Environmental Encyclopedia

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Environmental Encyclopedia 3

Salinity

ethics

had transformed the New World and contributed to

the modern environmental crisis. The result of this work was

Conquest of Paradise: Christopher Columbus and the Columbian

Legacy. One conclusion Sale reached in this book was that

the very cultures destroyed by the European invasion, those

of the Native Americans, had practiced many of the environ-

mental concepts to which modern societies must return if

the world is to survive.

Although Sale has expressed interest in writing novels,

his early books have been devoted to activist topics because

“the world is in such a mess, and it needs writing about.”

He continues: “I write my books to help save society and

the planet.”

[David E. Newton]

ESOURCES

OOKS

Sale, K. Dwellers in the Land: The Bioregional Vision. San Francisco: Sierra

Club Books, 1983.

———. Human Scale. New York: Coward, McCann & Geoghegan, 1980.

———. Rebels Against the Future: The Luddites and Their War on the

Industrial Revolution: Lessons For the Computer Age. Addison-Wesley, 1995.

———. The Conquest of Paradise. New York: Knopf, 1990.

———. The Fire of His Genius: Robert Fulton and the American Dream.

New York: Free Press, 2001.

———. The Green Revolution: The American Environmental Movement,

1962–1992. Hill and Wang, 1993.

ERIODICALS

Baker, J. F. “Kirkpatrick Sale.” Publishers Weekly (October 19, 1990): 41–42.

Saline soil

Soils containing enough soluble salts to interfere with the

ability of plants to take up water. The conventional measure-

ment that determines the

salinity

soil

is a deciSiemens

meter; soils are considered saline if the conductivity of their

saturation extract solution exceeds 4 deciSiemens meter-1.

This unit of measure closely approximates the ionic salt

concentration, and it is relatively easy to evaluate. The most

common salts are composed of mixtures of sodium, calcium,

and magnesium with chlorides, sulfates, and bicarbonates.

Other less soluble salts of calcium sulfate and calcium and

magnesium carbonate may be present as well. The

commonly less than 8.5.

In saline soils, there is often what is known as a perched

water table—water close to the surface of the land. This

phenomenon can be caused by restricting layers of fine clay

within the soil, or by the application of waters at a rate

greater than the natural permeability of the ground. When

the

water table

is so close to the top of the soil, water is

often transmitted to the surface where evaporation occurs,

1237

leaving the ions in the water to precipitate as salts. The

resulting complex of salts can be seen on the surface of the

soil as a white, crust-like layer.

The surface layers of a saline soil commonly have very

good soil structure, and this is important to understand

if the soil is to be reclaimed or leached of the high salt

concentrations. This kind of structure has relatively large

pores; water can flow quickly through them, which aids in

carrying away salty water, thus making it easier to flush out

the soil. Artificial drains can also be installed beneath the

surface to provide an outlet for water trapped within the

soil, and once these drains are in place, salt concentrations

can be further reduced by the application of good quality

water.

Excessive

irrigation

and the use of fertilizers and ani-

mal wastes can all increase the salinity of soil. The yields of

common crops and the level of agricultural production are

severely reduced in areas where salts have been allowed to

accumulate in the soil.

Salinization

can be so severe in some

cases that only salt-tolerant crops can be grown.

Leaching

is often necessary to reduce the levels of salt and keep the

soil suitable for crop production. But this process can remove

other soluble components from the soil and carry them into

the

waste stream

, polluting both

groundwater

and sur-

face water. The

environmental degradation

from this

form of

agricultural pollution

can be extensive, and a

method needs to be developed for leaching saline soils with-

out these consequences. If this problem cannot be solved,

it will no longer be possible to use some saline soils for

agriculture. As

population growth

continues and the global

demand for food increases, another approach might be the

development of more salt-tolerant plant

species

[Royce Lambert and Douglas Smith]

ESOURCES

OOKS

Brady, N. C. The Nature and Properties of Soils. 13th ed. New York: Macmil-

lan, 2001.

