The Nitrogen Cycle

The Nitrogen Cycle

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What is nitrogen used for?
Nitrogen is a component of many organic molecules. It forms an essential part of amino acids (which make up proteins) and DNA. Nitrogen is essential for all living cells.

What is the nitrogen cycle?
Nitrogen is the major component of earth's atmosphere. It enters the food chain by means of nitrogen-fixing bacteria and algae in the soil. This nitrogen which has been 'fixed' is now available for plants to absorb. These types of bacteria form a symbiotic relationship with legumes--these types of plants are very useful because the nitrogen fixation enriches the soil and acts as a 'natural' fertilizer. The nitrogen-fixing bacteria form nitrates out of the atmospheric nitrogen which can be taken up and dissolved in soil water by the roots of plants. Then, the nitrates are incorporated by the plants to form proteins, which can then be spread through the food chain. When organisms excrete wastes, nitrogen is released into the environment. Also, whenever an organism dies, decomposers break down the corpse into nitrogen in the form of ammonia. This nitrogen can then be used again by nitrifying bacteria to fix nitrogen for the plants.

Pop quiz:
How have humans interfered with the nitrogen cycle?

What are the effects of human interference in the nitrogen cycle?
When we cause nitrogen overload in an ecosystem, there are many drastic effects. Dumping of raw sewage contains nitrogenous wastes, along with urban runoff. When large amounts of nitrogen collect in a water body, eutrophication can result. This is an accumulation of excess nutrients which causes an algae bloom. The algae rapidly deplete all of the oxygen in the water, making it inhospitable for fish and other aquatic organisms. Eutrophication also brings about the deadly red tides. When plant communities are saturated with nitrogen, the soil can become acidified. This makes the soil inhospitable. Burning fossil fuels and wood contributes to a large amount of nitric oxide in the atmosphere. Nitric oxide can combine with oxygen gas to for nitrogen dioxide, which reacts with water vapor to form a strong acid (nitric acid). This can precipitate out of the atmosphere in the form of the deadly acid rain. The acid can damage trees and kill fish. The use of inorganic fertilizers and depleting nitrogen resources by overharvesting legumes (which have nodules in their roots formed by a symbiotic bacteria that fix nitrogen) and overmining nitrogen also alter an ecosystem.

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