Why Dissolved Oxygen Levels in Ponds are Important

Oxygen is one of the most important factors that influences the biological balance in ponds. The amount of dissolved oxygen (D.O.) available in ponds is quite low, around 8-12mg/l (8-12ppm) compared to the air we breathe in the atmosphere which contains about 20% oxygen (or 200,000ppm). Oxygen is dissolved into ponds in 3 main ways - by the atmosphere, pond plants and aeration supplied by the movement of water.

Plants and algae are important suppliers of oxygen during daylight hours when they undergo photosynthesis. In the evening, the process reverses due to plant respiration which they then consume oxygen.  Plants are also beneficial in ponds when they cover the surface providing shade that cools the water during hotter months and increases the D.O. levels.

    The amount of oxygen in ponds varies with the weather - levels are higher in cooler months when the water is colder and lower during hotter months when water is warmer. When large amounts of plants are removed from a pond abruptly or a large algae bloom has been eliminated with algaecides it may cause a D.O. crash which can negatively affect the biological balance in your pond.   Excess oxygen is also needed to consume dead algae debris as a result of the chemical treatment which may also cause fish to gasp at the surface of the water starving for air. Fish and other living things in the pond rely on good levels of D.O. and can suffer or expire if levels are below 5ppm.

Beneficial bacteria that break down waste in ponds are less efficient when oxygen levels are low. Anaerobic bacteria rely on higher D.O. levels, necessary for breaking down toxic ammonia produced by fish and decaying debris. Anaerobic bacteria that live in areas where the oxygen levels are very low -at the bottom in sediment, and under rocks -consume debris at a much slower rate than aerobic bacteria. Excess anaerobic bacteria cause foul odors, sulfur like smells and potential health problems with your fish (sores, fin streaking, and ulcers) or die off.

Fish can be good indicators of oxygen levels and other water quality issues that may not be visible to the naked eye. When fish gasp at the water surface this usually indicates a very low D.O. level. Other behaviors like isolation, lethargy and not eating when they should are other indicators that some factors need to be determined to find the best course of treatment.

Providing additional aeration in your pond using water pumps and air compressors helps to resolve these situations by supplying continuous sources of oxygen. Waterfalls, streams and fountain “spitters” can supply oxygen with pond pumps, while aerators supply air with compressors and diffusor discs.  Learn more about aerators, read Advantages Using Aerators.

At Nature Perfect Pond & Supply Store we can help you maintain a healthy pond and supply the best products for your unique pond setting- from small to large recreation lagoons. Stop by or set up an appointment to speak with our knowledgeable staff.