Freshwater teleost fish often experience natural and anthropogenic conditions that result in fluctuating energy availability, therefore the ability to acquire, transform and use energy is essential for the survival of these fish. Polychlorinated biphenyls (PCB's) are recognized as physiological sources of stress to fish as they incite defense mechanisms that are generally costly in terms of metabolic resources. Over time, such responses may decrease individual performance and possibly fitness by changes in foraging, migration and escape behaviors, and the population in terms of reproductive capacity due to the alterations in energy allocation following an exposure. The main goal of this study was to determine if a sublethal exposure to PCB-126 affects the energy budget of the fish and can therefore be responsible for functional deficiencies associated with their locomotion. Fish were injected low (100 mug/kg) and high (400 mug/kg) concentrations of PCB-126 and swimming performance parameters including critical swimming speed, metabolic rate and recovery ratios were evaluated. EROD activity was also measured in the liver as an indication of PCB-126 intoxication while blood and white muscle tissue metabolites were analyzed to quantify the physiological disturbance levels associated with this exposure. A significant decrease was observed in the swimming performance of rainbow trout for the low and high PCB-126 treatments as well as an impaired recovery with increasing level of PCB exposure following exhaustive exercise. This study also showed the occurrence of physiological disturbance by a reduction in the hepatosomatic and spleen somatic indices and elevation of plasma cortisol and glucose levels, as well as white muscle reductions in glucose and glycogen indicating higher metabolic costs during recovery and muscle restoration for PCB-exposed fish. Overall, this research provides insights into the sublethal effects of toxic organic compounds on fish.

In the environment, oxidized mercury (Hg) can be converted to more toxic chemical species, such as methylmercury (MeHg), as a result of both abiotic and biotic reactions. Hg and MeHg are present in aquatic ecosystems that flow into the Lake St. Francis region of the St. Lawrence River, but their origin is still being debated. A study of mercury and methylmercury contamination in Lake St. Francis in cooperation with the Raisin Region Conservation Authority (RRCA) is ongoing, in collaboration with the Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA) and the Great Lakes Program. A recent report detailed the experimental results for one portion of the area of concern, the Raisin River. The goal of the present project is to update and expand upon the previous work in order to include other existing and new data for this river and several other watercourses feeding Lake St. Francis. Special attention was paid to the MeHg hotspots in an attempt to link methylation and subsequent mobilization to different types of land use and nutrient profiles compiled from new and existing data. It was predicted that water draining off wetlands would have higher MeHg concentrations than water from catchments with other land use profiles. Total and methylmercury were expected to be correlated to the concentrations of nitrogen compounds, sulfate, phosphorus, dissolved inorganic carbon (DIC), and especially dissolved organic carbon (DOC). However, wetlands could not be correlated to MeHg as predicted but the area of crop land was correlated positively with the percentage of THg present as MeHg. Forest and impermeable areas were associated with a decrease in mercury. There was no difference in mercury during wet years compared to dry years when compared on an annual basis, but a significant seasonal difference exists between the two categories. MeHg was positively correlated to DOC, NH3, and BOD. THg was positively correlated to BOD, TSS, Escherichia coli, and fecal coliforms. The percentage of THg present as MeHg (%MeHg) was positively correlated to phosphorus. There were also some statistically significant negative correlations. Forest and impermeable area were negatively correlated with the quantity of MeHg, and impermeable area was negatively correlated with %MeHg. Greater predictor strength and more numerous significant correlations are expected under more thorough sampling and more data.

