Have you ever experienced touching the bottom of the pond only to realize that the water there is cooler than the surface? Well, that phenomenon is the start of a pond turnover!
Now, why do ponds turn over?
It happens because the water that stratified due to the temperature changes finally starts to mix.
If you’re still curious about this phenomenon, keep on reading!
To further understand what it means when a pond turns over, you should know what an annual stratification cycle is.
With that said, the following are the various stages your pond water experiences whenever the season changes:
The cycle starts during the summer when the sun’s scorching heat directly hits your pond’s water. Of course, the top will get warmer, but the deeper part won’t because only little sunlight reaches these depths.
Since cooler water is denser than warm water, the former will sink while the latter floats. This separation is what we call stratification.
In fact, the water separates into three parts during stratification: epilimnion, metalimnion, and hypolimnion.
The epilimnion is the shallowest layer or the one that gets exposed to the sun and wind. Hypolimnion refers to the densest or coldest part of your pond. Lastly, metalimnion is the transition layer between the two.
Considering that your pond’s water is stagnant throughout the mentioned seasons, the epilimnion, metalimnion, and hypolimnion don’t mix.
The first turnover occurs during fall when the temperature drops. The epilimnion starts cooling down to the extent that it starts sinking due to its density.
When the epilimnion reaches the hypolimnion, they get mixed. Once the two layers become uniform, the turnover process will be finished.
All the sediments resting on the bottom of the pond will get incorporated into the water. This often makes the water look murky, which gives off a foul odor.
In some cases, it can lead to the death of fish due to the low level of dissolved oxygen.
The cycle continues during the winter when the temperature is significantly lower than fall. People call this phase an inverse stratification because the surface of the pond water becomes cold instead of getting warm.
What happens is the surface water cools and sinks to the bottom. As a result, it makes the temperature uniform throughout the pond.
Over time, the surface gets colder than the rest of the hypolimnion when exposed to the wind. So, it becomes less dense and will subsequently float over the warmer water, forming ice.
The ice at the surface prevents the air from mixing the water’s layers.
When spring comes, the ice cover will eventually melt. Once it reaches a temperature similar to the hypolimnion, it’ll sink.
Of course, when it sinks, it’ll disrupt the bottom layer. Afterward, everything will get mixed together when the water comes in contact with the wind.
The water warms up again as time passes, setting itself up for summer stratification.
Unfortunately, there’s not much you can do when your pond turns over. It’s an inevitable occurrence because it’s an effect brought by the change of the season.
If the fish in your pond died due to the lack of oxygen during stratification, you have no choice but to restart. Adding new plants and fish can be costly, but it’s the only way to bring life back to your aquatic ecosystem.
However, if you want to know some preventive measures for future pond turnovers, you can follow these tips instead:
Sticking with a shallow pond is one of the quickest and most effortless preventive measures for pond turnovers.
If your pond has less than six feet of water, it’ll be easier for the epilimnion and the hypolimnion to get incorporated during a turnover.
As such, maintaining a uniform temperature wouldn’t be a problem either because there’s not a lot of water in the pond.
If your pond is deeper, installing a pond aeration system is the only preventive measure you can follow.
During a pond turnover, the dissolved oxygen level is critically low. So, a pond aeration system solves that problem because it produces a stream of bubbles that rise to the surface.
Since the pond has constant oxygenation from the bottom to the surface, there’s a possibility that stratification won’t occur.
A pond’s aeration system boosts fish growth rates, too. Moreover, it helps reduce the ammonia nitrogen concentration in the water.
So, why do ponds turn over? Well, it’s a natural occurrence brought about by the changes in the weather and the season.
The surface of your pond gets warmer during hot days. It becomes dense when it cools during colder days and eventually sinks to the bottom.
The water in your pond gets mixed, resulting in a pond turnover!
It’s inevitable, so you should keep a close eye on your fish to ensure that they’ll be able to survive when this happens.
Ben has a bachelor’s degree in construction engineering. When not constructing or remodeling X-Ray Rooms, Cardiovascular Labs, and Pharmacies, you can find him at home with wife and two daughters. Outside of family, He loves grilling and barbequing on his Big Green Egg and Blackstone Griddle, as well as working on projects around the house.
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