Nitrogen is recycled constantly through the Earth?s ecosystem. Natural processes convert nitrogen gas, which makes up 78 percent of the air, into essential chemical compounds. Plants and animals then use these nitrates to facilitate basic life functions.
When animals and plants die, nitrogen compounds seep into the soil. Plants convert these nitrates into growth proteins, and animals then feed on the plants. In this way, nitrogen is passed along the food chain. Bacteria also plays a part, converting waste nitrogen into gas that returns to the air. Even though nitrogen is continually being recycled, it's still possible to produce too much of it. Excessive fertilization and fossil fuel consumption by humans has increased the amount of nitrogen in the air, and this has led to increased air and water pollution.