<div>Mixing of stratified fluids due to motion of bubble swarms can happen through two major mechanisms. The first is the capture and transport of heavier liquid into the lighter layers by the bubble wake. The second is the mixing due to turbulent dispersion. Stratification also affects bubble dynamics in various ways, namely by reducing the horizontal and vertical bubble fluctuations and extent, altering the drag experienced by rising bubbles, and changing the wake dynamics. The objective of this study is to understand these explained phenomena by decoupling their effects from each other and studying them individually. CFD offers powerful capabilities to achieve the decoupling and perform in-depth analysis of the fluid flow. </div><div><br></div><div>Firstly, the study of mixing induced in stratified fluids by bubbly flow in a Hele-Shaw Cell will be performed. Simulations are run for a range of void fractions and Froude numbers. The confinement prevents turbulence production, and mixing occurs primarily due to transport of colder liquid into the hotter layers by the bubble wake. Bubbles move in a zigzag motion attributed to the periodic vortex shedding in their wake. We report the formation of horizontal clusters and establish a direct correlation between the size of clusters and the rise velocity of the bubbles. We report an increase in the buoyancy flux across the isopycnals as the void fraction increases. The fraction of energy production due to the buoyancy flux increases with the strength of stratification, giving rise to a higher mixing efficiency. At the same time, cross isopycnal diffusion is higher at weaker stratification strengths.</div><div><br></div><div>Subsequently, direct numerical simulations of up to 146 bubbles rising in unbounded stratified fluids are performed. Both the bubble dynamics and destratification effects caused by the bubble motion are analyzed. The importance of bubble deformability and bubble Reynolds numbers on the induced background mixing are studied by varying the $E\ddot{o}tv\ddot{o}s$ number in the range 1.55 to 4.95 and Reynolds number in the range 25 to 200. Highly deformable, high Reynolds number bubbles undergo path instabilities and give rise to higher levels of mixing. Liquid and bubble velocity fluctuations and pseudo-turbulence caused by the bubble motion in the unconfined setting are examined and are seen to play an important role in mixing statistics. An increase in turbulent kinetic energy (TKE) levels with void fraction is noted. TKE levels are seen to decrease slightly as the stratification strength is increased, indicating increasing stability and resistance to destratification. Regardless of the stratification strength, a kinetic energy spectrum slope value between $-3 \sim -3.25$ is reported depending on Reynolds number. The dependence of mixing parameters on the void-fraction of bubbles and stratification strength of the liquid is also presented. </div><div><br></div><div>Next, the study of buoyancy driven motion of a single air bubble in stratified liquid is undertaken. A range of parameters including Froude number, Reynolds number and Bond number are explored. The Reynolds and Bond numbers will be maintained at values where the bubble motion and wake can be assumed to be axisymmetric. Wake dynamics and drift-volumes associated with the bubble rising in the stratified fluid are analyzed. The presence of secondary and tertiary vortices, which are alternating in direction, in the wake of the bubble due to the negative buoyant force experienced by the isopycnals is reported. The isopycnals oscillate before coming back to their stable state and the frequency of oscillations increases with stratification strength. The dependence of drag coefficient, determined by an unsteady force balance, and steady state bubble velocities, on the above mentioned parameters are studied. Analysis of bubble rise in partial stratification reveals the differences between homogeneous and stratified mediums.</div><div><br></div><div>Since most stratified bubbly flows occur near the free surface, an attempt is made at modeling the bubble rise up-to the free surface and subsequent bubble bursting. A brief study of in-line bubble coalescence is also attempted and potential future work for bubbly flows with topological changes is discussed.</div>

The Menindee Lakes are a series of shallow floodplain depressions on the Lower Darling River, approximately 300 river kilometres upstream from the confluence with the River Murray, in southeastern Australia. The system is the fourth largest water storage in the Murray-Darling Basin (1,680 Gl) and comprises of seven shallow deflation basins: Lakes Malta, Balaka, Bijiji, Tandure, Pamamaroo, Menindee, Cawndilla, and Lake Wetherell. Lake Wetherell was created by the construction of the Menindee Main Weir and subsequent flooding of the main channel of the Darling River and surrounding floodplain. Each deflation lake is individually connected to the Darling River with the exception of Lake Cawndilla, which is connected to Lake Menindee by Morton Boolka Channel. The climate of the Menindee area is arid with a mean annual rainfall of 243.7 mm, average maximum temperature in January of 34.1° C and in July of 16.9° C. Due to the flat topography, local runoff is negligible and the impact of precipitation on the water budget of the lakes is negligible