The biogeochemical cycles of the biosphere relate to essential processes that take place within and between the major cells and organisms that make up living systems and that alter and shape them.
The word biogeochemical also implies the integration of the biological, geological, and chemical aspects of those cycles.
Biogeochemical cycles involve both organic and inorganic substances, including water as well as elements such as carbon, nitrogen, phosphorus, sulfur, and others.
The sun is the basic source of energy on which all life depends. This energy initiates life processes in the biosphere through photosynthesis, the main source of food and energy for green plants.
Out of the total solar insolation that reaches the earth’s surface, only a very small fraction (0.1 per cent) is fixed in photosynthesis.
Life on earth consists of a great variety of living organisms. These living organisms exist and survive in a diversity of associations. Such survival involves the presence of systemic flows such as flows of energy, water and nutrients.
Balance of the chemical elements is maintained by a cyclic passage through the tissues of plants and animals. The cycle starts by absorbing the chemical elements by the organism and is returned to the air, water and soil through decomposition.
These cycles are largely energised by solar insolation. These cyclic movements of chemical elements of the biosphere between the organism and the environment are referred to as biogeochemical cycles. There are two types of biogeochemical cycles –
The Water Cycle
The water cycle is the circulation of water on, above and below the surface of the Earth. It is also known as the hydrological cycle or the hydrologic cycle.
The repeating nature of this circulation process is driven by energy from the sun. This energy is absorbed by Earth’s land surface, warms it and evaporates water into the atmosphere.
Some evaporated water returns to Earth’s surface while some continues to rise into the sky.
All living organisms, the atmosphere and the lithosphere maintain between them a circulation of water in solid, liquid or gaseous form referred to as the water or hydrologic cycle
The Carbon Cycle
The Carbon Cycle is a complex chemical cycle of carbon found on Earth, which involves a change from one compound to others.
Carbon comprises the backbone of every living creature and its compounds form important parts of living organisms. Carbon is a crucial component in photosynthesis, respiration, and nitrogen fixation.
Such conversion results in the production of carbohydrate, glucose that may be converted to other organic compounds such as sucrose, starch, cellulose, etc. Here, some of the carbohydrates are utilised directly by the plant itself.
During this process, more carbon dioxide is generated and is released through its leaves or roots during the day. The remaining carbohydrates not being utilised by the plant become part of the plant tissue. Plant tissues are either being eaten by the herbivorous animals or get decomposed by the micro- organisms.
The Oxygen Cycle
Oxygen is produced by plants in photosynthesis. The process of photosynthesis involves the use of chlorophyll which absorbs energy from sunlight.
This energy transports electrons to carbohydrates that are converted into simple sugars with the help of carbon dioxide and water. Oxygen is produced as a by-product in this process.
The cycling of oxygen is a highly complex process. Oxygen occurs in a number of chemical forms and combinations. It combines with nitrogen to form nitrates and with many other minerals and elements to form various oxides such as the iron oxide, aluminium oxide and others.
Much of oxygen is produced from the decomposition of water molecules by sunlight during photosynthesis and is released in the atmosphere through transpiration and respiration processes of plants.
The Nitrogen Cycle
Nitrogen is an essential constituent of tissues and is particularly important in maintaining water balance and the acid-base balance within the body.
Solid nitrogenous wastes, such as hair and nails, are not eliminated from the body; approximately eighty per cent of the solid wastes are composed of carbon.
The major part of nitrogen elimination from the body is via the respiratory tract; elimination by this route represents respiration.
It is also an essential constituent of different organic compounds such as the amino acids, nucleic acids, proteins, vitamins and pigments.
Only a few types of organisms like certain species of soil bacteria and blue green algae are capable of utilising it directly in its gaseous form.
Generally, nitrogen is usable only after it is fixed. Ninety per cent of fixed nitrogen isbiological.
The principal source of free nitrogen is the action of soil micro-organisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil.
Nitrogen can also be fixed in the atmosphere by lightning and cosmic radiation. In the oceans, some marine animals can fix it. The minerals are returned to the soil and water through decomposition and flow.
