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Anthropogenic change in the Great Plains of North America within the past two centuries has facilitated extensive woody encroachment by eastern redcedar (Juniperus virginiana, hereafter redcedar). Conversion of grassland to redcedar woodland occurs rapidly as a result of the interaction between changing disturbance and land use patterns. In addition, redcedar encroachment causes compositional shifts in grassland floral and faunal assemblages, and may alter abiotic factors such that grassland restoration efforts are limited. The objectives of this study were to: 1) track vegetation and faunal assemblages in grasslands along a gradient of redcedar encroachment, 2) assess the capacity for experimental tree removal to promote re-colonization of grasslands by associated flora and fauna, and 3) examine the influence of scale on spatial relationships between small-mammal abundance and redcedar cover. During the first phase of my study, I examined herbaceous vegetation, woody vegetation, and small-mammal assemblages at grassland sites along a redcedar encroachment gradient in north-central Oklahoma. I noted hump-shaped trends in the capture rate, species diversity, and species evenness of small mammals along the redcedar encroachment gradient. In addition, higher levels of encroachment were associated with compositional shifts from grassland- to woodland-associated small mammals. Characteristics of the small-mammal assemblage along the gradient corresponded to increases in redcedar cover and the frequency of episodic management events within the past two decades. Experimental redcedar removal during the second phase of my study generally increased vegetation and faunal diversity in 2 years following treatment, and treatment sites having the highest pre-treatment levels of redcedar cover exhibited the greatest responses to tree removal. The results of my study suggested that within the time frame I examined, redcedar encroachment had altered the biotic characteristics of this system, but did not facilitate abiotic shifts capable of constraining rapid grassland recovery. Tree removal also appeared to modulate the effects of consecutive drought and flood years on small-mammal diversity during post-treatment. During the third phase of my study, I examined the strength of association between differences in percent redcedar cover and spatial abundance patterns of 4 common small-mammal species. I examined small-mammal abundance at three relatively small spatial scales (38, 154, and 616 m2) to determine how redcedar-mammal associations were stronger with increases in spatial scale. In addition, I determined whether the influence of spatial scale on redcedar-mammal associations varied along a gradient of redcedar encroachment. The strength of redcedar-mammal associations increased with spatial scale, but was strongest at sites having the lowest levels of encroachment. These results corresponded to variation in the spatial distribution of redcedar cover and compositional differences in the small-mammal species assemblage along the encroachment gradient. Studies examining the effects of woody encroachment will extend our understanding of successional processes and ensure that appropriate management is implemented in the conservation of these imperiled grassland ecosystems.

Tarnished plant bug is the most important insect pest of cotton in Mississippi. Management of this insect is difficult because of insecticide resistance as well and the overwhelming population densities in many areas of the Mississippi Delta. Given the level of plant bug infestation and damage observed in cotton over the past several growing seasons, information is needed to improve management of vegetative growth once fruit retention is reduced. Little data exists regarding the impact of nitrogen application on infestation by tarnished plant bug. In addition, growers have been progressively reducing seeding rates as seed and technology fees have increased over the past 15 years. Although seeding rates have been reduced, nitrogen application recommendations have not changed. This research was initiated to determine the relationship between crop management factors and tarnished plant bug and to further refine N rate recommendations in the presence of reduced plant populations.

An analysis of snow removal injury data from the National Electronic Injury Surveillance System (NEISS) revealed a persistent gender gap in injuries and deaths during snow clearing activities. In general, men, those who identified as White and those aged 60-79 represented the vast majority of injuries and deaths sustained during automated snow removal. Injuries and deaths from manual snow clearing had greater representation across gender lines, as well as across various age groups and race categories. This indicates that a greater cross-section of society relies on the standard shovel in comparison to the snow blower for snow removal. The most likely injuries sustained during shoveling were to the neck and back, while hand and finger injuries were far more common during the use of a snow blower. Similar percentages of cardiac (30%) and non-cardiac chest injuries (70%) were found for both manual and automated modes of snow removal. While the majority of cardiac chest injuries were in those aged 40-59 for shoveling and 60-79 for snow blowing, the majority of cardiac fatalities were in those aged 60-79 for both methods of snow removal. Daily all-cause mortality and daily deaths from acute heart attacks showed a weak but inverse relationship to daily maximum, minimum and average temperatures. Mortality related to temperatures had significant lag effects for two days. Daily all-cause and heart attack mortality were also significantly related to the depth of the existing snowpack. Snow to liquid ratios indicating differences between heavy, wet snow and dry, powdery snow were not significant. However, the water equivalent of the existing snowpack was significantly related to daily mortality. Comparisons between all age and elderly mortality showed weaker and opposite relationships for the elderly group suggesting the use of protective behaviors such as cold and snow avoidance.

