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Oxygen Depletion

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Michigan Environmental Education Curriculum
Water Quality - Pollutant Sources and Impacts

Microbes and higher plants and animals obtain the energy stored in the chemical bonds of organic matter, C(H2O), through the process of respiration:

C(H2O) + O2 Changes CO2 + H2O + Energy

Organisms that depend on others to produce that organic matter are called heterotrophs (or other-feeders). Examples of heterotrophs include bacteria, fungi and even people! We tap into the sun’s energy when we eat organic matter (e.g. pizza) and breathe in oxygen and then breathe back out carbon dioxide and water vapor.

If there is too much organic matter in a lake or river, oxygen can be consumed by bacterial respiration faster than it is re-supplied from the atmosphere. This can lead to oxygen depletion and fish kills. In rivers, oxygen depletion takes a special form called the dissolved oxygen sag curve. The oxygen concentration in the river drops rapidly following the discharge of a waste containing organic matter. Later, as the organic matter becomes used up, the oxygen resources of the river are replenished.

Oxygen Sag Curve

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