The Sulfur Cycle

 The Sulfur Cycle

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Sulfur is an essential element for the macromolecules of living things and is involved in the formation of proteins.

Sources of Atmospheric Sulfur

• Atmospheric sulfur enters the atmosphere in three ways: decomposition of organic molecules, volcanic activity and geothermal vents, and burning of fossil fuels by humans.
• Sulfur dioxide (SO2) is the main form of atmospheric sulfur.

Deposition of Sulfur on Land

• Sulfur is deposited on land through precipitation, direct fallout from the atmosphere, rock weathering, and geothermal vents.
• Rainfall dissolves sulfur dioxide in the form of weak sulfuric acid (H2SO4), which can fall to the ground as acid rain.
• Sulfur can also fall directly from the atmosphere as fallout, and weathering of rocks releases sulfates into the soil.

Terrestrial Ecosystems and Sulfur

• Terrestrial ecosystems use soil sulfates (SO42-) taken up by plant roots.
• When plants decompose and die, sulfur is released back into the atmosphere as hydrogen sulfide (H2S) gas.

Sulfur in the Oceans

• Sulfur enters the ocean through runoff from land, atmospheric fallout, and underwater geothermal vents.
• Some ecosystems rely on chemoautotrophs using sulfur as a biological energy source.
• Sulfur in the ocean supports marine ecosystems in the form of sulfates.

Human Activities and the Sulfur Cycle

• Human activities, such as burning fossil fuels, release large amounts of sulfur dioxide into the atmosphere, leading to acid rain.
• Acid rain lowers the pH of lakes, damaging aquatic ecosystems and affecting the man-made buildings