Earth and Environmental Sciences

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Advances in Rock Core VOC Analyses for High Resolution Characterization of Chlorinated Solvent Contamination in a Dolostone Aquifer
(University of Waterloo, 2008-05-14T12:54:53Z) Kennel, Jonathan
The current understanding of contaminant migration in fractured sedimentary rock aquifers is inadequate due to the difficulty in describing the geologic and hydrogeologic controls on contaminant fate and transport with appropriate detail. To address contamination at fractured rock sites, multiple methods focusing on different aspects of the hydrologic system are required, and particular emphasis needs to be placed on the rock matrix. This thesis shows the further development and utility of the decade-old rock core VOC method (i.e. CORETM), a rock matrix method, when used in conjunction with multiple high resolution datasets as it applies to a 100 m thick highly productive dolostone aquifer in Guelph, Ontario. The research site and surrounding area, located in the northwestern quadrant of the municipality of Guelph, was a productive zone for water supply until the early 1990s when the two closest municipal supply wells (Sacco, Smallfield) were shut down (1991, 1993 respectively) due to volatile organic compounds (VOCs) in the groundwater. Trichloroethene (TCE), a VOC, was used as a degreaser at the Guelph site and likely entered the groundwater more than 20 years ago. The thin overburden, shallow water table, relatively constant dolostone mineralogy, proximity to the UW analytical laboratory, relatively simple plume composition showing minimal degradation, and local importance make this an excellent study site for TCE fate and migration in fractured sedimentary rocks. This thesis is composed of four chapters. Chapter 1 provides a brief background to the rock core VOC method and gives the conceptual framework for the investigation. Chapter 2 focuses on the further development of the rock core VOC method by providing the field validation of a recently adapted extraction method for VOCs in rock core using microwave assisted extraction (MAE), demonstrating the importance of rapid field preservation of samples, and comparing to the industry standard purge and trap method for VOCs on solid matrices. Results indicate that the microwave assisted extraction (MAE) method typically provides equivalent or higher concentrations when compared with the shake-flask and purge and trap extraction methods, indicating more complete extraction or less loss during transfer and/or storage. The purge and trap method provided false negatives (i.e. non-detects) due to inadequate preservation, incomplete extraction, and the elevated detection limit for TCE. The necessity for field preservation was examined by comparing crushed rock samples preserved in methanol in the field to samples unpreserved in the field with a laboratory addition of methanol less than 12 hours later. Chapter 3 creates high resolution porosity and bulk density logs by using selected geophysical logging tools in combination with core derived physical properties for the purpose of calculating porewater concentrations from total contaminant mass concentrations obtained from the rock core VOC method and sample specific rock properties relevant to the conversion. This is beneficial because total mass estimates obtained from the rock core VOC method are not necessarily indicative of the groundwater concentrations given the presence of solid organic carbon controlled sorption. Chapter 4 is a demonstration of the discrete fracture network approach (Parker 2007) applied to the Guelph field site with emphasis on the insights gained through high resolution contaminant profiles generated from cored holes in or near the source area and along a transect. Together, these four chapters present a framework for investigating VOC contamination in fractured sedimentary rocks and with emphasis on evaluating recent advances in the rock core VOC methodology in a field site context.
Ammonium Attenuation and Nitrogen Dynamics in Groundwater Impacted By a Poultry Manure Lagoon
(University of Waterloo, 2011-06-21T17:44:26Z) Lazenby, Brent
Fertilizer application and manure use practice in agriculture has become one of the most common sources of dissolved nitrogen species to both ground and surface waters. Nitrogen, released as nitrate (NO3-), ammonium (NH4+) and/or organic nitrogen (DON) is subject to a variety of transformation and attenuation processes in groundwater, including sorption, nitrification, denitrification, dissimilatory nitrate reduction to ammonium (DNRA), ammonification and anaerobic ammonium oxidation (anammox). Of these, only denitrification and anammox represent complete attenuation of nitrogen, releasing nitrogen gas (N2). This study examines the occurrence and mechanisms of nitrogen attenuation in groundwater affected by a manure lagoon. Lagoon effluent is in strong contrast to background water with elevated chemical constituents including NH4+ (mean = 121 mg N/L) and DON (218 mg N/L), which are transported through a fast moving groundwater flow system. The NH4+ rich plume interacts with NO3- rich background water at an interface ~3 m below ground surface. Over 100 m of groundwater transport from the source, total nitrogen (TN) was consistently reduced by 90% over two years of study. This reduction can be largely attributed to dilution (~ 80%), but the remaining 10% reflects a component of nitrogen loss due to attenuation, reflecting 32 mg N/L in attenuation and a TN degradation rate of 0.4 mg/L/day. Localized zones of nitrification and denitrification are evidenced by loss of NO3- accompanied by elevated N2O emissions. Anammox is implicated by localized enrichment of δ15N with according decreases in both NO3- and NH4+ at the plume-background interface and through corroborating microbiological study. Ammonification of DON along the flow path, something not observed in similar studies, is conjectured to have a confounding effect on a detailed isotopic investigation by introducing a second source of NH4+ that is depleted in δ15N-NH4+.
