Sulphur Cycle Types: 2 Major Types of Sulphur Cycle | Environment

This article throws light upon the two major types of Sulphur Cycle. The types are:- 1. Gaseous Sulphur Cycle 2. Sedimentary Sulphur Cycle.

Sulphur Cycle Type # 1 . Gaseous Sulphur Cycle:

Sulphur enters the atmosphere through bacterial emission (H₂S), fossil fuel burning (SO₂), wind-blown sea salts (SO ^2-₄) and volcanic emissions (H₂S, SO₂, SO^2-₄).

Most of the sulphur in the form of SO₂ or H₂S is converted to SO₃ which dissolves in water droplets to form sulphuric acid.

The sulphur cycle is overloaded due to burning of fossil fuels.

As a result, SO₂ emitted into the atmosphere constitutes a significant fraction of total global sulphur transport. This increased amount of sulphur is changed to sulphuric acid in rain water causing adverse ecological effects.

Sulphur Cycle Type # 2. Sedimentary Sulphur Cycle:

In sedimentary phase, sulphur tied up in inorganic and organic deposits is released by weathering and decomposition. Sulphur so released as SO^2-₄ ion is carried to terrestrial and aquatic ecosystems. Sulphate ion is reduced after being absorbed from the soil by plants and bacteria and ultimately incorporated as the sulphydryl group (-SH) in proteins. SO

Some sulphates are reduced under anaerobic conditions directly to sulphides, H₂S or to elemental S by Desulphovibrio bacteria found at ocean bottom. H₂S thus produced escapes into the air and replenishes the sulphur lost by precipitation. H₂S is also oxidised by O₂ to sulphates by bacteria of genus Thiobacillus. Excess of sulphur combines with water resulting in acidic rain.