Environmental Encyclopedia

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Environmental Encyclopedia 3

Seals and sea lions

Seabrook Nuclear Reactor (Seabrook, New Hampshire). (Photograph by Tom Pantages. Reproduced by permission.)

ESOURCES

ERIODICALS

Shulman, S. “Embattled Seabrook Wins License at Last.” Nature (March

8, 1990): 96.

Wasserman, H. “Clamshell Alliance: Getting It Together.” Progressive

(September 1977): 14–18.

———. “Clamshell Reaction: Protest against Nuclear Power Plant at Sea-

brook, N.H. by Clamshell Alliance.” Nation (June 18, 1977): 744—749.

———. “Nuclear War by the Sea.” Nation (September 11, 1976): 203–205.

Seals and sea lions

Members of the suborder Pinnipedia, seals and sea lions are

characterized by paddle-like flippers on a pair of limbs. Most

pinnipeds are found in boreal or polar regions and are the

most important predators in many high latitude areas, feed-

ing primarily on fish and squid. Seals and sea lions catch

their prey during extended dives of up to 25 minutes at

depths of 2,625 ft (800 m) or more. Pinniped biologists

are interested in the physiological changes these animals

undergo during their dives. Known as mammalian dive re-

1267

sponse, a combination of reduced heart rate and a lowered

core body temperature enables these warm-blooded animals

to complete such dives.

Seals and sea lions must return to beaches and ice floes

each year to give birth. Here they raise their pups in large

congregations known as colonies. In some

species

the larger,

more aggressive males will form polygamous mating groups,

or harems, and claim and defend territories in these limited

breeding areas. Males that do not get to mate form “bachelor

male” groups in areas less suitable for weaning pups. Males

of most species of pinnipeds do not mate before age four

but may acquire harems when they attain large size and

fighting experience. Some individual seals have been known

to live as long as 46 years.

Because of the commercial value of their pelts, many

species of seals and sea lions are threatened by

hunting

One of the largest pinnipeds, the Stellar sea lion (Eumetopias

jubatus) has been steadily decreasing in numbers and is now

listed as endangered by the IUCN. Within 15 years, the

new pup count at the Marmot Island Rookery (the largest

known sea lion rookery in the world) decreased from an

Environmental Encyclopedia 3

Seals and sea lions

A Hawaiian monk seal. (Photograph by Jim Leupold. U.S. Fish & Wildlife Service. Reproduced by permission.)

average of 6,700 to only 804. The northern or Pribilof fur

seal (Callorhinus ursinus), which had been heavily exploited

for its fur and in steady decline since the mid-1950s, is now

listed as vulnerable. In California, the Guadeloupe fur seal

(Arctocephalus townsendi) is also listed as vulnerable. The

Monk seal (Monachus monachus) in the Mediterranean is

listed as critically endangered.

These animals are in danger from natural and man-

induced pressures, and the consequences of their demise are

unknown. Other than hunting, perceived competition with

fishermen,

pollution

, and

habitat

destruction are threaten-

ing pinnipeds. Despite the sanctions afforded by the

Marine

Mammals Protection Act

(1972), fishers continue to kill

seals that are “interfering” with fishing operations. Recent

revisions to the act require some vessels to include observers

who can monitor compliance with the law. Some environ-

mentalists contend that it is the fisher who “interferes” with

the seals. The California Department of Fish and Game

estimates that 2,000 seals die each year from accidental en-

tanglement in fishing nets.

In the summer of 1988, 18,000 harbor seals washed

up on European shores. They were discovered to be suffering

1268

from an acute viral infection, possibly due to an immune-

system breakdown. Chemical pollutants, mainly polychlori-

nated biphenyl (PCB), have been implicated in reduced

immune function in marine mammals, and levels of PCBs

have been constantly increasing in many coastal waters. A

connection has also been made between mass seal die-offs

and increasing temperature. Four of the six recorded mass

mortalities have occurred in the past 12 years, a period that

includes some of the warmest weather in the twentieth cen-

tury. Other pollutants, such as

heavy metals

, may also

affect seal health or reproductive ability.

Oil spills

also poison

seal food sources and reduce the insulation ability of the

seals’ fur.

Finally, the reduction of habitat for feeding and repro-

duction has not been investigated thoroughly. Reputedly

caused by reductions in prey-fish stocks due to

overfishing

and by development of coastal shorelines, this reduction may

negatively affect pinniped populations.

[William G. Ambrose Jr. and Paul E. Renaud]

Environmental Encyclopedia 3

Noah Seattle

ESOURCES

OOKS

Sumick, J. L. An Introduction to the Biology of Marine Life. 5th ed. Dubuque,

IA: W. C. Brown, 1992.

ERIODICALS

Gentry, R. “Seals and Their Kin.” National Geographic 171 (1987): 474–501.