Methylmercury (MeHg), the known toxic form of mercury is generally only 1-3% of total mercury (THg) in precipitation. As such it was thought to be an insignificant source to aquatic ecosystems; however, since other forms of mercury can be re-volatilized from the snowpack back to the atmosphere shortly after deposition the proportion and biological significance of MeHg in the snowmelt runoff is indeed an important source to downstream ecosystems. To assess the seasonal contribution of MeHg in runoff to the overall annual load of MeHg, the tributaries of two lakes, Dickie (DE) and Harp (HP) in the Haliburton-Muskoka district of Ontario were sampled on a weekly basis for MeHg, dissolved organic carbon (DOC) and conductivity over two years. Stream discharge was monitored on a continuous basis. In order to assess the amount of MeHg in the snowpack, snow cores from the watersheds were sampled during early spring. Additionally, bulk precipitation samples were collected using a wet-dry automated precipitation collector in the mercury deposition network (MDN) operated station in St. Anicet, Quebec every 4-6 weeks, for 26 months. The samples were analyzed for MeHg, and an annual deposition rate was calculated. THg and MeHg data obtained from the MDN was used to calculate a deposition rate for THg, and the proportion of MeHg. THg in wet deposition was 5.29-6.88 mug m-2 year-1, and MeHg was 0.15-0.19 mug m -2 year-1 and equivalent to 2.7-2.9 % of THg. Although low MeHg concentrations were measured in runoff during spring freshet, the high discharge rates resulted in quantities which were up to 33.9% of the annual amount of MeHg. The seasonal contribution of MeHg in runoff was found to be: spring>summer>fall> winter for the wetland rich DE and fall> spring> winter> summer for the wetland dull HP. Multiple regression analysis illustrated that DOC was the most significant predictor of MeHg (r2=0.32, p<0.01) across all data with a strong seasonal dependence of the DOC-MeHg correlation. The strongest correlation was found during spring freshet (r 2=0.65, p=0.001) followed by summer, winter and fall (r2= 0.37, 0.23 and 0.22 respectively, p<0.05 for all). The constant flow of water during the winter and strong correlation with DOC during snowmelt suggests a terrestrial source of MeHg even during the winter months, however, direct precipitation during spring and snowmelt were also found to contribute to the MeHg load during snowmelt runoff.

This thesis studies the chemical reactions of mercury in different oxidations states with several natural methyl-donors present in the aquatic environment. The importance of the abiotic pathway of mercury methylation was assessed by a thorough examination of the kinetics of these reactions in various experimental conditions, relevant to environmental situations. The amount of methylmercury formed in the course of the chemical reactions studied herein shows that the abiotic mercury methylation can be a very significant source of this compound in the environment. The thesis comprises three main chapters which describe the reactions of three major methyl-donors: methyl iodide, methycobalamine and methyl tin compounds with mercury. Reaction of mercuric ions with methyl iodide yields HgI+ and HgI2 as inorganic products and MeOH as the only organic product. The reaction kinetics are biphasic and the reaction rate decreases with pH, increases with temperature and the reaction stops in the presence of complexing agents such as iodide ions. Meanwhile, the reaction of Hg0(aq) with methyl iodide yields 1.1% methylmercury which is a relatively high yield for environmental reactions. We show that the role of methyl iodide in the geochemical cycle of mercury in the aquatic environment is two-fold: it promotes the formation of compounds such as HgI + and HgI2 which are less reactive towards chemical and biological methylation and it methylates Hg0 which is present when Hg2+ is reduced by reducing agents found in the aquatic environment. The reaction of mercuric ions with methylcobalamine is studied using methylaquacobaloxime as a model compound. The mechanism is an electrophilic attack of Hg2+ to the Co-C bond. It results in the cleavage of this bond and formation of Hg-C bond in the structure of methyl mercury. The reaction is first order to mercury and methylcobaloxime concentration and the value of the second-order rate constant is k = (6.8 +/- 0.2) M-1 s-1 at 21.1°C, at a pH of 1.5 and an ionic strength of 0.030 M (HNO3). The reaction rate decreases with pH, and increases with temperature and ionic strength. The yield of methyl mercury formation is as high as 75%. The presence of chloride completely shuts down the reaction. So, abiotic methylation of mercury by methylcobalamin could be a source of methylmercury formation in fresh waters which have low pH and low chloride concentrations. (Abstract shortened by UMI.)

