What factors affect dissolved oxygen?
The air is one source of dissolved oxygen, and aquatic plants, including algae, are another. The speed at which oxygen from the air enters and mixes through a waterbody depends on the amount of agitation at the water surface, the depth of the waterbody and the rate at which it mixes itself. As water temperature rises, oxygen diffuses out of the water into the atmosphere. Shallow flowing waterways usually have high dissolved oxygen concentrations. In still waters, such as lakes, dissolved oxygen concentrations often vary from the surface to the bottom, with little dissolved oxygen in the deep, poorly mixed, layers. Warm or saline water holds less dissolved oxygen than cold water or freshwater (see Table 4.6).
