The Phosphorus Cycle

 The Phosphorus Cycle

Photo from :https://www.sciencedirect.com/topics/earth-and-planetary-sciences/phosphorus-cycle (K.C. Ruttenberg, in Encyclopedia of Ocean Sciences, 2001)

I. Introduction to Phosphorus

• Phosphorus is a major component of nucleic acids, phospholipids, and also makes up the supportive components of bones.

II. Natural Occurrence of Phosphorus

• Phosphorus occurs in nature as the phosphate ion (PO4 3-).
• Phosphate runoff can occur from human activities and natural surface runoff when phosphate-containing rock is weathered and leached into rivers, lakes, and the ocean.
• Phosphate-containing ocean sediments form from ocean organisms and volcanic ash, aerosols, and mineral dust, and are moved to land over geologic time by uplifting of the Earth's surface.

III. Reciprocal Exchange of Phosphorus

• Phosphorus is exchanged between phosphate dissolved in the ocean and marine organisms.
• The movement of phosphate from the ocean to land and through the soil is slow, with an average residence time in the ocean between 20,000 and 100,000 years.

IV. Human Impact on the Phosphorus Cycle

• Excess phosphorus and nitrogen from fertilizer runoff and sewage cause excessive growth of algae.
• The death and decay of these organisms depletes dissolved oxygen, leading to dead zones in lakes and at the mouths of rivers, causing harm to aquatic organisms.

V. Examples of Dead Zones

• Dead zones are areas of water bodies where aquatic life cannot survive because of low oxygen levels. Dead zones are generally caused by significant nutrient pollution, and are primarily a problem for bays, lakes and coastal waters since they receive excess nutrients from upstream sources. The number of dead zones has increased, with over 400 present as of 2008.
• The Gulf of Mexico, particularly the Mississippi River basin, has one of the worst dead zones measuring over 8,463 square miles.