Human interference in the nitrogen cycle

Human activities have had several effects on the current nitrogen cycle.

One such intervention has been the addition of large amounts of nitric oxide (NO) to the atmosphere resulting from the burning of fossil fuels. This nitric oxide combines with oxygen to form nitrogen dioxide (NO₂), which in turn reacts with water vapor to form nitric acid (HNO₃). Droplets of nitric acid dissolved in rain or snow are components of acid deposition, which along with other air pollutants can cause damage to both terrestrial and aquatic ecosystems, corrode metals, and damage structures.

A second intervention is the release of nitrous oxide (N₂O), a greenhouse gas, and results primarily from agricultural activities including inorganic nitrogen fertilizer application and livestock wastes.

Third, agricultural runoff and the discharge of municipal sewage add nitrogen compounds to aquatic ecosystems. This excess nitrogen stimulates rapid growth of photosynthesizing algae (eutrophication). As these algae die, their decomposition robs the water of dissolved oxygen, which in turn causes other aquatic organisms, including many fishes, to die of suffocation.

Fourth, nitrates from fertilizer can also leach through the soil and contaminate groundwater. Nitrate-contaminated groundwater is dangerous, particularly for infants and children.   

Glossary  :

Fossil fuels: All of these fuels were formed from the remains of plants and animals that lived millions of years.  

Fossil: A remnant or trace of an organism of a past geologic age, such as a skeleton or leaf imprint, embedded and preserved in the earth's crust.