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The Global ETD Search service is a free service for researchers
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Showing 1 to 9 of 9 (0.078 seconds)Spelling suggestions: "subject:"progressive""
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Impacts of Retrogressive Thaw Slumps on the Geochemistry of Permafrost Catchments, Stony Creek Watershed, NWTMalone, Laura 08 May 2013 (has links)
Retrogressive thaw slumps are one of the most dramatic thermokarst landforms in periglacial regions. This thesis investigates the impacts of two of the largest hillslope thaw slumps on the geochemistry of periglacial streams on the Peel Plateau, Northwest Territories. It aims to describe the inorganic geochemistry of runoff across active mega-slumps, impacted and pristine tundra streams, as well as that of the ice-rich permafrost exposed in the slump headwalls. Slump runoff is characterized by elevated suspended sediments (911 g/L), high conductivity (2700 µS/cm), and high SO42- ( up to 2078 ppm). The runoff originates as a solute-rich meltwater near the slump headwall, and leaches and re-dissolves soluble salts (e.g., gypsum) as it flows along the mudflow. Conductivity increases until the runoff mixes with pristine tundra streams, diluting the slump runoff signal. SO42-/Cl- is used as a tracer to isolate the slump runoff signal in impacted waters, and suggests that the contribution of slump runoff to the Peel River has been increasing since the 1960s.
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Impacts of Retrogressive Thaw Slumps on the Geochemistry of Permafrost Catchments, Stony Creek Watershed, NWTMalone, Laura January 2013 (has links)
Retrogressive thaw slumps are one of the most dramatic thermokarst landforms in periglacial regions. This thesis investigates the impacts of two of the largest hillslope thaw slumps on the geochemistry of periglacial streams on the Peel Plateau, Northwest Territories. It aims to describe the inorganic geochemistry of runoff across active mega-slumps, impacted and pristine tundra streams, as well as that of the ice-rich permafrost exposed in the slump headwalls. Slump runoff is characterized by elevated suspended sediments (911 g/L), high conductivity (2700 µS/cm), and high SO42- ( up to 2078 ppm). The runoff originates as a solute-rich meltwater near the slump headwall, and leaches and re-dissolves soluble salts (e.g., gypsum) as it flows along the mudflow. Conductivity increases until the runoff mixes with pristine tundra streams, diluting the slump runoff signal. SO42-/Cl- is used as a tracer to isolate the slump runoff signal in impacted waters, and suggests that the contribution of slump runoff to the Peel River has been increasing since the 1960s.
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A Transfer Learning Approach for Automatic Mapping of Retrogressive Thaw Slumps (RTSs) in the Western Canadian ArcticLin, Yiwen 09 December 2022 (has links)
Retrogressive thaw slumps (RTSs) are thermokarst landforms that develop on slopes in permafrost regions when thawing permafrost causes the land surface to collapse. RTSs are an indicator of climate change and pose a threat to human infrastructure and ecosystems in the affected areas. As the availability of ready-to-use high-resolution satellite imagery increases, automatic RTS mapping is being explored with deep learning methods. We employed a pre-trained Mask-RCNN model to automatically map RTSs on Banks Island and Victoria Island in the western Canadian Arctic, where there is extensive RTS activity. We tested the model with different settings, including image band combinations, backbones, and backbone trainable layers, and performed hyper-parameter tuning and determined the optimal learning rate, momentum, and decay rate for each of the model settings. Our final model successfully mapped most of the RTSs in our test sites, with F1 scores ranging from 0.61 to 0.79. Our study demonstrates that transfer learning from a pre-trained Mask-RCNN model is an effective approach that has the potential to be applied for RTS mapping across the Canadian Arctic.
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Effects of past grazing management on songbirds and plants in rested pastures: the potential for grazing management to influence habitat in the landscape following livestock exclusionFischer, Samantha 20 September 2016 (has links)
Grasslands are the most threatened terrestrial ecosystem in the world, and as they decline the species that depend on them also decline. Variable stocking rates and resting rangeland could be used by range managers to manipulate plant cover and create wildlife habitat. I used generalized linear mixed-models to evaluate how effects of rest on vegetation and songbirds varied based stocking rates previously applied from 2006-2014 in Grasslands National Park, Canada. My results indicate, in the mixed-grass prairie, succession is retrogressive following rest, and both vegetation and songbirds are resilient to grazing. Recovery of songbirds was linked to the recovery of habitat structure. Songbirds with flexible habitat requirements, such as Savannah and grasshopper sparrows, responded rapidly to livestock exclusion. The retrogressive nature of succession in mixed-grass prairie offers managers an opportunity to take chances when attempting to create wildlife habitat with livestock grazing, as risk of irreversible change is relatively low. / October 2016
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Investigating Changes in Retrogressive Thaw Slumps in the Richardson Mountains (Northwest Territories, Canada) based on Tasseled Cap Trend Analysis of Landsat Image StacksBrooker, Alexander 06 March 2014 (has links)
This thesis applies a novel method of change detection, the Landsat Image Stack Trend Analysis method to the monitoring of retrogressive thaw slumps in the Richardson Mountains, NWT. This method represents a significant improvement upon previous methods of thaw slump monitoring, which utilized air photos and high-resolution satellite imagery. This method applies Tasseled Cap brightness, wetness and greenness indices to Landsat TM/ETM images acquired between 1985 and 2011 and analyzes the temporal change of each pixel for the different indices values. This method is useful in retrogressive thaw slump monitoring in two ways. First, by creating a map showing the linear change over time from 1985 to 2011, retrogressive thaw slumps can be easily identified, as they are more dynamic than the surrounding tundra. In total, 251 thaw slumps were identified within an area of roughly 18 000km2. Second, thaw slump activity, from initiation, growth and stabilization can be studied by plotting the annual vegetation index pixel values of adjacent pixels in a thaw slump. This method allows for the efficient extraction of annual thaw slump headwall retreat rates, provided the availability of cloud-free imagery. The retreat rates of 16 slumps were extracted, which were found to have an average annual retreat rate of 11.8 m yr-1.
