Knowra Thermal stratification Thermal stratification Thermal stratification is the vertical layering of water as temperature-dependent density differences limit mixing. In lakes, it commonly separates warm surface water from colder deep water.
Water density : Water density is mass per unit volume and varies with temperature, pressure, and dissolved substances. Temperature-dependent density differences create the layers that resist vertical mixing.
Epilimnion : The epilimnion is the warm, upper layer of a stratified lake, usually mixed by wind. It is the surface layer formed above the lake’s deeper, colder water.
Dissolved oxygen : Dissolved oxygen is molecular oxygen present in water and available to aquatic organisms. Stable layers can restrict oxygen replenishment in deep water, allowing concentrations to decline.
Polymictic lake : A polymictic lake mixes frequently, often because it is shallow or exposed to strong wind. Frequent mixing prevents the long-lived temperature layers typical of strongly stratified lakes.
Thermocline : A thermocline is a layer in a body of water where temperature changes rapidly with depth. It marks the steep temperature gradient commonly separating warm surface water from colder deep water.
Hypolimnion : The hypolimnion is the deep, cold layer of a stratified lake beneath the metalimnion. It is the lower water mass isolated from frequent surface mixing during stratification.
Eutrophication : Eutrophication is nutrient enrichment that increases biological production and can degrade aquatic ecosystems. Stratification can trap nutrients and oxygen-poor water, influencing blooms and deep-water conditions.
Holomixis : Holomixis is complete mixing of a lake’s water column from surface to bottom. Complete mixing erases the persistent vertical separation characteristic of thermal stratification.
Metalimnion : The metalimnion is the middle layer of a stratified lake, where temperature decreases rapidly with depth. This lake layer contains the thermocline that separates upper and lower water masses.
Dimictic lake : A dimictic lake mixes completely twice each year, typically in spring and autumn. Its seasonal mixing interrupts summer and winter stratification.
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