Aeration – Or Not?

By Bob Lusk

Bottom diffused aeration is a valuable asset to water quality.

Recently a Pond Boss subscriber asked, “ What are the pros and cons of aeration”? That’s a fair question, especially when someone is thinking about investing thousands of dollars in a system as they do their lake design due diligence.

The pros far outweigh the cons.

The pros are: You are buying an insurance policy to ensure, to the best of all our abilities, your pond water remains healthy. The very first principle of outstanding pond management is water quality. Happy, healthy water is the medium in which our plants and animals deserve to live. Left to its own devices, water behaves in ways we don’t necessarily prefer, which often leads to stressful circumstances, especially during the warmest and coldest months.

In nature, water moves horizontally with wind and wave action. When water moves from one side to another, the laws of physics won’t allow it to move far downward. A wave hits shore, turns downward a few feet and heads in the opposite direction. That’s natural. But, those waves don’t turn and push to the bottom, especially in the summer, when a lake needs aeration the most. And, it certainly can’t happen with ice cover. Bottom diffused aeration moves water vertically, from bottom to top.

Wind driven aeration is popular, especially where electricity isn’t available.

When water touches the atmosphere, several key biological things happen.  As organic matter that has fallen to the bottom of the lake decomposes, it consumes oxygen. Part of that process is release of other types of gas byproducts and nutrients, minerals, and metals. You ever notice when you wade the edge of some ponds and kick up that yucky black sludge there, you’ll smell something like a rotten egg? That’s sulfur-based gas releasing from the water into the atmosphere. That’s one byproduct of decomposition of organic matter. If not kicked up, it tends to stay put. Aeration expedites that process and keeps water consistently cleansing itself. If not consistently moving, organic matter builds up on the lake bottom, using all of the oxygen it can, becoming anaerobic (without oxygen) and can cause a buildup of toxins in the water, from the bottom up. As that stuff builds, it rises, and can be triggered to release all at once, tainting the water enough to cause a fish kill.

Another pro of aeration—mixing the water from bottom to top allows most of the lake’s water to contact the atmosphere, helping it keep oxygen saturation levels as high as possible. Oxygen is the key to life under water, especially for fish. Fish need it to breathe. Keep this next fact in mind, too. As temperature rises, water’s affinity for oxygen drops. Water in the 90’s can’t physically hold as much oxygen as water in the 30’s. Good pond management practitioners understand that.

Fountains are beautiful. Since they typically draw shallow, they’re not as valuable as aeration systems.

Aeration also minimizes the risk of stratification. When a lake stratifies, it does so because sunlight pushes heat downward as far as it can. Heat, being heat, typically wants to rise, which it does in the summer in a lake. That’s Nature’s lake design. Your lake ends up as a layer cake, a warm layer sitting on top of a cold layer. That warm water is the living part of the lake. That cold, deep layer is quickly robbed of its oxygen and can’t replenish it because it doesn’t contact the atmosphere. Aeration changes that. You’ve heard of a lake turning over? That happens, normally in the fall, when we get a cold front with rain and several cloudy days. That warm upper water layer temperature drops to the same temps as the lower layer. They mix, with the bad lower layer mixing with that upper layer, dropping oxygen levels, adding toxic gasses from below the thermocline (the dividing line between the warm and cool layers), often resulting in a fish kill. Got one of those calls right after a summer cold front. An Arkansas fishing club had it in a 30-acre lake. Had 8-10 pound bass floating, along with all size ranges of different species of fish. Major fish kill. Aeration minimizes that risk.

Water circulators are gaining in popularity to move and mix pond water in the right circumstance.

One other pro for aeration—moving water vertically helps give autonomy of water quality, top to bottom. Even though photosynthesis and respiration are normal processes that we want, those two processes can have an adverse effect in water of lower alkalinity. Aeration helps keep those biological processes on an even playing field. Here’s the bottom line for the pros of aeration: A properly designed bottom-diffused aeration system moves water from the bottom to the top, allowing most of the lake’s water to contact the atmosphere to release natural toxic gasses and replenish much-needed oxygen. As the water moves vertically, aeration helps create a consistent, autonomous state of water temperatures, oxygen levels, and chemistry, minimizing the effects of every day’s biology, especially decomposition of organic matter, photosynthesis, and respiration of plants. Here’s what I just said, in plain English. Aeration moves water to do what it can to keep the water the same, all over the lake, in spite of everything the lake would naturally do if left to itself. One other pro, that can also be considered a con, is that aeration allows the entire lake the opportunity to be productive, to hold fish and raise them. If the lake stratified, as non-aerated lakes and ponds tend to do, fish couldn’t survive for long beneath the thermocline. With fish capable of living top to bottom in an aerated pond or lake, they won’t be as easy to find and catch sometimes. That’s one of the complaints we hear about aerated lakes—fish aren’t as easy to catch, especially if they are deep.

Bottom diffused aeration is a valuable asset to water quality.

Here are the cons. First, the initial capital expense of buying the equipment. It’s a substantial outlay of dollars, not only to buy the equipment, but to install it. Secondly, aeration is no absolute guarantee you won’t have a fish kill at some point. I’ve seen well-aerated lakes still have a fish kill if the lake is overly fertile or has blue-green algae. Those fish kills aren’t related to oxygen depletion as much as they are related to toxicity by quickly decaying dead plankton and algae, including blue-green algae. Third, aeration won’t kill vegetation, but it can certainly go a long way to prevent it. The fourth one is buying equipment that will need maintenance. While not expensive to maintain, it still needs to be done, or your equipment will suffer.

Bottom diffusers send bubble plumes upward, pushing water toward the surface of your pond.

Here’s how I see it. Aerated lakes create as consistent water quality as possible, eliminating, or minimizing that issue as a potential problem as we grow the biggest and best fish for years to come. If we don’t have to deal with water quality issues, fish will be happier. If they have a happy home, they’ll do what they do best—eat, grow, have babies, and bite the business