What is what does it mean when a lake turns over?

Lake Turnover Explained

Lake turnover is a natural process where a lake's water mixes, typically occurring in the spring and fall. This mixing is crucial for the health and stability of the aquatic ecosystem. Here's a breakdown of what happens:

• Temperature Stratification: During the summer, the surface water warms and becomes less dense, creating a distinct layer called the epilimnion. The deeper water, known as the hypolimnion, remains cooler and denser. Between these layers is the thermocline, a zone of rapid temperature change. This stratification prevents mixing. In winter, the surface water cools, sometimes forming ice, while the deeper water remains warmer (but still cold).

• Fall Turnover: As the air temperature cools in the fall, the surface water cools as well. When the surface water temperature approaches the temperature of the hypolimnion (around 4°C, the temperature of maximum density for water), the water becomes uniformly dense throughout the lake. This removes the temperature gradient that prevented mixing. Wind action then easily mixes the entire water column, leading to fall%20turnover.

• Spring Turnover: In the spring, as the ice melts and the surface water warms, a similar process occurs. The surface water reaches the same temperature (around 4°C) as the deeper water, again creating a uniform density. Wind then mixes the water column, resulting in spring%20turnover.

• Consequences of Turnover: Lake turnover has significant effects on the lake ecosystem:

  • Nutrient Redistribution: Turnover brings nutrient-rich water from the bottom to the surface, fertilizing the epilimnion and supporting phytoplankton growth.
  • Oxygenation: Turnover replenishes oxygen in the deeper waters, making it habitable for aquatic life. The hypolimnion%20oxygen%20levels are very important.
  • Water Quality: Turnover can temporarily affect water clarity and taste due to the mixing of sediments and dissolved substances.

• Not All Lakes Turnover: Some deep lakes, especially in warmer climates, may only experience partial mixing or no mixing at all. These are called meromictic%20lakes. Their deep layers can remain stagnant for long periods.