An Analysis of Glacial Sediment Dispersion with Applications to Diamond Exploration, Lac de Gras, Northwest Territories
(University of Waterloo, 2020-09-21) Janzen, Robert
Diamond exploration is important to the economy of the Northwest Territories and Canada. In recent years, however, there has been a marked decline in the discovery rate of large diamond deposits. Emphasis is being put on improving geological models and developing new approaches of exploration in the hope of finding previously overlooked deposits. A proven approach in diamond exploration in the Northwest Territories and other similarly glaciated terrains has been to characterize the glacial cover to reveal secondary detrital dispersion of indicator minerals and geochemical pathfinders, which can help vector towards a buried kimberlitic source. Typically, only the surficial indicator mineral expression of a kimberlitic signature is known and mapped, which may lead to missed targets, especially in places with shifting ice flows and a complex glacial sedimentary record. This research, in the Lac de Gras area of Northwest Territories, uses a dataset containing both surface and subsurface data, from hand sampling and RC drilling, to bring new knowledge about the glacial geology and to improve our understanding of till production and related detrital dispersion in this prospective region. Erosional outcrop-scale paleo-ice flow indicators show an evolving history of ice-flow in a clockwise sequence starting in the southeast, then west, and finally to the northwest. The ice-flow indicators in the study area show that the northwest ice-flow phase is prominent accounting for 77% of all observations. The particle size distribution of surficial till samples is relatively homogenous, which lends support to the interpretation that the surface till forms a single till unit. The clast lithological analysis shows that the till contains all the different lithologies present in the study area in variable proportions, which appears to reflect a combination of processes and factors, such as bedrock hardness in the up-ice area versus in the dispersion area. The principal component analysis (PCA) of the major oxides shows the till is a mixture of the local bedrock material, but with end-member categories associated with the different bedrock lithologies mapped in the region. Notably, the till at depth, where till is thicker, appears to show a more distal signature than the overlying till or in areas of thin till. Kimberlite indicator mineral (KIM) patterns within the envelope of the Monument indicator train (MIT) indicate a shallow dispersal train that is best captured by surficial samples (i.e. max. depth of approx. 0.3m). The MIT is an area characterized by thin and highly discontinuous till and results show that the strong surficial dispersal from the Monument kimberlites only weakly extends in the shallow subsurface (i.e. below the first 0.3m). As a result, the MIT is not well-defined in the drill data. In addition, no clear palimpsest dispersal train associated with the older ice flow phases was found close to the Monument kimberlites. The till along the Coppermine indicator train (CIT) in the west-central portion of the study area is, on average, thicker than along the MIT. Results show a subsurface dispersal train that rises to the surface in the NW direction, consistent with the young NW ice flow phase and approximately parallel to the MIT. Also, there is a more subtle dispersal train extending to the SW that seems to start in the same area as the rising dispersal. This SW direction corresponds well with the oldest documented ice flow phase in the study area. The respective head of the two identified dispersal trains thus appear to be in the same area and suggest both dispersal trains emanate from the same local buried source. However, it is not possible to exclude the scenario of a more distal source, but it requires a more complex model involving sustained low effective stress and/or englacial transport during more than one ice flow phase. Till matrix geochemistry data that was available for this study proved to be of limited use for kimberlite dispersal train mapping and related glacial sediment transport reconstruction. A possible mixed signature from non-kimberlitic sources could not be separated. Therefore, the main available pathfinders for kimberlites also appear to trace dispersal trains from other rock sources such as mafic rocks and perhaps some metasedimentary rocks. Analysis of more elements using a total digestion procedure, along with multivariate analysis of the results, would be useful to further discriminate the more complex overlapping geochemical signatures. Overall, this study shows that the combined analysis of surface and subsurface till show some contrasting compositional characteristics, which may indicate more complex till stratigraphy or inheritance linked to older ice flow phases than previously considered. It may also have captured the signal of an unknown buried source, although this remains to be confirmed. This study suggests that drift prospecting may be enhanced in the Lac de Gras region by using more subsurface data and this could be critical for future success at the current maturity stage of the diamond district. It may be somewhat surprising given the till is typically relatively thin and discontinuous in this region, but it is clear that despite this situation, the few pockets of thicker till reveal more than what is recorded in the shallow and surficial till. Important corridors may be revealed where till is thicker on average and where surface landforms and bedrock depressions have possibly created till dispersal patterns that are different than the ones associated with previous discoveries.
Analysis of the Behaviour of Long-Runout Rock Avalanches Using Simple Energy Models
(University of Waterloo, 2021-05-06) Vanderwerff, Cassandra
Rock avalanches are a natural hazard of fragmented rock with extreme geomorphological impact and cause significant amounts of damage to the human population. This thesis develops and evaluates simple physics-based energy models to explain the high mobility of rock avalanches and to expand upon preceding research. A review of relevant literature is presented, and five major research topics are addressed. First, it is shown that the numerous models that have been adopted for avalanche fragmentation are not in consistent agreement about the energy spent during this process. Second, there appears to be a lack of consensus regarding whether entrainment of path substrate materials induces a gain or loss in energy is gained or lost from this behaviour. Third, it has been typically assumed that the apparent coefficient of friction for a rock avalanche remains constant – which is likely false. Fourth, it is shown that the environment, geology, degree of lateral confinement and failure mechanism are key variables that control the horizontal travel distance travelled yet are rarely accounted for in various models. Lastly, this thesis shows, through a preliminary analysis of a Galileo Scaling relationship between volume and the horizontal travel distance, that rock avalanche databases are scant in data, limiting analyses. Simple physics energy models were considered to examine rock avalanche behaviour as it pertains to the horizontal distance travelled. The simple physics energy models considered are sliding, entrainment, deposition, fragmentation, and impact. The simple sliding energy model examined the sliding motion exhibited by rock avalanches and the entrainment energy model considered the mass gained during an event. The deposition energy model examined mass loss and the fragmentation energy model observed the energy required to break a rock mass. Lastly, the impact energy model examined the energy lost when the failure mass impacts a lower slope. From the simple physics energy models, it was concluded that the horizontal distance travelled by a rock avalanche is not mass-dependent. Rather, the horizontal distance travelled appears to be dependent on the percentage of mass gained or lost with respect to the initial mass. Further, it was determined from the entrainment and fragmentation energy models that Heim’s Ratio is not a sufficient assumption for the apparent coefficient of friction value. A preliminary statistical analysis provided further insight into Galileo Scaling and its relation to rock avalanches. It was determined that there was a square-cube scaling relationship between the volume and horizontal distance travelled by a rock avalanche. This relationship was further examined through smaller datasets. By constraining the data into datasets of analogous events, the scatter reduced. With further research, this could be developed into an empirical model to potentially predict rock avalanche travel distances.
Analytical approach for modeling of multi well CO2 injection
(Elsevier, 2017-07-01) Robinson, Morgan; Leonenko, Yuri
Disposal of carbon dioxide (CO2) into underground geological formations is considered a viable strategy for the mitigation of global warming. It aims to reduce greenhouse gases emitted from point sources such as power plants. In order to select and evaluate a potential storage formation, many reservoir properties such as porosity, permeability, lateral and vertical extents, and a variety of residual fluid properties are considered. Injection design, which includes the placement of injectors and their flow rates, should be chosen to optimize injection capacity. One of the most important considerations to be addressed during design stage of sequestration is evaluation of pressure behaviour inside the reservoir during and after injection as the sequestered CO2 increases the pressure within the formation. In order to maintain the integrity of the reservoir the pressure needs to be maintained below the fracture pressure, typically at least 10% below. Thus evaluation of reservoir pressure is essential to ensure the reservoir remains under the maximum allowable pressure while sequestering the maximum amount of CO2 for long term storage in the reservoir. The optimal injection rates within a multi well injection site occur when the bottom-hole pressure at each injection site is at the maximum allowable pressure. In this study we present an analytical approach for modeling the pressure evolution during multi well CO2 injection into saline aquifers and using the model modify the injection rates to optimize injection capacity within a formation. We show that this optimization procedure significantly increases the capacity of formation as opposed to using the same injection rate at each wellbore.