Millar, R. W., and R. L. Danahue. Soils: An Introduction to Soils and Plant

Growth. 6th ed. Englewood Cliffs, NJ: Prentice-Hall, 1990.

Salinity

A salt is a compound of a metal with a nonmetal other than

hydrogen

or oxygen. NaCl (sodium chloride), or table salt,

is the best-known example. The solubility of various salts

in water at a standard temperature is highly variable. When

salts are dissolved in water, the result is called a saline solu-

tion, and the salinity of the solution is measured by its ability

to carry an electrical current. Salinity of water is one of the

components of

water quality

. Salinity is also measured

Environmental Encyclopedia 3

Salinization

soil

. Soil can become salinized from water containing

sufficient salts, from the natural degradation of soil minerals,

or from materials added to the soil such as

fertilizer

. Large

amounts of water may be required to leach the accumulated

salts from the root zone and prevent reduced plant growth

or plant desiccation. See also Soil profile; Water quality stan-

dards

Salinization

An increase in salt content, usually of agricultural soils,

irri-

gation

water, or drinking water is called salinization. Salini-

zation is a problem because most food crops, like the human

body, require fresh (nonsaline) water to survive. Although

a variety of natural processes and human activities serve to

raise the salt contents of

soil

and water, irrigation is the

most widespread cause of salinization. Almost any natural

water source carries some salts; with repeated applications

these salts accumulate in the soil of irrigated fields. In

arid

regions, streams, lakes, and even aquifers can have high

salt concentrations. Farmers forced to use such saline water

sources for irrigation further jeopardize the fertility of their

fields. In coastal areas, field salinization also results when

seawater floods or seeps into crop lands. This occurs when

falling water tables allow sea water to seep inland under

ground, or where

aquifer subsidence

causes land to settle.

Salinization also affects water sources, especially in arid re-

gions where evaporation results in concentrated salt levels

in rivers and lakes. Remedies for salinization include the

selection of salt-tolerant crops and flood irrigation, which

washes accumulated salts away from fields but deposits them

elsewhere.

Most of the world’s people rely on irrigated agriculture

for food supplies. Regular applications of water, either from

rivers, lakes, or underground aquifers, allow grain crops,

vegetables, and fruits to grow even in dry regions. California’s

rich Central Valley is an outstanding example of irrigation-

dependent agriculture. One of North America’s primary gar-

dens, the valley is naturally dry and sun baked. Canals car-

rying water from distant mountains allow strawberries, to-

matoes, and lettuce to grow almost year round. The cost of

this miraculous productivity is a gradual accumulation of

salts, which irrigation water carries onto the valley’s fields

from ancient sea bed sediments in the surrounding moun-

tains. Without heavy

flooding

and washing, Central Valley

soils would become salty and infertile within a few years.

Some of California’s soils have become salty and infertile

despite flooding. Similar situations are extremely widespread

and have been known since humankind’s earliest efforts in

agriculture. The collapse of early civilizations in Mesopota-

mia and the Indus Valley resulted in large part from salt

1238

accumulation, caused by irrigation, which made food sup-

plies unreliable.

Salts are a group of mineral compounds, composed

chiefly of sodium, calcium, magnesium, potassium, sulfur,

chlorine

, and a number of other elements that occur natu-

rally in rocks, clays, and soil. The most familiar salts are

sodium chloride (table salt) and calcium sulfate (gypsum).

These and other salts dissolve easily in water, so they are

highly mobile. When plenty of water is available to dilute

salt concentrations in water or wash away salt from soil,

these naturally occurring compounds have little impact.

Where salt-laden water accumulates and evaporates in basins

or on fields, it leaves behind increasing concentrations of

salts.

