Earth and Environmental Sciences

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Riparian vegetation and open water carbon greenhouse gas fluxes of urban stormwater ponds
(University of Waterloo, 2026-01-20) Zhou, Yanqin
Stormwater ponds (SWPs) are a common stormwater management technology in new urban developments and have been suggested to be significant sources of the carbon greenhouse gases (GHGs); e.g., carbon dioxide (CO2) and methane (CH4). However, they also sequester organic carbon (OC) and reduce the surface runoff of nutrients, hence, altering nutrient limitation patterns, trophic conditions, and GHG exchanges. Although numerous studies have focused on estimating open water GHG emissions in artificial ponds, there are limited studies that evaluate both open water and riparian vegetation fluxes from urban SWP systems comprehensively. This study quantified CO2 and CH4 fluxes from riparian vegetation and open water in two SWPs in the City of Kitchener, Ontario, located in residential (Activa pond) and industrial (Wabanaki pond) catchments. In Chapter 2, the goal was to compare flux pathways and net source-sink status and assess how land use, spatial variability between forebay and main basin zones, and pond design influence the GHG dynamics. Using vegetation and floating chambers, CO2 and CH4 fluxes were measured bi-weekly across all seasons, capturing net ecosystem exchange (NEE), ecosystem respiration (ER), and gross primary production (GPP) from riparian vegetation, plus the diffusive and ebullitive fluxes from the open water surface. Significant differences in the fluxes between the riparian vegetation and open water surfaces were observed. High photosynthetic activity allowed the riparian zone to function as a net carbon sink (-142.3 mol m-2 yr-1 for Activa and -140.5 mol m-2 yr-1 for Wabanaki). However, higher OC inputs from the industrial Wabanaki catchment enhanced sediment CH4 production, particularly in the forebay, resulting in higher vegetation CH4 emissions that weakened its GHG-sink strength relative to the residential Activa pond., resulting in CO2-equivalent fluxes of -141.4 mol CO2-eq m-2 yr-1 for Activa and only -94.8 mol CO2-eq m-2 yr-1 for Wabanaki. Although Activa had greater per-area vegetation CO2-equivalent uptake, its small riparian zone limited whole-pond removal, whereas Wabanaki’s extensive riparian area provided larger total CO2 uptake (-3.6 mol CO2-eq m-2 yr-1 for Activa and -132.1 mol CO2-eq m-2 yr-1 for Wabanaki). Open water fluxes were dominated by ebullitive CH4, which accounted for about 88% of the total CO2-equivalent flux (125.6 mol CO2-eq m-2 yr-1 for Activa and 119.6 mol CO2-eq m-2 yr-1 for Wabanaki), making the open water surface a net GHG source. The forebay of the ponds consistently acted as carbon GHG hotspots due to higher carbon loading, nutrient enrichment, and reducing conditions, while larger, deeper main basins mitigated emissions. Overall, both Activa and Wabanaki ponds ultimately acted as net GHG sources, with annual emissions of 189.6 kmol CO2-eq yr-1 at Activa and 349.9 kmol CO2-eq yr-1 at Wabanaki, driven primarily by CH4 emissions. These findings highlight the combined influence of land-use-driven carbon loading, riparian zone extent, and the contrasting behaviour of forebays and main basins in controlling stormwater pond GHG dynamics. In Chapter 3, the full dataset collected during the study period were presented. Based on field experience, we outline practical recommendations for municipalities, including linking monitoring objectives to decision-making, applying tiered spatial and temporal sampling, quantifying flux pathways, measuring key water and sediment drivers, integrating hydrologic data, and tracking vegetation cover for upscaling. Together, these approaches create a scalable, transparent framework for incorporating SWPs into city-scale GHG monitoring and management.
The Forces Behind the Flux: Methane, Carbon Dioxide, and Nitrous Oxide Dynamics and Their Environmental Drivers in Restored Agricultural Wetlands
(University of Waterloo, 2026-01-14) Meinzinger, Shayna
Wetlands provide vital ecosystem services such as water filtration and flood mitigation but are also significant natural sources of greenhouse gases (GHGs), particularly methane (CH₄). This study examined seasonal and spatial patterns of CH₄, carbon dioxide (CO₂), and nitrous oxide (N₂O) emissions from seven restored agricultural wetlands in the Ontario portion of the Lake Erie Basin, focusing on diffusive and ebullitive flux pathways. Emissions were measured across four seasons, alongside water quality parameters used to identify key environmental drivers. Dissolved oxygen (DO) emerged as a strong driver of GHG fluxes, with lower DO concentrations consistently promoting higher CH₄, CO₂, and N₂O emissions. Duckweed cover also enhanced CH₄ production by creating anoxic conditions. GHG emissions peaked during summer months with heightened biological activity, while winter fluxes, though reduced, remained detectable, emphasizing the contribution of cold-season processes. N₂O emissions remained consistently low throughout the year. Across sites, methane emissions were generally low relative to natural temperate wetlands, except at one nutrient-enriched outlier (Site MA). Spatial variation within wetlands was minimal, suggesting that sampling from a single representative location may be sufficient for long-term monitoring. These findings show that restored agricultural wetlands can act as both carbon sinks and GHG sources depending on local biogeochemical conditions. By identifying major environmental controls on emissions, this study advances understanding of GHG dynamics in restored wetlands, informs efficient monitoring and modelling considerations, and strengthens national inventory and restoration policy development.
The Enhancement and Optimization of CO₂ Sequestration in Saline Aquifers
(University of Waterloo, 2025-12-23) Firoozmand, Hasti
Geological storage of carbon dioxide in saline aquifers is widely recognized as a key strategy for achieving long-term emission reduction. Its effectiveness depends on the accurate estimation of storage capacity and the ability to enhance and optimize that capacity through engineering design. Yet these objectives remain challenging due to geological heterogeneity, limited subsurface data, and the need to manage reservoir pressure within safe operational limits. Reliable evaluation therefore requires methods that integrate geological characterization with pressure behavior and injectivity constraints while also identifying strategies that expand storage potential without compromising formation integrity. This thesis develops an integrated framework for evaluating, enhancing, and optimizing CO₂ storage in saline aquifers through a combination of conceptual, analytical, and numerical methods. The research begins by developing a systematic approach for generating credible CO₂ storage estimates that progress from regional-scale capacity to scenario-specific storage potential under any level of data availability. Existing estimation techniques are organized into a six-tier framework that connects static, analytical, and numerical methods within a single adaptive workflow. Designed as a practical decision-support tool, the framework guides users in selecting appropriate methods, inputs, and model complexity based on available geological and operational data. This structure enables early-stage screening and iterative refinement as more detailed geological and operational information becomes available. Application to the Nisku Formation in Alberta (Canada) validated the methodology and confirmed that pressure-constrained, uncertainty-aware estimates can be obtained from limited data and progressively refined toward realistic operational outcomes. Building on this foundation, an analytical optimization model was developed to extend analytical methods to coupled injection and brine production, allowing direct technical and economic assessment of storage enhancement through pressure relief. The model incorporates transient pressure behavior and economic parameters to evaluate how well spacing, the number of wells, the production-to-injection ratio, and carbon revenue together influence storage capacity and project net revenue. Since the interaction among these parameters is complex, the model serves as a rapid diagnostic tool for understanding their combined effects and for testing different design configurations under varying geological and economic conditions. Validation against numerical simulations for both multi-well injection and brine-production scenarios confirmed that the model provides a fast and reliable means of screening and comparing sequestration project designs. The thesis next evaluates horizontal injection as another means of enhancing CO₂ storage efficiency in saline aquifers. Numerical simulations were performed to examine how horizontal wells influence pressure distribution, plume evolution, and overall injectivity across different geological and design conditions. Results show that longer horizontal wells improve lateral CO₂ distribution, reduce near-wellbore pressure buildup, and delay plume contact with the caprock, thereby increasing effective storage capacity. However, the gains in capacity and pressure control diminish beyond a certain lateral length, indicating an economic threshold for well extension. Simulation results also indicate that formation permeability, anisotropy, and thickness strongly influence the magnitude of achievable improvement over vertical wells, with the most significant gains occurring in low-permeability and thin aquifers These findings provide practical guidance for optimizing well design to achieve efficient and stable storage performance. Finally, the tools and insights developed in this research were applied to the Cambrian Formation in Southwestern Ontario (Canada), a regionally extensive but data-scarce potential storage target near major emission sources. The framework structured the workflow for estimating capacity under data limitations, while the optimization and enhancement studies informed the treatment of injectivity and pressure constraints. The analysis progresses from formation-scale capacity estimation to single-well performance evaluation and the application of enhancement strategies, providing a clear understanding of both inherent and improved storage potential. Results indicate an effective regional capacity of about 0.6–1.1 Gt of CO₂, limited by pressure tolerance and a single-well storage potential below 0.5 Mt per year. Incorporating optimized horizontal wells and controlled brine production shows that these strategies can be highly effective in this region, where single-well performance remains below established industrial benchmarks. Together, these contributions provide an integrated pathway for the evaluation, enhancement, and optimization of CO₂ storage in saline aquifers. The research bridges theoretical estimation and practical implementation, offering defensible capacity ranges, efficient design-screening tools, and clear strategies for managing pressure and injectivity in support of secure, large-scale geological storage deployment.
