Sulphur is a component of certain proteins. It occurs in nature as an element and also as sulphate in soil, water, and rocks. It is an essential element for living organisms and plays a crucial role in many biological processes.
What is Sulphur Cycle?
The sulphur cycle is a biogeochemical cycle that describes the movement and transformation of sulphur in various forms within ecosystems. It can be defined as the process of transfer of sulphur between biosphere and geosphere.
Use and Release of Sulphur
The sulphur cycle begins with the weathering of rocks containing sulphur compounds, such as sulphides and sulphate minerals. Weathering of rocks releases these compounds are released into the soil and water. These compounds are assimilated by bacterial action and convert it into absorbable compounds.
Plants absorb it from the soil. Some plants have specialized root structures that allow them to absorb sulphate ions from the soil. Herbivores get organic sulphur from plant food and pass it on to carnivores. Some animals get sulphur from water as well.
Plants incorporate the absorbed sulphur into organic compounds through various metabolic processes. These compounds include amino acids, which are the building blocks of proteins, as well as vitamins and coenzymes. Sulphur is transferred up the food chain as animals consume plants.
Bacteria and fungi under aerobic conditions decompose dead plants and animals, excretory and fecal matter of animals to change organic sulphur to sulphates During decomposition, sulphur is released back into the environment in the form of inorganic compounds, such as hydrogen sulphide (H2S) or sulphate ions (SO42-). These sulfites are added to soil and water and reused by plants.
Under anaerobic conditions such as in marshes, some bacteria change organic sulphur to sulphides which is harmful to most organisms. But sulphur bacteria oxidize it to sulphates.
Soil and water also receive sulphates from rocks. Rainwater running over rocks gradually wears away these surfaces and carries off sulphur with it. Some of the sulphur leaks into the soil and some reaches ponds and lakes. A large part of it is carried by rivers to sea where it may get locked up in sedimentary rocks.
Wind may also erode the rocks and materials may be blown into the air as dust. Rain washes off a significant amount of this matter from the atmosphere into the oceans. Volcanic emissions also add sulphates to the soil and air. From the sea, sulphur returns to land through food chains and geological upheavals.
In aquatic ecosystems, sulphur compounds undergo chemical reactions and form hydrogen sulphide gas, which can be toxic to many organisms. However, certain bacteria called sulphur bacteria can oxidize hydrogen sulphide and convert it into sulphate, completing the cycle.
Another important process in the sulphur cycle is the combustion of fossil fuels, which releases sulphur dioxide (SO2) into the atmosphere. This gas can then react with water vapor to form sulfuric acid (H2SO4), contributing to acid rain. Sulphur can also be released into the atmosphere through volcanic eruptions.
Overall, the sulphur cycle involves the movement of sulphur between the atmosphere, lithosphere (rocks), hydrosphere (water bodies), and biosphere (living organisms). It plays a vital role in maintaining the balance of sulphur in ecosystems and is essential for the functioning of various biological processes.
References
- Shukla, R.S. and Chandel, P.S. (2001) Plant Ecology. S. Chand and Company Ltd., New Delhi.
- Verma, P.S., Agarwal, V.K. (1999). Cell biology genetics molecular biology evolution and ecology. New Delhi: S.Chand Co.(Pvt) Ltd.
- Libretexts. (2022b, December 24). 16.4F: The Sulfur Cycle. Biology LibreTexts.
