What Does it Mean When a Pond Turns Over?

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What Does it Mean When a Pond Turns Over?

One thing the gardening and landscaping worlds aren’t short on is jargon, and it turns out that jargon crosses over from the earth and into the water with terms like “pond turnover.” Don’t worry – pond turnover doesn’t mean your favorite backyard water feature has literally turned upside down – it simply refers to the various ways stagnant waters in a pond interact with each other.


Pond turnover occurs when stagnant pond waters either mix or stratify.

Pond Turnover: What Happens

As an isolated body of water, pond water does not flow. When that still water sits in its basin – be it a natural basin or otherwise – during the warm months of the year, the sun heats up the surface water while the cooler and more dense water settles to the bottom of the pond. Essentially, the layers of water become divided into different strata, according to the University of Kentucky College of Agriculture, Food and Environment.

The water near the bottom receives less sunlight, which typically makes it oxygen deficient, whereas the oxygen-rich upper strata, usually the first 6 feet or so of water, continues to sustain algae and plant life. As the plant life grows and eventually dies, it sinks to the bottom of the water, sucking up even more oxygen as it decomposes. What occurs is an anoxic environment, or an environment greatly bereft of oxygen

Eventually, especially in ponds deeper than about 6 feet, the surface layer can’t compensate for the oxygen deficiency, and the pond is unable to support fish, making turnover a big problem for fish owners and fisheries. An anoxic environment may even produce gases that are toxic to aquatic life, such as hydrogen sulfide, killing fish and algal bloom as it produces the signature dank smell of stagnant waters.

The Pond Turnover Cycle

As the Missouri Department of Conservation details, small bodies of water left unchecked in their natural environment often undergo an annual cycle of pond turnover. In summer, water stratifies into layers based on differences in temperature, density and levels of dissolved oxygen. A positive sort of turnover happens in autumn when temperatures start to dip to around 50 degrees Fahrenheit, and the top layer becomes heavier and sinks to the bottom.

After the fall winds and rains help the layers freely mix and circulate, beckoning a return of aquatic life, cold water reaches its maximum density near the surface in the winter season. This causes the water to separate into layers once again until the water near the bottom becomes deprived of oxygen. In the spring, another turnover occurs as the water warms up and achieves its most uniform temperature of the year, providing healthy levels of oxygen for aquatic life throughout.

Pond Turnover Prevention

So, that nasty top layer on a stagnant pond is definitely not something you want, but how do you ensure it doesn’t happen? Turnover is often a natural process; when pond water gently and naturally mixes with the water of a lake, turnover occurs too. Sometimes, cool rain and wind are all you need to prevent pond turnover, as they naturally cool the surface water and prevent stratification, encouraging the layers of the water to mix.

Sticking with a shallower pond or water feature with a depth of less than 6 feet is also a low-key prevention option, as shallower water simply has an easier time mixing and maintaining uniform temperature levels, especially with a little help from the rain and wind. The key is to prevent stratification. For deeper ponds, sources such as the University of Kentucky College of Agriculture, Food and Environment and Mossy Oak recommend mechanical aeration or mechanically assisted water circulation.


Writer Bio

Dan combines his decade-long experience as a freelance writer with hands-on experience in landscaping, flooring, painting, maritime maintenance and handyman work. Previously, he’s published with Black+Decker, Hunker, Geeks On Home, GardenGuides.com, Builder’s Capital, USA Today and others.

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