in comparison to evaporation, which exceeds 2.5 m year-1. Prior to regulation, the Menindee Lakes would fill when river levels were higher than the sill level of the feeder creeks. When river levels receded, the lakes drained back to the Darling River leaving a residual pool, which would evaporate. The Darling River is one of the most variable rivers in the world and prior to regulation the Menindee Lakes were often dry for extended periods. The large lakes (Cawndilla, Menindee, Pamamaroo and Tandure) would fill on average every once every one to two years and the longest droughts lasted five years. The small lakes (Bijiji, Balaka and Malta) filled on average every two to three years with the longest droughts lasting eleven years. Construction of the Menindee Lakes Scheme was completed in 1968 and is a series of small dams, regulators, weirs, channels and levees designed to conserve Darling River floodwaters. The main structure is the Menindee Main Weir, which raises the level of the river 12 m above the bed level, creating Lake Wetherell and filling Lakes Tandure, Bijiji, Balaka and Malta. This hydraulic head is used to gravity feed Lakes Pamamaroo, Menindee and Cawndilla. The hydrologic regime is now dictated by the operating procedures developed by the New South Wales Department of Infrastructure, Planning and Natural Resources. The priority of operations is to maximize the potential supply of water for all users and to maximize water quality within the lakes and Lower Darling River for human uses. Now the lakes are inundated for longer periods; rates of drawdown are more rapid and small to medium sized floods downstream of the scheme and in the Darling Anabranch have been eliminated. Despite increased permanency, large water level fluctuations are still common and drying cycles have not been lost entirely. Since the completion of the scheme Lake Malta has dried four times, Lake Balaka three times, Lake Bijiji twice, Lakes Tandure and Pamamaroo once, Lake Menindee five times and Lake Cawndilla four times. Of all of the lakes, Lake Malta is least impacted by regulation. The vegetation dynamics and role of the seed bank have not been extensively investigated in ephemeral systems. The seed bank provides a mechanism for species persistence through unfavourable conditions and colonisation during favourable conditions. In ephemeral lakes, large and aseasonal water level fluctuations are common which may result in long periods of unfavourable conditions. Plants growing in these environments must be able to persist through unfavourable conditions for growth and survival. The main objectives of this study were: - To investigate the seed density, species richness and composition of the seed banks of selected lakes. - To determine if there are any within lake patterns in seed bank density, species richness and composition. - Examine the effect of different water regimes on germination and recruitment from the seed bank. - Determine water regime preferences for germination and recruitment of common species. - Investigate vegetation change during an extended drought. - Determine flood tolerances of Xanthium occidentale, Cyperus gymnocaulos and Ludwigia peploides. - Investigate the interaction between nutrients and water regime on recruitment from the seed bank. No information regarding the seed banks of the Menindee Lakes was available; therefore, a reconnaissance study was undertaken. The aims of this study were to determine the seed density, floristic composition, zonation with respect to elevation, differences between and within lakes and germination strategy (pattern through time) of Lake Malta, Bijiji and Menindee seed banks. Results showed that the seed bank of each lake had a different floristic composition and Lake Menindee had a depauperate seed bank (Lake Malta 27 species and 6,300-43,983 seeds m-2, Lake Bijiji 24 species and 2243-27,417 seeds m-2 and Lake Menindee one species and 117-233 seeds m-2). Within each lake, the seed density, species richness and composition was spatially variable but no zonation with respect to elevation was observed. In Lake Bijiji, the sampling site on the northern shore of the lake had a significantly less dense and less species rich seed bank than the other locations; however, this was not present in Lake Malta. Over 90% of the total germination from the seed bank from all lakes occurred in the first six weeks. This study also provided evidence that the seed bank around the edges of the lakes was concentrated in zones of organic matter deposition (strandlines). The seed bank density and species composition of the strandlines and adjacent sediment was investigated in Lakes Cawndilla, Menindee, Tandure (large highly regulated lakes) and Malta (a small lake minimally impacted by regulation). Three hypotheses were tested in this study: 1. The strandline will have a denser and more species rich seed bank. 2. The strandline provides favourable microsites for germination and recruitment. 