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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Sublethal Effects of Crude Oil and Chemical Dispersant on the Eastern Oyster (<em>Crassostrea virginica</em>) at Multiple Life History Stages

Garcia, Sara Marie 15 March 2018 (has links)
Oil spills in the marine environment can threaten vulnerable ecosystems that support ecologically and economically significant organisms, such as the eastern oyster (Crassostrea virginica), in coastal habitats. The use of chemical dispersant (Corexit 9500) was applied as a cleanup effort in response to the Deepwater Horizon blowout to minimize crude oil slicks, but also resulted in increased concentrations of polycyclic aromatic hydrocarbons in the water column. The effects of increased soluble fractions of crude oil and dispersant components may be harmful to marine organisms. This study aimed to investigate possible sublethal impacts to the eastern oyster at multiple life history stages in order to understand potential implications on performance at an organismal, population, and ecosystem levels. Specifically, this study addressed 1) veliger swimming, 2) pediveliger settlement rates, 3) pollutant induced larval inactivity and 4) adult clearance rates after acute exposures to relevant concentrations (10 – 100 µL L-1) of water accommodated fractions of crude oil (WAF) and with a combination of chemical dispersant (CEWAF). No significant differences were observed in any tested swimming kinematics between controls and WAF or CEWAF treatments after 24 hour exposures for early staged veligers at concentrations up to 100 µL L-1 WAF and CEWAF. However, settlements rates of competent pediveligers were significant decreased compared to control (52.1 % s.d. 1.66) rates at concentrations of 50 µL L-1 WAF (30.9% s.d. 6.16) and 10 (41.2 % s.d. 0.857) and 50 (22.0% s.d. 1.23) µL L-1 CEWAF. Later staged larvae also showed increased vulnerability to oil pollution given that a higher percentage of organisms were inactive (48.3% s.d. 4.80) compared to early staged larvae (12.7% s.d. 7.68 ) after initial exposure at 50 µL L-1 CEWAF. Based on this result, we assumed effects of oil pollution were not manifested until the later larval life history stage evident by metamorphosis failure during the complex settlement transformation that results in reduced spat and eventually reduced adult oysters. Adult oysters were also exposed to increasing concentrations of WAF and CEWAF for 24 hours and feeding experiments were conducted in both clean seawater and the same oiled seawater conditions as their initial exposure. Oysters fed in oiled seawater had decreased clearance rates, but oysters fed in clean water had increased clearance rates, suggesting feeding efficiency can be returned to control rates when moved to the presence of clean water. However, our long term study conducted in clean seawater suggested of the oysters exposed to crude oil only (9.31 L h-1 g-1 s.d. 2.04) are able to return to clearance rates comparable to controls (7.69 L h-1 g-1 s.d. 1.89) after the 33 day time period but oysters exposed to crude oil with a combination of chemical dispersant (2.12 L h-1 g-1 s.d. 1.08) were not. Decreased feeding efficiency can have negative impacts on water quality in estuarine ecosystems that support productive habitats. Understanding the impacts of crude oil, and crude oil with a combination of chemical dispersant on ecologically significant organisms can aid in future oil spill response decisions in order to minimize environmental impacts.
2

Community-Oriented Policing and Crime Rates and Crime Clearance Rates in North Carolina

Johnson, Elizabeth Wrenn 01 January 2017 (has links)
While community-oriented policing was touted as a new paradigm in American policing, little data reflects its success in reducing crime and/or increasing crime clearance rates. Researchers have failed to definitively describe community policing as a successful style of policing, leaving much more research to be done on its effectiveness as a crime reduction method. Using Trojanowicz's seminal conceptualization of community-oriented policing as the foundation, the purpose of this correlational study was to determine whether there are statistically significant associations between community-oriented policing, crime rates, and crime clearance rates for the 9 municipalities of Carteret County, North Carolina. Data for community-oriented policing methods were collected from the police agencies via personal contact with an agency representative, while data for violent crime, property crime, violent crime clearance rates, and property crime clearance rates were obtained from the State Bureau of Investigation and the Federal Bureau of Investigation's Uniform Crime Report. The results of Spearman's rho and a chi-square test for independence indicated that there was a statistically significant relationship between community-oriented policing and the violent crime rate (p = .03), the violent crime clearance rate (p = .03) and the property crime clearance rate (p = .009). This study may enhance positive social change for police agencies in North Carolina by providing specific recommendations to better implement successful community policing strategies in their communities.

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