Watmough, Shaun

Agriculture may result in soil disturbances, including contamination by rare earth elements (REE) and trace elements (TEs) from agricultural inputs (e.g. fertilizers, pesticides). Regulations concerning agricultural inputs currently do not consider TE background concentrations, concurrent use of inputs, and emerging contaminants. Therefore, they may not sufficiently protect against TE contamination, including that of REEs as emerging contaminants. The objective of this work was to assess the concentration and distribution of TEs and REEs in agricultural soil and whether agricultural management alters soil geochemistry. Fourteen farms were sampled in southeastern Ontario, and the geochemistry of soils was analysed using ICP-MS and ED-XRF. Trace element concentrations exceeded environmental safety standards in some sites, including those characterized by historical contamination or elevated background concentrations. Concentrations of REEs are reported in Ontario agricultural soils, and the normalized REE values indicated enrichment of the middle REEs. Geographic location drives site geochemistry more than agricultural management.

Author Keywords: agriculture, phosphate fertilizer, rare earth elements, soil geochemistry, trace elements

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

Increasing wildfire frequency, driven by climate change, can change the concentration andcomposition of dissolved organic matter (DOM) exported from land into receiving waters by removing terrestrial vegetation, changing soil hydrology, and interrupting microbial degradation. In this thesis, I tested how wildfire impacts the molecular composition and reactivity of DOM. I compared DOM from boreal headwater streams in northwestern Ontario, Canada between 10 catchments recently affected and 10 comparable catchments that were undisturbed for at least 20 years. Using optical spectroscopy, ultra-high-resolution mass spectrometry, and incubation experiments, I found that burned streams had 29% higher average DOM concentrations and contained less bioavailable DOM, which resulted in microbes respiring more CO2 in burned streams rather than using carbon to build biomass. These results indicate that the impacts of wildfire on carbon sequestration have been underestimated and highlight the need to consider wildfire in forest carbon budgets.

Author Keywords: boreal forest, carbon flux, dissolved organic matter, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), headwater streams, Wildfire

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

Forests play a critical role in the global carbon cycle, acting as carbon sinks that remove and store an estimated 0.4 to 4.1 Pg of atmospheric carbon annually. However, historical acid deposition and timber harvesting have disrupted nutrient cycles, leading to nutrient-deficient soils that hinder tree growth, particularly for sugar maple (Acer saccharum), a keystone species in Ontario sensitive to soil acidity and calcium (Ca) depletion. This study evaluates the effects of non-industrial wood ash (NIWA) applied at 0, 2, 4, 6, and 12 Mg ha-1 on soil chemistry, nutrient concentrations, microbial activity, CO2 fluxes, and sugar maple growth over two years. NIWA increased soil pH and exchangeable base cations, especially in the organic horizon, with some increase in forest floor metals, though foliar levels remained safe. Enzyme activity responses were minimal, and fine root biomass declined at higher doses. Soil CO₂ fluxes rose sharply at 12 Mg ha⁻¹, suggesting pH-driven effects. NIWA improves soil chemistry, but long-term impacts remain uncertain.

Author Keywords: carbon flux, extracellular soil enzyme, non-industrial wood ash, sugar maple

Mining and smelting degraded landscapes are characterised by heavily eroded soils that are acidic, contaminated with toxic metals, and depleted of essential nutrients. Regreening degraded landscapes has been proposed to support global carbon (C) mitigation measures and protect biodiversity. One of the world's largest regreening programs in the City of Greater Sudbury, Canada has been ongoing since 1978 and involves liming and fertilizing selected areas followed by planting primarily jack pine (Pinus banksiana Lamb.) and red pine (Pinus resinosa Ait.) trees. The main objective of this thesis was to improve our understanding of biogeochemistry in the City of Greater Sudbury regreened forests, and to determine how nutrient pools and cycling change as stands age. I established a chronosequence of forested sites between 15–40 years-old and to account for the effects of erosion, each site was categorized as "stable" (<10% bedrock cover) or "eroded" (>30% bedrock cover). Individual tree growth and nutrient accumulation in aboveground biomass (AGB) did not differ between stable and eroded sites and were comparable to rates reported from pine plantations in similar ecozones. Aboveground nitrogen (N) pools were six times larger than N applied in fertilizer, suggesting N limitation is most likely not a concern. Rates of C cycling were generally similar to those measured at unimpacted jack and red pine plantations. The exception being a decrease in mineral soil and aggregate C concentrations. However, at the ecosystem-scale the loss of soil C is trivial in comparison to increases in AGB C pools, leading to an overall increase in total ecosystem C following regreening (550,547 Mg in aboveground C across the 19,649 ha regreening landscape). Litter decomposition rates were higher at the regreening sites using a site-specific litter compared to a general common litter, indicating a home-field advantage for local decomposers. Soil temperature varied at the regreening sites and higher soil temperatures were related to higher rates of soil respiration. The regreening sites are rich in calcium (Ca) and magnesium (Mg); and while soils were generally poor in phosphorous (P) and potassium (K), foliar concentrations of P and K were comparable to those of "healthy" red pines. Overall, the regreening program appears to have increased tree growth and produced jack and red pine plantations that are biogeochemically similar to conifer plantations unimpacted by over a century of mining and smelting impacts.

