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The amount of oxygen that dissolves in water can vary in daily and seasonal patterns, and decreases with higher temperature, salinity, and elevation. The maximum solubility of oxygen in water at 1 atm pressure (standard air pressure at sea level) ranges from about 15 mg/L at 0ºC to 8 mg/L at 30ºC—that is, ice-cold water can generally hold twice as much dissolved oxygen as warm water. This is key during summer months,
Dissolved oxygen comes from the atmosphere and from photosynthesis by aquatic plants, and is depleted through chemical oxidation and respiration by aquatic animals and microorganisms. Typically DO2 levels fall during nightfall until sunrise and photosynthesis commences.
The graph (1) shows typical pond levels and trigger point for turning on Aeration.
Deeper water receives oxygen through mixing by wind, currents, and inflows. Mixing and aeration also occurs at waterfalls and water inlets.
Dissolved oxygen can be reduced to very low levels during the winter months when water and en-trained gases are trapped under ice. Aeration via diffusers can help keep areas free from ice and release gases.