Earth and Environmental Sciences

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Controls on Microplastics Accumulation in Stormwater Ponds
(University of Waterloo, 2024-07-04) Nguyen, Thu Hang
Microplastics (MPs), or plastic particles that are less than 5 mm in diameter, are an emerging threat to aquatic and terrestrial ecosystems because of their potential toxicity and their resistance to degradation. In urban watersheds, stormwater runoff is a major carrier of MPs to downstream water bodies, which often drains into green infrastructure such as stormwater ponds (SWPs). The existing evidence indicates that SWPs may be effective at reducing the export loads of MPs from urban areas. However, the effectiveness of SWPs in retaining MPs and the controls on their accumulation in SWP remain understudied. Hence, it is significant to investigate MP occurrence and factors controlling MP distribution in SWPs. In this thesis, I aimed to (1) assess the variability in MP types, sizes, and abundances within SWP sediment and water samples, (2) determine the influence of sediment properties (e.g., organic carbon concentration, particle size) on the types, shapes and sizes of MPs accumulating in sediments versus within and between SWPs, and (3) investigate the impact of SWP characteristics on MP accumulation, including land use and land cover (LULC). I addressed these research objectives by collecting sediment and water samples from five SWPs with different LULC (industrial, residential, and commercial) in the City of Kitchener, Ontario, Canada, extracting MPs from environmental samples, and characterizing MP particles using laser direct infrared (LDIR) imaging spectroscopy. In Chapter 2, I extracted MPs from sediment cores in triplicates and determined MP counts and morphologies using the LDIR. I also analyzed sediment for grain size, mineralogy, and organic carbon (OC) content. The results revealed that the MPs accumulated in the sediments were predominantly fragments, with concentrations approximately 50 times higher than fibers, implying an important role of particle shape in controlling the accumulation of MP particles in SWP sediments. The highest fragment concentrations (2.3×108 particles kg dw-1) were found in the commercial SWP, while the highest fiber concentrations (4.5×106 particles kg dw-1) were found in the industrial SWP. Surface area-normalized MP accumulation rates in the forebays were generally 2-5 times higher than in the main basins. Sediment grain size and catchment impervious cover were significantly correlated with MP accumulation rates, with increasing MP concentrations observed with finer sediment grain size and higher catchment imperviousness. Polyamide and polyethylene were the two most abundant polymers found in the pond sediment, along with an overwhelming dominance of MP particles less than 50 µm. MP polymer composition and size distribution thus reflected the contribution of urban activities to MP pollution in a watershed. These findings indicate the important role of catchments’ land cover in the build-up and wash-off of sediments and MPs to downstream areas such as SWPs. In Chapter 3, I quantified and characterized MP shapes, types, and sizes in stormwater samples collected bi-monthly from 5 SWPs. In a one-year water sample collections, MPs appeared to fluctuate with significant seasonal variation throughout the year with the highest concentration recorded in a residential pond (up to 20,166 fragment L-1 and 559 fiber L-1). Polyamide and polyethylene accounted for approximately 80% of total MP in the pond water, while small-sized MPs make up 85% of the particles, highlighting the impact of catchment land use on MP occurrence in SWP. Precipitation, wind speed, and pond hydraulic loading were found to wash away surface MPs and dilute MP concentration in the water column. These findings demonstrate the diversity in MP profiles associated with climate factors, implying a need for long-term monitoring to address those spatial and temporal variability. The results from Chapters 2 and 3 overall provided an insight into MPs' preferential partitioning between two different environmental matrices, which can be applied in future research to assess the sources, transport, and fate of MPs in the freshwater ecosystem. Data from this research can be applied to generate MP accumulation rates across the Grand River watershed and eventually the Great Lakes. The outcomes from this study, moreover, actors influencing MP accumulation in urban catchments, and therefore, can support further studies on characterizing MP mass balance and budget for urban watersheds. Since SWPs are an effective indicator of local sources of MP pollution, understanding the MP from urban catchment can inform policymakers in a larger aquatic ecosystem to tailor management strategies accordingly. The research study presented in this thesis therefore contributes to the development of local policies and regulations, which not only address specific sources of MP pollution but also serve as models for larger-scale regulations aimed at protecting the freshwater environment.
Assessing the biodegradability of dissolved organic carbon in freshwater systems
(University of Waterloo, 2024-06-18) Green, Danielle
Dissolved organic carbon (DOC) is an important contributor to both carbon (C) cycling and other biogeochemical processes in aquatic ecosystems as it is the most mobile fraction of organic matter. The biodegradable fraction of DOC can be microbially degraded over time, producing carbon dioxide (CO2), a greenhouse gas (GHG) that is subsequently released to the atmosphere. In addition, microbial degradation-resistant DOC can accumulate in water bodies, causing chemical and physical changes to aquatic systems, resulting in decreased primary productivity, formation of anoxic zones, and negative implications on the aquatic food cycle. Although biodegradable DOC (BDOC) is widely studied, there is no agreed-upon standard method for assessing DOC biodegradability. Given its important control on CO2 production and natural functioning of aquatic ecosystems, it is essential to develop an accurate and reproducible method for quantifying BDOC in aqueous samples. In Chapter 2, I developed and evaluated a new method for determining BDOC in freshwater samples. The method includes filtering water samples to below 0.22 µm, to remove existing microbial cells, prior to inoculating the samples with a concentrated microbial inoculum produced by stepwise isolation of microbial cells from a peat sample. Additionally, I added solutions containing nitrogen (N) and phosphorus (P) (in the forms of ammonium nitrate (NH4NO3) and potassium phosphate (K2HPO4), respectively) to ensure that the microbes were not nutrient-limited. The samples were then capped with foam stoppers and incubated in the dark at 25⁰C on a shaker for 28 days to allow constant aeration during BDOC degradation. When applied to five freshwater samples collected from rivers, stormwater ponds, and a lake, and a glucose control, I observed that the amount of BDOC in the natural samples ranged from 15% to 53% and was 90% in the glucose control. Rates of BDOC degradation were calculated from DOC measurements at six sampling time points between days 0 and 28. I found that the DOC trends with time were best explained by two successive phases for BDOC degradation in all of the samples: an initial, fast, phase of BDOC degradation followed by a second, slower, phase of BDOC degradation where the rate constant for the second phase was between 5.57 and 565 times slower than for the initial phase. Changes in chemical characteristics of DOC measured using absorbance and fluorescence parameters including specific ultraviolet absorbance at 254 nm (SUVA254), humification index (HIX), and parallel factor analysis (PARAFAC) at each sampling time revealed that the initial, fast, phase of BDOC degradation often represents the utilization of small, non-aromatic compounds while the later, slower, phase of BDOC degradation often represents the utilization of more complex, aromatic compounds. The developed method provides a new approach to measure and characterize BDOC degradability and degradation kinetics that can be applied to future studies on biogeochemical processes in aquatic ecosystems. In Chapter 3, I examined the potential for CO2, a greenhouse gas, to be produced from two stormwater ponds (SWPs) in the City of Kitchener, Ontario, Canada by quantifying the biodegradability of DOC entering the ponds through the inlet sewers during rain events. Further, BDOC, the fraction of DOC that can be mineralized by microbes during respiration to produce CO2, was related to the optical properties of water entering each of the SWPs to determine if any statistically significant relationships exist between BDOC and the optical properties of water. In the two studied SWPs, one with industrial land use and one with residential land use in the catchment area, we found significant negative linear correlations between BDOC and SUVA254, HIX, biologic index (BIX), and humic-like and tryptophan-like PARAFAC components. Additionally, there were significant positive linear correlations between BDOC and DOC concentration, benzoic acid, and tyrosine-like PARAFAC components. These optical properties are influenced by characteristics of the SWP catchment areas including imperviousness and land use. Overall, these findings indicate that increased urbanization results in changes in optical properties of DOC entering SWPs, increasing the amount of BDOC and, in turn, the potential for increased CO2 emissions.
