Environmental Studies(ES)

ENVIRONMENTAL STUDIES

Lesson 10: Bio-geo-chemical cycles

Sulphur cycle

Sulphur is present normally as sulphates or sulphides. Sulphur cycle links soil, water and air. Under anaerobic conditions, organic sulphur is converted into sulfide, which gets oxidized under aerobic conditions. This sulphur dioxide is converted into sulphates or sulphides due to the atmospheric oxygen. Part of the sulphur dioxide dissolves in water to form sulphuric acid. Plants absorb organic sulfur from sulphates. It travels from primary consumers to decomposers which will be fixing this sulfur in the soil. This completes the sulphur cycle. Green bacteria are able to oxidize sulphide to elemental sulphur, where as purple sulphur bacteria can carry oxidation to sulphate stage. In the ecosystem sulphur is transferred from autotrophs to animals, then to decomposers and finally it returns to environment through death and decay of dead organisms .

The bio-geo chemical cycles are of two varieties – sedimentary and gaseous cycles, which recycle nutrients in the ecosystem. Both cycles involve the biotic and abiotic systems. Both are driven by the flow of energy and both are tied up with the water cycle or the hydrologic cycle. In the ecosystem, all are vicious cycles through which nutrients are transferred from autotrophs to animals, then to decomposers and finally it returns to environment through death and decay of dead organisms.