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Investigating Changes in Retrogressive Thaw Slumps in the Richardson Mountains (Northwest Territories, Canada) based on Tasseled Cap Trend Analysis of Landsat Image StacksBrooker, Alexander January 2014 (has links)
This thesis applies a novel method of change detection, the Landsat Image Stack Trend Analysis method to the monitoring of retrogressive thaw slumps in the Richardson Mountains, NWT. This method represents a significant improvement upon previous methods of thaw slump monitoring, which utilized air photos and high-resolution satellite imagery. This method applies Tasseled Cap brightness, wetness and greenness indices to Landsat TM/ETM images acquired between 1985 and 2011 and analyzes the temporal change of each pixel for the different indices values. This method is useful in retrogressive thaw slump monitoring in two ways. First, by creating a map showing the linear change over time from 1985 to 2011, retrogressive thaw slumps can be easily identified, as they are more dynamic than the surrounding tundra. In total, 251 thaw slumps were identified within an area of roughly 18 000km2. Second, thaw slump activity, from initiation, growth and stabilization can be studied by plotting the annual vegetation index pixel values of adjacent pixels in a thaw slump. This method allows for the efficient extraction of annual thaw slump headwall retreat rates, provided the availability of cloud-free imagery. The retreat rates of 16 slumps were extracted, which were found to have an average annual retreat rate of 11.8 m yr-1.
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Retrogressive Harmonic Motion as Structural and Stylistic Characteristic of Pop-Rock MusicCarter, Paul Scott 14 July 2005 (has links)
No description available.
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The Effects of Retrogressive Thaw Slump Development on Persistent Organic Pollutants in Lake Sediments of the Mackenzie River Delta Uplands, NT, CanadaEickmeyer, David 03 September 2013 (has links)
Using a comparative spatial and temporal analysis on sediment cores from 8 lakes in the Mackenzie River Delta uplands region, NT, Canada, this study assessed how persistent organic pollutant (POP) deposition to lake sediments was affected by: (1) the presence of retrogressive thaw slumps on lake shores; and (2) changes occurring with increased autochthonous primary productivity. POPs examined included polychlorinated biphenyls (PCBs), penta- and hexachlorobenzenes (CBzs), and dichlorodiphenyltrichloroethane and metabolites (DDTs). Surface sediments of slump-affected lakes contained higher total organic carbon (TOC)-normalized POP concentrations than nearby reference lakes unaffected by thaw slumps. Inorganic sedimentation rates were positively related to contaminant concentrations, suggesting that the influx of siliciclastic material reducing organic carbon in slump-affected lake water indirectly results in higher concentrations of POPs on sedimentary organic matter. This explanation was corroborated by an inverse relationship between sedimentary POP concentrations and TOC content of the lake water.
Deposition proxies of autochthonous carbon were not significantly correlated to POP fluxes of surface sediments, and historical profile fluctuations did not coincide with variation in POP deposition. Thus this study does not support the contention that algal-derived organic carbon increases the delivery of organic pollutants to sediments (the algal-scavenging hypothesis), as previously proposed for mercury. Higher POP concentrations observed in surface sediments of slump-affected lakes are best explained by simple solvent switching processes of hydrophobic contaminants onto a lower pool of available organic carbon when compared to neighbouring lakes unaffected by thaw slump development.
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The Effects of Retrogressive Thaw Slump Development on Persistent Organic Pollutants in Lake Sediments of the Mackenzie River Delta Uplands, NT, CanadaEickmeyer, David January 2013 (has links)
Using a comparative spatial and temporal analysis on sediment cores from 8 lakes in the Mackenzie River Delta uplands region, NT, Canada, this study assessed how persistent organic pollutant (POP) deposition to lake sediments was affected by: (1) the presence of retrogressive thaw slumps on lake shores; and (2) changes occurring with increased autochthonous primary productivity. POPs examined included polychlorinated biphenyls (PCBs), penta- and hexachlorobenzenes (CBzs), and dichlorodiphenyltrichloroethane and metabolites (DDTs). Surface sediments of slump-affected lakes contained higher total organic carbon (TOC)-normalized POP concentrations than nearby reference lakes unaffected by thaw slumps. Inorganic sedimentation rates were positively related to contaminant concentrations, suggesting that the influx of siliciclastic material reducing organic carbon in slump-affected lake water indirectly results in higher concentrations of POPs on sedimentary organic matter. This explanation was corroborated by an inverse relationship between sedimentary POP concentrations and TOC content of the lake water.
Deposition proxies of autochthonous carbon were not significantly correlated to POP fluxes of surface sediments, and historical profile fluctuations did not coincide with variation in POP deposition. Thus this study does not support the contention that algal-derived organic carbon increases the delivery of organic pollutants to sediments (the algal-scavenging hypothesis), as previously proposed for mercury. Higher POP concentrations observed in surface sediments of slump-affected lakes are best explained by simple solvent switching processes of hydrophobic contaminants onto a lower pool of available organic carbon when compared to neighbouring lakes unaffected by thaw slump development.
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