Most crop plants exposed to highly saline environ-

ments have difficulty taking up water and nutrients. Healthy

plants wilt, even when soil moisture is high. Leaves produced

in saline conditions are small, which limits the photosyn-

thetic process. Fruits, when fruiting is successful, are also

small and few. Seed production is poor, and plants are weak.

With increasing

salinity

, crop damage increases, until plants

cannot grow at all. Water begins to have a negative effect

on some crops when it contains 250–500

parts per million

(ppm) salts; highly saline water, sometimes used for irriga-

tion out of necessity, may contain 2,000–5,000 ppm or more.

For comparison, sea water has salt concentrations upwards of

32,000 ppm. In soil, noticeable effects appear when salinity

reaches 0.2%; soil with 0.7% salt is unsuitable for agriculture.

Another cause of soil salinization is subsidence. When

water is pumped from underground aquifers, pore spaces

within rocks and sediments collapse. The land then com-

pacts, or subsides, often lowering several meters from its

previous level. Sometimes this

compaction

brings the land

surface close to the surface of remaining

groundwater

Capillary action pulls this groundwater incrementally toward

the surface, where it evaporates, leaving the salts it carried

behind in the soil. Near coastlines such processes can be

especially severe. Seawater often seeps below the land surface,

especially when fresh-water aquifers have been depleted.

When seawater, with especially high salt concentrations,

rises to the surface it evaporates, leaving crystalline salt in

the soil.

In such cases, the salinization of the aquifer itself is also

a serious problem. Many near-shore aquifers are threatened

today by seawater invasions. Usually seawater invasions occur

when farms and cities have extracted a substantial amount

of the aquifer’s water volume. Water pressure falls in the

fresh-water aquifer until it no longer equals pressure from

adjacent sea water. Sea water then invades the porous aquifer

formation, introducing salts to formerly fresh water supplies.

Rivers are also subject to salinization. Both cities and

farms that use river water return their

wastewater

to the

Environmental Encyclopedia 3

Salinization

river after use. Urban storm sewers and

sewage treatment

plants often send poor quality water back to rivers;

drainage

canals carry intensely saline

runoff

from irrigated fields back

to the rivers that provided the water in the first place. When

dams

block rivers, especially in dry regions, millions of

cubic meters of water can evaporate from reservoirs, further

intensifying in-stream salt concentrations.

The

Colorado River

is one familiar example out of

many rivers suffering from artificial salinization. The Colo-

rado, running from Colorado through Utah and Arizona,

used to empty into the Sea of Cortez south of California’s

Imperial Valley before human activities began consuming

the river’s entire

discharge

. Farms and cities in adjacent

states consume the river’s water, adding salts in wastewater

returned to the river. In addition, the Colorado’s two huge

reservoirs, Lake Powell and Lake Mead, lie in one of the

continent’s hottest and driest regions and lose about 10% of

the river’s annual flow through evaporation each year. By

the time it reaches the Mexican border, the river contains

850 ppm salts, too much for most urban or agricultural uses.

Following a suit from Mexico, the United States government

has built a $350 million

desalinization

plant to restore the

river’s

water quality

before it leaves Arizona. The Colora-

do’s story is, unfortunately a common one. Similar situations

abound on major and minor rivers from the Nile to the

Indus to the Danube.

Salinization occurs on every occupied continent. The

world’s most severely affected regions are those with arid cli-

mates and long histories of human occupation or recent intro-

ductions of intense agricultural activity. North America’s

Great Plains, the southwestern states, California, and much

of Mexico are experiencing salinization. Pakistan and north-

western India have seen losses in agricultural productivity, as

have western China and inland Asian states from Mongolia

and Kazakhstan to Afghanistan. Iran and Iraq both suffer

from salinization, and salinization has become widespread in

Africa. Egypt’s Nile valley, long northern Africa’s most boun-

tiful bread basket, also has rising salt levels because of irriga-

tion and subsidence. One of the world’s most notorious case

histories of salinization occurs around the

Aral Sea

, in south-

ern Russia. This inland basin, historically saline because it

lacks an outlet to the sea, is fed by two rivers running from

northern Afghanistan. Since the 1950s, large portions of these

rivers’ annual discharge has been diverted for cotton produc-

tion. Consequently, the Aral Sea is steadily drying and shrink-

ing, leaving great wastes of salty, dried sea bottom. Dust

storms crossing these new deserts carry salts to both cotton

and food crops hundreds of miles away.

