Lake stratification
Encyclopedia
Lake stratification is the separation of lake
s into three layers:
The thermal stratification of lakes refers to a change in the temperature at different depths in the lake, and is due to the change in water's density with temperature. 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.
However, the temperature of maximum density for freshwater is 4 °C.
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. For example, in dimictic lake
s the lake water turns over during the spring and the fall. This process occurs more slowly in deeper water and as a result, a thermal bar
may form.
If the stratification of water lasts for extended periods, the lake is meromictic
. Conversely, for most of the time, the relatively shallower meres
are unstratified; that is, the mere is considered all epilimnion.
The accumulation of dissolved carbon dioxide
in three meromictic lakes in Africa
(Lake Nyos
and Lake Monoun
in Cameroon
and Lake Kivu
in Rwanda
) is potentially dangerous because if one of these lakes is triggered into limnic eruption
, a very large quantity of carbon dioxide can quickly leave the lake and displace the oxygen
needed for life by people and animals in the surrounding area.
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
s into three layers:
- EpilimnionEpilimnionThe epilimnion is the top-most layer in a thermally stratified lake, occurring above the deeper hypolimnion. It is warmer and typically has a higher pH, but lower dissolved oxygen concentration than the hypolimnion....
- top of the lake. - Metalimnion (or thermoclineThermoclineA thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...
) - middle layer that may change depth throughout the day. - HypolimnionHypolimnionThe hypolimnion is the dense, bottom layer of water in a thermally-stratified lake. It is the layer that lies below the thermocline.Typically the hypolimnion is the coldest layer of a lake in summer, and the warmest layer during winter...
- the bottom layer.
The thermal stratification of lakes refers to a change in the temperature at different depths in the lake, and is due to the change in water's density with temperature. 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.
However, the temperature of maximum density for freshwater is 4 °C.
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. For example, in dimictic lake
Dimictic lake
Dimictic lakes are lakes that mix from top to bottom during two mixing periods each year. Dimictic lakes are holomictic, a category which includes all lakes which mix one or more times per year. During winter they are covered by ice...
s the lake water turns over during the spring and the fall. This process occurs more slowly in deeper water and as a result, a thermal bar
Thermal bar
A thermal bar is a hydrodynamic feature that forms around the edges of holomictic lakes during the seasonal transition to stratified conditions, due to the shorter amount of time required for shallow areas of the lake to stratify.- Description :...
may form.
If the stratification of water lasts for extended periods, the lake is meromictic
Meromictic
A meromictic lake has layers of water that do not intermix. In ordinary, "holomictic" lakes, at least once each year there is a physical mixing of the surface and the deep waters...
. Conversely, for most of the time, the relatively shallower meres
Mere (lake)
Mere in English refers to a lake that is broad in relation to its depth, e.g. Martin Mere. A significant effect of its shallow depth is that for all or most of the time, it has no thermocline.- Etymology :...
are unstratified; that is, the mere is considered all epilimnion.
The accumulation of dissolved carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
in three meromictic lakes in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
(Lake Nyos
Lake Nyos
Lake Nyos is a crater lake in the Northwest Region of Cameroon, located about northwest of Yaoundé. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity...
and Lake Monoun
Lake Monoun
Lake Monoun is a lake in West Province, Cameroon, that lies in the Oku Volcanic Field . On August 15, 1984, the lake exploded in a limnic eruption, which resulted in the release of a large amount of carbon dioxide that killed 37 people. At first, the cause of the deaths was a mystery, and...
in Cameroon
Cameroon
Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...
and Lake Kivu
Lake Kivu
Lake Kivu is one of the African Great Lakes. It lies on the border between the Democratic Republic of the Congo and Rwanda, and is in the Albertine Rift, a part of the Great Rift Valley. Lake Kivu empties into the Ruzizi River, which flows southwards into Lake Tanganyika...
in Rwanda
Rwanda
Rwanda or , officially the Republic of Rwanda , is a country in central and eastern Africa with a population of approximately 11.4 million . Rwanda is located a few degrees south of the Equator, and is bordered by Uganda, Tanzania, Burundi and the Democratic Republic of the Congo...
) is potentially dangerous because if one of these lakes is triggered into limnic eruption
Limnic eruption
A limnic eruption, also referred to as a lake overturn, is a rare type of natural disaster in which carbon dioxide suddenly erupts from deep lake water, suffocating wildlife, livestock and humans. Such an eruption may also cause tsunamis in the lake as the rising CO2 displaces water. Scientists...
, a very large quantity of carbon dioxide can quickly leave the lake and displace the oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
needed for life by people and animals in the surrounding area.
External links
- "Density Stratification", part of an educational website Water on the Web operated by the University of Minnesota, Duluth. Retrieved 11-March-2007.
- Lake Stratification in Lake Lanier and its effects on the Chattahoochee River