The Phosphorus Cycle

In the phosphorous cycle, phosphorous atoms exist primarily in rock, not a gaseous state. When rock erodes, the phosphorous is released and becomes dissolved in streams, lakes and ground water.

Plants and algae use these free inorganic phosphates in the soil or water to produce organic molecules. Then by consuming the plants, heterotrophs tap into the phosphorous stores to build their own compounds. When organisms die, decomposers break up the phosphorous molecules and release inorganic phosphate to be used again by plants and algae, a process called phosphate mineralization.

While phosphates cycle quickly through organisms in the food chain, they have a longer residence time in water. Dissolved phosphate ions react to form insoluble compounds that precipitate in the ocean and become sediment, then rock, and as result of tectonic uplift, eventually return to the environment.

However, since the amount of phosphorous is limited in the environment, it must be provided to agricultural crop plants as fertilizer to get maximum yield. Excess phosphorous becomes run-off in aquatic ecosystems resulting in a variety of environmental problems such as algal blooms.