Before we start talking about the Nitrogen Cycle, I think that it is important to learn exactly where it falls into the environmental “cycle” – for lack of a better word – and about Nitrogen the element.

Nitrogen Cycle is one of Earth’s Biogeochemical or Nutrient Cycles. These cycles are the methods of which substances are cycled (or move through) the Earth’s biotic and abiotic environments. There are 5 basic biogeochemical cycles that you’ll typically learn about. These are:

[Water Cycle]

[Carbon Cycle]

Nitrogen Cycle

[Phosphorus Cycle]

[Sulfur Cycle]

 

So, what exactly is Nitrogen?

Nitrogen is a colorless and odorless element that was discovered in 1772 by Chemist and Physician Daniel Rutherford. On the periodic table it is seen by its chemical symbol “N” with an atomic number of 7. It can be found in many forms and is easily bonded with other elements. Nitrogen gas (N₂) makes up approximately 78.1% of Earth’s air, by volume, making it one of the most important elements in our atmosphere. On top of being so important to Earth’s atmosphere, it is one of the most important elements for living organisms. Through the Nitrogen Cycle, Nitrogen is converted from its basic form into usable forms for the environment by special bacteria.¹

 

The Nitrogen Cycle

The Nitrogen Cycle is a nutrient cycle found in terrestrial (on-land) ecosystems for living organisms to produce molecules such as amino acids, proteins, and nucleic acids. N₂ cannot be absorbed as a nutrient by multicellular plants and animals on its own. It requires the help of nitrogen-fixing bacteria to convert it into more usable states.

The Steps

Nitrogen Fixation

In the first step of the Nitrogen Cycle, N₂ is first deposited into the soil and bodies of water through precipitation.² N₂ is “fixed” by special bacteria in soil and blue-green algae (also known as cyanobacteria) combine N₂ with Hydrogen (H) in order to form ammonia (NH₃).³

It can also be fixed through man-made, industrial processes that create ammonia and nitrogen-rich fertilizers.²

 

Nitrification

Ammonia can only be taken up by some plants; and ammonia is highly toxic to many animals.

Residual ammonia is converted by nitrifying bacteria into Nitrites (NO₂^–) and Nitrates (NO₃^–).²

 

Assimilation

Nitrites and Nitrates are used by plants to produce amino acids, proteins, nucleic acids, vitamins, and other nutrients that animals, detritus feeders, and decomposers need to survive.² Some of these plants are eaten by herbivorous animals; and some of those animals become prey to larger carnivorous animals.

Ammonification

When plants and animals die or living organisms emit wastes the nitrogen in the organic matter reenters the soil. Microorganisms called decomposers break down this matter to produce more ammonia, which is, then, made available for other biological processes (such as restarting the cycle from Nitrification).²

 

Denitrification

Denitrification is when Nitrogen molecules make their way back into the atmosphere. Nitrates are converted back into N₂ in conditions with low oxygen (such as wet soils where few microorganisms can survive). Denitrifying bacteria will process nitrates in order to gain oxygen, leaving N₂ to return to the atmosphere as a byproduct.²

 

The Cycle Continues.

 

So, what happens to the rest of it?

Nitrates that are washed out of ground soil through leaching and runoff are eventually deposited into river and ocean sediment. This residual nitrogen gets lost into this sediment. Nitrogen suspended in the water column can be taken back into the atmosphere through precipitation.

 

What is its environmental role?

The Nitrogen Cycle is important because it is a key process where nitrogen converted into important vitamins and proteins necessary for terrestrial plants and animals to survive. The thing is that, with everything, nitrogen levels require balance. If there is a spike or drop in local nitrogen levels, it can be detrimental to all living organisms in that area.

 

Alterations & Effects

Humans can intervene with the Nitrogen Cycle in several ways. The two most abundant human-made forms of nitrogen can be found in fertilizers and fossil fuels. These things can drastically change the amount of available nitrogen for primary productivity in the environment.³

In terrestrial ecosystems, the addition of nitrogen can lead with a nutrient imbalance in plants, which can in turn alter a forest or ecosystem’s health and ultimately decline biodiversity. These increased nitrogen levels can also change the gaseous nitrogen storage in soils and plants as it is released into the atmosphere through the destruction of forests, grasslands, and wetlands to make way for commercial living.³

In aquatic ecosystems, the nitrogen cycle can become upset by excess nitrates entering bodies of water through agricultural runoff and sewage system discharge. While this movement of nitrogen into bodies of water is natural, excessive discharge can affect the chemical balance of aquatic life.³

Lastly, through the harvesting of nitrogen-rich crops, irrigation, and burning, naturally occurring nitrogen gets removed from topsoil. This leaves very little remaining for any plants that may continue to grow in these areas.³

All of these together create an unfortunately high level of greenhouse gases (such as nitrogen oxide) to take up Earth’s atmosphere. These gases can hold up to 300 times the warming potential per molecule of naturally occurring carbon dioxide. Ultimately destroying the stratospheric ozone layer of our atmosphere (which protects Earth form harmful UV-B radiation) and contributing to global warming.⁴

 

Can we fix it?

That’s where it gets tricky.

Earth’s human population is currently at nearly 8 Billion people and counting. We rely heavily on the mass production of, well, everything, in order to survive. Farms and plants are working harder and producing more than they ever have. Carbon emissions by various industries continues to grow. At this point, the damage that has been done to the Nitrogen Cycle may be visible for the next several decades, or even centuries.⁴

The statistics today, however, doesn’t make helping the matter impossible.

 While there may be little we can do at home compared to the affects of industry, communities can work together to push for more efficient use of materials.

Particularly in the agriculture industry, an example of a change that could cause positive affects on the nitrogen cycle includes optimizing the timing and amount of fertilizer that is being used. Turning to both traditional and selective breeding techniques (depending on the crop) could make the farming of these crops to become more efficient as well as favorable for consumption.⁴

While this is an issue that we can’t foresee going away anytime soon, we can still learn, educate, and advocate wherever possible for more sustainable industrial practicing. Remember that it’s all for the Earth.

 

 

We don’t have a Society if we Destroy the Environment.

~Margaret Mead

Sources:

1. (2016). Retrieved April 25, 2020, from https://periodic.lanl.gov/7.shtml
2. The Nitrogen Cycle. (n.d.). Retrieved April 25, 2020, from https://enviroliteracy.org/air-climate-weather/biogeochemical-cycles/nitrogen-cycle/
3. Miller, G. T., & Spoolman, S. (2012). What Happens to Matter in an Ecosystem? In Living in the Environment, AP edition (pp. 68-69). Belmont, C.A.: Brooks/Cole, Cengage Learning.
4. Too Much of a Good Thing: Human Activities Overload Ecosystem with Nitrogen. (2010). Science, (S10).