This thesis examines the accumulation of polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) in vegetation in order to develop an interpretative scheme to determine deposition velocities of semi-volatile organic compounds (SVOCs) onto vegetation. PBDEs are flame retardants used in a variety of consumables. Although relatively non-volatile, these compounds have been quantified around the world extending to otherwise pristine ecosystems providing empirical evidence for their long-range transport. However, modeling studies indicate that their long-range atmospheric transport (LRAT) potential is at best moderate. However, recent modeling studies have suggested that vegetation may play an important role in their global distribution. PAHs are also ubiquitous contaminants. These can be released through both natural and anthropogenic sources. Some are considered highly carcinogenic and their potential impact on human health may be due to their association to particulates. Although their environmental fate is perhaps better understood, the processes involved in surface-air exchange, particularly with vegetation, have not been well documented. Spruce needles and atmospheric (gaseous and particulate-bound) PBDE and PAH concentrations were monitored bi-weekly from February 2004 to June 2005 to examine potential weather-related and seasonal effects. An efficient extraction method for PBDEs from spruce needles was developed. Finally, using measured concentrations, surface-air exchange was considered and a modeling concept was developed to determine deposition velocities to vegetation. Following their emergence, spruce needle PBDE and PAH concentrations increase gradually over time although decreasing briefly following snowmelt with a minimum coinciding with the following year's bud burst. Atmospheric concentrations of PBDE and PAH, both gaseous and particulate-bound, were linked to daily weather events. PBDE gaseous concentrations increased with temperature, whereas PAH concentrations were generally highest in the winter, likely reflecting increased emission. Analysis of air mass back trajectories and local wind directions revealed that particulate-bound PBDEs, along with both gaseous and particulate-bound PAHs originated from local sources, whereas gaseous PBDEs were likely from distant sources. Using measured atmospheric PBDE and PAH concentrations, particulate-gas partitioning was examined. Particulate-gas distributions correlated significantly with log KOA values and a significant temperature dependence was observed for most compounds considered, except the higher PBDE congeners. From compounds exclusively associated to particulates, the particulate-bound deposition velocities were calculated at 3.8 and 10.8 m/h for PBDEs and PAHs, respectively. The different vP values obtained for PBDEs and PAHs may indicate association with different particulates. Net gaseous transfer velocities correlated significantly with log KOA values and ranged from 2.4 to 62.2 m/h for PBDEs and from negligible to 75.6 m/h for PAHs. These derived values were then used to monitor PBDE and PAH accumulation in vegetation through time, and these agreed well with measured values. This study provides the necessary background for modeling PBDE and PAH transport between air and coniferous vegetation globally.

Mercury methylation in aquatic systems has been linked to the activity of various anaerobic microbes, including sulfate-reducers (SRB), iron-reducers (FeRP) and methanogens (MPA). This study focuses on the biogeochemical factors, i.e., the relative importance of the diverse groups of anaerobic microbes, that affect net methyl mercury formation in freshwater. Methylation and demethylation were measured separately using enriched stable isotopes of mercury in microcosms treated with specific microbial inhibitors and abiotic control systems. Non-contaminated sediments from the Mer Blue wetland in Ottawa, Ontario, were used to test the proper set up and methods to be used for future experiments. Mercury-contaminated sediments of the St. Lawrence River (SLR) in Cornwall (Zone 1), Ontario, were investigated because they have been found to be a potential source of MeHg in the food web and the river system. In the Zone 1 SLR sediments, strong positive correlations were observed between methylation rate constants and sulfate reducing rates, as well as demethylation rates constants and methane production rates, indicating that SRB are primary methylators and MPA have the leading role in methylmercury demethylation. The inhibition of both SRB and MPA enhanced iron-reduction while MeHg production was not completely stopped, indicating that iron-reduction might however be another important process in MeHg production in the Zone 1 SLR sediments, probably by decreasing demethylation rather than favouring methylation, as shown by the strong negative correlation between Kd and iron-reduction rates. Similar findings were obtained for the Mer Bleue sediments, with the exception that SRB were involved in both methylation and demethylation. A new modified procedure for measuring mercury isotopes in sediment samples was also proposed. The procedure uses acid leaching-ion exchange-thiosulfate extraction (TSE) to isolate and purify the methylated mercury from the matrix. Major advantages of the TSE procedure include the extraction and analysis of a large number of samples in a short time, excellent analyte recoveries, and the lack of artefact formation. Recoveries between 94 and 106% were obtained for the standards CRMs, BCR 580 and IAEA 405. Comparisons between TSE and other procedures (distillation, acid-leaching) have shown good agreement of methylmercury values.

