In extreme cases, plants with very high levels of nitrogen absorbed from soils can poison farm animals that eat them [ 3 ]. Excess nitrogen can also leach—or drain—from the soil into underground water sources, or it can enter aquatic systems as above ground runoff. This excess nitrogen can build up, leading to a process called eutrophication. Eutrophication happens when too much nitrogen enriches the water, causing excessive growth of plants and algae. When the phytoplankton dies, microbes in the water decompose them.
Organisms in the dead zone die from lack of oxygen. These dead zones can happen in freshwater lakes and also in coastal environments where rivers full of nutrients from agricultural runoff fertilizer overflow flow into oceans [ 4 ].
Can eutrophication be prevented? People who manage water resources can use different strategies to reduce the harmful effects of algal blooms and eutrophication of water surfaces. They can re-reroute excess nutrients away from lakes and vulnerable costal zones, use herbicides chemicals used to kill unwanted plant growth or algaecides chemicals used to kill algae to stop the algal blooms, and reduce the quantities or combinations of nutrients used in agricultural fertilizers, among other techniques [ 5 ].
But, it can often be hard to find the origin of the excess nitrogen and other nutrients. Once a lake has undergone eutrophication, it is even harder to do damage control. Algaecides can be expensive, and they also do not correct the source of the problem: the excess nitrogen or other nutrients that caused the algae bloom in the first place!
Another potential solution is called bioremediation , which is the process of purposefully changing the food web in an aquatic ecosystem to reduce or control the amount of phytoplankton. For example, water managers can introduce organisms that eat phytoplankton, and these organisms can help reduce the amounts of phytoplankton, by eating them!
The nitrogen cycle is a repeating cycle of processes during which nitrogen moves through both living and non-living things: the atmosphere, soil, water, plants, animals and bacteria. In order to move through the different parts of the cycle, nitrogen must change forms. In the atmosphere, nitrogen exists as a gas N 2 , but in the soils it exists as nitrogen oxide, NO, and nitrogen dioxide, NO 2 , and when used as a fertilizer, can be found in other forms, such as ammonia, NH 3 , which can be processed even further into a different fertilizer, ammonium nitrate, or NH 4 NO 3.
There are five stages in the nitrogen cycle, and we will now discuss each of them in turn: fixation or volatilization, mineralization, nitrification, immobilization, and denitrification. In this image, microbes in the soil turn nitrogen gas N 2 into what is called volatile ammonia NH 3 , so the fixation process is called volatilization.
Leaching is where certain forms of nitrogen such as nitrate, or NO 3 becomes dissolved in water and leaks out of the soil, potentially polluting waterways. In this stage, nitrogen moves from the atmosphere into the soil. To be used by plants, the N 2 must be transformed through a process called nitrogen fixation. Fixation converts nitrogen in the atmosphere into forms that plants can absorb through their root systems.
A small amount of nitrogen can be fixed when lightning provides the energy needed for N 2 to react with oxygen, producing nitrogen oxide, NO, and nitrogen dioxide, NO 2.
These forms of nitrogen then enter soils through rain or snow. Nitrogen can also be fixed through the industrial process that creates fertilizer. This form of fixing occurs under high heat and pressure, during which atmospheric nitrogen and hydrogen are combined to form ammonia NH 3 , which may then be processed further, to produce ammonium nitrate NH 4 NO 3 , a form of nitrogen that can be added to soils and used by plants.
Most nitrogen fixation occurs naturally, in the soil, by bacteria. In Figure 3 above , you can see nitrogen fixation and exchange of form occurring in the soil. Some bacteria attach to plant roots and have a symbiotic beneficial for both the plant and the bacteria relationship with the plant [ 6 ].
The bacteria get energy through photosynthesis and, in return, they fix nitrogen into a form the plant needs. The fixed nitrogen is then carried to other parts of the plant and is used to form plant tissues, so the plant can grow. Other bacteria live freely in soils or water and can fix nitrogen without this symbiotic relationship. These bacteria can also create forms of nitrogen that can be used by organisms. This stage takes place in the soil.
What is nitrogen fixation and why is this important? What is the carbon cycle and why is it important? What is the nitrogen cycle and why is it important? What are the similarities and differences between the carbon cycle and nitrogen cycle? Why are microbes important in the carbon cycle and the nitrogen cycle? What is the difference between Carbon 12, 13, and 14?
Impact of this question views around the world. You can reuse this answer Creative Commons License. When plants and animals die or when animals excrete wastes, the nitrogen compounds in the organic matter re-enter the soil where they are broken down by microorganisms, known as decomposers. This decomposition produces ammonia, which can then go through the nitrification process. Nitrifying bacteria in the soil convert ammonia into nitrite NO 2 - and then into nitrate NO 3 -.
This process is called nitrification. Compounds such as nitrate, nitrite, ammonia and ammonium can be taken up from soils by plants and then used in the formation of plant and animal proteins.
Denitrification completes the nitrogen cycle by converting nitrate NO 3 - back to gaseous nitrogen N 2.
Denitrifying bacteria are the agents of this process. These bacteria use nitrate instead of oxygen when obtaining energy, releasing nitrogen gas to the atmosphere. Agriculture may be responsible for about half the nitrogen fixation on Earth through fertilisers and the cultivation of nitrogen-fixing crops. However, nitrogen in excess of plant demand can leach from soils into waterways. The nitrogen enrichment contributes to eutrophication.
Another problem can occur during nitrification and denitrification. When the chemical process is not completed, nitrous oxide N 2 O can be formed. This is of concern, as N 2 O is a potent greenhouse gas — contributing to global warming. A balance of nitrogen compounds in the environment supports plant life and is not a threat to animals.
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