Oxygen Depletion

Aeration • Algae Control • Biological Control • Chemical Control• Dissolved Oxygen • Fish Health • Oxygen Depletion • pH Levels • Temperature/Shading • Pond Home

Just as it was easy to oxygenize the water, a number of conditions can result in oxygen depletion. These conditions are most often associated with four factors: hot, cloudy, still weather, sudden death of phytoplankton or algal bloom, pond stratification or turnover, and organic waste decomposition.

Hot, cloudy, still weather

Hot water temperatures (approximately 86 ° F and above) are most common during hot, cloudy, still weather. These conditions generally occur at the end of July and are typically stable throughout September. During this time, cloud cover limits the amount of available light, which slows or inhibits oxygen creation through the photosynthetic process. In addition, the lack of wind stops pond circulation and restricts surface diffusion of atmospheric oxygen.

Sudden death of phytoplankton or algal bloom, “bloom crash”

The sudden death of phytoplankton or algal bloom may be the result of one of three factors: insufficient light for photosynthesis, inadequate pond nutrients, or the aging of the blooms. In addition, a significant amount of oxygen is used when dead phytoplankton/algae decay. When the phytoplankton bloom becomes too dense, excess amounts of oxygen are removed from the water for respiration.

Pond stratification or turnover

During the summer months, the upper 4-6 feet of pond water (generally in ponds 8ft or greater) are warmed more quickly then the water at deeper levels. Because the water toward the surface is lighter and cooler, it doesn't’t mix well with deeper, cooler water. As a result, the water towards the bottom of the pond becomes stagnant; oxygen is depleted and decaying organic matter and bacteria have the opportunity to produce toxic compounds. The deep layer will remain un-oxygenated and a sudden, heavy rain or cold front can cause the upper layer to mix, sinking below and forcing the un-oxygenated layer to rise above or combine with surface waters. This depletes oxygen levels in upper waters.

Organic waste composition

During the late summer, the number of fish in a commercial pond tends to increase. As the number of fish living in the water unit rises, the amount of waste and organic loads such as feces and uneaten food also increases and will begin to decompose. This requires vast amounts of oxygen, which generally exceeds the oxygen level available in the water. In addition, high waste loads can stimulate algal bloom to dense to be supported by pond.