Sai Leung Ng

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


A 1.93 m long sediment core (FL1-92) obtained from Fish Lake is used to reconstruct paleoenvironmental changes that have affected both the lake and the surrounding catchment area during the late Quaternary. The core is composed of an upper organic-rich section comprising partially humified unlaminated organic material, separated by a sharp lithologic break at a depth of 1.33 m from an inorganic sandy-textured basal section containing thin algal mats and the occasional mollusc shell.;Chronological control for the core is provided by {dollar}\sp{lcub}14{rcub}{dollar}C AMS dates of 8870 {dollar}\pm{dollar} 220 yr BP and 8400 {dollar}\pm{dollar} 80 yr BP on the algal mats, a date of 6210 {dollar}\pm{dollar} 340 yr BP immediately above the sharp lithologic discontinuity and a date of 1200 {dollar}\pm{dollar} 70 yr BP at a depth of 34 cm in the core. A modern age was obtained from algal gyttja at a depth of 2 cm. Chemical elements provide evidence of compositional changes within the core. Allochthonous and autochthonous contributions are identified by selective extraction. Oxidizable carbon (OC) and extractable silica (ESi) provide measures of biological productivity and complemented an analysis of the fossil diatom assemblages. A calibration data set comprising diatom assemblages from 93 contemporary water bodies yielded transfer functions for the prediction of past conditions of halinity and pH in the core. Glacio-isostatically controlled emergence of Truelove Lowland from the sea began prior to 10600 yr BP, resulting in the extensive deposition of marine sediments. Fish Lake first took the form of a shallow tidal lagoon. Isolation of the lagoon commenced by 6550 yr BP and was completed by 6210 {dollar}\pm{dollar} 340 yr BP, forming a brackish lagoon which persisted for approximately 600 years. By approximately 5950 yr BP, Fish Lake was completely fresh.;Soil development in the catchment resulted initially in the translocation of allochthonous Fe, Mn and K to the lake sediments. As the catchment slopes became vegetated and stabilized, erosion diminished and there has been a decrease in the concentrations of erosion indicators in the lake sediments. Following this was another period of enhanced erosion. In the last millennium, it appeared to have experienced a lower erosion rate and the erosion accelerated in the second half the last 1000 years.



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