Thesis (Ph. D.)--Johns Hopkins University, 2003. / Vita. U.M.I. no. 3068110. Includes bibliographical references (leaves 223-241).

Thesis (M.S.)--University of Wisconsin--Stevens Point, 2002. / Includes bibliographical references (leaves 65-71).

A diatom-salinity transfer function is developed for quantitative palaeosalinity reconstruction. from a data-set of 74 modem diatom samples and limnological data from Spanish salt lakes. Relationships between species and environmental data are explored using principal components analysis (PCA), detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) with variance partitioning. and a conductivity transfer function is derived by weighted averaging (apparent r = 0.91). A model for direct lake-level reconstruction is developed using lWINSPAN to explore the relationship between diatom species distribution and lake permanence. A survey is made of diatom preservation in the recent sediments of >50 lakes throughout Spain. and of the overall potential for Holocene reconstruction of a selected group of lakes. Diatoms are best preserved (least dissolved) in systems of southern Spain. and the Laguna de Medina is selected for analysis as a result. It is established by PCA that the correlated variables water depth and lake permanence. and salinity. are the most important factors influencing preservation. The diatom record preserved in the lower 6m of a lO.3m core from the Laguna de Medina is analysed. Application of the transfer function is shown to be unreliable due to the effects of fossil diatom dissolution and a lack of modem analogues. A modified transfer function is derived which includes partially-dissolved assemblages and improves the match with the surface set. but remains unreliable. Palaeosalinity reconstruction therefore relies on traditional palaeoecological techniques. Lake-level change is also reconstructed independently from changes in the relative abundance of taxa Separate palaeosalinity and lake-level reconstructions are derived from lithological and ostracod shellchemistry analysis. and the palaeoecology of ostracods, foraminifera, molluscs and plant macrofossils. The influence of human impact is assessed by comparison with the pollen and charcoal record. The diatom record is strong despite dissolution effects, and a consistent interpretation of lake-level change can be made based on different indicators. Lakes were high prior to c. 7860 yr BP; following a phase of low. fluctuating lake levels. maximum lake level was attained around 6000 yr BP. after which it declined gradually. The record shows affmities with African and Mediterranean lake-level data and makes an important contribution to an understanding of Holocene climate change in these regions.

The study traces the history and development of Loe Pool, a 50 hectare freshwater coastal lake near Helston, Cornwall. using a wide variety of palaeolimnological and associated research techniques. The principle upon which such research is based is that there is an intimate relationship between the history of a catchment and the lake into which it drains. In addition, the history of the shingle bar which now isolates Loe Pool from the sea is explored, as this has also had a significant bearing on the lake's physical and ecological development. The study uses a combination of lines of evidence to interpret the development of the lake-catchment system. Palaeolimnological techniques. employed include the examination of the physical nature of the lake sediments themselves, and chemical and biological analyses, in particular for sub-fossil diatoms. These are used to establish both a chronology of sediment deposition, and also a detailed history of the principal ecological changes experienced by the Pool. In addition, a considerable amount of historical documentary and cartographic 'material is incorporated in the study, in order to provide corroborative evidence of the major events that have taken place in the history of the lake and catchment. The results highlight the main influences on the lake, and in particular, those of the last two hundred years. Marine incursions dominated the lake's history up until the late 19th century, when both natural overspill of lake water and the customary practise by local residents of 'breaching the bar' ceased. Tin mining within the catchment has also had a major impact on the lake and has given rise to several periods of very rapid sediment accumulation, the most significant of which took place in the 1930's and 1930's. Following the cessation, in 1939, of all mining activity within the catchment, the discharge of treated sewage effluent, which had begun in 1930, became the dominant influence upon the lake's ecology. It is hoped that such an historical background will allow a more sympathetic management of the lake in future years.

No description available.

The Red Lake greenstone belt is considered to be one of Canada’s premier gold producing regions with the Red Lake Gold Mines having produced >24 million ounces of gold to date. The East Bay Trend is a large structural corridor that parallels the East Bay of Red Lake, Ontario and is interpreted to be a manifestation of the regional D1 structure that crosscuts this complexly folded greenstone belt. The southernmost 8 km of this corridor is host to a variety of small gold deposits that demonstrate an assortment of mineralization styles. This study aims to: (1) better define veining styles and characterize the mineralizing fluids using petrography, fluid inclusions, geochronology and stable isotopes, (2) compare barren and auriferous veins from deposits along the East Bay Trend, and (3) compare the fluid history of the East Bay Trend to the Campbell-Red Lake gold deposit to determine the gold potential along this trend.

No description available.

This thesis focuses on three areas of investigation: construction and calibration of gypsum cylinders for the measurement of water flow; quantification of the relationship between flow and macrophyte structure; and the prediction of surficial sediment size structure in the littoral. Near-bottom water flow at 34 littoral sites was quantified using gypsum dissolution. Plant surface area within three weedbeds in Lake Memphremagog (Que. - Vt.) explained 67% of the variance in flow when the effect of water depth was removed. A model relating waterflow within beds to average wind energy and plant surface area was constructed. A multivariate model developed and tested in the littoral of Lake Memphremagog explained 67% of the variance in the proportion of sediment $<$2 um in diameter (clay). The model included the physical variables of fetch, depth, and slope and biological measures of plant presence or absence and sediment organic matter. A second model required plant surface area and sediment organic matter to explain 83% of the variance in the proportion of clay at sites within weedbeds, near the depth of maximum plant biomass.

An understanding of the level of both genetic and morphological diversity within a taxon and how that diversity is structured within and across habitats is important when determining the conservation value of that taxon and for successful habitat management programs to be developed. Atlin Lake is a large lake in northern British Columbia and is one of the largest lakes that contain relatively unperturbed populations of lake trout (Salvelinus namaycush). As the top aquatic predator, lake trout in Atlin Lake are a key component of the lake’s fish community and are important for local fisheries. I assayed lake trout from Atlin Lake and other western lake trout populations at eight microsatellite DNA loci and for body morphology to determine: (i) the level of genetic variation present, (ii) the level of substructure that occurs in Atlin Lake, and (iii) whether there was a relationship between the genetic and morphological variation present. STRUCTURE analysis identified five subpopulations within Atlin Lake. Morphological analysis was used to differentiate between the samples collected throughout Atlin Lake. Cluster analysis of size corrected data separated the fish into two groups making Atlin Lake the smallest lake identified to date to possess more than one morphotype. Genetic and morphological groupings were found not to be correlated with each other. Finally, I was interested in whether each of the genetic subpopulations contributed equally to the local fisheries catches. A mixed stock analysis of samples collected from the commercial fishery and recreational anglers indicated that all of the genetic subpopulations contribute to the fishery along with lake trout subpopulations in the interconnecting Tagish Lake; suggesting that no one subpopulation is being depleted by the fisheries. Continued genetic monitoring, however, is necessary to see if the trends in fishery contribution are temporally stable. Future studies should focus on understanding the source of the morphological variation and maintenance of genetic substructure.

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