Simulation of vertical position of buoyancy regulating Microcystis aeruginosa in a shallow eutrophic lake |
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| Authors: | Brett B Wallace Mark C Bailey and David P Hamilton |
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| Institution: | (1) Centre for Water Research, University of Western Australia, Crawley, Western Australia, 6009, Australia;(2) Present address: Division of Environmental Engineering, School of Engineering, The University of Queensland, St Lucia, Queensland, 4072, Australia;(3) Present address: Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand |
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| Abstract: | Vertical distributions of the cyanobacterium Microcystis aeruginosa are examined in a shallow lake in relation to mixing and thermal stratification over three days. A model of buoyancy regulation by Microcystis aeruginosa, applicable for turbulent environments, is coupled with a one-dimensional hydrodynamic model. The coupled model is applied to Thomsons Lake in Western Australia to examine the relationship between buoyancy regulation and the daily stratification/destratification cycle. The vertical distribution of Microcystis aeruginosa in Thomsons Lake depends on the carbohydrate ballast dynamics and the colony size. When thermal stratification occurs, all the simulations show a similar general pattern of diurnal vertical migration of the Microcystis aeruginosa colonies. The colonies accumulate at the surface during the night and in the morning the colonies lose buoyancy, which leads to a reduction by ~ \sim 50% in colony concentration in the top 0.2--0.3 m of the water column. Afternoon winds redistribute the population over the entire water column. When the lake is fully mixed, the vertical migration pattern of the Microcystis aeruginosa colonies may be affected, depending on the colony size and the intensity of the mixing. |
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