The Nitrogen Cycle

The nitrogen cycle is a biogeochemical cycle which is fundamental to many life processes. The atmosphere consists of 78% nitrogen, in the form of nitrogen gas (N₂). Nitrogen gas is fixed by bacteria in the soil and lightning into more reactive nitrogen compounds, such as ammonia nitrates, which can be used by plants. The cycle follows five main processes: fixation, nitrification, assimilation,ammonification, and denitrification, which converts reactive compounds back into nitrogen gas. During these processes nitrogen gas is broken down and forms different nitrogenous compounds, travelling through different reservoirs such as the soil, plants, animals and bacteria.

The nitrogen cycle has been taking place for billions of years, but more recently humans have begun influencing the cycle by releasing nitrogen emissions from industrial processes, synthetic fertilizers and the burning of fossil fuels. This can cause an influx of nitrogen in one part of the cycle, which is then carried throughout the cycle. Excessive nitrogen pollution can have negative effects on the environment and impact ecosystems.

Figure 1: An overview of the nitrogen cycle. The coloured arrows depict the five main stages of the nitrogen cycle, fixation (blue), nitrification (green), denitrification (red), assimilation (purple), ammonification (orange). Black arrows show human influence which are synthetic fertilizer, fossil fuel burning, waste, and runoff (the process in which pollution affects water).