Environmental Encyclopedia

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Environmental Encyclopedia 3

Population growth

Populations increase through reproduction, but they

do not increase infinitely because of environmental limita-

tions, including disease, predation,

competition

for space

and nutrients, and

nutrient

shortages. These limits to popu-

lation growth are collectively known as environmental

resis-

tance

An important concept in environmental resistance is

the idea of

carrying capacity

. Carrying capacity is the

maximum number of individuals a habitat can support. In

any finite system, there is a limited availability of food, water,

nesting space, and other essentials, which limits that system’s

carrying capacity. When a population exceeds its environ-

ment’s carrying capacity, shortages of nutrients or other ne-

cessities usually weaken individuals, reduce successful repro-

duction, and raise death rates from disease, until the

population once again falls below its maximum size. A popu-

lation that grows very quickly and exceeds its environment’s

carrying capacity is said to overshoot its environment’s capac-

ity. A catastrophic

dieback

, when the population plummets

to well below its maximum, usually follows an overshoot. In

many cases populations undergo repeated overshoot-dieback

cycles. Sometimes these cycles gradually decrease in severity

until a stable population, in equilibrium with carrying capac-

ity, is reached. In other cases, overshoot-dieback cycles go

on continually, as in the well known case of lemmings.

Prolific breeding among these small arctic rodents leads to

a population explosion every four to six years. In overshoot

years, depletion of the vegetation on which they feed causes

widespread undernourishment, which results in starvation,

weakness, and vulnerability to predators and disease. The

lemming population collapses, only to begin rebuilding,

gradually approaching overshoot and another dieback. At

the same time, related populations fluctuate in response to

cycles in the lemming population: populations of owls and

foxes surge when lemmings become plentiful and fall when

lemmings are few. The grasses and forbs on which lemmings

feed likewise prosper and diminish in response to the lem-

ming population.

As a population grows, the number of breeding adults

increases so that growth accelerates. Increase at a constant

or accelerating rate of change is known as

exponential

growth

. If each female lemming can produce four young

females, and each of those produces another four, then the

population is multiplied by four in each generation. After

two generations there are 16 (or 24) lemmings; after three

generations there are 64 (34); after four generations there

are 256 (44) lemmings, if all survive. When environmental

resistance (predation, nutrient limitations, and so on) causes

a population to reach a stable level, without significant in-

creases or decreases over time, population equilibrium is

achieved. Generally we might consider stable (equilibrium)

1117

populations the more desirable situation because repeated

diebacks involve extensive suffering and death.

These principles of population biology have strongly

informed our understanding of human population changes.

Over the centuries the world’s human population has tended

to expand to the maximum allowed by available food, water,

and space. When humans exceeded their environment’s car-

rying capacity, catastrophic diebacks (usually involving dis-

ease,

famine

, or war) sometimes resulted. However, in many

cases, diebacks have been avoided through emigration, as in

European migrations to the Americas, or through technolog-

ical innovation, including such inventions as agriculture,

irri-

gation

, and mechanization, each of which effectively ex-

panded environmental carrying capacities. For tens of

thousands of years the human population climbed very grad-

ually, until about the year 1000, when it began to grow

exponentially. Where we once needed a thousand years (200

to 1200

A.D.

) to double our population from 200 million to

400 million, at current rates of growth we would require

only 40 years to double our population. Since the eighteenth

century, population theorists have increasingly warned that

our current pattern of growth is leading us toward a serious

overshoot, perhaps one that will permanently damage our

environment

and result in a consequent dieback. The only

course to avoid such a catastrophe, argue population theo-

rists, is to stabilize our population somewhere below our

environment’s carrying capacity.

Popular awareness of population issues and agreement

with the principle of population reduction have spread in

recent years with the publication of such volumes as The

Population Bomb by Paul Ehrlich, and The Limits to Growth

by Donella Meadows and others. The current population

debate, however has older roots, especially in the work of

Thomas Malthus, an English cleric who in 1798 published

An Essay on the Principle of Population as It Affects the Future

Improvement of Society. Malthus argued that, while un-

checked human population growth increases at an exponen-

tial rate, food supplies increase only arithmetically (a constant

amount being added each year, instead of multiplying by a

constant amount). The consequence of such a disparity in

growth rates is starvation and death. The remedy is to reduce

our reproductive rates, where possible by “moral restraint,”

but where necessary by force. Malthus’ work has remained

well-known principally because of its conclusion about social

policy: because providing food and shelter to the poor only

allows them to increase their rates of “breeding,” assistance

should be withheld. If the poorer classes should starve as a

result, argued Malthus, at least greater rates of starvation at

a later date would be avoided. This conclusion continues to

be promoted today by neo-Malthusians, who protest the

principle of aiding developing countries. Poorer countries,

neo-Malthusians point out, have especially dangerous

Environmental Encyclopedia 3

Population growth

Human population growth. (Illustration by Electronic Illustrators Group.)

growth rates. If wealthy countries provide assistance today

because they cannot bear to watch the suffering in poorer

nations, they only make the situation worse. By giving aid,

donor nations only postpone temporarily the greater suffer-

ing that will eventually result from artificially supported

growth rates.

