Lake Challa is a 5 km2, 97m deep freshwater crater lake located at 880m elevation on the southeast slope of Mount Kilimanjaro (Kenya-Tanzania). Information gained from a preliminary limnological survey of Lake Challa, presented here, will give insight into tropical limnological processes as well as aid in the paleoclimatological interpretation of a 25,000-yr diatom record. The survey, which included depth profiles of temperature, oxygen, pH and specific conductance, as well as epilithic and surface sediment diatom samples, revealed that Lake Challa is a meromictic lake which presently has at least 30 diatom species. A 22m sediment core, recovered in 2005, has well-preserved diatoms throughout its length. Diatom species assemblages were dominated by Nitzschia sp. 1 and Gomphocymbella sp. 1, for which the taxonomy is uncertain, and therefore general ecological characteristics were used in the data interpretation. An increase in Gomphocymbella sp. 1 may reflect an increase in the amount of benthic habitat and therefore lower lake levels. Diatom productivity may increase during periods of high precipitation and runoff which increases the total nutrient concentration, and high Nitzschia sp. 1 concentrations occur when input water has high Si:P ratios (warm, wet climate). Analysis of the diatom record suggests that Lake Challa experienced fluctuating intermediate lake levels from 25-21 thousand years before present (ka BP), low lake levels from 21-14.5 ka BP, sustained high lake levels from 14.5-11 ka BP, and high-intermediate lake levels from 11-5 ka BP but with short-term recessions at 10.6-11, 8.5 and 6.6 ka BP. After 5 ka BP, levels remained fairly stable, with a gradual decrease in lake level beginning at ~4 ka BP culminating at ~1.8 ka BP. Inferred climate changes from Lake Challa generally agree with other records in the area. Continuous sedimentary records from lakes in equatorial regions on which to base paleoclimatic reconstructions are rare. In conjunction with other biological and geochemical paleoproxy indicators, this high-resolution diatom record will help us better understand climate-driven environmental change in the vicinity of Mount Kilimanjaro, site of the only African ice-core record. / Thesis (Master, Biology) -- Queen's University, 2007-08-06 18:22:25.157

No description available.

A transitional climate and the presence of Thule sites make the Melville Peninsula an area of high importance for paleoenvironmental studies. Lake sediment cores and surface samples from Melville Peninsula were analyzed for diatom assemblages. Fragilarioid diatom species dominate assemblages from the interior of the peninsula since the middle Holocene. The greatest changes in diatom communities occurred during the transition from the Holocene Thermal Maximum to the Neoglacial, and in the post-Little Ice Age period. Species richness reached maximum values in the most recent period, reaching 50.8 species in surface sediments. Diatom-inferred pH reconstruction from two lakes did not indicate substantial change throughout the Holocene despite assemblage changes, showing the complexity of interpreting paleoclimate records dominated by Fragilarioids. Analysis of modern assemblages from the interior and East coast of Melville Peninsula confirm the importance of site size and water chemistry, as determined by bedrock geology, in determining diatom species distributions.

A transitional climate and the presence of Thule sites make the Melville Peninsula an area of high importance for paleoenvironmental studies. Lake sediment cores and surface samples from Melville Peninsula were analyzed for diatom assemblages. Fragilarioid diatom species dominate assemblages from the interior of the peninsula since the middle Holocene. The greatest changes in diatom communities occurred during the transition from the Holocene Thermal Maximum to the Neoglacial, and in the post-Little Ice Age period. Species richness reached maximum values in the most recent period, reaching 50.8 species in surface sediments. Diatom-inferred pH reconstruction from two lakes did not indicate substantial change throughout the Holocene despite assemblage changes, showing the complexity of interpreting paleoclimate records dominated by Fragilarioids. Analysis of modern assemblages from the interior and East coast of Melville Peninsula confirm the importance of site size and water chemistry, as determined by bedrock geology, in determining diatom species distributions.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 143-151). Also available via World Wide Web.

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Katharina Billups, College of Marine and Earth Studies. Includes bibliographical references.

Thesis (Ph.D.) in Earth Sciences--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 135-158).

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [124]-133).

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed July 21, 2009). PDF text: ix, 121 p. : ill., maps ; 6 Mb. UMI publication number: AAT 3352250. Includes bibliographical references. Also available in microfilm and microfiche formats.