. This does not occur in meromictic lakes Most lakes are
holomictic: at least once per year, the surface and the deep waters mix. In
monomictic lakes, the mixing occurs once per year; in
dimictic lakes, it occurs twice a year (typically spring and autumn), and in
polymictic lakes, the mixing occurs several times a year. In meromictic lakes, the layers of water can remain unmixed for years, decades, or centuries. Meromictic lakes can usually be divided into three sections or layers. The bottom layer is the
monimolimnion; the waters in this portion of the lake circulate little, and are generally
hypoxic and more saline than the rest of the lake. The top layer is the
mixolimnion, and essentially behaves like a holomictic lake. The area in between is the
chemocline, or chemolimnion. However, human influence can lead to cultural meromixis occurring. The increased use of
road salt as a deicing strategy, particularly in northern latitude regions, can disturb the natural mixing cycles in lakes by inhibiting mixing. As salt is flushed into aquatic systems at high concentrations in late winter/early spring, it accumulates in the deepest layer of lakes leading to incomplete mixing.
Stratification in meromictic lakes can be either
endogenic or ectogenic. Endogenic means the patterns seen in the lake are caused by internal events, such as organic matter accumulating in the sediments and decaying, whereas ectogenic means the patterns seen are caused by external causes, like an intrusion of saltwater settling in the
hypolimnion, preventing it from mixing. In the following decades after this disaster, active research and management has been done to mitigate gas buildup in the future through the Nyos Organ Pipes Program (NOPP). The NOPP program placed large organ pipes into
Lake Nyos, to reach the monimolimnion where harmful dissolved gases built up, that allow for gas release to the atmosphere, effectively degassing the monimolimnion. While it is mainly lakes that are meromictic, the world's largest meromictic basin is the
Black Sea. The deep waters below do not mix with the upper layers that receive oxygen from the atmosphere. As a result, over 90% of the deeper Black Sea volume is
anoxic water. The
Caspian Sea is anoxic below . The
Baltic Sea is persistently stratified, with dense, highly saline water comprising the bottom layer, and large areas of hypoxic sediments (see
Baltic Sea hypoxia). down to the left; only a small isthmus separates the lake from
Ofotfjord. is a meromictic lake near
Syracuse, New York. is a meromictic lake near
Waterloo, Ontario. is a meromictic lake in a volcanic crater near
Fallon, Nevada in
Washington == List of meromictic lakes ==