Oxygenating water

I’m growing about a dozen plants using an active hydroponics system. I use an aquarium-style bubbler/aerator to add air to a 35-gallon barrel of nutrient-enriched water. Would there be any benefit in adding oxygen from a tank prior to flooding the plants? I know how important it is to give the roots lots of oxygen.
Is adding pure oxygen to the water overkill?

Jumpen Jack Flash,
Seattle, Washington

When water comes in contact with air, it releases dissolved CO2 and captures oxygen, which is then dissolved in the water. In your system (using a bubbler), oxygen comes in contact with water in two ways. A small amount is absorbed from the bubbles traveling through the water. Most of the exchange takes place at the water’s surface. This is facilitated by the bubbling action, which causes the water to circulate quickly and constantly, bringing new water to the surface where it comes in contact with the air.

The larger the surface area, the more chance the air has to come in contact with the water for the exchange to take place. Once the water is saturated with oxygen it will not absorb more. The water’s saturation level is determined by temperature and water pressure.

Warm water holds far less oxygen than cool water. 70?F (21?C) water holds more than double the oxygen as 80?F (27?C) water. Just as a bottle of soda starts bubbling and releasing CO2 when it is opened and pressure is released, pressurized water holds more oxygen than unpressurized. So water at high altitudes holds less oxygen than in low-lying areas, where the atmospheric pressure is greater.

Using oxygen in the reservoir to super-saturate the water will not be very effective. The water reaches a saturation point and very little additional oxygen will dissolve. However, additional oxygen can be used in some hydroponics systems. Roots are exposed to air in NFT and tube systems. Oxygen can be injected into the water of flood systems as it is filling trays. In aeroponic systems, where the roots are hanging in air, the atmosphere can easily be enriched.

It is also possible to inject oxygen directly into some drip systems, such as one using hydrocultural pellets. The oxygen fills the air spaces between the pellets.

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