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Concept
Monomictic lake
Résumé
Monomictic lakes are holomictic lakes that mix from top to bottom during one mixing period each year. Monomictic lakes may be subdivided into cold and warm types.
Cold monomictic lakes are lakes that are covered by ice throughout much of the year. During their brief "summer", the surface waters remain at or below 4 °C. The ice prevents these lakes from mixing in winter. During summer, these lakes lack significant thermal stratification, and they mix thoroughly from top to bottom. These lakes are typical of cold-climate regions (e.g. much of the Arctic). An example of a cold monomictic lake is Great Bear Lake in Canada.
Warm monomictic lakes are lakes that never freeze, and are thermally stratified throughout much of the year. The density difference between the warm surface waters (the epilimnion) and the colder bottom waters (the hypolimnion) prevents these lakes from mixing in summer. During winter, the surface waters cool to a temperature equal to the bottom waters. Lacking significant thermal stratification, these lakes mix thoroughly each winter from top to bottom. These lakes are widely distributed from temperate to tropical climatic regions. One example is South Australia's Blue Lake, where the change in circulation is signaled by a striking change in colour.
The identification and categorization of monomictic lakes relies on the formation of both an epilimnion (warmer, less dense water) and hypolimnion (cooler, more dense water) separated by a thermocline a majority of the year. The distinct separation of these layers of the water column are collectively referred to as the thermal and density strata. Thermal and density stratification is a critical factor influencing the composition of the water column. Composition often refers to the presence of or lack of nutrients and organisms. In both cold and warm monomictic lakes, the epilimnion and hypolimnion are separated for a majority of the year. In warm monomictic lakes, the water is in a uniform, liquid form; in cold monomictic lakes, the body contains a layer of ice and is cooler in temperature.
Source officielle
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