Evaluation of the Potential Impacts of Submerging the Oxidized Tailings and Adding a Cover Layer at Mine Principale
(University of Waterloo, 2024-04-24) Agau, Majak
Oxidation of sulfide minerals generates acid and forms various secondary phases including Fe(III) (oxy)hydroxide phases, jarosite, and gypsum, which can attenuate hazardous metal(loid)s by precipitation, co-precipitation, and adsorption reactions within tailings. The abandoned Cu-Ag mine at Mine Principale, Chibougamau, Québec, has three tailings impoundments (Parcs, A, B, and C) that have oxidized for more than 50 years. This project focused on Parc B, where tailings are stored to an average depth of 8.0 meters below the ground surface (mbgs). The study involved mineralogical, chemical, and microbiological analyses to evaluate the potential impacts of the proposed elevated water table (EWT) technique on the partially oxidized tailings. The EWT involves raising the water table and maintaining it above reactive tailings. Increasing the water content limits sulfide-mineral oxidation by minimizing O2 ingress into the tailings, owing to its low diffusivity in saturated media. However, the EWT can cause direct dissolution of soluble secondary phases, and also can potentially induce reducing conditions that promote microbially catalyzed reductive dissolution of Fe(III) (oxy)hydroxide phases fueled by organic C compounds. In this study, mineralogical and selective chemical extraction techniques indicate the presence of various secondary phases including Fe(III) (oxy)hydroxides that are associated with significant amounts of hazardous metal(loid)s including Cu, Ni, Co, Zn, As and Pb in the oxidized zone, which is limited to a depth of about 1.5 mbgs in Parc B. Results of amplicon sequencing of 16S rRNA genes show significant abundances of Fe- and S-oxidizing bacteria and S-reducing bacteria but no presence of Fe-reducing bacteria. Solid-phase analyses indicate a low amount of total C in the oxidized tailings. These findings suggest that EWT technique can be an effective reclamation method for Mine Principale tailings if use in conjunction with another suitable method to address potential low-quality drainage resulting from the inducement of reducing conditions post EWT application.
Chlorophyll-a Mapping in a Large Lake Using Remote Sensing Imagery: A Case Study of Western Lake Ontario
(University of Waterloo, 2024-04-23) Shahvaran, Ali Reza
Western Lake Ontario (WLO) and Hamilton Harbour (HH) experience significant eutrophication challenges. Despite an overall decrease in the limiting nutrient phosphorus (P) inputs, recurrent nuisance (Cladophora) and cyanobacterial harmful algal blooms (cHABS) are observed in nearshore hotspots of WLO and HH, respectively. These events hint at a complex interplay of contributing factors including not only of P availability but nutrient enrichment in general, as well as invasive mussel species altering ecosystem dynamics, climate change, and other anthropogenic influences. As a result, continued and consistent monitoring is of paramount importance. Eutrophication in WLO and HH is also linked to the expanding urbanization within the Golden Horseshoe, which includes the Greater Toronto Area (GTA), along with nutrient point and nonpoint load sources from stormwater management systems and agricultural watersheds. Of importance are also the nutrient inputs flowing from Lake Erie through the Niagara River creating local productivity zones at the river mouth. Traditional field-based monitoring methods face limitations, including high costs, labour intensity, limited temporal resolution and inadequate spatial coverage. In that respect, remote sensing (RS) may offer an alternative approach, leveraging the water colour (optical properties) to detect optically active constituents (OACs) like Chlorophyll-a (Chl-a) that can provide proxies for phytoplankton abundance in algae. The distinct spectral signatures of Chl-a make multi-spectral imagery a valuable tool for water quality assessment that can complement ongoing in-situ monitoring. This thesis presents a comprehensive analysis aimed at enhancing the capacity for monitoring nearshore algal blooms in the oligo-mesotrophic WLO and eutrophic HH through publicly available high-spatial-resolution (< 100 m) RS satellites data, specifically Landsat 5, 7, 8, 9, and Sentinel-2. The research explores the optimal combinations of atmospheric correction methods and reflectance indexes to develop semi-empirical based Chl-a retrieval models specific to the (sub)regions considered. As an additional application, the satellite based Chl-a data are used to assess the spatial-temporal variability and trends of algal productivity over the past decade, identifying productivity hotspots and anomalies. The thesis is structured in five chapters, beginning with a general introduction in Chapter 1, followed by Chapter 2, which offers the necessary background for understanding the research presented in the thesis. Chapters 3 and 4 delve into comparative evaluations of Chl-a retrieval methods and time-series analysis of algal bloom dynamics, respectively. The thesis ends with Chapter 5, which synthesizes the main findings and offers conclusions and future research directions. Chapter 3 presents a comprehensive comparative evaluation of atmospheric correction processors and reflectance indexes, assessing their performance in Chl-a concentration retrieval from a multi-platform collection of satellite data. By analyzing satellite scenes from different platforms alongside in-situ measured Chl-a data, the chapter develops predictive linear regression models. The results highlight the superior performance of certain combinations, particularly ACOLITE-corrected Landsat 8 and Sentinel-2 imagery utilizing two band ratio indexes, that is blue-to-green or blue-to-red, in capturing Chl-a concentration with acceptable accuracy. Delving into the Chl-a dynamics, Chapter 4 presents a time-series analysis using Landsat 8 and 9 imagery from 2013 to 2023, to reconstruct the spatial-temporal patterns and hotspots in WLO and HH. After preprocessing a collection of Level-1 images with the optimal combination of atmospheric correction method and retrieval index, as identified in Chapter 3, a time-series collection of estimated Chl-a concentration maps are produced. By applying three algal growth indicators, namely bloom intensity, extent, and severity, along with averaging annual and monthly estimated Chl-a concertation maps and conducting a Mann-Kendall trend analysis, we are able to examine algal bloom dynamics, seasonality, and delineate areas of concern. The results should help in planning monitoring and design eutrophication management strategies for the region. The findings from this thesis underscore the potential of space-borne RS in advancing water quality monitoring that can inform management practices. By identifying the most effective methods for Chl-a concentration retrieval and providing a nuanced understanding of algal growth dynamics, the research in this thesis contributes to both fields of aquatic RS and water quality monitoring. The comparative analyses, model developments, and spatial-temporal investigations not only offer practical tools for water quality assessment but also set the stage for future studies leveraging machine learning and existing satellite datasets. The work demonstrates the critical role of tailored RS applications in addressing eutrophication issues, advocating for integrated monitoring approaches to sustain aquatic ecosystems in the face of changing environmental conditions.
Glacial Dispersion at the Canadian Malartic Gold Deposit
(University of Waterloo, 2024-04-19) Taylor, Caroline Emily
A novel drift prospecting approach detected components from previously established bedrock footprints at the world-class Canadian Malartic gold deposit within the site’s surrounding Quaternary sediments. The measured glacial dispersion of footprint components is significantly more extensive than the largest bedrock footprint. This new method could apply to similar high-tonnage disseminated gold deposits and other deposits with similar features. Drift prospecting methods included ice flow indicator mapping, surficial sediment sampling and characterization, particle size distribution analyses, till matrix geochemistry (major oxide, minor, and trace elements), glacial clast lithology, gold grain counts, and petrography. Our novel approach combined hyperspectral imaging analyses with petrographic analyses targeting glacial granules and pebbles. Within the study area, the direction of past ice flow phases evolves from ~210º to ~150º; it dominates towards ~170º. Multivariate analysis of till matrix major oxide geochemistry links clusters of samples to bedrock geology and postglacial processes. Till clast lithologies link to bedrock type. The spatial distribution of till matrix minor and trace element geochemical values reveals glacial dispersal trains for Au, Ag, Rb, W, and potentially Ba; however, glacial dispersal trains for Cs, Mo, Pb, and Sr are unclear (all listed elements have been previously reported as footprint components). Multivariate analyses of till matrix minor and trace element geochemistry link clusters of samples to footprint components (Mo has the highest first principal component positive loading in the relevant cluster), bedrock geology background values, and postglacial processes. Sand-sized gold grain counts from till and their morphology link to the phengitic white mica bedrock footprint associated with the deposit. Hyperspectral imaging analysis of bulk glacial clasts reveals dispersal extents that are significantly larger than the extent of the phengitic white mica footprint in bedrock (i.e, the most extensive bedrock footprint at the Canadian Malartic gold deposit). 4-8 mm tracer till clasts produce a dispersal extent 7.0-13.5 times larger while 2-4 mm tracer till clasts produce a dispersal extent 4.5-8.4 times larger than the bedrock footprint. Further, petrographic analyses of 42 highly phengitic 4-8 mm clasts classify 14 clasts as showing mineralogy and rock texture similar to the host quartz-monzodioritic, granodioritic, and meta-sedimentary rocks at the deposit. One of these clasts is mineralized with gold like the mineralization at the Canadian Malartic deposit, and this is the first reported instance of finding a mineralized clast using this novel technique. The Quaternary dispersion relative to the previously established bedrock footprints at the Canadian Malartic gold deposit is significant. Ongoing hyperspectral imaging and petrographic analyses of similar clasts may demonstrate numerous practical applications to exploration campaigns seeking other Canadian Malartic-type gold deposits or other deposits with similar characteristics.