Analytical Approach for Modeling of Multi Well CO2 Injection
(Elsevier, 2016-11-14) Robinson, Morgan; Leonenko, Yuri
Disposal of carbon dioxide (CO2) into underground geological formations is considered a viable strategy for the mitigation of global warming. It aims to reduce greenhouse gases emitted from point sources such as power plants. In order to select and evaluate a potential storage formation, many reservoir properties such as porosity, permeability, lateral and vertical extents, and a variety of residual fluid properties are considered. Injection design, which includes the placement of injectors and their flow rates, should be chosen to optimize injection capacity. One of the most important considerations to be addressed during design stage of sequestration is evaluation of pressure behaviour inside the reservoir during and after injection as the sequestered CO2 increases the pressure within the formation. In order to maintain the integrity of the reservoir the pressure needs to be maintained below the fracture pressure, typically at least 10% below. Thus evaluation of reservoir pressure is essential to ensure the reservoir remains under the maximum allowable pressure while sequestering the maximum amount of CO2 for long term storage in the reservoir. The optimal injection rates within a multi well injection site occur when the bottom-hole pressure at each injection site is at the maximum allowable pressure. In this study we present an analytical approach for modeling the pressure evolution during multi well CO2 injection into saline aquifers and using the model modify the injection rates to optimize injection capacity within a formation. We show that this optimization procedure significantly increases the capacity of formation as opposed to using the same injection rate at each wellbore.
Analytical Investigation of Gas Production from Methane Hydrates upon Thermal Stimulation
(University of Waterloo, 2020-02-14) Roostaie, Mohammad
In this study, analytical models are developed to investigate methane hydrate dissociation in porous media upon thermal stimulation employing wellbore heating. This work investigates how the wellbore’s external and internal structure affect the dissociation process. The models are based on both Radial (2D) and Cartesian coordinates (1D) to couple the wellbore heating process and the associated methane response in the hydrate dissociation in the reservoir. Different types of heat-sources are studied: i) a flat heat-source in the 1D cases with a constant temperature; ii) line heat-source in radial cases with a constant temperature; iii) wellbore heat-source in radial cases, employing both a constant temperature and a coaxial wellbore. Wellbore’s external layers consist of casing, gravel, and cement. In the coaxial wellbore heat-source, both conduction and convection heat transfers are considered. It consists of an inner tube and an outer structure (casing, gravel, and cement layers). The analytical solution employed a similarity solution, in which a moving boundary to separate the dissociated (containing produced gas and water) and undissociated (containing only methane hydrate) zones is assumed, to model the dissociation in the reservoir. Two different operating schemes have been studied for water inlet of the coaxial wellbore heat-source: i) inner tube; and ii) annulus section of the wellbore. The results of temperature distribution along the wellbore (for the coaxial heat-source), temperature and pressure distributions in the reservoir, hydrate dissociation rate, and energy efficiency considering various initial and boundary conditions and reservoir properties are presented and compared with those of the previous studies. Direct heat transfer from the heat source to the reservoir in the case with a line heat-source higher dissociation rate and gas production compared to those of the wellbore-heat-source models, considering the heat conduction in the wellbore thickness causes. Decreasing the heat-source pressure and increasing its temperature increases the dissociation rate and gas production. Employing them simultaneously also increases gas production but reduces energy efficiency. The wellbore thickness affects the energy efficiency of the process negatively. The two different operating schemes affect the process in almost the same way with slightly higher gas production in the case with annulus hot-water inlet because the annulus is in direct contact with the reservoir. Increasing the inlet water temperature and decreasing the wellbore pressure simultaneously results in a greater gas production and energy efficiency. Porosity, thermal diffusivity, thermal conductivity, and thickness of the reservoir have direct relation with the dissociation rate, but the permeability and gas viscosity of reservoir almost do not impact the process. The wellbore parameters, such as water flow rate, inlet temperature, and wellbore radius except the inner tube radius, directly impact the wellbore mean temperature and the dissociation process. The findings of this study make a major contribution to research on methane hydrate dissociation upon thermal stimulation with wellbore heating by analytically demonstrating, for the first time, how the wellbore structure affect the process.
Anatexis of former arc magmatic rocks during oceanic subduction: A case study from the North Wulan gneiss complex
(Elsevier, 2018-09-01) Li, Xiucai; Niu, Manlan; Yakymchuk, Chris; Yan, Zhen; Fu, Changlei; Zhao, Qiqi
Migmatites are widespread in the North Wulan gneiss complex from the South Qilian–North Qaidam orogenic belt, but their petrogenesis and ages are poorly constrained. Here, an integrated study of petrography, whole-rock geochemistry, geochronology, zircon trace element and Hf isotope analysis deciphers the nature and timing of partial melting in migmatitic amphibole-biotite gneiss. Zircon U–Pb geochronology reveals that the protoliths crystallized at 506–494 Ma followed by metamorphism and anatexis at ca. 465 to 450 Ma. Hafnium isotope compositions of inherited cores and anatectic rims are very similar, suggesting that partial melting occurred in a relatively closed isotopic system and new zircon rims grew via dissolution–reprecipitation of pre-existing zircon cores. Anatexis occurred by water-fluxed melting of mafic-intermediate rocks through the breakdown of biotite and growth of peritectic amphibole. The protolith of the migmatites records Cambrian arc magmatism in an active continental margin, which was induced by northward subduction of the South Qilian ocean slab. Contemporary arc-like magmatism and high-temperature/low-pressure metamorphism in the region suggest that anatexis in the North Wulan gneiss complex likely took place in a continental arc setting, which reflects the reworking of former arc magmatic rocks in a late stage of oceanic subduction.
Application of Biochar to Stabilize Mercury in Riverbank Sediments and Floodplain Soils from South River, VA under Conditions Relevant to Riverine Environments
(University of Waterloo, 2020-01-07) Wang, Alana Ou
Disposal of mercury (Hg) containing products related to industrial activities has led to large-scale watershed contamination across the globe, posing long-term risks to human health due to its persistent properties. Hg in terrestrial systems can re-enter aquatic systems directly through soil erosion and sediment resuspension, and indirectly through reductive dissolution of manganese (Mn) and iron (Fe) oxides, desorption from clays and other minerals, and breakdown of soil organic matter. Hg is transformed into methylmercury (MeHg), a well-known neurotoxin that accumulates through the food chain, mainly by microbially driven processes under anoxic conditions. Remediation of Hg in riverine environments is challenging due to dynamic redox oscillations caused by flooding and drainage which influence Hg mobility and bioavailability. Mercury sulfate (HgSO4) was used by a textile plant in Waynesboro, VA between 1920-1950s, and as a result of inadvertent discharge elevated Hg concentrations have been observed in the South River watershed since 1970, long after cessation of HgSO4 use. Biochars have been proposed for use in reactive capping mats or as soil amendments for in situ Hg stabilization. Studies evaluating the effectiveness of biochar for stabilizing Hg focus on the effectiveness under fully-saturated conditions, but how treatment systems respond to more environmentally relevant conditions, such as drying and rewetting, is less studied. This dissertation evaluates selected biochars for Hg stabilization in river bank sediments and floodplain soils collected along the South River using laboratory-scale experiments under conditions relevant to riverine environments, including flooding and drainage, fully-saturated anoxic, and drying and rewetting conditions. Five biochars selected for study were: hardwood biochar (OAK), sulfurized-hardwood biochar (MOAK), and biochar prepared from ethanol refinery by-products, including distillers` grains (DIS), anaerobic digestate (DIG), and a mixture of digestate and distillers` grains (75G25S). OAK was evaluated for potential application as a reactive capping mat as well as a soil amendment, and the other biochars were evaluated as soil amendments. To evaluate OAK as a reactive capping mat which intercepts flow paths under flooding and drainage conditions, the treatment system consisted of two sets of modified humidity-cell experiments operated for 100 weekly cycles. The weekly cycles started with dry air, water-saturated air, and were followed by an aqueous leach at day 7 of each week. Each set contained a source column and a treatment column. Source columns contained river bank sediment and floodplain soil collected from different locations along the South River. Treatment columns contained 50% v/v OAK and non-reactive quartz sand. South River water (SRW) was used as input solution for the source column containing river bank sediment, and acidic rain water (ARW) was used as an input solution for the source column containing floodplain soil. Leachates collected from the source columns were used as input solutions for the treatment columns. More than 80% Hg was retained in the treatment columns with limited formation of MeHg in both aqueous and solid phases. Results of micro X-ray fluorescence mapping (µ-XRF) indicate Hg retained on OAK co-occurred with Si, S, Fe and Cu within the biochar porous structure. Results of S K-edge X-ray absorption near edge structure (XANES) analyses indicate lower fractions of sulfoxide for OAK in treatment systems than in untreated OAK. These synchrotron-based analyses indicate that Hg accumulation in OAK when used as a reactive capping mat under flooding and drainage conditions can be attributed to retention of the Hg as particulates in the biochar porous structure as well as formation of complexes with O-containing functionalities on the biochar. OAK and MOAK were evaluated as soil amendments in a floodplain soil under anoxic saturated conditions using laboratory-scale microcosm experiments followed by drying and rewetting of the biochar-amended systems. Floodplain soil was mixed with or without biochars and equilibrated with SRW under anoxic conditions for up to 200 d, and solid materials collected at selected reaction intervals were dried under oxic conditions for 90 d and rewet under anoxic conditions for an additional 90 d. Limited Hg removal was observed in OAK-amended systems. Addition of MOAK enhanced Hg removal under anoxic conditions without promoting MeHg production. After drying and rewetting, Hg in OAK-amended systems was remobilized, likely due to association with dissolved organic carbon (DOC), while Hg in MOAK-amended systems remained at low concentrations. Increases in solid MeHg concentrations coupled with increases in aqueous Mn, Fe, SO42- and HS- concentrations in MOAK-amended systems were observed. 16s RNA pyrosequencing analysis suggests shifts in Hg methylating community composition toward sulfur-reducing bacteria (SRB). Drying and rewetting alters the structure of the microbial community, therefore generating conditions favourable for MeHg production in MOAK-amended systems. DIG, DIS, and 75G25S were evaluated as alternative soil amendments in floodplain soil following the same experimental protocol used to evaluate OAK and MOAK as soil amendments. Addition of digestate-based biochar (DIG and 75G25S) led to greater Hg uptake and lower MeHg concentrations than the addition of DIS. After drying and rewetting, increases in DOC concentrations were observed in digestate-biochar amended systems, while concentrations of Hg remained at low concentrations, suggesting Hg in digestate-based biochars was less likely affected by the release of DOC. Concentrations of MeHg in these biochar-amended systems remained at low concentrations, and solid MeHg content was 50% lower after drying and rewetting than under initial anoxic conditions. These experiments suggest that digestate-based biochars can potentially be used as soil amendment in fully-saturated anoxic environments with limited impacts from drying and rewetting on the system performance. MOAK and DIG were further evaluated as soil amendments under periodic wetting and drying conditions due to their greater control of Hg under anoxic conditions. The periodic wetting and drying conditions were mimicked using a modified humidity-cell experiment. Each wetting and drying cycle contained a wetting, leaching and drainage period, and a total of ten cycles was conducted. In wetting periods, SRW was added and the system was allowed to stagnate for 14 d, and then drained by gravity during leaching periods, after which solid materials were dried before the next wetting period. An early period of elevated leachate concentrations of THg, MeHg, DOC, and Mn, was observed in the soil control and biochar-amended systems. Limited Hg removal (up to 57%) was observed in the biochar-amended systems at steady state. Minimal MeHg (<0.6 ng L-1) was observed in soil control and DIG-amended systems, while MeHg concentrations were up to 158 ng L-1 in the MOAK-amended system during the early flush. THg and MeHg concentrations in the early flush were positively correlated with DOC and Mn concentrations. Concentrations of SO42- increased with decreases in pH and alkalinity in the MOAK-amended system. Initial release of elevated (SO42-) was observed in the DIG-amended system. S K-edge XANES spectra indicate polysulfur is the predominant S form in the biochar-amended systems. Results of 16s rRNA pyrosequencing suggest the microbial community in the MOAK-amended system shifted toward sulfur oxidizers, while the microbial community in the DIG-amended system was similar to the soil control. The greater abundances of sulfur oxidizers in the MOAK-amended system suggest MOAK is more available for microbial organisms to promote microbially-driven oxidation under periodic wetting and drying conditions. Results of this study suggest that Hg removal under conditions relevant to riverine environment depends on application methods, biochar properties and biogeochemical conditions. Biochars may be used as reactive material embedded in geotextiles for river bank stabilization and as soil amendments. Dynamic oscillations representative of riverine environments indirectly influences the effectiveness of Hg removal and may result in unintended consequences. Careful characterization of biochar properties and local environments are recommended prior to implementing large-scale biochar applications.
Application of Stable Isotope Geochemistry to Assess TCE Biodegradation and Natural Attenuation in a Fractured Dolostone Bedrock
(University of Waterloo, 2011-01-24T20:17:10Z) Clark, Justin
Isotopic methods have been developed over the last 10 years as a method for determining chemical interactions of chlorinated solvents. These methods are especially promising for. This study attempts to employ and develop compound specific isotopic analyses of TCE and cDCE, along with chemical data, to characterize the degradation of TCE in a fractured bedrock aquifers. The Smithville site is a contaminated field site with extremely high levels of TCE contamination that is currently undergoing monitored remediation. From December 2008 until April 2010 extended samples were collected from the site to provide additional data analyses including isotopic data. The redox conditions at the site are anoxic to reducing, with sulfate reduction and methanogenesis as dominant terminal electron accepting processes. Redox data indicates that well electrochemical conditions are highly variable within the site, including areas near the source zone that not very reducing. Documented changes in groundwater conditions to much more reducing environments indicate that oxidation of organic matter is occurring at the Smithville site in select wells. Chemical analyses of TCE, DCE, VC, ethene and ethane are employed determine whether reductive dechlorination was occurring at the site. Results of field testing indicate that many wells on site, especially in the proximity of the source zone, dechlorination products were found. The isotopic data had a high range in both carbon and chlorine isotopes. Chlorine isotopic data ranges from a δ37Cl(TCE) of 1.39 to 4.69, a δ37Cl(cDCE) of 3.57 to 13.86, a δ13C(TCE) of -28.9 to -20.7, and a δ13C(cDCE) of -26.5 to -11.82. The range in values indicate varying degrees of degradation throughout the site, with the same wells grouping together. Combined chemical, redox and isotopic data shows that degradation seems to be a removal process for TCE at the Smithville site. Concentrations of chemicals created as a result of TCE degradation verify degradation, especially in wells 15S9, R7 and 17S9. Historically production of DCE in significant amounts, above 1.0 ppb, was observed to only occur after 2003. In addition to this, DCE data shows that the percentage of DCE made up of cDCE is above 96%. This indicates that microbes most likely mediate the processes that formed DCE from TCE. The linear regression of the delta-delta plot for isotopic TCE data shows line that is likely a direct function of the carbon and chlorine isotopic fractionation imparted upon the original TCE released. The slope found is consistent with data collected from other studies though cannot be applied to determining the process directly given the range of variability in isotopic field data.