Naturally this conclusion is deeply offensive to devel-

oping nations and to those who sympathize with the plight

of poorer countries. Malthusian conclusions are especially

harsh in situations where military and economic repression,

often supported by North American and European govern-

ments, have caused the poverty. Those who defend aid to

developing countries argue that high reproductive rates often

result from poverty, rather than vice versa. Where poor nutri-

tion and health care make infant

mortality

rates high, par-

ents choose to have many children, thus increasing the odds

that at least some will survive to support them in their old

age. Assistance to poor countries, and to poor areas within

a single country, argue anti-Malthusians, helps to alleviate

the poverty that necessitates high birth rates. When people

become confident of their childrens’ survival, then birth rates

will drop and population equilibrium may be achieved.

1118

There are some ways in which ecological principles

of population dynamics do not necessarily fit the human

population. Improving health care and increasing life expec-

tancies have caused much of this century’s population expan-

sion. Wars, changes in prosperity, development and

trans-

portation

of resources, and social changes sometimes

increase or decrease populations locally. Immigration and

emigration tend to redistribute populations from one region

to another, temporarily alleviating or exacerbating popula-

tion excesses. Also unlike most animals, we have not histori-

cally been subject to a fixed environmental carrying capacity.

The

agricultural revolution

, the industrial revolution and

other innovations have expanded our environment’s capacity

to support humans. Some population theorists today, known

as technological optimists, insist that, even as the human

population continues to grow, our technological inventive-

ness will help us to feed and shelter the world’s population.

Even in the past 50 years, when the world’s population has

jumped from less than three billion to more than six billion,

world food production has exceeded population growth.

Technological optimists point to such historical evidence as

support for their position.

Environmental Encyclopedia 3

Eliot Furness Porter

Also unlike most animal populations, humans are, at

least in principle, able to voluntarily limit reproductive rates.

Most population theorists point to some sort of voluntary

restraint as the most humane method of preventing a disas-

trous population overshoot.

Family planning

programs have

been developed around the world in an effort to encourage

voluntary population limits. Furthermore, human societies

have been observed to go through a

demographic transi-

tion

as their economic and social

stability

has improved. A

demographic transition is a period when (infant) mortality

rates have decreased but people have not yet adjusted their

reproductive behavior to improved life expectancies. After

20 to 30 years, people adjust, realizing that more children

are surviving and that smaller families now have economic

advantages. The birth rate then begins to fall. While families

in poor countries often have five to ten children, the average

family in developed countries has about two children.

Because of family planning programs and demographic

transitions, birth rates around the world have fallen dramati-

cally in just the last 20 years. Where the average number of

children per woman was 6.1 in 1970, the average number

in 1990 was only 3.4. This rate still exceeds the minimum

replacement level (

zero population growth

level) of 2.1

children per woman, but if recent demographic trends con-

tinue the world’s population will stabilize within the first

decade of the twenty-first century.

No one knows exactly what the earth’s carrying capac-

ity is. Some warn that we have already surpassed our safe

population size. Others argue that the earth can comfortably

support far more people than it currently does. Many worry

about what would happen to other species if the human

population continues to expand. Most people agree that we

would benefit from a decrease in population growth rates.

How urgent the population question is and how best to curb

growth rates are issues that continue to be hotly debated.

[Mary Ann Cunningham Ph.D.]

ESOURCES

OOKS

Cunningham, W. P. Understanding Our Environment: an Introduction. Du-

buque, IA: Wm. C. Brown, 1993.

Ehrlich, P. R. The Population Bomb. New York: Ballantine Books, 1968.

Meadows, D. H., et al. Limits to Growth. New York: Universe Books, 1972.

ERIODICALS

Ehrlich, P. R., and A. H. Ehrlich. “The Population Explosion: Why Isn’t

Everyone As Scared As We Are?” Amicus Journal 12 (Winter 1990): 22–29.

Population Institute

Despite the fact they work with an annual budget of less

than $2 million, the Population Institute, an information,

1119

education, and communication organization that spreads the

word on population control, has been able to reach 172

countries, principally in the developing world. Based on the

philosophy that overpopulation affects all social, economic,

and political issues, the Institute’s goal is to bring world

population into balance with available environmental re-

sources. To do this, the organization disseminates informa-

tion via a World Population News Service which is picked

up in developing countries in newspaper articles, editorial

pieces, and radio and television broadcasts. In addition to

making people aware of the perils of overpopulation, the

Institute encourages birth control, without emphasizing any

particular method.

Once a year the Institute funds an international jour-

nalism award, the Global Media Award in Population Re-

porting. The winner spends about one week touring a coun-

try with a successful population control program, visiting

family planning clinics, and talking with government and

private officials. Governmental leaders within the country

usually present the award. The Institute benefits by keeping

in contact not only with leaders and people at the grassroots

level, but with local journalists.

Begun in 1969 by a Methodist minister with a strong

conviction that overpopulation was a major cause of human

misery, the Population Institute was one of the first groups

organized specifically around population control. No longer

connected to the Methodist church, the Institute is sup-

ported by grants from foundations, private individuals, and

the sale of its bimonthly newsletter, Popline. In 1980 its

domestic component split and formed the Center for Popu-

lation Options, also headquartered in Washington, D.C.