Hersh, S. “Saga of North Sea Seals (Phocine Distemper Virus).” Sea Fron-

tiers 36 (1990): 55.

Rosenberg, S. “Sea Lions of Monterrey.” Sea Frontiers 35 (1989): 97–103.

Stirrup, M. “A Sea Lion Mystery.” Sea Frontiers 36 (1990): 46–53.

Stolzenberg, W. “Seals Under Siege: A Heated Warning.” Science News

138 (1990): 84.

Paul Bigelow Sears (1891 – 1990)

American ecologist and conservationist

Born in Bucyrus, Ohio, Paul Sears obtained bachelor’s de-

grees in zoology and economics, then earned a Ph.D. in

botany from the University of Chicago. He spent most of

his career as professor or head of various botany departments.

In these positions, Sears researched changes in native

flora

as a result of human activities, conducted pioneering studies

of fossil pollen, and studied the relationship between vegeta-

tion and climatic change. A respected and influential ecolo-

gist, he served as president of the

Ecological Society of

America

(1948) and received the ESA’s “Eminent Ecologist

Award” in 1965. He spent the last ten years of his academic

career as chair of the graduate program in

conservation

Yale University and retired in 1960.

Sears was one of the few biological ecologists interested

human ecology

, writing cogently and consistently in a

field that he saw as a problem in synthesis. In his 1957

Condon Lecture at the University of Oregon, titled “The

Ecology of Man,” he mandated “serious attention to the

ecology of man” and demanded “its skillful application to

human affairs.”

He considered ecology a “subversive subject,” arguing

that if it were taken seriously, it would “endanger the as-

sumptions and practices accepted by modern societies, what-

ever their doctrinal commitments.” But Sears was a optimist

and believed that scientists would eventually agree because

the nature of their work mandated that they have “confidence

that the world hangs together.”

As a conservationist, Sears believed that one of the

basic lessons ecology teaches is that materials cycle and re-

cycle through natural systems. Thus, he became a strong

advocate of intensive

recycling

by human societies. He also

taught that a return to greater use of human muscle power

would be healthy for people because it would promote fitness

and

energy conservation

, as well as an impact on the

biosphere

1269

Sears was also one of the few prominent ecologists to

successfully write for popular audiences. At least one of his

popular books, Deserts on the March, first published in 1935,

has become a minor American classic, reprinted in a fourth

edition in 1980. The title provides an apt summary: in it,

Sears documents the mistakes American farmers made in

creating conditions that led to the disastrous

Dust Bowl

This book had a major influence on the

soil conservation

movement in the United States.

Throughout his life, Sears believed that the best way

to solve ecological problems was to teach every person about

their own immediate

environment

: “Each of us can begin

quite simply by learning to look about himself, wherever he

may be.” The touchstone of education, especially a scientific

one, should be “the final ability to read and enjoy the land-

scape. While there is life there is hope, but only for the

enlightened.”

[Gerald L. Young Ph.D.]

ESOURCES

OOKS

Sears, P. B. Deserts on the March. 4th ed. Norman: University of Oklahoma

Press, 1980.

———. “The Processes of Environmental Change by Man.” In Man’s Role

in Changing the Face of the Earth, edited by W. L. Thomas Jr. Chicago:

The University of Chicago Press, 1956.

———. Where There is Life: An Introduction to Ecology. New York: Dell,

1970.

Noah Seattle (1786 – 1866)

Duwamish chief

Noah Seattle (or See-athl) was a chief of the Duwamish or

Suquamish tribe, one of the Salish group of the Northwest

Coast of North America. Born in the Puget Sound area in

1786, Seattle lived there until his death on June 7, 1866.

He was baptized a Roman Catholic about 1830 and is buried

in the graveyard of the Port Madison Catholic Church.

Ironically, Native Americans were banned by law from living

in Seattle, Washington, the city named after him, one year

after the chief’s death.

By most accounts, Seattle was a great orator and a

skilled diplomat. Although he never fought in a war against

white people, he was a warrior with a reputation for daring

raids on neighboring tribes. Seattle owned eight Native

American slaves, but freed them after President Abraham

Lincoln’s Emancipation Proclamation. He was the first to

sign the Port Elliott Treaty negotiations of 1855, which

surrendered most Native American lands in the Puget Sound

area for white settlement. He gave two short speeches on

that occasion, which are preserved in the National Archives

Environmental Encyclopedia 3

Secchi disk

in Washington, D.C. Both speeches encouraged others to

sign the agreement and to cooperate with the United States

authorities.

Seattle has become famous in recent years as the author

of one of the most widely quoted pieces of environmental

literature in the world. Among some familiar passages are:

“How can you buy or sell the sky, the warmth of the land?

The earth is our mother. This we know, the earth does not

belong to man. Man belongs to the earth. Whatever befalls

the earth, befalls the sons of the earth. Man did not weave

the web of life; he is merely a strand in it. Whatever he does

to the web, he does to himself.”

