Phosphorus Cycle

Overview of Phosphorus cycle

Movement of Phosphorus atoms and molecules between sources and sinks

- ROCKS + SEDIMENT containing Phosphorus minerals = major sink/reservoir

Phosphorus cycle = SLOW compared to C/N cycle

- Long time for Phosphorus minerals to weather out of rocks/sediments and enter bodies of water

No gas phase of Phosphorus cycle

- Phosphorus = limiting nutrient -> plant growth restricted by phosphorus in the soil

Natural Sources of Phosphorus

1) weathering of rocks that contain P minerals

- Wind & rain break down rock & phosphate (PO4-3) is released and dissolved into water; rainwater carries phosphate into nearby soils & bodies of water

Note: Weathering is so slow that P is often a limiting nutrient in aquatic & terrestrial ecosystems

Synthetic Sources of Phosphorus

mining P minerals and adding P to synthetic fertilizers

- Synthetic fertilizers containing phosphates are added to lawns or agricultural fields;

- runoff carries P into nearby bodies of water

- P in detergents enter bodies of water via wastewater

Assimilation

P is absorbed by plant roots and assimilates into tissues,

assimilates into animal tissues when animals eat plants

Excretion/Decomposition

Animal waste, plant matter & other biomass is broken down by bacteria/soil decomposers that return phosphate to soil

Sedimentation

Phosphate doesn't dissolve very well into water -> much of it forms

solid bits of phosphate that fall to the bottom as sediment

(sedimentation),

- sediments are compressed and form rocks

Geological uplift

tectonic plate collision forcing up rock layers that form mountains; P cycle can start over again with weathering & release of phosphate from rock

Eutrophication

Because N/P are limiting nutrients in aquatic ecosystems, extra input from runoff and waste can lead to EUTROPHICATION (excess nutrients) -> which fuels algae growth

- ex. Algae bloom covers the surface of water,

blocking sunlight for deeper plants

- Algae eventually die-off; bacteria that break

down dead algae use up O2 in the water

- Lower O2 levels (dissolved oxygen) in water kills

aquatic animals, especially fish

- Bacteria use up even more O2 to decompose

dead aq. animals

- Creates positive feedback loop: less O2 →

more dead org. → more bacterial

decomposition → less O2