If contraceptive use is a valid indicator, things are

looking up for population control. Between 1970 and 2000,

contraceptive use rose from 9–64%. If use can be increased

to 72% within the next few years, World Bank statistics

predict that world population can be stabilized at 8.5–11

billion.

[Stephanie Ocko]

ESOURCES

RGANIZATIONS

Population Institute, 107 Second Street, NE, Washington, D.C. USA

20002 (202) 544-3300, Fax: (202) 544-0068, Email: , <http://

www.populationinstitute.org>.

Eliot Furness Porter (1901 – 1990)

American photographer

Born in Winnetka, Illinois, Eliot Porter’s fascination with

nature

(and birds in particular) was evident from a very

early age. His father, an architect with a keen interest in

Environmental Encyclopedia 3

Positional goods

Greek, Gothic, and Roman architecture and art, encouraged

his son’s insightful, artistic talents. Using the camera he

received as a gift from his father, the young Porter began

photographing primarily landscapes during the family’s so-

journs on islands off the coast of Maine. There he cultivated

an enthusiasm and love for naturalist photography. He noted

in the introduction of the classic book, Birds of America,

“...the most satisfactory outlet for expressing my excitement

over birds was the camera, rather than pencil or brush.”

Porter began his undergraduate education at Harvard

University in 1920. Casting aside his passion for photogra-

phy, he pursued the more practical major of chemical engi-

neering; he earned his bachelor’s degree (cum laude) in 1924.

He continued his education at Harvard’s Medical School

where he earned his doctor of medicine in 1929. Porter

used his degrees to teach biochemistry and bacteriology at

Harvard and Radcliffe College until 1939. In addition to his

teaching, Porter was working through the Harvard Biology

Department conducting numerous studies. By 1939, what-

ever attraction there had been to biochemistry diminished

and Porter turned his energies back to photography. Deter-

mined to transform bird photography from less-than-profes-

sional reportage to art, Porter became involved with the

Eastman Kodak company. Porter was awarded Guggenheim

Fellowships in 1941 and again in 1946 to finance experi-

ments with Kodachrome photography—a new venture for

Kodak. He believed that by using the new color film, the

photographer could provide a more sensitive interpretation

of the subject.

Finally achieving success with color film, Porter pro-

duced a number of bird photography publications, including

a photo-essay pairing his photos with specific Thoreau ex-

cerpts. The book, In Wildness Is the Preservation of the World,

was published by the

Sierra Club

. Porter produced subse-

quent books with the organization (Baja California—The

Geography of Hope and The Place No One Knew: Glen Canyon

on the Colorado), and later—until 1971—served on the Sierra

Club’s Board of Directors.

While Porter’s photography took him to locations

throughout the world (Greece, Iceland, Turkey, and the

Galapagos Islands), his most brilliant work came from his

travels in eleven of the United States. Birds of America—A

Personal Selection was the result of his trip and became one

of his best-known books. It combines rich, full-color photo-

graphs with anecdotal notes detailing his trials and tribula-

tions in taking them. Porter’s other publications include

Galapagos—The Flow of Wilderness, Antarctica, and Intimate

Landscapes.

Porter’s one-man exhibits have appeared in some of

the most influential art institutes and museums in the United

States, among them: the George Eastman House, Museum

of Modern Art, Metropolitan Museum of Art, and Stiel-

1120

glitz’s An American Place. He maintained membership in

several organizations including Advocates for the Arts,

American Civil Liberties Union, American Ornithologists’

Union, and the Audubon Society.

Porter died in November 1990 in New Mexico follow-

ing a heart attack; he had also suffered from Lou Gehrig’s

disease.

[Kimberley A. Peterson]

ESOURCES

OOKS

Porter, Eliot. Eliot Porter’s Southwest. New York: Henry Holt, 1991.

———. Nature’s Chaos. New York: Viking Penguin, 1990.

ERIODICALS

“Eliot Porter: For More Than 50 Years, This Master of Color and Light

Portrayed and Idealized the American Landscape.” Life 14 (February 1991):

80–85.

Henry, G. “Eliot Porter.” ARTnews 89 (Summer 1990): 178.

Portheria dispar

see

Gypsy moth

Positional goods

A concept coined by English economist Fred Hirsch (1931–

1978) to describe goods or activities whose value depends on

their exclusivity. For example, fame is considered a positional

good since by definition only a few people can be famous

and thus enjoy this “privilege.” If everyone were famous, no

one would be. Similarly, solitude on a mountain peak or in

the

wilderness

would qualify as a positional good, since if

one shared the peak or the wilderness with many other

people, one could not experience solitude. Ironically, a posi-

tional good tends to diminish its own value because of the

high demand it creates: as more people enjoy positional

goods, they no longer become exclusive or valued. For in-

stance, automobiles were once a positional good in America,

but as more and more people began owning cars, they were

no longer such a status symbol. A number of concerned

environmentalists contend that access to wilderness areas

should be restricted or limited to prevent the destruction of

this positional good.

