Understanding Spring Pond Turnover

In a pond ecosystem, dissolved oxygen levels play a key role in the functioning and health of pond organisms. Dissolved oxygen is the oxygen available to living things in the water. It can come from the atmosphere or be produced by aquatic plants and algae growing in the pond. The level of dissolved oxygen available in pond water can vary depending on the temperature of the water, the amount of plant material and organic matter present, and the movement of the water in the pond.  Shallower areas of the pond hold more dissolved oxygen than the deeper areas because of more photosynthesis taking place and more interaction with oxygen present at the pond’s surface.

Heavy rain events like spring thunderstorms can introduce large amounts of water to a pond and cause these varying zones of dissolved oxygen to mix quickly or turn over rapidly. For aquatic life like fish and frogs, dissolved oxygen levels are optimum at around 8–10 parts per million (ppm). When levels drop below 6 ppm or fluctuate rapidly, aquatic life is stressed, and fish kills can result.

Deeper ponds tend to experience these turnovers more frequently than shallow ponds because of greater variations in these different dissolved oxygen zones.

As a pond owner or manager, there are some things you can do to manage your pond for turnover, especially if it may be more prone to such events.

• Manage excess growth of aquatic plants or algae blooms – as plants die off, they can remove large amounts of oxygen from the water.
• Consider adding aeration to the pond – this will add atmospheric oxygen as well as keep the water column regularly mixing so as not to have such differences between the dissolved oxygen layers.
• Reduce excess nutrients entering the pond by utilizing a riparian buffer or other management practices– extra organic matter can also reduce dissolved oxygen levels.

Visit the Penn State Extension website for more information on managing your pond.