Environmental science

The Wabigoon River is known for an historic mercury (Hg) pollution source, caused by a chlor-alkali facility operating in the 1960s. As legacy Hg contamination continues to cause serious adverse health effects to the local communities living in the Wabigoon River region, it is imperative to undertake additional research to understand the deposition and transport of historical mercury in this system and more importantly, its conversion into methylmercury (MMHg) which renders it bioavailable for ongoing bioaccumulation. The aim of this dissertation was to evaluate the transport and accumulation of Hg species by doing a spatial and temporal analysis of concentrations of mercury and methylmercury along the Wabigoon River, as well as assessing rates of methylation and demethylation, identifying areas of higher methylmercury production. Results show that locations downstream from the pollution source still show elevated mercury concentrations, with levels at least five times higher in water and up to 134 times higher in sediments compared to background levels. Among selected study sites, the Hydroelectric dam, the Wabigoon Rapids wetland and Clay Lake were identified to have high capacity for methylmercury production in the system, with notably Clay Lake presenting a higher potential for methylmercury accumulation due to the observed lower methylmercury demethylation rate. Furthermore, the impact of wetting and drying cycles on Hg methylation in riverbed and wetland locations within the Wabigoon River system was investigated through a laboratory simulation. Findings indicated increased susceptibility of riverbed locations to wetting and drying cycles.

Author Keywords: Demethylation, Mercury, Methylation, Methylmercury, Wabigoon River

A meta-analysis revealed that while there is often a greater degree of contamination of soils and sediments with metals, contamination by mercury (Hg) is a large concern owing to its toxicity at low concentrations. The case study in Guyana characterized Hg and concentrations of other metals (As, Cd, Co, Cu, Mn, Ni, Pb, and Zn) in soil and sediment within gold mined areas. Metal concentrations were low in soil and sediment of sampled gold mines, while the concentrations of Hg were much higher in soil and sediment and contamination was not localized to the mine site. Moss bags and Hg passive air samplers (MerPAS) were deployed to measure atmospheric Hg around a gold mine in Mahdia, Guyana over a 90-day period as well as a 2-day period that encompassed a periodic burn (typically 2-hr). Mercury in moss and MerPAS were positively correlated over both deployment periods, but Hg concentrations measured during the 2-day event were several-fold higher in both moss and MerPAS compared with the 90-day exposure demonstrating that most of the Hg sorbed to both moss and passive samplers is lost during periods of inactivity. Using the 2-day deployment as a conservative estimate of atmospheric Hg exposure, Hg air concentrations around the burning station exceeded 100,000 ng m-3 averaged over a 48-hr period, and moss Hg concentrations were greater than 250,000 ng g-1 around the burning station, although Hg concentrations in both media decreased rapidly with distance. Mercury concentration in soil and sediment was strongly related to organic matter content, which tended to be higher away from the mine site. These controls of organic matter (carbon; C) cycling on Hg distribution and movement are clear at sites exposed to high atmospheric Hg and exist at the global scale, although Hg:C ratios in environmental media are greatly elevated at the gold mine site compared with the global average. Locally sourced biochar did not sufficiently improve physical properties (porosity) in overburden soil, which showed the worse plant response, possibly due to the high clay content that contributes to the "baked" condition of these soils and restrict root growth.

Author Keywords: Biochar, Environmental contamination, Gold mining, Mercury, Metals, Organic matter

Eutrophication is an ongoing global problem and agriculture is an important non-point source of nutrient loading. Specifically, nitrogen (N) and phosphorus (P) losses from agricultural landscapes continue to drive water quality issues. In southern Ontario, agriculture has intensified in recent decades, with major expansions of cash crop production and extensive tile drainage (TD). Through intensive monitoring of 12 tile outlets draining operational fields under the conventional corn-soybean-wheat rotation, this study examined differences in measured and volume-weighted total P, total N, and nitrate-N concentrations and loads over 28 months (October 2020- April 2023) amongst crop covers and between growing (GS; May – September) and non-growing seasons (NGS; October – April). Nitrogen concentrations (i.e., TN and NO3-N) in TD eluent were consistently high both between seasons and were found to be significantly highest from winter wheat (WW) fields in the NGS, and corn fields in the GS. Volume-weighted TP concentrations were not significantly different either amongst crop covers or between seasons, although TP losses tended to be highest from the cover crop (CC) fields in the NGS. Differences in N and P losses between years and amongst crop covers were attributed to differences in legacy soil nutrients, the establishment and decomposition of over-winter cover crops, and physical soil properties. The results of this study can inform agricultural management by addressing the urgent need for improved information around the relationship between agricultural practices and nutrient losses, especially in the NGS.

