How Is Nitrogen Gas Removed From The Atmosphere?

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The composition of Nitrogen Gas is 78.09% in the atmosphere which is more than any other gas. But, that nitrogen can’t be taken by the biological system so, it has to be converted into ammonia (NH3), nitrate(NO3), etc. to enter the biological system.

So, this is the main importance of the removal of nitrogen gas from the atmosphere into a biologically consumable manner.

Nitrogen gas is removed from the atmosphere by the process of Nitrogen Fixation in which molecular nitrogen in the air is converted into ammonia or related nitrogenous compounds in soil. Then Nitrification takes place which is actually the biological oxidation of ammonia to nitrite and then to nitrate.

The importance of nitrogen can’t be neglected in the biological system. Nitrogen is a crucially important component for all lifeforms just like carbon, oxygen, etc.

It’s so much important that you can’t even imagine the majority of the biomolecular structures without nitrogen in them. It is an important part of many cells and processes such as amino acids, proteins, DNA, RNA, chlorophyll in plants, etc.

Here, in this post, we’ll talk all about the nitrogen cycle only. It’s because the topic of how nitrogen gas is removed from the atmosphere is directly in co-relation with the Nitrogen Fixation process of the Nitrogen Cycle.

Nitrogen Cycle
Nitrogen Cycle (Image Source / CC BY-SA)

How Is Nitrogen Gas Removed From The Atmosphere?

We all know that the nitrogen gas (N2) available in the atmosphere can’t be directly consumed by the plants. So, the conversion of atmospheric nitrogen gas into a form usable by plants and other organisms is very much important.

Here below are the ways of how nitrogen gas is removed from the atmosphere and how it enters the biological system…

Nitrogen gas enters soil first

The very first step is to bring the atmospheric nitrogen in contact with the soil or mud so that the further process of the removal of nitrogen is carried on.

It is during the process of nitrogen fixation that the inert Nitrogen gas gets deposited into the soil from the atmosphere and surface water by undergoing precipitation.

That’s actually how the nitrogen gas enters the soil from the atomosphere naturally.

Below there’re some other ways of taking nitrogen in other forms.

Sometimes, dead plants or animals are decomposed by the decomposes and their nitrogen content is released back to the soil.

Nitrogen also enters the soil from the use of nitrogen-containing commercial fertilizer, grazing of animals, and the spreading of animal manure that adds up to the natural source of nitrogen.

The main sources of nitrogen include geographical sources, atmospheric precipitation, geological sources, agricultural or farming land, livestock and poultry farms, and urban waste management systems.

Another great organic sources of nitrogen found in every home are grass clippings, tea-coffee grounds, drain water, etc. are all great source of nitrogen for the soil.

The nitrogen that is absorbed by the soil is sooner or later gets broken down into two separate nitrogen atoms which combine with hydrogen to form ammonia (NH4+) and then it turns to Nitrite(NO2), and Nitrate(NO3) respectively.

Nitrogen Fixation by free-living bacteria

The process of nitrogen fixation by free-living bacteria means the conversion of atmospheric nitrogen to ammonia with the help of many freely living bacteria that live in the soil without any symbiotic association with other organisms.

This type of nitrogen-fixing bacteria includes species like Azotobacter, Bacillus, Clostridium, Klebsiella, etc. that acts on the atmospheric nitrogen that enters the soil and converts it into ammonia.

These organisms get their source of energy typically by oxidizing organic molecules released by other organisms, decomposition, or by utilizing other inorganic compounds.

They have an enzyme called nitrogenase in their body which is highly responsible for the reduction of nitrogen (N2) to ammonia (NH3).

The nitrogenase enzyme is usually inhibited by oxygen atom so they have developed a mechanism to stay anaerobic or behave as microaerophiles while fixing atmospheric nitrogen.

Nitrogen Fixation by symbiotic bacteria associated with plants

Nitrogen fixation by any symbiotic bacteria associated with plants means that some bacteria stay with close interactions with the plants to help fix the atmospheric nitrogen to ammonia, and in return, the bacteria get the plant’s root to stay.

There are various plants that show such symbiotic associations. One such is the Legume plants of the family Fabaceae.

Legumes form a unique symbiotic relationship with Gram-negative Rhizobium soil bacteria. Legumes allow the bacteria to infect their roots and form root nodules where the bacteria stay and convert nitrogen from the air into ammonia that the plant uses for its growth and development.

Examples of popular legume plants that help in nitrogen fixation are alfalfa, beans, clover, cowpeas, lupines, peanut, soybean, and vetches.

By Atmospheric fixation

The various natural phenomenons like lightning can help in the breakdown of the strong triple bonds of the Nitrogen atoms and can convert it to nitrates, which then falls on the earth via. rainfall.

When lightning strikes the nitrogen (N2) molecules, the enormous energy of lightning breaks and splits nitrogen molecules into two separate nitrogen atoms which enable them to combine with the oxygen in the atmospheric air forming nitrogen oxides.

In such a way, the inert dinitrogen (N2) gas of the atmosphere can directly enter the soil, oceans, etc. in the form of nitrates which can be easily consumed by the photosynthetic plants.

