Thesis (M.Sc. Biological Sciences)--University of Waikato, 2008. / Title from PDF cover (viewed March 10, 2009) Includes bibliographical references (p. 62-72)

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This thesis aims to improve the current understanding of the processes which control the flow variability of Greenland Ice Sheet (GrIS) outlet glaciers. The most recent Intergovernmental Governmental Panel on Climate Change (IPCC) report (Meehl et al., 2007) identifies that a critical limitation to forecasts of sea-level rise are uncertainties in modelling the ice dynamics of the GrIS. Using Synthetic Aperture Radar (SAR) feature tracking, seasonal velocities of land- and marine- terminating glaciers in a region in the northeast of Greenland are measured. Records of air temperature in conjunction with seasonal observations of supraglacial lake development, sea ice conditions and ice front positions, derived from SAR imagery, are used to investigate the controls on the observed variations in ice velocity. A clear link between ice velocities and glacier hydrology is found. These findings are consistent with observations from other glaciers in Greenland and are suggestive of a universal hydrological forcing of ice velocity for the whole of the GrIS ablation zone. Lake drainage events have been identified as a key factor in linking atmospheric changes, glacier hydrology and ice velocities in Greenland. For modelling purposes, a means of parameterising the distribution and evolution of supraglacial lakes is therefore needed. Assuming that water will pond in surface depressions, this thesis assesses the ability of using Digital Elevation Models (DEMs) for this purpose. High resolution DEMs are created using Interferometric SAR (InSAR) for two, separate regions of the GrIS. The positions and areal extent of surface depressions are compared with those of lakes observed in optical satellite imagery. The level of correspondence between the two datasets is found to be poor as a result of the resolution of the DEMs and the physical differences between surface depressions and lakes (e.g. lakes may not fill the capacity of the depression). An alternative method for parameterising the seasonal distribution of supra-glacial lakes, by extrapolating trends observed in current lake distributions, is investigated. The locations and evolution of lakes in the west of Greenland during the summer of 2003 are mapped using 47 Moderate Resolution Imaging Spectroradiometer (MODIS) images. Clear trends are identified in the distributions of lakes with elevation and are linked to the seasonal melt-cycle and to changes in ice thickness and its influence on surface depressions, tensile stresses and hydrofracturing. It may be possible to extrapolate these trends to other regions and higher elevations on the ice sheet, thereby enabling the distribution of lakes to be parameterised in ice sheet models. The findings of this thesis help to contribute to the understanding of the interaction between climate and ice dynamics in the context of the GrIS.

This thesis presents a combined modelling and observational study of an intermittently open and closed lake or lagoon (ICOLL) in south-eastern Australia. ICOLLs are a common, yet vulnerable type of estuary characterised by low freshwater inflow leading to a sand berm being formed across the entrance preventing oceanic flushing. The accumulation of nutrients during the closed phase, and the increased water residence time, can have detrimental effects on the estuary if the nutrient load cannot be assimilated. The general aim of this study was to develop a quantitative understanding of ecological processes in Intermittently Closed and Open Lakes or Lagoons (ICOLLs) through a combination of field work and ecological modelling. The field-based component of the studied was completed in Smiths Lake, NSW Australia. The field data shows that concentrations of NH3, NOx and Chlorophyll a in Smiths Lake gradually increases over time between the two studied opening events, before declining while the lake is open to the ocean. Phosphorus concentration is relatively low throughout both cycles. Of the 2 opening events, one was long (~ 3.5 months) and one was short (~3 weeks). Initially ammonia concentrations following this short open period were 2-4 times higher than the initial values from the previous 2 closures. The reduced open phase also resulted in more persistent stratification. The observations show that the duration of the open/closed phases will influence the physiochemical characteristics of the water column. A spatially resolved, eleven-box ecological model was developed for Smiths Lake. The process descriptions in the ecological model are based on a combination of physical and physiological limits to the processes of nutrient uptake, light capture by phytoplankton and predator/prey interactions. An inverse model is used to calculate mixing coefficients from salinity observations. When compared to field data, the ecological model obtains fits for salinity, nitrogen, phosphorus, chlorophyll a and zooplankton that are within 1.5 standard deviations of the mean of the field data. Simulations show that nutrient limitation (nitrogen and phosphorus) is the dominant factor limiting growth of the autotrophs during both the open and closed phases of the lake. The model is characterised by strong oscillations in phytoplankton and zooplankton abundance,typical of predator-prey cycles. A sensitivity analysis was completed using a simplified 1-box configuration, coupled with the existing ecological model. When small perturbations in the initial conditions of DIN, phytoplankton and zooplankton are implemented, the standard deviations of the state variables strongly attract to a declining oscillation, showing the variation between runs decreasing with time. The most sensitive parameters in the model were the feeding efficiency of small and large zooplankton, and the mortality of epiphytes and small zooplankton which all had normalised sensitivities of 1.28, 1.11, 1.01 and 1.05 respectively for a 10% change in parameter value. The non-linearity of the model is illustrated by increasing the percentage change of the parameter. For a 25% change in feeding efficiency of small and large zooplankton, the normalised sensitivity increased to 1.28 and 1.15 respectively, and for a 50% change, they increased further to 1.78 and 1.35 respectively. The ecological state variables were also sensitive to increased catchment loads and depths. The modelled system switches from seagrass dominated to algal dominated at loads over 10?? the current loads, with increased plankton biomass and suspended solids shading the seagrass. The spatially resolved ecological model is run for a variety of open/closed cycles to assess the impact of various opening regimes on the model state variables. The results indicate that Smiths Lake is capable of assimilating its current nutrient loads without persistent phytoplankton blooms or a decrease in seagrass biomass. When catchment loads are increased by 10?? or the duration of the lake open/closed cycle is increased there is a corresponding increase in seagrass biomass. In contrast, small and large phytoplankton both increase in biomass as the duration of the open phase increases. Small and large phytoplankton growth is generally limited by phosphorus, and seagrass growth is limited by nitrogen under normal catchment loads. Due to the shallow depths and low phytoplankton biomass, seagrass only becomes light limited when the nutrient and suspended solids loads are increased 10??. This switch to light limitation only decreases the biomass for short periods.

Thesis (Ph.D.)--York University, 2007. Graduate Programme in Biology. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR39060

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed February 25, 2010). PDF text: xii, 113 p. : ill. (some col.) ; 3 Mb. UMI publication number: AAT 3386574. Includes bibliographical references. Also available in microfilm and microfiche formats.