Author Keywords: Best management practices, Crop rotation, Over-winter cover crops, Seasonality, Tile drainage, Water quality

Climate-driven permafrost thaw releases microorganisms and dissolved organic matter (DOM) into northern lakes, where their interactions with microbial communities and seasonal processes shape greenhouse gas emissions. In a factorial experiment mixing DOM and microbes from thermokarst ponds and lakes, we found that both DOM and microbial identity strongly influenced degradation. Lake microbes preferentially consumed thermokarst DOM, producing 3× more CO₂ due to low growth efficiency, while thermokarst microbes altered DOM with little CO₂ release. A survey of 40 lakes across a climate gradient showed CO₂ fluxes peaking in spring from under-ice buildup and CH₄ fluxes peaking in fall after summer accumulation. Dissolved gas concentrations served as early indicators of these events, with CH₄ linked to reduced DOM and CO₂ to multiple pathways. Overall, DOM quality, microbial traits, and seasonal dynamics interact to control lake carbon cycling, emphasizing the need for year-round monitoring under climate change.

Author Keywords: Dissolved Organic Matter (DOM), Fluxes, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), Greenhouse Gases (GHGs), Lakes, Thermokarst

Glyphosate burndown and tillage, followed by the cultivation of cash crops, are frequently used techniques in LUC from perennial cropping systems (PS) to annual cropping systems (AS). Agricultural LUC can result in the loss of soil nitrogen (N) via emission of nitrous oxide (N2O), a potent greenhouse gas (GHG). The purpose of this thesis is to investigate the short-term impacts of agricultural LUC from PS to AS on soil health parameters and the nitrogen (N)-cycling bacterial communities responsible for nitrification and denitrification processes that result in the emission of N2O. The study field site was in Stone Mills, Ontario and comprised of four fields: two annual cropping systems were regularly cultivated for cash crops (AS), and two perennial cropping systems had not been cultivated for cash crops for over 50 years (PS). One PS was left intact while the other PS was subjected to LUC (converted system [CS]) from PS to AS within the study period. The results of this study indicate that PS promotes soil health, as illustrated through higher soil organic matter % (2.3 ± 0.2 %), beta-glucosidase activity (0.41 ± 0.04 mmol g-1 dry soil h-1), and N-acetylglucosaminidase activity (0.18 ± 0.03 mmol g-1 dry soil h-1). The PS soils exhibited higher nitrifier (6.0  0.3 log10 copies per g dry soil) and denitrifier (nirS, nirK and nosZI: 7.8  0.05, 8.1  0.1 and 5.0  0.1 log10 copies per g dry soil, respectively) gene abundances compared to AS (amoA, nirS, nirK and nosZI: 5.7  0.1, 7.7  0.04, 7.9  0.1 and 4.8  0.1 log10 copies per g dry soil, respectively). Moreover, LUC from PS to AS deteriorated soil health parameters and significantly decreased the nosZI/16S rRNA gene ratio, leading to potential N loss through N2O emissions. A laboratory incubation study revealed that the use of N-containing fertilizer in conjunction with easily metabolized C cumulatively resulted in 64.2% increase in N2O and 42.1% increase in CO2 fluxes in AS soils compared to PS soils. The AS soils also produced 69.8% more N2O and 13.4% more CO2 when compared to CS soils. The results suggest that the availability of C and N promote R-strategists, leading to increased production of CO2 and N2O. Additionally, results also suggest that LUC mediates fluxes depending on resource availability. The findings of this research demonstrate the significance of LUC in shaping N-cycling microbial communities and GHG emissions, emphasizing the importance of transitioning towards less intensive management practices to ensure the long-term sustainability of the agri-food system.

Author Keywords: annual, denitrification, greenhouse gas, laboratory incubation, nitrification, perennial

Advanced generation/backcrossed (non-F1) hybrids can be challenging to identify when their traits are similar to those of parental taxa, F1 hybrids, or both. This is particularly evident in the North American hybrid zone involving Typha latifolia, T. angustifolia, F1 T. × glauca and non-F1 hybrids. Cattails are challenging to differentiate based on gross morphological characteristics. Microscopic characteristics in female inflorescences have not been previously studied to differentiate parental taxa from non-F1 hybrids. To investigate whether researchers can use microscopic floret and bracteole characteristics for taxonomic identification, I compared pistillate flower length, bracteole length and width, and bracteole colour among taxa. I found that floret and bracteole characteristics can be useful for identifying T. latifolia but cannot accurately differentiate T. angustifolia and F1 T. × glauca from non-F1 hybrids. Further, a flowering bias can lead to the underestimation of the frequency of T. latifolia when using floral characters to examine the relative abundance of cattail taxa.

Author Keywords: advanced-generation hybrids, backcrossed hybrids, invasive species, morphology, species identification, Typha spp.

Phosphorus is the growth-limiting nutrient in freshwater environments. Dissolved organic phosphorus (DOP) refers to phosphorus within dissolved organic matter (DOM). Much of DOP is bioavailable, but it is poorly understood due to its complexity. This thesis explores the export DOP to Lake Erie from its tributaries, by investigating its speciation and concentration seasonally through weekly sampling of two tributaries and spatially across a river to lake transect. The rivermouth was a site of rapid transition, with lower concentrations of DOP in the lake than in the river and a greater proportion of P as DOP in the lake. Phosphomonoesters and aromatic DOM were coupled in the medium-sized Grand River, but not in the Upper Great Lakes-influenced Detroit River. Phosphodiesters and highly processed DOM were coupled in the Detroit River, but only during periods of low terrestrial inputs. Finally, we found that DOP is a large contributor to tributary phosphorus exports.

