Wind-driven mixing in the epilimnion of a deep lake can be suppressed when there is a weak near surface stratification, which occurs frequently during periods of strong solar heating and weak winds. Using data from a vertical chain of fast response thermistors, we analyze the frequency of near surface stratification in the top 2 meters of the epilimnion in Lake Opeongo, Ontario for the periods between May and August in 2009 and 2010. Near surface thermoclines (as defined by dT/dz > 0.2 °C m−1 between 1 and 2 m) occur for 24% of the sampling period in 2009, 37% of the sampling period in 2010 and correspond to periods of high values of gradient Richardson number. During daytime the epilimnion is stratified up to 45% of the time. At night, cooling generally leads to a more isothermal profile, but near surface thermoclines still form at least 20% of the time. Extended periods of near surface stratification (>1 h), account for more than 80% of the stratified period. We compare these findings with previous observations from the Experimental Lakes Area in Northern Ontario, and discuss the biological implications of episodic stratification.
Frequency of episodic stratification in the near surface of Lake Opeongo and other small lakes
Patricia Pernica, Mathew Wells; Frequency of episodic stratification in the near surface of Lake Opeongo and other small lakes. Water Quality Research Journal 1 August 2012; 47 (3-4): 227–237. doi: https://doi.org/10.2166/wqrjc.2012.001
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