based on their involvement in defense Ribosome Inactivating Protein (RIP), regulation of transcription (MYC7) and signaling allene oxide synthase(AOS). Transcript abundance was measured by semi-quantitative polymerase chain reaction (PCR) at different times and locations after IE, MW, jasmonic acid (JA), jasmonic acid-isoleucine (JA-Ile), glutathione and 12-oxophytodienoic acid(OPDA) treatments, all treatments are related to the defense response either by activating or regulating it. The results showed that RIP and AOS were only induced locally, whereas MYC7 had increased transcript abundance in distant tissues after IE. We concluded that IE induced signaling that affects the whole plant as indicated by the increased abundance of transcription factor MYC7. Genes involved more directly in defense accumulate only where the actual damage occurred. The data also suggests that MYC7 might play a significant role in distant signaling. Further experiments are necessary to characterize the transcriptional activity of this transcription factor.Item Uncertainty of remote sensing precipitation estimates(2013) Mazari, NewfelThis dissertation aims to quantify the uncertainty of remote sensing precipitation estimates. The focus is on radar rainfall estimation and satellite snow cover classification. The first part of this dissertation introduces a new approach to study the spatial, temporal and vertical variability of radar-estimated rainfall using a vertically pointing radar (Micro Rain Radar or MRR) in conjunction with a ground sensor (rain gauge) and rainfall estimates from the nearest weather radar (Next Generation Radar or NEXRAD). The MRR's direct rainfall estimates using the Mie theory has similar values when compared to the collocated gauge rainfall observations. It was found that MRR estimates are sensitive to the height resolution (the size of the vertical radar bin) and that the MRR rainfall may be biased in presence of bright band or other artifacts at higher elevations (above 2100 m). In the second part of the research multiple radar bin integrations are used to investigate reflectivity-derived rainfall accuracy and errors from two NEXRAD radars that cover the same network of 50 gauges in the Upper Guadalupe River Basin. It is found that, in addition to the size of the integration bin, there are other sources of uncertainty such as distance from the radar, amount of rainfall, and type of the rainfall event. The third research is a validation of a new NEXRAD rainfall product called Digital Storm Total Precipitation (DSP) using a dense gauge network in the Hill Country of Texas. The DSP is a product of high temporal and spatial resolutions intended for flash flood forecasting and warning. The validation process is based on three years of rainfall data, using statistical and analytical parameters. The accuracy of DSP is found to be highly dependent of the radar range and is also affected by seasonality, with more accurate measurements in warm season than in cold season. The DSP probability of rainfall detection is found to be always higher than gauges. Finally, the fourth part investigates the daily snow cover product of the Ice Mapping System (IMS) at a nominal resolution of 4 x 4 km. The product's accuracy and robustness are compared against snow depth measurements from a network of 197 meteorological stations in the Colorado Plateau and MODIS satellite estimates. IMS accuracy is found to be similar to MODIS accuracy with slightly lower values during ablation and accumulation periods. IMS classification errors are also significantly comparable to MODIS errors (both at 500 m or 4 km resolutions) with the exception of unstable periods (accumulation and ablation) where IMS errors can be close to 10% higher than MODIS errors.Item Zumwalt debris pile fire and Edwards Aquifer vulnerability(2009) Cunningham, Patricia KyleThe Zumwalt debris pile fire, the longest burning fire in Bexar County, Texas history, demonstrated the potential for contamination of the Edwards Aquifer, the sole source supply of drinking water for more than 1.7 million people. This fire burned for more than 3 months and required daily emergency response from local and state agencies. The debris pile covered more than 4 acres, was approximately 80 ft. tall, and was estimated to contain more than 171,000 cubic yards of material. The Zumwalt debris pile was located over the Edwards Aquifer Transition Zone (EATZ) but in effect was over the Edwards Aquifer Recharge Zone (EARZ). In the early days of the response it became evident that there was direct communication between the debris pile and the Edwards Aquifer. The emergency response to this fire demonstrated the vulnerability of karst aquifers and how rapidly contamination can move in fractured terrain. The potential contamination of aquifer water supplies is a concern for public health officials. Karst aquifers are particularly vulnerable. In the State of Texas private well owners have to rely upon themselves to ensure that their drinking water is free of contamination. Local water agencies must respond to events which have the potential to contaminate drinking water on a regular basis. Often they begin by locating and testing private wells in order to track contamination flow paths. The overall objective of thesis was to examine the emergency event and the data collected from the response to the Zumwalt debris pile fire. This will help shed a better understanding on how local, county, and state agencies handled this emergency event and spot light lessons learned to improve public health and safety.