Nitrogen surrounds us. Nitrogen (N) is required by all life on earth. N is also the most abundant gas in our atmosphere, existing primarily as N2, a form of N that almost all plants and animals cannot use. It is therefore termed non-reactive nitrogen (Nn-r). Reactive forms of nitrogen (Nr), nitrogen that can be used by organisms, is a small fraction of what’s naturally found in the atmosphere. However, humans learned in the early 1900s to change N2 into reactive forms of N to create N-based fertilizers to increase plant growth. Humans also began to burn fossil fuels, changing Nn-r to Nr. This Nr is the N that is most important to us. Reactive nitrogen causes a cascade of effects. Nr can enter ecosystems from the air or through fertilizer application to soils, having unintended effects. Nr cycles through many other forms that can move from the soil into water resources or to and from the atmosphere. For example, too much Nr in streams can cause overgrowth of algae that chokes out fish. Too much Nr in soils can damage non-crop plants, such as trees, and change soil chemistry. Nr that goes back to the air contributes to air pollution such as acid rain, ozone, and visibility problems. Nitrogen can then fall back to land and water in wet deposition (rain or snow), or as dry deposition of Nr particles and gases.
|ISWS Miscellaneous Publication MP 207