Oxygen - Aquatic Ecosystem

Oxygen is found in waters in dissolved form. It enters the aquatic ecosystem through the air water interface and by the photosynthetic activities of aquatic plants. Therefore, the quantity of dissolved oxygen present in an ecosystem depends on the rate at which these two processes occur. For example, the turbulence that occurs in waterfalls as well as wave activity that occurs in open water increase the rate of oxygen transfer from air to water (unless the water is already saturated with oxygen). The transfer of oxygen is also affected by the surface area of the waterway. A wide shallow section of a river has a larger surface area of oxygen transfer than a narrow deep segment. Further, the quantity of oxygen that is produced per unit area due to photosynthesis is related directly to the density of aquatic plants that are present in water.

Dissolved oxygen escapes the water body through air-water interface and through respiration of organisms (fish, decomposers, zooplanktons, etc). The amount of dissolved oxygen retained in water is also influenced by temperature as oxygen is less soluble in warm water. Warm water also enhances decomposer activity. Therefore, increasing the temperature of a water body increases the rite at which oxygen is depleted from water.