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The Phosphorus Cycle

Phosphorus normally occurs in nature as part of a phosphate ionAn atom, molecule or compound that carries either a positive (cation) or negative (anion) electrical charge., consisting of a phosphorus atom and some number of oxygen atoms, the most abundant form (called orthophosphate) having four oxygen: PO43-. Most phosphatesA salt or ester of a phosphoric acid,
an organic compound of phosphoric acid in which the acid group is bound to nitrogen or a carboxyl group in a way that permits useful energy to be released (as in metabolism),
a nutrient used in fertilizers.
are found as salts in ocean sedimentsSolid material that has been or is being eroded, transported, and deposited. Transport can be due to fluvial, marine, glacial or aeolian agents. or in rocks. Over time, geologic processes can bring ocean sediments to land, and weathering will carry terrestrial phosphatesA salt or ester of a phosphoric acid,
an organic compound of phosphoric acid in which the acid group is bound to nitrogen or a carboxyl group in a way that permits useful energy to be released (as in metabolism),
a nutrient used in fertilizers.
back to the ocean. Plants absorb phosphates from the soil. The plants may then be consumed by herbivores who in turn may be consumed by carnivoresAn organism that eats only the meat of other organisms.. After death, the animal or plant decays, and the phosphates are returned to the soil. RunoffThe topographic flow of water from precipitation to stream channels located at lower elevations. Occurs when the infiltration capacity of an area's soil has been exceeded. It also refers to the water leaving an area of drainage. Also called overland flow. 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 nucleotidesChemical compounds that consists of a heterocyclic base, a sugar, and one or more phosphate groups. The monomers of nucleic acids, with three or more bonding together in order to form a nucleic acid.
Nucleotides are the structural units of RNA, DNA
, which serve as energy storage within cells (ATP) or when linked together, form the nucleic acidsIs an organic compound composed primarily of different combinations of carbon, hydrogen, nitrogen, oxygen, and phosphorus. They are very complex compounds being created by the atomic linking of thousands of individual atoms. DNA or deoxyribonucleic acid, the genetic blueprint of life, is an example of a nucleic acid. DNA and RNA. Phosphorus is also found in bones, whose strength is derived from calcium phosphate, and in phospholipids (found in all biological membranes). Recent science indicates that phosphorous is the limiting nutrient for cyanobacteriaBacteria that have the ability to photosynthesize. algae and dynoflagelattes affecting such phenomena as Red Tide.

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 slowest biogeochemical cycles.

The Phosphorus Cycle

Source: Norman Hopkins 2006 (image 800x640)

Note: "Harvesting breaks up the natural cycle because it removes phosphorus from the Land" David A. Vaccari - Scientific American, June 2009

Phosphorus in Fertilizers

Together with Nitrogen and potassium, phosphorus is used in fertilizers both domestically and for farming. Fertilizer use is the major use for mined phosphorus, which consumes the mineral faster than the natural cycle is able to deliver it. The three countries producing most of the world's supply of phosphorus are China, the United States and Morocco. By the end of the century it is estimated that phosphorus supplies are likely to become a scarce resource. Although rising market prices could stimulate research to find new sources, and render more sources economic to produce and market, it will become necessary to use supplies more efficiently to stretch out available resources.

Increases in efficiency of use should become available from capture and recycling from waste, for example, where human and animal urine content is currently flushed away to the land. Changes in agricultural and forestry practices could limit phosphorus losses, for example, through soil erosion. Plowing back inedible harvested plant parts to the soil would conserve phosphorus.

Introduction of contaminants (heavy metals) into waste could be avoided so that more phosphorus may be recovered from contaminant free waste. As excess fertilizer runs off the land to contaminate ground water supplies, harmful algae blooms accelerate and submersed aquatic vegetation thrives in connected waterways. Control methods cause decay which depletes supply of dissolved oxygen needed for growth of microorganisms, prejudicing the productive capacity of the entire food chain. More efficient application of fertilizers could conserve phosphorus by reducing the excess quantities in the run off.

These and other methods to conserve phosphorus will only come from creative thinking and an awareness of the need, as that becomes more urgent with passing time .

Useful Links:
Phosphorus Cycle
U.S. Environmental Protection Agency, The Phosphorus Cycle
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