A NEW GLOBAL PROBLEM
A new global environmental problem has emerged from an unexpected
source: nitrogen. Nitrogen makes up 78% of Earth's atmosphere;
however, in its atmospheric form nitrogen is an unreactive gas,
unavailable to most living things. Now a new peer-reviewed
report from the Ecological Society of America (ESA) portrays
nitrogen as a triple threat: warming the planet via the
greenhouse effect, damaging the Earth's protective ozone layer,
and reducing biodiversity (the diversity of species upon which
ecological stability ultimately rests).[1] ESA is the nation's
professional organization for ecologists. Ecology is the branch
of biological science that deals with the relationships between
organisms and their environment.
Nitrogen problems arise when human activities --mainly industrial
agriculture and combustion of fossil fuels --"fix" nitrogen out
of the atmosphere by combining it with hydrogen or oxygen. In
its "fixed" forms, nitrogen becomes biologically active. Other
human activities (burning grasslands and forests, draining
wetlands, clearing land for crops) move nitrogen out of long-term
storage, making it available to living things.
Two big natural forces fix nitrogen from the atmosphere:
lightning and microorganisms, many of which work together with
legumes (for example, peas, beans, and alfalfa) and algae. As
every farmer knows, planting legumes adds nitrogen to the soil
because microorganisms on the plants' roots fix nitrogen from the
atmosphere.
Nitrogen fixation in the oceans is poorly understood; however, on
the land, natural forces fix somewhere between 90 and 140 million
metric tonnes (MMT) of nitrogen per year. (A metric tonne = 1.1
tons, or 2200 pounds.) Of this, lightning accounts for perhaps
10 million metric tonnes (MMT) and microorganisms account for the
rest.
Human activities now fix something just over 140 million metric
tonnes (MMT) per year, thus doubling (or more) the amount of
biologically active nitrogen on the land, according to ESA.
Doubling a natural flow of a chemical like nitrogen is "an
enormous effect on a global cycle," says Dr. William H.
Schlesinger of Duke University, one of the authors of the new ESA
report.[2]
Until 1940, human industrial activities fixed almost zero
nitrogen. Therefore biologically available nitrogen has increased
very rapidly. The ESA report says, "The immediacy and rapidity of
the recent increase in N[itrogen] fixation is difficult to
overstate." Indeed, a study in 1990 found that half of all the
nitrogen ever fixed by industrial processes has been produced
after 1980.
Many of the Earth's plant species are adapted to --and function
best in --soils and waters containing low levels of available
nitrogen. By doubling the amount of available nitrogen, and by
increasing the movement of nitrogen from place to place, humans
are disrupting ecosystems on a grand scale. "No place on earth
is unaffected," says the ESA report. Here is a listing of some
of the problems identified by the ESA report:
Nitrous oxide (N2O) added to the atmosphere is a potent
greenhouse gas, allowing sunlight in but refusing to allow heat
to escape, thus tending to warm the planet (just the way the
glass roof over a greenhouse captures the sun's energy and warms
the greenhouse). Nitrous oxide presently accounts for "a few
percent" of the global greenhouse gas problem, says the ESA
report.
When it reaches the stratosphere (6 to 30 miles up in the sky)
nitrous oxide contributes to the destruction of the Earth's ozone
shield. Reducing the ozone shield in turn increases the
ultraviolet radiation striking the surface of the Earth which, in
turn, damages some of the creatures that form the bottom of the
oceans' food chains,[3] and may harm other creatures (including
humans) as well.[4]
Nitrous oxide is increasing in the atmosphere at the rate of 0.2%
to 0.3% per year. It comes from many sources: fertilizers,
nitrogen-enriched groundwater, nitrogen-saturated forests,
burning of biomass (grasses and forests), land clearing for
crops, and manufacture of nylon.
Nitric oxide (NO) plays a key role in creating toxic ozone
near the ground. Ozone is the most harmful common air pollutant
to humans and vegetation. Ozone and other nitrogen compounds are
key components of the smog that now envelopes large areas of the
planet, especially urban areas.[5]
The final product of oxidizing NO is nitric acid, a key
component of acid rain, which is damaging forests in Canada, the
U.S. and Europe. Combustion of fossil fuels is the main source of
nitric oxide (20 MMT per year), followed by biomass burning (8
MMT per year). Human sources now account for 80% of all
atmospheric NO.
NH3, or ammonia, injected into the atmosphere is a major
source of nitrogen movement between ecosystems. Each year,
fertilizer contributes 10 MMT of ammonia to the atmosphere;
domestic animal wastes contribute 32 MMT, and biomass burning
adds 5 MMT. Humans contribute 70% of all the ammonia reaching
the atmosphere.
As a result of all these contributions of fixed nitrogen to
the atmosphere, fixed nitrogen is deposited back on land and
oceans at an increased rate. In the midwestern and eastern U.S.,
nitrogen deposition from the atmosphere onto the land is more
than 10 times as great as the natural rate. In parts of northern
Europe nitrogen deposition is now more than 100 times as great as
the natural rate.
Nitrogen deposited on the land tends to move into nearby
waters, carrying with it calcium and magnesium from the soil. As
a result, both the soils and the receiving waters tend to become
more acidic. After calcium in the soil has been depleted, then
aluminum begins to move into nerby waters with the nitrogen.
Aluminum is toxic to many aquatic species.
As sulfur dioxide emissions have been curbed in recent years,
nitrogen has become better-recognized as a source of
acidification in lakes. As areas of land become
nitrogen-saturated (meaning, they can't absorb any more of it),
nitrogen run-off and consequent acidification are increasing.
Another effect of all these changes is to create nutrient
imbalances in trees. Such imbalances can lead to reduced
photosynthesis, reduced forest growth and even to increased tree
deaths, according to the ESA report.
Ecologists in Minnesota treated 162 plots of land with varying
amounts of nitrogen and examined the results.[6] After 12 years
they found three important changes:
- Some plant species disappeared completely, driven out by
others that thrived better in a high-nitrogen environment. The
result was a loss of biodiversity as "weedy" species took over
and the land became biologically impoverished.
- When these weedy species died, their higher nitrogen content
put more nitrate nitrogen into the soil. Nitrate is highly
soluble in water and moves readily into local streams. In high
concentrations, nitrate is toxic to humans; at lower
concentrations it can cause blooms of algae, depleting oxygen and
upsetting the balance of aquatic ecosystems.
- Because the weedy plants were rich in nitrogen, bacteria and
fungi that feed on nitrogen decomposed them rapidly. Because of
the rapid decomposition, these plants did not capture and retain
any more carbon than the plants they had displaced. This was a
disappointing discovery. Ecologists had hoped that, by
encouraging plant growth, high nitrogen levels would capture
increased carbon, thus reducing the threat of global warming from
carbon dioxide, the main greenhouse gas. It turns out not to work
that way. Evidently, planting trees won't get us out of the
global warming jam.[7]
The nitrogen content of the Mississippi River has more than
doubled since 1965, and nitrate concentrations in the major
rivers of the northeastern U.S. have increased 3-to 10-fold since
1900, according to the ESA report. The same is true of European
rivers. Nitrogen from rivers is now reaching the Atlantic Ocean
at rates 2 to 20 times as great as during pre-industrial times.
Around the North Sea, the increase has been 6-to 20-fold.
Nitrogen entering the oceans is causing fertilization and
eutrophication of estuaries and coastal seas: "...it represents
perhaps the greatest threat to the integrity of coastal
ecosystems," says the ESA report. Eutrophication is the
excessive growth of plants, leading to oxygen deficiency which
has killed significant numbers of fin fish and shellfish in the
Chesapeake Bay, Long Island Sound, the Black Sea, the Baltic Sea,
and elsewhere.
Nitrogen-fed algae blooms have been identified as the source of a
major outbreak of cholera in South America in 1991. The algae
harbor the cholera-causing bacterium. In 1991, 500,000 people
fell ill and 5000 died when cholera erupted along the coastline
of Peru and quickly spread to 18 other countries.[8]
These nitrogen problems are not going to be easy to solve. The
ESA report says, "The momentum of human population growth and
increasing urbanization ensure that industrial N[itrogen]
fixation will continue at high rates for decades."
The ESA report suggests that, by 2020, industrial agriculture
will be contributing 134 MMT per year, up 68% from the 80 MMT it
contributes annually today. And by 2020, fossil fuel combustion
will be contributing 46 MMT per year, about twice its present
contribution.
Obviously these projections could prove wrong if the corporations
promoting industrial agriculture and fossil fuel combustion could
be brought under control. The Ecological Society of America's
report does not consider this possibility. In the section,
"Future Prospects and Management Options," the report only
considers slightly-less-wasteful ways of using nitrogen
fertilizer on industrial farms.
Disappointingly, ESA's report never acknowledges the really
viable alternative to industrial farming, which is ecological
farming that seeks to mirror and maintain the natural ecology in
which it is practiced.[9]
As the ESA report documents to a dismaying degree, the industrial
farming model is leading to widespread deterioration of global
ecosystems. It is not sustainable.[10]
Instead of the Henry Ford model, which aims to alter natural
ecological neighborhoods to maximize short-term yields of a few
specialized crops for export to world markets, the organic
farming model achieves higher yields[11] using less energy[12]
and emphasizes food locally produced for local people with local
control.[9] It is an ecological approach that views humans as
products of, and partners in, the local ecology, not masters of
it.
--Peter Montague
(National Writers Union, UAW Local 1981/AFL-CIO) |
| [1] Peter M. Vitousek and others, "Human Alteration of the Global
Nitrogen Cycle: Sources and Consequences," ECOLOGICAL
APPLICATIONS Vol. 7, No. 3 (August 1997), pgs. 737-750.
[2] William K. Stevens, "Too Much of a Good Thing Makes Benign
Nitrogen a Triple Threat," NEW YORK TIMES December 10, 1996, pgs.
C1, C8.
[3] Kirk D. Mallot and others, "Solar UVB-induced DNA damage and
photoenzymatic DNA repair in antarctic zooplankton," PROCEEDINGS
OF THE NATIONAL ACADEMY OF SCIENCES Vol. 94 (February 1997), pgs.
1258-1263.
[4] See Arjun Makhijani and Kevin R. Gurney, MENDING THE OZONE
HOLE; SCIENCE, TECHNOLOGY AND POLICY (Cambridge, Mass.: MIT
Press, 1995), Chapter 2.
[5] National Research Council, NITROGEN OXIDES (Washington, D.C.:
National Academy of Sciences, 1977).
[6] David A. Wedin and David Tilman, "Influence of Nitrogen
Loading and Species Composition on the Carbon Balance of
Grasslands," SCIENCE Vol. 274 (December 6, 1996), pgs. 1720-1723.
[7] See Peter M. Vitousek, "Can Planted Forests Counteract
Increasing Atmospheric Carbon Dioxide?" JOURNAL OF ENVIRONMENTAL
QUALITY Vol. 20 (1991), pgs. 348-354.
[8] Paul R. Epstein and others, "Marine Ecosystems," THE LANCET
Vol. 342 (November 3, 1993), pgs. 1216-1219.
[9] Frederick Kirschenmann, "Can Organic Agriculture Feed the
World?... And is That the Right Question?" in Patrick J. Madden
and Scott G. Chaplowe, editors, FOR ALL GENERATIONS: MAKING WORLD
AGRICULTURE MORE SUSTAINABLE (West Hollywood, California: World
Sustainable Agriculture Association, 1997), pgs. 154-172. $30.00
plus shipping and handling from the World Sustainable Agriculture
Association; phone: (310) 657-7202; fax: (310) 657-3884.
[10] P.A. Matson and others, "Agricultural Intensification and
Ecosystem Properties," SCIENCE Vol. 277 (July 25, 1997), pgs.
504-509.
[11] National Research Council, ALTERNATIVE AGRICULTURE
(Washington, D.C.: National Academy Press, 1989).
[12] Sharon Clancy, FARMING PRACTICES FOR A SUSTAINABLE
AGRICULTURE IN NORTH DAKOTA (Carrington, N.D.: Carrington
Research Extension Center, 1993). Phone: (701) 652-2951.
Descriptor terms: agriculture; fossil fuel combustion; nitrogen;
global environmental problems; studies; ecological society of
america; peter vitousek; farming; fertilizer; water pollution;
eutrophication; ozone depletion; acid rain; algae blooms; global
warming; greenhouse gases; nitrous oxide; nitric oxide; nitrogen
oxides; ecology; ammonia; soil depletion; aluminum; biodiversity;
species loss; air pollution; smog; ozone pollution; chesapeake
bay; long island sound; |
