Global ETD Search

121	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
122	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
123	Optical Properties of Organic Semiconductors: from Submonolayers to Crystalline Films Nitsche, Robert 23 November 2005 (has links) We have measured the optical properties of films of the organic semiconductors PTCDA (3,4:9,10-perylene-tetracarboxylic dianhydride) and HBC (peri-hexabenzocoronene), prepared by Organic Molecular Beam Expitaxy (OMBE), on different substrates by means of Differential Reflectance Spectroscopy (DRS). The optical setup enables us to directly follow the thickness dependent optical properties of the organic films, starting from submonolayer coverage up to thicker films on the order of 20 monolayers (ML) film thickness. Due to the different optical nature of the different substrates used, i.e., mica, glass, Au(111), and HOPG, the direct interpretation of the DRS signal is not feasible. Therefore, we have proposed a method by which the calculation of the optical constants n (index of refraction) and k (absorption index) of thin films on arbitrary substrates from just one spectral measurement (in our case the DRS) becomes possible. The results fulfill a priori a Kramers-Kronig consistency and no specific model is needed to express the spectral behavior of the optical constants. Based on our method, we have successfully calculated the optical constants, and therefore the absorption behavior, of films of different thickness of PTCDA on mica, glass, Au(111), and HOPG, as well as of HBC on mica, glass, and HOPG. Extrinsic effects due to island growth or the presence of a polarizable substrate (screening) have been accounted for. We have introduced a finite dipole model which considers the extended geometry and anisotropy of the organic molecules. The calculated absorption behavior is discussed in great detail in terms of spectral changes with varying film thickness, different growth modes, degree of ordering of the films, interactions with the substrates and oscillator strength. A direct observation of a monomer-dimer transition in solid films could be observed for the first time. Our results indicate an exciton delocalization over about 4 molecules for both molecules. info:eu-repo/classification/ddc/530 ddc:530

Page generated in 0.0547 seconds