Author Keywords: dissolved organic matter, dissolved organic phosphorus, enzymatic hydrolysis, Lake Erie, nutrient export, rivermouth

Rare earth elements (REEs) are in high demand globally for the green transition and high technologies. The growing demand leads to their release into aquatic ecosystems from various point and non-point sources, which creates urgency to investigate their fate and enrichment. This thesis further investigates the biogeochemical fate and REE uptake mechanisms throughout aquatic ecosystems. Rare earth element concentrations and fractionations were quantified to determine the natural uptake mechanism of three REE exposure pathways (dissolved, diet, and particulate) into aquatic organisms. Pelagic organisms accumulated heavy REEs, indicating they primarily uptake dissolved REEs. Benthic organisms were characterized by REE patterns specific for diet and particulate REEs. Furthermore, lanthanum (La) enrichment was investigated in a lake treated with La-based coagulants using La anomalies. Lanthanum enrichment in the water and organisms were directly related to La dispersion from sediments. This research provides information on preferential exposure pathways and REE enrichment in aquatic ecosystems.

Author Keywords: bioaccumulation potential, fractionations, lanthanum enrichment, metal organotropism, rare earth elements, uptake mechanisms

Acid mine drainage (AMD) and metal-contaminated tailings represent some of the most inhospitable aquatic environments on Earth, characterized by low pH, elevated metal concentrations, and chronic carbon limitation. Yet these systems support microbial consortia with remarkable resilience. Among the most conspicuous inhabitants is Euglena mutabilis, an acidophilic protist traditionally regarded as an indicator species of AMD but seldom thoroughly investigated. This thesis reframes E. mutabilis at the center of a fungal-algal-bacterial (FAB) consortium, demonstrating that its cadmium tolerance and persistence are emergent properties of the consortium.

Culture-based experiments revealed that E. mutabilis survival under cadmium stress declined when fungal and bacterial partners were disrupted, underscoring their indispensability. Glucose supplementation revealed the consortium's capacity for structural and metabolic reorganization: fungal hyphae bound algal cells into flocs, bacterial associates proliferated, and hormone production shifted. Hormone profiling suggested a distributed signaling system in which fungi contributed cytokinins (CKs) and gibberellins while algae produced methyl-thiolated CKs, jasmonic acid, and salicylic acid. Transmission electron microscopy revealed bacterial-like inclusions within algal vacuoles, suggesting facultative endosymbiosis or phagotrophic retention. Transcriptomic analyses revealed that cadmium stress suppresses light-harvesting complexes and growth-promoting hormone biosynthesis while activating metal transporters and chloroplast sequestration mechanisms.

Beyond stress physiology, the FAB consortium unlocked chemical diversity inaccessible to axenic cultures. Molecular networking revealed that environmental consortia consistently produced unique metabolite families, often linked to silent biosynthetic pathways. Metagenomic sequencing linked these products to bacterial gene clusters further supporting the view that metabolic innovation is an emergent property of the collective.

Together, these findings suggest that the FAB consortium should be understood not as a loose association but as a microbial superorganism. This framing extends beyond the holobiont concept by dissolving the hierarchy between host and symbiont: E. mutabilis, fungi, and bacteria are all indispensable, and the identity of the host itself becomes blurred.

By reframing E. mutabilis as the nucleus of a microbial superorganism, this work highlights both theoretical and applied significance. It advances ecological understanding of how life persists under geochemical extremes, while pointing to new opportunities for sustainable bioremediation and natural product discovery through the deliberate cultivation of naturally evolved microbial consortia.

Author Keywords: Algal symbiosis, Bioremediation, Co-culture, Hormones, Microscopy, Transcrioptomics

Wetlands are highly susceptible to the invasion of invasive species. The invasive hybrid cattail (Typha × glauca) is prevalent in the southeastern Prairie Pothole Region (PPR) wetlands. However, concerns arise about its recent proliferation in the northwestern PPR without maternal T. angustifolia. To determine taxonomic distribution, I used species-specific PCR-RFLP and microsatellite markers for genotyping 245 samples from 50 northwest PPR sites. I found 75% T. latifolia, 7% T. angustifolia, 16% T. × glauca, and 2% backcrossed or advanced-generation hybrids. F1 T. × glauca has expanded in western PPR without its mother species, and the low occurrence of later-generation hybrids indicates their recent range expansion. Additionally, T. angustifolia offspring make fewer hybrids, which suggests that reproductive barriers may limit hybridization between parental species. This study highlights the vulnerability of prairies to cryptic invasions by Typha hybrids, and early detection of invasive species is a critical factor in wetland management success.