3. All species present in the seed bank will bet hedge. The strandline seed banks of Lakes Cawndilla (strandline 25,753 seeds m-2 and adjacent sediment 2,730 seeds m-2), Menindee (strandline 7,427 seeds m-2 and adjacent sediment 646 seeds m-2) and Tandure (strandline 8,006 seeds m-2 and adjacent sediment 2,178 seeds m-2) were significantly denser and more species rich than the adjacent sediment, whereas there was large, species rich seed bank outside the strandline in Lake Malta strandline (70,180 seeds m-2 and adjacent sediment 54,266 seeds m-2). The organic component of the strandline may act to reduce evaporation from the soil and provide a favourable microsite for germination and recruitment. Of the 58 species present in all seed banks 37 bet hedged (had persistent seed banks). The effect of water regime on recruitment from the seed bank and the optimal water regime for germination and recruitment of common species were investigated in a pond experiment. This experiment had three aims: 1. To test the hypothesis that different water regimes will give rise to different plant communities from the same seed bank. 2. Determine optimal water regimes for germination and recruitment of common species. 3. To formulate a testable conceptual model describing recruitment from the seed bank under different, controlled water regimes. Different water regimes did give rise to different plant communities from the same seed bank. Myriophyllum verrucosum was the only species that germinated whilst submerged. All other species required exposed soil with high soil moisture to germinate. All terrestrial and floodplain species died if flooded, however several amphibious species were present that persisted whilst flooded, despite requiring exposed soil for germination. The conceptual model consisted of eight states (dependant on whether the soil was exposed or inundated, soil moisture content, duration of inundation and species present) that predicted which species would be present in each of the states (providing they were present in the seed bank). A series of surveys to investigate recruitment from the seed bank in the field during a period of extended drought was undertaken over 488 days. This study had four aims: 1. To investigate the relationship between the extant vegetation and selected environmental variables. 2. To test a conceptual model that predicts how the environment changes with fluctuating water levels. The model consists of five states (windows of opportunity) that the system switches between; depending water level, elevation and the species present in the seed bank and extant vegetation. The five states are: window of opportunity closed due to inundation, window of opportunity open for germination establishment and reproduction (exposed soil with high moisture content in the top 7.5 cm), window of opportunity closed for germination but open for establishment and reproduction (low soil moisture in the top 7.5 cm), window of opportunity closed for germination and establishment but open for reproduction (top 15 cm low soil moisture) and all windows of opportunity closed because the soil is dry (low soil moisture to 40 cm). 3. To test the part of the conceptual model derived from the pond experiment. 4. To investigate the change in the germinable seed bank as the window of opportunity for germination opens, plants recruit and replenish the seed bank. This aim tests the hypothesis that the species that recruit will reflect the seed bank before the window of opportunity for germination opens, then when the window of opportunity for germination opens the seed bank will become less similar and then recover (reflect the recruited vegetation) after the species present have replenished the seed bank. The floristic composition of Lake Malta was correlated with sediment exposure time and clay content, Lake Balaka with sediment exposure time, soil moisture and clay content, Lake Wetherell with elevation, canopy cover and elevation of the water relative to the quadrat and Lake Menindee with sediment exposure time, soil moisture, elevation and clay content. The floristic composition of Lake Cawndilla was not correlated with any of the measured environmental variables. As water levels fell the window of opportunity for germination opened once the sediment was exposed and closed when the sediment surface dried. The window of opportunity for establishment and reproduction did not close until the sediment dried further. For the most desiccation tolerant species the window of opportunity for growth and reproduction remained open. If the species composition of the seed bank was known, the pond model predicted the potential floristic composition. However, it did not take into account sediment exposure time. Extended drought in the Darling catchment meant that the lakes did not fill during the study period and the effect of flooding could not be investigated in the field. Therefore, a pond experiment to test the effect of flooding on Xanthium occidentale, Cyperus gymnocaulos and Ludwigia peploides was undertaken. Three hypotheses were tested: 1. Xanthium occidentale when top flooded for more than two weeks will die. Plants partially flooded will survive, increase above ground to below ground biomass ratio and grow when water levels fall. 2. Cyperus gymnocaulos when top flooded for two weeks will show no adverse effects and grow when water levels fall. When top flooded for more than two weeks the above ground biomass will senesce and resprout when water levels fall. Plants partially flooded will show no adverse effects. 