Human Impact on Nitrogen Cycle

Human activities are profoundly affecting the cycling of nitrogen in nature. Over 30 x 10⁶ metric tons/yr. of N₂ is fixed in the commercial production of fertilisers, an amount almost equal to that fixed biologically. The use of N₂ fertilisers affect the distribution of N₂ on earth. Much of the nitrogen in the harvested crops becomes animal and human waste in sewage waters and eventually enters the aquatic ecosystem through runoff and leaching. Nitrogenous compounds leached into the groundwater may be abundant in irrigation and drinking water where they can cause serious health hazards. Nitrogenous compounds entering the lakes have fertilising effect resulting in algal blooms and promote cultural eutrophication.

Excessive growth of phytoplankton in eutrophic lakes produces huge quantities of biomass and finally collapse due to nutrient exhaustion. The dead organisms are consumed by detrivores which use up the oxygen supply. This problem of cultural eutrophication is, however, more severe in the case of phosphorus additions rather than nitrogen. When fossil fuels are burned we add nitrogenous compounds to the air. Large quantities of nitrogen oxide (NO) are released from vehicles and most of the NU is converted to NO₂ by combining with ozone (O₃) in the atmosphere. NO₂ is a toxic gas for 6umans and a cause of smog. It combines with water to form nitric acid, HNO₃, which forms 30% of the strong acids in the acid rain.