Pond Management: New Tool Helps Reduce Oxygen Problems

As summer waters heat up, shallow water may appeal to fish (and anglers) because deeper water is denser and lacks oxygen. Photo: Linda Breazeale, Mississippi State University

Oxygen-related fish kills can completely wipe out otherwise healthy ponds, but there is a strategy pond owners can use to control this problem.

Anoxia — the lack of oxygen — can form in deeper water layers of a pond during warmer months. Deeper water is heavier and denser, which prevents it from mixing with warm surface water where air and oxygen-producing microorganisms are found. As deeper water becomes isolated, its oxygen levels are depleted, reducing fish habitat and increasing the risk of fish kills.

One tool to prevent fish kills is the use of destratification, which breaks up the temperature and density difference, allowing the pond to mix continuously throughout the year. A common design uses a compressor on the shore to pump air through hoses and out of diffusers on the pond bottom.

Diffusers release air in a column of small bubbles that rise to the surface, expanding and pushing water upward. Deeper water rises to the surface, and surface water sinks to replace it, creating a circulation effect. Water is oxygenated in the process.

Preventing fish kills isn’t the only advantage of installing destratification systems. One study found that fish production may increase due to more food and habitat in the pond.

It reported that the weight of largemouth bass supported by one pond fitted with a destratification system more than doubled after use. Bass production remained high for several years until the end of the study, suggesting that the pond’s carrying capacity had increased.

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Carrying capacity may increase because of expanded habitat during the summer. Waters deeper than 4-5 feet often have very low oxygen in the summer, restricting fish to the warmer, shallower waters. Destratification not only enhances food availability, but it also lowers the fishes’ energy costs by keeping them cooler.

Destratification may also change the chemical environment of the pond, influencing biological productivity. Research has shown that destratification affects many factors, including chemical processes, nutrient dynamics, and thermal and oxygen patterns. According to one study, productivity was three times higher in lakes that were aerated.

Regardless of the reason, destratification seems to benefit ponds and small lakes by maintaining oxygen and potentially increasing fish production. Costs of these systems vary based on pond size and power source availability.

For a 5-acre pond with available power, a destratification system may cost $4,000 to install and $1 to $2 per day to operate. Many pond owners will consider this a small price for not having to worry about fish kills, and the increase in productivity is a happy bonus.

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