Nitrogen Cycle
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted between its various chemical forms as it circulates through the atmosphere, terrestrial, and aquatic ecosystems.
Key Processes
| Process | Description |
|---|---|
| Nitrogen fixation | Conversion of N₂ to NH₃ by bacteria or industrial synthesis (Haber-Bosch) |
| Nitrification | Oxidation of NH₃ to nitrite (NO₂⁻) and nitrate (NO₃⁻) by bacteria |
| Assimilation | Uptake of inorganic nitrogen by plants and microorganisms |
| Ammonification | Decomposition of organic nitrogen back to NH₃ |
| Denitrification | Reduction of NO₃⁻ to N₂ by anaerobic bacteria |
| Anammox | Anaerobic oxidation of NH₄⁺ with NO₂⁻ to produce N₂ |
Anthropogenic Disruption
Human activities — primarily the Haber-Bosch synthesis of ammonia, fossil fuel combustion, and livestock production — have significantly accelerated the global nitrogen cycle, leading to reactive nitrogen (Nr) deposition in terrestrial and aquatic ecosystems.
According to the European Nitrogen Assessment (2011), Europe loses between €70 billion and €320 billion per year through the effects of excess reactive nitrogen on human health, ecosystems, and climate.
Relevance to Ammonia
Ammonia (NH₃) is the central molecule in the nitrogen cycle. It is the primary product of biological nitrogen fixation, the main substrate for nitrification, and a major atmospheric pollutant from agricultural sources.