Graduate Theses & Dissertations


Effect of SP600125 JNK Inhibitor on Cadmium-Treated Mouse Embryo Forelimb Bud Cells In Vitro
This study investigated the role of the JNK signaling pathway in cadmium-treated mouse embryo forelimb bud cells in vitro. Primary cultures of forelimb bud cells harvested at day 11 of gestation were pre-treated with JNK inhibitor SP600125, and incubated with or without CdCl2 for 15, 30, 60, 120 minutes and 24, 48 hours or 5 days. Endpoints of toxicity were measured through cell differentiation by Alcian Blue Assay and phosphorylation of JNK proteins by Western blot. The results demonstrated that, in the cell differentiation assay, inhibiting JNK activation by 20 μM SP600125 causes an enhanced toxic effect in limb cells and inhibits cell differentiation, whereas 2 μM decreases differentiated nodule numbers under both cadmium stress and normal conditions. In conclusion, the JNK pathway has an essential role in the differentiation processes of limb bud cells in normal growth conditions. Author Keywords: Cadmium, Cell Signaling, JNK, Limbs, Mouse Embryo, Teratology
Phosphorus forms and response to changes in pH in acid-sensitive soils on the Precambrian Shield
Catchment soil acidification has been suggested as a possible mechanism for reducing phosphorus (P) loading to surface waters in North America and northern Europe, but much of the research that has been conducted regarding P immobilization in pH manipulated soils has been performed at high P concentrations (> 130 μM). This study investigated how soil acidity was related to P fractionation and P sorption at environmentally relevant P concentrations to evaluate the potential influence of long term changes in soil pH on P release to surface waters. Total phosphorus (TP) concentrations declined between 1980 and 2000 in many lakes and streams in central Ontario; over the same time period forest soils in this region became more acidic. Soils were collected from 18 soil pits at three forested catchments with similar bedrock geology but varying TP export loads. The soil pH at the 18 study soil pits spanned the historic soil pH range, allowing for `space for time' comparison of soil P factions. Soils were analysed by horizon for P fractions via Hedley P fractionation. Batch P sorption experiments were performed on selected B-horizon soils at varied solution pH. Soil P fractions varied by horizon but were comparable among the three catchments, with only apatite (PHCl) differing significantly across catchments. Contrary to expectation, both soluble and labile P showed negative relationships with pH in some horizons. Mineral soils were able to sorb almost all (> 90 %) of the P in solution at environmentally relevant P concentrations (4.5 - 45.2 μM). Phosphorus sorption at environmentally relevant P concentrations was unrelated to solution pH but at high P concentration there was a positive relationship between P sorption and solution pH, suggesting a P concentration dependant P sorption mechanism. Phosphorus budgets indicate that P is accumulating within catchments, suggesting that P is being immobilized in the terrestrial environment. An alternative hypothesis, which attempts to explain both the decline in stream TP export and terrestrial P accumulation, is discussed. The results from this study suggest that acidification induced P sorption in upland soils are not a contributing factor to decreases in stream TP concentration in the study catchments. Author Keywords: central Ontario, Hedley fractionation, phosphorus, podzols, soil acidification, sorption
effects of environmental variables and dissolved organic matter characteristics on the diffusion coefficient of dissolved organic matter using diffusive gradients in thin films
The efficacy of the diffusive gradients in thin films (DGT) passive samplers to provide accurate measurements of free metal ions and those complexed with dissolved organic matter (DOM) was investigated. DOM controls the diffusive properties of DOM-complexed metal species in natural systems. Knowing the diffusion coeiffiecent (D) for DOM of different molecular weights (MW) and the major environmental variables influencing D is critical in developing the use of DGT passive samplers and understanding labile species. D and MW were determined for natural and standard DOM. No noticeable changes in DOM MW were observed during the diffusion process, suggesting that DOM remains intact following diffusion across the diffusive gel. Data analysis revealed that MW had the greatest influence on D, with a negative relationship between D and MW, except in tidal areas where ionic strength influence on D was significant. This study provides further characterization of the variables influencing D using the DGT technique. Author Keywords: Diffusion coefficient, Diffusive gradients in thin films, Dissolved organic matter, Flow field-flow fractionation, Principal Component Analysis, UV-Vis Spectroscopy
Variation in the δ15N and δ13C composition of POM in the Lake Simcoe watershed
The purpose of this study was to quantify the variation of baseline carbon and nitrogen stable isotope signatures in the Lake Simcoe watershed and relate that variation to various physicochemical parameters. Particulate organic matter samples from 2009 and 2011 were used as representatives of baseline isotopic values. Temporal data from two offshore lake stations revealed that δ15N of POM was lowest mid-summer and highest after the fall turnover. POM δ13C was variable throughout the summer before declining after fall turnover. Spatial data from the lake and the tributaries revealed that POM stable isotope signatures were highly variable. Various physicochemical parameters indicative of phytoplankton biomass were significantly positively correlated with POM δ15N and significantly negatively correlated with POM δ13C. The correlations were mostly significant in the tributaries, not the lake. Moreover, many of the correlations involving δ15N of POM were driven by extreme values in Cook's Bay and its tributaries. In general, it's likely that different processes or combination of processes were affecting the δ15N and δ13C POM in the Lake Simcoe watershed as physicochemical parameters alone could not explain the variability. Measuring the δ15N of ammonium and nitrate, as well as the δ13C of DIC would help discern the dominant nitrogen and inorganic carbon cycling processes occurring in the Lake Simcoe watershed. Author Keywords: δ13C, δ15N, isotopic baseline, particulate organic matter, spatial variation, stable isotopes
