Biogeochemical cycle

Biogeochemical cycle


Earth is a very diverse planet with various species that live on earth. Hence earth is composed of both living and non-living things. The source and quantity of all these substances on earth are fixed. All living things like viruses, bacteria, plants, animals, and the human body are composed of basic elements. All these elements have been circulating in the physical and biological environment since the creation of life on earth. As a result, a cycle is created on earth. The amount of these elements has not been exhausted from the time of the creation of the earth to the present time. This is because all these elements rotate in a circular motion between the physical and the living environment. So the storage of these elements is endless in the environment. Thus these elements combine to form a large natural cycle. This natural cycle is known as a biogeochemical cycle (2) & (4).

Biogeochemical cycle

About 40 elements are vital for life to sustain on the earth. Among these 40 elements, 6  are most needed and these 6 elements help in the formation of about 90% of the organism of plants, animals, and microorganisms. The 6 main elements of the body are carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus. These elements rotate in a cyclic way between the organism and its environment to form biogeochemical cycles (3).


The word bio means, “Organism”, geo means, “earth” or “part of the earth”. So literally, the term “biogeochemical cycle” means the rotation of various chemical elements from the physical environment to the organism’s body and from the organism’s body to the physical environment again.


The endless cyclical process by which the essential elements for the survival of an organism are circulated from the environment to the organism and from the organism to the environment is called the biogeochemical cycle. The organism receives nutrition from oxygen, carbon dioxide, nitrogen, sulfur, sodium, lead, copper, zinc, etc., and after the death of the organism, these elements are released back to the environment (1).

According to Furely and Newey’s 1983 concept, “The biogeochemical cycle refers to a large type cycle, where the inorganic matter is present. And those inorganic matters go through different organic stages and then come back to the inorganic state again”.

Classification of Biogeochemical cycle

There are three main types of biogeochemical cycles observed in nature. Such as-

1. Water cycle

The water cycle is the movement of water from the sea and the surface to the atmosphere and the return of water from the atmosphere to the surface and underground.

2. Gaseous cycle

The reservoir of the gaseous biogeochemical cycle is located in the atmosphere and hydrosphere. Examples of gaseous cycles are the carbon cycle, nitrogen cycle, and oxygen cycle.

3. Sedimentary cycle

The reservoir of the sedimentary biogeochemical cycle is located in the earth’s crust. Examples of sedimentary cycles are the sulfur cycle and phosphorus cycle (1).

Facts about Biogeochemical cycle

  • The biogeochemical cycles are very complex cycles.
  • The functionality of the biogeochemical cycle depends on the energy flow.
  • Biogeochemical cycles are active in both atmosphere, lithosphere, hydrosphere, and biosphere.
  • Plants and animals receive essential nutrients from the environment through this cycle.
  • The gaseous cycle in the biogeochemical cycle is completed quickly and the sedimentary cycle is completed slowly.
  • The carbon cycle is the simplest cycle of all the biogeochemical cycles.
  • Biogeochemical cycles maintain the stability and balance of elements in nature (3) & (5).

A detailed description of important biogeochemical cycles

There are some important biogeochemical cycles in the environment. The important biogeochemical cycles in the environment are described below.

1. Nitrogen cycle

The nitrogen cycle is one of the most important parts of the biogeochemical cycle. The transformation of nitrogen is accomplished through biological and physical processes.

Source of nitrogen

The total amount of nitrogen in the atmosphere is about 79% and is the primary source of the nitrogen cycle. Besides, nitrogen is found in the form of organic molecules, in the form of nitrates in the lithosphere. Nitrogen is also present in the form of amino acids.


The nitrogen cycle completed through the following pathways

1. Nitrogen fixation

The process by which atmospheric nitrogen gas turns into nitrogenous compounds and is bounded or stored in the soil by various microorganisms is called nitrogen fixation. Plants only absorb atmospheric nitrogen when it is converted to ammonia and nitrate. In a word, nitrogen fixation is the process of converting nitrogen gas to ammonia.

2. Ammonification

The method by which bacteria living in the soil (e.g. Bacillus, proteus, clostridium, pseudomonas, etc.) convert nitrogen compounds into ammonium is called ammonification. In fact, during the decomposition of dead plants and animals, these bacteria release excess ammonia into the environment. In this process, the proteins of the dead organism are first converted into amino acid and then ammonia as a result of the reaction of various bacteria located in the soil.

3. Nitrification

Nitrification refers to the addition of nitrogen to the soil. Nitrogen compounds from dead plants, animals, and other organic matter are decomposed by various bacteria. This decomposed nitrogen produces first ammonia, then nitrite, and finally nitrate compounds. The process by which nitrogen forms an organism returns or re-enters the soil is called nitrification. Bacteria that participate in nitrogen synthesis are called nitrifying bacteria, Such as Nitrobacter, nitrosamines, etc.

4. Denitrification

The process by which nitrate compounds in the soil are converted by bacteria and returned to the atmosphere as nitrogen gas is called denitrification. Some bacteria such as pseudomonas, thiobacillus, micrococcus, etc. participate in this process. These bacteria are called Denitrifying bacteria (1) & (2).

