The Phosphorus Cycle

Plants and animals need phosphorus for many biological processes

Phosphorus is a major component of DNA, RNA and ATP (adenosine triphosphate, the molecule cells use for energy transfer)

Phosphorus is a limiting nutrient (especially in aquatic environments) next to nitrogen because it’s important for successful agricultural yields

Phosphorus not having a gas phase limits the movement of phosphorus from the ocean back to terrestrial and freshwater environments making it a limiting nutrient.

Phosphorus is commonly added to soils in form of fertilizer

Phosphorus cycle - movement of phosphorus around the biosphere among sources and sinks

Primarily operates between land and water

Major reservoir: collection of rocks and sediments comprised of phosphorus-containing minerals

No gas phase but does enter atmosphere in very small amounts when dust is dissolved

Lack of gas limits the movement of phosphorus from the ocean back to terrestrial and freshwater environments, which is why it is a limiting nutrient

Phosphorus rarely changed its form

Typically found in the form of phosphate (PO4-3)

Processes: Assimilation, mineralization, sedimentation, geologic uplift, weathering

Assimilation: Plants and animals on land take up inorganic tissues and assimilate it as organic phosphorus

Waste products & eventual dead bodies of organisms are decomposed by fungi and bacteria causing the mineralization of organic phosphorus back into inorganic phosphorus

Sedimentation: Due to poor solubility, much of the phosphorus precipitates out as sediment in the ocean

Geological Uplift: over time, geological forces can lift ocean sediment layers up as mountains

Weathering: breaking down or dissolving of rocks and minerals on the surface of the Earth which results in phosphorus being brought to terrestrial and aquatic habitats

Humans mine the phosphate sediments that are found in the geologically uplifted mountains to produce fertilizer

The use of fertilizers increases the leaching of phosphorus into waterways causing a rapid increase in algal population - algal bloom (some produce harmful toxins)

As algae die, their decomposition consumes a lot of oxygen, creating a dead zone where aquatic animals can no longer survive.

There is virtually no phosphorus found in the atmosphere because soil conditions do not allow bacteria to convert chemical forms of phosphorus into gaseous forms

the level of phosphorus in soil often limit plant growth on land and in many freshwater streams and lakes because most soils contain little phosphate unless phosphorus is applied to the ground in soil, and in water, phosphate salts are only slightly soluble in water so not much is available to aquatic plants

How do humans alter the phosphorus cycle?

• Mine large quantities of phosphate rock to make commercial inorganic fertilizers. 

• We reduce the available phosphate in soils due to agriculture or forestry practices 

• We disrupt aquatic system with phosphate from runoff of animal wastes and fertilizers and discharges from sewage treatment systems.

• What are the consequences of these human effects?

  • Acid mine drainage/ tailings/ habitat destruction

  • Loss of nutrient reduces overall plant growth

  • Increase in hypoxic zones