Evolution of the Laurentide Ice Sheet in north-central Ontario from subglacial sediments
(University of Waterloo, 2024-03-12) Taves, Robin
Till stratigraphic analysis of 10 sediment bluffs near Ogoki Post in the Hudson and James Bay Lowlands.
Proterozoic zircon dates from auriferous zones at the Island Gold deposit: implications for late gold remobilization in the Superior Province
(University of Waterloo, 2024-02-13) Gagnon, Sophie Marie
The Island Gold deposit is a high-grade Archean orogenic gold deposit within the Michipicoten greenstone belt of the Superior Province. Hosted within the ~2750 Ma felsic to intermediate Wawa metavolcanic assemblage, gold mineralization has been constrained to between ~2680 and 2673 Ma. However, anomalous Proterozoic ages have been discovered within auriferous alteration zones, suggesting that late hydrothermal activity may have affected the deposit and potentially remobilized gold. Mineralization is hosted within quartz (± carbonate) veins, with minimal mineralization within the surrounding altered host rock. To investigate the occurrence and spatial distribution of these anomalous young ages within the deposit, samples along an alteration gradient (weakly to strongly altered) adjacent to auriferous quartz ± carbonate veins, and from differing depths within the ore zone were examined. U–Pb LA-ICP-MS analyses of zircon from strongly altered auriferous zones yielded Archean protolith dates as well as Mesoproterozoic and early Paleozoic to late Mesozoic dates. Compared to Archean zircons in the host metavolcanic rocks, the younger zircons have generally higher concentrations of heavy rare earth elements and moderate enrichment in Y, Ta, U, and Th. We interpret the Mesoproterozoic ages to represent fluid–rock interaction during the Mid-Continent Rift, whereas the Paleozoic to Mesozoic grouping may be related to alkalic/kimberlitic activity within the area associated with the Great Meteor Hotspot track. It is unclear if these fluids had compositions amenable for large-scale gold mobilization, but they may have played a role in locally distributing gold throughout the Island Gold deposit. An increasing number of reported Proterozoic dates from accessory minerals in Archean gold deposits suggests that post-Archean processes are a potential complication for understanding the distribution of gold and has regional implications for gold exploration in the Superior Province.
Use of Fe isotopes to examine Fe cycling in Boreal Shield lakes: implications for cyanobacterial bloom development and ancient biogeochemical cycling
(University of Waterloo, 2024-01-26) LIU, KAI
Stable iron (Fe) isotopes have only been used recently to explore biogeochemical Fe processes in terrestrial and aquatic ecosystems. The δ⁵⁶Fe values in natural samples range from −4‰ to 4‰. An increasing number of studies have focused on Fe isotopes in marine settings. However, few studies have focused on lake systems and only in extreme environments such as meromictic ferruginous lakes. This thesis has applications in two distinct fields, freshwater eutrophic research and early Earth evolution. Phytoplankton blooms have been studied extensively in lake ecosystems. Despite the fact that macronutrients phosphorus and nitrogen are commonly known as dominant factors controlling the blooms, the critical role of micronutrient Fe has been proposed in recent studies. However, current understanding of the sources and availability of Fe for phytoplankton blooms and Fe cycling in lakes in general remains limited. Although the mechanisms that result in the deposition of banded iron formation in the Archean ocean remain a subject of debate, it is proposed that photoferrotrophy played a significant role in the oxidation of Fe(II) in anoxic Archean oceans. Studies investigating the occurrence and significance of photoferrotrophy have primarily focused on meromictic and ferruginous lakes. However, such lakes are thought to be rare on a global scale. To explore the potential application of stable Fe isotopes for tracing biogeochemical Fe cycling in Boreal Shield lakes, δ⁵⁶Fe values of dissolved, particulate, and sediment Fe were measured in two small dimictic Boreal Shield headwater lakes: manipulated eutrophic Lake 227, with annual cyanobacterial blooms, and unmanipulated oligotrophic Lake 442. Within these small lakes, the range in δ⁵⁶Fe is large (ca. −0.9 to +1.8‰), spanning more than half the entire range of natural Earth surface samples. Two layers in the water column with distinctive δ⁵⁶Fe of dissolved (DFe) and particulate Fe (PFe) were observed in both lakes, despite large differences in trophic states. During cyanobacterial blooms in Lake 227, selective uptake of isotopically light Fe modifies δ⁵⁶Fe, resulting in Δ⁵⁶Fe dis-part of up to 1‰ between dissolved and particulate Fe in the epilimnion while little fractionation was observed in the epilimnion of Lake 442. In the anoxic layers in both lakes, upward flux from sediments dominates the dissolved Fe pool with an apparent Δ⁵⁶Fe dis-part of −2.2 to −0.6‰. Large Δ⁵⁶Fe dis-part and previously published metagenome sequence data suggest active Fe cycling processes in anoxic layers, such as microaerophilic Fe(II) oxidation or photoferrotrophy, could regulate biogeochemical cycling. Large fractionation of stable Fe isotopes in these lakes provides a potential tool to probe Fe cycling and the acquisition of Fe by cyanobacteria, with relevance for understanding biogeochemical cycling of Earth’s early ferruginous oceans. To further explore the effect of phytoplankton blooms on biogeochemical Fe cycling in the epilimnion and metalimnion of L227, seasonal variations in Fe concentrations, Fe speciation and Fe isotope compositions of dissolved Fe (DFe), particulate Fe (PFe) and total Fe (TFe) were reported in the oxic layers of L227 and L442. Biological uptake of Fe by phytoplankton results in a decrease in DFe, an increase in PFe and a decrease in TFe in the oxic epilimnion and metalimnion during the blooms. The prevalence of Fe(II) in the particulate Fe coupled with the depletion of Fe(II) in the dissolved Fe during the blooms suggest that diazotrophic cyanobacteria and chlorophytes in L227 likely utilize dissolved inorganic Fe(II) rather than organic complexed Fe(III), highlighting the importance of Fe(II) during iron acquisition. Uptake of isotopically light Fe by phytoplankton results in a diagnostic change in the dissolved and particulate δ⁵⁶Fe in the oxic layers. As a result, dissolved δ⁵⁶Fe is more positive than particulate δ⁵⁶Fe in the oxic layers of L227, with Δ⁵⁶Fe dis-part of 1.02 ± 0.33‰ (2σ) during the peak of the first bloom and Δ⁵⁶Fe dis-part of 0.56 ± 0.05‰ (2σ) during the second bloom. The difference in Δ⁵⁶Fe dis-part observed during the first bloom and the second bloom suggests that uptake of Fe by chlorophytes might produce distinct Fe isotope fractionation compared to diazotrophic cyanobacteria, possibly due to the differences in their uptake kinetics, the specific Fe-uptake mechanisms and associated enzymatic processes. The consistency in TFe concentration and Fe isotope composition of TFe in the epilimnion throughout the first and second blooms suggest that the settling flux of particulate Fe is limited during the blooms, likely due to efficient retention by phytoplankton. In contrast, during the decline of the bloom, the settling of isotopically light particulate Fe(II) associated with biomass to profundal sediment caused total δ⁵⁶Fe in the epilimnion to become isotopically heavier. During the peak of the first bloom, the large Δ⁵⁶Fe dis-part, the more negative particulate δ⁵⁶Fe, and the more particulate Fe concentrations in the metalimnion compared to what has been observed in the epilimnion suggest that cyanobacteria could migrate to the upper zone of the anoxic hypolimnion to uptake Fe under Fe-limited conditions. Modelling results showed that isotopically light PFe and TFe measured in the metalimnion during the peak of the first bloom are best explained by the migration of cyanobacteria below the redox boundary for the uptake of dissolved Fe(II). The observed seasonal variation in Fe concentration, speciation and isotope compositions associated with the progression of two annual blooms show great potential in understanding the role of Fe in the formation of cyanobacterial bloom and determining the availability and source of Fe for cyanobacterial uptake. To explore the Fe processes and Fe sources in the anoxic hypolimnia of Boreal Shield lakes, seasonal variation in Fe concentrations and Fe isotope compositions of dissolved Fe and particulate Fe in the anoxic hypolimnia along with the Fe concentrations and Fe isotope compositions of porewater Fe and bulk sediment Fe in bottom sediment cores were reported in four Boreal Shield lakes: one eutrophic Lake 227 and three oligotrophic Lake 221, Lake 304 and Lake 442. In the oxic layers of all lakes, dissolved δ⁵⁶Fe is more positive than particulate δ⁵⁶Fe, likely modified by a combination of multiple processes including biological uptake, photochemical reduction of particulate Fe(III), complexation of dissolved Fe and dissolved organic matter, photolysis and microbial decomposition. The observed Δ⁵⁶Fe dis-part in the oxic layers of all lakes ranges from 0.06 ± 0.09‰ (2σ) to 1.02 ± 0.33‰(2σ), with the higher values likely arising from biological uptake. In contrast, the δ⁵⁶Fe values of dissolved and particulate Fe are reversed in the anoxic hypolimnia of all lakes, with negative Δ⁵⁶Fe dis-part fractionations of −0.91 ± 0.58‰ (2σ) in L221, −0.87 ± 0.81‰ (2σ) in L227, −1.06 ± 0.26‰ (2σ) in L304 and −0.72 ± 0.25‰ (2σ) in L442. Particulate Fe from the epilimnia is likely reduced completely by dissimilatory iron-reducing bacteria at the redox boundary, supported by the similarity in δ⁵⁶Fe between dissolved Fe in the anoxic hypolimnia and particulate Fe in the epilimnia of all lakes. The highly positive δ⁵⁶Fe values of particulate Fe in the anoxic hypolimnion and the large Δ⁵⁶Fe dis-part fractionations indicate in situ active Fe cycling in the anoxic hypolimnion. The most plausible explanation for the large Δ⁵⁶Fe dis-part fractionations in the anoxic hypolimnion is microbial oxidation, possibly photoferrotrophy, supported by the 16S rRNA gene sequencing and genome-resolved metagenome sequencing analysis. An increase in the magnitude of Δ⁵⁶Fe dis-part with depth and over time was observed in L221, L227 and L304, likely due to the variation of the oxidation rates, supported by increased particulate Fe concentrations with depth and time. The high concentration and negative δ⁵⁶Fe values of porewater Fe(II) suggest that DIR dominates organic mineralization pathways in sediment cores from the bottoms of L227, L304 and L442. The DIR-produced porewater δ⁵⁶Fe is further modified by the diagenetic formation of siderite in the upper section of sediment cores and the diagenetic formation of pyrite in the deeper section. Temporal and spatial variation in Fe isotope fractionation in the anoxic hypolimnia, along with the Fe isotope signatures in the sediment, suggest active Fe cycling in four lakes, highlighting the potential of seasonally anoxic Boreal Shield lakes to serve as analogues of the late Archean ocean.
