What Is Lake Turnover?

What Is Lake Turnover?Lake turnover is a natural phenomenon that can occur in any given lake during rapid changes in weather temperatures.  A turnover is the rapid mixing of lake water.  Turnover can have devastating effects on fish, plants, and amphibians that live in the lake.  Anytime a turnover occurs, dissolved oxygen levels can be at stake.  Learn how turnovers can happen and how to prevent their devastating effects.

 

How Does a Turnover Happen

Cold water water is more dense than warm water; bodies of water like lakes become layered based on temperature.  This is called stratification. The cold water sinks to the bottom while the warm water floats to the top.   There are typically three layers, the epilimnion (top), thermocline (middle), and hypolimnion (bottom).  Once the top and bottom layers are the same temperature (and therefore density), wind and rain and cause the water to mix easily.

During summer, in a poorly circulated lake, only the surface water is aerated and warmed by the sun.  The water at the bottom of the pond is the coldest, densest, and contains the least amount of oxygen.  The seasons change and slowly the water at the surface cools down and eventually is the same temperature as the cold water at the bottom. If there is more oxygen depleted than oxygenated water, the overall levels of oxygen in the lake can fall during the turnover.  This is when a fish kill could occur due to poor oxygen levels.

Spring turnovers occur as the weather warms up after winter, and the top layer warms up again.  During the wintertime, the warmest water is at the bottom, which is where all of the pond life will live during the winter. Ice is less dense than water; ice floats to the top of the lake.   As the ice melts, the surface temperature will rise and eventually equal the warmer water at the bottom of the lake, which has been slowly depleting of oxygen and accumulating harmful gases.

 

How to Prevent Lake Turnovers

Lake turnovers cannot be prevented as they are a natural occurrence, but proper aeration systems can help mitigate the harsh effects of a turnover. The main danger of a turnover is the overall diffused oxygen levels falling when the water is mixed.  Maintaining a consistent mix of water all year long helps maintain healthy levels of dissolved oxygen levels.  A sub surface aeration system will help keep the lake evenly oxygenated and consistent temperatures.  A diffuser will release bubbles from the bottom of the lake, and as the bubbles float upwards, they will mix the water and help gases release.  A floating fountain can also increase circulation, which increases oxygenation and gas release, but is only recommended for lakes less than 15 feet deep.  

 

Mitigating the harmful effects of lake turnovers is important for the health of fish and plants in the lake.  Healthy lakes maintain that balance of consistent temperatures and oxygen levels throughout the water.  Sub surface aeration systems are the most helpful resource in maintaining healthy water consistency and quality as you prevent lake turnover.