Posterity

see

Future generations

Environmental Encyclopedia 3

Postmodernism and environmental ethics

Postmodernism and environmental

ethics

Environmental ethics

are a set of norms that a society

accepts as a foundation for mediating and guiding their

behavior towards the

environment

. In Western society, we

have used our science, as well as other traditions (e.g. capital-

ist economics, humaneness, aesthetics), to form the founda-

tion of our environmental behavior. We are in the midst of

a search for new ethical foundations.

Deep ecology

has

offered one possible route, Eastern religions have been an-

other source for advancing our ethics, and yet none of these

has proved palatable in our Western social systems.

Western science has guided the environmental interac-

tions of our society which in turn has dominated global

development processes, but this pattern has some definite

shortcomings. While science has served to develop our un-

derstanding of

nature

and enhanced our knowledge of the

ecological difficulties that we have created for ourselves,

the system of which science is part has been very slow in

responding to what many suggest is an ecological crisis.

Sorting the science from the politics and the ethics of our

society is not an easy task. Yet, science has been the target

of criticism in the environmental arena because, while it has

the power to expose the depth of our ecological crisis, it has

done little in that regard. Critics point to that inaction as a

negative structural attribute of how embedded science has

become in our society.

An alternative proposed from within the humanist

tradition in the social sciences suggests that science can only

produce a false construction of nature. From this viewpoint

science is tied to traditions that inevitably create an end

product related to the position from which the observer

views nature. Further it holds that all views of nature are

constructed by humans who cannot step outside of ourselves

to view the reality we think exists. Thus, no views are more

or less closer to reality; they are all merely our creation. This

alternative approach falls under the rubric of postmodernism

and is elucidated through one of the principal methods in

the postmodernist tool kit, deconstruction.

The deconstructionist approach of the postmodernist

suggests that, even thought the views of all are equally wor-

thy, an imbalance of power has been created by the dominant

classes. The disempowered classes attempt to create a bal-

ance, a struggle which proceeds by dissecting everything

down to its bare power relationships, so that having been

revealed the wrong can be corrected. Deconstruction is a

term that does not differ significantly from any other critical

analytical method, but it pays particular homage to power

and position, supposedly more conscientiously than other

methods.

1121

Nature “out there” then becomes a series of construc-

tions made by humans with different positions within a

continuum of power relations. Nature is the invention of

humans in power and is constantly reinvented by people in

those same positions. To the postmodernist, the present

invention of nature, held by the current cadre of largely

male, largely Caucasian scientists has given us a biased view

of nature. The postmodernist wish is to level all points of

view, so that life is seen as a struggle of words and nature

becomes another, albeit large, “text” (a metatext). A rather

curious outcome of this view of life is the idea that things

in nature are doing what they do only because we think of

them doing it. Furthermore, those who wish to protect na-

ture may then become a force of oppression against those

of other social orders who are struggling to gain power.

Thus, a thinly disguised structuralist approach emerges.

Power creates a framework within which the powerful strug-

gle to remain empowered, and the remainder struggle to

gain power. Environmental views supported by science are

the handmaiden of the power elite and can only succeed in

supporting the status quo.

While there is undoubtedly a cultural context in which

nature is understood and in which science operates, this does

not necessarily mean that context is equivalent to the content

of nature. Even though reality may be seen as having been

invented by words and the human shaping of sensory data,

nevertheless there is much commonality across cultures re-

garding what we see in nature. The postmodernist view

appears to be remote from the natural world, occupying an

anthropocentric stronghold where humans are dominant.

Interestingly, while humanists thus refer to a nature made

by humans, scientists have since Darwin referred to humans

as having been created by nature through natural selection.

The diametrically opposed view points under discus-

sion here are not new; they merely reflect the range of

opinions humans have always held about their relationship

with nature. However, the postmodernist expression of hu-

man opinion about nature outlined above seems to be a

position that is distinctly unhelpful, especially at this time

in our existence. The heart of the environmental problems

we currently experience has been blamed to a large degree

on humanity’s separation of itself from nature, and any pro-

posal that maintains or widens that gap may exacerbate the

problems. The postmodernist critique seems to ignore the

power and influence that nature has on us, and instead uses

an intricate semantics to describe the power we have over

each other.

Most naturalists and ecologists are immediately struck

by the apparent naivete

of a position that denies the creative

strength in nature and the complex architecture of life pro-

vided by natural selection. A postmodern view is that our

knowledge of distributions of organisms is a construct of

Environmental Encyclopedia 3

John Wesley Powell

the way we have studied distributions, and the whole idea

species

is merely a human distinction. The notion of

objective criteria devised by, critiqued by, and used by scien-

tists is rendered unusable. The postmodern view renders the

concept that ecological tolerance of the organisms, historical

events, and climate create a relationship based on a combina-

tion of determinist relationships and stochastic events a mere

artifact regardless of how many people agree to the concepts.

This of course leads to a conclusion which provides little

guidance for environmental ethics.

That does not mean that the entire postmodernist

critique leads to the same less than useful conclusions.

