lake stratification

Lake stratification refers to the development of distinct vertical layers in deep, permanent bodies of freshwater. These layers are primarily caused by differences in temperature and the resulting density variations of the water.1

In temperate regions, lakes typically exhibit a dimictic thermal pattern, meaning they mix twice a year, in spring and autumn. During summer, the surface water warms and forms an upper layer called the epilimnion, which is separated from the colder, deeper layer, the hypolimnion, by a zone of rapid temperature change called the thermocline. Water circulates within these layers but not between them.123

As the surface water cools in autumn, it becomes denser and sinks, leading to a complete mixing of the lake's waters, known as overturn. This mixing continues until ice forms, insulating the lake from further wind action. The lake stratifies again in summer.14

These thermal differences significantly impact the distribution of dissolved oxygen and carbon dioxide, with the epilimnion often having high oxygen levels and the hypolimnion having low levels. This stratification is crucial for aquatic life, as oxygen availability can determine survival.1