September 28, 2021

Fall Pond Aeration: Why It’s Important

Why aeration in autumn is essential to a healthy pond.

At HIBLOW USA we receive many calls at the end of summer asking if pond aeration is needed in the fall, or if they should turn off our pump and store it until spring. They also ask if the pump can handle colder temperatures. The answer is yes to both.

Many argue that fall is the most important time of the year to run the pond aerator. Sudden drops in temperature, a reduction in sunlight, strong storms, and an increase of organic debris all contribute to reduction in oxygen levels that directly impact the health of the pond.

Reduction in oxygen from plants

Aquatic plants, due to photosynthesis, create oxygen for ponds. Naturally, as the cold sets in and there is less sunlight, algae and other aquatic plants start to die off or go dormant. The green plants that survive produce much less oxygen because of the reduction in sunlight.

Increase in organic matter

Organic debris is most prevalent in the fall. As leaves change color and drop to the ground, they and other dying aquatic vegetation are swept into the pond. Fertilizer and decaying insects/ animals also find their way into the water, further impacting the water composition. Nature uses beneficial micro-organisms (aerobic bacteria) – which require oxygen to live and thrive – to decompose organic matter. With the influx of debris in the pond, more oxygen is needed to speed up the decomposition. If there is not sufficient oxygen, the organic matter will be slow to decompose and can build up at the bottom of the pond. Not only will this make for a major spring cleanup, the condition can contribute to fish kill in the winter.

pond aerator, pond air pump, pond aeration

Pond turnover

During summertime, without proper water circulation, ponds will settle into 3 layers – known as thermal stratification. The top layer (epilimnion) is the warmer water near the surface. The bottom layer (hypolimnion) is the cooler water at the bottom. The layer in between is the metalimnion. Within the metalimnion is a horizontal plane called the thermocline – the point of sudden temperature change. If you have ever jumped into a lake or pond and felt an instant difference in temperature, you passed through the thermocline.
As the temperatures drop, the warmer water at the top of the pond increases in density and sinks to the bottom. Eventually with the addition of windy days, the pond will mix, and the temperature will become more consistent throughout. The biggest concern is a sudden drop in temperature or a major storm that turns the pond over suddenly. If this happens, anoxic (anaerobic) water at the bottom of the pond can mix throughout the water column and deplete oxygen levels. This leads to a reduction of beneficial bacteria and the possibility of a major fish kill.

Benefits of subsurface aeration

Bottom diffused aeration increases dissolved oxygen levels helping to offset the reduction in oxygen from plants. Aeration allows for beneficial aerobic bacteria to multiply, speeding up the consumption of organic matter that has accumulated in the pond. Subsurface aeration also circulates water to make temperatures and oxygen levels more consistent at all depths – preventing the devastating effects of sudden turnover.

Year-long pond aeration is recommended for best results. If you need help selecting the right size pump, check out our pumps sizing article.

If you have any questions, please give us a call, or send an email.
Phone: 734-944-5032, Email:

Author: Mike Miner

September 28, 2021

Posted in:

Pond & Aquaculture

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