<p> Entrapped gas (V g) greatly affects peatland biogeochemistry and hydrology by altering volumetric water content, buoyancy, hydraulic conductivity and generating overpressure zones. These over pressure zones affect hydraulic gradients which influence water and nutrient flow direction and rate. The loss of this entrapped gas to the atmosphere via ebullition (bubbling) has been proposed as the dominant transport mechanisms for CH4 from peatlands, releasing significant amounts of CH4 to the atmosphere in a single event. Atmospheric pressure has been linked to ebullition events and is known to affect gas volumes; similarly, temperature affects gas production and volume. This thesis investigates the relationship between these environmental factors (atmospheric pressure and temperature) on both V g and ebullition processes. </p> <p> An incubation experiment using six peat cores at three incubation temperatures ( 4 °C, 11 °C, 20°C) was conducted in 2004 where each core was incubated in a sealed PVC cylinder and instrumented to measure Vg, pore-water C~ concentrations, and ebullition (volume and C~concentrations). Temperature data for each incubation group and atmospheric pressure were measured within the laboratory setting. </p> <p> Increasing bulk density was associated with decreased frequency of ebullition events and higher average ebullition volumes, indicating a relationship between bulk density ebullition characteristics. Future work will be needed to identify the direct relationship between V g, bulk density and ebullition. </p> <p> Evaluation of ebullition and atmospheric pressure data revealed a strong relationship between periods of falling pressure and ebullition events where 71% of measured events (n = 391) occurred during periods of decreasing pressure. Investigation of falling pressure characteristics revealed that drop duration (days) had a more significant effect on total ebullition volumes than did magnitude (kPa). As such, long periods of decreasing pressure trigger greater gas releases via ebullition than short decreases of large magnitude. This has implications for the prediction and modelling of ebullition events in natural systems, and for the estimation of CH4 fluxes and carbon budgets of peatlands. </p> The V g variability model accounted for changes in V g caused by gas transfer between aqueous and gaseous phases (Henry's law) and thermal and pressure induced volume changes (Ideal gas law) using measured temperature and atmospheric pressure data. Gas loss via ebullition and CH4 production were also accounted for. Good agreement was found between measured and modeled V g values where gas contents were greater than 10% (average r2 value of 0.78). Accuracy of the model indicates a general understanding of the processes, however it also suggests that further factors are influencing internal gas dynamics that require further investigation. </p? / Thesis / Master of Science (MSc)

Biofuel additives have been designed to reduce vehicular emissions to the atmosphere to limit the effects of greenhouse gases on global climate change. The chemical properties of common biofuel additives exhibit ideal characteristics for use in gasoline and diesel, while limiting emissions from exhaust. As biofuel additives begin to be administered regularly to gasoline and fuel sources, the compounds will appear in spill sites, posing a risk to groundwater sources. The interactions that occur between common biofuel additives and trapped gases below the water table were analyzed in this work to further understand the potential consequences on quasi-saturated groundwater zones. The behaviour of trapped gases contaminated with different biofuel additives were analyzed in laboratory experiments conducted in a two-dimensional flow cell to demonstrate the mechanisms of gas flow through a capillary barrier resulting from modified interfacial properties in the presence of a chemical surfactant. Contamination of gas-fluid interfaces by applied biofuel additives at the pore scale resulted in the breakthrough of gas through the capillary barrier. Gas migration terminated at a critical pool height proportional to the reduction in interfacial tension induced by the administered biofuel additives. To further demonstrate the relationship between interfacial tension and critical gas pool height, an interfacial tension-macroscopic invasion percolation model was developed to simulate the transport mechanisms and behaviours of gas flow when an immobile pool is contaminated with 1-Butanol. The findings in this study provide a fundamental understanding of the mechanisms and behaviours of gas mobilization in the presence of common biofuel additives. / Thesis / Master of Science (MSc) / The use of biofuel additives in gasoline and diesel fuels has become an attractive alternative to fully petroleum-based fuels to reduce the release of vehicular greenhouse gases to the atmosphere. As fuel spills and storage tank leaks continue to be a primary source of groundwater contamination, the appearance of biofuel additives in contaminated systems will appear below the subsurface as they continue to be administered to modern gasoline and diesel fuels. This work investigated the consequences of biofuel contamination of groundwater systems containing gas trapped within pore spaces through the use of laboratory experiments and numerical modelling. Contamination of these systems with different biofuel additives displayed a similar response, in which gas had mobilized from within pore spaces and released to the atmosphere. Mobilization of trapped gas in groundwater can alter the primary hydraulic properties that characterize a particular hydrogeologic system.