Distorted nutrient cycles

When discussing climate change it is primarily the global carbon cycle that is in focus. Human activities have a strong impact also on global nutrient cycles, primarily nitrogen and phosphorus. Increasing levels of phosphorus in the marine environment is believed to have been the key driver behind earlier global scale ocean anoxic events, potentially explaining past mass extinctions of marine life. The nitrogen cycle is more complex than that of phosphorus as it is a biological cycle rather than a geological one. There is also a bigger variety of nitrogen species (ammonium, nitrate, nitrite, nitrous oxide etc) that can interact in various processes. The amount of these reactive nitrogen species (reactive as opposed to nitrogen gas, N2, which is inert) is increasing rapidly. Human activities now convert more N2 from the atmosphere to reactive nitrogen species than all of the Earth’s terrestrial processes combined (Rockström et al. 2009). Nitrogen contributes to anoxia in the marine environment, but also to climate change through nitrous oxide. Nitrous emissions also contribute to acidification, formation of ground level ozone, and nitric oxides have a strong negative impact on human health in urban environments all over the world.

The key remedy to the potential threat from these distorted nutrient cycles is simple in theory: increased recycling of nutrients to avoid increasing levels of reactive nitrogen species and phosphorus emissions into the environment.


Rockström, J., W. Steffen, et al. (2009). “A safe operating space for humanity.” Nature 461(7263): 472-475.

Rockström, J., W. Steffen, et al. (2009). “Planetary boundaries: Exploring the safe operating space for humanity.” Ecology and Society 14(2): 32.