SULFUR CYCLE

1. ESSENTIAL STEPS

1.1. 1. Mineralization of organic sulfur to the inorganic form, hydrogen sulfide H

1.2. 2. Oxidation of sulfide and elemental sulfur and related compounds to sulfate.

1.3. 3. Reduction of sulfate to sulfide

1.4. 4. Microbial immobilization of the sulfur compounds and subsequent incorporation into the organic form of sulfur.

2. RESERVOIR

2.1. found in the Earth's crust in gypsum and pyrite

2.2. found in the ocean as sulfate anions, dissolved hydrogen sulfide gas and elemental sulfur.

2.3. Freshwater

2.3.1. contains sulfate, hydrogen sulfide and elemental sulfur

2.4. Land

2.4.1. contain sulfate

2.5. Atmosphere

2.5.1. contains sulfur oxide and methane sulfonic acid ; volcanic activity releases some hydrogen sulfide into the air.

3. SOURCES

3.1. Inorganic sulfur

3.1.1. Sulfates

3.1.2. Sulfites

3.1.3. Thiosulfate

3.1.4. Sulfides

3.1.5. Sulfur fertilisers

3.1.6. Fossil fuels

3.1.7. Acid rains

3.2. Organic sulfur

3.2.1. Plant and animal residues

3.2.2. Amino acids

3.2.3. Volcano