Graduate Theses & Dissertations

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Effect Assessment of Binary Metal Mixtures of Ni, Cu, Zn, and Cd to Daphnia magna
Mixtures of metals occur in surface waters, toxicity of which has drawn world-wide attention due to their crucial role in both ecotoxicology and regulations. The present research was undertaken to study the acute toxicity of binary mixtures of Ni, Cu, Zn, and Cd to the freshwater organism, Daphnia magna. The experimental approach included single and binary metal toxicity tests based on the 48h acute toxicity bioassay of Environment Canada. The acute toxicity of single metals followed the order of Cd > Cu > Zn > Ni. Based on the calculated 48h EC50 value of single metals, a toxic unit (TU) approach was used to combine two metals in a binary mixture, in which 1TU was equal to the 48h EC50 value of a metal in single exposure. The toxicity of binary metal mixtures to D. magna followed the order of Cu-Cd > Cu-Zn > Zn-Cd > Cu-Ni > Zn-Ni > Cd-Ni, which demonstrated three types of toxicity (i.e., less than additive, additive, and greater additive). Predictions from additivity models (including concentration addition (CA) and independent action (IA) models), a generalized linear model (GLM), and a biotic-ligand-like model (BLM-like) were compared to the bioassay results. The CA and the RA models also predicted three types of toxicity of the binary metal mixtures (i.e., less than additive, additive, and greater than additive). However, the CA model mostly overestimated the toxicity of binary mixtures. Predictions from the GLM supported the inclusion of the interaction between two metals in a mixture to predict the toxicity of binary metal mixtures. The binary metal toxicity was also predicted using a BLM-like model based on the calculated concentrations of free ionic forms of the metals, affinity constants, and toxic potency of each metal. In this model, it was hypothesized that the toxicity of metal mixture is the result of competition of metals with Ca2+ at biotic ligands, which can lead to whole-body deficiency of Ca2+ in D. magna. The BLM-like model provided the toxic potency of single metals with the following order, Cu > Cd > Zn > Ni. Although the prediction of the BLM-like model was not in good agreement with the observed toxicity of binary metal mixtures, an overestimation of risk of mixture toxicity was obtained using this model, which could be promising for use in environmental risk assessment. Author Keywords: biotic ligand model, concentration addition, Daphnia magna, independent action, metal toxicity, modeling
Observation-based assessment of atmospheric sulphur surrounding a major aluminum smelter in British Columbia, Canada
Recent developments at an aluminum (Al) smelter in Kitimat, BC resulted in a permitted increase of 27 to 42 tonnes of sulphur dioxide (SO2) emissions per day. Gaseous SO2 is a pollutant known to contribute to acidic deposition through processes of wet and dry deposition and can additionally react in-atmosphere to form particulate sulphate (pSO42-). Between June 2017 to October 2018, an extensive network consisting of ion exchange resin (IER) column, passive-diffusive, and active filter-pack samplers was established to provide an estimate of total annual S deposition and pSO42- variation throughout the Kitimat Valley. Filter-pack sampling determined the relative concentration of pSO42- increased downwind of the smelter. Comparison of observation-based and modelled total annual deposition suggested CALPUFF was accurate in representing the spatial viability of S deposition (R2 = > 0.85). However, the model appeared to overpredict near-field deposition suggesting the potential of underestimation further downwind of the smelter. Author Keywords: aluminum smelter, atmospheric deposition, filter-pack sampler, ion-exchange column sampler, pSO42-, SO2
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
Seasonal habitat use and movement of native brook trout (Salvelinus fontinalis) in urban headwater streams
Coldwater streams are becoming increasingly impacted due to urbanization. Using environmental surveys, mark-recapture and telemetry, I assessed factors influencing seasonal brook trout (Salvelinus fontinalis) habitat use and movement in urban headwater streams in central Ontario between 2017-18. Generalized additive models were used to assess which habitat variables best explained seasonal yearling and older brook trout abundance, while generalized least squares models were used to assess overall trends in radio-tagged brook trout movement. My research demonstrated dynamic patterns in habitat use and movement by urban stream-dwelling brook trout. Yearlings were primarily influenced by water quality (stream temperature, conductivity), while older brook trout were most strongly influenced by stream morphology (depth, undercut bank). Movement occurred disproportionately around the spawning season and was more limited in the smaller, more altered stream. These findings may be used to inform fisheries managers on crucial timing and location of brook trout habitat refugia within urbanized environments. Author Keywords: Brook trout, coldwater stream, groundwater, habitat use, radiotelemetry, urbanization
Nitrogen Retention of Terricolous Lichens in a Jack Pine Forest in Northern Alberta
