Reactive nitrogen is necessary to grow food. It is often the limiting factor for plant growth, and without it, farming yields would be substantially lower. However, the overuse of nitrogen fertilizers has led to high levels of nutrient run off, causing algal blooms and therefore anaerobic dead zones in rivers, lakes, and oceans.
The Planetary Boundary for nitrogen is a maximum of 62 Tg N/year of intentionally fixated nitrogen. This indicator is scalable, but not easily comparable to human activity. Further, it does not consider downstream denitrification processes that can reduce the environmental impacts of nitrogen use.
The Planetary Quota indicator for nitrogen is net nitrogen consumed ≤ 62 Tg N. This includes virtual nitrogen that is lost to the environment during the production of food and accounts for the removal and recycling of nitrogen from the human nitrogen cycle. The limit is based on the premise that the Planetary Boundary value is based on the maximum flow of nitrogen to waterways. Net nitrogen consumed will eventually end in waterways. This limit can be compared to the nitrogen footprint of any scale of human activity. Current annual nitrogen consumption exceeds the PQ for nitrogen.
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