Many pond and lake owners are keen on the idea of adding aeration to their waterbody to improve the overall health of their given aquatic system, but they are typically uneducated when it comes to the pros and cons of aeration, and how it relates to the stratification process that occurs in lakes and ponds. This makes it difficult to discuss aeration and its potential benefits in a private body of water without also introducing the topic of stratification. To put it simply, stratification is the seasonal layering of warm and cold water throughout the water column, which occurs primarily in the winter and summer months.
During the winter months, the surface waters will typically freeze, while slightly warmer and more dense water (around 39⁰F) will settle towards the bottom of the pond. This slightly warmer water often provides a place of refuge from the freezing surface waters for fish and other aquatic organisms; however, oxygen depletion can become a concern since the water towards the bottom of the pond typically holds less oxygen due to a lack of photosynthesis and a lack of oxygenation from natural sources such as wave action. Summer stratification holds the same concept of layering, but with the difference being that the surface water is usually significantly warmer than the water at the bottom. These layers are known as the epilimnion (surface) and the hypolimnion (bottom), while the line separating the two layers is known as the thermocline. Cold water is able to carry more oxygen than warm water, however the cold water at the bottom of a pond/lake is typically oxygen deficient compared to the surface water due to wind/wave action and high rates of photosynthesis at the surface. This stratification can create the potential for an oxygen crash if the water were to mix during an event like a heavy rain storm, which could ultimately lead to a fish kill.
This is where aeration typically begins to sound appealing to lake and pond owners who are wanting to protect their livestock from oxygen crashes. Aeration (particularly bottom-diffused aeration) has many benefits that include limiting seasonal stratification, increasing overall dissolved oxygen, and aiding in the decomposition of organic materials through microbial processes. Many lake and pond owners want to achieve these benefits, but may not realize that their waterbody is not a good candidate for something like bottom-diffused aeration due to factors such as pond depth, excessive muck, or already having a pond that is polymictic and mixes on its own several times throughout the year. A bottom-diffused aerated pond that is too shallow with excessive muck may see increases in algae or nuisance weed growth due to the diffuser stirring up the muck and thus releasing excess nutrients into the water column that would otherwise be locked up. A thoroughly mixed pond in the winter may also remove the warmer water refuge at the bottom of the pond and cause more stress on livestock. Luckily for non-ideal situations there are options such as surface aerators that can work well in relatively shallow or “mucky” ponds since they do not have to pull water from deeper areas, which can also reduce the risk of unnecessarily mixing ponds during the more extreme seasons.
It is our duty as Aquatic Specialists to use the above information to analyze each waterbody on a situational basis, and educate the owners on these topics. By doing so, we can provide the best recommendations for care and equipment, which ultimately optimizes the overall health of our clients’ lakes and/or ponds.
Clay Luce
Aquatic Specialist
Toledo, OH Branch