Generally called the speech, letter, or lament of Chief

Seattle, this text exists in many forms. It has been set to

music, called the Fifth Gospel in religious services, and used

to sell everything from toilet tissue to recyclable plastic bags.

A version was used by artist Susan Jeffers in 1991 to accom-

pany drawings in a best selling children’s book called, Brother

Eagle, Sister Sky. This piece is a poetic, moving, environmen-

tally sensitive work that supports beliefs about the reverence

of Native Americans for the earth. Unfortunately, there is

no evidence that Chief Seattle ever said any of the wise

words attributed to him.

Historian Rudolf Kaiser has traced the origins and

myths surrounding the Chief Seattle text. The first report

of what we now know as Seattle’s speech appeared in an

article by Dr. Henry A. Smith published in the Seattle Sunday

Star on October 29, 1887, as part of a series of old pioneer

reminiscences. Smith was recalling remarks made by the

Chief in 1854 on the arrival of Governor Stevens to the

territory. Although 33 years had passed since the event,

Smith wrote that he clearly remembered the “grace and

earnestness of the sable old orator.”

As Smith reconstructed it, the speech was dark and

gloomy, the farewell of a vanishing race. “Your God loves

his people and hates mine...It matters but little where we

pass the remainder of our days. They are not many...Some

grim Nemesis of our race is on the redman’s trail, and wher-

ever he goes he will still hear the sure approaching footsteps

of the fell destroyer.” This version was mostly a justification

for displacement of the native peoples by the pioneers. Smith

remembered the Chief saying that the President’s offer to

buy Native American lands was generous “for we are no

longer in need of a great country.” This version has no

mention of the web of life or other ecological concepts.

In 1969 Smith’s stuffy Victorian prose was translated

into modern English by poet William Arrowsmith. Two

year later, Ted Perry wrote the script for a film called Home

produced by the Southern Baptist Convention. He used

some quotes from Arrowsmith’s translation together with a

great deal of imagery, symbolism, and sentiments of 1970s

environmentalism

. Perry is the source of 90% of what we

1270

now know as Seattle’s speech. Over Perry’s objections, the

film’s editors attributed the text to Chief Seattle to make it

seem more authentic.

The piece has since assumed a life of its own. Some

obvious inconsistencies exist, such as “hearing the lovely cry

of the whippoorwill” or having “seen a thousand rotting

buffaloes on the

prairie

, left by the white man who shot

them from a passing train.” Chief Seattle lived his whole

life in the Puget Sound area and died 13 years before the

railroads reached the West Coast. He never heard a whip-

poorwill or saw a buffalo. Many people who use the speech

are unperturbed by evidence that it is untrue. It so perfectly

supports their view of Native Americans that they believe

some Native American should have said these things even

if Seattle did not.

This story is a good example of a myth that persists

because it fits our preconceived views. In Chief Seattle, we

seem to find an unsophisticated primitive who spoke in

poetic, beautiful language and prophesied all the evils we

now experience. Indigenous cultures probably contain much

ecological wisdom that can be taught to others, but care

must be taken not to blindly accept mythological texts such

as this.

[William P. Cunningham Ph.D.]

ESOURCES

OOKS

Kaiser, R. “Chief Seattle’s Speech(es): American Origins and European

Reception—Almost a Detective Story.” In Indians in Europe, edited by C.

F. Feest. Gottingen, 1985.

Secchi disk

A simple instrument used to measure the transparency of

surface water bodies such as lakes and reservoirs. A Secchi

disk is a metal, plastic, or wooden disk that is 8–12 in (20–

30 cm) in diameter. It may be white or have alternating

black and white quadrants. A long calibrated rope is attached

to the center of the disk. Researchers use the disk by lowering

it into the water, usually from the shaded side of a boat,

and measuring the depth at which it just disappears from

sight. The disk is then lowered a little more and then raised

until it reappears. The average of the depths at which the

disk disappears and then reappears is known as the Secchi

depth. The amount of

sediment

, algae, and other solids in

the water affects clarity and depth of light penetration and

thus, Secchi depth. Scientists use this measure of transpar-

ency as a simple indication of

water quality

, often by com-

paring Secchi depth measurements over a period of time to

track changes in the clarity of a particular water body.

Environmental Encyclopedia 3

Secondary recovery technique

Testing water clarity with a secchi disk. (Photo-

graph by W.A. Banaszewski. Visuals Unlimited. Repro-

duced by permission.)

Second World

The former Soviet Union and those (formerly) communist

states that were politically and economically allied with it

are often informally called the Second World. The term

1271

developed after World War II to distinguish communist

bloc states from powerful capitalist states (

First World

) and

from smaller, nonaligned developing states (

Third World

These terms developed as a part of theories that the world’s

countries together made up a single dynamic system in which

these three sectors interacted. Although the term is often

used to indicate countries and regions of intermediate eco-

nomic strength, its proper meaning has to do with political

economy, or the politics of communist-socialist economics.

