Indeed, it cycles, or moves, through the biosphere in various forms. And in large, concentrated amounts, some of those other forms can cause problems. Ammonia plays a role in the nitrogen cycle, and is perhaps as good a place as any in the cycle to start. Ammonia is produced as animal waste decomposes. Ammonia can represent an odor problem for hog farmers inside buildings in which hogs are raised, and it can contribute to causing respiratory problems for the animals.
Ammonia is subject to a process called nitrification.
When the right bacteria come in contact with ammonia, they nitrify it, or turn it into nitrate, a form of nitrogen plants can use. Plants assimilate nitrate and turn it into amino acids and proteins, which is what nourishes animals when they eat plants. In the right place and the right amount, ammonia and nitrate are good. The production of ammonia is a necessary step toward the production of nitrate, and nitrate nourishes plants, which nourish animals. Problems can arise, however, if nitrate becomes concentrated in excessive amounts in rivers, streams, lakes or other surface waters.