Environmental science

Due to their effective antibacterial and antifungal properties, silver nanoparticles (AgNPs) have quickly become the most commonly used nanomaterial, with applications in industry, medicine and consumer products. This increased use of AgNPs over the past decade will inevitably result in an elevated release of nanoparticles into the environment, highlighting the importance of assessing the environmental impacts of these nanomaterials on aquatic ecosystems. Although numerous laboratory studies have already reported on the negative effects of AgNPs to freshwater organisms, only a handful of studies have investigated the impacts of environmentally relevant levels of AgNPs on whole communities under natural conditions. This thesis examines the effects of chronic AgNP exposure on natural freshwater littoral microcrustacean, benthic macroinvertebrate and pelagic zooplankton communities. To assess the responses of these communities to AgNPs, I focused on a solely field-based approach, combining a six-week mesocosm study with a three-year whole lake experiment at the IISD – Experimental Lakes Area (Ontario, Canada). Our mesocosm study tested the effects of AgNP concentration (low, medium and high dose), surface coating (citrate- and polyvinylpyrrolidone [PVP]-coated AgNPs), and type of exposure (chronic and pulsed addition) on benthic macroinvertebrates in fine and stony sediments. Relative abundances of metal-tolerant Chironomidae in fine sediments were highest in high dose PVP-AgNP treatments; however, no negative effects of AgNP exposure were seen on biodiversity metrics or overall community structure throughout the study. I observed similar results within the whole lake study that incorporated a long-term addition of low levels of AgNPs to an experimental lake. Mixed-effects models and multivariate methods revealed a decline in all species of the littoral microcrustacean family Chydoridae in the final year of the study within our experimental lake, suggesting that this taxon may be sensitive to AgNP exposure; however, these effects were fairly subtle and were not reflected in the overall composition of littoral communities. No other negative effects of AgNPs were observed on the pelagic zooplankton or benthic macroinvertebrate communities. My results demonstrate that environmentally relevant levels of AgNPs have little impact on natural freshwater microcrustacean and benthic macroinvertebrate communities. Instead, biodiversity metrics and community structure are primarily influenced by seasonal dynamics and nutrient concentrations across both lakes. This thesis highlights the importance of incorporating environmental conditions and the natural variability of communities when examining the potential risks posed by the release of AgNPs into the environment, as simplistic laboratory bioassays may not provide an adequate assessment of the long-term impacts of AgNPs on freshwater systems.

Author Keywords: Benthic macroinvertebrates, IISD - Experimental Lakes Area, Littoral microcrustaceans, Silver nanoparticles, Whole lake experiment, Zooplankton

Thawing permafrost due to increasingly warm temperatures in northern subarctic regions is releasing mercury. The consequent formation of thaw ponds in the peatland palsa valley of the Sasapimakwananisikw (SAS) river in Whapmagoostui-Kuujjuarapik, Québec may provide a pool for MMHg formation and a potential risk to aquatic and human life, if these ponds facilitate MMHg export through hydrological connections to nearby waterways. Hg methylation and MMHg demethylation activities were examined in thaw pond sediments using a Hg tracer isotope incubation experiment. Analysis by coupling gas chromatography cold-vapor atomic fluorescence spectrophotometry (GC-CVAFS) with inductively coupled mass spectrometry (ICP-MS) techniques showed that MMHg was produced at a higher rate and within the first 2 h of incubation for both summer and winter seasons. For thaw ponds SAS1A, SAS1B and SAS2A, MMHg was formed at 0.0048 % h-1, 0.0012 % h-1, and 0.0008 % h-1, respectively during winter and at 0.0001 % h-1, 0.0016 % h-1, and 0.0010 % h-1, respectively during summer. Detection of MMHg losses were not as expected likely due to limitations of the combined tracer spike and overestimation of the in situ ambient mercury levels. Physical and chemical properties vary within ponds, among ponds and between winter and summer. SAS1B's location nearby an organic carbon rich palsa may be ideal to study DOC – Hg interactions. Variability in pond characteristics including depth, surface area, age, pH, temperature, colour, oxygen concentration, total dissolved and suspended solids, conductivity, carbon, mercury, ammonium, calcium, magnesium, sulfate, total phosphorous, potassium, and sodium between seasons indicate the challenge of predicting future environmental impacts of climate change related thaw pond creation in the north.

