Improve Dissolved Oxygen To Avoid Fish Kills

The quickest way to increase dissolved oxygen in a pond is with surface aeration. This method involves installing an aeration system that enhances oxygen exchange at the water's surface, which is particularly effective in ponds that are 6 feet deep or less. This method is also the safest way to quickly introduce oxygen. Bottom aeration requires a slow start up over a 2 week period. This is to reduce the risk of introducing too many nutrients or other toxins that can stir up from pond sediments.

Ponds can suffer from low dissolved oxygen for a number of reasons.

Several factors can reduce oxygen levels in a pond, including:

• Temperature: Warmer water holds less dissolved oxygen.
• Organic Matter Decomposition: The breakdown of organic materials consumes oxygen.
• Algal Blooms: Excessive algae can deplete oxygen, especially at night when they respire.
• Overcrowding of Fish: Too many fish can lead to increased oxygen consumption.
• Stagnation: Lack of water movement can hinder oxygen exchange.
• Pollution: Nutrient runoff can lead to eutrophication, causing oxygen depletion.

Times when dissolved oxygen can crash quickly:

Planktonic algae bloom crash after multiple overcast days. Planktonic algae produces oxygen during the day, but removes it in the evening. When there are multiple days with a lack of sunlight, the growth can die back and reduce overall oxygen.

Post algaecide or herbicide application, growth begins to die back. As vegetation decomposes it consumes oxygen from the water.

Drastic changes in water temperature from a cold snap can cause mixing of separated water and drop overall oxygen quickly. This can also happen from a major rain event.

Prior to installation, the dissolved oxygen was measured in 1 foot increments in the deepest point of the pond. The deepest point is 10 feet deep. We typically recommend surface aeration on ponds that are 6 feet deep or less, as surface aeration does have limitations. While this is true, the goal was to improve overall oxygenation in the water column.

The initial reading was taken in the morning, when oxygen levels are generally lowest. Levels ranged from 0.32 mg/L at the deepest point, 2.38 mg/L at 7 feet, and 8.5 mg/L at the surface. At the time of the readings there was a visible planktonic algae bloom that reduced visibility to less than 12".

The following morning, dissolved oxygen readings were taken from the same location as the previous morning. Oxygen levels rose slightly at 8-10 feet depths. At 7 feet the dissolved oxygen increased to 5.79 mg/L from 2.38 mg/L. At 6 feet deep, the level increased from 3.8 mg/L to 6.32 mg/L.

Readings were taken again at 5pm. Surface readings were higher than morning readings due to biological activity within the pond. The following morning readings were taken again at 8am. Levels were almost identical to the previous morning.

Within just 24 hours, healthy oxygen levels can be restored to protect the pond.

Implementing these practices can help prevent fish kills and maintain a healthy aquatic environment.