Author Keywords: biogeochemistry, degraded landscape, forests, nutrient cycling, regreening, soil carbon

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

This research evaluates the degree to which nutrients are included in forest management planning. First, the thesis evaluates forest management plans globally to determine the extent to which countries consider key nutrients (N, P, Ca, Mg and K) in their forest management plans. This is followed by a case study in Muskoka, Ontario, of a pilot wood ash recycling program with the goal of restoring calcium and other nutrients in the forests. This pilot project aims to evaluate the benefits of using wood ash as a forest fertilizer, as evidence that the practice merits approval by the provincial government. A text-based literature analysis of current regulations and the Environmental Compliance Approval (appendix 3) submitted to the provincial government for this project was undertaken as this project is currently a not approved practice by the government. Interviews were completed with key stakeholders and experts in the field to understand the benefits and policy hurdles of this program. Based on the documents analysed in this study, it was concluded that both globally and in Canada, nutrient management is not the focus of forest management plans. With respect to the pilot wood ash program, this thesis concluded that there is not enough data published to make the government departments comfortable with approving wood ash as a soil fertilizer. Nevertheless, there is much community support and many perceived benefits to this project, but more supporting data is needed.

Author Keywords: Forest, Nutrients, Sustainability, Wood-ash

Increased mining activity in the Canadian Arctic has resulted in significant changes to the environment that may be influencing some tundra-nesting bird populations. In this thesis I examine the direct and indirect effects of mining on birds nesting in the Canadian Arctic. I first perform a literature review of the effects that mining in the Arctic has on northern environments and wildlife and outline several ways in which mines affect Arctic-breeding birds. By using the Program for Regional and International Shorebird Monitoring (PRISM) Arctic plot-based bird survey data from across the Canadian Arctic, collected from 1995 to 2018, I identify the effects of distance to mining operations on the occupancy patterns of Arctic-breeding bird species. Six species' densities were significantly impacted by mine proximity (Canada/Cackling Goose, Long-tailed Duck, Long-tailed Jaeger, Pectoral Sandpiper, Savannah Sparrow, and Rock Ptarmigan) across five major mine sites. Each species has its own unique relationship to distance from mining activity.

Author Keywords: Bird populations, Canadian Arctic, Mining, Mining activities, PRISM, Tundra-nesting birds

Row crop agriculture and associated land use practices including tile drainage and conservation tillage have been cited as a probable cause of re-emerging eutrophication in the lower Great Lakes. In this thesis, I sought to quantify and evaluate the effect of agricultural land cover and land use changes on total phosphorus (TP) and nitrate-nitrogen (NO3-N) concentrations and export in north shore Lake Ontario tributaries. This included (a) a long-term data analyses at 12 large watersheds (47 to 278 km²) using historical land cover and water quality data (1971-2010), and (b) a space-for-time study examining 12 small sub-catchments (< 8 km²) with majority (> 50%) row crop, pasture, or forest cover. Concentrations of TP were greatest in urbanized watersheds and declined particularly during the first decades of the study period, while NO3-N concentrations were greatest and steadily increased in agricultural catchments with increasing row crop cover. The space-for-time approach revealed that TP concentrations were similar across agricultural land uses and that export was most dependent on runoff. Meanwhile, NO3-N concentrations and export were greatest in row crop catchments and were positively related to row crop area. These results suggest that increases in row crop cover and associated agricultural practices including increased nutrient amendments and tile drainage may be responsible for increased NO3-N concentrations and export in northern Lake Ontario tributaries.

Author Keywords: agriculture, Lake Ontario, nitrogen, phosphorus, streams, Water quality