In recent years, with the shrinking role and then disintegra-

tion of the communist bloc, the term has become much less

common than those of First and Third Worlds.

Secondary recovery technique

The term secondary recovery technique refers to any method

for removing oil from a

reservoir

after all natural recovery

methods have been exhausted. The term has slightly different

meanings depending on the stage of recovery at which such

methods are used.

The oil trapped in an underground reservoir is typically

mixed with water,

natural gas

, and other gases. When a

well is sunk into the reservoir, oil may flow up the well pipe

to the earth’s surface at a rate determined by the concentra-

tion of these other substances. If the gas pressure is high,

for example, the oil may be pushed out in a fountain-like

gusher.

Flow out of the reservoir continues under the influence

of a number of natural factors, such as gravity, pressure of

surrounding water, and gas pressure. Later, flow is continued

by means of pumping. All such recovery approaches that

depend primarily on natural forces are know as primary

recovery techniques.

Primary recovery techniques normally remove no more

than about 30% of the oil in a reservoir.

Petroleum

engineers

have long realized that another fraction of the remaining oil

can be forced out by fluid injection. The process of fluid

injection involves the drilling of a second hole into the

reservoir at some distance from the first hole through which

oil is removed. Some gas or liquid is then pumped down

into the second hole, increasing pressure on the oil remaining

in the reservoir. The increased pressure forces more oil out

of the reservoir and into the recovery pipe.

The single most common secondary recovery tech-

nique is water

flooding

. When water is pumped into the

second well, it diffuses out into the oil reservoir and tends

to displace oil from the particles to which it is absorbed.

This process forces more of the residual oil up into the

recovery pipe.

Water flooding was used as early as 1900, but did not

become legal until 1921. A common practice was to drill a

Environmental Encyclopedia 3

Secondary recovery technique

series of

wells

, some of which were still producing and

others of which employed water injection. As the former

became exhausted, they were converted to water injection

wells and another group of producer wells were drilled. The

process was repeated until all available oil was recovered

from the field.

Recently, more sophisticated approaches to fluid injec-

tion have been developed from a reservoir. The two fluids

that have been used most extensively in these approaches are

liquid

hydrocarbons

and

carbon dioxide

. The principle

behind liquid hydrocarbons is to find some material that

will mix completely with oil and then push the oil-mixture

that is formed out of the reservoir into the recovery pipe. A

commonly used hydrocarbon for this process is liquified

petroleum gas (LPG), which is completely miscible with oil.

Since LPG is fairly expensive, only a small volume is

actually used. It is pumped down into the reservoir and

followed by a “pusher gas.” The pusher gas, often

methane

is inexpensive and can be used in larger volume. The pusher

gas forces LPG into the reservoir where it (the LPG) mixes

with residual oil.

This system has worked well in the laboratory, but

not so well in actual practice. The LPG has a tendency to

get lost in the reservoir to an extent that it does not effectively

remove very much residual oil.

The most effective fluid now available for injection

appears to be

carbon

dioxide. A mixture of carbon dioxide

and water is pumped down into the reservoir and followed

by an injection of pure water that drives the carbon dioxide-

water mixture through the reservoir. As carbon dioxide

comes into contact with oil, it dissolves in the oil, causing

it to expand and break loose from surrounding rock. The

oil-carbon dioxide-water is then pumped out of the recovery

pipe where the carbon dioxide is removed from the mixture

and re-used in the next recovery pass.

The carbon dioxide process has been effective in re-

moving oil after water flooding has already been used and

only 25% of the oil in a reservoir still remains. In most cases,

however, it is more efficiently used with reservoirs containing

a larger fraction of residual oil.

Fluid injection is one type of secondary recovery tech-

nique. Another whole group of methods can also be used

to extract the remaining oil from a reservoir. If these methods

are employed after fluid injection has been tried, they are

often referred to as tertiary recovery techniques. If they are

used immediately after primary recovery, they are known

as secondary recovery techniques. A whole set of recovery

techniques can be called by different names, therefore, de-

pending on the stage at which they are used. It is becoming

more common today to refer to any method for removing

the residual oil from a reservoir as an enhanced recovery

technique.

1272

Another technique for removing residual oil from a

reservoir makes use of surfactants. A surfactant is a substance

whose molecules are attracted to water at one end and oil

at the other end. The most familiar surfactants are probably

the soaps and

detergents

found in every home.

If surfactants are injected into an oil reservoir, they

will form emulsions between the oil and water in the reser-

voir. The oil is essentially washed off particles of rock in the

reservoir the way grease is washed off a pan by a household

detergent. The emulsion that is formed is then pushed

through the reservoir and out the producer pipe by a flood

of water pushed down the injection pipe.