The Athabasca Oil Sands in Alberta, Canada is one of the largest point sources emitters of NOx in Canada and there are concerns that elevated nitrogen (N) deposition will lead to widespread eutrophication impacts, including altered species composition, similar to what has occurred in several parts of Europe. Atmospheric deposition rates as high as 25 kg N ha-1 yr-1 have been measured close to the industrial center. The role of the forest floor in regulating these potential eutrophication effects was investigated following a 5-year enrichment study in which N was applied as NH4NO3 above the canopy of a jack pine (Pinus banksiana Lamb) stand in northern Alberta close to Fort McMurray at dosages ranging from 5 – 25 kg N ha-1 yr-1 in addition to background deposition of 2 kg N ha-1 yr-1. Chemical analysis of lichen mats revealed that apical (upper) lichen tissue N concentration increased with treatment, as did the necrotic tissue. When expressed as a pool, the fibric-humic (FH) material held the largest quantity of N across all treatments due to its relatively large mass. Soil net N mineralization and net nitrification rates did not differ among N inputs after five years of application. A 15N tracer applied to the forest floor showed that N is initially absorbed by the apical lichen, FH material, and the foliage of the vascular plant Vaccinium myrtilloides in particular. After 2 years, the FH 15N pool size was elevated and all other measured pools were depleted, indicating a slow transfer of N to the FH material. Applied 15N was not detectable in mineral soil. The microbial functional gene ammonia monooxygenase (amoA) was undetectable using PCR screening of mineral soil microbial communities in all treatments, and broad fungal/bacterial qPCR assays revealed a weak treatment effect on fungal/bacterial ratios in mineral soil. This work suggests that terricolous lichen mats, which form the majority of ground cover in upland jack pine systems, have a large capacity to effectively retain elevated N deposition via the formation of stable humus. Author Keywords: Biogeochemistry, Boreal Ecology, Lichen, Nitrogen Enrichment, Oil Sands
Groundwater Recharge in a Managed Forest on the Oak Ridges Moraine, Southern Ontario
Groundwater recharge was estimated and compared in two open grasslands, three mixed deciduous forest stands (100+ years in age), three young red pine plantations (27 ¨C 29 years in age) and two old red pine plantations (62 ¨C 63 years in age) on the Oak Ridges Moraine, southern Ontario, Canada. Recharge was estimated using a 1-d water balance with measured precipitation, throughfall, stemflow, snowpack water equivalent and soil water storage, and modelled evapotranspiration. Throughfall distribution beneath red pine canopies showed no consistent variation with distance from the tree boles. Old red pines were not major stemflow producers and although the young red pines showed a slight tendency to focus stemflow (focussing ratio > 1), the inclusion of focussed stemflow when calculating recharge at the stand scale made little difference. Conversely, sugar maple (the predominant species in the mixed deciduous stands) showed a strong tendency to focus throughfall proximal to tree boles and produce large quantities of stemflow, resulting in relatively high soil moisture contents and enhanced opportunities for recharge within ~ 0.5 m of tree boles. Inclusion of these focussed inputs resulted in a ~ 11 ¨C 18 % increase in stand scale recharge estimates. The interpretation of land cover control on recharge was complicated by variations in soil texture between sites. Soil texture and its influence on soil water storage capacity resulted in temporal variations in recharge, with sites exhibiting large storage capacities producing less recharge in the fall and greater recharge in the spring than sites with limited storage capacities. Recharge estimates for the entire study period or seasonal values for sites grouped on the basis of soil water storage capacities showed a general trend of increasing recharge in the order: old red pine ¡Ö young red pine ¡ú mixed deciduous forest ¡Ö open grasslands. The disparity between the red pine plantations and the other sites was driven in large part by greater modelled evapotranspiration in the red pine plantations. The similarity in recharge between mixed deciduous forests and open grasslands was the result of focused inputs and less soil evaporation and transpiration in the mixed deciduous forests compared to the open grasslands. The results of this study suggest planting red pine on grasslands on the Oak Ridges Moraine will initially decrease recharge and this decrease will continue as the red pines mature. However, as the red pine plantations are succeeded by mixed hardwood stands recharge will recover to that of the initial grasslands. Author Keywords: Groundwater Recharge, Land Cover Type, Oak Ridges Moraine, Stemflow, Throughfall, Water Balance
Evidence for hybrid breakdown in the cattail (Typha) hybrid swarm in southern Ontario
Heterosis, expressed as phenotypic superiority over parental species, typically peaks in first generation hybrids (F1s), while later generations (F2 +) exhibit lower fitness. The decrease in hybrid fitness is called hybrid breakdown. The overall incidence of hybrid breakdown in invasive hybrid zones remains poorly understood. The Laurentian Great Lakes (LGL) region contains a hybrid zone comprised of: native Typha latifolia, Typha angustifolia, and hybrid Typha × glauca. F1 T. × glauca display heterosis and are invasive, while later generation hybrids are relatively rare. To investigate possible hybrid breakdown, I compared seed germination and plant growth of backcrossed and advanced-generation (F2) hybrids to F1s and T. latifolia. I found evidence for hybrid breakdown in F2s and backcrossed hybrids, expressed as reduced growth and germination rates. Expression of hybrid breakdown in F2s and backcrosses may explain their relative rarity in the LGL hybrid zone. Author Keywords: Advanced-generation hybrids, Backcrossed hybrids, Hybridization, introgression, Invasive species, plant competition
