Pond rotation is a phenomenon that would go unnoticed were it not for the sometimes dire consequences. A slight rotation can leave the water cloudy for a couple of days.
Severe rotation can kill thousands of fish and leave your property smelling like a rotten egg from a month ago.
What is the rotation of the pond? How does it affect my pond? How do I prevent rotation from happening?
The purpose of this blog is to answer these questions, helping the average homeowner find a solution to their pond rotation problem.
What is pond rotation?
Pond rotation is a term used to describe the mixing of stagnant or ‘stratified’ water in a pond. Stratification is an event whereby 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 inhabit. The middle layer of a pond is known as a thermocline; In this ‘transition’ layer, the temperature of the water and the level of dissolved oxygen decrease with depth.
Finally, the lowest layer of a pond is called the hypolimnium. This layer is the coldest and the most oxygen-deprived of the three, since it is protected from any atmospheric conditions by the two previous layers. The rotation 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 into a uniform temperature and density. The exact 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. it sinks and accumulates at the lowest level, hypolimnion, because gravity naturally pulls it there. Unfortunately, this layer has little or no oxygen that would help aerobic or oxygen-breathing bacteria break down the material. Instead, bacteria that don’t 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 digest.
This toxic gas is trapped in the hypolimnium and is released all at once when the levels mix. So how does this rotation affect your pond? It does four things:
- The toxic gases released poison the fish, causing the fish to die.
- Aerobic bacteria gain access to organic matter once locked to the bottom, rapidly absorbing all the oxygen from the water and suffocating the fish.
- The smell of the released gases fills the surrounding area, including your home, with stale odors.
- Dirty hypolimnion muddies the water, making the pond look very dirty
How do I prevent rotation from happening?
Two things need to happen to prevent the ill effects of pond rotation. The first thing you have to do is mix the layers of your pond to prevent stratification. The second thing you should do is provide oxygen throughout the pond, favoring 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 get enough air to breathe. Both are important to avoid fish kills and noxious odors.