This doctoral thesis investigated the impact of the arbuscular mycorrhizal (AM) symbiosis, an ubiquitous and beneficial association between plant roots and soil fungi, toward plant growth, stress tolerance, and metal uptake in relation to extrinsic metal conditions ranging from low (e.g. trace) to high (e.g. toxic) exposure levels. The investigative strategy is divided into two main parts: (1) statistical meta-analysis and (2) experimental analysis. In the first part, an extensive literature review in the field of metal phytoremediation was conducted in order to construct a meta-dataset consisting of various plant physiological and soil ecological parameters which were ultimately extracted from nearly 30 published works. Meta-analytical statistical tools were then used to examine general trends and perspectives in metal phytoextraction and metal stress tolerance (Chapter 2), to establish an inherent role for the AM symbiosis therein (Chapter 3), and to discuss the potential for plant investment in symbiotic associations as an extrinsic stress tolerance strategy in complement to the plant's intrinsic stress resistance mechanisms (Chapter4). From these findings, a series of conceptual models were proposed depicting the plant growth and metal uptake in relation to increasing metal exposure levels by integrating the primary AM-induced mechanisms of 'enhanced uptake' and 'metal biosorption'. In the second part, in vitro root-organ (Chapter 5) and greenhouse culture systems (Chapters 6 and 7) were designed using the micronutrient zinc (Zn) as a typical metal contaminant to test various parameters of AM-plant growth and metal uptake, for which the proposed conceptual models were used as a framework for developing new hypotheses regarding plant-soil interactions. The methods and analytical techniques included Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) for the determination of soil- and plant-Zn concentrations, differential root staining and microscopic analysis for the assessment of AM-root colonization, and standard physiological metrics for the determination of plant health 'status. In brief, I showed that the AM symbiosis plays a dynamic role in plant development and stress tolerance first by enhancing the uptake of limiting metal nutrients, and then by reducing the uptake of potentially toxic metal contaminants due to metal biosorption under metal toxicity conditions. Accordingly, I also suggested that such mechanisms contribute in buffering the proximal growth environment, and thereby increasing soil's resiliency. Altogether, I consider the revised models depicting the impact of the AM symbiosis on plant and soil systems to be a relevant tool in environmental remediation practices.

In this dissertation the 180°-flip motion and morphology in polyethylene we studied by solid-state NMR. An explanation of the varying (ultra)drawability of semicrystalline polymers in terms of αc-relaxation chain mobility is proposed. Crystalline domains composed of “polyethylene-like” chains in soil organic matter are detected and characterized. In high-density polyethylene (HDPE) and in ultra-high molecular-weight polyethylene (UHMWPE) fibers, the 180° chain-flip motions are observed in terms of changes in the 13C-13C dipolar couplings. In the HDPE sample, the motion is observed directly via two-dimensional exchange spectroscopy, stimulated-echo decays, and 1D lineshape changes. The data yield an activation energy of 122 ± 10 kJ/mol. In the fibers, the narrowing of natural-abundance 13C-13C dipolar satellites indicates a flip rate of 1000/s at 360 K. An explanation of the varying (ultra)drawability of semicrystalline polymers is proposed, based on NMR evidence of αc-relaxation-associated helical jumps and chain diffusion through the crystallites of “α c-mobile” polymers. The chain motions provide a mechanism by which these polymers can be ultradrawn to draw ratios >30, without melting. Other semicrystalline polymers that lack a crystalline α-relaxation only have draw ratios of <14. The structure of ultradrawn UHMWPE fibers is investigated by solid-state NMR. A crystallinity of (88 ± 2)% was determined by traditional 1H NMR and a new adaptation of the 13C NMR direct-polarization method. 1H spin diffusion yields amorphous domain sizes of 10 ± 5 nm, and crystalline regions of 100 ± 50 nm diameter. A second, highly mobile, amorphous phase, making up (0.8 ± 0.2)% of the sample, was detected by 1H NMR. The fraction of partially mobile, oriented interfacial material or tie-molecules in the fiber was found to be ∼5%. Crystalline domains composed of poly(methylene) chains have been unambiguously detected by solid-state NMR and wide angle X-ray scattering in several samples of soil organic matter, including surface soil (peat), humic acids from surface soil and young coal, and humins. The crystallite thickness is deduced from the NMR-detected melting range and 1H spin diffusion experiments. The crystallites are expected to have long residence times in the soil and may be related to the formation of petroleum.

