Knowing the control of landscape position in greenhouse gas (GHG) emission from the Prairie pothole region is necessary to provide reliable emission estimates needed to formulate strategies for reducing emission from the region. Presented here are results of a study investigating the control of landscape position on the flux of nitrous oxide (N2O) and methane (CH4) from an agricultural soil. Field flux of N2O and CH4 and associated soil parameters from the Upper, Middle, Lower and Riparian slope positions were monitored from spring to fall of 2005, and spring of 2006, at the Manitoba Zero-Tillage Research Association (MTRZA) farm, 17.6km North of Brandon, MB. The field site consisted of a transect of 128 chambers segmented into the four landscape positions, with either all chambers or a subset of the chambers (32) sampled on select days. Spring thaw is an important period for annual inventory of N2O emission, thus, soil samples were also collected from the four slope positions in fall 2005, and treated in the laboratory to examine how antecedent moisture and landscape position affect the freeze-thaw emission of N2O from soil. Daily emissions of N2O and CH4 for 2005 were generally higher than for 2006, the former being a wetter year. There was high temporal variability in N2O and CH4 emission, with high fluxes associated with events like spring thaw and fertilizer application in the case of N2O, and rapid changes in soil moisture and temperature in the case of CH4. There was a high occurrence of hotspots for N2O emission at the Lower slope, associated with its high soil water-filled porosity (WFP) and carbon (C) availability. The Riparian zone was not a source of N2O emission, despite its soil WFP and organic C being comparable with the Lower slope. The hotspot for CH4 emission was located at the Riparian zone, associated with its high soil WFP and C availability. The Upper and Middle slope positions gave low emission or consumed CH4, associated with having low soil WFP and available C. This pattern in N2O and CH4 emission over the landscape was consistent with examination of entire 128 chambers on the transect or the 32 subset chambers. Significantly lowering the antecedent moisture content of soil by drying eliminated the freeze-thaw emission of N2O, despite the addition of nitrate to the soil. This was linked to drying slightly reducing the denitrifying enzyme activity (DEA) of soil. The highest and earliest freeze-thaw emission of N2O was from the Riparian zone, associated with its high antecedent moisture content, DEA and total organic C content. The addition of nitrate to soil before freezing failed to enhance freeze-thaw emission of N2O from the Upper, Middle and Lower slope positions, but increased emission three-fold for the Riparian zone. Despite the greater potential of the Riparian zone to produce N2O at thaw compared to the Upland slopes, there was no spring-thaw emission of N2O from the zone on the field. This was because this zone did not freeze over the winter, due to insulation by high and persistent snow cover, vegetation and saturated condition. The denitrifying potential and freeze-thaw N2O emission increased in going from the Upper to the Lower slope position, similar to the pattern of N2O emission observed on the field. The localization of hotspots for N2O and CH4 emission within the landscape was therefore found to be driven by soil moisture and C availability. When estimating GHG emission from soil, higher emission index for N2O and CH4 should be given to poorly-drained cropped and vegetated areas of the landscape, respectively. The high potential of the Riparian zone for spring-thaw emission of N2O should not be discountenanced when conducting annual inventory of N2O emission at the landscape scale. When fall soil moisture is high, snow cover is low, and winter temperature is very cold, freeze-thaw emission of N2O at the Riparian zones of the Prairie pothole region may be very high.

