Nitrogen, a fundamental element, constitutes approximately 78% of Earth’s atmosphere as inert diatomic nitrogen gas (N₂). While this form is harmless and essential for life, human activities have dramatically increased “reactive nitrogen” compounds. Reactive nitrogen, which includes forms like nitrates, ammonia, and nitrogen oxides, is biologically active and can cause significant environmental and health problems when present in excess.
Harm to Aquatic Environments
Excess reactive nitrogen impacts aquatic ecosystems, initiating eutrophication. This occurs when nitrogen runoff from agricultural fertilizers and wastewater enters water bodies, stimulating rapid algal growth. Dense algal blooms cover the surface, blocking sunlight from underwater plants and killing them.
When algae die, bacteria decompose them, consuming dissolved oxygen. This oxygen depletion creates hypoxic or anoxic “dead zones.” The Gulf of Mexico, for instance, experiences a large recurring dead zone each summer due to nutrient pollution from the Mississippi River Basin. These dead zones result in loss of aquatic biodiversity and disrupt food webs.
Atmospheric Degradation
Nitrogen compounds contribute to atmospheric degradation. Nitrogen oxides (NOx), primarily from fossil fuel combustion in vehicles and power plants, form ground-level ozone. This ozone is a major component of photochemical smog, which can cause respiratory issues. NOx also reacts with water and oxygen to form nitric acid, a primary contributor to acid rain.
Acid rain damages forests, acidifies soils, and corrodes infrastructure. Nitrous oxide (N₂O) is also a concerning nitrogen compound. N₂O is a potent greenhouse gas, with a warming potential significantly higher than carbon dioxide. It persists in the atmosphere for an average of 114 years. N₂O is also the leading cause of stratospheric ozone depletion, an issue for the ozone layer.
Direct Risks to Human Well-being
Reactive nitrogen compounds pose direct risks to human health through contaminated drinking water and air pollution. Nitrates in drinking water, often from agricultural runoff and wastewater, are hazardous for infants under six months. When ingested, nitrates convert to nitrites in the gut, combining with hemoglobin and reducing oxygen transport. This condition, methemoglobinemia or “blue baby syndrome,” causes bluish skin discoloration and can be life-threatening.
Inhaling nitrogen oxides (NOx) and particulate matter leads to respiratory problems. Exposure to elevated nitrogen dioxide (NO₂) irritates the respiratory tract, aggravating asthma and increasing susceptibility to infections. Long-term exposure to NO₂ may contribute to chronic lung diseases like bronchitis and chronic obstructive pulmonary disease (COPD).
Impacts on Land Ecosystems
Excess nitrogen deposition alters terrestrial environments, impacting soil chemistry and plant communities. When reactive nitrogen accumulates, it can lead to acidification, reducing soil pH and depleting base cations like calcium and magnesium. This change creates nutrient imbalances, affecting the availability of other nutrients for plant growth.
Over-enrichment of nitrogen favors fast-growing, nitrogen-loving plant species. These species often outcompete native plants adapted to lower nitrogen conditions, reducing overall plant biodiversity. This shift in plant communities can disrupt ecosystem stability and negatively affect forest health.