An approach to improve direct runoff estimates and reduce uncertainty in the calculated groundwater component in water balances of large lakes
(Journal of Hydrology, 2015-10-30) Wiebe, Andrew J.; Conant Jr., Brewster; Rudolph, David L.; Korkka-Niemi, Kirsti
Groundwater is important in the overall water budget of a lake because it affects the quantity and quality of surface water and the ecological health of the lake. The water balance equation is frequently used to estimate the net groundwater flow for small lakes but is seldom used to determine net groundwater flow components for large lakes because: (1) errors accumulate in the calculated groundwater term, and (2) there is an inability to accurately quantify the direct runoff component. In this water balance study of Lake Pyhäjärvi (155 km2) in Finland, it was hypothesized a hydrograph separation model could be used to estimate direct runoff to the lake and, when combined with a rigorous uncertainty analyses, would provide reliable net groundwater flow estimates. The PART hydrograph separation model was used to estimate annual per unit area direct runoff values for the watershed of the inflowing Yläneenjoki River (a subwatershed of the lake) which were then applied to other physically similar subwatersheds of the lake to estimate total direct runoff to the lake. The hydrograph separation method provided superior results and had lower uncertainty than the common approach of using a runoff coefficient based method. The average net groundwater flow into the lake was calculated to be +43 mm per year (+3.0% of average total inflow) for the 38 water years 1971–2008. It varied from −197 mm to 284 mm over that time, and had a magnitude greater than the uncertainty for 17 of the 38 years. The average indirect groundwater contribution to the lake (i.e., the groundwater part of the inflowing rivers) was 454 mm per year (+32% of average total inflow) and demonstrates the overall importance of groundwater. The techniques in this study are applicable to other large lakes and may allow small net groundwater flows to be reliably quantified in settings that might otherwise be unquantifiable or completely lost in large uncertainties.
Aqueous speciation of selenium during its uptake by green algae Chlamydomonas reinhardtii
(University of Waterloo, 2013-05-03T19:38:06Z) Zhang, Xu
Selenium (Se) is a micronutrient, yet elevated Se can be toxic to aquatic organisms. The range of Se concentrations within which Se uptake goes from insufficient to toxic is very narrow. It is thus important to understand the Se biogeochemical cycle in aquatic systems. In this thesis, the study focuses on changes in Se speciation during uptake by green algae. An optimized method was adopted to quantify and speciate Se in water using flow-injection atomic fluorescence spectroscopy coupled with high-pressure liquid chromatography. Details on the method are given here. For the uptake experiments, the uptakes of four Se species (selenite (Se-IV), selenate (Se-VI), selenocystine (Se-Cys) and selenomethionine (Se-Met)) by the green algae Chlamydomonas reinhardtii were compared. This thesis reports that the algae take up higher amounts of organic Se than inorganic Se. Selenomethionine (Se-Met) had the most rapid uptake, during which Se-Cys was produced. For all experiments, Se-IV was produced and found to sorb onto the algae cells, revealing that Se-IV is an important intermediate compound. Mass balance calculations revealed that more than 90% of Se was lost during uptake, probably to the atmosphere. This study also investigated the release of Se during algae decay to simulate the fate of Se during early-diagenesis. Selenium-rich algae cells were mixed with estuarine sediments at the sediment–water interface in a series of column incubations experiments. During the 7-week incubations, Se speciation was measured at the water–sediment interface and in pore water samples. We found that all the Se released to the pore water was in the form of Se-Cys. Although preliminary, these results highlight the key role of organic-Se species in the biogeochemical cycle of Se in the aquatic environment.
Aqueous Stability and Transport of Catalytic Nanoparticles for Groundwater Remediation
(University of Waterloo, 2015-05-14) Lentz, Adam
Nanoparticles (NP) are increasingly being used for in situ groundwater remediation because of their catalytic properties and the potential to inject them directly into the subsurface. Here, the aqueous stability and transport in porous media were evaluated for two types of NP: 1) catalytic and magnetically separable controlled superparamagnetic iron oxide NP aggregates (CSA) in 100, 240, and 340 nm diameter sizes and 2) palladium NP (Pd-NP) 5-50 nm in diameter. The Pd increases reaction rates, and the polymeric coatings (polyacrylamide on CSA and polyvinylpyrrolidone on Pd-NP) improve colloidal stability and transport. Investigations, under environmentally relevant conditions, into the longevity of Pd on the surface of CSA found that < 5 % of the Pd was released from the CSA over 4 months. Thus, sufficient Pd remained on the CSA surface to maintain catalysis during field-scale applications. To evaluate the aggregation and settling of NP, suspension tests were conducted in environmentally relevant NaCl, MgSO4, and CaCO3 solutions. The addition of Pd onto the surface of CSA did not lead to detectably altered NP stability. Increased settling of CSA was observed with increases in CSA size, ionic strength (IS), and ion charge. The lowest stability was observed for the 340 nm diameter CSA NP, with greater stability observed for the 240 nm, and the greatest for the 100 nm size. The greatest aggregation was observed for solutions containing CaCO3 (complete settling within 3 hr), followed by MgSO4; minimal aggregation was observed for the NaCl solutions and ultrapure water suspensions (minimal settling over 1-4 days, dependent on NP size). Decreased stability of larger NP (340 nm vs. 100 nm) suggests different mechanisms of settling and stability, relative to 10-100 nm NP reported elsewhere in the literature. The Pd-NP remained suspended for over a week in all solutions tested. The small size and the non-magnetic nature of the Pd-NP, rather than their surface charge, may have affected the stability relative to the 100-340 nm CSA. Column transport studies evaluated the mobility of NP in Ottawa silica sand porous media with a 0.7 mm mean diameter. The breakthrough test protocol was 5 pore volumes (PV) of NP suspension followed by 5 PV of elution with ultrapure water. The protocol for experiments with low mobility NP included input of a total of 20 PV: 5 PV of NP suspension, 5 PV of elution with the same solution, 5 PV of ultrapure water at the same flow rate, and 5 PV of ultrapure water input at a higher flow rate. Inverse modeling with the CXTFIT option of the STANMOD 1-D transport model was used to determine retardation of the NP and the % NP input concentration that eluted. There were strong linear correlations between fitted NP input concentration and the calculated % of NP eluted. Model results indicated conservative transport with ≈100 % elution, no retardation, and an attachment efficiency (α) = 0.0 for all NP transport experiments in ultrapure water. Minimal mobility (< 5 % elution, attachment efficiency α > 2.4) of CSA was observed after 20 cumulative pore volumes in 1.3 and 5.1 mM ionic strength (IS) CaCO3 solutions, except for the case of 100 nm CSA at 1.3 mM IS CaCO3 (85 % elution, α = 0.03). The Pd-NP were fully mobile in 1.3 mM IS CaCO3 solution. Calculated attachment efficiencies were above the theoretical threshold of 1, indicating that non-colloidal filtration theory attachment mechanisms, such as ripening, aggregation, or straining, controlled NP transport. Modest detachment was observed following both replacement of the CaCO3 input solution with ultrapure water and after increasing the flow rate. With a column test in 8.6 mM IS CaCl2 solution, minimal elution of NP was observed following 10 PV; however, complete detachment occurred when ultrapure water was flushed through the column. Reversible