Hydrogeochemistry and Trace Element Mobility in an Acidic High-Sulfide Tailings Impoundment After 40 Years of Oxidation
(University of Waterloo, 2024-01-25) Starzynski, Hannah Lucy
Abandoned mine sites can create a legacy environmental contamination issue when the generation of acid mine drainage is allowed to continue with insufficient or absent remediation measures. The South Bay mine, a former underground Cu-Zn mine located in northwestern Ontario, is once such site with historical contamination. The mine wastes at South Bay contain high concentrations of sulfide minerals which continue to oxidize decades following mine closure, leading to acidic seepage with high concentrations of dissolved metals impacting the surrounding lakes. This aim of this study is to provide a characterization of the current hydrogeology, geochemistry, mineralogy, and microbiology of the South Bay tailings so that this information can inform future remediation work. Instrument installation and collection of core samples of the tailings was performed at five locations within the tailings impoundment area. Pore-water samples were collected from piezometer and soil water sampler nests. Sub-samples of tailings cores were collected and analysed using optical microscopy, scanning electron microscopy, selective extractions, total carbon/sulfur, X-ray diffraction, X-ray fluorescence, synchrotron, and DNA sequencing techniques. Mineralogical analysis indicated that pyrite was the main sulfide mineral in the tailings, with lesser amounts of sphalerite and chalcopyrite and trace amounts of pyrrhotite, galena, and arsenopyrite. The oxidation zone in which sulfide minerals are depleted is restricted to the upper 0-15 cm of tailings. The moisture content within the tailings is relatively high, contributing to a low O2 diffusion rate into the tailings. High proportions of acidophilic microorganisms capable of catalyzing Fe and S oxidation reactions were found in the shallow tailings. Sulfide oxidation modelling has indicated that oxidation of sulfide minerals in the South Bay tailings may continue for decades to millennia before all sulfide minerals are depleted in the vadose zone. Prolonged sulfide mineral oxidation has led to acidic pore waters with pH as low as 1.26 with high concentrations of dissolved metals, including Fe, Zn, Cu, As, Pb, and Co. The lowest pH and highest concentrations of dissolved metals tends to occur in the shallow tailings near the region of active sulfide-mineral oxidation. High concentrations of dissolved rare earth elements (REEs), up to 9.45 mg/L total REEs, were also found within the shallow acidic pore-waters. Dissolution of gangue minerals and secondary minerals contributes to acid neutralization, with pH increasing to circumneutral values below the water table. Metals and metalloids may be attenuated through adsorption or co-precipitation with secondary mineral phases. Copper was found to be attenuated through covellite precipitation, Pb was attenuated through anglesite precipitation, and As was attenuated by adsorption or co-precipitation with Fe(III) (oxy)hydroxides. Metal(loid)s sequestered within Fe(III) (oxy)hydroxides may be susceptible to remobilization through reductive dissolution should environmental conditions imposed by future remediation efforts induce strong reductive conditions.
Integrated hydrologic model calibration under non-stationary climates
(University of Waterloo, 2024-01-17) Song, Mohan
With global climate change, quantifying water availability for management under non-stationary conditions is, and will continue to be, a major challenge. When hydrologic models are calibrated to historic climatic conditions, they may lack the ability to simulate future extreme climates. This research quantified changes in model calibration under non-stationary climate conditions using the Harold L. Disney Training Center (HLDTC) site in Kentucky, USA for demonstration. An integrated hydrologic model of the site was developed using HydroGeoSphere (HGS) and was calibrated using PEST. Hydraulic conductivity (K), specific storage (Ss), and surface friction coefficient parameters were calibrated under four different climate scenarios based on two moderately-extreme precipitation events during the observation period: a. the entire observation record, including the two moderately-extreme precipitation events (base scenario), b. the entire observation record minus the short duration event (April 2017), c. the entire observation record minus the long duration event (February 2018), and d. the observation record without either event. The results demonstrate that the inclusion of observations from extreme precipitation events impact the calibration of the hydrologic model. The variations in K and Ss were the highest between scenarios of all the calibration parameters tested, while the ridge surface friction, topsoil hydraulic conductivity, or clayey sand specific storage remain unchanged. K has the greatest decrease in lateral K (x and y direction) of the clayey sand layers in Scenario D, and greatest increase in lateral K of fractured rock formation in Scenario C. This indicates the importance of lateral flow in the fractured rock during the shorter duration precipitation event. Ss changed in the fractured rock formation in Scenario B, indicating the importance of storage in the fractured rock during the longer duration precipitation event. The model constructed by this study can better capture shorter duration moderately-extreme precipitation events, demonstrated by a better match between observed and simulated hydraulic heads in Scenario C. The results also suggest that not only the presence or absence of these events informs model calibration, but the timing and duration of these events influences the parameters it informs.
Modelling effects of stormwater best management practices on urban stormwater runoff phosphorus
(University of Waterloo, 2024-01-15) Zhou, Bowen
Phosphorus (P) is a key limiting nutrient for algal growth in freshwater whose excess loading to freshwater bodies contributes to cultural eutrophication and the associated symptoms of water quality deterioration. Urban stormwater is a significant contributor of P to downstream ecosystems from various point and non-point sources and via a variety of transport and emission pathways. Stormwater best management practices (BMPs) such as stormwater ponds (SWPs, a type of traditional stormwater BMP) and bioretention cells (BRCs, a type of low-impact development (LID) BMP) have the potential to attenuate P loads from urban areas and hence mitigate eutrophication risks to aquatic ecosystems. Despite their rapidly growing implementation worldwide, the effects of these stormwater BMPs on urban stormwater P concentrations and loads remain poorly understood. In this thesis, I assess the effects of urban stormwater BMPs on P export, with the goal of determining (1) what are the knowns and unknowns regarding the sources, pathways, and influence of stormwater BMPs on urban P export, (2) what are the dominant internal processes that control P reduction in BRC, based on process-based modelling, (3) what are the general effects of BRCs on urban stormwater runoff P and how are they different from the effects on nitrogen (N), and (4) how to predict the effects of BMPs on urban stormwater runoff P through the use of data-driven models, and what are the potential influencing factors. I address these research questions by reviewing urban P sources discussed in the literature, quantifying P mass balance in a BRC facility in Mississauga, ON, assessing effects of urban stormwater BMPs on P export based on data from the International Stormwater BMP Database, and through the development of process-based and data-driven BMP P models. In Chapter 2, I review the existing literature and analyze data from the International Stormwater BMP Database (ISBD) to summarize the sources, pathways and speciation of urban stormwater P, and the effects of urban stormwater BMPs on P export. This study acts as an introduction to the issues of P in urban stormwater runoff and identifies the research gaps associated with understanding effects of stormwater BMPs on urban stormwater P export. I show, based on both previous literature and the data in the ISBD, that the effects of stormwater BMPs on urban P export remain highly uncertain and unknown. There is a lack of predictive tools for estimating effects of stormwater BMPs on urban P export, and I go on to fill this research gap in Chapters 3, 4, and 5. Following Chapter 2, I address my research questions by developing a process-based P model for a BRC facility in Mississauga, ON. This model is calibrated using field monitored data for flow, water quality and filter media soil chemistry (from core samples). In Chapter 3, the model simulates the multi-year P partitioning, accumulation and export in this stormwater BMP. I show, via the analysis of model simulation results, that exfiltration to underlying native soil was principally responsible for decreasing the surface water discharge from the BRC (63% runoff reduction), while accumulation in the filter media layer was the predominant mechanism responsible for the reduction in P outflow loading (57% retention of total P (TP) inflow load). Of the P retained within the filter media layer, only 11% was stored in easily mobilizable forms. There were no signs that the P retention capacity of the BRC was approaching saturation after 7 years of operation. Thus, my results demonstrate sustained efficient P load reduction by this BRC. In Chapter 4 I evaluate the general effects of BRCs on urban stormwater runoff P concentration and loading by analyzing data from a large number of BRCs in the ISBD from across the United States. I further compare the influence of BRCs on P and N export. I also introduce the data-driven approach in Chapter 4 by training a random forest model to predict the reduction and enrichment effects of BRCs and compare the importance of different explanatory variables. I show that while BRCs typically enrich concentrations of TP and soluble reactive P (SRP), the corresponding outflow loads of TP and SRP, were generally lower, mainly because of reductions to surface runoff volumes via exfiltration to the subsurface. This finding raises questions regarding the relative importance of this infiltrating P to the subsurface environment and potential impacts to groundwater quality. Because they are generally more efficient in reducing N loads than P loads, BRCs tended to decrease the N:P ratio of stormwater runoff, potentially altering nutrient limitation patterns in receiving aquatic ecosystems. My findings also imply that the impacts of BRCs on P and N concentrations, speciation, and loads in urban runoff are highly variable. This variability can be partly accounted for by some explanatory variables related to the climate, watershed and BRC characteristics, and predicted by machine learning (ML) methods such as the random forest model. Random forest modeling identified inflow concentrations and BRC age as key variables modulating the changes in TP, SRP, and total N concentrations between inflow and outflow. For dissolved inorganic N, the BRC’s storage volume and drainage area also emerged as important explanatory variables. Chapter 5 also focuses on the ISBD, similar to Chapter 4, but the analysis of P control performance is expanded to six categories of BMPs. I compare the accuracy of different data-driven models for the prediction of BMP P reduction/enrichment factors, through the use of different ML methods. I show that although LID BMPs are generally more efficient at reducing runoff quantity, they are more likely to enrich TP and SRP concentrations compared to traditional BMPs leading to poorer P load reduction performance amongst LID BMPs. Both traditional and LID BMPs are more likely to enrich SRP concentration when influent SRP concentration is low, in watersheds with higher imperviousness and in drier climates. The influence of LID BMPs on SRP concentration is also more sensitive to climate, watershed and BMP characteristics compared to traditional BMPs. I show that the random forest model provides the most accurate estimation of BMPs effects on urban stormwater P concentrations when compared to models produced using other ML methods. This study suggests that switching to LID BMPs has the potential to increase eutrophication risks and requires further examination. It also proposes that ML methods, especially use of the random forest model can represent a more robust approach to estimate the effects of stormwater BMPs on urban runoff P by accounting for both P reduction and enrichment effects. My results show that that BRCs and other stormwater BMPs have highly variable effects on urban P export. I show that although the BRC I investigated in Mississauga, ON, exhibits efficient reduction of P export, it appears to be atypical and that BRCs and other LID BMPs are generally more likely to enrich P concentration compared to traditional BMPs based on data from a large number of BMP systems in the ISBD. This concentration enrichment may further impact the quality of groundwater and surface waterbodies. Considering the global environmental policy trend to promote replacement of traditional stormwater BMPs with LID BMPs, the findings of this thesis should serve as a caution to policy makers, as understanding of the effects of stormwater BMPs on urban P export remain incomplete.
EVOLUTION OF MULTI-ARC ACCRETION SYSTEMS: A CASE STUDY FROM THE SOUTHERN BEISHAN OROGEN, CENTRAL ASIAN OROGENIC BELT, NW CHINA
(University of Waterloo, 2023-12-18) Hong, Tong
The Central Asian Orogenic Belt (CAOB) is characterized as an accretionary orogen, evolved for ca. 800 m.y from late Mesoproterozoic to early Mesozoic. Its terminal collision and accretion generally commenced in the west and terminated in the east, creating the Tien Shan suture and Solonker suture, respectively. The Beishan Orogen is a southern-central segment of the Central Asian Orogenic Belt, located in Northwest China. It connects the two sutures and contains some of the youngest ophiolitic complexes, arc terranes, and sedimentary basins in the CAOB. Hence, investigations of the southern Beishan Orogen can contribute to correlating the geology on both sides and establishing an integrated tectonic history of the Paleo-Asian Ocean’s closure. Through detailed mapping at 1:25000 scale in southern Beishan, five distinctive tectono-stratigraphic packages have been identified, from south to north, including the Shiyaozi Complex, the Baidunzi Complex, the Ganquan Complex, the Liuyuan Complex, and a cover sequence forming the Heishankou Basin. The Baidunzi Complex comprises a mixture of sheared and transposed metasedimentary and syn-kinematic meta-plutonic rocks, ranging from greenschist to amphibolite facies. The metasedimentary sequences contain Carboniferous-Permian marble and meta-calcareous clastic rocks, which were intruded by syn-tectonic arc magmatic rocks (Baidunzi Intrusive Suite). Collectively these rocks represent a continental arc setting. A massive sheet of bedded quartzite in this complex, displaying no age signatures younger than 1.0 Ga, stands as the most probable candidate for Precambrian basement, with an inferred affinity to the Tarim Craton. The Baidunzi Complex was overthrusted by the Ganquan Complex, which primarily consists of two sequences separated by unconformities and thrust faults. The lower sequence exhibits minimal reworking and lacks continent-derived materials in its stratigraphy. U-Pb zircon dating of this sequence yielded ages ranging from 295 to 285 Ma, without zircon inheritance. In contrast, the upper sequence is dominated by epiclastic sedimentary rocks, structurally and/or unconformably overlying rocks of the lower sequence. Both sequences display geochemical characteristics typical of island arcs, with an increase of εHf values over time. They correlate temporally and tectonically with the adjacent back-arc ophiolitic rocks within the Liuyuan Complex, an ophiolite mélange formed in a backarc setting. Together they represent an arc-backarc system, with arc-trench migration leading to the progressive incorporation of juvenile components in the source. A cover sequence forming a Permian foreland basin, with typical fold-and-thrust style deformation, developed unconformably on the Ganquan and Liuyuan Complexes. From bottom to top, it consists of black shale, an unconformably overlying flysch-like sedimentary unit, and a syn-orogenic conglomerate with clasts of rocks from all the underlying sequences. The sedimentary record and structural analyses of this basin suggest south-verging deformation, associated with a collisional event involving the Ganquan arc-Liuyuan Backarc system over the Baidunzi Complex. Subsequently, this thrust-and-fold belt experienced a phase of north-verging deformation, aligning with the amalgamation of the Shiyaozi Complex from the southernmost region toward the Baidunzi Complex. The overall field relationships record a transition from a passive to an active margin (Baidunzi Complex), formation and accretion of a relatively juvenile arc, and collision during the Permian.
