Aquatic ecology and Biodiversity

Unit 6- Biogeochemical cycles

6.2. Carbon cycle

Carbon is the basic constituent of living organisms. It is present as carbohydrates, fats, proteins and nucleic acids. In the atmosphere, it is present as CO₂ at the rate of 0.03 - 0.04 %. Cycling of carbon through a path of atmosphere, lithosphere, hydrosphere and biosphere is called the carbon cycle. The carbon cycle consists of two parts, the terrestrial and the aquatic carbon cycle. The aquatic carbon cycle is concerned with the movements of carbon through marine ecosystems and the terrestrial carbon cycle is concerned with the movement of carbon through terrestrial ecosystems
The process of oxygen generation is called photosynthesis. During photosynthesis, plants and other producers transfer carbon dioxide and water into complex carbohydrates, such as glucose, under the influence of sunlight. The oxygen that is produced during photosynthesis will sustain heterotrophic life forms or consumers, such as animals and most micro organisms. Carbon dioxide is released back into the atmosphere during respiration of consumers, which breaks down glucose and other complex organic compounds and converts the carbon back to carbon dioxide for reuse by plants. Carbon that is used by producers, consumers and decomposers cycles fairly rapidly through air, water and biota. But carbon can also be stored as biomass in the roots of trees and other organic matter in soil and ocean sediments for many decades. This carbon is released back into the atmosphere by decomposition
In the aquatic ecosystems, carbon dioxide can be stored in rocks, skeletons of living organisms, particularly corals and molluscs in the seas and sediments. Carbon dioxide that is present in water will be present as either carbonate or bicarbonate ions. These ions are an important part of natural buffers that prevent the water from becoming too acidic or too basic. When the sun warms up the water, carbonate and bicarbonate ions will be returned to the atmosphere as carbon dioxide.