attachment of NP was observed in CaCl2 solutions, whereas irreversible attachment was observed in CaCO3 solutions. Synchrotron-based microtomography, a non-destructive imaging technique, which provides 3-D images of NP distribution on the pore-scale, both spatially and temporally, was used to evaluate Pd-NP transport. Tomography was used to collect images both above and below the Pd absorption-edge. Images collected below the absorption edge were subtracted from above-edge images to obtain absorption-difference images. Segmented and difference images were then multiplied together. These processes allowed for the determination of profiles of porosity, aqueous phase greyscale value, and silica phase greyscale value for each slice. Profiles of porosity enabled images to be lined up based on characteristic patterns for each column. With little variation in silica greyscale values from one image to another, aqueous phase attenuation values increased in the presence of the Pd-NP and decreased after the NP were flushed. The resolution was insufficient to image individual NP, but did allow for quantification of Pd-NP in a non-ideal silica-grain porous media. This study indicated that CSA and Pd-NP transport depends on the aqueous environment and NP size and stability. Pd NP could be viably transported through a CaCO3-rich aquifer to catalyze remediation reactions. The CSA could potentially be transported in CaCO3-free solutions in non-carbonate aquifers during in situ remediation applications. This study further validated the usefulness of tomography for transport studies of Pd-NP in silica grains.
Assessing hydrological processes controlling the water balance of lakes in the Peace-Athabasca Delta, Alberta, Canada using water isotope tracers
(University of Waterloo, 2007-05-22T21:16:26Z) Falcone, Matthew
One of the world’s largest freshwater deltas (~4000 km2), the Peace-Athabasca Delta (PAD), is located at the convergence of the Peace and Athabasca rivers and Lake Athabasca in northern Alberta, Canada. Since the early 1970s, there has been increasing concern regarding the ecological impacts on the PAD after flow regulation of the Peace River began in 1968, decreased discharge in the Peace and Athabasca rivers as a result of hydroclimatic changes in Western Canada, and increased Athabasca River water usage by oil sands development to the south. This thesis is part of an ongoing, multi-disciplinary project assessing current and past hydrological and ecological conditions in the PAD. Research conducted in this thesis aims to better understand the processes controlling water balance of lakes in the PAD using mainly stable water isotope data collected from lakes and their input sources. Isotope data are used to describe and quantify hydrological processes for individual lakes (seasonal and annual) and across the delta and are supported by other chemical and hydrometric data. An isotopic framework in d18O-d2H-space is developed for the PAD using evaporation-flux-weighted local climate data, and isotopic data collected from a reference basin, lakes throughout the PAD, and lake input sources (i.e., snowmelt, rainfall, and river water). The framework is comprised of two reference lines, the Local Meteoric Water Line, which is based on measured isotopic composition of precipitation, and the Local Evaporation Line, which is based on modelled isotopic composition of reference points. Evaporation pan data is used to assess short-term variations in key isotopic reference values, which are important for addressing short-term changes in the isotopic signature of shallow basins. This framework is used in subsequent chapters including assessment of seasonal and annual water balance of two hydrologically-contrasting shallow lakes, and to quantify the impacts of flood water and snowmelt on a set of 45 lakes in spring 2003. Five years of isotope data using time-series analysis and the isotopic framework suggested that a perched (isolated) lake and its catchment (forest and bedrock) in the northern, relict Peace sector captured sufficient rain, snow, and runoff to maintain a relatively stable water balance, and also that a low-lying lake in the southern, active Athabasca sector was regularly replenished with river water in both spring and summer. Snowmelt and rainfall were found to have diluted the perched basin by an average of 16% and 28 % respectively, while spring and summer floods were found to almost completely flush the low-lying lake. Using the spring 2003 regional dataset, flooded lakes were separated from snowmelt-dominated lakes through use of suspended sediment concentrations, isotope data, and field observations. Application of an isotope mixing model translated d18O values into a range of replenishment amount by either river water or snowmelt, which compared well with hydrological conditions at the time of sampling and previously classified drainage types of the lakes. Spatial mapping of replenishment amounts illustrated flooding of much of the Athabasca sector due to ice-jams, except for two sub-regions isolated from flooding by artificial and natural northern diversion of flow from the Athabasca River. It is also shown that most of the relict landscape of the Peace sector was replenished by snowmelt except for a few low-lying lakes close to the Peace River and its tributaries. Overall, improved understanding of lake and regional hydrology in the PAD, especially the ability to quantify the affects of various lake inputs, will improve the ability to develop effective guidelines and management practices in the PAD as lakes respond to future changes in climate and river discharge.
Assessing Microbial Viability and Biodegradation Capabilities in Sandstone
(University of Waterloo, 2017-11-17) Secord, Elaine
Environmental practitioners have demonstrated enhanced in situ bioremediation (EISB) in homogeneous unconsolidated soils to remediate chlorinated solvents. However, EISB has not been fully investigated in bedrock environments. In addition, there is limited research in the literature that has evaluated bacteria viability in the primary porosity of bedrock for the purpose of reductive dechlorination in the low permeability units of bedrock. Studies that involve bacterial transport in low permeability geological material are typically limited by slow diffusion rates. In this thesis, electrokinetics (EK) was used to overcome slow diffusion rates, and limited bacteria-contaminant-electron donor interactions, by increasing the hydraulic conductivity within the sandstone, in a paired EK-bioaugmentation (EK-Bio) experiment. Idaho Gray andstone cores were artificially contaminated with the aqueous solvent, trichloroethene (TCE), and KB-1 bacteria, a commercially available reductive dechlorinating bacterial consortium, were transported into the cores to assess the ability of bacteria to reductively dechlorinate the solvent. Three goals were outlined to address the main objectives of bacteria viability assessment and dechlorination capabilities: 1) Develop an apparatus at the bench-scale to test EK in bedrock; 2) Determine if amendments could be transported through the primary porosity of bedrock using EK; and 3) Evaluate whether dechlorination of TCE could be promoted in bedrock following the addition of amendments using EK. Four columns were treated with EK to deliver and continuously saturate the cores with TCE contaminant, KB-1 bacteria, and lactate electron donor for about ten days. One core was immediately sampled (baseline), one core incubated for five weeks, and two replicate cores incubated for nine weeks in an anaerobic environment. Results showed that as incubation time increased, vcrA and bvcA reductase gene concentrations increased and fermentation products were metabolized. Although chlorinated ethene concentrations were below detection in the long term incubated cores, dechlorination of TCE was not explicitly observed, as complete mass balance could not be achieved. EK transport was an effective tool to migrate amendments into Idaho Gray sandstone and KB-1 bacteria could thrive within the primary porosity of the sandstone.