Studies were conducted in the field and in containers in Mississippi from 2017-2019 to optimize Italian ryegrass control in corn production. Most fall-applied residual herbicides provided ≥ 90% Italian ryegrass control 56 days after treatment (DAT) in both field and container experiments. Oxyflurofen provided 95% Italian ryegrass control 28 DAT but only 81% control 56 DAT in field plots. S-metolachlor plus atrazine followed by paraquat produced the highest return on investment for both site-years. The timing of removal study indicates the optimum time to remove Italian ryegrass relative to corn planting is approximately three to four weeks prior to planting. In the droplet size study, Italian ryegrass control when S-metolachlor was sprayed with the TTI was lower than when S-metolachlor was sprayed with the AIXR in containers 28 DAT. Italian ryegrass control when paraquat was sprayed with the AIXR was greater than when paraquat was sprayed with the TTI.

Excessive release of nitrogen (e.g., ammonia and organic nitrogen) into natural water systems can cause serious environmental problems such as algal blooms and eutrophication in lakes and rivers, threating the aquatic life and ecosystem balance. Membrane aerated biofilm reactor (MABR) and anaerobic ammonia oxidation (Anammox) are new technologies for wastewater treatment with an emphasis on energy-efficient nitrification and denitrification. Microplastic (MP) is an emerging contaminant in wastewater and sludge treatment that has a negative effect on the environment and public health. For these relatively new technologies and contaminants, mathematical models can enhance our understanding of the removal mechanisms, such as reaction kinetics and mass transport. In this study, mathematical models were developed and utilized to simulate the removal of nitrogen and MP in biological reactions in wastewater treatment processes. Firstly, a comprehensive MABR model was developed and calibrated using a pilot-scale MABR operation data to estimate the important process parameters where it was found that biofilm thickness, liquid film thickness and C/N ratio are key parameters on nitrification and denitrification. Secondly, a mathematical model for Anammox process was developed and calibrated using previous experimental results to simulate the wastewater treatment using Anammox process, reflecting the importance of dissolved oxygen on the nitrogen removal using Anammox bacteria. Thirdly, a granule-based Anammox mathematical model was built and calibrated using other simulation results from previous Anammox studies, showing the significance of operational conditions (e.g., granule diameter and dissolved oxygen) on the success of Anammox enrichment process. Fourthly, an enzyme kinetic mathematical model was constructed and calibrated with lab-scale experiments to simulate the MP reduction using hydrolytic enzymes under various experimental conditions where it was found that anaerobic digesters can be an innovative solution for MP removal during the wastewater treatment processes. Based on the main findings in this study, it can be concluded that mathematical models calibrated with various experimental results are efficient tools for determining the important operational parameters on the nitrogen and MP removal and helping in the design and operation of large-scale removal applications. / Thesis / Doctor of Philosophy (PhD) / Nitrogen and microplastic (MP) are serious contaminants in wastewater that can cause critical environmental and public health problems. Nitrogen can cause algal blooms, threatening the aquatic ecosystem while MP can be ingested by the biota (e.g., fish and seabirds), causing serious damage in the food chain. Nitrogen removal in the conventional biological wastewater treatment is relatively expensive, requiring high energy cost and large footprint for the wastewater treatment facilities. MP removal is also difficult in the conventional wastewater and sludge treatment processes. Therefore, new technologies, including membrane aerated biofilm reactor (MABR), anaerobic ammonia oxidation (Anammox) and hydrolytic enzymes processes, are implemented to improve the nitrogen and MP removal with a reduced energy and resources consumption in wastewater and sludge treatment processes. Numerical models are considered as an efficient tool for better understanding of these novel technologies and the competitive biological reaction in these technologies coupled with accurate estimation of process rates of the reactions. In this thesis, different numerical models were developed and calibrated to estimate the important model parameters, assess the effect of operational conditions on the removal mechanisms and determine the dominant parameters on the removal of nitrogen and MP in the wastewater treatment processes. These numerical models can be used for better understanding of the removal mechanisms of nitrogen and MP, helping in the design and operation of removal systems and addressing novel technologies in large-scale nitrogen and MP removal applications.

No description available.

No description available.