Pond rotation: what is it and how to stop it

Pond rotation is a phenomenon that would go unnoticed were it not for the sometimes dire consequences. A slight renewal can leave the water cloudy for a couple of days.

Severe rotation can kill thousands of fish and leave your property smelling like a month-old rotten egg.

What is the rotation of the pond? How does it affect my pond? How can I prevent a rotation from occurring?

The purpose of this blog is to answer these questions, helping the average homeowner find a solution to their pond rotation problem.

What is the rotation of the pond?

Pond renovation is a term used to describe the mixing of stagnant or “stratified” water in a pond. Stratification is an occurrence in which water separates into three distinct layers, like a cake of layers, each with its own different temperature and dissolved oxygen levels.

The top tier, known as epilimnion, is made up of lighter, warm water that is high in dissolved oxygen; this is where fish tend to live. The middle layer of a pond is known as a thermocline; In this “transitional” layer, the temperature of the water and the level of dissolved oxygen decrease with depth.

Finally, the lowest layer of a pond is known as the hypolimnion. This layer is the coldest and the most oxygen-deprived of the three, since it is protected from any atmospheric condition by the two previous layers. The renovation of the pond is when the climatic conditions favor the mixing of these layers.

As the autumn air cools the epilimnion to a temperature lower than that of the lower layers, it becomes denser and sinks, mixing the layers together at a uniform temperature and density. Quite the opposite occurs after winter, and the cycle continues annually. Sometimes cold rains and strong winds can also trigger additional mid-summer rotation.

How does rotation affect my pond or lake?

Organic matter such as dead plants and fish, leaves, etc. sink and accumulate at the lowest level, the hypolimnion, because gravity naturally pulls it there. Unfortunately, this layer has little to no oxygen that would help aerobic or respiratory oxygen bacteria break down the material. Instead, bacteria that do not breathe oxygen or anaerobic do the job. Not only are these bacteria seventeen times slower Than their aerobic counterparts, they also release toxic gases like methane, hydrogen sulfide, and ammonia as they are digested.

This toxic gas is trapped in the hypolimnion and is released all at once when the levels mix. So how does this rotation affect your pond? It does four things:

  1. The toxic gases released poison the fish, causing the fish to die.
  2. Aerobic bacteria gain access to organic matter once they are locked to the bottom, quickly sucking all the oxygen out of the water and suffocating the fish.
  3. The smell of the released gases fills the surrounding area, including your home, with stale odors.
  4. Dirty hypolimnion clouds your water, making your pond look very dirty

How can I prevent rotation from occurring?

Two things need to happen to avoid the ill effects of pond rotation. The first thing you should do is mix the layers your pond to prevent stratification. The second thing you should do is provide oxygen throughout the pond, promoting the consumption of organic matter by aerobic bacteria.

The air will not only prevent the production of toxic gases, but it will also ensure that your fish have enough air to breathe. Both are important to avoid fish kills and noxious odors.

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