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Knowledge gaps pertaining to the remediation of freshwater lakes impacted by oil spills have persisted despite recent record highs for oil production and transportation across vulnerable regions in North America. The multiyear Freshwater Oil Spill Remediation Study (FOReSt), conducted at the IISD-Experimental Lakes Area in Canada, is focusing on the efficacy of minimally invasive methods for remediating oil spills in freshwater boreal lakes. In this thesis, the impacts and remediation of diluted bitumen (dilbit) and conventional heavy crude oil (CHV) spills were investigated (year 1), as were a variety of different remediation methods for spills of dilbit on different shoreline substrates (year 2). Two common small-bodied fish, fathead minnows (Promephales promelas) and finescale dace (Chrosomus neogaeus), were used to assess exposure to petrogenic polycyclic aromatic compounds (PACs) in model enclosed shoreline ecosystems impacted by spills and remediated using minimally invasive techniques. Short-term exposure to PACs, the most toxicologically relevant compounds in oil, was assessed in fish using biliary metabolite concentrations. In year one, finescale dace and fathead minnows residing in oil treated enclosures each had biliary pyrene metabolite concentrations that were positively correlated with pyrene concentrations in the water of the enclosures. Three months after the initial spills, fish in the enclosure receiving dilbit were significantly more exposed to PACs than fish in reference enclosures that did not receive oil. In year two, both finescale dace and fathead minnows residing in oil-treated exposures, regardless of shoreline substrate, showed increased exposure to PACs compared to fish in reference enclosures and the pristine lake environment two and a half months after the spills. No significant differences in exposure were observed among the remediation treatments. Biliary PAC metabolite concentrations were positively predicted by parent PAC concentrations in periphyton. PACs in periphyton two and a half months after oil introduction were positively correlated with PACs in the enclosures one week after spills, suggesting fish also had increased exposure to periphyton-bound alkyl-PACs. This thesis validates the use of small-bodied fish in assessing PAC exposure following freshwater oil spills and demonstrates the difficulties in estimating exposure using environmental concentrations in natural systems.

The environment during early life history strongly impacts phenotypic development in all organisms, which further influences developmental trajectory and ecological fitness later in life. Depending on the developmental stage and magnitude of change in the environment, phenotypes may become irreversible and thus have a long-lasting effect later in life. This thesis was designed to better understand how changes in the environment may influence plasticity and variation of metabolic phenotypes of Lake Sturgeon (Acipenser fulvescens) within the first year of life. Broadly speaking, the thesis tested two hypotheses that 1) all measured phenotypes would be plastic; and 2) durations of environmental effects on phenotypic development would be correlated with distinct developmental windows. Studies were developed to examine 1) short-term effects of temperature or diet on metabolic phenotypes such as metabolic rate, energy density, fatty acid profiles, and growth (Chapters 2 and 3) and 2) longer-term effects of temperature or diet during early life on these metabolic phenotypes (Chapters 4, 5 and 6). The first experimental chapter (Chapter 2) examined ontogenetic development of metabolic rate and demonstrated that dietary shifts between Artemia to bloodworm resulted in cessation of growth with elevated routine metabolic rate. Chapter 3 examined how fatty acid profiles and plasma cortisol concentration were influenced by environmental temperature and showed that decreasing temperature led to increases in mono- and polyunsaturated fatty acids in both phospholipids and triglycerides, and food deprivation resulted in lack of difference between baseline and peak cortisol concentrations. Chapter 4 examined how temperature during early life influenced plasticity of growth and showed that temperature post-dietary transition resulted in a transient effect on growth and energy metabolism without long-term effects post-winter. Chapter 5 examined how temperature during early life could influence growth and fatty acid metabolism when fish were exposed to colder temperatures later in life and demonstrated that elevated temperatures resulted in a longer-term effect on growth but lack of transcriptional responses of desaturating fatty acids when exposed to a cold temperature (3.5°C) later in life. The final experimental chapter, Chapter 6 examined longer-term effects of diet at the onset of exogenous feeding on metabolism and growth and demonstrated that an enriched diet resulted in prolonged effects on growth, digestive enzyme activity and survival prior to a simulated overwintering. This doctoral thesis research revealed that all measured metabolic phenotypes were plastic, but subtle changes in temperature and diet during early life history resulted in transient or prolonged effects on growth and metabolism in age-0 lake sturgeon. Results will aid our understanding of cohort and population dynamics as well as contribute to the development of conservation strategies for lake sturgeon, a species at risk or endangered across its natural range.

