Question

Which of the following are examples of the sedimentary biogeochemical cycle?
A) Nitrogen cycle
B) Carbon cycle
C) Sulphur cycle
D) Phosphorous cycle
Select the correct answer using the code given below

1. A and B
2. C and D
3. A, B, C
4. A, C, D

Answer 1

Correct Answer - Option 2 : C and D

The correct answer is C and D.

• Organisms need a constant supply of nutrients to grow, reproduce and regulate various body functions. The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc., present in the soil at any given time, is referred to as the standing state. It varies in different kinds of ecosystems and also on a seasonal basis.
• Nutrients are never lost from the ecosystems, rather they are recycled time and again indefinitely. The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling.
• Another name of nutrient cycling is biogeochemical cycles (bio: living organism, geo rocks, air, water).

 

Nutrient cycles are of two types

1. Gaseous- the reservoir for the gaseous type of nutrient cycle (e.g., nitrogen, carbon cycle) exists in the atmosphere
2. Sedimentary- for the sedimentary cycle (e.g., sulfur and phosphorus cycle), the reservoir is located in Earth‟s crust.

• Environmental factors, e.g., soil, moisture, pH, temperature, etc., regulate the rate of release of nutrients into the atmosphere. The function of the reservoir is to meet with the deficit which occurs due to an imbalance in the rate of influx and efflux.

Other cycles-

1. Water Cycle-

• The hydrologic cycle is the continuous circulation of water in the Earth-atmosphere system which is driven by solar energy. Water on our planet is stored in major reservoirs like atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, and groundwater. Water moves from one reservoir to another by the processes of evaporation, transpiration, condensation, precipitation, deposition, runoff, infiltration, and groundwater flow.
• Water as an important ecological factor determines the structure and function of the ecosystem. Cycling of all other nutrients is also dependent upon water as it provides their transportation during the various steps. It acts as a solvent medium for their uptake of nutrients by organisms.

     

      2. Carbon Cycle-

• Carbon is a minor constituent of the atmosphere as compared to oxygen and nitrogen. However, without carbon dioxide life could not exist, because it is vital for the production of carbohydrates through photosynthesis by plants. It is the element that anchors all organic substances from coal and oil to DNA (deoxyribonucleic acid the compound that carries genetic information).
• Carbon is present in the atmosphere, mainly in the form of carbon dioxide (CO2). Carbon cycle involves a continuous exchange of carbon between the atmosphere and organisms. Carbon from the atmosphere moves to green plants by the process of photosynthesis, and then to animals. By process of respiration and decomposition of dead organic matter returns back to the atmosphere. It is usually a short term cycle.
• Some carbon also enters a long term cycle. It accumulates as un-decomposed organic matter in the peaty layers of marshy soil or as insoluble carbonates in bottom sediments of aquatic systems which take a long time to be released.
• In deep oceans, such carbon can remain buried for millions of years till geological movement may lift these rocks above sea level. These rocks may be exposed to erosion, releasing their carbon dioxide, carbonates and bicarbonates into streams and rivers.
• Fossil fuels such as coals, oil and natural gas etc. are organic compounds that were buried before they could be decomposed and were subsequently transformed by time and geological processes into fossil fuels. When they are burned the carbon stored in them is released back into the atmosphere as carbon dioxide.

 

      3. Nitrogen Cycle-

• Nitrogen is an essential constituent of protein and is a basic building block of all living tissue. It constitutes nearly 16% by weight of all the proteins that is, converted to ammonia, nitrites or nitrates before it can be taken up by plants.
• Nitrogen fixation on earth is accomplished in three different ways:
  a) By microorganisms (bacteria and blue-green algae)
  b) By man using industrial processes (fertilizer factories) and
  c) To a limited extent by atmospheric phenomena such as thunder and lighting
• Certain microorganisms are capable of fixing atmospheric nitrogen into ammonium ions. These include free-living nitrifying bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguminous plants and symbiotic bacteria living in non-leguminous root nodule plants (e.g. Rhizobium) as well as blue-green algae (e.g. Anabaena, Spirulina).
• Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialised bacteria: Nitrosomonas bacteria promote the transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.
• The nitrates synthesised by bacteria in the soil are taken up by plants and converted into amino acids, which are the building blocks of proteins. These then go through higher trophic levels of the ecosystem. During excretion and upon the death of all organisms nitrogen is returned to the soil in the form of ammonia.
• Certain quantities of soil nitrates, being highly soluble in water, are lost to the system by being transported away by surface run-off or groundwater. In the soil as well as oceans there are special denitrifying bacteria (e.g. Pseudomonas), which convert the nitrates/nitrites to elemental nitrogen. This nitrogen escapes into the atmosphere, thus completing the cycle.
• The periodic thunderstorms convert the gaseous nitrogen in the atmosphere to ammonia and nitrates which eventually reach the earth’s surface through precipitation and then into the soil to be utilized by plants.

 

      4. Phosphorus Cycle-

• Phosphorus plays a central role in aquatic ecosystems and water quality. Unlike carbon and nitrogen, which come primarily from the atmosphere, phosphorus occurs in large amounts as a mineral in phosphate rocks and enters the cycle from erosion and mining activities. This is the nutrient considered to be the main cause of excessive growth of rooted and free-floating microscopic plants in lakes.

 

• The main storage for phosphorus is in the earth’s crust. On land, phosphorus is usually found in the form of phosphates. By the process of weathering and erosion, phosphates enter rivers and streams that transport them to the ocean.
• In the ocean, once the phosphorus accumulates on continental shelves in the form of insoluble deposits. After millions of years, the crustal plates rise from the seafloor and expose the phosphates on land. After more time, weathering will release them from rock and the cycle’s geochemical the phase begins again.

 

       5. 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, sulphides and organic sulphur.
• It is released by weathering of rocks, erosional runoff and decomposition of organic matter and is carried to terrestrial and aquatic ecosystems in a salt solution.
• The sulphur cycle is mostly sedimentary except two of its compounds hydrogen sulphide (H2S) and sulphur dioxide (SO2) add a gaseous component to its normal sedimentary cycle.
• Sulphur enters the atmosphere from several sources like volcanic eruptions, combustion of fossil fuels, from the surface of the ocean and from gases released by decomposition. Atmospheric hydrogen sulphide also gets oxidised into sulphur dioxide.
• Atmospheric sulphur dioxide is carried back to the earth after being dissolved in rainwater as weak sulphuric acid.