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.
Assessing Stratigraphic Controls on the Secondary Detrital Footprint from Buried Mineralization and Alteration at the Highland Valley Copper Mine, British Columbia
(University of Waterloo, 2020-01-24) Reman, Andrea
Mineral exploration is progressively shifting to deeper targets, including those buried under thick unconsolidated sediments. It is thus becoming increasingly important to understand the sedimentary successions of the shallow subsurface (0-200m) in order to enhance exploration strategies to locate and characterize buried targets. One strategy is to investigate the sedimentary sequence overlying known mineralized and altered zones. As such, this study aims to characterize stratified unconsolidated sediments overlying mineralized as well as altered zones at the Highland Valley porphyry copper system (HVC), in south-central British Columbia, and investigate their effects on dispersion patterns of indicator minerals and geochemical pathfinders. Stratigraphic logging and sedimentary facies analysis of ten drillcores have produced a new stratigraphic framework of the unconsolidated sediment cover and a refined depositional environment interpretation. Four geological cross-sections and an interpreted seismic profile improve our understanding of the stratigraphic architecture of the valley fill sediments in the vicinity of the Highland Valley Pit, as well as across the J.A. target, located four km to the east. Two new, previously unreported units are described from this study: a deeper, older till unit as well as a deglacial sequence overlying the older till unit. This study also reveals important lateral stratigraphic and sedimentary facies changes over relatively short distances. Two major ice advance and retreat cycles, the 1st one being older than 50 ka, and additional minor oscillations of ice margins during the last deglaciation of the area, are recognized in the stratigraphic record. Petrophysical (density, porosity, magnetic susceptibility, resistivity, and chargeability) and sedimentological (grain size) property measurements are presented for the major cover units, which can help better resolve the geophysical footprint of buried targets. Stratigraphic units interpreted to have formed by meltwater related processes and deposited in ice-marginal or proglacial settings generally have a higher proportion of locally-derived lithologies relative to other units, while tills have a more dominantly distal signature. Several porphyry copper indicator minerals, such as pyrite, chalcopyrite, and jarosite, are found in each of the Quaternary sediment cover sub-units analyzed. The strongest overall footprint of mineralization is found in two deep, poorly-sorted outwash and two deeper subglacial tills. They contain variably abundant indicator minerals (e.g. pyrite, chalcopyrite, Mn-epidote, chromite) and elements (Cu, Mo, W, As) that are indicative of porphyry copper mineralization. The source of most of these indicators is predominantly the Guichon Creek batholith that hosts the mineralization, but some indicators may be derived from distal volcanic rocks and volcanogenic sediments outside of the batholith. Coarse grain size and felsic lithology distinguished Guichon Creek batholith material from the others. Hyperspectral techniques were applied to determine the abundance of prehnite (distal alteration footprint) and kaolinite (proximal alteration footprint) in large (>2 mm) clasts. Overall, results are consistent with the abundance of clasts sourced from Guichon Creek batholith (lower prehnite content and higher kaolinite content = higher GCB clast abundance). This finding suggests the technique may be used to get insights into the proximity of the source of clasts relative to buried HVC-type mineralization. Subsurface till units also appear to have higher abundances of several indicator minerals (e.g. pyrite, chalcopyrite, jarosite) and geochemical pathfinders of mineralization (e.g. Cu, Mo, W, As) and alteration (e.g. Mg, Te, Bi) compared to previously published surficial till data. Oxidation of the surficial till and water-mineral interactions in the deeper (water-saturated) tills may explain some of the observed differences (esp. for mobile elements); however, re-entrainment of pre-existing sediments is another important mechanism to consider. The strongest footprint signal occurs in the deepest tills. Mineralized and altered bedrock thus appears to have been more accessible to glacial erosion during the older glacial phases due to less preserved sedimentary cover in depressions. Indirect sources (sediment re-entrainment) may have contributed to the footprint signal in the surficial till, perhaps more than shallow mineralized sources in some places. Overall, this study provides several refinements to the stratigraphic framework of the sedimentary cover at HVC, as well as new insights into the occurrence and abundance of HVC-related indicator minerals and pathfinders in these units. One important implication of this study is that dilution up the stratigraphy is clear but limited at HVC; however, it could be greater in other prospective thick drift areas; stronger dilution in surficial units is possible, which could mask a clear subsurface footprint and buried sources of importance.
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.
