Why is Nitrogen an Important Parameter in Water Analysis?

Nitrogen is an essential elemental nutrient for all living organisms, including includes plants, animals, and humans. Nitrogen is a vital element in the atmosphere, appearing in its inert form (N2), and accounts for about 78% of the atmosphere by volume. Nitrogen was discovered in the 1700’s by Scotsman Carl Schelle, Swede Daniel Rutherford, and Englishman Henry Cavendish independently during this era. Though the discovery of Nitrogen is generally given credit to Rutherford since his work was published first (1).

Nitrogen plays a vital role in several industries including food preservation, agricultural, chemical, pharmaceutical, and manufacturing. Common nitrogen-containing compounds used in the industry comprise ammonia, nitric acid, organic nitrates, and cyanides. Synthetic ammonia and nitrates are common in industrial fertilizers and well-known nitrogen-containing pharmaceutical drugs include caffeine, morphine, and amphetamines.

Nitrogen plays a vital role throughout our world, and . Nitrogen plays an important role throughout the ecosystem and in human & industrial practices. In the ecosystem, we also experience a nitrogen cycle, similar to the water cycle.

What is the Nitrogen Cycle?

The nitrogen cycle is the flow of nitrogen through the ecosystem in its' various chemical forms. These forms include organic nitrogen, ammonium (NH4+), nitrite (NO2-), nitrous oxide (N20), nitric acid (NO), or inorganic nitrogen gas (N2). The nitrogen cycle documents the transformation of inorganic nitrogen gas into organic nitrogen that is then accessible to plants, which is essential to all animal life. The steps of the nitrogen cycle include nitrogen fixation, nitrogen assimilation, ammonification, nitrification, and denitrification. These steps also do not occur in sequential order altogether.

Nitrogen fixation is the conversion of nitrogen gas (N2) into nitrites and nitrates. Most fixation occurs through symbiotic bacteria known as diazotrophs, which are bacteria that contain a nitrogenase enzyme that utilizes nitrogen gas and hydrogen to produce ammonia (1). The ammonia that is produced is then transformed by the bacteria into other organic compounds.

Nitrogen assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment (2).

Ammonification is when bacteria or fungi convert organic nitrogen from deceased animals or animal waste back into ammonium (1). Several enzymes are required to execute this process.

Nitrification is the conversion of ammonium to nitrate. This process is mainly done by bacteria that reside in the soil and other nitrifying bacteria (1). Different types of bacteria are responsible for converting nitrogen into its' different forms. For example, Nitrosomonas bacteria are responsible for the oxidation of ammonia into nitrate (NO2-). 

Denitrification is the process of reducing nitrogen back into nitrogen gas (N2), the final step in the cycle. Again, this step in the process is done by another type of bacteria. Under anaerobic conditions, this bacteria uses nitrate as an electron acceptor in place of oxygen during respiration (1). By using nitrate during respiration, the byproduct is nitrogen gas.

Below is a diagram of the nitrogen cycle outlining where each step occurs in the ecosystem.