Author Keywords: demethylation, mercury, methylation, methylmercury, SAS, thaw ponds

In the Wabigoon/English River system, mercury concentrations downstream from Dryden, ON, where there was a former chlor-alkali plant, remain elevated in sediments and biota. Understanding the current extent and severity of mercury contamination downstream from the former chlor-alkali plant is of great interest in furthering the clean-up of mercury within the traditional territory of Asubpeeschoseewagong Netum (Grassy Narrows) First Nation. The objective of this study was to evaluate the current level and extent of mercury contamination within sediments, crayfish, Hexagenia mayflies, yellow perch, spottail shiner and walleye in the Wabigoon/English River system. An additional objective was to use mercury stable isotope analysis to distinguish between legacy mercury from the former chlor-alkali plant and mercury from geogenic sources. Mercury contamination within surface sediments and biota at locations as far as 178 kms downstream of the historical source of mercury contamination are elevated relative to the reference lake, Wabigoon Lake. Isotope ratios in young of the year fish and sediments collected from within the system were distinct from fish from the reference lake, Wabigoon Lake, indicating that anthropogenic mercury contamination is distinguishable from geogenic mercury.

Warming climates have had various consequences on terrestrial and aquatic food webs that are expected to persist. There is evidence suggesting that certain organisms are better equipped to handle changing climates compared to others. Therefore, the purpose of my thesis was to study the adaptability of Daphnia under temperature stress and nutrient limitation. First, to examine the effects of dietary phosphorus limitation and temperature on daphniid life-history and population growth, a series of experiments were conducted in the laboratory. In general, I found that Daphnia body growth rates and life-history traits to food carbon to phosphorus (C:P) ratios change with temperature. Next, I identified a protocol to limit the genomic DNA (gDNA) from ribonucleic acid (RNA) extractions. I found that using a modified phenol-chloroform extraction protocol was the most effective way to remove gDNA from extracted Daphnia RNA samples. Overall, results from this study show that temperature and food quality interactions are more complicated than previously thought. Furthermore, the RNA extraction protocol developed will be useful in future studies examining gene expression responses in Daphnia.

Author Keywords: ecological stoichiometry, gene expression, life-history, nutrient limitation, RNA puritiy, temperature

Microcontaminants originating from wastewater effluent and run-off from agricultural lands may be present in the sources of drinking water for rural and Indigenous communities in mixed-use watersheds. In this study, a convergent parallel mixed-methods design was applied to assess measured and perceived risks of contamination in the sources of drinking water for two communities; the Six Nations of the Grand River community in Ontario and the community of Soufriere in St. Lucia, West Indies. The overall goal of the project was to assess how measured and perceived risks of exposure to chemical and biological contaminants in drinking water sources could inform water management strategies for the communities. Quantitative data obtained from the analysis of water samples collected indicated that the highest levels and occurrence of fecal bacteria were found in the Soufriere watershed while the highest concentrations and occurrence of pesticides were found in the Grand River watershed. In the Grand River watershed, conventional treatment of water followed by activated carbon filtration and UV disinfection removed fecal bacteria and also removed many chemical microcontaminants with efficiencies as high as 98%. Data from both watersheds indicated that there was a strong positive correlation between the levels of caffeine and sucralose (i.e. indicators of wastewater contamination) in water samples and the levels of either Total Coliforms or fecal bacteria of human origin. Human health risk assessments of individual pesticides and pesticide mixtures performed by applying a hazard quotient (HQ) and hazard index (HI) model, respectively indicated that there were no apparent risks to human health from those microcontaminants. Qualitative data obtained from face-to-face interviews with water managers and health professionals working in the two communities, which were collected and analysed concurrently but independently, illustrated that there were cross-cultural similarities and differences in factors influencing the perceptions of risks associated with the sources of drinking water. These perceptions of risks were mainly influenced by factors such as heuristics or informal and informal reasoning, cognitive-affective factors, social-political institutions and cultural factors. These factors may have also influenced water managers and health professionals, as they often recommended more "soft" strategies for managing water resources in the communities.

Key words: pesticides, fecal bacteria, microcontaminants, POCIS, measured risks, perceived risks, water management, First Nations, Grand River, Soufriere, St. Lucia

Author Keywords: fecal bacteria, measured risks, microcontaminants, perceived risks, POCIS, water management

This study examined dissolved organic matter (DOM) and labile Mercury (from diffusive gradient in thin films (DGT)) in the Quesnel river, British and the Goose creek tributary of the Churchill river, Manitoba. DOM properties were measured with optical measurements of absorption coefficient (a254), spectral slopes (S275-295, SR) and fluorescence indices (HIX, BIX, FI). The DOC proxy measurements (a254) were almost 10 times higher at the Churchill site (Mean a254 116.77 cm-1) compared with the Quesnel river site (Mean a254 12.06 cm-1) during the study periods. While DGT labile Hg concentrations at the Quesnel site (2.17 to 98.97ppt) were almost 10 times more than the levels reported at the Churchill site (0.03 to 9.06 ppt). Fluorescence indices and the rise of labile Hg concentrations in spring indicated mostly terrestrial sources of DOM at both the sites. Spectral slopes and fluorescence indices substantiated that Churchill site had high molecular weight, complex and more humic DOM compared with Quesnel. DOM at both the sites was prone to temporal variation and affected by environmental conditions. Correlation between DGT labile-Hg and DOM parameters suggested that DGT collected Hg-organic complexes along with inorganic labile-Hg complexes.

