ABSTRACT
Nitrogen is an element essential to life. It is abundant in the atmosphere, mostly as dinitrogen (N2), representing roughly four- fths by volume or three-fourths by weight of the total gas, the rest being mainly oxygen and small amounts of carbon dioxide and trace amounts of other common gases. Small amounts of oxides of nitrogen are also present. In soil, sediment, freshwater, and ocean water, nitrogen exists in both inorganic and organic forms. Geomicrobially important inorganic forms include ammonia and ammonium ion, nitrate, nitrite, and gaseous oxides of nitrogen. Table 13.1 (Fenchel and Blackburn, 1979; Brock and Madigan, 1988) lists the estimated abundance of some of these forms as well as that of organic nitrogen in the environments (see also Stevenson, 1972). Geomicrobially important organic nitrogen compounds include humic and fulvic acids, proteins, peptides, amino acids, purines, pyrimidines, pyridines, other amines, and amides.
