Watch for Pond Turnovers!
It’s springtime and that usually brings rains, and this year is no exception! With
periods of heavy rain and warm temperatures pond owners need to be aware of pond turnovers.
Generally, when someone mentions a “turnover,” the first thing that comes to mind
is dead fish.
Sheridan, Ark. – Watch Out for Pond Turnovers!
It’s springtime and that usually brings rains, and this year is no exception! With periods of heavy rain and warm temperatures pond owners need to be aware of pond turnovers. Generally, when someone mentions a “turnover,” the first thing that comes to mind is dead fish.
To understand why pond turnovers occur, we need to understand some basics about water. Water density, or weight, varies at different temperatures, and is densest at 39 °F. Colder water is lighter (that is why ice floats), and warmer water is lighter. In fact, you may have noticed while swimming that the water at the surface is warm, but at your feet, it is cold. This horizontal layering of different water temperatures is called “stratification.”
During spring, the surface of the pond heats up and stratification begins. Layers of warm water form at the surface, and colder layers are found deeper in the pond. These layers usually resist mixing, and the lake will remain stratified until fall when cooler temperatures cause surface layers to cool and gradually mix with layers below.
In the surface layers, oxygen is being produced by photosynthesis of small plants, or plankton, and oxygen is also entering the water by exchange with the air. Because of stratification, this oxygen does not enter the deeper layers where it is too dark for plants. Also, dead plants and animals sink into the deep layers, where they decompose and use up oxygen. You end up with a pond with plenty of oxygen, plants, and fish in the shallow water, and no oxygen, plants, or fish in the deep water.
This can become a problem if the water in the pond mixes suddenly, which is called “turnover.” When a turnover occurs, the water mixes and the oxygen in the water may become too low for animals to survive. Larger fish usually die first. You may observe fish at the surface trying to get oxygen. All species of pond fish will die during a turnover. Some smaller fish may survive because they can breathe at the surface where oxygen is diffusing into the water.
Fall turnovers happen every year in most ponds, and are typically harmless if they occur gradually. Summer turnovers are usually much more harmful. These are typically the result of heavy thunderstorms, which produce several inches of cold rain. The cloud cover and cold winds cool the surface layers, and the rush of cold rainwater causes the surface layers to mix with the water below. The oxygen is quickly used up by decomposing materials, and fish start to suffocate. Summer turnovers can happen from about May until October, and are usually caused by changing weather conditions.
Aeration systems can be used to prevent stratification and pond turnovers, or bottom draw-off devices can be attached to standpipes to remove stagnant water from deep in the pond. Reducing nutrients that go into the pond will keep algae blooms down, which provides less dead material to use up oxygen. Also, do not over fertilize or overfeed, and keep excessive animal wastes out of the pond.
If you notice that a turnover is occurring, and you catch it before too many fish have died, there may be emergency steps you can take to save fish. Provide emergency aeration if possible. Spray water across the surface using a pump and hose, or use an outboard motor to create a “rooster tail” of water across the pond. Anything that will mix air and water and provide an oxygenated refuge may help save some fish.
For more information on pond management visit our website at www.uaex.edu or contact the Grant County Extension Service at 870-942-2231.
Brad McGinley is a County Extension Agent with the University of Arkansas Division of Agriculture, located in Grant County. You may reach him at 870-942-2231 or 202 West Pine St., Sheridan, AR 72150, or by email at email@example.com. Follow him on Facebook at www.facebook.com/grant.extension.
By Brad McGinley
County Extension Agent - Agriculture
The Cooperative Extension Service
U of A System Division f Agriculture
Media Contact: Brad McGinley
County Extension Agent - Agriculture
U of A Division of Agriculture
Cooperative Extension Service
202 West Pine Street, Sheridan AR, 72150
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