This describes the Nitrogen Cycle.

The Nitrogen Cycle The nitrogen cycle represents one of the most important nutrient cycles found in terrestrial ecosystems (Figure 1). Nitrogen is used by living organisms to produce a number of complex organic molecules like amino acids, proteins, and nucleic acids. The largest store of nitrogen is found in the atmosphere where it exists as a gas (mainly N2). The atmospheric store is about one million times larger than the total nitrogen contained in living organisms. …

…systems, the added nitrogen can lead to eutrophication. *Increased deposition of nitrogen from atmospheric sources because of fossil fuel combustion and forest burning. Both of these processes release a variety of solid forms of nitrogen through combustion. *Livestock ranching. Livestock release a large amounts of ammonia into the environment from their wastes. This nitrogen enters the soil system and then the hydrologic system through leaching, groundwater flow, and runoff. *Sewage waste and septic tank leaching.