The activities of humans have severely altered the nitrogen cycle. The additional nitrogen entering the groundwater system eventually flows into streams, rivers, lakes, and estuaries. In these systems, the added nitrogen can lead to eutrophication . Increased deposition of nitrogen from atmospheric sources because of fossil fuel combustion and forest burning. Both of these processes release a variety of solid forms of nitrogen through combustion.
Livestock release a large amounts of ammonia into the environment from their wastes.
This nitrogen enters the soil system and then the hydrologic system through leaching, groundwater flow, and runoff . Sewage waste and septic tank leaching .