The surfactant method works well in the laboratory,

although it has been less successful in the field. Surfactants

tend to adsorb on rock particles and get left behind as the

water pushes forward. Methods for overcoming this problem

are now being explored.

One of the fundamental problems with recovering

residual oil in a reservoir is that oil droplets often have

difficulty in squeezing through the small openings between

adjacent rock particles. The use of surfactants is one way of

helping the oil particles slip through those openings more

easily. Another approach is to increase the temperature of the

oil in the reservoir, thereby reducing its viscosity (tendency to

flow). As it becomes less viscous, the oil can more easily

force its way through pores in the reservoir.

One of the earliest applications of this principle, the

steam soak method, was first used in Venezuela in 1959. In

this method, steam is injected into one part of the reservoir

and the producer pipe is closed off. After a few days, the

pipe is reopened, and the loosened oil flows out. This process

is repeated a few times before a change is made in the method

and steam is piped in continuously while the producer pipe

remains open.

Steam injection works especially well with heavy oils

that are not easily displaced by other secondary recovery

techniques. It is now used commercially in a number of

fields, primarily in Venezuela and California.

A dramatic form of secondary recovery is in situ (in

place)

combustion

. The principle involved is fairly simple.

A portion of the oil in the reservoir is set on fire. The heat

from that fire then warms the remaining residual oil and

reduces its viscosity, forcing it up the producer pipe.

In practice, the fire can sometimes be made to ignite

spontaneously simply by pumping air down the

injection

well

. In some cases, however, the oil must actually be ignited

at the bottom of the well. The temperature produced in this

process may reach 650–1200°F (350–650°C) and the region

of burning oil may creep through the rock at a speed of 1–

12 in (3–30 cm) per day. As the fire continues, air, and

usually water, are continually pumped into the injection well

to keep the combustion zone moving. Under the best of

Environmental Encyclopedia 3

Seed bank

circumstances, in situ combustion has recovered up to half

of all the oil remaining in a reservoir.

Research has demonstrated that each recovery method

is suitable for particular kinds of reservoirs. Oil viscosity,

rock porosity, depth of the reservoir, and amount of oil

remaining in the reservoir are all factors in determining

which method to use. To date, however, the only method

that has proved to be practical in actual field situations is

steam injection.

[David E. Newton]

ESOURCES

OOKS

Dickey, P. A. Petroleum Development Geology. 3rd ed. Tulsa, OK: PennWell

Books, 1986.

Secondary standards

Pollution control

levels that affect the welfare of plants,

animals, buildings and materials. Secondary standards may

relate to either

water quality

air pollution

under the

control of either the

Safe Drinking Water Act

or the

Clean

Air Act

. These so-called “welfare effects” are thought not to

affect human health but primarily crops, livestock, vegeta-

tion, and buildings. Secondary standards can refer to effects

to which some monetary value could be ascribed, such as

damage to materials,

recreation

natural resources

, com-

munity property, or aesthetics.

Primary standards

, on the

other hand, refer to

pollution

levels that affect human

health.

Second-hand smoke

see

Cigarette smoke

Secure landfill

see

Landfill

Sediment

A mixture of sand,

silt

, clay, and perhaps organic compo-

nents.

Soil

eroded from one location and deposited in an-

other is identified as sediment. The sedimentary fraction

has the ability to carry not only the mineral (sand, silt,

and clay) and organic (

humus

) components, but also other

components that may be attached such as

nitrogen

com-

pounds, herbicides, and pesticides. These riders are of high

concern to those involved in environmental studies. Products

applied to the soil in one location and beneficial to that

1273

system may be transported to other locations where the effect

is detrimental to the

habitat

of other life forms. Care must

be exercised: 1) when applying supplementary items to the

soil, and 2) to develop systems that keep sediment from

finding its way into the streams and water bodies.

Sedimentation

The deposition of material suspended in a liquid. Sedimenta-

tion is normally considered a function of water deposition

of the finer

soil

separates of sand,

silt

, and clay, but it may

also include organic debris. Sometimes this is referred to as

the

siltation

process, although there may be other fractions

of material present other than silt. The term can be applied

to wind-transported sediments as well. Sedimentation can

be both harmful and beneficial. River and stream channels,

reservoirs, and other water bodies may be degraded because

of the deposition of

sediment

materials. Many of the most

important food- and fiber-producing soils of the world have

been developed from the deposition of fine particulates by

both water and wind. In some cases, large topographic land

forms are the result of long-term sedimentation processes.

Seed bank

A seed bank is the reservoir of viable seeds present in a

plant community. Seed banks are evaluated by a variety of

methods. For some

species

, it is possible to make careful,

direct counts of viable seeds. In most cases, however, the

surface substrate of the

ecosystem

must be collected and

seeds encouraged to germinate by exposure to light, mois-

ture, and warmth. The germinating seedlings are then

counted and, where possible, identified to species.