The Role of Transverse Faults in Late Gold Mineralization: A Structural Study of the Maskinonge Lake Fault, Michipicoten Greenstone Belt, Ontario
(University of Waterloo, 2023-10-25) Adam, Zachary
The Maskinonge Lake fault is a late NW-striking fault that occurs at a high angle to the structural features of the gold-producing Goudreau Lake Deformation Zone (GLDZ) in the Michipicoten greenstone belt. The fault is populated with zones of high-grade gold mineralization along its strike and represents an uncommon setting for orogenic gold deposits in the Superior Province. Three phases of fault movement (D4–D6) are identified that postdated the main structural features of the GLDZ (D1–D3). D4 dextral shearing resulted in the initiation of the Maskinonge Lake fault and the development of fault-parallel foliation. The fault was reactivated during D5 sinistral progressive brittle-ductile deformation and included the emplacement of steeply dipping fault-parallel quartz vein arrays and extensional en echelon veins. Structural analysis of these veins shows that structures associated with D5 deformation are subvertical and occurred during transpression. D6 sinistral faulting is responsible for the brecciation of earlier features and ~1 km of strike-slip stratigraphic displacement with little to no vertical movement. The Pine-Breccia gold occurrence is found along the Maskinonge Lake fault and consists of rocks that have undergone pervasive silica alteration within the fault zone. The centre of the alteration halo contains a gold- and copper-bearing fault-filling “main vein”. Both the fault and main vein are located along the contacts of a NW-trending Matachewan dyke, while gold concentrations in the main vein are enhanced at the intersection between the Maskinonge Lake fault and ENE-striking shear zones. These structural controls provide additional constraints for favourable sites of mineralization along late high-angle transverse faults and support these structures as viable gold exploration targets.
How a dry year affects spatial variability of ground thaw and changes the hydrology of a small Arctic watershed
(University of Waterloo, 2023-09-28) Dakin, Brampton
The summer of 2021 in the Inuvik area, NWT was warm and dry. As recorded in Siksik Creek, a sub-catchment of Trail Valley Creek located 50 km north-east of Inuvik, this was the 7th warmest summer and driest July recorded to date. This presented a unique opportunity to study the drying phenomena of Arctic ecosystems. This is pertinent to the study of permafrost degradation, as the drying phenomena is still vastly understudied and there are few datasets available that record abnormally dry conditions in Arctic catchments. These data sets are needed to properly show the influence that this has on active layer thicknesses. It is unknown whether these conditions may pose a risk to permafrost, if this is spatially variable, and what other processes might amplify or hinder this. The main objective of this thesis is to explore how a dry year affects active layer thaw and the hydrology of Siksik Creek so that we may better understand how catchments such as Siksik will respond to ongoing climate change. To do this a mix of field results and modelling was used to show and quantify how these may affect active layer thaw as well as water balance components. The three main research chapters of this thesis divide this by analyzing active layer thaw as physically measured in the catchment to previous years, by using the model GEOtop to assess how this affects water balance components, and then by simulating wetter conditions to show the affect soil moisture has. Field data were collected from May 25th to August 29th in Siksik Creek during the summer of 2021, where the data collected included active layer thicknesses, depth to the water table, as well as stratigraphy and soil thicknesses across a variety of terrain type throughout the entirety of the catchment. This study specifically focused on measuring these data across hummocks and inter-hummocks throughout the catchment, as these features are ubiquitous in the Mackenzie uplands. In addition to analyzing the 2021 field data, the GEOtop physically based hydrology model was used to explore the processes controlling active layer thicknesses, water table depths, and various water balance components over the course of the summer of 2021. GEOtop is designed to handle microtopographies, such as hummocks and other terrain features. Further, we compare the physical and simulated results from the summer of 2021 to a more normal and wetter year (2016) to assess the differences that soil moisture has on the hydrology and active layer thaw of Siksik Creek. We explored how the movement of water impacted thaw depths in these landscapes, how spatial variability of thaw is influenced by soil moisture, and by the terrain features that control this. We found that peat thicknesses in this area are controlled by the presence of hummocks, where peat is thickest between hummock mounds in an area called the inter-hummock zone. This variability of peat thicknesses directly controls the spatial variability of soil moisture, and this had implications on thaw. In Chapter Two it was found that thaw for the summer of 2021 was shallower than expected in the inter-hummock zones by as much as 20cm compared to similar studies in Siksik and in similar landscapes in Alaska. This chapter also showed that the overlying vegetation, specifically lichens and mosses, were statistically linked to peat thicknesses representative of hummocks and inter-hummocks - where lichens tended to be overtop of hummocks, and mosses overtop of inter-hummocks. This correlation was then used with UAV imagery, taken in mid-June, to map mosses and lichens across the catchment and by proxy the locations of hummocks and inter-hummocks. This map was built into the model GEOtop to simulate Siksik Creek for the summer of 2021. Starting in Chapter Three, the modelled portion of this thesis covered a wide aspect of simulations, where the influence of hummocks was assessed, as well as shrubs and snow when they were added to the model, and finally assessing the role soil moisture plays within all of these various processes. It was found that hummocks, when they were specifically discretized and compared to a simple soil column, reached freshet and max discharge sooner by as much as two days, a lag that existed in the evapotranspiration outputs as well. However, these results were relatively consistent and the only major difference between these two simulations was seen in the 2d active layer depth maps. It was found that microtopography by the end of the summer seemed to influence local patterns of thaw more than larger topographical features such as natural depressions in the landscape did. When shrubs and snow were added to the model domain and simulated it was found that the presence of snow or lack thereof was the main component of difference in the discharge and evapotranspiration data. The active layer depth maps changed between simulations, with the shrub only simulations having the lowest degree of thaw, with a degree of variability seen between simulations. In comparison, the water table depths hardly changed between simulations, and it was hypothesized that the dryness of the summer and the lack of soil moisture was the main culprit for this. To test if this was the case, in Chapter Four, precipitation and snow water-equivalent data was taken from a wetter year (2016) and replaced the values for the dry summer of 2021. This was done so that only moisture available to the system was changed. It was found that soil moisture was in fact the main cause for this lack of variability. The wetter simulations because of this had deeper thaw throughout the catchment, with both the extent, max thaw depths, and min thaw depths increasing. The water table depths on the other hand became shallower and the ground surface was much more inundated with water. The spatial variability in the water table depth maps was found to match where the presence of taller shrubs in the catchment exist, where these areas had the least amount of soil moisture and the shallowest thaw depths. Whereas the areas with the highest amount of soil moisture content had the deepest thaw depths in the catchment. Overall, this thesis helps to improve our understanding of how peat catchments similar to Siksik Creek might respond to either the wetting or drying of the Arctic. This thesis also advances our understanding on the controls of soil moisture variability and ground thaw, as well as its spatial variability. One can infer from this study that for posterity it is the warm and wet summers rather than the warm and dry summers that pose the largest risk to permafrost and its degradation.
The influence of soil moisture, oxygen, and temperature on naphthalene biodegradation and CO2 and CH4 effluxes
(University of Waterloo, 2023-09-22) Ye, Jane
Petroleum hydrocarbons (PHCs) are essential to the functioning of the industrialized world yet serve a potential threat to human and ecosystem health when they inadvertently enter the environment. In recent decades, recognition of natural attenuation as a viable approach to PHC remediation is increasing. Natural attenuation includes the biodegradation of PHCs through respiration, fermentation, and methanogenesis, processes which are also central to the biodegradation of natural background soil organic matter. Biodegradation of both PHCs and natural soil organic matter are a major component of the global carbon cycle and an important source of atmospheric greenhouse gases (GHGs). As a biologically mediated set of reactions, environmental factors like temperature and moisture are important controls on the rates and pathways of biodegradation. It is therefore important to understand the influence of these environmental factors on PHC biodegradation and associated carbon dioxide (CO2) and methane (CH4) effluxes to improve predictions of PHC remediation efficiency and soil GHG emissions under ongoing and future climate change. In Chapter 2, I investigated the effect of soil moisture on PHC biodegradation kinetics, using naphthalene as a representative PHC compound. I performed microcosm incubations with naphthalene-spiked soil at 60, 80, and 100% water-filled pore space (WFPS) under oxic headspace, and at 100% WFPS under anoxic headspace. Incubations lasted 44 days. The results showed that the total naphthalene in soil decreased to below detection after Day 9, 17, and 44 in incubations at 60, 80, and 100% WFPS under oxic headspace, respectively. At 100% WFPS under anoxic headspace, total soil naphthalene concentrations decreased over time but were still detectable past Day 44. Fitting of the naphthalene data to first order decay equations revealed two distinct kinetic regimes of degradation in the oxic incubations: an initial fast regime characterized by an apparent first order rate constant on the order of 10-1 day-1 followed by dominance of a slower degradation regime. In the anoxic incubations, only the slow end-member regime was observed with a corresponding rate constant of 10-2 day-1. Porewater electron acceptor and organic acid data indicated that in the fast regime, naphthalene degradation was dominated by microbial respiration pathways, while in the slow regime fermentative pathways dominated. Results from Chapter 2 imply that spatial and temporal fluctuations in soil moisture – and the associated oxygen (O2) availability – can cause order-of-magnitude variability in the degradation kinetics of PHCs in the vadose zone. In Chapter 3, I investigated the effect of temperature and O2 availability on CO2 and CH4 accumulations in the presence of naphthalene. I performed naphthalene-spiked microcosm incubations under oxic or anoxic headspace at temperatures of 10, 20, and 30°C. Time series data of net accumulated CH4, accumulated CO2, consumed O2, accumulated dissolved inorganic carbon (DIC), and consumed organic acids (OAs) were analyzed using Arrhenius temperature sensitivity curve-fitting. Q10 temperature sensitivity quotients were estimated from this analysis, indicating a greater temperature sensitivity of anaerobic CO2 and CH4 production processes than their aerobic equivalents. I observed that methanogenesis under anoxic conditions had a particularly high Q10 of 9. Overall, findings from this research confirm our understanding of field biodegradation rates. PHC biodegradation in oxic, drier zones is expected to be 10 times faster than in anoxic, saturated zones. The two distinct regimes of biodegradation activity identified in Chapter 2 could also be used as simplified representations of PHC biodegradation when modelling variable moisture and oxygen conditions. Chapter 3 additionally suggests that the CH4:CO2 ratio of soil carbon emissions from anoxic soils may potentially increase with warming temperature. Thus, PHC contaminated sites may see increasing GHG emissions potential, but also increasing contaminant biodegradation rates, in a warming climate, especially those located in saturated soils and cold regions. These expected alterations in soil carbon fluxes are important for the consideration of site managers concerned with site-scale carbon cycling and GHG emissions.