Rather, the very aspect of a critique that causes us to examine

our position may be an important and valuable tool. We

have relied heavily on science and found at the center of

ecology

some powerful, yet largely incorrect, metaphors

firmly rooted in our conception of nature. The ideas of

balance,

succession

, and homogeneity in nature have all

fallen by the wayside in the past two decades. Those readjust-

ments have given ecologists pause because they are strong

examples of how viewpoint can influence our interpretation

of nature, one that was originally thought to have been

discovered by an objective science. Are there more miscon-

ceptions that we hold about ecology and environment that

need to be examined? Clearly the possibility exists, and it

serves us well to search for those by any and all reasonable

methods. That postmodernism creates the notion that all

human perspectives are inherently equal may create an obsta-

cle to clear thinking about proposing a comprehensive ethic

towards the environment. At this time we need to synthesize

a more positive relationship between nature and humanity

to bring all of our cultures into an integrated understanding

of nature. However, a revised ethical foundation for human-

ity’s relationship with the environment may benefit from

the tradition of critical thinking that various philosophical

positions bring. An examination of biases linked to our

present position.

[David A. Duffus]

Potable water

see

Drinking-water supply

John Wesley Powell (1834 – 1902)

American philosopher, geologist, anthropologist, and sci-

entific explorer

John Wesley Powell—civil-war veteran, college professor,

long-time head of the U.S.

Geological Survey

, member

of the

National Academy of Sciences

, president of the

1122

American Association for the Advancement of Science, and

instrumental in the establishment of the National Geo-

graphic Society, the Geological Society of America, the U.S.

Geological Survey, the Bureau of Ethnology, and the Bureau

of Reclamation—is best-known for two expeditions down

the Green and Colorado Rivers.

Born in Mount Morris, New York, of English-born

parents, Powell was discouraged from education by his father

who believed that the ministry was the only purpose for

which one needed to be educated. The younger Powell how-

ever, worked at a variety of jobs to support his attendance

at numerous schools, but never completed a degree. His

hard-won recognition as a scientist is based in large part on

self-taught concepts and methods that he applied all his life

and in everything he did.

Powell made significant contributions to

conserva-

tion

and

environmental science

. He was an early and ar-

dent student of the culture of the fast-disappearing North

American Indians tribes, and his work ultimately led to the

creation of the Bureau of Ethnology, of which he was the

first director. He served as the second Director of the United

States Geological Survey (USGS) from 1881 to 1894, and

as such he instigated extensive topographic mapping projects

and geological studies, stimulated studies of soils,

ground-

water

, and rivers, and advocated work on flood control

and

irrigation

. His Irrigation Survey led eventually to the

creation of first the

Reclamation

Service and then the

Bu-

reau of Reclamation

Powell was the author of the Report on the Lands of

the Arid Region of the United States, published in 1878.

Through this document, he became an early advocate of

land-use planning. Powell was open to controlled develop-

ment and suggested that “to a great extent, the redemption

of...these lands will require extensive and comprehensive

plans...” In his role as director of the USGS, in his writings,

his work on various commissions, and in public hearings,

Powell advocated that the federal government assume a ma-

jor role to insure an orderly and environmentally sound

settlement of the

arid

lands of the West.

Wallace Stegner

argues that Powell’s ultimate impor-

tance derives from his impact as an agent of change, from

setting in motion ideas and agencies that still benefit the

country today. He also widens Powell’s impact, asserting

that Powell’s ideas, through his friend and employee W. J.

McGee, heavily influenced the whole conservation move-

ment at the beginning of the twentieth century. Powell

informed the American public of the grandeur and vulnera-

bility of the arid lands and canyon lands of the West. The

legacy of that heritage is the Grand Canyon still largely

unspoiled as well as a better understanding of

land use

possibilities on arid and all lands.

[Gerald L. Young Ph.D.]

Environmental Encyclopedia 3

Power plants

John Wesley Powell. (Corbis-Bettmann. Reproduced

by permission.)

ESOURCES

OOKS

Murphy, D. John Wesley Powell: Voyage of Discovery. Las Vegas: KC Publica-

tions, 1991.

Stegner, W. Beyond the Hundredth Meridian: John Wesley Powell and the

Second Opening of the West. New York: Penguin Books, 1992.

ERIODICALS

Robinson, F. G. “A Useable Heroism: Wallace Stegner’s Beyond the Hun-

dredth Meridian.” South Dakota Review 23 (1985): 58–69.

Power lines

see

Electromagnetic field

Power plants

The term power plant refers to any installation at which

electrical energy is generated. Power plants can operate using

any one of a number of fuels: oil,

coal

, nuclear material, or

geothermal steam, for example. The general principle on

which most power plants operate, however, is the same. In

such a plant, a fuel such as coal or oil is burned. Heat from

the burning fuel is used to boil water, converting it to steam.

The hot steam is then used to operate a steam turbine.

1123

A steam turbine is a very large machine whose core

is a horizontal shaft of metal. Attached to the horizontal

shaft are many fan-shaped blades. As hot steam is directed

at the turbine, it strikes the blades and causes the horizontal

shaft to rotate on its axis. The rotating shaft is, in turn,

attached to the shaft of an electric generator. The pressure

of hot steam on turbine blades, is therefore, ultimately con-

verted into the generation of a electric current. One of the

first steam turbines designed to be used for the generation

of electricity was patented by Charles Parson in 1884.