In most cases, the majority of seeds are found in surface

layers. For example, the organic-rich forest floor contains

almost all of the forest’s seed bank, with much smaller num-

bers of seeds present in the mineral

soil

The seeds of some plant species can be remarkably

long-lived, extending the life of the seed bank. For example,

in northeastern North America, the seeds of pin cherry

(Prunus pensylvanica) and red raspberry (Rubus idaeus) can

persist in the forest floor for perhaps a century or longer.

This considerably exceeds the period of time that these ru-

deral species are present as mature, vegetative plants during

the initial stages of post-disturbance forest

succession

However, because these species maintain a more-or-less per-

manent presence on the site through their persistent seed

bank, they are well placed to take advantage of temporary

opportunities of resource availability that follow disturbance

of the stand by

wildfire

, windstorm, or harvesting.

Environmental Encyclopedia 3

Seepage

The seeds of many other plant species have only an

ephemeral presence in the seed bank. In addition to some

tropical species whose seeds are short-lived, many species in

temperate and northern latitudes produce seeds that cannot

survive exposure to more than one winter. This is a common

trait in many grasses, asters, birches, and most conifers,

including pines, spruces, and fir. Often these species produce

seeds that disperse widely, and can dominate the short-lived

seed banks during the autumn and springtime. Species with

an ephemeral presence in the seed bank must produce large

numbers of well-dispersed seeds each year or at least fre-

quently, if they are to successfully colonize newly disturbed

sites and persist on the landscape.

Although part of the plant community, seed banks are

much less prominent than mature plants. In some situations,

however, individual plants in the seed bank can numerically

dominate the total-plant density of the community. For

example, in some cultivated situations the persistent seed

bank can commonly build up to tens of thousands of seeds

per square meter and sometimes densities which exceed

75,000 seeds per square meter. Even natural communities

can have seed banks in the low tens of thousands of seeds

per square meter. However, these are much larger than the

densities of mature plants in those ecosystems.

The seed bank of the plant community is of great

ecological importance because it can profoundly influence

the vigour and species composition of the vegetation that

develops after disturbance.

[Bill Freedman Ph.D.]

ESOURCES

OOKS

Harper, J. L. Population Biology of Plants. San Diego: Academic Press, 1977.

Grime, P. Plant Strategies and Vegetation Processes. New York: Wiley, 1979.

Seed dressings

see

Methylmercury seed dressings

Seepage

The process by which water gradually flows through the

soil

. Seepage is the cause of a variety of environmental

problems. For example, pesticides used on a farm may enter

groundwater

and be transported by seepage to a human

water supply. In some cases, toxic or radioactive wastes stored

in sealed tanks underground have gotten into water supplies

by seepage after the tanks have rusted and broken apart. See

also Water quality

1274

Selection cutting

A harvesting method that removes mature trees individually

or in small groups. The resulting gaps in the canopy allow

understory trees to develop under the protection of the re-

maining overstory. Among all regeneration methods selec-

tion cuttings offer seedlings the most protection against sun

and wind. They also protect against the

erosion

soil

and

maintain aesthetic value in forests. On the negative side,

selection

logging

can damage the remaining trees and re-

quires highly skilled labor and more expense. Because most

of the overstory remains, selection cutting favors shade-

tolerant

species

and is not appropriate when the goal is

growth of light-demanding species. See also Clear-cutting

Sellafield (U.K.)

see

Windscale (Sellafield) plutonium

reactor

Sense of place

Every adult seems to remember a special place from their

past: a place of refuge as a child; sites of family vacations;

a grandparent’s farm; somewhere shared with a loved one

at a special time. Many people, though often with some

embarrassment, will confess to a favorite place in the present

where they can go to be alone, to gather with friends, or

spend leisure time. Places we can identify with—and that

feel special. A literature about that identification with

place—that sense of place—has burgeoned in the last two

decades of the twentieth century.

Yet, contemporary literature, both fictional and fac-

tual, is packed with documentation of alienation, root-

lessness, displaced people, loss of connection to any particular

place, loss of identity and character in suburb and city. In

1957, in America as a Civilization, Max Lerner documented

the loss of community and the quest to regain it, claiming

“this is what I call the problem of place in America, and

unless it is somehow resolved, American life will become

more jangled and fragmented than it is, and American per-

sonality will continue to be unquiet and unfulfilled.” As the

century ends, an increasing number of scholars, thinkers,

and writers are advocating a reinhabitation of place, a

recla-

mation

of the spirit and sense of place as a solution to

numerous contemporary problems, including

environmen-

tal degradation

, sustainability, and social alienation.

Sense of place as a phrase has at least two meanings.

