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[pt] A caracterização de cristais osciladores de quartzo (QTF) foi realizada nesta dissertação com o objetivo de implementá–los como sensores de um microscópio de força atômica (AFM). O QTF possui várias vantagens em relação aos cantilevers tradicionais de silício. Utilizado em modos dinâmicos de operação do AFM, o QTF possui maior fator de qualidade e rigidez, permitindo melhor sensibilidade em força e o uso de baixas amplitudes de oscilação para imageamento do que cantilevers tradicionais. Nesse trabalho, parâmetros mecânicos e elétricos do QTF foram medidos. Além disto, um estudo da influência da adição de massa nos braços do QTF foi realizado. Para a implementação do QTF no AFM, um sistema de feedback composto de um amplificador lock–in e um amplificador diferencial foi desenvolvido e testado. Adicionalmente, um novo cabeçote para o microscópio foi desenvolvido para adaptar o QTF ao microscópio. / [en] The characterization of quartz tuning forks (QTF) was performed in this dissertation, aiming to implement them as sensors at an atomic force microscope (AFM). The QTF has several advantages over traditional silicon cantilevers. Used in dynamic AFM modes, the QTF has higher quality factor and stiffness, allowing better force sensitivity and lower amplitudes of oscillation for imaging than traditional cantilevers. In this work, electrical and mechanical parameters of the QTF were obtained. Furthermore, a study of the influence of additional mass on the QTF prongs was performed. To implement the QTF at the AFM, a feedback system composed of a lock–in amplifier and a differential amplifier was developed and tested. Additionally, a new microscope head was designed to adapt the QTF to the microscope.

Mercury contamination of the North Fork Holston River below Saltville, Virginia has nearly extirpated most mussel populations. Because natural recovery of these populations has not occurred, this research combined field and laboratory assessments to determine the extent of ecological impairment in the river. In situ 60-day Asian clam (Corbicula fluminea) growth studies in 2005 showed a positive correlation (p=0.03) between low clam growth and sediment mercury levels. Because of severe low flow conditions of the NFHR in late 2005 conductivity dissipation from a point source brine discharge downstream rarely reached background level (~345 µS/cm) and was observed as high as 690 µS/cm 640 m below the discharge site. In addition, conductivity doubled in the river section adjacent to the remediated Ponds 5 and 6 (rm 81.6 and 80.4). Such low flow conditions (mean flow < 50 ft3/sec) occur in the NFHR approximately every five years. This low flow situation also evidenced a thick white flocculent or floc observed to accumulate at the base of the two remediated ponds. Analysis of the flocculent determined it to be high in aluminum (1.9-38 mg/L) and iron (2.0-51.0 mg/L), well above US Environmental Protection Agency Water Quality Criteria limits (0.0087 and 1.0 mg/L, respectively); riverine sediments collected below the accumulated floc also had high levels of calcium (240,000-380,000 mg/kg) and mercury(0.62-1.7 mg/kg). Acute tests with juveniles of Villosa iris and <24-hr old Ceriodaphnia dubia were used to measure the toxicity of the brine discharge, which had a conductivity of ~ 14,000 µS/cm. Results of these tests indicated C. dubia to be more sensitive than V. iris; however, chronic toxicity test results were similar for V. iris and C. dubia. The Lowest Observed Adverse Effect Concentration (LOAEC) for mussel survivorship after 28 days was 10,000 µS/cm, while the LOAEC for growth was 5,000 µS/cm. LOAECs for the C. dubia 7-day chronic were 25 % (survivorship) and 12.5 % (reproduction), while mean conductivity at these two concentrations was 4,054 and 2,211 µS/cm, respectively. Toxicity tests conducted with Pond 6 dyke cut discharges resulted in similar lethal concentrations for C. dubia and V. iris. Forty-eight hour LC50s of these discharges ranged from 12.07-15.95 % for C. dubia, and 17.36-18.95 % for V. iris. Dyke cut discharges also exhibited exceedingly high alkaline pH (11.5-12.2), which caused 100 % mortality to C. dubia in 15 min. The Pond 5 and 6 dyke discharges are the likely source for the flocculent accumulation at the base of the two remediated pond areas. The combined effect of mercury, aluminum and iron, along with periodic fluxes of high conductivity and alkaline pH during low flow conditions may contribute to low mussel recruitment downstream of Saltville, VA. / Master of Science

The Clinch River (CR) and North Fork Holston River (NFHR) contain some of the most diverse freshwater mussel assemblages in the United States; however, both rivers are experiencing declines in mussel populations. The first component of this study used histological evaluations and water quality data to determine whether mussels were negatively impacted in the CR zone of decline (ZD) and to inform future management of freshwater mussels in the river. In the 91 kilometer (km) section from Carbo, Virginia (CRKM 431) downstream to Speers Ferry, Virginia (CRKM 340), referred to as the ZD, mussel density decreased >90% from 1979 to 2014 at key sites such as Semones Island (CRKM 378.3) and Pendleton Island (CRKM 364.2). Laboratory propagated mussels were placed in cages in the river for one year from June 2012 to May 2013 at four sites within the ZD and four sites in reaches where mussel populations remain stable or are increasing, a zone of stability (ZS). The survival, growth and histological results indicated that there are continuing impacts to mussels in the ZD. Research investigating impacts to the ZD and methods to improve water quality in this zone are needed. The laboratory component of this study examined sublethal effects of potassium (K⁺), chloride (Cl⁻), and un-ionized ammonia (NH₃-N) on mussel tissues at concentrations relevant to those found in the NFHR. Historical industrial activities at Saltville, Virginia, as well as continued pollution of the NFHR from chemical waste ponds at this location, are believed to be significant contributors to mussel declines. Contaminant seepages from the waste ponds that include Cl⁻, K⁺, and NH₃-N have been shown to be toxic to adult and juvenile mussels. A three-month laboratory study was conducted to assess impacts to organ tissues (gills, digestive glands, kidneys, and gonads) of adult Villosa iris exposed to environmentally relevant concentrations of K⁻ (4 and 8 mg/L), Cl⁻ (230 and 705 mg/L), and NH₃-N (0.014 and 0.15 mg/L) using histological evaluations. No detectable differences were observed among the histological endpoints from mussels held in treatments and control (p>0.05). The study design was modified and repeated using increased concentrations of K⁺ (8, 16, and 32 mg/L) and Cl⁻ (705, 1410, and 2820 mg/L) for a two-month exposure period. Due to issues with maintaining NH3-N in mussel holding chambers, the second study did not the second study did not include NH₃-N exposures. Control mussels in both studies had a higher abundance of lipofuscin in kidneys and degraded cytoplasm in the digestive gland diverticula compared to baseline mussels, indicating that captivity influenced mussel tissues. Future studies are needed to more thoroughly address these captivity effects. Both survival and histological data in the second test showed a significant negative effect of the increased concentrations of Cl⁻ and K⁻, which were representative of those found at some sites in the NFHR downstream of Saltville, Virginia. / Master of Science