Global ETD Search

1	Impacts of Retrogressive Thaw Slumps on the Geochemistry of Permafrost Catchments, Stony Creek Watershed, NWT Malone, 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. retrogressive thaw slump periglacial streams geochemistry Richardson Mountains
2	Impacts of Retrogressive Thaw Slumps on the Geochemistry of Permafrost Catchments, Stony Creek Watershed, NWT Malone, 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. retrogressive thaw slump periglacial streams geochemistry Richardson Mountains
3	Retrogressive Thaw Slumps: Indicators of Holocene Climate Changes in the Richardson Mountains-Peel Plateau, Northwestern Canada Frappier, Roxanne January 2017 (has links) The ongoing climate warming is expected to increase thermokarst activity and their impacts by inducing permafrost degradation and active layer deepening. A retrogressive thaw slump, which represents the most dynamic thermokarst landform, was investigated in the Richardson Mountains-Peel Plateau region. The exposed material at the thaw slump represents an opportunity to characterize the cryostratigraphy of the uppermost 5 m of permafrost. Analyses of the stratigraphy, sedimentology, isotope geochemistry and radiocarbon dating is presented. Six sites were also identified on an elevation-vegetation gradient to provide complementary data on thaw layer thickness. Summer air temperatures, vegetation cover type, mesoscale conditions modifying the snowpack, timing of the snow accumulation and winter air temperature inversions are identified as the main drivers of thaw layer thickness in the region. The physical and chemical parameters of the massive ground ice exposed at the thaw slump are characteristic of buried glacier ice that experienced water infiltration and partial refreezing. The layer between the massive ground ice units and the thaw layer in the thaw slump is identified as a relict thaw layer and represents the period of maximum active layer deepening. It dates to the Holocene thermal maximum, which represents a period of important thermokarst activity that resulted in widespread paleo-thaw unconformities across northwestern Canada. Association of the region’s thaw slump activity with paleoclimatic parameters provide indication that the combination of formerly glaciated continuous permafrost, hummocky rolling moraine terrain, stream-incised relief, and massive ground ice, coupled with major rainfall events, represents a set of condition that is favourable to thaw slump activity. thaw slump climate warming Holocene thermokarst permafrost ground ice
4	Effect of Shoreline Subsidence and Anthropogenic Activity on Northwest Territories’ Lakes. Houben, Adam James January 2017 (has links) Thawing permafrost – in the form of shoreline retrogressive thaw slump events – influence adjacent arctic tundra lake systems near Inuvik, NT. Slump-affected lakes demonstrated lower organic matter and key nutrients such as phosphorus (P), as well as greater water clarity. Key terrestrial permafrost soil indicators such as U, Sr, and Li, were identified to be elevated in slump-affected lakes, while other more biologically important metals (e.g. Fe, Mn) were significantly lower in affected lakes. These physical-chemical changes led to increasing P-limitation for both phytoplankton and periphyton, resulting in lower phytoplankton biomass (Chl-a). Using P as covariate in ANCOVA analysis, slump-affected lakes were also lower in phytoplankton biomass (Chl-a) relative to other study landscapes across the Canadian low-Arctic. Slump-affected lakes also exhibited lower organic matter leading to lower overall Hg concentrations within slump-affected lakes. However, this same reduction in dissolved organic carbon (DOC) has also led to an increase in bioavailable Hg, and increased bioaccumulation of Hg in both periphyton as well as macroinvertebrate species in our most disturbed lakes with DOC concentrations less than 6 and 9 mg DOC/L, respectively. A negative correlation between Hg bioaccumulation and DOC above these concentrations was also observed, and is the typical condition within reference lakes. The legacy impacts of mining were also observed in lakes within 25 km of the Giant Mine roaster stack in the Yellowknife region. Increases in both arsenic (As) and methyl mercury were measured in lakes nearer to the mine, with As concentrations well above water quality guidelines in lakes within 17 km of the roaster stack. This research highlights the necessity of baseline environmental monitoring prior to resource development, as well as the potential for compounded influences of such development within sensitive permafrost regions exposed to thawing. Climate Change Permafrost Thaw Slump Freshwater Nutrients Primary production Mercury Mining Arsenic
5	Effect of Permafrost Thaw Slumps on Benthic Invertebrates and on Concentrations of Persistent Organic Pollutants in Lakes of the Mackenzie Delta Uplands, NT Rebecca, D'Onofrio January 2014 (has links) Permafrost thaw slumping along lakeshores in lakes of the Mackenzie Delta Uplands, NT is known to alter water chemistry significantly. Its impact on benthic communities and persistent organic pollutant (POP) behaviour in lakes is not known. Benthic invertebrate communities responded to slumps through changes to community composition and size spectra. Larger taxa tended to dominate in lakes with slumps. Variability in biomass size spectra was related to total dissolved nitrogen concentration and slump size. Concentrations of POPs in Gammarus were negatively correlated with total phosphorus and positively correlated with the percentage of the catchment slumped. Lakes with slumps generally had higher mean concentrations of POPs in Gammarus (ex. ΣPCBsDisturbed = 27.54 ng/g lipid, ΣPCBsUndisturbed = 16.97 ng/g lipid; ΣDDT Disturbed =18.47 ng/g lipid and ΣDDTUndisturbed =10.86 ng/g lipid). Benthic invertebrate biomass was also negatively correlated with concentrations of contaminants in Gammarus, supporting the biomass dilution hypothesis. Thaw slumps have large enough impacts on the physico-chemical characteristics of lakes that they alter benthic invertebrate community composition and size-structure, and contaminant concentrations in Gammarus. Permafrost thaw slump Persistent Organic Pollutant POP Size Spectra Benthic macroinvertebrate
6	The Effects of Retrogressive Thaw Slump Development on Persistent Organic Pollutants in Lake Sediments of the Mackenzie River Delta Uplands, NT, Canada Eickmeyer, 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. permafrost retrogressive thaw slump permafrost thaw thermokarst Mackenzie River Delta Mackenzie River Delta uplands Northwest Territories Inuvik, NT persistent organic pollutant POP contaminant deposition sediment autochthonous primary productivity polychlorinated biphenyls PCBs hexachlorobenzene pentachlorobenzene dichlorodiphenyltrichloroethane dichlorodiphenyltrichloroethylene dichlorodiphenyldichloroethane DDT DDTs solvent switching algal scavenging hypothesis algal scavenging lake sediment Arctic global warming paleolimnology deposition proxy Rock-Eval pyrolysis inferred chlorophyll a visual reflectance spectroscopy organic contaminant extraction 210 Pb dating lead 210 dating
7	The Effects of Retrogressive Thaw Slump Development on Persistent Organic Pollutants in Lake Sediments of the Mackenzie River Delta Uplands, NT, Canada Eickmeyer, 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. permafrost retrogressive thaw slump permafrost thaw thermokarst Mackenzie River Delta Mackenzie River Delta uplands Northwest Territories Inuvik, NT persistent organic pollutant POP contaminant deposition sediment autochthonous primary productivity polychlorinated biphenyls PCBs hexachlorobenzene pentachlorobenzene dichlorodiphenyltrichloroethane dichlorodiphenyltrichloroethylene dichlorodiphenyldichloroethane DDT DDTs solvent switching algal scavenging hypothesis algal scavenging lake sediment Arctic global warming paleolimnology deposition proxy Rock-Eval pyrolysis inferred chlorophyll a visual reflectance spectroscopy organic contaminant extraction 210 Pb dating lead 210 dating

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