Challenges and Opportunities for Sustainable Nitrogen Management in Dairy Systems
(University of Waterloo, 2025-12-19) Lakhanpal, Garima
Nitrogen (N) is central to agricultural productivity, yet its mismanagement drives water and air pollution across the world. Ireland’s grass-based dairy systems are among the most N-intensive in the European Union (EU), with high inorganic and organic fertilizer sustaining productivity but creating persistent surpluses that threaten groundwater and surface water quality. Despite major policy efforts, Ireland continues to struggle to meet EU Water Framework Directive (WFD) chemical targets for good water status. However, Ireland is still seeking the renewal of its Nitrates Derogation, which allows exceptionally high stocking rates up to 220 kg N ha⁻¹ yr⁻¹. This tension between economic needs and environmental compliance defines one of the country’s greatest agri-environmental challenges. The EU is moving toward tighter nutrient limits and nature restoration objectives, making it essential to understand whether sustainable dairy production can coexist with future regulatory expectations. One of the main obstacles to achieving water-quality goals is the temporal disconnect between management interventions and measurable improvements, which can erode stakeholder confidence and obscure the true impact of mitigation policies. In Ireland, the EU WFD program of measures (PoMs) is carried out under the Nitrates Directive, which include nutrient management, land management and farmyard management strategies to protect water quality. These lags are increasingly attributed to legacy N i.e., reactive N accumulated in soils and subsoils from past surpluses that continue to leach long after inputs decline. While groundwater legacy effects are recognized (i.e., the time it takes water to travel through the soil termed hydrologic time lag), few studies worldwide have directly quantified soil legacy N (i.e., biogeochemical time lags), and none had done so in Ireland prior to this research. Understanding the scale, distribution, and persistence of these soil pools is critical for designing realistic mitigation timelines and adaptive policies. The overarching aim of my research was therefore to assess N dynamics and environmental outcomes in Irish dairy systems by evaluating mitigation scenarios and quantifying legacy soil N accumulation to understand how current and historical management, drainage class, and hydrogeological setting influence both near-term losses and the pace of environmental recovery. I combined process-based modelling, multi-decadal farm data, deep soil coring, and groundwater monitoring to connect farm management decisions with both short- and long-term system responses. Together, these studies form the first integrated assessment of soil N legacies in Irish dairy systems. In Chapter 2, I used the €riN-MDSM model to simulate N flows, surpluses, and losses in a well-drained dairy farm operating under derogation conditions. This model, developed to represent N cycling in Irish grass-based systems, quantifies losses of nitrate (NO₃⁻), ammonia (NH₃), nitrous oxide (N₂O), and dinitrogen (N₂) from urine, dung, slurry, dairy soiled water, and fertilizer. I simulated a range of management scenarios, including reduced inorganic N rates (200–225 kg N ha⁻¹) and organic rates (170–430 kg N ha⁻¹), substitution of calcium ammonium nitrate (CAN) with protected urea, and restrictive grazing during vulnerable winter–spring months. Results showed that integrated approaches combining restrictive grazing, protected urea, and reduced fertilizer inputs lowered NO₃⁻ leaching by up to 44 % and NH₃ volatilization by 31 %, bringing water losses close to the 30 kg N ha⁻¹ threshold for good groundwater quality. These findings demonstrated that substantial environmental gains are possible through system-level optimization, but that even under improved management, N surpluses remain high, implying persistent risks to water and air quality. This modelling work provided a critical benchmark for assessing what levels of mitigation might be achievable within the derogation framework and highlighted the need to understand how historical surpluses continue to affect recovery, setting the stage for the legacy N analyses that followed in the next phase of this research study. In Chapter 3, I conducted a 24-year investigation (2001–2024) at Moorepark Teagasc Research Farm (known as Curtins Research Farm locally) in southern Ireland, a well-drained, karstic site with low denitrification potential. I reconstructed multi-decadal N budgets from detailed farm records and collected 75 soil cores across 15 paddocks, 1m deep profiles representing a gradient of historical management intensity. Annual N surpluses frequently exceeded 200 kg N ha⁻¹ yr⁻¹, leading to cumulative soil N accumulation of 4,000–5,500 kg N ha⁻¹ in the top 50 cm. Groundwater NO₃⁻ loads declined from over 70 kg N ha⁻¹ in the early 2000s to under 30 kg N ha⁻¹ by 2024, yet concentrations have plateaued rather than continuing to fall. This persistent signal alludes that subsoil N stored from past decades continues to mineralize and leach, sustaining groundwater nitrate levels despite reduced inputs. These findings provide the first direct quantification of legacy soil N in Irish dairy systems, showing that deep soil stores act as long-term sources of reactive N, constraining the pace of water quality recovery even when surface management improves. In Chapter 4, I expanded the investigation to include the Johnstown Castle Teagasc Dairy Research Farm, a variably drained site in the southeast with finer-textured soils and higher denitrification potential. I analyzed 45 soil cores from 9 paddocks, 1 m deep profiles covering an 18-year management period and compared results to those from Curtins. Despite lower annual surpluses (~100–150 kg N ha⁻¹ yr⁻¹), Johnstown Castle soils contained 4,000–11,000 kg N ha⁻¹ in the upper 50 cm, substantially higher than the well-drained Curtins profiles. The difference reflected higher clay and silt content, which enhanced N retention through adsorption and organic-mineral associations, as well as shallower water tables and moderate denitrification that reduced nitrate transport to groundwater but trapped nitrogen in the soil profile. These results revealed a clear trade-off: well-drained systems potentially act as “fast transmitters,” showing rapid leaching but quicker recovery when management improves, whereas variably drained systems are possibly “slow retainers,” buffering groundwater in the short term but accumulating persistent legacy N stores that prolong recovery. By linking long-term management records, soil data, and investigating groundwater trends across these contrasting systems, I demonstrated that N accumulation is governed by the interaction of soil texture, soil drainage class, hydrology, denitrification potential, and historical management intensity. Across both sites, total soil N accumulation exceeded 3,000–11,000 kg N ha⁻¹, far higher than values reported for most temperate cropland systems, confirming the exceptional capacity of Irish grassland soils to store reactive N from decades of intensive management. This thesis makes several novel contributions. It provides the first empirical evidence of soil legacy N magnitudes in temperate dairy grasslands, quantifies their long-term influence on water quality and nitrate dynamics, and develops a conceptual framework concerning drainage, soil texture, and hydrology to N retention and release. It also demonstrates how soil legacy N can be reframed as both a risk and a resource—a potential nutrient reservoir that, if managed strategically, could offset fertilizer needs during the transition to lower-input systems. These findings have direct implications for Ireland’s compliance with the EU Nitrates and WFD. Current six-year reporting cycles are too short to capture recovery in legacy-affected catchments, creating the perception of policy failure. Integrating soil monitoring to 1 m depth alongside existing high-resolution catchment and groundwater networks would enable more accurate assessment of progress and support realistic, site-specific mitigation timelines. Legacy N must be explicitly incorporated into nutrient models, regulatory assessments, and PoMs to ensure that both soil and water systems are managed as coupled components of the nitrogen cycle. Ultimately, this research underscores that Ireland’s path to sustainable dairy production requires addressing both current N surpluses and historical legacies. The methods and evidence developed here — combining modelling, deep soil sampling, and long-term monitoring offer a blueprint for future national assessments and international comparisons. As EU policy evolves toward stricter nutrient limits and nature restoration goals, understanding and managing legacy N will be fundamental to aligning agricultural productivity with environmental resilience.
Isotopic Study of Bromine: Determining Bromine Isotope Fractionation During Evaporation and Diagenesis
(University of Waterloo, 2025-12-02) Ryuh, Yon-Gyung
Stable isotopes of bromine (δ⁸¹Br) and chlorine (δ³⁷Cl) provide new opportunities to trace geochemical processes in various natural systems. While chlorine isotopes have long been applied in diverse hydrologic and geochemical fields, bromine isotopes have only recently drawn attention. Recent analytical advances have revealed unexpectedly large δ⁸¹Br variations in formation waters and evaporite deposits, yet the controls on the δ⁸¹Br variability remain incompletely understood. Resolving the fractionation mechanisms and the relationship between bromine and chlorine isotopes is essential. Understanding δ⁸¹Br-δ³⁷Cl systematics can support interpretations of evaporite basin evolution, and groundwater sources and mixing, and identification of diagenetic overprints in the subsurface. This thesis integrates three complementary approaches, including a global synthesis of published δ⁸¹Br-δ³⁷Cl datasets, controlled seawater evaporation experiments, and analyses of paleo-evaporite sequences. The integrated work provides insights into when and how stable bromine isotopes fractionate, and when and why its isotopic behavior decouples from that of stable chlorine isotopes. The synthesis of published datasets harmonizes unconnected studies to enable a comparison of the isotopic behaviors of bromine and chlorine across hydrologic and lithologic settings. The laboratory experiments isolate mineral-specific isotopic behavior and incorporation of bromine during sequential mineral precipitation under well-constrained conditions relevant to natural evaporative concentration of seawater. The analyses of paleo-evaporite sequences reveal how depositional signatures can be subsequently modified by post-depositional processes, and how such processes alter the isotopic and geochemical signature of bromine from chlorine. The global comparison of δ⁸¹Br and δ³⁷Cl values in groundwater and surface waters reveals a consistent pattern: δ⁸¹Br often diverges from δ³⁷Cl, with broader scatter and distinct behaviors across settings. The data show that δ⁸¹Br values often cannot be predicted from δ³⁷Cl values alone, highlighting that the two halogens respond to overlapping but non-identical processes differently. Multiple regression approaches and the comparisons among them indicate additional fractionation pathways, beyond simple mass-dependent behavior, differentially affect bromine and chlorine. Relatively high δ⁸¹Br values often cluster under specific geologic or hydrologic contexts, including organic complexation/decomposition, atmospheric interaction, elevated temperature-pressure regimes, and cryogenic processes. The comprehensive review provides a structured map of where bromine and chlorine behave similarly, where they diverge, and what that implies for interpreting natural datasets. Controlled seawater evaporation experiments demonstrate that bromine isotopes fractionate during sequential mineral precipitation, and crucially, that detectable shifts are observed before halite saturation. To better understand the underlying mechanisms, a laboratory evaporation series using synthetic seawater was conducted with continuous monitoring and stepwise sampling of brines, precipitates, and gas traps. Precipitates were characterized mineralogically, and both precipitates and coexisting brines were analyzed for δ⁸¹Br and δ³⁷Cl values to evaluate isotope fractionation during evaporation and mineral formation. Carbonates, gypsum, and halite have distinct δ⁸¹Br signatures consistent with differing pathways of Br incorporation, while δ³⁷Cl values are consistently higher in minerals than in coexisting brines. Capture of bromine in the gas phase sampled during the experiment confirms volatilization as an additional fractionation pathway for bromine isotopes. These experimental results explain why δ⁸¹Br values can vary widely, and differently from δ³⁷Cl, during progressive evaporation, mineral formation, and volatilization. Analyses of paleo-evaporite sequences show that primary depositional signals can be systematically reshaped by post-depositional modification. To evaluate depositional and post-depositional signals, basin-wide stratigraphic sampling for Br, Cl, δ⁸¹Br and δ³⁷Cl analysis across evaporite horizons and locations in the Salina Formation in the Michigan Basin was combined with lithological characterization. Br/Cl ratios were examined with petrographic indicators of diagenetic overprints, and basin-evolution context from previous studies was integrated. Paired measurements of δ⁸¹Br and δ³⁷Cl were then linked to these signatures. Consistent with the compiled groundwater and surface water datasets, evaporite δ⁸¹Br and δ³⁷Cl values often show weak correlation, reflecting multiple fractionation pathways rather than a single control acting on both isotopes simultaneously. Diagenetic processes often produce path-dependent shifts: either δ³⁷Cl or δ⁸¹Br values can increase, decrease, or remain unchanged depending on the processes involved (e.g., dissolution-reprecipitation, fluid-salt interaction, thermal regimes, organic interaction). The δ⁸¹Br–δ³⁷Cl dataset provides clear basin-evolution interpretations in complex evaporite records. The combined results establish that bromine isotopes are particularly sensitive to specific geochemical processes and that their variability cannot be explained by chlorine isotope systematics alone. This research contributes three main advances: (1) it provides a systematic review and defines the variability of bromine isotopes associated with diverse hydrogeologic settings; (2) it demonstrates experimentally that bromine isotopes fractionate significantly during evaporation and mineral precipitation, including prior to halite saturation; and (3) it shows that natural evaporite systems preserve complex isotopic signatures that integrate depositional and post-depositional processes, and that these signals are better understandable when both halogens are considered. Overall, this thesis develops a conceptual framework for bromine isotope geochemistry and demonstrates the value of Br-Cl dual isotope systematics to disentangle overlapping depositional and diagenetic processes, with implications for groundwater studies and evaporite basin evolution.
