What is the Earth's Nitrogen cycle?
Nitrogen is the most abundant element present in the atmosphere. It is a necessary component in many of the complex acids and proteins used by life on Earth.
How does it work?
Gaseous Nitrogen isn't useful to most plants and animals, and therefore solid forms of the element must be found before they can be assimilated. These chemicals, ammonium and nitrate (an ion), are created in small amounts by lightning but predominantly by nitrogen fixing bacteria. Nitrogen can then pass into they hydrologic system in a dissolved state, or be buried in the soil as dead organic matter.
The Human Factor
Farmers have long been aware that Nitrogen limited environments don't grow lush vegetation, thus they spread Nitrogen rich fertilizers on their crops to encourage unchecked growth. Most farmers however apply fertilizer liberally, often over-fertilizing by more than three times the necessary amount. This extra Nitrogen eventually makes its way through the ground water to rivers, and eventually into the ocean. River deltas and other aquatic ecosystems develop dead zones, or more technically hypoxic zones, where neither plants nor animals can survive due to the lack of oxygen caused by the effects of the Nitrogen rich runoff.
Artwork by Maija Swanson and Nick Olejniczak