Pond Aeration 101

Pond aeration is the process of increasing or maintaining the amount of dissolved oxygen in a pond. It involves the natural or mechanical movement of water that breaks the pond’s surface layer, to bring the water into contact with the air. Increased air contact results in higher and more consistent levels of oxygen in the water – a key component of a healthy aquatic ecosystem.

Wind, heavy rain and waterfalls are natural sources of aeration in a lake or pond. When these are not present (or inconsistent), mechanical circulators and aerating fountains are used to keep dissolved oxygen at optimal levels.

Bodies of water that are not properly circulated naturally “stratify” into layers based on temperature, oxygen level and density. This is when the water column separates into a layer of warm, oxygen-rich water (the epilimnion) at the surface, a dividing layer (the thermocline), and cold, oxygen-poor water (the hypolimnion) near the bottom. 

Stratification can wreak havoc on a pond resulting in several problems. Most notably, ponds in temperate regions can see the thermocline collapse as the weather cools in the fall. This results in a rapid mixing of the water column, which causes oxygen depletion and can cause large-scale fish kills. (Fish kills caused by stratification don’t only occur during the winter. Heavy rains can break up warm-weather stratification, leading to mass death in the summer months.)

Additionally, stratification will create a deep layer of foul-smelling muck at the bottom of the pond or lake.

Without proper pond aeration, aerobic bacteria on the pond floor do not receive the necessary oxygen to break down organic material that falls from the warmer, oxygen-rich layers above. This results in thick deposits of muck – essentially rotting organic material.

Muck is rich in nutrients, which can lead to the unchecked growth of algae, unwanted floating plants, unhealthy fish, mosquito breeding and more. Pond muck impacts both water clarity and the overall aesthetic value of the pond. Unchecked overtime increased levels of muck lead to pond eutrophication which is the slow death of the pond.

Poor pond aeration results in:

• Foul smells; typically described as rotten eggs or spoiled meat
• A thick layer of muck on the bottom
• Unwanted plant growth or algae blooms
• Poor water clarity
• Unhealthy or dying fish
• Poor pH readings
• High concentrations of phosphorus and nitrogen

The easiest way to achieve proper pond aeration and oxygenation is to install an aerating fountain, circulator or diffuser.

Aerating fountains use an electric motor and turbine assembly to pull cooler water from the pond bottom and push it to the surface in a fountain like decorative pattern. They can be used in shallow ponds (sometimes requiring as little as 30 inches/76cm of water) and are meant to combine powerful aeration with aesthetic enhancement.

There are several types of pond aeration systems also known as pond circulators:

• Aspirators transfer oxygen from the surface into the water column through a venturi tube. This creates no surface spray.
• High-volume aerators pump large amounts of water above the surface. These are most typically used in severe and industrial environments, such as wastewater ponds.
• Mixers circulate water horizontally in order to break up stagnant or stratified water.
• Diffusers act as underwater “bubblers,” aerating, destratifying and circulating pond or lake water without disturbing natural surroundings.

If a pond is foul smelling, overrun with algae or simply isn’t producing large enough fish, poor aeration is likely a root cause of the problem. Increased water movement and contact with air can help turn a stagnant body of water into a thriving, healthy system.  Realize not all pond fountains aerate. An aerating fountain that will positively impact a pond needs to add minimum of 2lbs/1Kg of oxygen per horsepower!