Integration of Borehole Geophysical Logging with Hydraulic Tomography Analysis for Improved Groundwater Flow and Transport Predictions
(University of Waterloo, 2025-11-11) Wang, Chenxi
Hydraulic Tomography (HT) has been demonstrated to be a robust approach to characterize the subsurface heterogeneity, which employs the inversion of head data collected from multiple pumping tests to estimate the spatial distribution of hydraulic properties (e.g., hydraulic conductivity (K) and specific storage (Ss)). However, the resolution of K and Ss tomograms is reduced when the number of pumping tests and observation density gradually decrease. Another issue is that HT’s ability to predict solute/heat tracer transport behavior has not been rigorously examined for complex aquifer systems. Previous studies showed that different types of data (e.g., geological, geophysical, and other hydraulic testing data) carrying non-redundant information can be integrated with HT analysis to improve the mapping of K heterogeneity. This thesis evaluates the effectiveness of integrating geophysical logging data with HT analysis for improved imaging of K distributions. Furthermore, a heat tracer test was conducted in a highly heterogeneous glaciofluvial deposit to investigate the feasibility of reproducing the spatial distribution of observed temperature responses based on a heat transport model with HT K estimates. Five sequential studies are documented in this thesis to explore the integration of borehole geophysical logging with HT analysis for improved mapping of K and porosity heterogeneity, which enables enhanced predictions of groundwater flow and solute/heat tracer transport: (1) Study I integrated two conventional geophysical logging surveys, including electrical conductivity (EC) and gamma ray (GR) logging, with HT analysis to yield 2D K fields in a numerical sandbox experiment. A new spatial conditioning term was proposed to better delineate the hydrostratigraphy from geophysical logging data, which was used to derive the initial guess of K fields for geostatistical inverse modelling of HT analysis. The HT K models with comparative initial guesses of K distributions were evaluated based on their predictive capabilities for groundwater flow and solute transport. After demonstrating the effectiveness of integrating geophysical logging with HT analysis for improved K estimation in a numerical sandbox study, the subsequent studies were conducted at the North Campus Research Site (NCRS) underlain by a highly heterogeneous glaciofluvial deposit. (2) Study II conducted nuclear magnetic resonance (NMR) logging at the NCRS. Compared to conventional geophysical logging surveys, NMR logging can directly provide K estimates, as well as total porosity and effective porosity measurements. The petrophysical relationship between NMR signals and K was site-specifically optimized, and the NMR-derived downhole K profiles were compared with a variety of hydraulic measurements to evaluate their accuracy and resolution along boreholes. (3) Study III constructed 3D K fields based on downhole NMR K profiles and evaluated the representativeness of these K models. Various spatial interpolation approaches were employed to generate spatial K patterns. A multi-level heterogeneity characterization approach was proposed to better represent the layered porous medium at the NCRS. The model performance to predict groundwater flow was examined through simulating the observed drawdown responses from multiple pumping tests. (4) Study IV integrated NMR logging with HT analysis for improved characterization of subsurface heterogeneity. To highlight the importance of incorporating high-resolution initial K distributions to reduce the smoothness of K tomograms, a limited HT calibration dataset with fewer pumping tests and decreased observation density was utilized for model calibration. The effectiveness of this integration was evaluated through a comparative case study using varying numbers of head data for calibration and different spatial interpolation techniques for constructing initial NMR K models. (5) Study V conducted a heat tracer test at the NCRS, in which a dense monitoring network was installed to record temperature responses. The ability of various characterization approaches (e.g., HT analysis) to accurately map K heterogeneity was investigated by reproducing the complex spatial distribution of the temperature breakthrough curves (BTCs). Additionally, NMR-derived effective porosity was used to map a heterogeneous porosity field. Lastly, the sensitivities of heat tracer plume migration to flow, transport, and thermal parameters were investigated. The main contributions of these studies are: (1) conventional geophysical logging survey can provide hydrostratigraphic information to improve the resolution and accuracy of HT estimates; (2) NMR logging yields reliable downhole K estimates for interbedded layers of gravel, sand, silt and clay; (3) after spatial interpolation, 3D K models can be constructed based on NMR logging, which offers reasonable drawdown predictions to pumping tests; (4) integrating NMR logging with HT analysis can provide more representative K estimates consistent with the depositional environment, and the integrated models can still yield reliable K estimates at high resolution when only a limited head data is available for calibration; and (5) the complex temperature response from a heat tracer test can be best reproduced using HT analysis and NMR logging to represent the heterogeneous K and effective porosity fields. Based on their robust performance in predicting groundwater flow and solute/heat transport at different scales, this work advocates the joint use of HT analysis and borehole geophysical logging to characterize subsurface heterogeneity.
Integrated analysis of global lakes and reservoirs: Global reservoirs modeling database, climate-driven changes in thermal stratification, depth-area-volume relationships, dam operation, and downstream phosphorus export
(University of Waterloo, 2025-09-23) Yu, Shengde
Inland freshwater bodies, including lakes, reservoirs, and wetlands, are critical components of the global freshwater system. They play essential roles in water storage, flow regulation, biodiversity, nutrient cycling, and many other ecosystem services including food production and local climate regulation. However, human interventions such as dam construction, urbanization, intensive agriculture, and climate change significantly alter their hydrological and ecological functions. This underscores the importance of data integration and modeling tools to predictively understand and effectively manage these water bodies to ensure their sustainability and resilience under changing climate and environmental conditions. With this thesis, I aim to contribute to the comprehensive, global-scale analysis of inland water bodies. I present a new global reservoir water modeling database, abbreviated GRM, that can be coupled with hydrodynamic and water quality simulations. The use of GRM is illustrated by computing temperature changes in nearly 7000 large reservoirs between 1980 and 2019. I also present a database of depth-area-volume (D-A-V) relationships for over 1.4 million lakes and reservoirs worldwide. These relationships provide easy access to essential bathymetric information to users interested in carrying out modeling studies. The D-A-V database is complemented by a Python package that generates bathymetric representations for multidimensional water quality modeling. Lastly, for a reservoir in southern Ontario, I analyze how controlling water level, and the positioning of dam outflow gates can be used to reduce the outflow of total and bioavailable phosphorus, which, more generally, opens the possibility of considering dam operation strategies that help protect downstream water bodies from eutrophication impacts. Chapter 1 provides an overview of the significance of inland water bodies and the impacts of anthropogenic activities on their biogeochemical dynamics. The chapter reviews existing global databases on lakes and reservoirs, highlighting their strengths and limitations. I further argue that existing global-scale biogeochemical modeling studies of inland waters have primarily relied on simple box models and empirical relationships that lack the ability to capture the complex temporal and multidimensional physical-geochemical-biological interactions in these ecosystems. This gap sets the stage for developing the comprehensive global multidimensional model database presented in Chapter 2. Chapter 2 describes the development of the Global Reservoir Modeling (GRM) database that integrates multiple existing global datasets to facilitate reservoir hydrodynamic and water quality modeling on a global scale. The current GRM database version brings together 40 years (1980-2019) of diverse data series for nearly 7,000 reservoirs worldwide. The corresponding data are extracted from the following datasets: GRanD for reservoir attributes, ReGeom for bathymetric data, WaterGAP for streamflow, and ERA5 for meteorological parameters. With these data, GRM can generate compatible input files for hydrodynamic and water quality simulations with the popular CE-QUAL-W2 model. Thus, GRM offers researchers a practical and readily usable tool to model changes in reservoir water temperature and mixing regimes and their impacts on water quality, whether for a single or a large selection of the GRanD reservoirs. Chapter 3 offers an example of the type of global-scale assessments that can be performed with GRM by calculating the temporal trajectories of the thermal gradients in all the reservoirs included in GRM from 1980 to 2019. For each reservoir, a 30×30 depth-length bathymetry is generated by GRM, which is then used in the multithreaded, process-based CE-QUAL-W2 model to calculate the temperature distribution as a function of space and time. The results are illustrated globally by mapping both the surface-to-bottom temperature difference and the distributions of thermocline depth for 1980, 2000, and 2019. The findings confirm not only a widespread increase in surface-to-bottom temperature differences (on average by 0.39 ℃ per decade) but also a generalized deepening of the thermocline, on average by 1.2 m (around 0.3 m per decade) between 1980 and 2019. The results confirm that global reservoir thermal stratification has both intensified and migrated downward over the past four decades. Chapter 4 compiles depth–area–volume (D-A-V) relationships for over 1.4 million lakes and reservoirs by merging HydroLAKES and GLOBathy. The resulting GLRDAV database contains > 17 million equations—five polynomial functions (orders 1–5) and one power function for both depth–area and depth–volume—evaluated at 0.1 m depth increments. Validation against ReGeom, GRDL, and in-situ Texas Water Development Board surveys show that 4th- and 