3. Ludwigia peploides when top flooded will rapidly increase above ground biomass in order to reach the water surface. Each species generally responded as hypothesised. Xanthium occidentale also produced adventitious roots and lost stem rigidity when partially flooded. Cyperus gymnocaulos showed reduced growth rates when partially flooded compared to plants that were not flooded. Water regime is only one factor that may influence the floristic composition derived from the seed bank. A pond experiment was undertaken to test the hypothesis that the combination of different soil nutrient concentrations and water regime will give rise to different plant communities from the same seed bank. The effect of different nutrient loadings however, had no effect on floristic composition and the differences could be explained by differences in water regime. The sediment seed banks of the Menindee Lakes provide a mechanism for survival through droughts and floods. They are spatially variable and the strandline accounted for the majority of seed around the edges of the large regulated lakes. All but one species present in the seed banks of all lakes sampled required exposed sediment with high soil moisture to germinate and many species were very desiccation tolerant (especially terrestrial and floodplain species). Most species were intolerant to flooding as juvenile or adults; however, there were a few amphibious species present. Water regime influences the floristic composition derived from the seed bank but soil texture is also an important factor, whereas nutrients appeared to have no effect. / Thesis (Ph.D.)--School of Earth and Environmental Studies, 2004.

This thesis is concerned with the conceptual foundations of environmental law and policy in the Great Lakes basin, the world's largest freshwater ecosystem. The Great Lakes regime is now widely recognized as one of the most advanced international environmental management regimes in existence. Over the past two decades, toxic contamination has emerged as a highly pressing ecological issue in the Great Lakes basin. In Canada and the United States, the ecosystem approach, a comprehensive and integrated approach to environmental management, has been adopted both bilaterally and domestically in the Great Lakes' complex environmental policy framework to guide the protection of ecological integrity. There has been extensive discussion of the ecosystem approach, particularly from scientific and managerial perspectives; however, the economic content of the concept has been largely neglected, despite the importance of considering all relevant perspectives in the development of law and policy. This thesis is divided into five chapters. After discussing in Chapter 1 the ecological and institutional contexts and methodological issues of the analysis, this thesis defends, in Chapter 2, the view that economic theory has relevance to issues of environmental law and policy. In addition to highlighting the main contours of welfare and environmental economic theory, a main conclusion, and an essential premise upon which the analysis proceeds, is that economics remains a useful analytical approach to environmental issues, despite some important criticisms. Subsequently, in Chapter 3, the analysis shifts to an examination of four bilateral and domestic Great Lakes instruments that form the core of Great Lakes toxic pollution policy: (i) the Great Lakes Water Quality Agreement; (ii) the Great Lakes Binational Toxics Strategy; (iii) the Canada-Ontario Agreement; and (iv) the Final Water Quality Guidance for the Great Lakes System. After outlining key principles underpinning each instrument, the thesis underscores common themes running through the collective policy framework. The ecosystem approach constitutes a unifying concept in this framework. The ecosystem approach is examined from an economic perspective in Chapter 4. After identifying key elements of the ecosystem approach, this chapter highlights important parallels between fundamental welfare and environmental economic notions. One main conclusion is that economic concepts and approaches, such as environmental valuation, externalities, and self-interest, form an integral part of the ecosystem approach. Finally, Chapter 5 identifies some directions for further research. Given that, as the thesis seeks to establish, economic theory constitutes an important, albeit not sole, perspective on the ecosystem approach, a key challenge will be to facilitate interdisciplinary analysis and cooperation leading to effective operationalization of the concept.

Between the mid-eighteenth and the mid-nineteenth centuries, the Crown coordinated a revolution in land usage in the Kawartha Lakes, as elsewhere in the colony, through 'civilization' and land redistribution. Attempts to change native society and build settler communities did not quite unfold the way the government intended. 'Civilization' helped the Mississauga farm and taught skills that eased interaction with colonial society, but they continued to produce much of their food by traditional means. Speculation isolated settlers and made land acquisition more difficult, though some speculators provided essential services. Most immigrants bought land privately and many were not able to establish themselves as farmers. Preferential grants were particularly poor at distributing land to settlers and Crown or Clergy Reserves sales were much more likely to transfer property directly to users. The transition to agricultural land usage occurred largely through the state's mediation of conflicting claims to access.

