Biogeochemical Cycles: Sulfur

By John Tortella and Larry Choi

What is a Biogeochemical Cycle?

• The pathways through which minerals cycle throughout both the biotic (biosphere) and abiotic (lithosphere, atmosphere and hydrosphere) ecospheres of the earth.

What is Sulfur?• It is element number 16 on the periodic table, denoted with the

symbol “S”• It is a non-metal and at standard temperature and pressure (STP),

Sulfur is a bright yellow crystalline solid.• It is found in every living cell and two amino acids: cysteine and

methionine, making it an essential element for life.• It's a component of vitamin B1 and biotin, the antioxidant

glutathione, the anticoagulant heparin, and coenzyme A, which drives energy production in cells. Sulfur is also a part of the biological cement which forms skin, hair, nails, and the cartilage that shapes the nose and pads in joints.

• It is present in the atmosphere mainly from the burning of fossil fuels and volcanic emissions.

Sulfur Cycle

Pathway of Movement

• Sulfur is emitted into the atmosphere primarily through volcanoes and energy production (through the burning of coal and other fossil fuels)

• Through acid rain containing sulfuric acid, sulfur enters the ocean (Hydrosphere) and soil (Lithosphere).

• From the soil, plants absorb sulfur, in turn, the plants are consumed by animals (meaning the sulfur returns to the Biosphere).

• When plants and animals die sulfur is returned into the soil through decomposition.

• The sulfur eventually makes its way back into rocks and the magma erupted by volcanoes or is extracted by humans.

Common Sources of uptake of Sulfur for Humans

• Egg yolks, garlic, cauliflower, cabbage, horseradish, meat, fish, and onion.

Chemical Reactions Involved

• Most of the sulfur emissions in the atmosphere come from the burning of coal or other petroleum fossil fuels in the form of sulfur dioxide gas (SO2). The SO2 reacts with water to form sulfuric acid, which falls as acid rain. These concentrations are usually greatest in industrial areas and are affected by wind and weather patterns.

• Incomplete combustion of a Hydrocarbon: Fuel + Air -> Heat + Water + Carbon Dioxide + Sulfur Dioxide

• Chemical processes involving Sulfur in the atmosphere can also help to produce hydrogen

Organic Reservoirs

• Plants• Soil• Animals• Fossil Fuels

Inorganic Reservoirs

• Freshwater• Salt Water/Oceans• Sediment• Volcanoes

Impact of Human Intervention

• The burning of coal, natural gas, petroleum and other fossil fuels has led to significant increases in the amount of sulfur in the atmosphere.

• Due to human intervention, sulfur is being drilled, pumped and burned at a steadily increasing rate, increasing sulfate deposition/pollution. Otherwise, without human impact, sulfur stays in rocks for millions of years until it is extracted by tectonic events, eventually becoming released through erosion and other weathering processes.

Effects of the Increased Sulfur in the Atmosphere

• Burning of fossil fuels ultimately leads to acid rain which is bad because its low pH (of about 4) can cause damage to surfaces on the earth’s surface.

• Benefits are that Sulfur has various great medicinal uses and is essential to the health of all living things.