5th-order polynomials deliver the highest accuracy. Lower-order polynomials and the power function perform adequately for small, simple basins but not for large waterbodies. A Python package, named “Global Waterbody Calculator”, provides streamlined access to all 17 million equations and coefficients, facilitating rapid bathymetric reconstruction for hydrodynamic and water-quality models. The tool rasterizes shoreline vii polygons at 1 arcsecond (~30 m) resolution and rapidly generates full 3-D GeoTIFF bathymetry on a standard desktop, enabling immediate visualization and 3-D model-ready inputs. Chapter 5 applies the CE-QUAL-W2 model to Fanshawe Reservoir (Ontario, Canada) to test how 33 dam operation scenarios—three dam withdrawal elevations crossed with eleven water-level elevations from 0 to +10 m relative to the current conditions—alter phosphorus retention by the reservoir. Under baseline operation (normal withdrawal, 0 m water level) the reservoir retains only 13% of incoming total phosphorus (TP) annually and can become a net TP and dissolved phosphorus (DRP) source in summer. Switching to surface withdrawal alone boosts the annual TP retention to 20 %, while combining surface withdrawal with a +10 m pool-raise pushes summer retention of TP above 78% and the annual retention to 52%. These gains stem from a four-fold lengthening of the water residence time (peaking at 149 days) and the hydraulic isolation of the P-rich hypolimnion. However, these dam operation and water level conditions also prolong bottom-water hypoxia (with dissolved oxygen < 2 mg/l for around 48 days). The modeling highlights the trade-off between maximizing phosphorus retention and avoiding in-reservoir deoxygenatiom, underscoring the need for seasonally targeted, adaptive dam management. Finally, Chapter 6 synthesizes the thesis’s key insights and charts a path forward. It emphasizes how the new global datasets (GRM and GLRDAV) and the Fanshawe case study together advance our understanding of the links between hydrodynamics, nutrient cycling, and dam operation. Looking ahead, this chapter calls for coupling “big-data” archives with process-based and machine-learning models, building reservoir-scale digital twins, and incorporating sediment and groundwater interactions to assess long-term climate and management impacts. Strengthening this predictive framework will be instrumental in safeguarding lakes and reservoirs under accelerating environmental change.
The Quaternary stratigraphy of the Gods and Yakaw rivers area, northeastern Manitoba
(University of Waterloo, 2025-09-18) Mesich, Nickolas
Reconstructing the spatiotemporal dynamics of past glaciations provides a long-term perspective that is essential to understanding how Earth systems respond to climate change over different timescales. While most ice sheet reconstructions focus on the last glaciation, incorporating stratigraphic records from older glaciations enhances our understanding of past glacial-interglacial cycles. The western Hudson Bay Lowland (HBL) in northeastern Manitoba preserves thick Quaternary sediment sequences (20–70+ m) spanning multiple glacial-interglacial cycles, influenced by two major ice spreading centers of the Laurentide Ice Sheet (the Keewatin dome to the northwest and the Quebec-Labrador dome to the east). This study revisits the Quaternary stratigraphy along the Gods and Yakaw rivers in the western HBL using contemporary techniques, including a detailed, multi-parameter approach to characterize tills, combining field observations, paleo-ice flow indicators (till fabric analysis, lodged boulder striations), and till composition (matrix geochemistry, clast-lithology counts). For this thesis, a hybrid lithostratigraphic-allostratigraphic approach was employed across ten sections to reconstruct local glacial dynamics and establish an updated stratigraphic framework. Results confirm a complex, laterally variable stratigraphy. The revised framework includes 21 delineated stratigraphic units: 15 tills correlated using primarily paleo-ice flow indicators and stratigraphic position, and 6 sorted sediment units defined by allostratigraphy. Several key findings emerge from this framework, including: (1) A more detailed reconstruction of local glacial dynamics, (2) recognition of at least 4 sub-till sorted sediment units interpreted as ice-free intervals, and (3) a relative stratigraphy that extends the Quaternary record in the region, possibly back to MIS 12 or even older. Sediment provenance and ice-flow indicator analysis suggest that older tills (units 1t–11t) were dominantly sourced from a Quebec-Labrador dome, while younger tills (units 13t–20t) exhibit more complex signatures. This shift between units 11t and 13t may reflect changes in paleo-ice sheet configuration, bedrock availability to glacial erosion, or entrainment of pre-existing sediment. Although some till units appear superficially similar, they are interpreted as discrete tills deposited during separate ice-flow phases rather than products of glaciotectonic stacking. An alternative explanation invoking glaciotectonism is considered; however, variability of paleo-ice flow indicators, the absence of pervasive deformation structures, and a regional context unfavourable to large-scale glaciotectonism opposes this interpretation. These findings have broad implications for both ice sheet modeling and mineral exploration. In ice sheet modeling, incorporating records from older glacial-interglacial cycles provides key constraints to long-term ice sheet reconstructions, improving understanding of ice sheet response to climate change, which leads to better predictions of future changes. In mineral exploration, understanding glacial dynamics in thick-drift regions helps establish dispersal directions and sediment provenance, which may either 1) improve the interpretation of indicator mineral source, or 2) confirm a long history of inheritance and overprinting that requires the development of new techniques.
Evaluating remote sensing and modeling approaches for estimating net ecosystem exchange in Canadian peatlands
(University of Waterloo, 2025-09-17) Hettinga, Katie
Peatlands represent a type of wetland, that has accumulated a layer of organic material or peat, resulting in high organic carbon (C) accumulation in this ecosystem. Peatlands hold up to one-third of the global organic C stock, and specifically peatlands located at high latitudes in the Northern Hemisphere, or northern peatlands, store a large proportion of the of the total peatland organic C stock. However, this organic C may be in jeopardy, as warmer temperatures may lead to increases in both the C uptake and output. There is some uncertainty as to how northern peatlands C sink function will be impacted by climate warming, and conventional models of peatland C cycling have been constrained to site-specific applications rather than national-scale analyses. Moreover, in-situ measurements are limited in northern peatlands, due to the remoteness of these sites, but also due to equipment limitations under low temperature and light conditions. In this thesis, I specifically looked at one component of C flux, the net ecosystem exchange (NEE) of CO2. To enable forecasting of NEE of CO2 fluxes in peatlands under future scenarios, or to generate real-time estimates where no in-situ measurements exist, machine learning algorithms trained on in-situ CO2 fluxes from the eddy covariance (EC) technique must be applied. Remotely sensed or gridded climate data products represent potentially important inputs to these modeling applications, as they are widespread both geographically and temporally enabling flux estimation for broader geographic domains. In Chapter 2, I explored the possibility of using the remotely sensed and modeled Soil Moisture Active Passive Level 4 Global Daily EASE-Grid Carbon NEE (SMAP-NEE) data product to determine NEE in Canadian peatlands. I acquired nine years (2015–2023) of SMAP-NEE data for five peatlands. I also acquired a subset of year-round eddy covariance NEE (EC-NEE) measurements within this time frame at each of the five peatland sites. The analyses showed that the SMAP-NEE data product reports a stronger growing season (GS) sink and a weaker non-growing season (NGS) source than the EC-NEE measurements. As a result of this finding, I used the relationship between SMAP-NEE and EC-NEE to produce a Corrected-SMAP-NEE dataset, which provides an estimate of seasonal and annual CO2 budgets. The data analyses of the Corrected-SMAP-NEE dataset showed that NGS CO2 emissions represent a variable proportion (33%–256%) of the GS CO2 uptake, and when these NGS emissions were accounted for, the annual CO2 sink strength was reduced proportionally. Furthermore, this study showed that longer growing seasons were consistent with greater annual net CO2 uptake at these five peatland sites from 2015-2023. The findings highlight the importance of considering the NGS when evaluating annual northern peatland C budgets. This chapter also provides evidence that existing algorithms leveraging remotely sensed and gridded climate data products to model NEE need improvement for peatlands. In Chapter 3, I compiled year-round measurements of EC-NEE from 15 Canadian peatland sites and coupled these target data with 34 hydroclimatic predictor variables (features) from remote sensing and gridded climate data products. The models were trained, validated, and tested using four algorithms: ElasticNet Regression (EN), Light Gradient-Boosting Machine (LGBM), Random Forest Regression (RFR), and Support Vector Regression (SVR). A comprehensive feature importance and selection workflow including hierarchical clustering, Gini importance, and minimum redundancy maximum relevance (mRMR) analysis was followed. Model performance stabilized at eight features, which were (relative importance shown in parentheses): evapotranspiration (40%), shortwave radiation (19%), burn area index (11%), normalized difference snow index (10%), snow water equivalent (7%), climate water deficit (4%), wind speed (4%), and soil moisture (4%). I found the best performing model to be the RFR model with these eight features (R2 = 0.76; RMSE = 0.31 g C m−2 day−1). I also assessed the generalizability and transferability of the top-performing model via a leave-one-ecoregion-out sensitivity analysis as well as on six external validation sites. The RFR model had the highest generalizability within the Taiga Plains ecoregion and the lowest generalizability within the Boreal Plain ecoregion. When testing the model on the external validation sites, performance metrics were comparable to the internal testing data for sites outside of the ecoregions represented in the training data. The findings demonstrate that the eight-feature models can be confidently upscaled to national extents, offering a clear pathway to improve Canada’s spatially explicit CO2 emission inventories.
