Ponds and Lakes… A matter of Oxygen

We’ve all seen it, and smelled it! The unsightly algae bloom that covers your once pristine pond is back with a vengeance. Not only does the slimy, greenish brown substance hurt the eyes and nose, the algae is compromising the water quality for both fish and irrigation use. As algae grows, it accumulates closer and closer to the surface to gather sunlight. As a result, the lower depths are shaded leaving the first few feet of water deficient in oxygen production. Most issues with lower oxygen levels occur in the summer months, as the warmer water holds less oxygen, yet the eco-system of the pond requires more. Nitrites, ammonia, and carbon dioxide can also deplete the volume of oxygen.

Oxygen is introduced into ponds and lakes basically from two sources, photosynthesis and from the air by the means of diffusion. Photosynthesis is considered by many biologists to be the most important source, which is the process plants use for the manufacturing of nutrients. On a bright sunny day, plants are adding oxygen to the pond as a by-product of photosynthesis. After sunset, the oxygen is not being produced yet the plants and fish in the pond continue to deplete the oxygen levels. Quite often a desirable balance between the oxygen production and the oxygen depletion cannot be achieved without some type of assistance, and if left unchecked, the oxygen level can drop low enough to stress or even kill fish.

The levels of oxygen from pond to pond, even on the same property, can vary greatly. Every pond is a unique eco-system with it’s own unique characteristics. Over the course of a summer’s day the oxygen levels in any given pond may vary, but typically the concentration is highest in the latter part of the afternoon, and the oxygen concentration is lowest just prior to sunrise. Most issues with oxygen depletion occur starting in the late spring and continuing until October. This is a stressful time of year for a pond, as the respiration rates of the aquatic life increase as the water warms, and the oxygen is depleted more rapidly. As the water warms it’s capability to hold oxygen is greatly diminished. Decaying plants and algae can also be a big drain on the oxygen too, as the decomposing matter uses a considerable amount. Summer weather can also cause the surface water of your pond to absorb more heat, which in turn creates a layer of warmer water floating over a deeper layer of cooler water. The warmer water has all of the naturally produced oxygen absorbed, and quite often these two layers of water may not mix together for days or weeks at a time, especially in deeper bodies of water. Wind and a hard rain can assist in cooling the top layer of water, making it heavier and more apt to sink and mix with the deeper water.

What can be done to add oxygen while at the same time ridding yourself of unwanted growth in an eco-friendly yet cost and time effective way? Chemicals and treatments are an option, yet quite often the infusion of oxygen is the best solution. This is done naturally by rainfall and photosynthesis, but you can lend Mother Nature a hand by the introduction of an aeration system. Although many variations in the types of aeration systems are available, most can be classified as either surface or bottom aeration.

Fountains, Display Aerators, and agitators are all considered to be surface aeration systems. These work by pumping water into the air, and as the water falls back to the pond’s surface, it captures oxygen molecules from the atmosphere which are in turn mixed thru the body of water. The agitated water movement not only works to disperse the oxygen, it also assists in creating a strong surface current that moves floating algae and debris to the water’s edge for easier clean-up. These styles also can assist in mixing the layers of warm and cooler water in a pond during the summer months, as they are generally designed to pull water up from the deeper levels which in turn is dropped onto and mixed with the warmer surface water. The surface aerator, with many display patterns available, is generally an aesthetically pleasing addition to the pond. Even though costs can vary considerably depending on size and style, there are many options available on the market for even the most modest budget. Installation on many manufacturers equipment is quite simple, and can take less than a couple of hours.

Bottom aerators, also known as sub-surface aerators, vary in style and design, but most function using the same principal of releasing air thru a diffuser near the bottom of the pond. The advantage of bottom aeration over surface aeration is the ability to add oxygen thru the entire water column, however this style of aerator does very little to create surface current or water dispersion to move algae. Care should be taken when utilizing a bottom aerator to avoid plants growing at the bottom of the pond, as these can block the flow of oxygen and require removal and cleaning of the unit.

As far as power consumption, both styles can be found in both 110 and 220 volt power applications, along with a few manufacturers offering solar options. Most systems are being designed for ease of installation and minimum maintenance, so that grounds crews can handle the day-to-day operation on their own. A ground fault protected power source is mandatory for any installation, and care should be taken to check the local ordinances and regulations.

Whether it be surface or bottom aeration, water biologists agree that some sort of oxygen infusion is necessary for all ponds at some time or another. It’s imperative the pond professional communicate the differences between aeration systems and help clients make the best decision possible for their own unique situation.