Phosphorus cycle

Phosphorus cycle

The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movements of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth.

Phosphorus in the environment

Phosphorus is an essential nutrient for plants and animals in the form of ions PO43- and HPO42-. It is a part of DNA-molecules and RNA-molecules, molecules that store energy (ATP and ADP) and of fats of cell membranes. When Phosphorus is in a compound (phosphate), it plays an important role in holding the DNA and RNA together. [] Phosphorus is also a building block of certain parts of the human and animal body, such as the bones and teeth.

Phosphorus cycle is also known as a Sedimentary cycle because the cycle does not enter the atmosphere and stays in rock sediments, sand,and ocean floor. Where it is trapped until erosion occurs and the Phosphorus is released.

Phosphorus forms parts of important life sustaining molecules but is not very common in the biosphere. Phosphorous does not enter the atmosphere remaining mostly on land and in rock and soil minerals. 80 percent of the phosphorus is used to make fertilizers and a type of phosphorus such as dilute phosphoric acid is used in soft drinks. Phosphates may be effective in such ways but they also cause pollution problems in lakes and streams. Over enrichment of phosphate can lead to algal bloom, because of the excess of nutrients. This causes more algae to grow, bacteria consumes the algae and causes more bacteria to increase in numbers. They use all the oxygen in the water during cellular respiration, causing many fish to die.

Phosphorus normally occurs in nature as part of a phosphate ion, consisting of a phosphorus atom and some number of oxygen atoms, the most abundant form (called orthophosphate) having four oxygens: PO43-. Most phosphates are found as salts in ocean sediments or in rocks. Over time, geologic processes can bring ocean sediments to land, and weathering will carry terrestrial . Plants absorb phosphates from the soil, then bind the phosphate into organic compounds. The plants may then be consumed by herbivores who in turn may be consumed by carnivores. After death, the animal or plant decays, and the phosphates are returned to the soil. Runoff may carry them back to the ocean or they may be reincorporated into rock.

The primary biological importance of phosphates is as a component of nucleotides, which serve as energy storage within cells (ATP) or when linked together, form the nucleic acids DNA and RNA. Phosphorus is also found in bones, whose strength is derived from calcium phosphate, and in phospholipids (found in all biological membranes).

Phosphates move quickly through plants and animals; however, the processes that move them through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowestbiogeochemical cycles.

However, recent findings suggest that phosphorus is cycled through the ocean on the timescale of 10,000 year, suggesting that the phosphorus cycle may play a role in global warming.

Plants bind the phosphate into organic compounds. (Phosphate is not very common in biospheres)

Unlike other cycles of matter compounds, phosphorus cannot be found in air as a gas. This is because at normal temperature and circumstances, it is a solid inthe form of red and white phosphorus. It usually cycles through water, soil and sediments. Phosphorus is typically the limiting nutrient found in streams, lakes and fresh water environments. As rocks and sediments gradually wear down, phosphate is released. In the atmosphere phosphorus is mainly small dust particles.

Phosphorus is one of the longest cycles, and takes a long time to move from sediments to living organisms and back to sediments."'

Initially, phosphate weathers from rocks. The small losses in a terrestrial system caused by leaching through the action of rain are balanced in the gains from weathering rocks. In soil, phosphate is absorbed on clay surfaces and organic matter particles and becomes incorporated (immobilized). Plants dissolve ionized forms of phosphate. Herbivores obtain phosphorus by eating plants, and carnivores by eating herbivores. Herbivores and carnivores excrete phosphorus as a waste product in urine and feces. Phosphorus is released back to the soil when plants or animal matter decomposes and the cycle repeats.


* [ Part III of "Matter cycles": The phosphorus cycle, Lenntech Water treatment & air purification, Holding B.V. 2006]
* [ Environmental Literacy Council - Phosphorus Cycle]
* [ Monitoring and assessing water quality, section 5.6 Phosphorus - EPA]
* [ Prentice Hall Biology, Kenneth R. Miller and Joseph Levine 2001]
* [ Katie Corbin-Soil Microbiology]
* []

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