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Physics and Chemistry of Water

  1. Kenneth F. Steele,
  2. Kristofor R. Brye

Published Online: 15 APR 2005

DOI: 10.1002/047147844X.pc401

Water Encyclopedia

Water Encyclopedia

How to Cite

Steele, K. F. and Brye, K. R. 2005. Nitrogen. Water Encyclopedia. 4:517–520.

Author Information

  1. University of Arkansas, Fayetteville, Arkansas

Publication History

  1. Published Online: 15 APR 2005


Nitrogen (N) is ubiquitous in the environment and in the correct form is an essential nutrient for plants and animals. About 26.5% of Earth's nitrogen is in rocks and essentially all of the remainder (73%) is in the atmosphere as an inert monotomic gas (N2) that comprises 78% of the atmosphere. Only a small amount of nitrogen is present in the hydrosphere and biosphere, but nitrogen is a crucial nutrient there. For nitrogen to be used by organisms, it must be in a usable form; it must be combined or “fixed” with oxygen or hydrogen. The most common fixed form of nitrogen in ground water is the anionic oxide—nitrate (NO3), and the second most common form is the cationic form–ammonium (NH4+). Approximately 85% of the nitrogen in stream water is in the form of organic N and most of the rest (NO3 and NH4+) is derived from the decomposition of organic matter. N2 is converted to organic nitrogen predominantly by microorganisms and certain plants. About 96% of the nitrogen in soil is bound in organic matter, and nitrate is a product of organic matter degradation. Nitrogen occurs in five oxidation states, −3, 0, +1, +3 and +5, that are primarily the result of bacteria-induced oxidation.


  • nitrogen;
  • nitrate;
  • nitrite;
  • ammonia;
  • ammonium;
  • nitrogen cycle;
  • nitrification;
  • denitrification;
  • ammonification;
  • fixation;
  • toxicity of aquatic nitrogen species;
  • nitrogen isotopes;
  • nitrosomonas