High-Temperature Metamorphic Reactions from the Macro-Scale to the Micro-Scale
(University of Waterloo, 2025-09-02) Dyer, Sabastien
Metamorphic reactions are the basis of metamorphic petrology and the lens through which we interpret metamorphic rocks and processes. They serve both as tectonic indicators, revealing the pressure--temperature history of a rock, and as tectonic drivers, responsible for the production of fluids and melts that are critical to many geological processes in the crust. At high temperatures, two types of reactions that have emphasized importance are melting reactions that have implications for large-scale crustal reworking and reactions that grow accessory minerals that we use to date petrological processes. Zircon is the most common geochronometer, but its behaviour at high temperatures is poorly understood. Zircon-forming reactions were investigated in granulite-facies meta-granitoids in the Grenville province to better understand how zircon grows during metamorphism at high temperatures. Zircon growth occurred during retrogression as a result of melt crystallization and titanomagnetite breakdown. With this information, the dates of metamorphic zircon that were measured were interpreted as cooling dates, and provided additional context that suggests that the major orogenic phase of Grenville Orogen may have begun tens of millions of years earlier than previously thought. Zircon was also used as a proxy to investigate the kinetics of trace elements in intergranular melt during melt crystallization in a migmatite. Key trace elements including Hf, U, Th, Y, and heavy rare earth elements were analyzed in multiple metamorphic zircon rims to compare relative concentration of zircon that grew coevally in the same thin section. The significant differences observed in concentration of these elements across zircon grains suggests rates of diffusion of these key trace elements are slower than zircon growth in migmatites. Zircon growth probably occurred as a result of size-dependent interface-controlled growth, implying that Zr diffusion was relatively fast in the melt. On the macro-scale, evidence of regionally extensive H2O-fluxed melting reactions have been observed in multiple distinct tectonic environments across the globe, yet there is no generic tectonic model that explains regional-scale H2O-fluxed melting in the crust. Regional scale H2O-fluxed melting was studied in the Muskoka domain of the Grenville province. In the Muskoka domain, H2O-fluxed melting dominated throughout the region and until now, the source and mechanism of the H2O transport into the Muskoka domain has been unclear. Multiple examples of pegmatites with amphibole and leucosome-rich reaction selvages were found throughout the domain that show how H2O may have been transported into and through the Muskoka domain. Using a two-stage melting model, it was shown that melt generated at depth through hydrate-breakdown melting contains enough H2O to readily melt the rocks in the Muskoka domain through diffusive H2O-fluxed melting, with no fluid exsolution required. Metamorphic reactions are used to understand regional tectonics, but there are significant gaps in our understanding of these reactions on both the micro-scale and the macro-scale. The geochronological tools that are used to unravel metamorphism are based on micro-scale processes that are still poorly understood. Simultaneously, our understanding of macro-scale tectonic processes involving H2O transport in the crust, which influence our interpretation of metamorphic rocks, is limited with H2O-fluxed melting. This thesis addresses our limits of understanding and shows how understanding metamorphic reactions allows us to better understand regional tectonics.
Spatiotemporal Variability in Groundwater–Surface Water Exchange Within a Perennial Stream: Alder Creek, Southwestern Ontario
(University of Waterloo, 2025-08-28) Zanatta, Corey
Groundwater discharge plays a crucial role in sustaining streamflow within creeks and rivers year-round while also supporting the aquatic life that live in them. However, due to numerous external pressures such as increased groundwater usage, changes in land uses, and climate change, these water bodies are under increased strain, putting increased emphasis on the need to protect and preserve them. To do this requires an increased understanding of groundwater-surface water interactions, which are complex processes that are challenging to accurately identify and quantify. This work seeks to strengthen understanding of these complex processes. This involved the application of numerous small-scale techniques related to temperature readings, infrared imaging and hydraulic gradients to locate zones of groundwater discharge during reconnaissance of a moderately sized watershed to identify suspected gaining reaches for further study. At these identified study sites, detailed studies were completed to verify the reconnaissance results, quantify the groundwater-surface water exchange and assess its seasonal and temporal variability. This was done through the application of a combination of techniques, which involved monitoring hydraulic gradients, estimating streambed hydraulic conductivities, using temperature profiles and Darcy’s law to estimate groundwater fluxes, developing flow nets of study reaches, and performing differential stream gauging. The reconnaissance proved effective at identifying signs of groundwater discharge throughout the watershed, based on clusters of cold streambed readings and infrared imaging differentiating groundwater discharge near and along the streambank from their surroundings based on temperature contrasts. The reconnaissance ultimately led to the identification of two sites exhibiting groundwater discharge conditions. At these study sites, groundwater discharge conditions were confirmed based on upward hydraulic gradients, upward Darcy fluxes and largely upward temperature profile fluxes, in depth follow up infrared imaging, and differential stream gauging identifying gaining conditions. Based on the point scale techniques of Darcy fluxes and temperature profile fluxes, groundwater-surface water exchange was found to exhibit similar spatial patterns with groundwater discharge appearing often highest in the areas of the study reaches where discharge was identified during the reconnaissance while signs of recharge were also found, highlighting the spatial variability along the reaches of study. While effective at assessing spatial variability, these point measurement techniques were unable to accurately quantify groundwater discharge because they greatly underestimated the benchmark of differential stream gauging. This was attributed to the point measurement technique’s ability to only account for the vertical component of groundwater discharge, which was found to be small, indicating a significant alternative source of groundwater discharge. Based on a lack of instrumentation immediately at the streambanks, and visible discharge at some streambank locations, the discrepancy was attributed to groundwater discharge near the streambanks. Flow nets were initially unsuccessful in accounting for this significant component of groundwater discharge, which was attributed to the inability to accurately represent the high hydraulic conductivities near the streambank because of limited field data. When applying a higher, but reasonable, hydraulic conductivity value, the estimates of discharge were much more in line with differential stream gauging estimates, suggesting a significant component of groundwater discharge entering near the streambank. Groundwater-surface water exchange was also found to be influenced by temporal variability, as seen by the increase in groundwater discharge measured between the winter and summer using the point measurement techniques. Hydraulic conductivities were influenced by changes in water viscosity, while bi-weekly and continuous monitoring of vertical and horizontal hydraulic gradients indicated the presence of groundwater discharge conditions and showed variability with time. Continuous datasets provided even greater insight, including identifying seasonal trends and the reversal of hydraulic gradients in responses to extreme flow events. Continuous monitoring, though differential stream gauging, also indicated variability in groundwater-surface exchange over the overall gaining stream reach. These results highlight the importance of considering variability when assessing groundwater- surface water interactions. The findings of this study make clear the significant complexity that exists with regards to groundwater-surface water interactions, and the many challenges that must be considered in order to better comprehend these processes.