Assessment of Nitrate Export in Agricultural Sub-Catchments of the Grand River Watershed: An Isotope Approach
(University of Waterloo, 2015-02-20) Cummings, Thomas Fraser
Nitrate (NO3-) is one of the most widespread contaminants in freshwater systems globally. This is largely due to high fertilizer application rates that are required to maximize crop yield. Elevated NO3- concentrations can cause detrimental health effects to both humans and aquatic ecosystems. While the drinking water standard for NO3- in Canada is 10 mg N/L, this level is often surpassed in small headwater agricultural streams and tile drainage. Inorganic (synthetic) and organic (manure) fertilizers are the greatest non-point sources of NO3- to freshwater and groundwater systems in Canada. Inherent isotope fractionation during production of inorganic and organic fertilizers allows these N sources to be differentiated using the isotopic ratios of nitrogen and oxygen. Small agricultural catchments play an important role in nutrient export to larger freshwater systems, however the source and timing of export is often unknown. The main objective of this thesis is to better understand the sources and processes governing NO3- concentration and export in four small agricultural catchments where large changes in nutrient concentration can occur over the course of a year. Land-use within these catchments is predominantly agriculture (>77%). Geochemical and isotopic analysis of the four creeks, the Conestogo River, the Grand River as well as tile drain and shallow groundwater piezometers located along one creek (Boomer Creek) was undertaken. NO3- concentration varied seasonally, concomitantly with stream discharge, with increased concentrations and export occurring during the non-growing season at scales from small watershed to the Grand River. Peak concentrations (>10 mg N/L) occurred in late fall and early winter and lowest concentrations (<5mg N/L) occurred during the summer months. Median NO3- concentrations from tile drains (5.9 mg N/L) were much higher than that of groundwater samples (0.1 mg N/L). Further, groundwater NO3- concentrations remained consistently low even at times of high discharge and high NO3- concentrations in both the tiles and the creek, indicating that the creek is more influenced by water discharging from tile drains and not that of groundwater. The studied creeks NO3- export varied seasonally with the greatest export occurring in all creeks during spring melt on both a per day basis and over the duration of the melt compared to other seasons. Summer low flow NO3- concentrations in the Conestogo River is a function of the NO3- concentration within the Conestogo Reservoir. Annual precipitation amounts as well as reservoir residence time are believed to be the largest factors governing reservoir NO3- concentrations and thus summer Conestogo River NO3- concentrations. δ15N and δ18O analysis of NO3- was used to examine NO3- sources as well as seasonal changes in N-cycling processes. Both δ15N and δ18O were lower (+ 6 to + 8‰ and - 2 to + 1‰) in the fall and winter months with higher values (> + 10‰ and > + 4‰) during the summer for all creeks with the exception of the δ18O of Swan Creek. Increased isotopic values occurred at lower NO3- concentrations and concomitant increases in both 18O and 15N in an expected ratio (approx. 1:2) providing strong evidence of the occurrence of denitrification. Annual fluctuations in concentrations of N2O and CH4 are also consistent with active denitrification. δ15N-NO3- values corrected for the isotopic effects caused by denitrification were consistent with that of values reported for manure (+ 8‰). Despite the δ15N being within that of manure, the source of NO3- to these watersheds is inconclusive as a result several NO3- sources also falling within the same range. Isotopic analysis suggests that Boomer Creek stream water is similar to water discharging from tile drains along Boomer Creek. NO3- concentration and isotope data from tile drains and Boomer Creek indicate a strong influence from tile drains on annual stream NO3- concentration and export. The influence of tile drains will only become greater as 30 million meters of new tiles are installed annually in Ontario. Understanding nutrient dynamics in small watersheds is vital to understanding and predicting water quality in larger surface water systems. This study re-emphasises the fact that understanding the seasonality in annual NO3- export requires knowledge of the N sources and processes that govern N transformation. Only with this knowledge can effective best management practices be implemented to successfully maintain surface and ground water quality.
Assessment of saltwater origin in the Rub’ al-Khali basin and its relation to the formation of sabkha Matti
(University of Waterloo, 2021-01-15) Saeed, Waleed
The Rub’ al Khali sand sea is the largest uninterrupted sand desert on Earth that occupies an area of approximately 650,000 km2 of the Arabian Peninsula. Yet, the desert basin is underlying by one of the largest multi-level aquifer systems of the arid world that is the Rub’ al Khali (RAK) structural basin. In this study, water resources in the Cenozoic aquifer systems within the RAK basin were assesses using a combination of geological, hydraulic, hydrochemical, and isotopic approaches. The main goal of this research is to initiate the building of a conceptual model of the regional hydrogeology of the RAK basin in order to assess the constraints and opportunities of the available water resources for future developments. The study shows that the RAK basin is a potential source of fresh to brackish water, with total dissolved solids concentrations (TDS) less than 10,000 mg/l. However, groundwater with up to 200,000 mg/L TDS has been found in the vicinity of a potential discharge zone, known as sabkha Matti. An isotope and solute evaluation was applied to identify the origin and mechanisms of this salinization in three major Tertiary aquifers in the RAK basin. The studied geological succession comprises sedimentary rocks of the Lower Paleocene to Lower Miocene age, and the aquifers primarily consist of the Umm Er Radhuma, Dammam, and Hadrukh. It is demonstrated that the groundwater chemistry evolved from a low- (< 2,000 ppm) to high- (>120,000 ppm) salinity Na-Cl water type, regardless of the aquifer. The similarity in water types between the groundwater from the different formations suggests that the same origin and geochemical processes may be controlling the salinity and major ion chemistry in these aquifers. The suite of hydrogeological, hydrochemical (Cl vs. Br), and isotopic (Cl vs δ18O and Br vs δ81Br) data indicate that the source of solutes is associated with the entrapment of evaporated paleo-seawater (connate water) in nearshore and lagoonal environments during the time of deposition. Moreover, the results from the 87Sr/86Sr ratios show no evidence of significant vertical connectivity between the three Tertiary aquifers. Instead, the data support that evaporated paleo-seawater was trapped in each aquifer individually during the time of deposition, and that each has evolved similarly through water-rock and redox reactions. The stable isotopic compositions of δ18O, δ2H, and 14C show that the entrapped paleo-seawater was partially flushed out by fresh meteoric water during the wet Late Pleistocene and Early Holocene periods. Sabkha Matti (SM) is a flat salt covered portion in the further northeastern part of the Rub al Kali sand sea and is underlain by the larger RAK structural basin. SM is the largest continues salt flat in the Arabian Peninsula and it extends about 150 km south from the western Abu Dhabi coastline and across the border between the United Arab Emirates and Saudi Arabia. The Matti sabkha is a potential discharge point for regional groundwater systems in the RAK topographic basin. The hydrogeochemical evolution of this sabkha and its role in the regional hydrogeological system of the RAK basin was assessed by using a combination of geological, hydraulic, hydrochemical, and isotopic approaches. A compilation of the geologic structure and lithology in combination with boron isotope data attributed the origin of salinity in the regional aquifers underlying SM to the entrapment of ancient seawater in a coastal lagoon environment during the depositional time of the late Oligocene-Miocene formations. Major ionic constituents and strontium isotope ratios from the trapped paleo-seawater were observed to resemble those obtained from the near-surface sabkha brine. These data, along with hydrostatic head measurements, suggest that the origin of the solutes in SM is associated with brines ascending from the underlying formations. The data also show that solute concentrations in SM are increasing over time through a combination of evaporation, mineral dissolution by recharge, and density-driven convection mechanism that circulates the solutes. On the other hand, stable isotopes of waters (δ18O, δ2H) and radio isotope data (14C and 3H) suggest that the existing waters in the sabkha and the underlying aquifers are relatively recent and were recharged during the wet phase in the Late Pleistocene-Holocene between 3,200 and 14,000 BP. This study shows that the water and solutes in SM are a combination from different sources. Furthermore, A hydrologic budget was constructed for SM, where water fluxes were calculated on the basis of hydraulic gradient and conductivities measured in both shallow and deep wells. Evaporation rates from the surface of the sabkha indicate that the annual rainfall is lost by surface evaporation. Steady-state estimates within a rectilinear control volume of the sabkha indicate that about 1 m3/year of water enters by lateral groundwater flow; 2 m3/year of water exits by lateral groundwater flow; 20 m3/year enters by upward leakage; 780 m3/year enters by recharge from rainfall; and 780 m3/year are lost by evaporation. As per the source of solutes, the water flux multiplied by its solute concentration indicates that nearly all the solutes in the sabkha were derived by upward leakage from the underlying regional aquifers rather than weathering of the aquifer framework, from precipitation, or other sources.

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