First, the particular characteristic of a place that makes it

what it is. For example, though few people have visited

Antarctica

, most have some sense, an image in their mind’s

eye, of what that continent is like. That image may be

Environmental Encyclopedia 3

Septic tank

realistic, or unrealistic, or may be dramatically simplified,

but it will usually be based on physical characteristics that

the place actually does have.

The second meaning is the particular sense that indi-

viduals have of places they know by experience; we all have

a sense of many places that we have visited, but a sense of

the same place is experienced in many ways by many different

people. Even after a visit to Antarctica, for example, people

will return with a variety of different views, depending on

their reasons for being there, on how long they stayed, and

on how much they know about the place. An explorer will

carry one view, a natural scientist studying how organisms

adapt to extreme environments will bring back a quite differ-

ent view, and a tourist yet another viewpoint. Yi-Fu Tuan

even claimed that “sense of place...implies a certain distance

between self and place that allows the self to appreciate a

place.”

For many, a third meaning is the only one of conse-

quence: that one can gain a sense of place only from being

or becoming deeply involved with a place and by coming to

know that one place and its inhabitants intimately. This is

the meaning implicit in the claim that modern Americans

must regain a sense of place to counteract their mobility and

alienation from

environment

. The poet Gary Snyder refers

to this when he claims that “there are many people on the

planet now who are not ‘inhabitants.’ He teaches that spirit

of place is accessed only through knowledge gained by direct

experience in a specific locale; “Know the plants” has become

almost his mantra. When you really know the plants, you

are beginning to get a sense of the place, a sense of what is

possible and a sense of how to live there in harmony with

the site and setting.

Interwoven with the concept of place is the sense of

home. We all have a sense of many places (in the first two

meanings of the phrase), but a feeling of home is always

associated with a sense of that specific place where home is

thought to be. Home can be a dwelling, a town, even a state

or a nation (in the sense of “homeland”)—or all of these—

but it always is a place, at one or several scales. Most of us

live in some degree of intimacy with the place we call home;

even if that is restricted to a dwelling, it is a place we

know and are to some degree comfortable with. Beyond the

dwelling, and even our identity with region and nation, to

recognize what it means to say “the earth is our home” might

change the way we behave toward the world on which we live.

Scholars and students agree that sense of place in

all three meanings is best developed by increasing one’s

knowledge of the locality in question. A full sense of the

third meaning can only be developed by really getting to

know one place well. That usually means living there, becom-

ing engaged with the surroundings, getting involved with

the community, making enough of a commitment of time

1275

to get beyond the surface. It takes real effort to get to know

the plants (even in cities, to know what the trees and shrubs

are in the parks and on the streets, and to know why those

particular

species

are there rather than others), to know, in

rural areas, what crops are planted and why, to know the

climatic patterns and the reasons for those patterns. If such

a sense of place could be enhanced and strengthened, this

might change the way people use energy in their homes

and cars, interact with other parts of the environment, and

consider how connected each of us really is to the particular

places where we live.

Some of the best American literature focuses on the

complex relationships of an individual writer with a specific

place. For example, Henry David Thoreau’s Walden Pond

trumpeted the personal significance and the transcendence

of one small place. More recently, Aldo Leopold’s struggle

to reclaim a ravaged farm in the sand counties of Wisconsin

has become a metaphor for attempts to understand the im-

portance to human lives of being immersed in the workings

of a place of one’s own. Annie Dillard’s mystical tome on

Tinker Creek has, as a modern day Walden, helped many

better understand the spirit of place. And, the “Refuge”

Terry Tempest Williams found on the shores of the Great

Salt Lake has generated empathy for the human condition

and for the natural world with which it is so entwined.

If, says the poet Wendell Berry, you don’t know where

you are, you don’t know who you are. People who have a

better sense of who they are by knowing more about the

places where they are, start paying attention to the impact

those places have on their lives. Recognizing that place and

identity are related, that place and well being cannot be

disconnected, should lead to taking better care of those

places.

[Gerald L. Young Ph.D.]

ESOURCES

OOKS

Swan, J., and R., eds. Dialogues With the Living Earth: New Ideas on the

Spirit of Place From Designers, Architects, and Innovators. Wheaton, IL:

Quest Books-Theosophical Publishing House, 1996.

Tall, D. From Where We Stand: Recovering a Sense of Place. Baltimore: The

Johns Hopkins University Press, 1993.

ERIODICALS

Cuba, L., and D. M. Hummon. “A Place to Call Home: Identification

With Dwelling: Community, and Region,” The Sociological Quarterly 34,

no. 1 (Spring 1993): 111–131.

Septic tank

Nearly 20 million homes, which include almost 30% of the

population of the United States, dispose of their

waste-

Environmental Encyclopedia 3

Septic tank

water

through an on-site disposal system. The most com-

monly used type of system is the septic tank, which is an

individual treatment system that uses the

soil

to treat small

wastewater flows. The system is usually used in rural or

large lot settings where centralized wastewater treatment is

impractical. Septic tank systems are designed specifically for

each site, using standardized design principles that are usu-

ally state-regulated. Septic tank systems commonly contain

three components: the septic tank, a distribution box, and

a drainfield, all of which are connected by conveyance lines.