Gas hydrate formation and dissociation: predictive, thermodynamic, and dynamic models
(University of Waterloo, 2025-06-27) Hosseini, Mostafa
Gas hydrates are a type of crystalline compound consisting of water and small gas molecules. A wide range of applications of gas hydrates in storing natural gas in the form of artificially created solid hydrates, known as solidified natural gas technology, gas separation processes, and seawater desalination technology, has attracted great interest in scientific and practical studies. Gas hydrate formation may also cause deleterious effects, such as blockage of gas pipelines. Therefore, accurate prediction of equilibrium conditions for gas hydrates is of great interest. In this regard, machine learning-based models were proposed to predict methane-hydrate formation temperature for a wide range of brines. A comprehensive database including 987 data samples covering 15 different brines was gathered from the literature. After data cleaning and preparation, three different models, namely multilayer perceptron (MLP), decision tree (DT), and extremely randomized trees (ET), were trained and tested. The ET model achieved the best performance with a root mean squared error (RMSE) of 0.6248 K for the testing dataset. Moreover, in an additional independent testing with MgBr2 samples, ET achieved an RMSE of 0.3520 K, confirming its strong generalization ability. The order of model accuracy was ET greater than MLP greater than DT. Compared to previous studies, the developed models achieved similar or better accuracy while covering a wider range of brine types. The findings of this study can be used as a reliable tool to predict methane-hydrate formation PT curves for pure water, single-salt brines, and multi-salt brines. The research further focuses on improving the prediction of equilibrium conditions in methane hydrate systems by incorporating diverse water-soluble hydrate formers and applying advanced machine learning techniques. Methane hydrates, which naturally form under high pressure and low temperature, can be more efficiently formed or dissociated by altering thermodynamic conditions using these hydrate formers. Accurate prediction of these conditions is crucial for optimizing gas storage and energy applications. Molecular descriptors and operational parameters, such as mole fraction and pressure, were used as input variables to predict equilibrium temperature. Machine learning methods, including Decision Trees (DT), Random Forests (RF), Support Vector Machines (SVM), and Multi-Layer Perceptron (MLP), were employed, using a novel former-based data-splitting approach rather than traditional sample-based methods. The RF model achieved the best results, with R2 = 0.930, RMSE = 1.71, and AARD = 0.48%. Feature selection, preprocessing, and Shapley Additive Explanations (SHAP) provided valuable insights into variable importance. Additional findings from the reduced model revealed that even less influential features significantly impacted distance-based models such as SVM and MLP. Interaction analysis through SHAP dependency plots highlighted the critical interplay between polar surface area and rotatable bonds in hydrate formation conditions. This work advances methane hydrate research by offering a more accurate and interpretable framework for predicting hydrate equilibrium, addressing key gaps in previous studies, and extending its applicability to a broader range of systems. Moreover, the introduction of a former-based data-splitting method improves generalization across different hydrate formers, while the use of SHAP values for model interpretability offers deeper insights into the relationships between molecular descriptors and hydrate equilibrium conditions. This study paves the way for improved selection of hydrate formers in hydrate systems. In addition to the phase equilibrium studies, this research also addresses the behavior of gas hydrates under confinement, focusing on hydrate dissociation in porous media. Understanding the dissociation behavior of gas hydrates in confined porous media is crucial for evaluating their stability and potential applications in energy storage, carbon capture, and climate modeling. Two distinct approaches were developed, namely a thermodynamic activity model and machine learning (ML) models, to predict equilibrium dissociation temperatures of gas hydrates in porous media of varying pore sizes. The activity model accounted for capillary effects and surface interactions and was validated against an unfiltered experimental dataset. For CH4 hydrates, the model achieved an AAD% of 0.17%, and for C3H8 hydrates, an AAD% of 0.62%. Complementary machine learning models (DT, RF, SVM, MLP) were trained using pore diameter, pressure, and gas critical properties as features. Group-based data splitting, with propane data reserved for testing, ensured robust evaluation. Among ML models, the SVM achieved the best predictive performance with an AAD% of 0.52%. SHAP analysis revealed that critical temperature, system pressure, and pore size were dominant predictors. The study also noted that experimental scatter was linked to pore structure variability and procedural differences, with larger pores showing convergence to bulk hydrate behavior. The combined modeling framework effectively captures hydrate behavior across a wide range of confined conditions, offering valuable predictive capability for both industrial and geological hydrate systems. In conclusion, the integration of physics-based and data-driven modeling enables accurate prediction of hydrate dissociation temperatures across a range of porous media. These findings support the development of predictive tools for hydrate systems in both geological and industrial applications. Finally, to complement the thermodynamic and equilibrium predictions, the dynamic transport behavior of hydrate particles in pipelines was investigated through CFD–DEM simulations. The dynamic behavior of hydrate particles suspended in water-dominated horizontal pipe flow using a two-way coupled CFD–DEM framework based on OpenFOAM and LIGGGHTS via CFDEM® coupling was explored. Multiphase flow simulations were conducted across inlet velocities of 0.2, 0.5, and 0.8 m/s and hydrate volume fractions of 2%, 5%, 8%, 15%, and 20%. Pressure drop behavior was quantified by extracting pressure gradients between two axial positions (z = 0.10 m and z = 0.49 m) early in the simulation. Results indicated that pressure drop increases with hydrate volume fraction at all flow velocities, with clustering phenomena becoming more prominent at higher solid loadings. Cross-sectional velocity profiles visualized the early evolution of particle clustering, wall interactions, and domain depletion. Increased flow velocity enhanced particle suspension but reduced domain uniformity over time. Time-resolved analyses of pressure drop, drag force, particle velocity, interparticle forces, and radial migration were conducted to explore flow regime transitions and mechanical resistance. Early clustering near the pipe walls was observed under dense flow conditions, driven by cohesive and frictional forces, leading to partial stratification and localized energy dissipation. The study highlights the importance of considering early-time flow dynamics, where suspension quality and transport resistance are most sensitive to hydrate loading. These findings contribute to a deeper understanding of hydrate slurry transport in multiphase pipeline systems and offer practical guidance for improving flow assurance models and mitigation strategies in subsea energy operations.
Methane consumption by a landfill cover soil under variable soil moisture and temperature conditions
(University of Waterloo, 2025-05-12) Lam, Christina
Methane (CH4) is a significant greenhouse gas (GHG) that contributes to climate warming when released into the atmosphere, with over 80 times the warming potential of carbon dioxide (CO2) over a 20-year period. Landfills are one of the largest anthropogenic sources of CH4, and hot-spots of CH4 emissions in landfill cover soils represent a large proportion of emissions that are thus a target for mitigation. These hot-spots can enrich microbes that consume CH4 and produce CO2 as a less potent GHG, via CH4 oxidation. CH4 oxidation rates are modulated by multiple environmental variables including soil moisture and temperature. Therefore, it is important to investigate the interactive effects of these factors on CH4 oxidation rates, to further understand the response of CH4 oxidation activity under changing conditions whether via seasonality or climate change. In Chapter 2, I conducted a closed-headspace batch experiment with cover soil from a hot-spot of a former landfill to measure CH4 consumption and CO2 efflux rates associated with variations in soil moisture and temperature simultaneously. Soil samples were incubated under a factorial design of 5 soil moisture contents ranging from 11 to 47% WFPS (water-filled pore space), and 6 temperatures ranging from 1 to 35°C. At each temperature and WFPS combination, CH4 was spiked into the headspace, and headspace CH4 and CO2 concentrations were measured over 2 hours to calculate CH4 consumption and CO2 efflux rates. The maximum CO2 efflux rate was observed at the maximal WFPS and temperature conditions of this experiment (91.5±10.3 nmol h-1 g DW-1 at 47% WFPS and 35°C), while the maximum CH4 consumption rate was observed at intermediate soil moisture and temperature conditions (1.86±0.05 nmol h-1 g DW-1 at 25% WFPS and 25°C). The results from this experiment showed the preliminary optimal conditions for CH4 consumption and associated CO2 efflux within this range of tested soil moisture and temperature conditions, and served as a baseline for the experimental design of Chapter 3. In Chapter 3, I conducted a series of closed-headspace batch incubations with cover soil from the same hot-spot site to expand on the findings from Chapter 2. The incubations assessed the CH4 consumption and CO2 efflux rates under simultaneous variations of soil moisture and temperature, with modifications including a wider range of soil moistures, and higher concentrations and subsequent injections of CH4. Soil samples were incubated under a factorial design of 5 soil moisture contents ranging from 20 to 100% WFPS, and 4 temperatures ranging from 1 to 35°C. At each temperature and moisture combination, CH4 was spiked into the headspace through multiple consecutive injections, and headspace CH4 and CO2 concentrations were measured to calculate CH4 consumption and CO2 efflux rates. The maximum CH4 consumption rate was observed at the moderate soil moisture and temperature conditions (330±12.3 nmol h-1 g DW-1 at 60% WFPS and 25°C), while the maximum CO2 efflux rate was observed at the maximal WFPS and temperature conditions used in the incubations (652±85.0 nmol h-1 g DW-1 at 100% WFPS and 35°C). A diffusion-reaction model was developed to simulate and fit the observed data to represent the effects of temperature and soil moisture on the CH4 consumption and CO2 efflux rates, predicting similar optimal conditions to the observed experimental data. Temperature sensitivity analysis (Q10) also supported the CH4 consumption being via CH4 oxidation. These results provide insight into how seasonal changes in soil moisture and temperature impact CH4 oxidation rates, and therefore also net CH4 emissions, in landfill cover soils and other environments. Overall, the results from Chapters 2 and 3 together emphasize that the dominant controls on the optimal soil moisture for CH4 consumption are the interactive effects of moisture limitation of microbial activity and of gas (CH4 and O2) diffusion, whereas for the CO2 effluxes, the dominant controls are the interactive effects of moisture limitation of gas (O2) diffusion and solute mobility. The difference in optimal conditions for CH4 consumption and CO2 efflux rates also highlight the presence of different microbial groups underlying the various soil processes. These findings can be expanded on for further understanding of CH4 oxidation activity at hot-spots and for the development of tools for mitigation of CH4 emissions from landfills.
Heat Production and Transfer in Earth’s Continental Crust
(University of Waterloo, 2025-04-15) Kinney, Carson
Planetary differentiation through tectonism reflects heat production and transfer, reducing internal energy and shaping planetary interiors. Geologic heat originates from two primary sources: primordial heat from planetary formation and the radiogenic decay of isotopes like U, Th, and K. Shearing can generate heat on local scales, but heat transfer predominantly occurs through conduction, where energy flows from hotter to cooler regions via atomic vibrations. In tectonically active areas, advection of magma and convection in fluids are more efficient mechanisms. Local heat transfer often relies on one dominant process, while large-scale systems involve a mix of conduction, convection, and advection. The causes and proportions of each heat source and mantle and crustal radiogenic contributions remain challenging to quantify. Understanding the re-distribution of heat-producing (i.e., radioactive) elements during metamorphism and crustal differentiation is achieved via combining natural observations with trace element and accessory mineral modelling. Six potential end-members were considered for the protolith of mid-crustal tonalite-trondhjemite-granodiorite packages—often considered the product of lower-crustal melting. Model results suggest heat-producing elements partition subequally between solid and melt at typical pressure-temperature conditions for crustal differentiation. Accessory minerals like apatite, feldspar, amphibole, and epidote are primary repositories for radioactive elements, with their stability in pressure-temperature space governing heat removal from the lower crust. Observations from the Archean Kapuskasing uplift reveal a similar partitioning pattern during mafic rock melting, supporting the notion that radiogenic heat equally influences mantle and crustal processes. Examining the crustal heat-production record provides insights into continental growth, thickness, and preservation. A database of crustal rocks, including trace element compositions and crystallization ages, reveals trends in heat production over time with implications for basalt formation and crustal evolution. While Archean mantle melting produced less heat-producing basalt than today due to higher degrees of partial melting, the total crustal heat-production rate has remained relatively constant. However, modern crust exhibits more significant variability, suggesting recent enrichment in heat-producing elements contrasts with a more homogenized Archean crust. Crustal growth pulses marked by mafic-to-felsic transitions imply a cyclic nature of crustal differentiation, with crustal thickness remaining stable due to self-organizing thermal processes. Trace element substitution in autocrystic zircon is a valuable tool for reconstructing deep geologic processes, but some influences on these proxies remain underexplored. Elevated titanium rims on volcanic zircon, often attributed to magma recharge, could also result from adiabatic ascent. Modelling shows that decompression melting and system expansion during ascent drive cooling, while subvolcanic boiling induces crystallization and latent heat release. Zircon growth during ascent can record these processes, and high-titanium rims may form in a single magma pulse without recharge, emphasizing the importance of multiple geochemical tools to interpret magma evolution. Ultra-high temperature (UHT) metamorphism represents the thermal extreme of crustal processes, yet its mechanisms and energy sources remain debated; common explanations include mafic underplating or mantle upwelling. The Frontenac Terrane in southeastern Ontario records UHT conditions during the Mesoproterozoic. Back-arc sedimentation between 1390–1200 Ma preceded Shawinigan (~1180–1160 Ma) and Ottawan (~1060 Ma) orogenic events. Granitic and minor mafic intrusions during Shawinigan times triggered regionally advective UHT metamorphism preserved through subsequent reheating events. The Frontenac Terrane provides critical insights into the Grenville Province assembly, with felsic intrusions providing a plausible mechanism for UHT conditions during orogenesis. Heat production and transfer fundamentally shape Earth's structure and behaviour. Radiogenic heat from U, Th, and K and primordial heat drive crustal and mantle dynamics. Although incompatible with most rock-forming minerals, heat-producing elements are preferentially incorporated into accessory minerals like apatite and zircon, depleting their source rocks. Increased melting reduces system-wide heat production as these elements concentrate in the melt. Advective heating is crucial for crustal growth, enabling magmas to ascend nearly adiabatically and providing a heat source for crustal reworking. These processes dictate metallogenic fluid generation, crustal heterogeneity, and long-term crustal stabilization.
