Lämpötilakerrostuminen

Lämpötilakerrostuminen, also known as thermal stratification, refers to the phenomenon where a body of water separates into distinct layers based on temperature. This typically occurs in lakes and ponds during different seasons. In the summer, the sun heats the surface water, creating a warm upper layer called the epilimnion. Below this is a transitional zone of rapid temperature change known as the thermocline. Deeper down, the water remains cold, forming the hypolimnion.

This stratification prevents the mixing of these layers. Consequently, the epilimnion is rich in oxygen due to atmospheric exchange and photosynthesis, while the hypolimnion can become depleted of oxygen, especially if there is decomposition of organic matter.

During autumn, as the surface water cools, its density increases. Eventually, it becomes as dense as the hypolimnion, leading to the breakdown of stratification. This process, called autumn turnover or fall mixing, allows oxygen to be distributed throughout the entire water column and nutrients from the bottom to rise to the surface.

In winter, if the water freezes, a reverse stratification can occur. The coldest water (just above freezing) will be at the surface under the ice, while the densest water (around 4 degrees Celsius) will be at the bottom. Spring turnover, similar to autumn turnover, occurs as the ice melts and the surface water warms, re-establishing a uniform temperature and mixing the water column again. Lämpötilakerrostuminen significantly influences the distribution of oxygen, nutrients, and aquatic life within a water body.