Twenty years later, entrepreneurs had already put such tur-

bines to use for the generation of electricity for street lines,

subways, train lines and individual appliances.

Most early power plants were fueled with coal. Coal

was the best-know, most abundant fossil fuel at the time.

It had several disadvantages, however. It was dirty to mine,

transport, and work with. It also did not burn very cleanly.

Areas around a coal-fired power plant were characterized

by clouds of

smoke

belching from smokestacks and films

of ash deposited on homes, cars, grass, and any other exposed

surface.

By the 1920s interest in oil-fired power plants began

to grow. The number of these plants remained relatively

low, however, as long as coal was inexpensive. But, by the

1960s, there was a resurgence of interest in oil-fired plants,

largely in response to increased awareness of the many harm-

ful effects of coal

combustion

on the

environment

. One

of the most troublesome effects of coal combustion is

acid

rain

. Coal contains trace amounts of elements which pro-

duce acid-forming oxides when burned. The two most im-

portant of these elements are sulfur and

nitrogen

. During

the combustion of coal, sulfur is oxidized to

sulfur dioxide

and nitrogen to nitric oxide. Both sulfur dioxide and nitrogen

oxide undergo further changes in the

atmosphere

, forming

sulfur trioxide and nitrogen dioxide. Finally, these two oxides

combine with water in the atmosphere to produce sulfuric

and nitric acids.

This series of chemical reactions in the atmosphere

may take place over hundreds or thousands of miles. Oxides

of sulfur and nitrogen that leave a power plant smokestack

are then carried eastward by prevailing winds. It may be

many days or weeks before these oxides are carried back to

earth—now as acids—in rain, snow, or some other form of

precipitation. During the 1960s and 1970s, many authorities

became concerned about the possible effects of

acid

precipi-

tation on the environment. They argued that the problem

could be solved only at the source—the electric power-gener-

ating plant.

One approach to the reduction of pollutants from a

power plant is the installation of equipment that will remove

undesirable materials from waste gases. An electrostatic pre-

cipitator is one such device which removes particulates. It

Environmental Encyclopedia 3

Power plants

attaches electrical charges to the particulates in waste gases

and then applies an opposing electric field to a plate that

attracts the particulates and removes them from the waste

gas stream.

Scrubbers

filters

, and

cyclone

collectors also

remove harmful pollutants from waste gases.

Another approach to acid rain and other power-plant-

generated

pollution

problems is to switch fuel from coal to

oil or

natural gas

. Although

petroleum

and natural gas

also contain sulfur and nitrogen, the concentration of these

elements is much less than it is in many forms of coal. As

a result, a number of electrical utilities began to retrofit their

generating plants in the 1960s and early 1970s to allow them

to burn oil or natural gas rather than coal. This change-over

is reflected in the increased use of petroleum by electrical

utilities in the United States between 1965 and 1975. Con-

sumption increased more than six-fold in that ten year pe-

riod, from about 100 million barrels per year to more than

6,700 million barrels per year. Interestingly enough, the use

of coal by utilities did not drop off during the same period,

but continued to rise from about 200 million short tons to

over 300 million short tons annually.

This pattern of

fuel switching

turned out to be short-

lived, however. Although oil and natural gas are relatively

clean fuels, they also appealed to utilities because of their

relatively low cost. The

oil embargo

instituted by the

Orga-

nization of Petroleum Exporting Countries

(OPEC) in

1973 altered that part of the equation. Worldwide oil prices

jumped from $1.36 per million

Btu

in 1973 to $2.23 per

million Btu in 1975, an increase of 64 percent per million

Btu in just two years. A decade later, the price of oil had

more than doubled. And, the situation was even worse for

natural gas. The cost of a million Btu of this resource sky-

rocketed from 36.7 cents in 1970 to 69.3 cents in 1975 to

$2.23 in the mid-1980s.

Suddenly, the conversion of power plants from coal

to oil and natural gas no longer seemed like such a wonderful

idea. And the utilities industry began once more to focus

on the fossil fuel in most plentiful supply—coal. Between

1975 and 1990, the fraction of power plants powered by oil

and natural gas dropped from 12% to 4% for the former

and from 24% to less than 10% for the latter. In the same

period, the fraction of plants powered by coal rose from

46%–57%.

Power plants using

fossil fuels

, of whatever kind, are

not the world’s final solution to the generation of electricity.

In addition to the environmental problems they cause, there

is a more fundamental limitation. The fossil fuels are a

nonrenewable resource. The time will come—sooner or

later—when coal, oil, and natural gas supplies will be de-

pleted. Thus, research on alternatives to fossil-fuel-fired

plants has gone on for many decades.

