Why are Nitrogen Concentrations an indicator of Water Quality?

Abnormal levels of Nitrogenous Compounds generally indicates pollution. Most of the nitrogen found in water originates from the decay from the remains of plants and animals. Ammonia Nitrogen is the most common form of nitrogen from an effluent involving the biological breakdown of animal waste products. Since it is readily oxidizes to either nitrite or nitrate under aerobic conditions, high amounts of this pollutant may indicate a fairly fresh or recent pollution event. Although to a lesser extent than nitrate-nitrogen, ammonia can be utilized by aquatic plants and algae to support their growth. Examples of sources of this type of nitrogen would be from wastewater treatment plants, failing septic tank systems, and runoff from livestock farms. When dissolved oxygen is readily available, bacteria quickly oxidize ammonia to nitrate through a process known as nitrification. Other types of bacteria produce ammonia as they decompose dead plant and animal matter. Depending on temperature and pH (a measurement of “acidity”), high levels of ammonia can be toxic to aquatic life. High pH and warmer temperatures increase the toxicity of a given ammonia concentration. High ammonia concentrations can stimulate excessive aquatic production and indicate pollution. Important sources of ammonia to lakes and streams can include: fertilizers, human and animal wastes, and by-products from industrial manufacturing processes. Techniques to prevent high ammonia concentrations involve filtration of runoff water especially from barnyards and other areas where animals may be kept in larger numbers, proper septic system maintenance, and not over-fertilizing yards or fields.
In order to understand and remove nitrogen when it threatens the stability of your water source, you must understand the different forms of nitrgen and some commonly referred to terms that you will be dealing with.    

• Total Nitrogen is the sum of all nitrogen forms (TKN + NO2 + NO3)
• Total Kjeldhal Nitrogen (TKN); this is the sum of NH3 + Organic Nitrogen
• Ammonia Nitrogen (NH3)
• Nitrite (NO2)
• Nitrate(NO3)
• Nitrogen Gas (N2)
• Refractory Nitrogen is the Nitrogen that is not biologically decomposable

Each of these nitrogen components play a role in the overall nitrogen manifestation in water quality. For example, for every 1 part ammonia(NH3) converted to nitrate (NO3) - 7.1 parts of alkalinity are depleted, and for every 1 part nitrate (NO3) removed - 3.6 parts alkalinity are recovered.  

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 field and lawns and discharges from car exhausts. Bacteria in water quickly convert nitrites [NO2-] to nitrates [NO 3 -] and this process uses 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. 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. Nitrite/nitrogen levels below 90 mg/L and nitrate levels below 0.5 mg/L seem to have no affect on warm water fish. Because nitrogen is such an involved chemical, its consequences exceed simply water quality and extend to their consequences to organisms.

On one hand, you do not want nitrogenous compounds to rise too high.  Monitoring studies conducted at national and state levels show that nitrogen (N) concentrations in groundwater exceed health standards more often than other common contaminants, such as pesticides. A nationwide survey conducted by EPA showed that 1.2 percent of community and 2.4 percent of private drinking water wells exceeded the 10 parts per million (ppm) nitrate-nitrogen (NO3-N) standard. Though it rarely occurs, you also do not want nitrogen to drop too low. Nitrogen-containing compounds act as nutrients in streams, rivers, and reservoirs. Nitrite/nitrogen levels below 90 mg/L and nitrate levels below 0.5 mg/L seem to have no affect on warm water fish.