Author Keywords: Churchill, Diffusive gradient in thin films, Dissolved organic matter, Labile Hg, Mercury, Quesnel

As wild turkeys (Meleagris gallopavo silvestris) move farther north, informed management decisions are critical to support the sustainability of this reintroduced species. We tracked roost tree selection and patterns of the network of roost trees, for wild turkeys, over 2 years in Peterborough, ON, using GPS and VHF transmitters. Wild turkeys showed preference for taller and larger roost trees, with winter roosts closer to buildings. The roost network exhibited a scale-free network, meaning certain roosts served as hubs, while other roosts were less frequently used. The fine scale results suggest that roost trees are selected for predator avoidance, and that selection changes with the season, probably because of its influence on foraging ability. At a larger scale, winter roosts were chosen for their proximity to supplemental food sources. These findings demonstrate the dependence of wild turkeys on humans and the supplemental sources we unintentionally provide.

Currently, UAVs are deployed to measure crop health in a timely manner by mapping vegetation indices. A study using two different fields was conducted in order to search for a relationship that may exist between crop health and soil fertility. A UAV equipped with sensor technology was used for mapping of vegetation indices which were then statistically compared to soil nutrient data collected via soil sampling. Elevation data was also collected which was then statistically compared to soil nutrients as well as crop health. Results of this study were unfortunately impacted by variables outside of the researcher's control. Moisture became the greatest limiting factor in 2016 followed by an excess of rain in 2017. Results did not show any promising correlations as moisture uncontrollably became the defining variable. Further research in a more controlled setting will need to be conducted in order to explore this potential relationship.

Author Keywords: Agriculture, Multispectral Imagery, Precision Agriculture, Proximal Soil Sensing, Remote Sensing, Unmanned Aerial Vehicle

Anthropogenic atmospheric emissions and subsequent deposition of nitrogen (N) can affect N-sensitive habitats and lead to shifts in plant species community composition. This study assessed the effects of N deposition on plant community composition for Jack pine forests across northwestern Canada and across a smaller subset of sites surrounding the Athabasca Oil Sands Region (AOSR) using 'gradient forest' analysis. Predictor influence on community composition varied depending on the scale of the study and relatively

distinct thresholds were identified for different plant groups. In the larger scale study, a total deposited nitrogen (TDN) threshold of 1.5 – 3 kg N ha-1yr-1 was well suited to protect predominantly lichen species, consistent with lichen-based critical loads from other studies. Across the smaller scale study, a TDN threshold of 5.6 kg N ha-1yr-1 was primarily associated with vascular species changepoints but did include some important N-indicator lichen and bryophyte species.

Author Keywords: critical loads, gradientForest, Jack pine, Nitrogen deposition, species composition

Environmental monitoring and investigation of metal biogeochemical cycling has been

carried out in the Pearl River Estuary (PRE), an important and complex system in Southern

China. In this study, rare earth element (REE) patterns as well as isotope ratios (i.e., Zn and Cd)

were evaluated as tools to identify contamination sources in environmental compartments (i.e.,

water and suspended particles (SP)) as well as in oysters collected from estuarine sites. Results

show elevated concentrations (also called anomalies) of Pr, Nd, Dy and Ho, relative to other

REE elements, in water samples, potentially from REE recycling and other industrialized

activities in this area. Unlike water samples, no REE anomalies were found in SP or oysters,

suggesting that the dominate REE uptake pathway in oysters is from particles. Secondly, site to

site variations in Zn isotope ratios were found in water and SP, showing the complexity of the

source inputs in this area. Also, in estuarine locations, larger spatially differences in Zn isotope

ratios were found in water collected in wet season than those in dry season, which may due to

mixing of different source inputs under the water circulations in different seasons.

A series of laboratory experiments were conducted during which changes in Zn isotope

ratios were measured during uptake under varying salinity and Zn concentrations and during

depuration. Neither in vivo Zn transportation among the various tissues within the oysters nor

water exposure conditions (i.e., different salinities or Zn concentrations) caused Zn isotopic

fractionation in the oysters.

Cd and Zn isotope ratios were also determined in oysters obtained from the PRE. Large variations in Cd and Zn isotope ratios suggest that oysters were receiving contaminants from different input sources within the PRE. A consistent difference (approximately 0.67‰) was observed for Zn isotope ratios in oysters collected from the east side of the PRE compared to those from sampling locations on the western side of the PRE, suggesting different Zn sources in these two areas. Ultimately, by combining biogeochemistry with physiology, this study represents a first attempt to assess pollution status, monitor contaminants using oysters and model/identify contamination sources using both REEs and metal isotope ratios.