1.6 Phosphorus Cycle

What is the phosphorus cycle?

the movement of P atoms'/molecules between sources and sinks/reservoirs

What is a major reservoir for P containing minerals?

Rocks and sediments

Is the P cycle fast or slow? Why?

the P cycle is very slow compared to the other three cycles (N, C, H₂O).

This is because it takes a long time for P minerals to be weathered out of rocks and carried into the soil/H₂O

What effect does the P cycle have on plant growth?

P is a limiting nutrient to plant growth (controls plant growth) because it has a slow cycle.

Why is P crucial for our nutrients?

it is needed in every living animal because it is used in ATP, DNA, and even some bones and teeth

What is a major natural P source?

the natural weathering of rocks with P minerals

• broken down by wind/rain. rocks break down into phosphate (PO₄^-3) and release them/dissolve them into water (rain)

What is a major synthetic P source?

mining of phosphate minerals, adding it to fertilizers and detergents/cleaners

• lead to runoff and wastewater

Assimilation (P cycle)

P is absorbed by plant roots and into tissues

Animals eat plants/animals assimilated with P

same as assimilation from N cycle!

Excretion/Decomposition

animal waste/plant matter broken down by decomposers return phosphate into the soil

same as ammonification in N cycle!

Sedimentation

where phosphate forms solid bits that fall to the bottom of a body of water as sediment

the water’s pressure then turns the sediment into sedimentary rock

Geological Uplift

tectonic plate collisions force rock layers up to form mountains

resets the P cycle, refreshes weathering source

What happens in eutrophication?

When there is too much N and P (limiting nutrients), algae can quickly grow into an algae bloom

• algae blocks sunlight, killing aquatic plants beneath it

  • algae die off

    • bacteria use up all the oxygen in the water to decompose algae (aerobic process)

      • loss of oxygen kills fish

        • decomposers use more oxygen

          • eventually, a DEAD ZONE is formed

This is a positive feedback loop!