The Deepwater Horizon (DwH) blowout released 5.0x1011g C from gaseous hydrocarbon into the water column and up to 6.0x1011g C from oil (Joye et al., 2011). Oil was visible on the surface, but <0.01% of the gaseous hydrocarbon escaped the water column (Kessler et al., 2011; Yvon-Lewis et al., 2011). Metabolically efficient methanotrophs consumed the gases, converting them into either CO2 or biomass. For this study, we analyzed carbon isotopes, δ13C and Δ14C, in suspended particulate organic carbon (POC) to detect the fate of some of the hydrocarbons. Suspended particulate organic carbon has a residence time of 5-10 years in the water column (Druffel and Williams, 1990) and is composed of floating biomass including mucus, plankton, bacteria, fecal pellets and other organic particles greater than 1μm. POC too large to float sinks and is then classified as sinking POC. Marine snow is an example of sinking POC. Suspended and sinking POC can be composed of the same types of biomass, however they can be formed from different carbon sources and different areas of the water column. The primary focus of this study is on suspended POC. We hypothesized that the DwH event caused depleted δ13C and Δ14C signatures in POC that we would see fade over time and with distance away from the blowout, horizontally and vertically in the water column. Our second hypothesis was that carbon isotope signatures should also differ between natural hydrocarbon seep sites and non-seep sites. We also wanted to determine the percent carbon in each sample from methane or oil derived carbon and the total amount of POC in our sampling area in the Gulf of Mexico composed of carbon from hydrocarbons. Our data set was compared to sediment carbon isotope data from the Gulf of Mexico to rule out one possible alternative hypothesis that could cause depleted carbon isotope signatures, sediment resuspension. To complete these objectives, POC samples were collected from Desoto Canyon and other seep and non-seep sites across the Northern Gulf of Mexico in 2010, 2012 and 2013. Seawater was filtered, collecting the POC on glass microfiber filters, which were then acid fumed, dried and analyzed for δ13C and Δ14C. The hydrocarbon plume from the DwH blowout was detected in 2010 POC samples. Over 2010, 2012 and 2013 sampling years, δ13C signatures ranged from −17.8 / to −35.2 /. Radiocarbon signatures ranged from 71.2 / to −755.5 /. Percent carbon from modern, methane and oil derived carbon for 29 deep POC samples was estimated to contain 58% ±; 19% modern, 33%±;19% methane and 9%±;5% oil. We found no yearly variation between signatures on POC samples collected in the deeper waters, which suggests that the Gulf of Mexico always has depleted carbon isotope signatures at deeper depths and the effect of the oil spill, although clearly detectable in 2010, was relatively minor on suspended POC. GC600, a well known and active seep, appears to have the same qualitative impact on the POC carbon isotope signatures as the blowout. The blowout released an estimated 4.6−6.0x1011g C from oil into the water column. Through direct recovery, skimming, or burning, 35.5% of the released oil was removed from the environment leaving 2.9−3.9x1011g C from oil behind that could possibly be incorporated into POC. Adding the 5.0x1011g C from gaseous hydrocarbons to the oil left in the water column, there is an estimated 7.9−8.87x1011g C released from the wellhead. We calculated the total POC reservoir in our sampling area of 9.4x1010 m2 of the Gulf of Mexico, to be 2.1x1012 to 4.4x1012g C. If 100% of the remaining hydrocarbons were assimilated into biomass, the hydrocarbons from the blowout would make up 20−42% of the total POC reservoir in the Gulf of Mexico. Du and Kessler (2012) estimate that of the 0.47x1012g of hydrocarbons released, 0.1x1012 g C were converted into biomass, which makes up only 2−5% of the total POC reservoir we calculated. As suggested above, our data suggest that the deep Gulf of Mexico always has depleted carbon isotope signatures, implying that the bacteria in the water column of the Gulf of Mexico acts as a buffer, reducing the impact of the blowout and natural seeps on global climate by preventing methane from reaching the atmosphere. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2014. / November 6, 2014. / Deepwater Horizon, methane, POC, Radiocarbon / Includes bibliographical references. / Jeffrey Chanton, Professor Directing Thesis; Olivia Mason, Committee Member; Yang Wang, Committee Member.