The purpose of this descriptive exploratory study was to investigate and report patterns of participation and motivational orientations of Institutes for Learning in Retirement (ILR)participants enrolled in ILR programs in the Great Lakes region. In addition, the study sought to identify relevant demographic characteristics for this segment of the population and the effects of ILR upon participation and participants' perceived life satisfaction.The Great Lakes region ILR participant profile was most likely to be female, between the ages of 66 and 70, married and living with spouse. She shared a relatively high economic status and extensive formal educational experience and was affiliated with her ILP program 1 to 2 years.Motives for ILR participation were examined using the Educational Participation Scale (EPS) A-Form (Boshier, 1991). Two influential motives for participation emerged. The first was "Cognitive Interest", the joy of learning for the sake of learning. "Social Contact," having an opportunity to meet new people and make friends, was the second major reason for participation.The perceived life satisfaction or subjective well being of ILR participants was explored using the Life Satisfaction Index A-Form (LSIA) (Neugarten, et al, 1961). Overall respondents revealed a perceived positive life satisfaction. Positive indications of well being include hopeful outlooks for the future, social interactions and sense of accomplishment.Results of this study indicate that the pursuit of intellectually stimulating adult educational programs offered within- a socially stimulating environment appeal to lifelong learners enrolled in Institutes for Learning in Retirement programs. This study supports the conclusion of previous investigators that intellectual stimulation is a strong underlying motivation for participation. The second major finding with regard to reasons for participation in ILR programs was the importance of "social contact." / Department of Educational Leadership

This thesis is concerned with the conceptual foundations of environmental law and policy in the Great Lakes basin, the world's largest freshwater ecosystem. The Great Lakes regime is now widely recognized as one of the most advanced international environmental management regimes in existence. Over the past two decades, toxic contamination has emerged as a highly pressing ecological issue in the Great Lakes basin. In Canada and the United States, the ecosystem approach, a comprehensive and integrated approach to environmental management, has been adopted both bilaterally and domestically in the Great Lakes' complex environmental policy framework to guide the protection of ecological integrity. There has been extensive discussion of the ecosystem approach, particularly from scientific and managerial perspectives; however, the economic content of the concept has been largely neglected, despite the importance of considering all relevant perspectives in the development of law and policy. This thesis is divided into five chapters. After discussing in Chapter 1 the ecological and institutional contexts and methodological issues of the analysis, this thesis defends, in Chapter 2, the view that economic theory has relevance to issues of environmental law and policy. In addition to highlighting the main contours of welfare and environmental economic theory, a main conclusion, and an essential premise upon which the analysis proceeds, is that economics remains a useful analytical approach to environmental issues, despite some important criticisms. Subsequently, in Chapter 3, the analysis shifts to an examination of four bilateral and domestic Great Lakes instruments that form the core of Great Lakes toxic pollution policy: (i) the Great Lakes Water Quality Agreement; (ii) the Great Lakes Binational Toxics Strategy; (iii) the Canada-Ontario Agreement; and (iv) the Final Water Quality Guidance for the Great Lakes System. After outlining key principles underpinning each instrument, the thesis underscores common themes running through the collective policy framework. The ecosystem approach constitutes a unifying concept in this framework. The ecosystem approach is examined from an economic perspective in Chapter 4. After identifying key elements of the ecosystem approach, this chapter highlights important parallels between fundamental welfare and environmental economic notions. One main conclusion is that economic concepts and approaches, such as environmental valuation, externalities, and self-interest, form an integral part of the ecosystem approach. Finally, Chapter 5 identifies some directions for further research. Given that, as the thesis seeks to establish, economic theory constitutes an important, albeit not sole, perspective on the ecosystem approach, a key challenge will be to facilitate interdisciplinary analysis and cooperation leading to effective operationalization of the concept. / Law, Peter A. Allard School of / Graduate

No description available.

