Biogeochemical Cycles Poster

The Phosphorus Cycle

Rocks containing phosphate

Phosphorus circulates through water, the earth's crust, and living organisms. In contrast to all other cycles of water, carbon, and nitrogen, the phosphorus cycle does not include the atmosphere. A major reservior for phosphorus is phosphate salts containing phosphate ions (PO43-) in rock formations and ocean sediments. Phosphate is one molecule of phosphorus containing four molecules of oxygen, PO43-

Phosphorus is an important component in the backbone of DNA and RNA. Every organism needs this to build these structures and to transmit genetic information and synthesize proteins.

Plants can absorb phosphate directly through their roots.

Water runs over exposed phosphorus containing rocks as it slowly erodes away inorganic compounds that contain phosphate ions. A plant's roots can absorb the weathered phosphate from rocks. Plants uptake this through their roots and incorporate this into other animals. This phosphorus is transferred by food webs from producers to consumers like a moose, and eventually including detritus feeders and decompose-rs.


After the moos has eaten the plant matter, later on when the moos dies it's carcass will turn into inorganic phosphate. This in turn, is used for plants to take up back the phosphate, thereby completing the phosphorus cycle.

Phosphate can be lost from the cycle

When phosphate washes from the land into streams and rivers it is carried to the ocean. There it is deposited as marine sediment and remains trapped for millions of years. Human activities also affect the phosphorus cycle by removing large amounts of phosphate from the earth to make fertilizer. Soil can be eroded from fertilized crop fields and carry large quantities of phosphate into streams, lakes, and the ocean, where it stimulates the growth of producers. Phosphorus-rich runoff from the land can also produce huge populations of algae, which can upset the chemical cycling and other processes in lakes.