Actually the triple bond of the atmospheric dinitrogen molecules is so strong that it makes the gas chemically inert and less reactive. Lighting has the power to break that bond and free the nitrogen atoms.

And, it is also to be noted that each bolt of lightning can carry enough electrical energy just in order to break the strong bonds of nitrogen molecules in the atmosphere. After the bonds are broken, the free nitrogen atoms quickly bond to oxygen atoms present in the atmosphere, forming nitrogen dioxide (NO2).

Recent studies have shown that each bolt of lightning on average in the several mid-latitude and subtropical thunderstorms is able to turn around 7 kilograms (15.4 pounds) of nitrogen into chemically reactive nitrates and so on.

By Industrial fixation

In the industrial nitrogen fixation process, the free nitrogen (N2) gas from the atmosphere is chemically treated to combine with other elements forming more-reactive nitrogen compounds such as ammonia, nitrates, or nitrites.

Just like take the example of the fertilizer production industries where a huge amount of nitrogen-containing plant fertilizers like Ammonium nitrate, Urea, Calcium ammonium nitrate, etc. are manufactured using the atmospheric nitrogen and other compounds. These fertilizers when used adds nitrogen content directly to the soil.

A very famous Industrial fixation nitrogen process is the Haber (or Haber-Bosch) process which is used to produce Ammonia in a huge amount in the industries.

In the Haber Process, nitrogen from the air under high pressure combines with hydrogen derived mainly from natural gas (methane) into ammonia. The reaction is reversible and the production of ammonia is exothermic. The catalyst is actually slightly more complicated than pure iron.

Just like the agriculture industry, in many manufacturing processes as well, the use of large volumes of nitrogen is crucial to success. The manufacture of nitrogen gas has countless applications, especially in the oil and gas industry a lot.

Nitrogen gas from the atmosphere is also used in industries for Nitrogen blanketing, Nitrogen purging, Gas lifting, Gas-assisted injection molding, Nitrogen Sparging for Wine, etc.

All of these highly helps in fixing nitrogen from the air to the soil directly or indirectly.

By Nitrification (Aerobic ammonium oxidation)

Nitrification is the process of biological oxidation of ammonia to nitrite followed by the oxidation of nitrite to nitrate. Nitrification is done all under the presence of oxygen i.e. in aerobic conditions.

Plants can use ammonia as a nitrogen source but this ammonia can’t be taken directly by the plants as its highly toxic to them.

So, the ammonia has to be converted into nitrites and nitrates which is then easily consumed by plants by the process of assimilation.

Nitrites are formed by the oxidation of Ammonia with the help of Nitrosomonas bacterium species. It’s an intermediate process that forms hydroxylamine (NH2OH) using two different enzymes, ammonia monooxygenase & hydroxylamine oxidoreductase.

Later, the produced nitrites are converted into nitrates by Nitrobacter.

This conversion is very important or else ammonia will be released back to the atmosphere without even entering the Nitrogen cycle.

By Nitrification (Anaerobic ammonium oxidation)

This is the same nitrification process of converting ammonia to nitrite and nitrate, all under the absence of oxygen i.e anaerobically.

Traditionally, it was thought that all kinds of nitrification processes were carried out under aerobic conditions i.e. in the presence of oxygen. But, recently a new type of ammonia oxidation occurring under anoxic conditions was discovered.

This Anaerobic ammonium oxidation type of nitrification process is also known as Anammox.

Bacteria belonging to Phylum Planctomycetes carries out this type of nitrification. Example: Brocadia anammoxidans

This type of bacteria oxidize ammonia by using nitrite as the electron acceptor to produce nitrogen gas.

This type of bacteria is mainly found in the ocean ecosystem, including low-oxygen zones of the ocean, coastal and estuarine sediments, mangroves, and freshwater lakes.


Conclusion

The abundance of nitrogen in the atmosphere is 78.09% which is actually more than any other element but, this nitrogen is in a chemically inert and stable form. In order to get that nitrogen into the life forms, it has to be removed from the air and then need to be released to the soil, oceans, etc.

That’s why nitrogen fixation comes into place. This is actually the removal process of atmospheric inert nitrogen to the soil in order to be used in the nitrogen cycle.

So, the nitrogen first enters the soil via. rainfall, precipitation, surface water, fertilizers, etc. Atmospheric fixation and Industrial fixation also helps in bringing that nitrogen to the soil.

This nitrogen is then converted to Ammonia by either the free-living bacteria or by the symbiotic bacteria.

Now, that ammonia can’t be directly taken by the plants as it is highly toxic. So, ammonia is next converted into nitrites and then to nitrates which can now be easily consumed by the plants.

Now, the next Nitrogen assimilation takes place which is actually the formation of organic nitrogen bio-compounds for the plants like amino acids, etc. from those nitrates.

So, in total it is all of the processes of how the nitrogen from the atmosphere enters the soil and then it gets converted to nitrates and then it finally enters the plant, as a whole is termed the process of removal of atmospheric nitrogen biologically.

That’s in short how the whole nitrogen is removed from the atmosphere to enter the biological bodies.

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