Kesäkerrokset

Kesäkerrokset, often translated as "summer layers" or "summer cottages," refers to a phenomenon in certain Finnish lakes. It describes a distinct stratification of water that forms during the warmer months. Typically, a lake develops three main layers: the epilimnion, metalimnion, and hypolimnion. The epilimnion is the uppermost, warmest, and most oxygenated layer, which is mixed by wind. Below this is the metalimnion, a transition zone where the temperature drops rapidly. The deepest layer, the hypolimnion, is the coldest and often has lower oxygen levels.

This stratification is crucial for aquatic life. The epilimnion is where most photosynthesis occurs due to sunlight penetration and nutrient availability. The hypolimnion provides a refuge for cold-water species during hot summers. However, prolonged stratification can lead to oxygen depletion in the hypolimnion, a process known as eutrophication, which can harm fish populations. In the autumn, as surface waters cool, the layers mix, a process called turnover, which replenishes oxygen throughout the water column. Kesäkerrokset is a natural part of a lake's annual cycle in temperate climates like Finland.