September 25, 2020

Should I Aerate My Pond in the Fall?

Why aeration in autumn is essential to a healthy pond

Perhaps the most important time to aerate a pond is in the fall.  Cooler temperatures, strong storms, less sunlight, and an increase in organic debris all impact the oxygen levels and health of a 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 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.

Aeration to the rescue

The good news is subsurface aeration systems significantly increase oxygen levels helping to offset the reduction in oxygen from plants.  Aeration allows for aerobic bacteria to multiply exponentially, speeding up the consumption of organic matter that has accumulated in the pond.  Additionally, an aeration system circulates water to make temperatures more consistent at all depths – preventing sudden turnover.

Year-long 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 25, 2020

Posted in:

Pond & Aquaculture

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