Reactive nitrogen

Reactive nitrogen ("Nr") is a term used for a variety of nitrogen compounds that support growth directly or indirectly. Representative species include the gases nitrogen oxides (NO_x), ammonia (NH₃), nitrous oxide (N₂O), as well as the anion nitrate (NO₃). Most of these species are the result of intensive farming, especially the (mis)use of fertilizers. Although required for life, nitrogen is stored in the biosphere in an unreactive ("unfixed") form N₂, which supports on a few life forms. Reactive nitrogen is however "fixed" and is readily converted into protein, which supports life, leading to depletion of oxygen in fresh waters by eutrophication.