Dimictic lake

Dimictic lake

A dimictic lake is a type of lake that experiences two periods of mixing each year. These periods typically occur in the spring and autumn, when the water temperature and density become uniform throughout the lake, allowing for complete mixing from the surface to the bottom.

Characteristics

Dimictic lakes are commonly found in temperate regions where seasonal temperature variations are significant. During the summer, the lake stratifies into distinct layers, with warmer, less dense water on the surface (the epilimnion) and cooler, denser water at the bottom (the hypolimnion). The middle layer, known as the metalimnion or thermocline, acts as a barrier to mixing.

In the winter, the surface water cools and may freeze, forming an ice cover. The water beneath the ice remains relatively stable, with the densest water (at approximately 4°C) at the bottom.

Mixing Periods

• Spring Mixing: As the ice melts and the surface water warms, the temperature and density of the water column become uniform, leading to complete mixing. This process is known as spring turnover.
• Autumn Mixing: In the autumn, the surface water cools, increasing in density and sinking, which again leads to uniform temperature and density throughout the lake, resulting in autumn turnover.

Ecological Impact

The mixing periods are crucial for the distribution of oxygen and nutrients throughout the lake. During the stratified periods, the hypolimnion can become depleted of oxygen, affecting aquatic life. The mixing periods help to reoxygenate the deeper waters and redistribute nutrients, supporting the lake's ecosystem.

Examples of Dimictic Lakes

Many lakes in the temperate regions of the world are dimictic. Some well-known examples include:

• Lake Mendota in Wisconsin, United States
• Lake Constance in Europe

Related Pages

• Lake
• Mixing
• Epilimnion
• Hypolimnion
• Thermocline
• Spring turnover
• Autumn turnover
• Stratification (water)