Lake stratification

Lake stratification is the formation of distinct vertical water layers, usually because temperature differences create density differences that limit mixing.

Thermal stratification: The separation of water into layers by temperature-dependent density differences. It is the most common form of lake layering and explains the seasonal density structure.
Water density: Mass per unit volume of water, varying with temperature, pressure, and dissolved substances. Density contrasts provide the restoring force that resists vertical mixing.
Lake eutrophication: The enrichment of a lake with nutrients that can stimulate excessive biological production. Stratification can isolate nutrient-rich deep water from surface production, then redistribute nutrients during mixing.
Dimictic lake: A lake that mixes twice each year and typically stratifies during summer and winter. It is the common temperate pattern of seasonal stratification and turnover.
Thermal bar: A seasonal zone of water near 4 °C that separates colder nearshore water from warmer offshore water in some lakes. It can temporarily restrict exchange between nearshore and offshore waters during spring warming.
Thermocline: A water layer in which temperature changes rapidly with depth. This steep temperature gradient commonly separates a lake’s warm surface layer from deeper water.
Density stratification: The vertical arrangement of fluid layers with different densities. Lake stratification is one aquatic expression of this broader physical pattern.
Hypoxia (environmental): A condition in which dissolved oxygen is too low to support many aquatic organisms. Restricted exchange with the atmosphere can let deep water lose oxygen during stratification.
Monomictic lake: A lake that mixes once each year, with water remaining unfrozen during its mixing season. Its single annual turnover contrasts with the two mixing periods of dimictic lakes.
Lake meromixis: The persistent separation of a lake into layers that do not fully mix. It is an extreme, long-lasting outcome of density stratification.

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