What is Aeration?
Any procedure by which oxygen is added to water can be considered a type of water aeration. This allows for various techniques to add dissolved oxygen to the water; but they also have varying degrees of successful benefits.
Natural aeration is a type of both sub-surface and surface aeration. Through the natural process of photosynthesis, under water aquatic plants, like seaweed, release oxygen into the water providing it with the necessary oxygen for fish and for aerobic bacteria to break down excess nutrients. Oxygen can also be driven into the water when the wind disturbs the surface of the water body; and natural aeration can occur through a movement of water caused by an incoming stream, waterfall, or even a strong flood. Just be aware that excess minerals and nutrients can be carried into the water which promotes algae growth and sediment build-up; ultimately resulting in oxygen depletion.
Mechanical aeration improves water circulation as well as increases dissolved oxygen levels by destratifying or mixing the separated layers in the lake. Some mechanical circulation systems, like lake fountains, do set up a movement pattern in the water, but are not typically designed to destratify a lake. Water is usually only drawn from a few feet below the surface which does not mix the layers that have developed.
Fine bubble aeration is an efficient way to transfer oxygen to a body of water. A compressor on shore pumps air through a weighted hose, which is connected to a number of diffusers under water. These diffusers come in the shape of discs, plates, or tubes made of PVC or perforated membranes made from EPDM rubber. Air pumped through the diffuser membranes is released into the water.
Fine bubble aeration maximizes the surface area of the bubbles which transfers more oxygen to the water per bubble. Additionally, smaller bubbles take more time to reach the surface so not only is the surface area maximized, but so is the amount of time each bubble spends in the water, allowing it more time to transfer oxygen to the water. As a general rule, smaller bubbles and a deeper release point will generate a greater dissolved oxygen rate.
This aeration technique is sometimes referred to as the “air-lift” method of circulation, since bottom waters are “lifted” to the lake surface through the action of the injected air.
What happens without aeration?
Lakes and earthen bottom ponds have many different functions: they collect sediment and storm water run-off, they attract fishing enthusiasts, and they beautify communities who enjoy them year-round. But when left unmanaged, they can develop imbalances that may jeopardize the life of the body of water as well as its inhabitants.
With little or no water movement during the summer months, the temperature of a lake’s water will cause layers to separate out (stratify), the way that oil and water separate in that science experiment from grade school. The upper (warmer) levels or surface of the pond, receives oxygen where the water comes in contact with the air. Unfortunately, the temperature of a body of water directly affects the amount of dissolved oxygen it can hold. Following Henry's law, as water becomes warmer, oxygen becomes less soluble in it. The lower (cooler) levels of the pond are not able to receive oxygen and become an anaerobic (without or lacking oxygen) zone. The levels will not mix until weather cools the surface water, most commonly in the fall, and the separated layers become closer to the same temperature. This is called turnover. Toxic gasses from the lower layers spread throughout the pond, possibly causing devastating fish kills.
Oxygen depletion, also known as hypoxia, is an environmental phenomenon where the concentration of dissolved oxygen in the water decreases to a level that can no longer support living aquatic organisms. This can happen when nitrates and phosphates, from lawn fertilizers, cow manure, agricultural fertilizer, detergents, or human waste, run off into rivers and lakes, promoting the growth of algae and other plant life; then algaecides and/ or herbicides are used excessively, which takes oxygen from the water. As dead algae decompose, oxygen is consumed in the process, resulting in low levels of oxygen in the water. Harmful algal blooms (HAB), among other things, can destroy aquatic life in affected areas. Shallow lakes are more susceptible to dissolved oxygen depletion since they have a smaller amount of water compared to deeper lakes.
How Does Aeration Improve Water Quality?
Aeration does not only enhance water quality by stabilizing pH, reducing alkalinity, preventing anaerobic conditions, and removing carbon dioxide, but can also greatly decrease the cost of pond treatments.
Destratification through aeration has the potential to reduce algae feeding phosphorous in some lakes… depending if the lake’s phosphates come from internal sources, like natural decay from fish waste and decomposing plants in the mucky build-up on the bottom of the pond. Increased oxygen in the lower parts of the lake will improve the function of beneficial aerobic (using oxygen) bacteria that reduce the excess nutrients that build up in the bottom. Less nutrients in the water equals fewer algae blooms and better control over invasive aquatic plants and healthier fish.
Some Technical Points to Consider:
It’s important to understand what aeration can and cannot do for your lake so you do not end up with unexpected or unwanted results - and possibly a waste of money. It is not a cure-all for a lake’s problems.
For example, if the air diffuser is positioned too far above the lake bottom, an anaerobic (without oxygen) zone will remain below it. However, if the diffuser is placed on or too near the lake bottom- or if the aeration system is oversized (mixing too vigorously) – sediments may be stirred up and be resuspended in the lake. If the aeration system is undersized, mixing will be incomplete. In a very large lake, mixing will be limited unless more than one device is used.
For more information on pond and lake maintenance in regards to aeration, take a look at Atlantic Water Garden’s Pond and Lake Management handout. Not only does is discuss the importance of aeration but it discusses sizing your aeration system as well as the different components. Shop lake aeration units here online.