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The Sulphur Cycle


The Sulphur Cycle
The sulphur cycle is one of many biochemical processes where a chemical element or compound moves through the biotic and abiotic compartments of the Earth, changing its chemical form along the way. As with both the carbon and nitrogen cycles, sulphur moves between the biosphere, atmosphere, hydrosphere and lithosphere (the rigid outer layer of the Earth). In biology, the water, oxygen, nitrogen, carbon, phosphorus and sulphur cycles are of particular interest because they are integral to the cycle of life.

Sulphur, which is present in the amino acids cysteine and methionine as well as the vitamin thiamine, is a vital part of all organic material. Plants acquire their supply from microorganisms in the soil and water, which convert it into usable organic forms. Animals acquire sulphur by consuming plants and one another. Both plants and animals release sulphur back into the ground and water as they die and are them selves broken down by microorganisms. This part of the cycle can form its own loop in both terrestrial and aquatic environments, as sulphur is consumed by plants and animals and then released again through decomposition.
But this isn’t the only iron that sulphur has in the fi re. Elemental sulphur is found around volcanoes and geothermal vents, and when volcanoes erupt, massive quantities of sulphur, mostly in the form of sulphur dioxide, can be propelled into the atmosphere.
Weathering of rocks and the production of volatile Sulphur compounds in the ocean can also both lead to the release of sulphur. Increasingly, atmospheric Sulphur is a result of human activity, such as the burning of fossil fuels. Once in the air, the Sulphur dioxide reacts with oxygen and water to form sulphate salts and sulphuric acid. These two compounds dissolve well in water and may return to Earth’s surface via both wet and dry deposition. Of course, not all the sulphur is getting busy; there are also vast reservoirs in the planet’s crust as well as in oceanic sediments.

Sulphur and the climate
Human activities like burning fossil fuels and processing metals generate around 90 per cent of the sulphur dioxide in the atmosphere. This sulphur reacts with water to produce sulphuric acid and with other emission products to create sulphur salts. These new compounds fall back to Earth, often in the form of acid rain. This type of acid deposition can have catastrophic effects on natural communities, upsetting the chemical balance of waterways, killing fish and plant life. If particularly concentrated, acid rain can even damage buildings and cause chemical weathering.
However, the environmental impact of sulphur pollution isn’t entirely negative; atmospheric sulphur contributes to cloud formation and absorbs ultraviolet light, somewhat offsetting the temperature increases caused by the greenhouse effect. In addition, when acid rain deposits sulphur in bodies of wetlands, the sulphur-consuming bacteria quickly out-compete methane-producing microbes, greatly reducing the methane emissions which comprise about 22 per cent of the human-induced greenhouse effect.
The Sulphur Cycle, Sulphur and the climate,

What is sulphur?
Sulphur is one of the most important and common elements on Earth. It exists in its pure form as a non-metallic solid and is also found in many organic and inorganic compounds. It can be found throughout the Earth’s environment, from the soil, air and rocks all the way through to plants and animals.
Because of its bright yellow colour, sulphur was used by early alchemists in their attempts to synthesise gold. That didn’t pan out, but people still found many useful applications for it, including making black gunpowder. Today sulphur and sulphur compounds are used in many consumer products such as matches and insecticides. Sulphur is also a common garden additive, bleaching agent and fruit preservative, and is an important industrial chemical in the form of sulphuric acid.
Early users mined elemental sulphur from volcanic deposits, but when the demand for Sulphur outstripped supply towards the end of the 19th century, other sources had to be found. Advances in mining techniques enabled the extraction of sulphur from the large salt domes found along the Gulf Coast of the United States.
Both volcanic and underground sulphur deposits still contribute to the global supply, but increasingly, industrial sulphur is obtained as a byproduct of natural gas and petroleum refi nery processes.