Sex-Specific Graphs
Sex-specific genetic structure is a commonly observed pattern among vertebrate species. Facing differential selective pressures, individuals may adopt sex-specific life historical traits that ultimately shape genetic variation among populations. Although differential dispersal dynamics are commonly detected in the literature, few studies have investigated the potential effect of sex-specific functional connectivity on genetic structure. The recent uses of Graph Theory in landscape genetics have demonstrated network capacities to describe complex system behaviors where network topology intuitively represents genetic interaction among sub-units. By implementing a sex-specific network approach, our results suggest that Sex-Specific Graphs (SSG) are sensitive to differential male and female dispersal dynamics of a fisher (Martes pennanti) metapopulation in southern Ontario. Our analyses based on SSG topologies supported the hypothesis of male-biased dispersal. Furthermore, we demonstrated that the effect of the landscape, identified at the population-level, could be partitioned among sex-specific strata. We found that female connectivity was negatively affected by snow depth, while being neutral for males. Our findings underlined the potential of conducting sex-specific analysis by identifying landscape elements that promotes or impedes functional connectivity of wildlife populations, which sometimes remains cryptic when studied at the population level. We propose that SSG approach would be applicable to other vagile species where differential sex-specific processes are expected to occur. Author Keywords: genetic structure, Landscape Genetics, Martes pennanti, Population Graph, sex-biased dispersal, Sex-Specific Graphs
Hybridization Dynamics between Wolves and Coyotes in Central Ontario
Eastern wolves (Canis lycaon) have hybridized extensively with coyotes (C. latrans) and gray wolves (C. lupus) and are listed as a `species of special concern' in Canada. Previous studies have not linked genetic analysis with field data to investigate the mechanisms underlying Canis hybridization. Accordingly, I studied genetics, morphology, mortality, and behavior of wolves, coyotes, and hybrids in and adjacent to Algonquin Provincial Park (APP), Ontario. I documented 3 genetically distinct Canis types within the APP region that also differed morphologically, corresponding to putative gray wolves, eastern wolves, and coyotes. I also documented a substantial number of hybrids (36%) that exhibited intermediate morphology relative to parental types. I found that individuals with greater wolf ancestry occupied areas of higher moose density and fewer roads. Next, I studied intrinsic and extrinsic factors influencing survival and cause-specific mortality of canids in the hybrid zone. I found that survival was poor and harvest mortality was high for eastern wolves in areas adjacent to APP compared with other sympatric Canis types outside of APP and eastern wolves within APP. Contrary to previous studies of wolves and coyotes elsewhere, I hypothesized that all Canis types exhibit a high degree of spatial segregation in the Ontario hybrid zone. My hypothesis was supported as home range overlap and shared space use between neighboring Canis packs of all ancestry classes were low. Territoriality among Canis may increase the likelihood of eastern wolves joining coyote and hybrid packs and exacerbate hybridization. Canids outside APP modified their use of roads between night and day strongly at high road densities (selecting roads more at night), whereas they responded weakly at lower road densities (generally no selection). Individuals that survived exhibited a highly significant relationship between the difference in their night and day selection of roads and availability of roads, whereas those that died showed a weaker, non-significant response. My results suggest that canids in the unprotected landscape outside APP must balance trade-offs between exploiting benefits associated with secondary roads while mitigating risk of human-caused mortality. Overall, my results suggest that the distinct eastern wolf population of APP is unlikely to expand numerically and/or geographically under current environmental conditions and management regulations. If expansion of the APP eastern wolf population (numerically and in terms of its geographic distribution) is a conservation priority for Canada and Ontario, additional harvest protection in areas outside of APP may be required. If additional harvest protection is enacted, a detailed study within the new areas of protection would be important to document specific effects on eastern wolf population growth. Author Keywords: Canis, coyotes, eastern wolves, hybridization, resource selection, survival
Constraints on phenotypic plasticity in response to predation risk
