Approaches To Aeration

There are many ways in which to aerate a body of water. Most of the available devices used today are covered here. The main objective for using an aeration system is to provide sufficient dissolved oxygen to the water column. Oxygen is the single most important water quality parameter. The sufficient amount of oxygen varies from pond to pond and lake to lake. Much of it centers on the biological oxygen demand (B.O.D.) and water temperature. All living organisms in an aquatic ecosystem need oxygen. Although fish consume oxygen from the water column, their excrement asserts a higher B.O.D. As feces and other organic litter builds up on the bottom, it forms sediment composed of a large percentage of organic material. Microorganisms, on the bottom of the pond, feed upon this organic matter and subsequently use up the available oxygen. During nighttime hours, plants and algae further reduce the available oxygen.

There are four approaches lake and pond managers take when designing an aeration system; Eplilmnetic, Diffused, Directional Flow and Hypolimnetic Aeration.

Epilimnetic (Surface) Aeration

Adds dissolved oxygen to the top layer of the water column (the Epilimnion). These devices quickly add large amounts of oxygen into a small area. Epilimnetic surface aerators function by moving a large volume of water (800 - 1300 gpm) approximately 2 - 4 feet into the air where the water takes on atmospheric oxygen before it returns to the lake or pond. As a result of the massive amount of water being pumped into the air and splashing back down onto the pond's surface, a wave action radiates outward from the device toward the pond or lake perimeter. This process thereby increases gas transfer within the pond, inducing circulation as the water mixes and improving water quality while producing generally warm temperatures and high oxygen content (important to fish and other creatures) throughout the layer.

It is important to note that epilimnetic surface aeration does nothing to improve conditions in the hypolimnion or at the soil/water interface, which is often where aeration is needed the most. Epilimnetic surface aeration uses more electricity than other types of aeration that produce an equivalent amount of dissolved oxygen.

Diffused (Bottom) Aeration

Destratifies the water column making oxygen levels and temperature uniform throughout the lake or pond, thus the lake tends to be warmed. Diffused bottom aeration systems pump air into the water. Systems of "fine bubble diffusers" are placed near the bottom of the water body. Compressed air is pumped through underwater airlines to the diffusers. The air then bubbles out through the diffuser membrane and rises through the water column to the surface. When released at the bottom of a pond or lake, compressed air naturally begins to migrate towards the surface of the water. As air travels up the water column the pressure, surrounding the bubbles slowly decreases causing the bubbles to increase in size. A slight current begins to develop. The current draws oxygen-depleted water and noxious gases from the bottom, oxygenates it and transports it to the surface. When the diffused air bubbles reach the lake or pond's surface, a gentle boiling is produced. The "boil" allows the noxious gases to escape the pond. These systems are extremely effective in destratifying a water body and are Aquatic Biologists, Inc. preferred method of aeration due to its many benefits.

Directional Flow

Used to turn stagnant, still or low flowing water into a stream environment while adding oxygen into the water column. Creating the stream environment may help limit the reproduction of mosquitoes in your area. In summer months, directional flow devices can be used to keep floating debris out of bays, marinas and canals; as well as around docks and beaches. Many directional flow devices can be angled downward to destratify ponds to about 18' in depth. Circulators can also be used to eliminate stagnant water and may reduce mosquito breeding grounds in the summer; and in winter months to prevent winter kill of your fish population.

Hypolimnetic Aeration

This method brings oxygen to the hypolimnion without destratifying the water column. A major advantage of this method is that different temperature layers are maintained, allowing a diverse fishery to be developed. Cold water fish (e.g. trout) are able to live in the colder water available within the hypolimnion while warm water fish species (e.g. blue gills, bass) are able to live and thrive within the epilimnion.