Investigating the sources and fate of monomethylmercury and dimethylmercury in the Arctic marine boundary layer and waters
Monomethylmercury (MMHg), the most bioavailable form of mercury (Hg) and a potent neurotoxin, is present at elevated concentrations in Arctic marine mammals posing serious health threats to the local populations relying on marine food for their subsistence living. The sources of MMHg in the Arctic Ocean surface water and the role of dimethylmercury (DMHg) as a source of MMHg remain unclear. The objective of this research was to determine the sources and fate of methylated Hg species (MMHg and DMHg) in the marine ecosystem by investigating processes controlling the presence of methylated Hg species in the Arctic Ocean marine boundary layer (MBL) and surface waters. A method based on solid phase adsorption on Bond Elut ENV was developed and successfully used for unprecedented measurement of methylated Hg species in the MBL in Hudson Bay (HB) and the Canadian Arctic Archipelago (CAA). MMHg and DMHg concentrations averaged 2.9 ± 3.6 (mean ± SD) and 3.8 ± 3.1 pg m-3, respectively, and varied significantly among sampling sites. MMHg in the MBL is suspected to be the product of marine DMHg degradation in the atmosphere. MMHg summer (June to September) atmospheric wet deposition rates were estimated to be 188 ± 117.5 ng m-2 and 37 ± 21.7 ng m-2 for HB and CAA, respectively, sustaining MMHg concentrations available for bio-magnification in the pelagic food web. The production and loss of methylated Hg species in surface waters was assessed using enriched stable isotope tracers. MMHg production in surface water was observed from methylation of inorganic Hg (Hg(II)) and, for the first time, from DMHg demethylation with experimentally derived rate constants of 0.92 ± 0.82 x 10-3 d-1 and 0.04 ± 0.02 d-1 respectively. DMHg demethyation rate constant (0.98 ± 0.51 d-1) was higher than that of MMHg (0.35 ± 0.25 d-1). Furthermore, relationships with environmental parameters suggest that methylated Hg species transformations in surface water are mainly biologically driven. We propose that in addition to Hg(II) methylation, the main processes controlling MMHg production in the Arctic Ocean surface waters are DMHg demethylation and deposition of atmospheric MMHg. These results are valuable for a better understanding of the cycle of methylated Hg in the Arctic marine environment. Author Keywords: Arctic Ocean, Atmosphere, Demethylation, Dimethylmercury, Methylation, Monomethylmercury
Aeolian Impact Ripples in Sand Beds of Varied Texture
A wind tunnel study was conducted to investigate aeolian impact ripples in sand beds of varied texture from coarsely skewed to bimodal. Experimental data is lacking for aeolian megaripples, particularly in considering the influence of wind speed on ripple morphometrics. Additionally, the modelling community requires experimental data for model validation and calibration. Eighteen combinations of wind speed and proportion of coarse mode particles by mass were analysed for both morphometrics and optical indices of spatial segregation. Wind tunnel conditions emulated those found at aeolian megaripple field sites, specifically a unimodal wind regime and particle transport mode segregation. Remote sensing style image classification was applied to investigate the spatial segregation of the two differently coloured size populations. Ripple morphometrics show strong dependency on wind speed. Conversely, morphometric indices are inversely correlated to the proportion of the distribution that was comprised of coarse mode particles. Spatial segregation is highly correlated to wind speed in a positive manner and negatively correlated to the proportion of the distribution that was comprised of coarse mode particles. Results reveal that the degree of spatial segregation within an impact ripple bedform can be higher than previously reported in the literature. Author Keywords: Aeolian, Impact Ripples, Megaripple, Self-organization, Wind Tunnel
Effects of Silver Nanoparticles on Lake Bacterioplankton
Silver nanoparticles (AgNP) released into aquatic environments could threaten natural bacterial communities and ecosystem services they provide. We examined natural lake bacterioplankton communities' responses to different exposures (pulse vs chronic) and types (citrate and PVP) of AgNPs at realistic environmental conditions using a mesocosm study at the Experimental Lakes Area. An in situ bioassay examined interactions between AgNPs and phosphorus loading. Bacterial communities exposed to high AgNP concentrations regardless of exposure or capping agent type accumulated silver. We observed increases in community production during additions of polyvinylpyrrolidone (PVP) -capped AgNPs and that site and nutrient-specific conditions are important to AgNPs toxicology in aquatic systems. Toxicological effects of AgNP are attenuated in natural conditions and differ from results from laboratory studies of AgNP toxicity. Our results demonstrate more studies are needed to fully assess the risk posed by these novel chemicals to the environment. This work could be useful in forming risk assessment policies which are largely based on lab studies and typically demonstrate strong toxic effects. Author Keywords: bacterial production, bacterioplankton communities, ecological stoichiometry, Experimental Lakes Area, mesocosms, silver nanoparticles
Assessing the population genetic structure of the endangered Cucumber tree (Magnolia acuminata) in southwestern Ontario using nuclear and chloroplast genetic markers.
