Dissolved oxygen (DO) is the lifeline of the aquatic ecosystem. Without oxygen, both fish and desirable aquatic vegetation can die. Oxygen is present in water in much smaller amounts than it is in the air we breathe. Maintaining adequate oxygen levels in the water is critical to the health of the pond, and that’s what pond aeration is good for.
Oxygen enters pond water naturally through atmospheric diffusion and by photosynthesis of aquatic plants and algae. The diffusion rate of oxygen increases with increasing wind and wave action. Unfortunately, small, community ponds do not receive the same degree of wave action that occurs on larger lakes and reservoirs. Secondly, these ponds often have denser fish populations which create a higher oxygen demand in the water.
During daylight hours, aquatic plants and algae produce oxygen as a byproduct of photosynthesis. However, this process reverses at night when the plants consume oxygen during respiration. This natural day/night cycle causes 24 hour fluctuations in dissolved oxygen levels. In ponds with excessive plant or algae growth, the oxygen levels can be elevated in late afternoon but dangerously low just before sunrise. Even a very short time without oxygen can be fatal to fish and aquatic insects. Water temperature is another major factor in oxygen response. Cooler water holds more oxygen that warm water. Therefore, monitoring oxygen levels in community ponds is most important during the “dog days” of summer. The majority of oxygen related fish kills in community ponds occur at night during the months of July, August, and September.
Dissolved oxygen influences many other biological processes that occur in a pond. Higher oxygen levels typically result in fewer outbreaks of noxious algae blooms. When oxygen levels are good, the beneficial pond bacteria are more efficient at using up nutrients which would otherwise be used in the production of algae. Likewise, increased oxygen levels near the pond bottom encourage the breakdown of organic “muck” by aerobic bacteria. This results in a reduction of bad odors that can emanate from the pond surface during certain times of the year.
Adding supplemental pond aeration with either surface fountains or bottom-diffused aeration systems is a great investment for the health of your pond. Surface fountains not only provide aesthetic benefits but also increase surface diffusion of oxygen. As a result, fountains provide a buffer against the harsh environmental conditions that can cause large scale fish kills. Surface fountains also disrupt the water surface and eliminate stagnant water conditions where mosquito larvae thrive.
Bottom-diffused pond aeration systems work from the bottom up. They do not provide aesthetic benefits; however, they eliminate thermal stratification and promote oxygen rich conditions near the pond bottom. The resulting increase in biological activity near the pond bottom provides many benefits to the overall health of the pond. Bottom aeration systems are both more energy and cost efficient than surface fountains.