Buoyant Arctic cod (Boreogadus saida) eggs are found at the surface or at the ice-water interface in winter. While winter temperatures in saline waters fall below 0 degrees C, the temperature in areas affected by under-ice river plumes is slightly higher. Under-ice river plumes may therefore provide thermal refuges favoring the survival of the vulnerable early life stages of Arctic cod. Thermal refuges would allow early hatchers to survive, benefit from a long growing period, and add to the number of individuals recruiting to the adult population: These expectations define the freshwater winter refuge hypothesis. More than 42 rivers drain into Hudson Bay making it particularly well suited to test this hypothesis. Whereas the bulk of Arctic cod observed in Hudson Bay hatch between mid-April and June, some larvae hatch as early as January. We used two independent but complementary methods to test the hypothesis: (1) Lagrangian model simulations that traced back the planktonic trajectories of the sampled larvae and (2) measurements of the concentration of strontium-88 in the otolith cores. Throughout the Hudson Bay system, Lagrangian simulations revealed that early hatchers were more likely to hatch in lower surface salinities and that larvae reaching larger prewinter lengths were likely to have hatched near or within estuaries. Analysis of otolith microchemistry showed that larvae with low strontium-88 concentration in the otolith core, indicating a low salinity hatch location, had hatched earlier and thus had a longer growth period before freeze-up. These results show the potential for Arctic cod persistence in the Arctic where freshwater input is projected to increase and the ice regime is predicted to become more seasonal, provided that the surface temperatures remain below embryonic and larval lethal limits.

As part of the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP), several climate modeling centers performed a coordinated pre-study experiment with interactive stratospheric aerosol models simulating the volcanic aerosol cloud from an eruption resembling the 1815 Mt. Tambora eruption (VolMIP-Tambora ISA ensemble). The pre-study provided the ancillary ability to assess intermodel diversity in the radiative forcing for a large stratospheric-injecting equatorial eruption when the volcanic aerosol cloud is simulated interactively. An initial analysis of the VolMIP-Tambora ISA ensemble showed large disparities between models in the stratospheric global mean aerosol optical depth (AOD). In this study, we now show that stratospheric global mean AOD differences among the participating models are primarily due to differences in aerosol size, which we track here by effective radius. We identify specific physical and chemical processes that are missing in some models and/or parameterized differently between models, which are together causing the differences in effective radius. In particular, our analysis indicates that interactively tracking hydroxyl radical (OH) chemistry following a large volcanic injection of sulfur dioxide (SO2) is an important factor in allowing for the timescale for sulfate formation to be properly simulated. In addition, depending on the timescale of sulfate formation, there can be a large difference in effective radius and subsequently AOD that results from whether the SO2 is injected in a single model grid cell near the location of the volcanic eruption, or whether it is injected as a longitudinally averaged band around the Earth.

Mercury is a potent toxicant whose concentration in the environment has increased markedly due to human activity. However, uncertainties exist on sources and sinks of mercury, including those associated with mineral dust, with the Sahara Desert being the largest aeolian dust source worldwide. To characterize mercury associated with Saharan dust export to the Atlantic Ocean, aeolian dust (>2.2 µm in size) and soil samples were collected from the Canary Islands and Cabo Verde, ~400 and 800 km off the west coast of Africa. The sources of the dust samples were determined by back-trajectory analysis, and mercury content was characterized via direct mercury analysis. Mercury concentrations differed significantly (p 70%) over the Atlantic Ocean, had a mean mercury concentration of 29.8±31.3 ng/g (w/w), or 1.40±1.34 pg/m3 (w/v); this result is in the lower end of the data reported for remote coastal locations on a w/v basis, but lower than any on a w/w basis. Saharan-origin dust, defined as dust with a back trajectory predominantly (>70%) over the Sahara Desert, had a higher mean mercury concentration of 72.8±7.43 ng/g, or 4.64±2.15 pg/m3. Concentrations of mercury in dust samples were found to increase as back trajectories passed over a larger extent of the western African land surface relative to the Atlantic Ocean water surface. Finally, particulate-bound mercury (PBM) concentrations measured at Cabo Verde were used to estimate the flux of particulate mercury to major dust-impacted regions of the Atlantic Ocean, an area comprising 21.3 million km2. The PBM flux to this region is estimated at 6.5±2.2 t/y if all dust originates from the Sahara, or 3.6±1.6 t/y if the dust is of mixed Saharan and Atlantic origins. These numbers represent only ~1% to 3% of the total mercury deposition to the region estimated by current global mercury models. Surface soil mercury concentrations measured in the Canary Islands further support minimal mercury inputs from Saharan dust. Our study thus suggests the current models may have considerably overestimated Saharan dust contribution to mercury deposition.

The extraction of bitumen from Alberta’s oil sands region generates large volumes of oil sands process-affected water (OSPW) that are stored in tailings ponds. New policy directives are planning to intentionally release OSPW into surrounding freshwater ecosystems. Presently, no water quality standards exist for the main toxic constituent of OSPW - naphthenic acid fraction components (NAFCs). To aid in the establishment of safe-release thresholds of OSPW, we exposed embryo fathead minnow (Pimephales promelas) to OSPW-derived NAFCs (2.5-54 mg/L) from 1-day post-fertilization to hatch in semi-natural conditions. Observations on embryo heart rate, embryo development, and basal activity at hatch were examined, to assess the developmental and behavioural toxicity of NAFCs. Embryo heart rates declined with increasing exposure concentration. NAFCs caused embryo mortality (LC50=26.76 mg/L) and development impairments at hatch (EC50=14.38 mg/L). Non-viable fish displayed pericardial and yolk sac edemas, craniofacial defects, and spinal curvatures that increased in severity with increasing exposure concentration. Acute narcosis, cardiac dysfunction, oxidative stress, and alteration in gene expression were probable modes of toxic action. At concentrations above 21 mg/L, fish displayed erratic and repetitive twitching patterns indicative of nervous system impairment. Post-hatch mass increased with increasing exposure concentration, potentially as a short term, compensatory-like response. Additionally, a reduction in basal activity was observed for fish exposed to 2.5 and 6.5 mg/L. This result suggests there could be sublethal effects for fish exposed to NAFC concentrations much lower than those known to cause mortality and developmental impairments. Taken together, these results provide important toxicological information to inform future regulatory policies for the management of OSPW in Alberta, Canada.