1124

Thirty years ago, many people believed that

nuclear

power

was the best solution to the world’s need to produce

large amounts of electricity. Indeed, the number of nuclear

power plants in the United States grew from 6 in 1965 to

95 in 1985. By 1992, 421 nuclear plants were in commercial

operation worldwide, supplying 17% of the world’s electric-

ity. But enthusiasm for nuclear power plants began to wane

in the 1980s. One reason for this trend was the serious

accidents at the

Three Mile Island Nuclear Reactor

(Mid-

dletown, Pennsylvania) in 1979 and at the

Chernobyl Nu-

clear Power Station

(Chernobyl, Ukraine) in 1986. An-

other reason was the growing concern about disposal of

the ever-increasing volume of dangerous radioactive wastes

produced by a nuclear power plant. In any case, no new

nuclear power plant has been ordered in the United States

since the Three Mile Island accident and 65 plant orders have

been canceled since that event. Forty-nine nuclear plants are

now under construction in other parts of the world, but this

number is only a quarter as many as were under construction

a decade ago. Indeed, between 1990 and 1991, the total

installed nuclear generating capacity worldwide declined for

the first time since commercial nuclear power generation

began. Given current economic and political conditions, a

major revival of the nuclear power industry seems unlikely.

A nuclear power plant operates on much the same

principle as does a fossil-fuel power plant. In a nuclear power

plant, water is heated not by the combustion of a fuel like

coal or oil, but by

nuclear fission

reactions that take place

within the reactor core. Some scientists anticipate that an-

other type of nuclear power plant—the fusion reactor—may

provide a long-term answer to the world’s electrical power

needs. In a fusion reactor, atoms of light elements are fused

together to make heavier elements, releasing large amounts

of energy in the process.

Nuclear fusion

is the process by

which stars make their energy and is also the energy source

in the

hydrogen

bomb. Research efforts to develop an eco-

nomic and safe method of controlling fusion power have

been underway for nearly 40 years. Although progress has

been made, a full-scale commercial fusion power plant cur-

rently appears to be many decade in the future.

Other types of power plants also have been under

investigation for many years. For example, it is possible to

operate a steam turbine with hot gases that come directly

from geothermal vents. In locations where geysers or other

types of vents exist, geothermal power plants are an economi-

cal, safe and dependable alternative to fossil-fueled and nu-

clear power plants. In the early 1990s, for example Pacific

Gas and Electric in northern California obtained about eight

percent of its electrical power from geothermal plants.

Finally, power plants that do not use heat at all are

possible. One of the oldest forms of power plant is, in fact,

the hydroelectric power plant. In a hydroelectric power plant,

Environmental Encyclopedia 3

Prairie

the movement of water (as from a river) is directed again

turbine blades, causing them to rotate. In 1970, 16 percent of

all electric power in the United States came from hydropower

although that portion has now fallen to less than eight

percent.

Proposals for wind power generated-electricity,

tidal

power

plants, and other alterative energy sources as substi-

tutes for fossil fuels and nuclear power have been around

for decades. During the 1960s and 1970s, governments ag-

gressively encouraged research on these new technologies,

offering both direct grants and tax breaks. Since 1980, how-

ever, the United States government has lost interest in alter-

native methods of power generation, preferring instead to

encourage the growth and development of more traditional

fuels, such as coal, oil and petroleum. See also Geothermal

energy; Ocean thermal energy conversion; Solar energy;

Tidal power; Wind energy

[David E. Newton]

ESOURCES

OOKS

Brown, L. R., et al. Vital Signs, 1992. New York: Norton, 1992.

McGraw-Hill Encyclopedia of Science & Technology. 7th ed. New York:

McGraw-Hill, 1992.

ERIODICALS

Balzhiser, R. E., and K. E. Yeager. “Coal-fired Power Plants for the Future.”

Scientific American 257 (September 1987): 100–107.

Swain, H. “Power Plants Threaten Shenandoah’s Air.” National Parks 65

(March-April 1991): 14.

Ppb

see

Parts per billion

Ppm

see

Parts per million

PPP

see

Partnership for Pollution Prevention

Ppt

see

Parts per trillion

Prairie

An extensive temperate grassland with flat or rolling terrain

and moderate to low precipitation. The term is most often

applied to North American

grasslands

, which once ex-

1125

A prairie. (Photograph by Robert J. Huffman. Field Mark

Publications. Reproduced by permission.)

tended from Alberta to Texas and from Illinois to Colorado,

but similar grasslands exist around the world. Perennial

bunchgrasses and forbes dominate prairie

flora

.Indry

cli-

mate

prairies, a lack of precipitation prohibits tree growth

except in isolated patches, such as along stream banks. In

wetter prairies, periodic fires are essential in preventing the

incursion of trees and preserving open grasslands. Histori-

cally, huge herds of large mammals and scores of bird, rodent,

and insect

species

composed native prairie

fauna

. During

the nineteenth and twentieth centuries most of North Amer-

ica’s native prairie

habitat

and its occupants disappeared in

the face of agricultural settlement, cattle grazing, and fire

suppression. Today the geographic extent of native prairie

plants and animals is severely restricted, but pockets of re-

maining prairie are sometimes preserved for their ecological

interest and genetic diversity.

While grasses make up the dominant vegetation type

in all prairies, grass sizes and species vary from shortgrass

prairies, usually less than 20 inches (50 cm) high, to tallgrass

prairies, whose grasses can exceed 7 ft (2 m) in height.