Land use changes and salinization: Impacts on lake phosphorus cycling and water quality
(University of Waterloo, 2023-09-05) Radosavljevic, Jovana
Over the past few decades, there has been a rapid global increase in urbanization accompanied by the conversion of natural or agricultural land into more impervious land cover. This ongoing acceleration of global urbanization has raised significant concerns regarding the deterioration of water quality in urban lakes, such as worsening eutrophication symptoms. Eutrophication of inland waters, primarily driven by phosphorus (P) enrichment caused by human activities, is characterized by increased primary production that, in the most extreme cases, results in harmful algal blooms. Additionally, anthropogenic salinization has emerged as another stressor affecting the health of urban freshwater ecosystems. Although the ecological ramifications of both P enrichment and salinization on freshwater ecosystems are recognized, their combined impacts on water quality have hitherto been considered separately. The work presented in this thesis is based on an extensive acquisition and analysis of data for a lake currently located along the edge of the Greater Toronto metropolitan area: Lake Wilcox. Before the most recent phase of rapid urban development, the lake’s watershed underwent the conversion of its original forested land cover to agricultural use. Based on the data, I investigated the following questions: (1) How did the successive historical changes in land use/land cover (LULC) impact the water quality and P cycling in the lake?; (2) How has the rapid expansion of imperviousness during urban growth impacted the lake’s eutrophication symptoms, in particular, the oxygenation of the deeper water and the remobilization of P from the bottom sediments?; (3) How effective have agricultural and urban stormwater best management practices been in mitigating the external input of P to Lake Wilcox?; (4) Of the road salt applied in the watershed during winter, how much reaches the lake and how much is retained in the watershed?; and (5) What is the rate of salinization of Lake Wilcox and management intervention could help the lake recover from excessive use of the road salt? To address these research questions for Lake Wilcox, I combined sediment core analyses, statistical data time series tests, and mass balance modeling. I further evaluated the transferability of the findings for Lake Wilcox to other lakes in North America. In this final research activity, I tested the key hypothesis that emerged from my work on Lake Wilcox, namely that the changes in a freshwater lake’s mixing regime caused by salinization exacerbates eutrophication symptoms, even in cases where the external P inputs to the lake are reduced. In chapter 2, a dated sediment core, recent water quality data, and historical records were used to reconstruct changes in P loading to and cycling in Lake Wilcox associated with changes in land use/land cover (LULC) since the 1920s. The lake’s originally forested watershed was cleared for farming and, starting in the 1950s underwent agricultural intensification. Since the 1980’s, urbanization rapidly increased the watershed’s impervious land cover, now accounting for about 60% of the total surface area. The results illustrate the absolute and relative changes in P external and internal loading resulting from the LULC changes and the implementation of various agricultural and urban stormwater management practices. By analyzing the sediment core data, I reconstructed the historical P loading patterns, as well as the response of the lake's P dynamics to the evolving human activities in the watershed. The results of this chapter highlight the large differences in the impact of agricultural versus urban land use on the lake’s P budget and cycling, and on other aspects of the lake’s biogeochemistry. Chapter 3 focuses on the most recent phase of rapid urbanization of Lake Wilcox’ watershed. Of particular interest is to understand why Lake Wilcox remains in an apparent eutrophic state even though external P inputs to the lake have been declining since the 1980s. I analyzed 22 years of water chemistry, land use, and climate data (1996–2018) using principal component analysis (PCA) and multiple linear regression (MLR) to identify the contributions of climate and urbanization to the observed changes in water chemistry. The results show that the progressive salinization of the lake impacts the lake mixing regime by strengthening thermal stratification during summer. A major consequence is a worsening oxygen depletion of the hypolimnion that increases internal P recycling in the lake. My research therefore establishes a novel link between salinization and eutrophication symptoms. Building on the significant increase in salinity presented in the earlier chapters, Chapter 4 delves into a deeper investigation of the road salt management practices in the watershed of Lake Wilcox. I delineate the changes in geochemical water type in the period 2000-2020 while using mass balance calculations for dissolved chloride and sodium to reconstruct the yearly salt loading to the lake and the amounts of salt ions that are retained within the watershed. Results showed that further increase in salinity may eventually inhibit the fall overturn of the lake. They also point to the large salt legacies accumulating in the watershed, likely in soil and groundwater compartments. The fate of these legacies will require further research to determine the long-term risks they pose to water resources and receiving aquatic ecosystems. In chapter 5, I use water chemistry data for several other urban lakes in Ontario, Wisconsin, and Minnesota to analyze how lake salinization intersects with water temperature and lake morphometry to modify lake stratification. The goal is to determine to what extent salinization in these lakes can cause eutrophication-like symptoms such as those seen in Lake Wilcox. Trend analyses of chemical and physical variables are carried out for all the lakes, and the Brunt-Väisälä frequency is used as a measure of the summer stratification intensity. The results consistently indicate that salinity is becoming an increasingly stronger regulator of water density than temperature in urban freshwater lakes experiencing cold winters. Overall, my research demonstrates that rising salinity can have a significant impact on water column stratification of freshwater lakes. This, in turn, can reduce the oxygenation of the hypolimnion and enhance internal P loading from the sediments. These findings thus highlight that the management of salt inputs to urban lakes, including de-icing salt applications in cold and cold-temperate regions, should be taken into consideration to control lake eutrophication symptoms.
Assessing Sensitivity of Subsurface Mine-Dewatering Activities to Climate Change
(University of Waterloo, 2023-09-01) Calvert, Adam
Underground mining activities require constant removal of groundwater from their void spaces to maintain dry and safely accessible excavations for ore extraction in a process known as dewatering. The nature and degree of dewatering activities is heavily dependent on the amount of groundwater that can reach the mined areas and, conversely, dewatering of mines has a significant effect on the regional groundwater flow in their vicinity. Furthermore, groundwater supply to mining areas may be linked to climatic conditions, connected surface water bodies and the geologic structures that link the surface and subsurface. Typically, fully saturated groundwater models are used in industry to simulate site conditions and to plan mine dewatering infrastructure. These models often take historical climate averages into account when determining recharge to groundwater from the surface, and they do not typically account for feedback between groundwater and surface water systems. While this has been sufficiently accurate in the past, it is expected that the progression of climate change will yield future estimates of groundwater recharge that differ significantly from historical averages. These changes may be captured more accurately with fully coupled methods of simulating groundwater and surface water simultaneously in areas with large surface water bodies overlying aquifers, or in locations where geologic structures provide significant preferential pathways between the surface and subsurface. Here, we explored the changes in predicted dewatering rates for a real mining property in Central Quebec when considering a typical, industry standard fully saturated groundwater model with historically averaged recharge and a fully integrated groundwater/surface water iii model that incorporates results from future climate scenarios. The two models were constructed, parameterized, and calibrated for a site in Central Quebec. Simulations of underground mine dewatering were run with both models, and the predicted dewatering rates from each model were compared. Simulation results demonstrated that the fully integrated groundwater/surface water model with future climate yielded an estimated rate of dewatering that was approximately 2% higher than that predicted by the fully saturated groundwater model with historical climate averages.
