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Observations of Vertical Diffusivities in a Shallow Tropical Reservoir

Author(s): Peipei Yang; Zikun Xing; Derek A. Fong; Stephen G. Monismith; Kok Meng Tan; Edmond Y. M. Lo

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Keywords: Shallow tropical lakes; Vertical eddy diffusivities; Heat flux method; SCAMP

Abstract: Tropical lakes are of key importance as fresh water supply sources in tropical regions. One of the biggest threats to tropical lakes is nuisance algal blooms which at times can be harmful to human health. Research shows that thermal and flow dynamics, through their effects on the light and nutrient accessibility to phytoplankton, have a strong bearing on the growth of phytoplankton. We report herein observations and analysis of vertical diffusivities which impacts on the evolution of the surface mixed layer and the vertical transport of nutrients for a shallow tropical reservoir, that of Kranji Reservoir in Singapore. A one-dimensional method, the heat flux method (Jassby and Powell 1975; Henderson-Sellers 1985) is applied to obtain estimates of the vertical mixing in Kranji Reservoir using water temperature and meteorological data collected over a 2-month extensive field experiment conducted in 2007. To fit the assumptions and particularly the heating duration, a time period of 1100-1500 hr is selected for heat flux method when the water body is strongly stratified. The vertical eddy diffusivity, Kz varies with depth and spans two orders of magnitude, from 10-5 to 10-3m2/s. The results are also in the same range of eddy diffusivity deduced from the temperature microstructure measured by a Self-contained autonomous MicroP rofiler (SCAMP).


Year: 2012

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