EARTH SCIENCE > TERRESTRIAL HYDROSPHERE > WATER QUALITY/WATER CHEMISTRY > GASES > DISSOLVED OXYGEN
A colorless, odorless, gaseous element, constituting 21 percent of the volume of the atmsophere, and essential for aerobic forms of life. Gaseous oxygen has a chemical forumla of O2. Despite its abundance in air, the concentration of oxygen in water is usually quite low, at just a few parts per million. Nevertheless, this concentration is a good indicator of water quality. If it is too low, many organisms, including fish, will die.
Porteous, A. 1996. Dictionary of Environmental Science and Technology. John Wiley and Sons. p. 392. Websters College Dictionary. 1991. Random House.