Nitrogen and water quality

Nitrogen is one of the most abundant elements; about 80 percent of the air we breath is nitrogen. It is found in the cells of all living things and is a major component of proteins. Inorganic nitrogen may exist in the free state as a gas N2, or as nitrate NO3-, nitrite NO2- or ammonia NH3. Organic nitrogen is found in proteins, and is continually recycled by plants and animals. The nitrogen cycle is shown below:

Environmental Impact: Nitrogen-containing compounds act as nutrients in streams, rivers, and reservoirs. The major routes of entry of nitrogen into bodies of water are municipal and industrial wastewater, septic tanks, feed lot discharges, animal wastes (including birds and fish), runoff from fertilized agricultural fields and lawns, and discharges from car exhausts. Bacteria in water quickly convert nitrites [NO21-] to nitrates [NO3-] and this process use up oxygen. Excessive concentrations of nitrites can produce a serious condition in fish called "brown blood disease." Nitrites also can react directly with hemoglobin in the blood of humans and other warm-blooded animals to produce methemoglobin. Methemoglobin destroys the ability of red blood cells to transport oxygen. This condition is especially serious in babies under three months of age as it causes a condition known as methemoglobinemia or "blue baby" disease. Water with nitrate levels exceeding 1.0 mg/L should not be used for feeding babies. High nitrates in drinking water can cause digestive disturbances in people, but nitrite/nitrogen levels below 90 mg/L and nitrate levels below 0.5 mg/L seem to have no affect on warm water fish.

The major impact of nitrates/nitrites on fresh water bodies is that of enrichment or fertilization called eutrophication. Nitrates stimulate the growth of algae and other plankton, which then provide food for higher organisms (invertebrates and fish); however an excess of nitrogen can cause over-production of plankton, and as they die and decompose they use up the oxygen which causes other oxygen-dependent organisms to die.

Criteria: Nitrates/nitirites should remain below 10 mg/L in water to be used as a domestic water supply.


2007 Arizona Board of Regents for The University of Arizona