NUTRIENT CYCLE - CARBON CYCLE or C CYCLE

CARBON CYCLE

1.     The Biosphere contains a complex mixture of carbon compounds in a dynamic equilibrium of Formation, Transformation And Decomposition. 

2.     The producers, through the process of Photosynthesis, reduce the carbon dioxide from the atmosphere to organic carbon.

3.     This then passes through consumers and decomposers, then usually re-enters the atmosphere through respiration and decomposition.

4.     Additional return from producers and consumers occur through the non - biological process of combustion.

5.     Even though the amount of CO₂ in the atmosphere is of major concern, in fact, the atmosphere reservoir for carbon is the smallest and the oceans hold the largest amount, serving as a vast “sink” for CO₂ .

6.     Apart from the daily production and consumption of carbon, the earth has significant reserves of bound carbon in the form of inorganic deposits such as limestone and organic fossil fuel deposits consisting of mainly coal and petroleum.

7.     Due to the combustion of fossil fuels, weathering and dissolution of carbonate rocks, and volcanic activity, some of the bound carbon returns to the atmospheric aquatic reservoir as carbon dioxide or carbonic acid.

Typically reservoirs for carbon (expressed in billion tonnes)² are :

•  Oceans – 40,000
•  Fossil Fuels, Rocks and Minerals – 5,000-10,000
• Vegetation and Soil – 2,000
• Atmosphere – 750

Thus, the oceans store more than 50 times as much as the atmosphere. Human activity releases roughly 7.0 billion tonnes of carbon (in the form of CO₂) into the atmosphere every year. This is a small amount compared to that held by the atmosphere, and an even smaller figure compared with that held in the oceans. Out of the 7.0 billion tonnes, only 3.0 billion tonnes accumulate in the atmosphere and the rest is taken up by the Oceans and the Terrestrial plants. The exact mechanism by which the sea water interacts with the air above it to remove CO₂ is not clearly understood but the Oceanic reservoir tends to regulate the atmospheric CO₂ concentration.

Even though the net amount of 3.0 billion tonnes added to the atmosphere each year is a tiny fraction of the total held by the atmosphere, it assumes significance because the natural processes and the environment maintain a dynamic equilibrium whereas the human activity puts an additional burden on nature, thereby disrupting the delicate balance. Any global event that alters the exchange of CO₂ between the atmosphere and the ocean can significantly affect the concentration of CO₂ in the atmosphere.

Studies have shown that plants tends to grow faster in a CO₂ enriched atmosphere, but this benefit is offset by denudation of forests by man thereby decreasing nature’s ability to remove the excess CO₂ from the atmosphere. As a result, a detectable increase in the concentration of atmospheric CO₂ has been observed.

Reference Books :

Environmental Pollution Control Engineering, C.S. Rao .