This is the continuation of the article titled “Oxygen in Ponds” by Ben Helm of www.watergardenersbible.co.uk, concerning Dissolved Oxygen Concentration (DOC). In the first post, I discussed the occupants of the pond and how they affect and rely on DOC. Now let’s look at the individual factors that can cause the DOC to drop.
In an ideal pond scenario, plenty of DOC would exist and we wouldn’t have to concern ourselves with this problem. But most ponds have few too many plants, overfed fish and the fish stocking level is too great. All of these factors could easily deplete the oxygen to dangerous levels. So, let’s clarify these factors a little more:
With the warmer temperatures and all occupants in the pond active, more oxygen is being consumed. During the daytime, plants are natural oxygen contributors, even exceeding their own oxygen demand. They still consume oxygen at night, however, they are not producing it. If there are algal problems, this can help to deplete the oxygen at night because they, too, consume oxygen at night. This all can lead to a DOC drop at night. If algaecides are used, this attracts considerable bacterial activity, again consuming yet more oxygen. Do you see how this could lead to a devastating situation?
Temperature has a huge impact on the DOC. The higher the water temperature, the lower the amount of dissolved oxygen that can be held in the water. And the warmer water temperatures will result in a higher oxygen demand because all of the occupants are active thus consuming more oxygen.
Pond treatments will limit the amount of dissolved oxygen in the pond in two ways:
- First, any dissolved substance added to the pond will limit the pond’s ability to hold oxygen. So, always read and follow the label on any additives placed into the pond. Many treatments will recommend aeration for this reason.
- Second, many treatments will increase the amount of organic matter that will be broken down. This will increase the activity of the bacteria, which also will consume oxygen.
In the final post, we will discuss prevention and quick fixes for a low DOC.