Assessing Critical Metal Incorporation in Ca-Carbonate Minerals using Cyanobacteria: Application to Mine Site Environments
(University of Waterloo, 2025-03-28) Lei, Benjamin
Meeting the current global market demand for critical metals will require an increase in the number of mining operations in Canada. While mining will generate mine tailings, which can be an environmental concern, tailings also present an opportunity for carbon sequestration and metal recovery. Carbon sequestration in mine tailings can be implemented by using divalent cations from the tailings to form stable carbonate minerals. Ultramafic mine tailings typically contain an abundance of divalent cations, including various transition metals, that can be incorporated into carbonate minerals. During this process, critical metal enrichments are possible, and thus tailings may become valuable sources of metals as high-grade ore deposits continually become less accessible for mining. Microorganisms, including cyanobacteria, can contribute to carbonate mineral precipitation, however, this process is understudied with respect to transition metal incorporation into biogenic carbonate minerals. This thesis explores the application of these processes to ultramafic mine sites through two laboratory experiments using a pure culture of cyanobacteria, 𝘚𝘺𝘯𝘦𝘤𝘩𝘰𝘤𝘰𝘤𝘤𝘶𝘴 𝘭𝘦𝘰𝘱𝘰𝘭𝘪𝘦𝘯𝘴𝘪𝘴. In the first experiment, a biosorption study explores the metal sorption abilities of 𝘚. 𝘭𝘦𝘰𝘱𝘰𝘭𝘪𝘦𝘯𝘴𝘪𝘴 in a nutrient limited environment. The second experiment examines the incorporation of transition metals into precipitates during microbial mineral carbonation. In Chapter 2, the ability of 𝘚. 𝘭𝘦𝘰𝘱𝘰𝘭𝘪𝘦𝘯𝘴𝘪𝘴 to remove Co²⁺ and Ni²⁺ from solution via biosorption in a nutrient limited environment what tested in a lab experiment. Comparison between nutrient enriched conditions and a nutrient deficient condition (simulating an ultramafic mine site solution) was conducted in mono-metal and di-metal systems. The results revealed that measured nickel and cobalt concentrations were lowest in the first 3 days of the experiment, which indicates a fast metal removal rate. The biosorption of nickel and cobalt was upwards of 34.2–49.4% removal of metal from solution. Imposing nutrient limitations caused increased production of extracellular polymeric substances (EPS), which can increase metal sorption, and resulted in a decrease in measured nickel concentrations in solution in the di-metal system. The findings from this experiment indicate that inducing additional stress through metal exposure and nutrient limitations can increase the metal biosorption capacity of 𝘚. 𝘭𝘦𝘰𝘱𝘰𝘭𝘪𝘦𝘯𝘴𝘪𝘴. In Chapter 3, a microbially induced carbonate precipitation experiment was conducted to test the incorporation of nickel and cobalt into biogenic calcium carbonate mineral precipitates. These results are preliminary due to an experimental failure that occurred. Nevertheless, the measured concentrations of dissolved cobalt and nickel in solution indicated metal(s) removal success of up to 89.5% and 94.5% in the first day after metal addition. Observation of the biofilms using scanning electron microscopy (SEM) revealed nanometer-scale amorphous calcium carbonate (ACC) precipitates. This preliminary result suggests that inducing calcium carbonate precipitation may remove dissolved metals solution. The results from Chapter 2 and Chapter 3 together reveal that 𝘚. 𝘭𝘦𝘰𝘱𝘰𝘭𝘪𝘦𝘯𝘴𝘪𝘴 can quickly remove metals from solution, which could be applied to both metal recovery and remediation projects. Data from this research could be applied to the development of photobioreactors at ultramafic mine sites. The outcomes suggest that inducing nutrient limitation can enhance metal removal by increasing metal binding through enhanced EPS production. The research presented in this thesis will contribute to the development of sustainable mine operations, with the aim of recovering metals from tailings, and lowering CO₂ emissions, thereby working towards net-neutral mining operations.
TECTONIC EVOLUTION OF THE BAIE VERTE MARGIN, NEWFOUNDLAND
(University of Waterloo, 2025-01-17) Scorsolini, Ludovico; van Staal, Cees; Yakymchuk, Chris
Located along the Early Paleozoic Laurentian continental margin in Newfoundland, the Baie Verte Margin tectonistratigraphy and tectono-metamorphic evolution have been controversial for decades. Here, the results of a detailed field, petrological and geochronological study are presented, where Baie Verte Margin is subdivided into three tectono-metamorphic units separated by tectonic contacts: the East Pond Metamorphic Suite (EPMS) basement, EPMS cover, and the Fleur de Lys Supergroup (FdLS). Each unit exhibits a distinct metamorphic and structural evolution recorded during the subduction, exhumation, and post-collisional history of this ancient margin. The combination of thermodynamic modelling, petrochronology, and structural analysis provided insights into the P-T-t-d paths of the studied units, allowing a better understanding of their role during the evolution of the Taconic subduction system. High-pressure (HP) to ultra-high-pressure (UHP) conditions were reached between 483 and 475 Ma during the D1 phase, with the EPMS cover recording eclogite-facies metamorphism at ~2.8 GPa and 620°C. Subsequent decompression resulted in a β-shaped pressure-temperature-time (P-T-t) path, with near-isothermal decompression to ~2 GPa and heating to 860°C during exhumation. A multi-stage exhumation model is proposed for the EPMS eclogites: 1) buoyant rise through a low-density mantle wedge and 2) subsequent ascent at shallower crustal levels, facilitated by external tectonic forces and slab break-off, as evidenced by Late Taconic magmatism. While the EPMS cover re-equilibrated at UHP conditions, the EPMS basement and FdLS experienced decompression and Barrovian metamorphism during late-D1, indicating decoupling of the units during this stage. Coupling between the units occurred along a D2 shear zone during retrograde metamorphism, spanning 475–452 Ma. Two exhumation scenarios are proposed to explain the tectonic evolution of the margin: (i) Following late D1 detachment, the EPMS basement and FdLS were exhumed to crustal levels while the EPMS cover was subducted deeper into the mantle. Tectonic extrusion along D2 shear zones, potentially aided by melt weakening, then emplaced the EPMS cover between the two units. (ii) Alternatively, sequential detachment occurred from the top to the bottom of the slab, resulting in deeper subduction of lower units, followed by their exhumation through back-folding and crustal wedge thrusting. The Silurian F3 folding deforms both D1-2 structures in each unit and the D2 shear zones that bound them, suggesting that the continental wedges, which recorded different tectono-metamorphic paths after early D1, were juxtaposed before the onset of deformation associated with the Salinic Orogeny. Later deformation phases, D4 and D5, are probably related to tectono-metamorphic activity related to the Acadian and Neo-Acadian orogenies. This research improves our understanding of the dynamic tectono-metamorphic evolution of the Baie Verte Margin, emphasizing the role of fluids, thermal perturbations, and deformation in driving metamorphic reactions, and exhumation. The findings contribute to understanding the mechanisms controlling HP-UHP terrain evolution in subduction zones and highlight the complex interactions between subduction, exhumation, collision, and magmatism throughout the Taconic orogeny.
