1. Aim: What are the phosphorus and sulfur cycles?

2. General Facts about Phosphorus
Needed by living things for nucleic acid and ATP. Component of bones and teeth.
HAS NO ATMOSPHERIC FORM, but is released from rock through weathering and erosion and finds its way to bodies of water.
Inorganic phosphates (PO4-3 ) are absorbed by producers and are used to make organic phosphate compounds. (DNA, ATP, etc.)
Organic phosphate compounds move through the ecosystem via the food web.
Phosphate is returned to the environment via decomposition. If an organism leaves an ecosystem, it takes its phosphate with it!
Too much phosphate in the environment leads to eutrophication.
In some ecosystems, guano (bird manure) provides a convenient supply of concentrated phosphate.

3. Phosphorus Cycle

5. General Facts about Sulfur
Sulfur is found in the environment as H2S , SO2 , SO4-2 , and elemental S.
Sulfur is needed to make certain amino acids. Di sulfide bonds help stabilize certain proteins.
Sulfuric acid rain (H2SO4 ) affects the ecosystem’s pH.
Sulfur oxides (SO2 ) affect global climate. They block UV rays and prevent them from being converted into heat. Sulfur oxides are involved in global cooling and offset greenhouse gases.
Most sulfur is found in solid form in rocks such as iron disulfide (pyrite) and calcium sulfate (gypsum).
Sulfur is released into the air or water by the weathering and erosion of sulfur-containing rocks or by volcanic emissions.

6. General facts about sulfur (2)
Anaerobic bacteria in tidal flats, freshwater wetlands, and flooded soils convert sulfate (SO4-2 ) to H2S. (to the atmosphere) or metal sulfides (to the ground)
H2S can be used by anaerobic bacteria as a source of energy (deep sea vents). Aerobic bacteria convert it to sulfate again.
Certain marine algae create volatile DMS (dimethyl sulfate) which becomes airborne and seeds clouds.
Sea spray release sulfates into the air.
Desert dust contains high levels of calcium sulfate.

7. Sulfur Cycle

8. Summary Videos
Phosphorus cycle: =related
Sulfur cycle: