Problems with nitrogen pollution

by David Bainbridge and Mark George


ne of the central challenges in environmental economics has been the valuation of environmental resources and services. This valuation usually takes place within a framework of a benefit and cost analysis of projects affecting environmental resources, nature's services, or natural resource damages. These assets include air, surface and groundwater, woodlands, unique natural landscapes, and much more.

These environmental assets provide several essential functions: ecological system support, waste removal (sometimes referred to as waste "sinks"), and amenities which are consumed directly by individuals (clean air, water for household use and recreational services in natural areas). Along with other economic goods and services, all of these functions contribute, directly or indirectly, positively or negatively, to our well being. The environmental functions, and therefore the assets which provide them, are also economic goods or services because in modern society they are not free. Their provision, maintenance or conservation entails giving up the production of some alternative goods or services even though their use does not always involve market transactions and explicit prices may not exist.

Nitrogen pollution is a good example of the challenge of costing these non-market transactions. Nitrogen gas (N2) makes up more than 70 percent of the innermost layer of the atmosphere. But this large reservoir of the earth's nitrogen cannot be used directly as a nutrient by plants because they cannot absorb nitrogen gas. As a result, nitrogen is often the limiting factor for the growth of plants and animals in ecosystems. This is one reason farmers use nitrogen fertilizer to support crop growth.



A little science: the nitrogen cycle

  The conversion of atmospheric nitrogen gas into chemical forms that are useful to plants, nitrogen ions (N03-) and ammonium ions (NH4+), is called nitrogen fixation, and is done primarily by cyanobacteria in soil and water and by rhizobium bacteria living in small nodules on roots of a wide variety of plants. These plants convert organic nitrate ions and ammonium ions in soil into DNA, proteins and other nitrogen containing nutrients. Animals, in turn, get their nitrogen from eating plants or other animals. After nitrogen has served its purpose in living organisms, bacteria and other organisms convert the nitrogen-rich organic compounds, wastes, castoff particles and dead organisms into simpler inorganic compounds such as water-soluble salts containing ammonium ions (NH4+). Other specialized bacteria, primarily anaerobic (without oxygen) bacteria in the soil or in sediments at the bottom or of lakes, oceans, swamps, and bogs, then convert these inorganic forms of nitrogen back into nitrite (N02-) and nitrate (N03-) ions, and then into nitrogen gas, which is released into the atmosphere to begin the cycle again.


Nitrogen and humans


Preindustrial nitrogen cycling is assumed to have been roughly in balance, and atmospheric levels of nitrous oxide (N20) measured in bubbles in glacier ice hovered around 285 ppm for many thousands of years. But human activity in the last 200 years has thrown the system severely out of balance. The nitrous oxide level in the atmosphere has risen rapidly and is close to 310 ppm. More than 3.2 million tons of nitrogen are deposited in the United States each year from the atmosphere. Atmospheric deposition of nitrogen compounds may occur through wet deposition in fog, freezing rain, hail, rain and snow, or in dry deposition as droplets, gases, and particulates.

Nationally, the largest sources of this nitrogen are point sources. Coal- and oil-burning electric utilities and large industries account for more than 50 percent of national nitrogen emissions. These atmospheric inputs have been largely ignored because they do not fit the traditional definition of a nonpoint source. For example, releases of nitrogen into the air from point sources, such as the combustion process of power plants and industries, are called nonpoint sources of water pollution when that nitrogen reaches water bodies through precipitation.


What goes up


More than half of the nitrogen emitted from fossil fuel-burning plants, vehicles, and other sources in the United States is deposited on US watersheds. Areas of the country with the greatest rainfall and worst atmospheric pollution tend to have the highest loads of nitrogen deposition from the atmosphere. In the Northeastern United States, atmospheric deposition of nitrogen in rain, snow, and other forms accounts for about one third of the total nitrogen inputs to watersheds. The amount of nitrogen carried by streams also is generally highest where runoff is greatest.

Because nitrogen is a natural component of ecosystems, it was not recognized as a threat for a long time; many people actually thought increased nitrogen levels would be beneficial. But, more and more studies are showing that it is likely to cause severe declines in native plant communities by favoring weedy, high-nitrogen-response plants.

In Southern California, the major problem is the particulate dryfall from nitrogen added by combustion of fossil fuels for transportation and equipment. Autos, trucks, buses, planes, leaf blowers, lawn mowers and jet skis all add their nitrous oxides to the atmosphere. The nitrous oxide combines with other compounds to become the black dust that quickly covers a car or awning in urban areas.

Old cars without pollution controls may produce more than 3.3 grams per mile, while new cars can be as low as 0.2 grams per mile driven. If you drive 9,600 miles a year, you could be adding as much as 70 pounds of nitrogen to your local environment. Southern California atmospheric levels can approach 25 mg/cubic meter of air and these little dust particles add up, reaching annual deposition of levels up to more than 80 pounds per acre. This is almost double the world average application of nitrogen fertilizer used on cropland.


Too much of a good thing


Studies are just beginning in California, but where these nitrogen additions have been studied for a longer time, the results have been catastrophic. While many environmentalists have gotten caught up in the struggle to reduce exotic weed dispersion, off-highway vehicle activities and development, it is becoming increasing clear that it may be disruptions in more basic ecosystem processes can cause long term damage to native plant communities and may be the more serious problem. Nitrogen pollution is a good example.

A twelve year study of Minnesota grasslands showed that added nitrogen decreased species diversity and dramatically changed community composition. Species richness declined by 50 percent and bunch grasses were replaced by weedy European grasses. In England, diversity in meadow plots dropped from 30 species to 3 at higher nitrogen levels over 90 years.

Recent reports from Sweden, where deposition can exceed 100 pounds per acre, are equally alarming. In some areas, the beneficial mycorrhizal fungi have produced no fruiting bodies for six years. All of the work to preserve local biodiversity in California, and especially in San Diego, with an estimated cost approaching $1 billion for the Multiple Species Conservation Plans, may be derailed unless we can control nitrogen pollution.


What can be done about it?


Research is needed to determine the effects of nitrogen on San Diego's ecosystems and waterways, and planning to reduce future impacts. These can be funded by impact fees on gasoline sales, airport operations and ship traffic. This money should come from existing taxes (make the polluter pay), but new impact fees could be added.

San Diego used an estimated 1.1 billion gallons of gas in 1997. A fuel tax increase of five cents per gallon would provide $55 million for environmental restoration and treatment to offset nitrogen pollution.

According to San Diego International Airport's Operations Department, more than 14.8 million passengers (a combination of incoming and outgoing) utilized Lindburgh Field in 1998. More than 90,000 tons of freight and 33,000 tons of mail were also shipped through the facility. Had there been a $1 per passenger environmental maintenance fee, $15 million could have been collected for environmental improvement. Attaching similar fees to freight and mail could also generate significant financial resources. Flight operations at Miramar MCAS should also be assessed and a nitrogen pollution abatement fee should be collected.

Ship traffic is also a major source of pollutants as diesel engines are very big emitters and the residual fuels they burn increase pollutants. Worldwide ship operations produce enough nitrogen to equal almost half the United States emissions. A port fee should be assessed for pollution loading.

These funds could be used to treat damaged ecosystems, perhaps through the San Diego Environmental Restoration Department or through grants and contracts. They could also support educational programs, develop cleaner engine technologies and promote cleaner transportation options such as bicycling and flywheel-powered busses.

Ultimately, we may have to spread amendments to absorb and mitigate against nitrogen pollution, much as Sweden has added lime to 8,000 lakes to offset acid rain from power plants in England and Europe. This would be very expensive, but current generations have an obligation to fulfill in providing future generations with their fair share of healthy resources and adequate quality of life. Improving the quality of the environment locally, nationally, and internationally must be a top priority for policy makers.

  David Bainbridge is Coordinator of Environmental Studies at United States International University, San Diego, CA.