Reconstructing Late Holocene Environmental Change in the Pevensey Levels: Stratigraphic and Paleoenvironmental Insights from Horse Eye and North Eye, UK
(University of Waterloo, 2025-01-14) Drew, Kian; Ross, Martin; Johnston, John
This thesis investigates the stratigraphic framework and paleoenvironmental evolution of the Pevensey Levels, focusing on the depositional histories of the sediment covering the bedrock-cored islands Horse Eye and North Eye in East Sussex, United Kingdom (UK). Low-lying coastal systems such as the Pevensey Levels are sensitive to climatic variability, geomorphological changes, and human interaction, yet detailed stratigraphic and environmental reconstructions are limited for these landscapes. By combining field observations, sedimentological analyses, and laboratory analyses, this research enhances the understanding of climatic events, geomorphological factors, and anthropogenic influences that have shaped this low-lying coastal-lagoonal landscape over the Holocene. A multiproxy laboratory approach- including laboratory methods that include laser diffraction grain size analysis, portable X-ray fluorescence (pXRF), loss on ignition (LOI), X-ray diffraction (XRD), and AMS radiocarbon dating- was applied to create a stratigraphic framework for reconstructing the stratigraphy and environmental history of the sediment on these bedrock-cored islands. The stratigraphic analyses reveal a broadly consistent depositional sequence across both islands, transitioning from lower marine silty clays at the base to organic-rich peat layers and finally to upper terrestrial clayey silts. Despite this similarity, there are differences that emerge: North Eye’s stratigraphy includes sand-dominated units, attributed to its thinner sediment cover, bedrock exposure, and localized sediment contributions during episodic higher-energy depositional events. In contrast, Horse Eye’s thicker sediment cover and more continuous peat layers indicate prolonged lower-energy deposition and water-logged conditions. Additionally, the lithologic and stratigraphic analyses conducted in this thesis offer a higher level of detail compared to earlier studies, providing localized depositional variability. These findings distinguish this research from earlier work in the area, which provided generalized stratigraphic data for North Eye and focused on broader regional depositional sequences within the Pevensey Levels. The integration of results from the different techniques identified a temporal alignment between localized responses in the sediment with key climatic events, such as the globally recognized 4.2 ka event- a period characterized by dry climates in some regions but has remained poorly understood in Western Europe. At the Pevensey Levels, the stratigraphy during this period reveals an increase in sand content, indicative of heightened depositional energy and fluctuating hydrological conditions, providing new insights into how this global climatic phase may have influenced low-lying coastal landscapes in the UK. The findings also align temporally with documentation of human modifications during the late Holocene, including drainage and land reclamation. For example, lenticular laminations and an increase in sand content in the upper stratigraphy align with documented medieval drainage efforts in this region. This thesis situates these modifications within a regional context, noting how anthropogenic activities may have influenced sedimentary processes in dynamic coastal environments. This thesis provides a new framework for understanding the evolution of the Pevensey Levels within a broader regional context by drawing comparisons with adjacent systems such as the Romney Marsh and Somerset Levels. While the Pevensey Levels exhibit broadly similar depositional patterns to adjacent systems, including marine-to-terrestrial transitions, there are localized differences in sediment depositional processes due to geomorphological controls, such as the differences in size and shape of the bedrock islands, as well as their location with respect to their proximity to sediment sources. The Pevensey Levels’ stratigraphy is more influenced by bedrock-controlled sedimentation near the bedrock-cored islands, landforms that are not present in the Romney Marsh. These regional comparisons reveal variations in depositional energy, peat development, and anthropogenic modifications, offering new insights into the factors shaping coastal-lagoonal systems during the Holocene.
Host phases of redox-sensitive trace metals and an evaluation of trace metal ratios as redox proxies in Ordovician organic-rich sedimentary rocks.
(University of Waterloo, 2024-10-22) Miller, Brianna; Kendall, Brian
Methods for classifying bottom water redox conditions using trace metal ratios are currently being developed, which has increased the importance of identifying primary host phases. Past studies are not in agreement regarding the primary host phases of Thallium (Tl), Rhenium (Re), Molybdenum (Mo), Uranium (U), and Vanadium (V) in organic-rich sediments. Tl is thought to be predominately hosted by pyrite and clay minerals, particularly illite. The central debate for Re and Mo host phases is between pyrite and organic matter, with clay minerals being a less important host. U is found in a wide variety of host phases including carbonates, pyrite, phosphates, or organic matter. Finally, V enrichment is hypothesized to be influenced by organic matter and clay minerals. The concentrations of redox-sensitive trace metals, when normalized to Al content, have been used to identify the bottom water redox conditions during sediment deposition. In a few recent studies, researchers developed enrichment parameters of V, Re, U, and Mo, as well as Re/Mo ratios, which could be used to classify ancient depositional environments. However, it is unclear to what extent ocean redox classification schemes developed based on observations of modern marine sediments can be applied to ancient oceans. A 2M HNO3 acid leach was the procedure used in this study and is based on methods summarized in past work. The 2M HNO3 leach is very effective at dissolving pyrite and can target reactive forms of organic matter and some clay minerals (especially metals adsorbed to clay mineral surfaces). For a subset of samples, total digestions were performed on the residue left behind following 2M nitric acid digestions to evaluate the amount of trace metals remaining. After the 2M nitric acid leach and subsequent total digestion of the residues, the multi-elemental analysis was done using the Agilent 8800 Triple Quadrupole Inductively Coupled Plasma Mass Spectrometer (QQQ-ICP-MS). A total of 19 rock powder samples were sent to Activation Laboratories Ltd (ActLabs) for quantitative X-ray diffraction analysis. All samples were also previously analyzed using whole rock digestions. The mineral analysis was used in tandem with elemental data (organic and inorganic carbon, sulfur, aluminum, phosphorus) to identify the primary host phase for each redox-sensitive trace metal. The prominent host phases for Tl are organic matter and pyrite, with some hosted in clay minerals. Re can be found within organic matter and pyrite but also exhibits the potential to be hosted in certain clay minerals. The results from this study support the previous studies that organic matter is the primary host of Mo in non-euxinic environments. U was found to have been primarily hosted by organic matter and pyrite, with some being hosted in clay minerals. The primary host phases for V within these shales are organic matter and pyrite. Regarding local redox conditions, the trace metal ratios did not agree with each other for most cores. All cores had Mo/Al values of <5 µg g-1/% which indicates the sediments were deposited in settings that could have been oxic, suboxic, or dysoxic. However, the V/Al and Re/Mo ratios contradict this interpretation, suggestive of anoxic and/or euxinic local redox conditions at multiple localities. The U/Al values that are between 1-5 µg g-1/% ambiguously indicate either euxinic, suboxic, or dysoxic conditions. Only one core from the Collingwood Member showed consistent agreement among proxies, pointing to oxygenated bottom waters in this case. These thresholds probably should not be used to establish the local redox conditions of bottom waters during the Early Paleozoic or Precambrian when paleogeography and global ocean redox states were significantly different from the modern ocean.
Long-term evaluation of an organic-carbon permeable reactive barrier remediating mine-impacted groundwater and the potential of emulsified vegetable oil to increase treatment performance
(University of Waterloo, 2024-10-17) Miller, Austin; Blowes, David; Carol, Ptacek
Degradation of water resources by acid mine drainage (AMD) and metal contaminants from the oxidation of mine wastes that are improperly managed is a global environmental concern. An established economical and passive method for managing the transport of oxidation products in groundwater is the installation of an organic-carbon permeable reactive barrier (PRB) to promote the growth of sulfate reducing bacteria (SRB) and dissimilatory sulfate reduction (DSR) in situ. A detailed biogeochemical evaluation was conducted on a PRB remediating AMD from an abandoned Ni-Cu mine after 26 years of treatment, providing the first long-term evaluation of this technology. Pore-water concentrations of Ni decreased from 97µg L⁻1 to < 25 µg L⁻¹ while Fe decreased by 402 mg L⁻¹ (77% of mean influent) through the PRB. Pore-water SO4 decreased by 1,243 mg L⁻¹ (70% of mean influent) coinciding with an increase in alkalinity and pore-water ẟ34Sₛₒ₄, suggesting DSR is actively occurring. There are distinctly different populations of putative SRB present within the sampled PRB material compared to the surrounding aquifer material. Low abundances of S and Fe oxidizing prokaryotes were detected, which may oxidize Fe-sulfide phases; re-mobilizing Fe and S or result in the formation of Fe(III) (oxy)hydroxide phases. A preponderance of S immobilized within the PRB is in the form of acid volatile sulfur with mineralogical investigations identifying FeS phases often replacing organic carbon in plant cellular material and framboidal pyrite. These results demonstrate that the PRB is still operating as designed with complex organic carbon compounds supporting a diverse microbial community that sustain rates of DSR to effectively precipitate Fe sulfides, decrease the acid potential of groundwater and immobilize contaminants. Column experiments were designed to evaluate the incorporation of emulsified vegetable oil (EVO) into solid-phase organic carbon through soaking and injection to promote and sustain treatment performance. Column effluent compositions demonstrate soaking organic-carbon in EVO resulted in high levels of Fe removal for the duration of observation (315 days). Moreover, an EVO injection re-established treatment after removal rates declined, providing a viable alternative to PRB replacement to maintain effective treatment system performance and extend PRB lifespan.
Graphical Analysis of Publicly Available Monitoring Well Databases to Evaluate and Categorize Groundwater Recovery Across Alberta, Canada
(University of Waterloo, 2024-09-09) Brunet, Melanie; Stotler, Randy
A graphical analysis method is applied over the province of Alberta, Canada using publicly available water level data from standard monitoring wells to evaluate and categorize aquifer recovery. Agriculture in the province relies heavily upon surface water for irrigation, which is increasingly unreliable due to climate change and increasing climate variability. Due to an expected future reliance on groundwater, it is necessary to better understand groundwater flow and aquifer characteristics across Alberta to prevent over-allocation of groundwater resources. Water level data from provincial monitoring well hydrographs are examined and graphically analyzed to broadly characterize recovery in agriculturally significant regions of the province of Alberta, Canada. Through this analysis, the presence of a recharge boundary within a recovery curve can be ascertained. Of the 292 monitoring wells originally screened, recovery curve analysis is conducted on 49 monitoring wells. Using graphical analysis of recovery curves within monitoring well hydrographs, the presence or absence of recovery or aquifer replenishment in an area immediately surrounding monitoring well screens is determined. 785 recovery curves from the 49 monitoring wells are subsequently categorized as either “enhanced recovery”, “normal recovery”, or “inconclusive”, with continuing discussion and analysis focusing on results from 36 wells located in three significant aquifers within the province. These aquifers include the Paskapoo aquifer, aquifers within the irrigation districts of southern Alberta, and surficial aquifers within agriculturally rich regions of the province. Results demonstrate the presence of a potential recharge signal deviating from standard Theis recovery curve in 97.22% of the 36 monitoring wells studied. In individual wells, recovery curve classifications vary over time, with some recovery curves being classified as “normal recovery”, and some being classified as “enhanced recovery”, showing signs of a possible recharge boundary. This classification depends on the characterization of late-time recovery curve behavior, as pumping signals transition to regional aquifer signals over time. Analyzed hydrographs show the influence and effects of changes in groundwater pumping on surrounding water levels, including through change in water policy. This method provides information about the presence or absence of recharge over a large area, in contrast to traditional methods of determining recharge which cover smaller areas in comparison. However, a comprehensive database of monitoring well data are required to facilitate analysis, as 48.76% of recovery curves analyzed were classified as “inconclusive”. It is recommended that results from this method are paired with data such as climate indices or agricultural usage, to help determine possible correlations between results and climatic, geographic, or agricultural factors.

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