Epilimnion

The epilimnion ( Epilimnial ) is called in the physical limnology the upper heated and strongly moving water layer in a stratified stagnant waters. The epilimnion is separated by the thermocline, the metalimnion, from the lower water layer, the hypolimnion.

In the epilimnion is ( warming) is built by the absorption of sunlight on the day on your own stratification. Simultaneous wind action can prevent such a stratification if necessary, and lead to a phase homogeneous heating. When evening decreasing sunlight and the nocturnal cooling of the surface it comes within the epilimnion to convection currents which homogenize the entire epilimnion and may even be able to include the upper layers of the Metalimnions in the mixing.

Not to be confused is the epilimnion with the Mixolimnion, which represents the upper, years cyclically included in the circulation layer as opposed to monimolimnion in meromictic lakes.

In spring, the stratifying force increases the sunlight and exceeds the daily mean more and more by the mixing power of the wind effect and the nocturnal cooling. In this phase, the thickness of the epilimnion increases more and more in favor of Metalimnions. In autumn, the heat balance is negative. The cooling supported by the preponderance of the mixing processes. The epilimnion is colder and always thicker. More and more water from the metalimnion is blended with up. The net effect of this process is the autumn circulation.

On the origin of water layers occurs due to the density anomaly of water.