Author(s): Peter R. B. Ward; Emily A. Cousins; Ken J. Hall; Thomas G. Northcote; Thomas P. Murphy
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Abstract: Comprehensive physical measurements were made at two adjacent lakes (Mahoney and Green Lake, British Columbia) for several months during the summer and autumn. Mahoney Lake is strongly salinity stratified (total dissolved solids [TDS] near the bottom are 85,000 mg l～ (-1) ), resulting in permanent stagnation and unusual temperature gradients in the lower layers, while Green Lake exhibits normal dimictic characteristics, with TDS no greater than 2500 mg l～ (-1). Field data loggers deployed at each lake measured water temperature, air temperature and wind speed and direction. Monthly manual measurements were also made of vertical salinity and temperature profiles. During the spring preceding the period of measurement, high surface run-off contributed unusually large fresh water inputs to the lakes. Both lakes exhibited signifcant losses of potential energy of stratification between June and October due to the processes of wind driven transport and penetrative convection. For Mahoney, the losses in potential energy of stratification were largely due to penetrative convection, with wind induced mixing contributing 28% of the total. Wind mixing for Green Lake was almost 100% larger than for Mahoney while average penetrative convective mixing was 34% larger. An efficiency factor of 0.20 for the penetrative convective energy, larger than values of about 0.13 previously reported in the literature, was found to fit the measured loss of potential energy of stratification well.
Year: 1989