General Information:

Nitrogen makes up 78% of the atmosphere as gaseous molecular nitrogen, but most plants can use it only in the fixed forms of nitrate and ammonium (for specific information on ammonium, please refer to Ammonia section). Nitrate and nitrite are inorganic ions occurring naturally as part of the nitrogen cycle (Smith, 1990).

Nitrogen Cycle:

The nitrogen cycle is composed of four processes. Three of the processes--fixation, ammonification, and nitrification--convert gaseous nitrogen into usable chemical forms. The fourth process, denitrification, converts fixed nitrogen back to the unusable gaseous nitrogen state (Smith, 1990).

In temperate zones, soil nitrate concentrations will vary seasonally with temperature and moisture levels. Fall and winter rains thoroughly remove all nitrates from the soil. No nitrate is naturally added to the soil during the late fall and winter because the cold weather prohibits mineralization and nitrification processes.

During the spring and summer, the increased nitrogen-fixing activity of organisms and the addition of fertilizer causes the concentration of nitrates in the soil to steadily increase. Most of this nitrate is absorbed by plants. Thus, the removal of crops in the fall increases the chances for large flushes of nitrate from the soil to water bodies. Some leaching may occur in the spring if crops are not well- established enough to absorb the nitrogen (Gower, 1980).

Numerical Categories: Limits Suggested to Maintain Designated Use:

Designated Use Limit (mg/l)(AWWA 1990)
Nitrate (NO3-N):
      Human Consumption 10.0
      Aquatic Life
            Warmwater fish 90.0
            Brewing 30.0
Nitrite (NO2-):
      Human Consumption 1.0
      Aquatic Life
           Warmwater fish 5.0
      Human Consumption 10.0
      Agriculture (Livestock etc.) 100.0
      Aquatic life
           Estuaries (recommended)
               maximum diversity 0.1* (and phosphorus 0.01)
               moderate diversity 1.0* (and phosphorus 0.1)

Health Effects:

Environmental Effects:

The growth of macrophytes and phytoplankton is stimulated principally by nutrients such as phosphorus and nitrogen. Nutrient-stimulated primary production is of most concern in lakes and estuaries, because primary production in flowing water is thought to be controlled by physical factors, such as light penetration, timing of flow, and type of substrate available, instead of by nutrients (McCabe et al., 1985).

Excessive aquatic plant production may negatively impact fresh water and estuarine environments in the following ways:
  1. Algal mats, decaying algal clumps, odors, and discoloration of the water will interfere with recreational and aesthetic water uses.
  2. Extensive growth of rooted aquatic macrophytes will interfere with navigation, aeration, and channel capacity.
  3. Dead macrophytes and phytoplankton settle to the bottom of a water body, stimulating microbial breakdown processes that require oxygen. Eventually,dissolved oxygen will be depleted.
  4. Aquatic life uses may be hampered when the entire water body experiences daily fluctuations in dissolved oxygen levels as a result of nightly plant respiration. Extreme oxygen depletion can lead to death of desirable fish species.
  5. Siliceous diatoms and filamentous algae may clog water treatment plant filters and result in reduced time between backwashing (process of reversing water flow through the water filter in order to remove debris).
  6. Toxic algae (occurrence of "red tide") have been associated with eutrophication in coastal regions and may result in paralytic shellfish poisoning (Mueller et al., 1987).
  7. Algal blooms shade submersed aquatic vegetation, reducing or eliminating photosynthesis and productivity (Dennison et al., 1993; Batiuk et al., 1992)


  1. Nonpoint:
  2. Point source: Industries that use nitrates in manufacturing may release nitrate in the effluent water. Nitrate is used in the following processes: meat curing, production of fertilizer, explosives, glass, heat-transfer fluid, and heat-storage medium for solar-heating applications (Kubek et al., 1990). Additional nitrates may be contributed by sewage treatment systems and sewage treatment bypass outfalls (during high flow periods). Estuaries may be particularly susceptible to nutrient enrichment from offshore sewage pipe outfalls (Kennish, 1992).

Regional Trends of Nonpoint Source Pollution in the United States:

The origin of nitrogen pollution usually differs according to the region in which the water body is located.

Mode of Transport:

Sampling Techniques

A. Nitrate-Nitrogen (APHA, 1992)

  1. Ultraviolet Spectrophotometric Screening Method:
  2. Ion Chromatography Method:
  3. Nitrate Electrode Method:
  4. Cadmium Reduction Method: Nitrate is reduced to nitrite in the presence of cadmium. The nitrite concentration is determined by diazotizing with sulfanilamide and coupling with NED dihydrochloride to form a colored azo dye that is measured colorimetrically.
  5. Automated Cadmium Reduction Method:
  6. Titanous Chloride Method: Nitrate is determined potentiometrically using an NH3 gas-sensing electrode after nitrate is reduced to NH3 by a titanous chloride reagent. (Proposed 1992)
  7. Automated Hydrazine Reduction Method: Nitrate is reduced to nitrite by hydrazine sulfate. The nitrite concentrations is determined by diazotizing with sulfanilamide and coupling with NED dihydrochloride to form a colored azo dye that is measured colorimetrically. (Proposed 1992)
B. Total Kjeldahl Nitrogen (APHA, 1992; EPA, 1984)
  1. Digestion followed by distillation.
  2. Automated Phenate Colorimetric Method: Reaction produces indophenol, an intensely blue compound.