BIOGEOCHEMICAL CYCLES

• Bio geochemical cycles refer to the flow of such chemical elements and compounds between organisms and physical environment. Chemicals taken in by organisms are passed through the food chain and come back to the soil, air and water through mechanisms such as respiration, excretion and decomposition.
• Such cyclic exchange of material between the living organisms and their non-living environment is called bio geochemical cycle.
• The bio geochemical cycles can be divided into two types, the gaseous bio geochemical cycle and sedimentary bio geochemical cycle.

1. Gaseous bio geochemical cycle: In the gaseous cycle, the main source of nutrients are atmosphere and water bodies evaporation. It consists various cycles like carbon cycle, nitrogen cycle, oxygen cycle etc. The gaseous cycle is more rapidly circulated than the sedimentary cycle due to large atmospheric reservoir.
2. Sedimentary cycle : In this cycle, the main source of nutrients are soil and rocks of the earth crust. It consists various cycles like sulphur cycle, calcium cycle, iron cycle etc. 

• Following are some important bio geochemical gaseous cycles :

1. Carbon cycle
2. Nitrogen cycle
3. Water cycle
4. Oxygen cycle
5. phosphorus cycle
6. Sulphur cycle

1. Carbon cycle :

• It will be divided in two components which are given below:

1. Terrestrial carbon cycle
2. Aquatic carbon cycle.

1. Terrestrial carbon cycle:

• The terrestrial carbon cycle is concerned with the movement of carbon on land.
• All living things are consume carbon which is present in an organic matter.
• We can see a pictorial description of a carbon cycle above.
• We largely used fossil fuels in various area for different purposes. This combustion of fossil fuels highly spread CO2 in our atmosphere. This CO2 consumes by the plants through the respiration activity. They uses CO2 to produce energy or food. So they are the producers and animal who take the energy from plants by consume it are known as consumers. Consumers releases CO2  in atmosphere by respiration activity. So it make a carbon cycle among them.
• After the death of consumers and producers their decay body is decomposed by the bacterias and they are release CO2 in atmosphere. Some part of their decay body is converted into fuel also.
• This is called terrestrial carbon cycle.

2. Aquatic carbon cycle:

• The aquatic carbon cycle is concerned with the movement of carbon in marine system.

2. Nitrogen cycle :

• The chief reservoir in atmosphere is nitrogen .It is present in atmosphere of 78%. This is also present in the bodies of living organisms and in soil. However free nitrogen can not be directly utilized by the organisms.
• Above figure shows the detail of nitrogen cycle operating in the ecosystem.The nitrogen cycle accomplish in four steps which are given below:

       1. Nitrogen fixation

       2. Ammonification

       3. Nitrification

       4. De-nitrification

• Lightning and some nitrogen fixing bacteria trapped the atmospheric nitrogen and oxidized to nitrate. This step is known as the nitrogen fixation.
• The nitrate is formed and taken up by the animals and plants. After the death of both animals and plants, Thier bodies would decay and their waste would decompose by the bacteria and convert it into ammonia. This process is known as ammonification.
• These ammonium salts are converted into nitrite. This process is known as nitrification.
• After the nitrification, Nitrite returns to the nitrate. This process is known as de-nitrification.
• In this way, the whole cycle becomes completed. This cycle is known as the nitrogen cycle.

3. Water cycle :

• The water cycle is also known as hydrological cycle.
• It refers to the continuous circulation of water within the Earth’s hydrosphere. Water moves into and from the various reservoirs on, over, and under the surface of the Earth, and in the process transforms into its various phases of solid (ice), liquid (water), and gas (vapor), with the total mass of water remaining fairly constant. 
• The physical processes of evaporation, condensation, sublimation, precipitation, transpiration, and runoff are responsible for sustaining the water cycle. 
• Heat energy is also exchanged during the cycle, with this store and release of heat affecting climates worldwide. 
• The water cycle is highly crucial to maintaining life on Earth, as it replenishes the world’s freshwater resources and moderates extremes in climate.

4. Oxygen cycle :

• Oxygen cycle, along with the carbon cycle and nitrogen cycle plays an important role in the existence of organis on the earth. 
• The oxygen cycle is a biological process which helps in maintaining the oxygen level by moving through three main spheres of the earth which are:

1. Atmosphere
2. Lithosphere
3. Biosphere.

• This bio geochemical cycle explains the movement of oxygen gas within the atmosphere, the ecosystem, biosphere and the lithosphere. The oxygen cycle is interconnected with the carbon cycle.
  The atmosphere is the layer of gases presents above the earth’s surface. The sum of all Earth’s ecosystem makes a biosphere. Lithosphere, which is the solid outer section along with the Earth’s crust and it is the largest reservoir of oxygen.

  Stages of the Oxygen Cycle

  The steps involved in the oxygen cycle are:

  Stage-1: All green plants during the process of photosynthesis, release oxygen back into the atmosphere as a by-product.

  Stage-2: All aerobic organisms use free oxygen for respiration.

  Stage-3: Animals exhale Carbon dioxide back into the atmosphere which is again used by the plants during photosynthesis. Now oxygen is balanced within the atmosphere.

5. Phosphorus cycle :

• Above figure shows the complete phosphorus cycle operating in the ecosystem.
• Many rocks contains phosphorus usually in the form of phosphate which is released in atmosphere by various weathering process. This phosphate are consume by the plants, who are called producers. 
• After that some animals consume plants for energy. This food chain transfers phosphate among living organisms.
• When these animals and plants are died their decay body and waste are decompose by bacteria which are known as decomposer and eventually phosphorus are back in form of phosphate salt to the land. This cycle is called phosphorous cycle.
• Phosphorous is essential for the growth of animals, bones and teeth.

6. Sulphur cycle : 

• Above figure shows the complete cycle of sulphur cycle in ecosystem.
• Plants and animals are depended on continuous supply of sulphur and its compound for synthesis of some amino acids and protine.
• In the sulphur cycle, The sulphur comes into contact with air and converted into sulphate. The sulphate is taken up by plants and microorganisms. Which is in organic form. Then animals consume the plants and food chains transfers sulphur in  living organisms.
• When this organisms died, their body will be decompose by bacteria. This decomposing of their decay bodies release sulphur in atmosphere and rest part of their body are mixed up in soil.
• This cycle is known as sulphur cycle.