Similar term(s): Biogeochemical cycles, nutrient cycles.
A natural process in which elements are continuously cycled in various forms
between different compartments of the environment (e.g., air, water, soil,
Examples include the carbon, nitrogen and phosphorus cycles
(nutrient cycles) and the water cycle.
The carbon cycle includes the
carbon dioxide by plants through, its
ingestion by animals and its release to the atmosphere through respiration and
decay of organic materials. Human activities like the burning of fossil fuels
contribute to the release of carbon dioxide in the atmosphere.
The nitrogen cycle involves the uptake of nitrogen form the
atmosphere by a process called fixation which is carried out by microbes or
industrial processes. Decomposition of biological waste by microbes can return
nitrogen to the atmosphere. Nitrogen is mainly used by humans as a fertilizer in
farmlands, but its excessive usage can lead to serious problems (such as
The phosphorus cycle involves the uptake of phosphorus by
organisms. Phosphorus in the environment is mainly found in rocks, and natural
weathering processes can make it available to biological systems. After
decomposition of biological waste, it can accumulate in large amounts in soils
and sediments. Phosphorus is used by humans as a fertilizer in farmlands and in
detergents. Overuse of phosphorus can lead to eutrophication.
The water cycle is the process by which water travels in a
sequence from the air (condensation) to the earth (precipitation) and returns to
the atmosphere (evaporation). It is also referred to as the hydrologic cycle.
Human use of water can transform the water cycle through irrigation or the
construction of dams, for example.
Ecosystem(s) - Nutrients
To read about this term in context:
GreenFacts Summary on Ecosystem Change:
Español: Ciclo medioambiental
Français: Cycle naturel