1.6 Phosphorous Cycle - APES

Phosphorous Cycle Basics

Movement of P atoms & molecules b/w sources & sinks/reservoirs

Rocks & sediments containing P minerals = Major reservoirs

P cycle is very slow compared to C/H₂O/N cycles

Takes a long time for P minerals to be weathered out of rocks & carried into soil/bodies of water

No gas phase of P (Doesn’t enter atmosphere)

• B/c it cycles so slowly, it is a limiting nutrient, meaning plant growth in ecosystems is often limited by P availability in soil/water

P IS NEEDED BY ALL ORGANISMS FOR DNA, ATP (ENERGY), BONE & TOOTH ENAMEL IN SOME ANIMALS

Phosphorus Sources

Major natural source of P is weathering of rocks that contain P minerals

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

• Weathering is so slow that P is often limiting nutrient in aquatic & terrestrial ecosystems 

Synthetic

(Human) sources of P = Mining phosphate minerals & adding to products like synthetic fertilizers & detergents/cleaners 

• Synthetic fertilizers containing phosphates are added to lawns or ag. → Fields; runoff carries P into nearby bodies of water → Phosphates from detergents & cleaners enter bodies of water via wastewater from homes

Assimilation & Excretion/Decomp. 

Just like N, P is absorbed by plant roots & assimilate into tissues; animals assimilate P by eating plants/other animals 

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

Assimilation & excretion/decomp form a mini-loop within P cycle just like assimilation & ammonification in N cycle, photosynthesis & rest. in C cycle 

Sedimentation and Geological Uplift

Phosphate doesn’t dissolve very well into water; much of it forms solid bits of phosphate that fall to the bottom as sediment (sedimentation)

P sediments can be compressed into sed. rock over a long time of periods by pressure of overlying water

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 (Too much N & P)

B/c they’re limiting nutrients in aq. ecosystems, extra input of N & P lead to eutrophication (Excess nutrients) which fuels algae growth

• Algae blooms → Covers Sunlight → Kills plants below that depend on sunlight

Creates Positive Feedback Loop: Less O₂ → More dead org. → More bacterial decompostion → Less O₂