Doctor of Philosophy / Department of History / James E. Sherow / This project examines ecological change in Lake Huron during the nineteenth and twentieth century and investigates the causative role of the commercial fisheries in that change. The repeated failures of various regional and international efforts designed to improve management of the lake’s fisheries are also examined. The fundamental argument is that economic considerations were the primary motivations for policy development related to the Great Lakes fisheries. Historically management programs and legislation were shaped by local and regional economic interests. The central focus of this project is Lake Huron. Anthropogenic changes in that lake’s environment dramatically affected the lives and relationships of its non-human inhabitants. The same changes also transformed relationships among human beings who relied on the lake’s resources. Commercial fishermen who operated in the waters of both the United States and Canada relied on the lake for their livelihood, but as the twentieth century commenced the supply of marketable fishes decreased. Competition accelerated and fishermen introduced new technologies and increased their quantity of fishing gear in an effort to maximize their catches in response to fluctuating returns. Economic considerations were of primary concern to both fishermen and government bureaucrats. Lake Huron’s status as an international borderland further complicated the situation. Analysts in both the United States and Canada recognized the dramatically changing conditions of the lakes as reflected through the woes of the commercial fishery. Nonetheless, the germane state, provincial and national governments repeatedly failed in their attempts to develop a cooperative management plan. By the second half of the twentieth century Lake Huron’s embattled biome stood in stark contrast to the once seemingly endless numbers of fishes and flora that sustained the lake’s web of life for hundreds of years.

The invasion of ecosystems by alien species is a growing threat to the delivery of ecosystem services. This study explored the spatial distribution of water hyacinth in the Benoni Lakes and made analysis of its impact on water availability and usability in order to understand the evolution and its propagation rates. The study used satellite imagery for lake level modelling using Remote Sensing and Geographical Information Systems for calculations of area covered by weeds in each lake from 2002 to 2012.The modelling approach illustrates the potential usefulness in projecting invasive plants under climate change and enabled the quantification of long term changes in aquatic weeds. The results showed that aquatic infestations in lakes may be used as powerful predictors of correlations between plant abundance and climate change. The study therefore informs decision makers to identify areas where invasion is likely to occur and increase surveillance for early invaders. / Environmental Sciences / M. Sc. (Environmental Management)

<p>The Earths climate is changing at a higher rate, i.e between 1861 and 1994 the annual mean temperature in Scandinavia increased with 0,68º C and according to recent climate models the annual mean temperature is likely to rise with another 3º C during this century.</p><p>A warmer climate in many ways is associated with changing conditions for lake ecosystems. An expected higher water temperature and a stronger summer stratification of the water column increases the risk of anoxic conditions at the lake bottom. Thus anoxic conditions are likely to cause a phosphate leakage from the sediment, i.e. a higher internal loading of phosphate.</p><p>In this project, the extremely warm summer of 2002 has been used as an example for a possible scenario for a future climate. By comparing levels of phosphorus in the summer of 2002 with a ten-year median value, a phosphorus related sensitivity to climate change has been analyzed for 55 Swedish lakes. This sensitivity has then been related to several parameters of which in particular the lake morphometry and the land use in the catchment of the lake influenced the climatic sensitivity of the lake to climatic change.</p> / <p>Jordens klimat förändras i en allt snabbare takt. Mellan 1861 och 1994 steg årsmedeltemperaturen i Skandinavien med 0,68º C. Enligt aktuella klimatmodeller förväntas årsmedeltemperaturen i Skandinavien öka med ytterligare 3º C det närmaste seklet.</p><p>Ett varmare klimat innebär på flera sätt nya förutsättningar för ekosystemen. Genom höjda vattentemperaturer och en starkare stratifikation sommartid ökar risken för syrefria förhållanden i sjöar. Då sedimentet under syrefria förhållanden kan läcka fosfat innebär detta en ökad internbelastning av fosfor.</p><p>I detta projekt har den extremt varma sommaren 2002 använts som ett möjligt framtida klimat. Genom att jämföra fosforhalter sommaren 2002 med ett medianvärde för 10 år har den fosforrelaterade känsligheten för klimatförändringar kunnat analyseras för 55 svenska sjöar. Denna känslighet har sedan relaterats till diverse parametrar så som sjöns morfometri och avrinningsområdets sammansättning.</p>