Mercury (Hg) in the environment has deleterious ecological and health affects for humans and wildlife and is primarily transferred to humans through the consumption of marine biota (USEPA, 2001). These ecological and health concerns are exacerbated by the production of methylmercury (CH3Hg+; MMHg) in aquatic ecosystems. Sulfur isotopes (δ34S) are an indicator of the strength of sulfate reduction associated with MMHg production. In chapter 1, we assessed the relationship between MMHg concentrations and reduced-sulfur stable isotope δ34S signals in four coastal consumer organisms (length = 26–75 mm) from Florida's Big Bend seagrass meadows: pinfish (Lagodon rhomboides); pigfish (Orthopristis chrysopter); black sea bass (Centropristis striata melana); and shrimp (Tozeuma carolinense and T. serratum). We found a significant correlation between depleted δ34S signatures in fauna tissue (R2 = 0.27; p < 0.001; total n = 179) with higher MMHg concentrations. A correlation was observed in lower δ34S isotopic signatures and higher MMHg concentrations of consumers from the southern region of the study area indicating a "hotspot" of net mercury methylation in the sediments near Tampa Bay, Florida. To better understand the sources of Hg to coastal pinfish and to assess the contribution of pinfish annual egress to offshore food webs, chapter 2 applies isotopic tracing (C, N, S) combined with mercury (Hg) concentrations and isotope ratios in sediments, juvenile pinfish, juvenile gag grouper (Mycteropera microlepis), and adult gag grouper and pinfish to assess exposure pathways of MMHg in the northeastern Gulf of Mexico. We found that pinfish from the northern and southern Big Bend regions had distinct Hg sources. Southern pinfish had enriched δ202Hg and, when combined with lower pinfish δ34S values and lower sediment δ202Hg values, suggested elevated microbial methylation/demethylation in the southern region. The southern, coastal pinfish exhibited similar Δ199Hg as offshore gag grouper suggesting pinfish from this region represent an important Hg source to offshore reef fish species and/or these two cohorts are exposed to the same Hg source. Results suggested that estuaries can be an important source of MMHg to adjacent, offshore commercially important reef species and confirmed the utility of Hg isotope analysis to identify multiple marine Hg sources and inform our understanding of the pathways of MMHg bioaccumulation in estuarine food webs. In the northern Gulf of Mexico (nGOM), the Hg cycle is further complicated by the influence of the Mississippi River (MR) and potentially confounded, since April 2010, by the Deepwater Horizon (DWH) oil spill. Approximately 3.0-4.9% of oil-derived carbon released during the Deepwater Horizon oil spill was deposited on the seafloor (Chanton et al., 2014; Valentine et al., 2014) causing local, but persistent, oxygen depletion (Kessler et al., 2011). In these low-oxygen environments, the formation of monomethylmercury (MMHg) is promoted and may have led to higher MMHg concentrations in commercially important reef fish species. Expanding our research to include the entire nGOM shelf, slope, and the far-reaches of the deep Gulf canyons, chapter 3 explores Hg cycling using benthic and pelagic fishes as indicator-samples. Fish in the western study region appeared to rely more on benthic feeding, as indicated by enriched δ13C values and depleted δ34S values. Fish species closer to the MR plume had enriched δ15N and depleted δ202Hg and Δ199Hg values suggesting the MR influenced the nutrient and Hg cycle in the northeastern GOM. Cutthroat eels (~1,000 m) had higher MIF signatures than slope snake eels (~250 M) and, when combined with decreasing δ13C values with depth, suggested the presence of near-surface derived Hg in the deep DeSoto Canyon. Our results highlighted the importance of the deposition of Hg associated upper water column OM such as the marine snow pelagic carbon. Chapter 4 investigates whether more reducing conditions cause by DWH led to higher levels of mercury in commercially important reef associated organisms. We compared pre-spill (collected 2007-09) and post-spill (collected 2012) fish species of similar length from hard-bottom reefs on the West Florida Shelf. Light stable isotope analyses of carbon, nitrogen, and sulfur was employed to assess feeding ecologies of those species exhibiting higher MMHg concentrations following the oil spill. Some species, like porgy, showed significant increase in Hg concentration. This increase may have been associated with a shift to a more pelagic, higher trophic feeding regime. The significance of this study is that it shows that the oil spill had an effect on the mercury cycling but that the effect is not uniform for each fish species. / A Dissertation submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Spring Semester 2016. / January 11, 2016. / Bioaccumulation, Deepwater Horizon oil spill, Florida Big Bend, Isotope, Mercury, Pinfish / Includes bibliographical references. / Jeffery Chanton, Professor Co-Directing Dissertation; William Landing, Professor Co-Directing Dissertation; Xiaojun Yang, University Representative; Yang Wang, Committee Member; Dean Grubbs, Committee Member.