Sulphur Cycle
The Sulphur reservoir is in the soil and sediments where it is locked in organic (coal, oil and peat) and inorganic deposits (pyrite rock and Sulphur rock) in the form of sulphates, Sulfide and organic Sulphur.
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It is released by weathering of rocks, erosional runoff and decomposition of organic matter and is carried to terrestrial and aquatic ecosystems in salt solution.
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The Sulphur cycle is mostly sedimentary except two of its compounds hydrogen Sulfide (H2S) and Sulphur dioxide (SO2) add a gaseous component to its normal sedimentary cycle.
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Sulphur enters the atmosphere from several sources like volcanic eruptions, combustion of fossil fuels, from surface of ocean and from gases released by decomposition. Atmospheric hydrogen Sulfide also gets oxidized into Sulphur dioxide. Atmospheric Sulphur dioxide is carried back to the earth after being dissolved in rainwater as weak Sulfuric acid.
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Whatever the source, Sulphur in the form of sulphates is taken up by plants and incorporated through a series of metabolic processes into Sulphur bearing amino acid which is incorporated in the proteins of autotroph tissues.
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It then passes through the grazing food chain.
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Sulphur bound in living organism is carried back to the soil, to the bottom of ponds and lakes and seas through excretion and decomposition of dead organic material.