What sets the timing and duration of the spring overturn in Lake Simcoe?
Session: 56. - Science for a Healthy Lake Simcoe
Jing zhi Li, University of Toronto Scarborough, [email protected]
Bernard Yang, University of Toronto, [email protected]
Joelle Young, ONT Min. of the Environment, [email protected]
Mathew Wells, University of Toronto Scarborough, [email protected]
Abstract
The timing and duration of the spring turnover sets the initial concentration of dissolved oxygen in the hypolimnion of dimictic lakes. A previous study in Lake Simcoe suggested the summer stratification starts between day 160 to 180 of the year, with the implication being that spring overturn lasted until this point. However, our observations and analysis made on the 30 years of bi-weekly data and 3 years of high frequency data suggested DO depletion starts very close to the mean ice-off day of DOY 118. We will present new observations that suggest the spring overturn is actually very brief, with the most significant mixing occur under the ice. Any subsequent significant mixing is essentially shutdown once the water column warms above 4oC. In a warming climate, the duration of ice is expected to be even shorter, suggesting that in future spring overturn could occur even earlier, and hence there could be an increase in the duration of time for oxygen depletion in the lake’s hypolimnion. This means rather than the present 5-6 months between the spring and fall overturn, there could be 6-7 months of stratification in a warmer climate, making Lake Simcoe more susceptible to deep water hypoxia.
1. Keyword
oxygen
2. Keyword
hydrodynamics
3. Keyword
Lake Simcoe