Composite liners are used in landfills to isolate solid waste from the local environment. The combination of a high-density polyethylene (HDPE) geomembrane and compacted clay liner (CCL) is commonly used worldwide. In the Ontario region, bentonite sand mixtures (BSMs) and the local clay i.e. Leda clay, can be considered as appropriate CCL materials. However, the interface failure between smooth HDPE and CCL is a critical issue for landfill safety. The shear stress behavior and strength parameters at the interface between the HDPE and CCL can be affected by many factors, such as temperature and chemicals. The temperature difference between winter and summer in the Ontario region is approximately 50°C, which causes a freeze-thaw (F-T) phenomenon in local landfills. Leachate and heat are generated during the solid waste stabilization process. Landfill leachate usually contains a high concentration of cations, which can carry heat, thus affecting the landfill liner properties. As a result, the interface shear stress behavior and strength parameters are affected by the aforementioned conditions. In this thesis, a series of experiments were conducted on the shear stress behavior at the interface of Leda clay / HDPE and bentonite sand mixture (BSM) / HDPE. In order to understand the influence of the F-T phenomenon, the samples were tested by varying the number of F-T cycles. Meanwhile, in order to understand the combined influence of cations and heat, the samples were saturated with different solutions, i.e. distilled water, potassium chloride and calcium chloride solutions. Then they were cured in an oven with different temperatures and room temperature, respectively. All of the laboratorial shear tests have been performed by using a direct shear machine. Results show that the BSM /HDPE and Leda clay/ HDPE interfaces are both influenced by the F-T cycles. The BSM/HDPE interface shear of the samples between 0 and 5 F-T cycles has more obvious differences, while the friction angle of compacted Leda clay/HDPE exhibits distinct reduction in the first 3 cycles, after which, the difference becomes hard to differentiate. The results also indicate that both high temperature and high concentration of cations from leachate can slight reduce the interface shear stress of BSM/HDPE. However, the combined influence of thermal-chemical conditions is not much more obvious compared to the effects of a single thermal or chemical condition. The BSM materials, which were saturated with different solutions, are also tested by using X-ray diffraction to examine the mineral changes in the BSM. The calcium and potassium cations convert sodium-bentonite into calcium-rich bentonite and illite/semectie mixtures, respectively. Nevertheless, the changess of clay part caused by the combined effect of heat and leachate have limited influence on the BSM/HDPE interface shear behavior.

L'objectif de ce travail est de comprendre le processus d'altération des calcaires oolithiques et d'estimer leur cinétique d'altération en fonction des conditions climatiques présentes en France. Pour y répondre, des cycles de vieillissement accéléré, basés sur les paramètres issus de l'étude bibliographique et sur les données de température et de précipitations réelles, ont été définis. Ensuite, des lots d'échantillons de deux calcaires oolithiques ont subis ces vieillissements. Les mesures réalisées pour déterminer l'endommagement ont été choisies en fonction de leurs caractéristiques métrologiques et de leur pertinence. Les résultats obtenus ont été comparés avec les mêmes mesures réalisées sur des calcaires altérés de façon naturelle prélevés sur site. Ainsi, les liens entre le processus d'altération des calcaires et les caractéristiques mécaniques, physiques et surtout microstructurales des calcaires ont été établis. Cette analyse a également abouti à des cinétiques d'altération. Les résultats ont été validés par l'étude d'un autre calcaire oolithique sous d'autres conditions climatiques. Enfin, l'influence de changements climatiques éventuels sur les cinétiques d'altération a été déterminée à l'aide d'un outil statistique / The objective of this work is to understand the weathering process of oolitic limestone and estimate their weathering kinetics under French climatic conditions. Accelerated ageing cycles, based on parameters deduced from a literature review and on temperature and precipitation data, have been defined. Then samples of two oolitic limestones have undergone these ageing. The measurements used to determine damage were chosen based on their metrological characteristics and their relevance. The results were compared with the same measurements performed on naturally weathered limestone. Thus, the relationships between the weathering process of oolitic limestone and their mechanical, physical and microstructural characteristics have been established. This analysis also led to weathering kinetics. The results were validated by the study of another oolitic limestone under different climatic conditions. Finally, the influence of a potential climate change on the weathering kinetics was determined using a statistical tool

The expansion of urban and suburban areas is a world-wide phenomena. One product of this development is a dramatic increase in impermeable surfaces and a consequent increase in stormwater runoff. Bioretention cells are one best management practice frequently used to mitigate the environmental impacts of urban stormwater runoff. To ensure that a bioretention cell will continue to perform adequately in the long term, it is imperative that the environmental conditions it will experience and their effect on its performance through time are considered during its design. Although bioretention cells are frequently used for stormwater management, very few quantitative data exist on how they perform through time and in varied physical environments. In regions with seasonal freeze-thaw cycles, it is important to understand the effects of freeze-thaw cycles on the infiltration rate of bioretention cell soil mixtures so that the integrity of the design will not be compromised by seasonal change. This project uses laboratory tests to investigate the effects of freeze-thaw cycles and sediment input on the infiltration capacity of three different bioretention cell soil mixtures. These results will provide an analog for long-term changes in bioretention cell infiltration rates due to freeze-thaw cycles, providing critical data on which soil mixture would be best implemented in geographic regions susceptible to freeze-thaw activity. Furthermore these results will inform design standards for bioretention cells to ensure their long-term performance.