Bull Trout (Salvelinus confluentus) occur in many major watersheds in northwestern North America and are identified as “Threatened” or a “Species of Special Concern” in both Canada and the United States. Non-native fishes, including Brook Trout (Salvelinus fontinalis), are one assumed major contributor to declines of Bull Trout populations. Further understanding of how introduced species are affecting Bull Trout populations may help with their recovery. Metabolic rate is an estimate of the amount of energy being used by an organism, and one of the common ways of estimating metabolic rate in fish is through respirometry. In the following research chapters, I conducted intermittent-flow respirometry experiments both in a laboratory setting and a field setting to compare physiological performance via standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS) of Bull Trout and Brook Trout across a range of ecologically relevant temperatures. The temperatures tested are found in the habitat both species currently occupy, as well as temperatures that may be seen in future climate scenarios. Brook Trout tested in Chapter 2 maintained a relatively stable AS across the range of temperatures tested (5, 10, 15, 20, 23°C) and appear to be thermal generalists, well adapted to live in various thermal environments. Brook Trout showed a peak in AS at 15°C, increasing SMR with temperature, and a peak in MMR estimates between 15 and 20°C. Results from Chapter 3 revealed that wild juvenile Bull Trout and Brook Trout have comparable SMR, MMR, and AS when living in sympatry in the natural environment, at least at the temperatures tested (~3°C and ~10°C). Brook Trout have historically been seen as a major threat to Bull Trout populations based on prior studies that have looked at interactions between the species and generally found an advantage for Brook Trout over Bull Trout. However, the results from this study showed similar metabolic rates in both species living in sympatry. The results further suggest that Brook Trout may not have the physiological or temperature related advantages that are expected, at least in regards to aerobic scope

The Little Ice Age, beginning in Europe in the 14th century, saw a period of climatic cooling and increased precipitation where food sources dwindled and famine became rampant, particularly in urban city centers. This study focuses on the Black Friars population (13th-17th centuries) to explore changes in stress in Denmark at the onset of the Little Ice Age. This study specifically explores the periods before and after the turn of the 14th century. Forty-five adult individuals were analyzed for cribra orbitalia, porotic hyperostosis, and enamel hypoplastic lesions. Results showed no statistically significant differences between the prevalence of these stress indicators between either time period; however, reduced age at death and increased lesion frequency was more prevalent post-1300. It was expected that increased stress would be evident in those buried after the turn of the 14th century due to the many challenges associated with wide spread climatic cooling; however, the reliance on nutrient rich marine resources and alms provisions may have helped lessen the burden of these stressors during this period of climatic hardship. Additionally, while famine characterized the beginning of the 14th century, agricultural rebound shortly after this period may have also influenced the stress levels observed.

In fishes, differences in egg incubation, water temperature, and substrate can have a significant impact on phenotypic development. This is particularly relevant during the first year of life when growth rate peaks and influences an individual’s life history trajectory. In the present study, Lake Sturgeon, Acipenser fulvescens, were reared in different environments for approximately one year. In the first year, sturgeon were reared in 3 temperature regimes (with or without substrate) that mimicked hatchery conditions or river temperature profiles. In the second year, embryos were incubated in MacDonald jars or adhered to substrate and newly hatched larvae were reared in different thermal environments (16, 18 and 20°C) for two weeks during the first month post-hatch. All treatments were then transferred to a common garden set-up where tanks were fed by river water at ambient temperature and natural light cycles. Fish were deprived of food when water temperature reached 1.5°C, then food was re-introduced when water temperature exceeded 2°C, approximately 4.5 months later. Yolksac volumes, body length and mass were assessed during both years. In the first year, there were differences in yolk sac absorption between substrate treatments in the first two weeks post-hatch, and differences in larval length between temperature treatments following the overwintering. In the second year, red muscle fibre area and myonuclear counts were assessed and volitional downward swimming and forced escape responses were tested. Growth rate in the first three months of life was highest in the 20°C group of fish but converged in all treatments during winter. Growth rate in fish raised in warmer waters during early life once again exceeded cooler water treatments post-winter, suggesting growth phenotype was fixed in early life, showing little phenotypic plasticity, and was temperature dependent. Thus, increased growing temperature during early life history results in development of a fast-growing phenotype post the first winter. Overall, there was an absence of significant differences between results for muscle fibre area and myonuclear counts between incubation and temperature treatments and the presence of significant differences between time points indicating a strong evolutionary pressure to maintain plasticity in muscle structure and swimming performance.