The septic tank serves to separate solids from the

liquids in the wastewater. All sources of wastewater, includ-

ing those from sinks, baths, showers, washing machines,

dishwashers, and

toilets

, are directed into the septic tank,

since any of these waters can contain disease-causing

micro-

organisms

or environmental pollutants. The size of the

septic tank varies depending on the number of bedrooms in

the home, but an average tank holds 1,000 gal (3,790 l) of

liquid. Wastewater in a septic tank is treated by

anaerobic

bacteria that digest organic materials, while encouraging the

separation of solid materials from the wastewater. The solids

accumulate and remain in the septic tank in the form of

sludge

, which collects at the bottom of the tank, and also in

the form of scum, which floats on the top of the wastewater.

Periodically (for example, every two or three years) the indi-

gestible sludge and scum (referred to as septage) are removed

from the tank by pumping and are disposed of in a septage

disposal system (like a municipal

sewage treatment

sys-

tem). Unfortunately, many homeowners do not properly

maintain septic systems by pumping them out as frequently

as every two to three years and often wait until there is a

back up in the system or some other type of problem. Periodic

pumping is designed to prevent the solids from leaking out

of the septic tank in the wastewater

effluent

. The effluent

from the septic tank is a cloudy liquid that still contains

many pollutants (including

nitrogen

compounds, suspended

solids, and organic and inorganic materials) and microorgan-

isms (including bacteria and viruses, some of which that may

be potentially pathogenic), which require further treatment.

Treatment of the wastewater effluent from the septic

tank is continued by transporting the wastewater by gravity

to a soil

absorption

field through a connecting pipe. The

absorption field is also referred to as the soil drainfield or

the

nitrification

field. The absorption field consists of a

series of underground perforated pipes covered with soil and

turf, which may be connected in a closed loop system. The

wastewater enters a constructed gravel bed (the trench)

through perforations in the pipe, where it is stored before

entering the underlying unsaturated soil. The wastewater is

treated as it trickles into and through the soil by

filtration

and

adsorption

processes as well as by

aerobic

degradation

processes before the wastewater enters the ground water.

1276

Filtration removes most of the suspended solids and may

also remove microorganisms. Adsorption is the process by

which pollutants and microorganisms are attracted to and

held on the surfaces of soil particles, thus immobilizing them.

Adsorption attracts such nutrients such as

phosphorus

and

some forms of nitrogen (mostly ammonium [NH

]) and is

most effective when fine-textured soil is used as the adsorp-

tion medium. However, soils with a very fine texture, such

as soils high in clay, may have too low permeability to allow

much wastewater to pass through the soil. Microbial degra-

dation results in the removal of many remaining nutrients

and organic materials. If the volume and type of soil underly-

ing a soil absorption system are adequate, most pollutants

(with the exception of nitrate nitrogen) should be removed

before the wastewater reaches the

groundwater

Estuaries (bays, harbors, etc.) often experience nitro-

gen

from septic systems along the shore (within

656 mi [200 m] of the shore or greater in sandy soil environ-

ments). Typically on-site disposal systems such as septic

tanks cannot remove more than 50–60% of the nitrogen

(mostly in the form of nitrate) and it ends up in the nearby

coastal waterway, which is a problem because many of the

estuaries around the world are experiencing problems with

eutrophication as a direct result of overloading of nitrogen.

Although some difficulties can arise with septic sys-

tems, there are some simple practices that can prevent com-

mon problems. For example,

groundwater pollution

and

surfacing of untreated or poorly filtered effluent from a septic

tank system can be prevented by ensuring that excessive

amounts of water are not allowed to enter or flood the

drainfield. Reduced production of wastewater, or

water

conservation

, is recommended to prevent system overload.

Water from roof drains, basement sump pump drains, and

other rain water or surface water

drainage

systems should

be directed away from the absorption field. The functioning

of the system can also be damaged by the addition of such

materials as coffee grounds, wet-strength towels,

dispos-

able diapers

, facial tissues, cigarette butts, and excessive

amounts of grease, which can clog the inlet to the septic

tank, or if carried out of the septic tank, may impede drainage

of wastewater in the soil absorption field. The septic tank

should be pumped more frequently if a

garbage

disposal

is used.

Groundwater

pollution

can also be caused by the addi-

tion of hazardous

chemicals

to the septic tank system, which

may be transported through the system to the ground water

without removal or treatment in the system. Hazardous

chemicals may be found in such commonly used products as

pesticides, solvents, latex paint, oven cleaners,

dry cleaning

fluids, motor oils, or degreasers.

Siting requirements for a soil absorption system de-

pend on the amount of daily sewage flow and site conditions