Biology (B)

Biogeochemical Cycles

The chemical elements and water that are needed by organisms continuously recycle in ecosystems. They pass through biotic and abiotic components of the biosphere. That’s why their cycles are called biogeochemical cycles. For example, a chemical might move from organisms (bio) to the atmosphere or ocean (geo) and back to organisms again. Elements or water may be held for various periods of time in different parts of a cycle.

• Part of a cycle that holds an element or water for a short period of time is called an exchange pool. For example, the atmosphere is an exchange pool for water. It usually holds water (in the form of water vapor) for just a few days.
• Part of a cycle that holds an element or water for a long period of time is called a reservoir. The ocean is a reservoir for water. The deep ocean may hold water for thousands of years.

The rest of this lesson describes three biogeochemical cycles: the water cycle, carbon cycle, and nitrogen cycle.

CK-12 Foundation, Biology. http://creativecommons.org/licenses/by-nc-sa/3.0/