Dissolved Oxygen (Science Experiments)
How does a low level of dissolved oxygen affect the ecosystem in the water?
Goldfish Breath: How does a decrease in the dissolved oxygen level affect the breathing rate of goldfish?
What turns a body of water into a "dead zone" where nothing can live? One condition that can wipe out most living things in a stream, river, or lake is a low level of dissolved oxygenOxygen molecules that have dissolved in water.. The term dissolved oxygen refers to molecules of oxygen that have been dissolved in water. Some of these molecules enter the water from the surrounding air, especially if the water tumbles over falls and rapids. Other dissolved oxygen in the water is a "by-product" of . During photosynthesis, green plants, including those that live in the water, use the energy in sunlight to combine carbon dioxide and water to produce carbohydrates and oxygen. The oxygen is expelled by the plant and enters the water.
The level of dissolved oxygen in water can reach as high as 8 or 9 parts per million. The United States Environmental Protection Agency (EPA) considers water to be healthy if it contains at least 5 parts...
(The entire section is 4024 words.)
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Dissolved Oxygen (Encyclopedia of Public Health)
Dissolved oxygen is the amount of oxygen present in fresh water, such as a stream, or freshwater lake. A certain amount of dissolved oxygen is required to sustain fish, animals, and other aquatic life. Any decrease in dissolved oxygen can cause changes, usually negative, in an aquatic system. These include fish kills and loss of aquatic ecosystems. Changing aerobic conditions to anaerobic conditions can cause putrefactive decomposition, which creates sulfides, mercaptanes, and amines. In liquid wastes, the level of dissolved oxygen determines whether the biological changes are brought about by aerobic or by anaerobic organisms. Anaerobic conditions are generally considered undesirable because of the foul odors produced, such as that caused by hydrogen sulfide. Since both aerobic and anaerobic organisms exist in nature, it is important to maintain aerobic conditions in water.
Maintaining aerobic conditions is also important in natural bodies of water that receive potential pollutants. The transformation and decomposition of organic matter in water occur best under aerobic conditions due to the consumption and oxidation of organic substrates by aerobic microbes. The oxygen is replenished through several mechanisms, one being the simple diffusion of the oxygen from the atmosphere into the water. Additionally, aquatic plants and algae produce oxygen through photosynthesis and the natural movement of water.
The level of dissolved oxygen can decrease in several ways, primarily through increased aerobic microbial action. It can also decrease from increases in water temperature.
Dissolved oxygen determination serves many purposes. For example, it serves as the basis of the biological oxygen demand (BOD) test. These tests are used in the evaluation of domestic and industrial waste's capacity to pollute. Determining the residual dissolved-oxygen in a stream at various time intervals aids in the measurement of biochemical oxidation.
MARK G. ROBSON
(SEE ALSO: Ambient Water Quality; Biological Oxygen Demand; Water Quality)
Morgan, M. (1997). Environmental Health, 2nd edition. Englewood, CO: Morton Publishing Company.
Nadakavukaren, A. (2000). Our Global Environment, 5th edition. Prospect Heights, IL: Waveland Press.