Gullies are significant contributors of sediment to streams in the southeastern USA. This study investigated gully erosion in the clay-rich soils of east Tennessee under a humid subtropical climate. The aims of this study were to (1) estimate long-term erosion rates for different gully geomorphic settings, (2) compare patterns of erosion for the different settings, and (3) model the response of gully erosion to freeze-thaw events. Erosion was measured weekly from June 2012 to August 2018 using 105 erosion pins distributed in gully channels, interfluves, and sidewalls. Erosion rates were estimated from average slopes of lines of best fit of pin lengths versus time. Maximum and minimum temperature was calculated daily using an on-site weather station and freeze-thaw events were identified. Gully erosion was modeled using antecedent freeze-thaw activity for the three geomorphic settings. Long-term erosion rates in channels, interfluves, and sidewalls were 2.5 mm/year, 20 mm/year, and 21 mm/year, respectively; however, week-by-week erosion was statistically different between the three settings, indicating different erosive drivers. Models of erosion with lagged freeze-thaw variables explained up to 34.8% of the variability in erosion variables; sidewall erosion was most highly related to freeze-thaw activity. Freeze-thaw in prior weeks was an important variable in all erosion models.

Soil is the most widely used material in the construction of various civil infrastructure. Various types of soils are extensively used in its natural or compacted form in the construction of dams, canals, road and railway subgrades, and waste containment structures such as soil covers and liners. These infrastructure and foundation soils are exposed to the influence of environmental factors. In the permafrost and seasonally frozen regions, soils can be in different states (e.g., saturated or unsaturated, frozen or thawed, or combinations of them) due to the variations in moisture content and temperature. The soil-water characteristic curve (SWCC), which is the relationship between soil water content and suction, is used in the interpretation and prediction of unsaturated soils behavior. Similarly, the soil-freezing characteristic curve (SFCC), which is the relationship between unfrozen water content and subzero temperature, is used in the prediction and interpretation of frozen soils behavior. In this thesis, the SWCC and SFCC of two Canadian soils (i.e. Toronto silty clay (TSC) and Toronto lean clay (TLC)) were extensively investigated for better understanding the fundamental relationship between SWCC and SFCC. The soil resilient modulus (MR) is a key material property used in the rational design of pavements. Experimental investigations were undertaken to determine the MR of five Canadian soils (i.e., TSC, TLC, Kincardine lean clay (KLC), Ottawa Leda clay (OLC), and Indian Head till (IHT)), considering the influence of moisture and temperature, with the aid of an advanced triaxial testing equipment. Two simple models were proposed for estimating the MR of frozen soils, in this thesis. In addition, an artificial neural network (ANN) model was developed for estimating the MR of the five Canadian soils considering various influencing factors. The conclusions from the various studies in this thesis are succinctly summarized below. (1) Four expressions (i.e. power relationship, exponential relationship, van Genuchten equation, and Fredlund and Xing equation) that are widely used for representing the SFCC were selected for providing comparisons between the measured and fitted SFCCs for different soils. The results suggest that the exponential relationship and van Genuchten equation are suitable for sandy soils. The power relationship reasonably fits the SFCC for soils with different particle sizes, but not for saline silts. The Fredlund and Xing equation is flexible and provides good fits for all the soils. (2) The SFCC and SWCC of TSC and TLC were experimentally determined, analyzed, and compared. Many factors influence the reliable measurement of SFCC, which include sensors’ resolution and stability, sensor calibration for each soil, and thermodynamic equilibrium condition. The hysteresis of SFCC for the two soils is mainly attributed to the supercooling of pore water. The quantitative dissimilarity in the measured SFCC and SWCC may be attributed to specimen structure variations during compaction and saturation, and during freezing / thawing processes, and cracks formation due to sensors insertion. In addition, some fundamental differences may exist between the drying / wetting and freezing / thawing processes, resulting in dissimilarity. (3) Two novel models were proposed for the estimation of MR of frozen soils. The semi-empirical model extends the mechanics of unsaturated soils and employs SFCC for prediction. Several coarse- and fine-grained saturated soils were used to validate this model. The empirical hyperbolic model was proposed considering that the frozen MR versus subzero temperature relationship resembles hyperbola. This model was validated on coarse- and fine-grained soils under saturated / unsaturated conditions. The hyperbolic model has wider application since it can be used for both saturated and unsaturated frozen soils. Both the models are simple and promising. (4) The MR of five Canadian soils subjected to wetting and freezing was determined by using the GDS ELDyn triaxial testing system. A freezing system was established for controlling the desired testing temperatures within the soil specimens. The results suggest: (i) The effect of subzero temperature on the MR is significant. (ii) For TLC, KLC, OLC, and IHT, the frozen MR versus subzero temperature relationship of the saturated specimen typically has steeper slope than specimen at the optimum water content, for the temperature range from 0 to -5 °C. (iii) The effect of stress levels on the frozen MR depends on soil type, water content, and subzero temperature. Lastly, (iv) Loading frequency does not show a significant influence on the frozen MR. (5) The MR of the five Canadian soils was determined considering wetting and freeze-thaw (F-T) conditions. The results suggest: (i) The F-T cycles result in weak soil structure due to reduction in suction, particles movement, loss of cohesion, and formation of cracks / channels. (ii) The critical numbers of F-T cycles were determined as 1, 1, 2, and 1 for TLC, KLC, OLC, and IHT at the optimum water content, respectively. (iii) The percentage of reduction in MR after the critical number of F-T cycles was strongly related to the plasticity index for specimens tested at the optimum water content. (iv) The wetting process results in the decrease in suction and enlargement of soil pores. Consequently, relatively low MR values were measured at high water contents, and the effect of F-T cycles becomes insignificant. Finally, (v) The effect of stress levels on the MR was dependent on the initial water content of the specimen and soil type.