Following the gradual east-west decrease in precipitation

rates on the Great Plains, eastern tallgrass prairies gradually

gave way to midgrass and then shortgrass prairies in western

states. On their margins, prairie grasslands extended into a

mixed “parkland,” or “savanna,” with bushes and scattered

Environmental Encyclopedia 3

Prairie dogs

trees such as oak and juniper. Characteristic prairie grasses

are perennial bunchgrasses, which have deep, extensive root

systems and up to a hundred shoots from a single plant.

Bunchgrasses typically grow, sprout, and flower early in the

summer when rainfall is plentiful in the prairies, and their

deep root systems make the long-lived plants resistant to

drought

, hail, grazing, and fire. In addition to the dominant

grasses, vast numbers of flowering annual and perennial

forbes—herbaceous flowering plants that are not grasses—

add color to prairie landscapes.

Prairie plant species are well adapted to live with fire.

Under natural conditions fires sweep across prairies every

few years. Prairie fires burn intensely and quickly, fed by

dry grass and prairie winds, but they burn mainly the dry

stalks of previous years’ growth. Below the fire’s heat, the

roots of prairie plants remain unharmed, and new stalks

grow quickly, fertilized by ashes and unencumbered by accu-

mulations of old litter. Before European settlement, many

prairie fires were ignited by lightening, but some were started

by Indians, who had an interest in maintaining good grazing

land for

bison

, antelope, and other game animals.

Well into the nineteenth century, prairie habitats sup-

ported a tremendous variety of animal species. Vast herds

of bison, pronghorn antelope, deer, and elk ranged the grass-

lands; smaller mammals from mice and

prairie dogs

badgers and fox lived in or below the prairie grasses. Carni-

vores including grey

wolves

, coyotes, cougar, grizzlies,

hawks, and owls fed on large and small herbivores. Shore-

birds and migratory waterfowl thrived on millions of prairie

pothole ponds and marshes. Most of these species saw their

habitats severely diminished with the expansion of agricul-

tural settlement and cattle grazing range. Prairie soils, mainly

mollisols, are rich and black with a thick, fertile organic

layer composed of fine roots,

microorganisms

, and

soil

Where water was available, this soil proved ideal for growing

corn, wheat, soybeans, and other annual crops. Where water

was scarce, nutritious bunchgrasses provided excellent graz-

ing for cattle, which quickly replaced buffalo, elk, and ante-

lope on the prairies in the middle of the nineteenth century.

Prairie habitat and animal species have also lost ground

through fire suppression and wetland

drainage

. Farmers

and ranchers have actively suppressed fires, allowing trees,

exotic annuals, and other non-prairie species to become es-

tablished. Widespread

wetlands

drainage has seriously di-

minished bird populations because of habitat loss. Especially

in wetter northern and eastern regions, canals were cut into

prairie wetlands, draining them to make arable fields. This

practice continues today, even though it destroys scarce

breeding grounds for many birds and essential migratory

stopovers for others.

In recent decades increased attention has been given

to preserving the few remaining patches of native prairie in

1126

North America. Public and private organizations now study

and protect prairie grasslands and wetlands, but the long-

term value of these efforts may be questionable because most

remnant patches are small and widely separated. Whether

genetic diversity can be maintained, and whether habitat for

large or ranging animals can be reestablished under these

conditions, is yet to be seen.

[Mary Ann Cunningham Ph.D.]

ESOURCES

OOKS

Cushman, R. C., and S. R. Jones The Shortgrass Prairie. Boulder, CO:

Pruett Publishing Co., 1988.

Smith, R. L. Ecology and Field Biology. 3rd ed. New York: Harper and

Row, 1980.

Whittaker, R. H. Communities and Ecosystems. 2d ed. New York: Macmil-

lan, 1975.

Prairie dogs

Prairie dogs, members of the genus Cynomys, belong to the

squirrel family of the order Rodentia. There are five

species

of prairie dogs found on North American plains and plateaus

from southern Saskatchewan, Canada to northern Mexico:

Utah (C. parridens), Gunnison’s (C. gunnisoni), white-tailed

(C. leucurus), black-tailed (C. ludovicianus ), and Mexican

(C. mexicanus).

The explorer Meriwether Lewis, explorer of the Amer-

ican West, described prairie dogs as barking squirrels, which

“bark at you as you approach them, their note being much

like that of little toy dogs.” These barking calls, including

barks, chirps, and whistles, are used to communicate greet-

ings, social status, and approaching or retreating danger.

Prairie dogs as social animals live in colonies, or

“towns,” which consist of extensive and complex under-

ground burrows one to five meters deep. Cone-shaped

mounds at the entrance of the burrows are used as look-out

points; they also prevent water from entering the burrows.

The burrows contain several chambers, including one near

the entrance where the prairie dogs can listen for above-

ground activity, as well as one or more nesting chambers

where young prairie dogs sleep and are cared for. Prairie

dogs generally prefer to eat grasses and herbs. They also clip

vegetation in the vicinity of their colonies to provide clear

views of predators. They spend daylight hours above-ground,

grooming each other, grazing on grass, tumbling in play,

and defending their family territorial boundaries.