Magnolia acuminata (Cucumber tree) is the only native Magnolia in Canada, where it is both federally and provincially listed as endangered.Magnolia acuminata in Canada can be found inhabiting pockets of Carolinian forest within Norfolk and Niagara regions of southwestern Ontario. Using a combination of nuclear and chloroplast markers, this study assessed the genetic diversity and differentiation of M. acuminata in Canada, compared to samples from the core distribution of this species across the United States. Analyses revealed evidence of barriers to dispersal and gene flow among Ontario populations, although genetic diversity remains high and is in fact comparable to levels of diversity estimated across the much broader range of M. acuminata in the USA. When examining temporal differences in genetic diversity, our study found that seedlings were far fewer than mature trees in Ontario, and in one site in particular, diversity was lower in seedlings than that of the adult trees. This study raises concern regarding the future viability of M. acuminata in Ontario, and conservation managers should factor in the need to maintain genetic diversity in young trees for the long-term sustainability of M. acuminata in Ontario. Author Keywords: conservation genetics, cpDNA, forest fragmentation, Magnolia acuminata, microsatellites, population genetic structure
CO2 dynamics of tundra ponds in the low-Arctic Northwest Territories, Canada
Extensive research has gone into measuring changes to the carbon storage capacity of Arctic terrestrial environments as well as large water bodies in order to determine a carbon budget for many regions across the Arctic. Inland Arctic waters such as small lakes and ponds are often excluded from these carbon budgets, however a handful of studies have demonstrated that they can often be significant sources of carbon to the atmosphere. This study investigated the CO2 cycling of tundra ponds in the Daring Lake area, Northwest Territories, Canada (64°52'N, 111°35'W), to determine the role ponds have in the local carbon cycle. Floating chambers, nondispersive infrared (NDIR) sensors and headspace samples were used to estimate carbon fluxes from four selected local ponds. Multiple environmental, chemical and meteorological parameters were also monitored for the duration of the study, which took place during the snow free season of 2013. Average CO2 emissions for the two-month growing season ranged from approximately -0.0035 g CO2-C m-2 d-1 to 0.12 g CO2-C m-2 d-1. The losses of CO2 from the water bodies in the Daring Lake area were approximately 2-7% of the CO2 uptake over vegetated terrestrial tundra during the same two-month period. Results from this study indicated that the production of CO2 in tundra ponds was positively influenced by both increases in air temperature, and the delivery of carbon from their catchments. The relationship found between temperature and carbon emissions suggests that warming Arctic temperatures have the potential to increase carbon emissions from ponds in the future. The findings in this study did not include ebullition gas emissions nor plant mediated transport, therefore these findings are likely underestimates of the total carbon emissions from water bodies in the Daring Lake area. This study emphasizes the need for more research on inland waters in order to improve our understanding of the total impact these waters may have on the Arctic's atmospheric CO2 concentrations now and in the future. Author Keywords: Arctic, Arctic Ponds, Carbon dioxide, Carbon Fluxes, Climate Change, NDIR sensor
Hydroclimatic and spatial controls on stream nutrient export from forested catchments
Winter nutrient export from forested catchments is extremely variable from year-to-year and across the landscape of south-central Ontario. Understanding the controls on this variability is critical, as what happens during the winter sets up the timing and nature of the spring snowmelt, the major period of export for water and nutrients from seasonally snow-covered forests. Furthermore, winter processes are especially vulnerable to changes in climate, particularly to shifts in precipitation from snow to rain as air temperatures rise. The objective of this thesis was to assess climatic and topographic controls on variability in stream nutrient export from a series of forested catchments in south-central Ontario. The impacts of climate on the timing and magnitude of winter stream nutrient export, with particular focus on the impact of winter rain-on-snow (ROS) events was investigated through a) analysis of long-term hydrological, chemical and meteorological records and b) high frequency chemical and isotopic measurements of stream and snow samples over two winters. The relationship between topography and variability in stream chemistry among catchments was investigated through a) a series of field and laboratory incubations to measure rates and