Environmental Sciences Commons^™

Topographic Influences On Trends And Cycles In Nutrient Export From Forested Catchments On The Precambrian Shield, Samson G. Mengistu

Electronic Thesis and Dissertation Repository

This dissertation explored topographic controls on spatial and temporal patterns in water yield and nutrient (carbon, nitrogen and phosphorus) export from forested headwater catchments in the Turkey Lakes Watershed in central Ontario, where other factors contributing to differences in water yield and nutrient export, including climate, geology, forest, and soils, are relatively constant. Topographic characteristics, including (a) hydrological flushing potential (expansion of water table into nitrate-N producing areas); (b) hydrological storage potential (area of wetlands, which can alternatively allow water and nutrients to bypass wetlands when storage capacity is filled with water or to trap them when not filled); and …

Geography, News Media Discourse, And Water Management: A Case Study Of The Devils Lake Outlet, Daniel J. Bednar

Electronic Thesis and Dissertation Repository

This thesis explores the print news media discourse surrounding the dispute between Manitoba and North Dakota over a flood mitigation plan in Devils Lake North Dakota. In order to do so, critical discourse analysis was applied to news media from a seventeen year period during the dispute. Findings were compared between media sources as well as to pertinent policy documents. The thesis finds that the political arena provided by local newspapers as well as the discourses of scale, confrontation, history, and economics had the largest effect on the dispute’s public face. A total of nine findings within these areas are …

Diatoms In Castor Lake (North-Central Washington, Usa) – Proxies Of Climate And Hydrologic Variation, Kelly D. Hollingshead

Electronic Thesis and Dissertation Repository

This research provides a high temporal resolution (1 sample / 2-3 years) record of hydrologic variation for the last 2,000 years using a lake sediment record from Castor Lake, a closed-basin system in Washington, USA. The core was dated using ¹³⁷Cs, ¹⁴C, and tephrochronology. Approximately 600 diatoms were identified and enumerated in 198 samples from a Castor Lake freeze core and Livingstone-piston core. A diatom-inference model for salinity was applied to reconstruct fossil diatom salinity. Diatom-inferred salinity for the last century tracked Palmer Drought Severity Index, indicating diatom community composition tracks effective moisture and can be used to …

Examining Atmospheric Dust Deposition And Its Effects On Alpine Lakes In The Uinta Mountains, Utah, Oliver J. Squire

Electronic Thesis and Dissertation Repository

The composition and effects of atmospheric dust on remote alpine lakes were investigated using geological and paleolimnolgical techniques. Short cores (< 50 cm long) were retrieved from five lakes on the eastern side of the Uinta Mountains, Utah. Sediment core chronologies are based on 210 Pb and 14C dates. Dust and lake sediment core samples were analyzed for their particle size distribution, mineralogy, and chemistry. Dust was fine grained (< 10 μm) and was enriched (i.e., 50X greater concentrations) in 31 major, minor and trace elements relative to local bedrock material. In lake sediments, changes in the concentrations of key dust elements were recorded beginning in ~ AD 1900. Elements that increased in all five lakes included metals (Bi, Pb, Sb, Sn) and the nutrient P. The metals Cu and Cd also increased in four lakes. These changes are coincident with European settlement, the onset of mining, and the intensification of agriculture. The findings of this thesis show that atmospheric deposition in the Uinta Mountains is unique in composition relative to the last several hundred years. Percentage organics also increased during this period indicating increased productivity. Cladocera community composition recorded changes potentially caused by variations in atmospheric deposition of Ca in this region, although results were inconclusive.

Assessing The Potential Health Risk Of Cyanobacteria Harmful Algal Blooms And Cyanotoxins In Lake Naivasha, Kenya, Melissa H. Raffoul

Electronic Thesis and Dissertation Repository

Cyanobacteria harmful algal blooms (cyanoHABs) pose a threat to water quality and human health. The Lake Naivasha, Kenya community expressed concern about these events which prompted this study of influences, characteristics and health impacts of cyanoHABs. While eutrophication of Lake Naivasha was caused by years of nutrient loading from agricultural activities, land use changes and improper sewage treatment, results suggest that lake-wide cyanoHAB formation was controlled by shifts from drought to flood conditions, followed by relative stability. Particulate concentrations of the liver toxin microcystin were less than provisional guidelines; however, our limited knowledge on long-term microcystin impacts is limited and …

Reconstructing Fire Severity From The Oxygen-Isotope Compositions Of Plant Char, Michael W. Hamilton

Electronic Thesis and Dissertation Repository

This study assessed whether variations in the oxygen-isotope compositions of char formed from biomass burning could be related to burning severity. Ground samples of oak (Quercus alba), pine (Pinus resinosa), and grass (Andropogon gerardii) were charred for 5 and 30 minutes at constant temperatures between 200 and 900°C under oxygenated versus anaerobic conditions. Char oxygen-isotope values became progressively depleted of ¹⁸O by up to 25.8‰ for wood and 16.5‰ for grass as temperature, duration of burning, and amount of oxygen increased. The primary reason for the decrease in oxygen-isotope values is the loss …

Ozone Measurements And Transport, Mohammed Kedir Osman

Electronic Thesis and Dissertation Repository

Ozone intrusions from the stratosphere to the troposphere occur as part of the Brewer-Dobson circulation, but the details of the microphysics of the process are unresolved. This research mainly focuses on near-tropopause regions, and examines stratospheric ozone intrusions into the troposphere across this stable zone. My research objective is to identify the small-scale atmospheric dynamical features responsible for the intrusion of stratospheric ozone into the troposphere, and to determine their relative importance from case to case.

Windprofiler radars, together with frequent ozonesonde launches, have been used to detect stratospheric ozone intrusions. This work has been supplemented by numerical simulation via …

Effects Of Chemical And Mechanical Weathering Processes On The Degradation Of Plastic Debris On Marine Beaches, David A. Cooper

Electronic Thesis and Dissertation Repository

Plastics are an integral part of everyday life, and the use of plastic products for consumer goods, food packaging, recreational and commercial fishing and medical and sanitary applications continues to increase. The durability, low cost, light weight and hydrophobic nature of plastic make it a desirable material for numerous applications; however, these same characteristics make plastic debris in natural environments a pervasive problem. Increases in plastic use and low economic incentive for recovery, result in accumulation of debris in marine environments. Degradation of plastics through chemical weathering occurs in the open ocean or along shorelines where polymers are exposed to …