Welcome to the RFF Weekly Policy Commentary, which is meant to provide an easy way to learn about important policy issues related to environmental, natural resource, energy, urban, and public health problems.
This week's commentary focuses on nitrogen. Andrew Manale provides an insightful discussion of the sources of reactive nitrogen, its environmental impacts, and why a comprehensive portfolio of policy approaches is needed to contain nitrogen pollution.
Too much of a good thing leads to a decline in our well-being.
Nitrogen is an essential element in the building blocks of life, making up 80 percent of the Earth’s atmosphere. Though it surrounds us in vast quantities, nitrogen exists in a form that is biologically inaccessible (inert), with only about a thousandth of one percent biologically available. Nature, through the electrical process of lightening, biological fixation and combustion, makes it available in a reactive form (rN), literally out of thin air. With it, life blooms because it is generally the limiting factor for growth. Too much in its reactive form, though, and the fragile systems within which higher life forms, such as mammals and reptiles, flourish fail.
Before the discovery in 1909 by the German chemist Fritz Haber of a ready means for capturing large quantities of rN from the air, societies recycled it. Human "night soil" and animal manure was captured and applied to the land to fertilize plants. It was scarce, hence it was valuable. Elsewhere where there were virgin lands, such as in the New World, early settlers mined soils for their nitrogen and then moved on when soils failed. Haber's technological breakthrough made reactive nitrogen abundant. Forty percent of all humans on this planet owe their existence to anthropogenically created reactive nitrogen because of the additional food production it has facilitated. But with abundance comes waste and ever more rN lost to the environment, harming ecological systems more than it benefits them.
Excess rN causes myriad environmental problems. It contributes to the formation of ozone, a major air pollutant. Too much of it as a fertilizer reduces the biodiversity of ecosystems. It contributes significantly to the pollution that degrades the quality of rivers, lakes, streams, and estuaries for all uses. It has caused severe eutrophication of 44 estuaries along the nation’s coasts. The excess rN that causes hypoxia (low oxygen levels) in marine environments now accounts for over 200—and growing—dead zones around the world, a number that has doubled in just 10 years.
When rN is applied as chemical fertilizer or deposited as acid rain, it acidifies waters and soils, damaging crops and forests and lowering economic output. In drinking water, it can cause health problems in infants, such as blue-baby syndrome. And, where oxidation of rN occurs, such as in agricultural soils, nitrate-saturated rivers and streams, and episodic dead zones, it forms nitrous oxide (N2O), a greenhouse gas with 300 times the warming potential of carbon dioxide, the primary greenhouse gas.
Humans have more than doubled the total annual global production of rN over natural levels, a rate that is accelerating. Fertilizer, the major source of rN, accounts for some 38 percent that is anthropogenically introduced. Other sources include burning of biomass, land clearing, and the draining of wetlands, all of which release stored (sequestered) rN back into the environment (33 percent); legumes, such as soybeans (19 percent); and combustion of fossil fuels (10 percent and growing). With economic growth in the developing world, the imbalance of reactive nitrogen in ecosystems will correspondingly increase as wealth drives meat and dairy consumption and the crops that feed livestock. Wealthier societies also consume more electrical power, generated through the combustion of fossil fuels. Fertilizer demand currently grows at over 3 percent and electricity generation at 2.9 percent a year.
The problem of increasing levels of rN in the environment would not be so severe were the rate at which the reverse process—the rate at which reactive nitrogen is converted back to inert nitrogen (denitrification) or the rate at which reactive nitrogen is biologically sequestered in soils and plants—growing as well. No longer can we count on natural denitrification and sequestration processes, such as those that occur in wetlands or seasonally wet agricultural soils and marine environments, nor grasslands and forests to serve as "sinks," for tilling soil releases rN from its organic complex. There are plenty of economic incentives to increase the amount of reactive nitrogen introduced into the environment; few or no private incentives exist for denitrification, except where clean water is scarce.
Certainly, successful national control programs for nitrogen are in place, yet there are gaps in controls. Clean Air Act regulations cover emissions of nitrogen oxides. Clean Water Act regulations cover emissions from large point sources, such as sewage treatment plants. However, continued economic growth—and hence industrial and commercial activity—only heightens the need to do ever better to maintain current levels. Moreover, not all sources of rN are regulated. Agriculture, which is largely outside the regulatory authority of the Environmental Protection Agency, is the primary user of fertilizer. Voluntary interventions for managing the loss of rN have had mixed success. Atmospheric emissions have increased fivefold since preindustrial times, with atmospheric deposition rates now exceeding natural rates by more than tenfold.
More importantly, interventions to date have treated rN as a conventional pollutant for which a control technology is identified and imposed. Many of these interventions simply shift reactive nitrogen from one medium to another rather than destroy or capture it in long-term storage, such as in sustainably managed soils. Nitrogen contained in municipal sewage sludge applied to the land and not managed sustainably can be released to water bodies in rainwater runoff. Thus excess rN in the environment is a systems issue, where sources, sinks, and control options vary across the landscape. Economic interests, left unchanged, favor increased generation and environmental emission of reactive nitrogen.
Imbalance of rN in the air, water, and soil is perhaps the best single indicator that the environment is not being managed sustainably. Nitrogen is tied to other chemical cycles, such as carbon and water. Mismanagement of one leads to imbalances of the others.
The following example illustrates the magnitude of the problem. The great majority of rN is locked up, at least temporarily, in soil organic matter—one and a half million times a million metric tons of rN (1500 petagrams or Pg). All plants and animals, in contrast, only contain one percent as much (15.2 Pg). Most of this organic rN is contained in arctic and boreal soils that have, for thousands of years under permafrost conditions, accumulated carbon and hence rN, because nitrogen and carbon exist in fixed ratios depending upon the ecosystem. If ecosystems are managed unsustainably, especially given the increasing threat of global warming, that stored nitrogen could be released, overwhelming any current regulatory effort at control of rN.
Just reducing fertilizer use, as economic theory has dictated in the past, will not suffice if a major source of emissions of reactive nitrogen comes from broadscale land modifications and land use changes. As developed and developing nations demand more agricultural production of food, feed, fiber, and now fuel, the problem only escalates. The seemingly small changes to our ecosystems over many generations— such as the draining of wetlands, the straightening of rivers, agricultural monoculture, and confined animal feeding operations—aggregate to the very large impact experienced today.
Without a new focus on reducing excess rN in the environment, decline in well-being, evidenced by degradation of habitat and our soils and water, will ultimately affect human health whether through degraded water quality or increasing global temperatures or loss of biological species. A systems problem, such as rN, requires a system solution that addresses the multiple objectives inherent in managing ecosystems and the linkages between levels of rN in soil, water, and air with management of the carbon cycle and water resources.
How does one deal with a "systems" reactive nitrogen problem? Store it, through land use and management practices that put carbon back into the soil, and protect and restore wetlands which sequester rN. Destroy it by protecting aquatic and terrestrial systems that denitrify reactive rN. And, of course, what civilizations that preceded us learned through wisdom accumulated through the ages—we can recycle it, making commercial use of waste products containing rN and transforming waste to a valued commodity.
Views expressed are those of the author.
RFF does not take institutional positions on legislative or policy questions.
The views expressed do not necessarily represent those of U.S. Environmental Protection Agency or other federal entities.
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