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Previous studies have shown that soil erodibility and critical shear stress are highly influenced by weathering processes such as freeze-thaw cycling and wet-dry cycling. Despite over forty years of research attributing changes in soil properties over time to climate-dependent variables, little quantitative information is available on the relationships between streambank erodibility and critical shear stress and environmental conditions and processes that enhance streambank erosion potential. The goal of this study was to investigate temporal changes in streambank erodibility and critical shear stress due to surface weathering. Soil erodibility and critical shear stress were measured monthly in situ using a multi-angle submerged jet test device. Environmental and soil data were also collected directly at the streambank surface to determine freeze-thaw cycles, soil moisture, soil temperature, bulk density, soil erodibility, critical shear stress, and other atmospheric conditions that could impact bank erosion potential. Statistical tests, including a nonparametric alternative to ANOVA and multiple comparison tests, were used to determine if temporal changes in soil erosion potential were greater than spatial differences. Regression analyses were also utilized to identify the factors contributing to possible changes in soil erodibility, critical shear stress, and bulk density. The nonparametric alternative to ANOVA in combination with Dunn's nonparametric multiple comparison test showed soil erodibility was significantly higher (p=0.024) during the winter (November - March) and the spring/fall (April - May, September - October). Regression analyses showed 70 percent of soil erodibility variance was attributed to freeze-thaw cycling alone. Study results also indicated that bulk density is highly influenced by climate changes since gravimetric water content and freeze-thaw cycles combined explain as much as 86 percent of the variance in bulk density measurements. Results of this study show significant amounts of variation in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes, specifically changes in soil moisture and temperature. These results have potential implications for streambank modeling and restoration projects that assume constant values for soil erodibility. Watershed models and restoration designs should consider the implications of changing soil erodibility during the year in model development and stream restoration designs. / Master of Science

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