Hydraulic Tomography Analyses of Different Datasets for Subsurface Heterogeneity Characterization at Various Scales
(University of Waterloo, 2023-08-21) LUO, NING
Hydraulic Tomography (HT) has been evaluated to be a robust approach for high-resolution characterization of subsurface heterogeneity. However, geostatistics-based HT may produce overly smooth distributions of hydraulic parameters such as hydraulic conductivity (K) and specific storage (Ss) when hydraulic head data used to constrain the inversion is limited. Furthermore, only a few HT studies have been performed for large-scale field problems due to the difficulty in conducting dedicated HT surveys at large-scale sites, as well as due to uncertainty regarding model conceptualization. This thesis documents four studies designed to investigate the performance of HT in characterizing the spatial distributions of K and Ss at various scales through the inclusion of different types of data for inverse modeling. Study 1 investigates the effect of prior geological information on K and Ss heterogeneity characterization through Transient Hydraulic Tomography (THT) analysis of laboratory sandbox data. Study 2 explores the feasibility of THT analysis of long-term municipal well records for large-scale heterogeneity characterization through synthetic experiments, while Study 3 extends the synthetic study to a field application utilizing data from a wellfield in Kitchener, Ontario, Canada by addressing uncertain initial and boundary conditions for inverse modeling. Finally, Study 4 evaluates the usefulness of field cross-hole flowmeter measurements in mapping spatial K distribution through Steady-State Hydraulic Tomography (SSHT) analysis at a highly heterogeneous field site located on the University of Waterloo. Results from these studies mainly reveal that: (1) the incorporation of prior geological information into geostatistical inverse models improves characterization significantly when pumping tests and drawdown measurements are sparse; however, attention must be paid when constructing geological models for reliable structure information, (2) existing municipal wellfield records could be utilized for large-scale heterogeneity characterization using the approach of HT when uncertainties regarding initial and boundary conditions are well addressed for inverse modeling, and (3) the integration of cross-hole flowmeter measurements with hydraulic head data improves characterization results in terms of revealing K heterogeneity details and predicting independent hydraulic test data. Overall, the body of work presented in this thesis advocates the inclusion of additional datasets that carry non-redundant heterogeneity information for geostatistical inverse modeling and demonstrates the feasibility of utilizing alternative datasets in HT for subsurface heterogeneity characterization at large-scale sites.
Influence of Dynamic River Stage on The Vulnerability of Water Wells and Structure Foundations in Cold Regions
(University of Waterloo, 2023-07-12) Yin, Haoyu
Groundwater is important for people in Northern Canada, yet the groundwater protection protocols and water well vulnerability assessments designed for other warmer regions of Canada may not be applicable to communities in Northern Canada due to the unique hydrogeological characteristics there. The seasonal melt of snow and ice leads to intense river stage fluctuations and might cause flooding issues for the adjacent floodplain; however, their influences on the vulnerability of drinking water wells and nearby infrastructure are not fully understood. This research considers a case study at Carmacks, central Yukon, where an integrated surface-subsurface numerical modelling code was used to examine these processes. The model results indicate that the annual variation in the river stage temporarily reverses the direction of the hydraulic gradient between the surface water body and the adjacent aquifer. Stream reaches that gain groundwater under lower river stages can become losing streams during the high stage periods, which facilitates the transport of solute from the river to the adjacent aquifer. Additionally, the model shows that the annual river stage variation can temporarily alter the size and orientation of the region that contributes water to pumping wells, which means new environmental threats could become important. In terms of travel time, the model results suggest that annual river stage variation accelerates the transport of river-origin solutes to the adjacent aquifer, and higher river peaks facilitate more rapid solute migration. Thus, the natural protection of the soil travel path against microbial pathogens may become inefficient and water wells may become more vulnerable. The model results also demonstrate that higher peak river stages are more likely to cause basement inundation in buildings on the riverbank than average peaks, and that the duration of basement inundation varies at different locations.
Passive sampling to understand and predict sources of wastewater and agricultural contamination in rural watersheds
(University of Waterloo, 2023-07-12) Vucenovic, Allison Noelle
Passive sampling techniques have emerged as valuable tools in environmental monitoring, offering distinct advantages over traditional discrete sampling methods. Discrete sampling techniques are only representative of the time of sampling, often over or underestimating concentrations of constituents in flowing surface waters. Passive samplers contain a collecting medium which accumulates and concentrates constituents to a higher level of detection, and reduces variability associated with discrete sampling. To identify and differentiate non-point sources in rural catchments, this study used passive samplers, including the diffusive gradient in thin-films (DGT) and polar organic chemical integrative sampler (POCIS), along with discrete sampling to detect a range of anthropogenic and agricultural tracers and nutrients. Passive samplers were deployed for select compounds including nutrients (PO4-P, NO3-N, NH4-N), anthropogenic tracers (caffeine, carbamazepine, gemfibrozil, ibuprofen, naproxen, sulfamethoxazole, acesulfame potassium, sucralose), and agricultural tracers (glyphosate, aminomethylphosphonic acid (AMPA)). Among the passive samplers deployed, the Metsorb®-DGT, selective for phosphate-bearing compounds, was evaluated for competition impacts between PO4-P and glyphosate. Competition between analytes can occur for sorbents selective for a range of compounds with similar properties. A new sampler using a weak anion exchange (WAX) resin was developed for the uptake of artificial sweeteners acesulfame potassium (ACE-K) and sucralose (SUC). Passive samplers were deployed at three distinct locations (Hamlet, Agricultural, and Mixed-land Sites), for 3 to 14 days, while discrete samples were collected every 3 days over 2 weeks in Fall of 2021 and Spring of 2022. The effect of potentially competing ions between phosphate-bearing compounds was evaluated by deploying triplicate Metsorb®-DGT sampler in a solution of high PO4-P and low glyphosate and AMPA. Strata-DGT samplers were developed as a potential sampler for the uptake of ACE-K and SUC and deployed in the Spring 2022 sampling event. The goals of this thesis were to (1) use DGT and POCIS to delineate anthropogenic contamination from agricultural activities to surface waters in rural communities, and to compare their effectiveness to discrete samples and (2) further develop and evaluate DGT samplers. DGT and POCIS had comparable concentrations with 64% of compounds not statistically different (ρ > 0.05) from discrete samples. Diffusive boundary layer (DBL) corrections were applied to Spring 2022 DGT samples, increasing the mean absolute error between DGT concentrations (CDGT) and discrete concentrations (CACTIVE) by 32% for all compounds. Phosphate was elevated at the Hamlet Site (74 ± 8.2 µg L-1) in discrete samples compared to the Agriculture Site during the Fall 2021 sampling season. The Hamlet Site land use was 40% urban and 60% agriculture, while the Agriculture and Mixed-land Sites were 94% and 88% agricultural land use, respectively. Tracers consistently showed elevated concentrations of ACE-K (412 ± 202 µg L-1) and SUC (17,089 ± 5370 µg L-1) in discrete samples across both sampling seasons as well as all other anthropogenic tracers at the Hamlet Site, while glyphosate and AMPA were elevated at the Agriculture Site (0.86 ± 1.66 µg L-1 and 1.41 ± 0.85 µg L-1, respectively). Principal component analysis (PCA) and correlation coefficients indicated a positive relationship between phosphate and anthropogenic tracers at the Hamlet Site. Biological markers (Human-specific Bacteroides), specific to human fecal contamination, were also elevated at the Hamlet Site compared to the other sites. The results of this study clearly show septic system contamination in a headwater stream and suggest impacts of septic systems to these surface water bodies may be an underappreciated nonpoint source of nutrients. There was no apparent competition on the Metsorb®-DGT sampler at initial concentrations of 104 µg L-1 of PO4-P, 0.372 µg L-1 of glyphosate, and 2.14 µg L-1 of AMPA as uptake was mostly linear after 6 days of deployment. Strata X-AW resin was not a suitable binding medium for artificial sweeteners, resulting in concentrations only 39% of discrete samples for ACE-K at the Hamlet Site. Overall, an array of passive samplers was helpful to distinguish nonpoint sources of septic system from agricultural contamination in rural head-water streams. Passive samplers generally showed comparable results to discrete samples, with the exception of ACE-K, and reduced the variability and additional sampling and analysis associated with discrete sample collection.

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