2. Oxygen cycle

Oxygen is the basic element for all living organisms. The process by which the atmospheric oxygen circulates from the environment to the organism’s body and from the organism’s body to the environment and maintains the balance of oxygen in the earth is called the oxygen cycle.

Source of oxygen

The atmosphere is the main source of oxygen. The total amount of oxygen in the atmosphere is about 21%. Besides oxygen also found in the oceans. About 60- 80% of the oxygen produced on earth comes from the oceans. Various phytoplankton, green plants produced some oxygen.


There are two stages in the oxygen cycle.

  • In the first stage, oxygen is taken from the environment for respiration and combustion. All the animals present in the environment receive oxygen from the atmosphere for respiration. During the combustion of fossil fuels (wood, coal, petroleum, diesel, kerosene, paper, etc.) the oxygen in the atmosphere is absorbed. Besides oxygen is removed from the atmosphere during volcanic eruptions and during the formation of oxides of various minerals like copper, iron, lead, etc.
  • In the second stage, Oxygen re-enters the environment through In the process of photosynthesis. The green plant produces oxygen and releases it into the atmosphere in the process of photosynthesis. As a result, the balance of oxygen in the environment is maintained. In addition, oxygen is produced from the ozone gas off the coast and re-enter the atmosphere. At high levels of the atmosphere, the sun’s ultraviolet rays cause water vapor to dissolve into water and oxygen molecules and marge into the atmosphere (2) & (4).

3. Carbon cycle

The carbon cycle refers to the circular flow of carbon in the physical environment and the living environment. Carbon is an essential element for the existence of the living environment. The carbon element is constantly rotating between the atmosphere and biosphere and forms a carbon cycle.

Source of carbon

Carbon is found in the atmosphere in the form of gaseous carbon dioxide. The percentage of carbon dioxide in the atmosphere is 0.04. Carbon is found in the lithosphere in the form of diamond, graphite, coal, petroleum, natural gas, etc.


With the help of the food chain in the environment, when herbivores take plants as food or carnivores take herbivores as food, then the carbon of nature is transmitted to the organism. Carbon dioxide gas is then produced by respiration and returns to nature. After the death of plants and animals, the microorganisms decompose in that dead body. As a result, carbon dioxide gas is produced and released back into the atmosphere. Thus carbon dioxide circulates from the environment to the organism and from the organism to the environment. In this way, the balance of carbon dioxide in the environment is maintained (5).

4. Phosphorus cycle

The process by which natural phosphorus circulates from the physical environment to the living environment and again from the living environment to the physical environment and maintains the balance of phosphorus in the atmosphere is called the phosphorus cycle.

Sources of phosphorus

Phosphorus is found in mineral phosphate. Most of the phosphorus compounds are deposited in the rocks and sediments of the lithosphere. The main sources of phosphorus in nature are insoluble ferric and calcium phosphates in rocks.


  • Phosphorus is released in the form of phosphate in the terrestrial environment. Various small and large plants located in the terrestrial environment take this phosphate directly from the soil. This phosphorus enters the body of terrestrial animals from plants through the food chain. Phosphate is excreted from the animal’s body through animal excretion and returns to the physical environment. Thus the terrestrial phosphorus cycle is completed.
  • Phosphorus cycles also occur in aquatic regions. Phosphates are transferred to the river, seawater, lakes, and groundwater by the erosion and sedimentation process. Various plants and animals live in the aquatic environment. Plants absorb phosphorus and use it to build their bodies. When an aquatic animal takes this plant as food, the presence of phosphorus in the body of the plant is transferred to the animal body. When an animal dies, phosphorus is released into the aquatic atmosphere. In this way, the aquatic phosphorus cycle is completed (2) & (3).

5. Sulfur cycle

Sulfur is a very important substance for all organisms. Sulfur flows in cycles from the organic environment to the physical environment and again from the physical environment to the organic environment to form the sulfur cycle.

Sources of Sulfur

Sulfur is found in the form of sulfate in the lithosphere and hydrosphere, in the form of gaseous hydrogen sulfide and sulfur dioxide in the atmosphere. Volcanic eruptions, decomposition of organic matter, combustion of fossil fuels, etc. are also sources of sulfur in the atmosphere.


There are two phases in the sulfur cycle. One is the natural environmental phase or environmental phase and the other is a biological phase.

  • In the environmental phase, green plants absorb sulfate, which is dissolved in water and soil from the atmosphere. Sulfate molecule converted into a protein molecule. Sulfur is required for the formation of nodules in the roots of some plants.
  • In the biological phase, the sulfur stored in plants is spread to the different animals by the food chain in the environment. Excess sulfur is then returned to the environment through the decomposition of animal’s dead bodies, waste substances, etc. (3) & (4)


The elements carbon, oxygen, nitrogen, phosphorus, sulfur, etc. are the primary component of the cell and protoplasm. So the supply of those elements to the organism is necessary for the formation of the cell. The elements rotate from the environment to the organism and again from the organism to the environment and form biogeochemical cycles. So the biogeochemical cycle is very important for all organisms. The biogeochemical cycles also maintain the balance of all these elements in the environment (1) & (5).

Written By: Manisha Bharati

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