discern controls on nitrogen mineralization and nitrification and b) analysis of high resolution spatial data to assess relationships between topographic metrics and seasonal stream chemistry. Warmer winters with more ROS events were shown to shift the bulk of nitrate (NO3-N) export earlier in the winter at the expense of spring export; this pattern was not observed in other nutrients [i.e. dissolved organic carbon (DOC), total phosphorus (TP), sulphate (SO4), calcium (Ca)]. Hydrograph separation revealed the majority of ROS flow came from baseflow, but the NO3-N concentrations in rainfall and melting snow were so high that the majority of NO3-N export was due to these two sources. Other nutrient concentrations did not show such a great separation between sources, and thus event export of these nutrients was not as great. Proportionally, catchments with varying topography responded similarly to ROS events, but the absolute magnitude of export varied substantially, due to differences in baseflow NO3-N concentrations. Field and laboratory incubations revealed differences in rates of net NO3-N production between wetland soils and upland soils, suggesting that topographic differences amongst catchments may be responsible for differences in baseflow NO3-N. Spatial analysis of digital elevation models revealed strong relationships between wetland coverage and DOC and dissolved organic nitrogen (DON) concentrations in all seasons, but relationships between topography and NO3-N were often improved by considering only the area within 50 or 100m of the stream channel. This suggests nutrient cycling processes occurring near the stream channel may exert a stronger control over NO3-N stream outflow chemistry. Overall, topography and climate exert strong controls over spatial and temporal variability in stream chemistry at forested catchments; it is important to consider the interaction of these two factors when predicting the effects of future changes in climate or deposition. Author Keywords: biogeochemistry, forest, nitrate, south-central Ontario, stream chemistry, winter
Models of partitioning, uptake, and toxicity of neutral organic chemicals in fish
Models of partitioning, uptake, and toxicity of neutral organic chemicals in fish Alena Kathryn Davidson Celsie A novel dynamic fugacity model is developed that simulates the uptake of chemicals in fish by respiration as applies in aquatic toxicity tests. A physiologically based toxicokinetic model was developed which calculates the time-course of chemical distribution in four tissue compartments in fish, including metabolic biotransformation in the liver. Toxic endpoints are defined by fugacity reaching a 50% mortality value. The model is tested against empirical data for the uptake of pentachloroethane in rainbow trout and from naphthalene and trichlorobenzene in fathead minnows. The model was able to predict bioconcentration and toxicity within a factor of 2 of empirical data. The sensitivity to partition coefficients of computed whole-body concentration was also investigated. In addition to this model development three methods for predicting partition coefficients were evaluated: lipid-fraction, COSMOtherm estimation, and using Abraham parameters. The lipid fraction method produced accurate tissue-water partitioning values consistently for all tissues tested and is recommended for estimating these values. Results also suggest that quantum chemical methods hold promise for predicting the aquatic toxicity of chemicals based only on molecular structure. Author Keywords: COSMOtherm, fish model, fugacity, Partition coefficient, tissue-water, toxicokinetics
Absorbance and Fluorescence Characteristics of Dissolved Organic Matter in North Atlantic, Pacific and Arctic Oceans
This thesis was designed to quantify absorbance and fluorescence characteristics of dissolved organic matter (DOM) in North Atlantic, Pacific and Arctic Oceans. DOM was described in water masses of distinct sources and formation pathways as well as in regions where environmental forcings such as deep water upwelling, enhanced biological activity and receipt of freshwater discharge were prevalent. Influence of sea ice on DOM in Beaufort Sea mixed layer (0 to 30 m) seawater was investigated based on sea ice extent as well as freshwater fractions of meteoric (fmw) and sea ice melt water (fsim) calculated from oxygen isotope ratio (δ18O). The effect of DOM exposure to simulated solar radiation was also assessed to determine the resilience of fluorescent fractions of DOM to photodegradation. This research aims to further our ability to trace DOM in marine environments and better understand its transformation pathways and predict its fate as part of the oceanic carbon cycle in a changing climate. Author Keywords: Absorbance, Arctic Ocean, Dissolved organic matter, Fluorescence, Parallel Factor Analysis, Sea Ice


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