Inducible defenses are plastic responses by an organism to the perception of predation risk. This dissertation focuses on three experiments designed to test the hypothesis that plastic ability is limited by energetic constraints. Chapter 1 provides a general introduction to phenotypic plasticity research and the theoretical costs and limitations affecting the expression of plastic traits. In Chapter 2, I tested the hypothesis that costs of early plasticity may be manifested by a reduced response to risk in later life stages. I found that amphibian embryos are able to detect and respond to larval predators, but that the energetic cost of those plastic responses are not equivalent among behavioural, growth, and morphological traits, and their expression differs between closely-related species. Chapter 3 explicitly examines the relationship between food resource availability and plasticity in response to perceived predation risk during larval development. Food-restricted tadpoles showed limited responses to predation risk; larvae at food saturation altered behaviour, development, and growth in response to predation risk. Responses to risk varied through time, suggesting ontogeny may affect the deployment of particular defensive traits. Chapter 4 examines the influence of maternal investment into propagule size on the magnitude of the plastic responses to predation risk in resulting offspring. I found that females in better body condition laid larger eggs and that these eggs, in turn, hatched into larvae that showed greater morphological plasticity in response to predation risk. Maternal investment can therefore affect the ability of offspring to mount morphological defenses to predation risk. Last, Chapter 5 provides a synthesis of my research findings, identifying specific factors constraining the plastic responses of prey to perceived predation risk. Overall, I found constraints on plastic responses imposed by the current environment experienced by the organism (resource availability), the prior experience of the organism (predator cues in the embryonic environment), and even the condition of the previous generation (maternal body condition and reproductive investment). Together, these findings both provide new knowledge and create novel research questions regarding constraints limiting phenotypic variation in natural populations. Author Keywords: behaviour, inducible defense, Lithobates pipiens, morphometrics, phenotypic plasticity, predation risk
Habitat Preferences and Feeding Ecology of Blackfin Cisco (Coregonus nigripinnis) in Northern Algonquin Provincial Park
Blackfin Cisco (Coregonus nigripinnis), a deepwater cisco species once endemic to the Laurentian Great Lakes, was discovered in Algonquin Provincial Park in four lakes situated within a drainage outflow of glacial Lake Algonquin. Blackfin habitat preference was examined by analyzing which covariates best described their depth distribution using hurdle models in a multi-model approach. Although depth best described their distribution, the nearly isothermal hypolimnion in which Blackfin reside indicated a preference for cold-water habitat. Feeding structure differentiation separated Blackfin from other coregonines, with Blackfin possessing the most numerous (50-66) gill rakers, and, via allometric regression, the longest gill rakers and lower gill arches. Selection for feeding efficiency may be a result of Mysis diluviana affecting planktonic size structure in lakes containing Blackfin Cisco, an effect also discovered in Lake Whitefish (Coregonus clupeaformis). This thesis provides insight into the habitat preferences and feeding ecology of Blackfin and provides a basis for future study. Author Keywords: allometric regression, blackfin cisco, habitat, hurdle models, lake whitefish, mysis
Stoichiometric food quality affects responses of Daphnia to predator-derived chemical cues
While both resource quality and predator-derived chemical cues can each have profound effects on zooplankton populations and their function in ecosystems, the strength and nature of their interactive effects remain unclear. We conducted laboratory experiments to evaluate how stoichiometric food quality (i.e., algal carbon (C):phosphorus (P) ratios) affects responses of the water flea, Daphnia pulicaria, to predator-derived chemical cues. We compared growth rates, body elemental content, metabolic rates, life history shifts, and survival of differentially P-nourished Daphnia in the presence and absence of chemical cues derived from fish predators. We found effects of predator cues and/or stoichiometric food quality on all measured traits of Daphnia. Exposure to fish cues led to reduced growth and increased metabolic rates, but had little effect on the elemental content of Daphnia. Elevated algal C:P ratios reduced growth and body %P, increased respiration, and increased body %C. Most of the effects of predator cues and algal C:P ratios of Daphnia were non-interactive. In contrast, the declines in daphnid survival and related population growth rates that arose because of poor food quality were amplified in the presence of predator-derived cues. Our results demonstrate that stoichiometric food quality interacts with anti-predator responses of Daphnia, but these effects are trait-dependent and appear connected to animal life-history evolution. Author Keywords: Daphnia, ecological stoichiometry, indirect predator effects, life history, phosphorus, predator-prey relationships

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Graduate student theses produced at Trent University. You may also browse theses and dissertations by year, program, or author.

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