Phosphorus Cycle

Phosphorus Cycle

The Phosphorus Cycle

The phosphorus cycle describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike other major biogeochemical cycles, phosphorus does not have a significant atmospheric component.

• Phosphorus Forms: Phosphorus is found primarily as phosphate ions (PO43-) in rocks and soil.

• Weathering of Rocks: The main source of phosphorus is the weathering of rocks, which releases phosphate into the soil and water.

• Absorption by Plants: Plants absorb phosphate ions from the soil, incorporating them into organic molecules such as nucleic acids and ATP.

• Consumption by Animals: Animals obtain phosphorus by eating plants or other animals. Phosphorus is essential for bones, teeth, and cellular energy transfer.

• Return to Soil: When plants and animals die, decomposers break down organic matter, returning phosphate to the soil.

• Aquatic Transfer: Some phosphate is carried by runoff into aquatic systems, where it can be used by aquatic organisms or settle as sediment.

• Geological Uplift: Over millions of years, geological processes can uplift phosphate-rich sediments, exposing them to weathering and restarting the cycle.

• Human Impact: Activities such as agriculture and the use of fertilizers can increase phosphorus runoff, leading to eutrophication in aquatic systems.

Key Points:

• Phosphorus is a limiting nutrient in many ecosystems due to its low natural availability.

• Unlike nitrogen and carbon, phosphorus does not cycle through the atmosphere.

• Human activities can accelerate phosphorus loss from soil and increase its input to water bodies.

Example: Excess phosphorus from agricultural runoff can cause algal blooms in lakes, which deplete oxygen and harm aquatic life.

Diagram: The Phosphorus Cycle

The diagram in the notes illustrates the following steps:

• Weathering of rocks releases phosphate into soil and water.

• Plants absorb phosphate; animals obtain it by eating plants.

• Decomposition returns phosphate to soil.

• Runoff carries phosphate to aquatic systems, where it can settle as sediment.

• Geological uplift exposes new phosphate rocks.

Summary Table: Key Steps in the Phosphorus Cycle

Step	Description
Weathering	Phosphate released from rocks into soil and water
Absorption	Plants absorb phosphate ions from soil
Consumption	Animals eat plants, obtaining phosphorus
Decomposition	Organic phosphorus returned to soil by decomposers
Runoff	Phosphate carried to aquatic systems
Sedimentation & Uplift	Phosphate settles as sediment; geological uplift exposes new rock

Additional info:

• Phosphorus is a key component of DNA, RNA, and ATP, making it essential for all living organisms.

• Unlike nitrogen and carbon cycles, the phosphorus cycle is much slower due to the lack of a gaseous phase.