Nitrogen Pollution: Too Much of a Good Thing

Nitrogen is an essential nutrient for agricultural production across the globe, but between 20-60% of the nitrogen applied to agricultural fields is lost to the environment. This wasted nitrogen has created an ongoing crisis for biodiversity, climate and human health over the last 50 years. A growing body of research has shown that we need to reduce the amount of nitrogen entering US waterways and atmosphere to meet our climate and biodiversity goals.

Nitrogen is indispensable to US agriculture, but we are applying too much of it: Nitrogen is a key nutrient required for the synthesis of DNA and proteins, the growth of plants and animals, and therefore the yields of agricultural systems. Primarily existing as a gas in our atmosphere, nitrogen can be fixed into solid form through both industrial and biological processes. Before the invention of mineral fertilizer, biological nitrogen fixers such as legumes and bacteria were the main source of nitrogen in terrestrial ecosystems, and nitrogen was one of the main limits on the amount of biomass on the planet. However, since the invention of the Haber-Bosch process, the amount of nitrogen entering the environment globally every year has almost doubled by one estimate (~130 TG), with around half of that (~66 TG) being wasted. That waste pollutes ground and surface water, contributes to smog and climate change, and is an economic loss to farmers.

Excess Nitrogen is harmful to biodiversity: Many terrestrial and aquatic ecosystems are not adapted to the amount of nitrogen that is they are now receiving. Too much nitrogen in water bodies can lead to huge algal blooms that deplete oxygen and kill aquatic life. Nitrogen deposition from the atmosphere can disrupt fragile terrestrial ecosystems and threaten endangered insects and mammals. Up to 78 species are currently listed under the ESA due to the harms caused by nitrogen pollution.

Excess Nitrogen is harmful to human health: Drinking water contaminated with large amounts of nitrogen is associated with increased risks of colon, thyroid, kidney and stomach cancer. Excessive nitrate exposure during pregnancy can lead to birth defects as well as "blue baby syndrome" in newborns. Nitrogen oxides (NO + NO2) emitted from soils through the breakdown of nitrogen also contributes to smog formation and air pollution.

Excess Nitrogen contributes to climate change: Nitrogen in the environment can naturally be broken down by microorganisms widely present in soils and water into nitrous oxide (N₂O), a potent greenhouse gas. N₂O then breaks down in the stratosphere by reacting with ozone. This combination of factors means that nitrous oxide is long-lived (since it only reacts with ozone), a potent greenhouse gas (298 times more effective than carbon dioxide), and an ozone depleter.

Reducing agricultural nitrogen waste is not just possible, it's good business: Reducing nitrogen loss from agricultural fields can simultaneously address climate, biodiversity and health crises. Adding nitrogen trapped in organic matter through amendments such as compost, planting legumes, and crop residue can serve as a slow-release fertilizer. Optimizing the timing, amount and form of nitrogen applied to match weather patterns can reduce runoff. Agricultural practices such as planting trees and grasses near water bodies and growing cover crops can trap nitrogen on fields to be used later by crops, reducing the need for fertilizer application and helping to trap nitrogen before it enters the water, reducing biodiversity and drinking water impacts.

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