Photo credit: Samy Ndala (Congo DR) Review: Abdel Rahman El Gamal (Founder of the website)
The supersaturation of dissolved oxygen (DO) is often observed near the surface of water bodies as a result of the strong the photosynthetic activity resulting from phytoplankton abundance. This occurs during bright sunlit days in eutrophic water bodies such as rivers, lakes and/or fish ponds. The supersaturation of oxygen during daylight is always followed by much lower oxygen levels at night when the photosynthesis ceases while the respiration by all living organisms continues.
For illustration, the dissolved oxygen in the inserted photo reads 14.8 mg/l which is much higher that the saturation levels of dissolved oxygen. For example, the 100% DO saturation is 8.09 mg/l at water temperature of 26°C and 7.81 mg/l at 26°C. This photo was taken during August in a freshwater fish pond in Egypt where temperature is usually at highest and so the sun light. One can notice the dark green color of pond water indicating the abundance of phytoplankton in the water. It may worth mentioning that in highly productive fish ponds, some DO may be lost to the atmosphere through oxygen supersaturated surface waters.