![]() ![]() In temperate regions where lake water warms up and cools through the seasons, a cyclical pattern of overturn occurs that is repeated from year to year as the cold dense water at the top of the lake sinks (see stable and unstable stratification). However, the temperature of maximum density for freshwater is 4 ☌. Cold water is denser than warm water and the epilimnion generally consists of water that is not as dense as the water in the hypolimnion. The thermal stratification of lakes refers to a change in the temperature at different depths in the lake, and is due to the density of water varying with temperature. Lake stratification is stable in summer and winter, becoming unstable in spring and fall when the surface waters cross the 4☌ mark. Typical mixing pattern for many lakes, caused by the fact that water is less dense at temperatures other 4☌ (the temperature where water is most dense). These changes can further alter the fish, zooplankton, and phytoplankton community composition, in addition to creating gradients that alter the availability of dissolved oxygen and nutrients. Rising air temperatures have the same effect on lake bodies as a physical shift in geographic location, with tropical zones being particularly sensitive. ![]() However, changes to human influences in the form of land use change, increases in temperature, and changes to weather patterns have been shown to alter the timing and intensity of stratification in lakes around the globe. Typically stratified lakes show three distinct layers: the epilimnion, comprising the top warm layer the thermocline (or metalimnion), the middle layer, whose depth may change throughout the day and the colder hypolimnion, extending to the floor of the lake.Įvery lake has a set mixing regime that is influenced by lake morphometry and environmental conditions. Lake stratification is the tendency of lakes to form separate and distinct thermal layers during warm weather. ![]()
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