Avoiding salinization is difficult. Where farmers have

a great deal of capital to invest, as in California’s Central

Valley and other major agricultural regions of the United

States, irrigators install a network of perforated pipes, known

1239

as tiles, below their fields. They then flood the fields with

copious amounts of water. Flooding washes excess salts

through the soil and into the tiles, which carry the hypersa-

line water away from the fields. This is an expensive method

that wastes water and produces a toxic brine that must be

disposed of elsewhere. Usually this brine enters natural rivers

or lakes, which are then contaminated unless their volume

is sufficient to once again dilute salts to harmless levels.

However this method does protect fields. More efficient

irrigation systems, with pipes that drip water just near plant

roots themselves may be an effective alternative that contam-

inates minimal volumes of water.

Water can also be purified after agricultural or urban

use. Purification, usually by reverse osmosis, is an expensive

but effective means of removing salts from rivers. The best

way to prevent water salinization is to avoid dumping urban

or irrigation wastes into rivers and lakes. Equally important

is avoiding evaporation by reconsidering large dam and

res-

ervoir

developments. Unfortunately, most societies are re-

luctant to consider these options: reservoirs are widely viewed

as essential to national development, and wastewater purifi-

cation is an expensive process that usually benefits someone

else downstream.

Perhaps the best way to deal with salinization is to find

or develop crop plants that flourish under saline conditions.

Governments, scientists, and farmers around the world are

working hard to develop this alternative. Many wild plants,

especially those native to deserts or sea coasts, are naturally

adapted to grow in salty soil and water. Most food plants

on which we now depend—wheat, rice, vegetables, fruits—

originate in nondesert, nonsaline environments. When do-

mestic food plants are crossed with salt-tolerant wild plants,

however, salt-tolerant domestics can result. This process was

used to breed tomatoes that can bear fruit when watered

with 70% seawater. Other vegetables and grains, including

rice, barley, millet, asparagus, melons, onions, and cabbage,

have produced such useful crossbreeds.

Equally important are innovative uses of plants that

are naturally salt tolerant. Some salt-adapted plants already

occupy a place in our diet—beets, dates, quinoa (an Andean

grain), and others. Furthermore, careful allocation of land

could help preserve remaining salt-free acreage. Planting

salt-tolerant fodder and fiber crops in soil that is already

saline can preserve better land for more delicate food crops,

thus reducing pressure on prime lands and extending soil

viability. See also Salinization of soils

[Mary Ann Cunningham Ph.D.]

ESOURCES

OOKS

Frenkel, H., and A. Meiri, eds. Soil Salinity: Two Decades of Research in

Irrigated Agriculture. New York: Van Nostrand Reinhold, 1985.

Environmental Encyclopedia 3

Salinization of soils

National Research Council. Saline Agriculture. Washington, DC: National

Research Council, 1990.

Scabocs, I. Salt-Affected Soils. Boca Raton, FL: CRC Press, 1989.

Shainberg, I., and J. Shalhevet. Soil Salinity Under Irrigation. Berlin:

Springer-Verlag, 1984.

Salinization of soils

Salinization

soil

involves the processes of salt accumula-

tion in the upper rooting zone so that many plants are

inhibited or prohibited from normal growth. Salinization

occurs primarily in the semi-arid and

arid

portions of the

earth. Salinization is commonly thought to occur only in

the hot climatic regions, but may be found in cooler to cold

portions of the earth where precipitation is very limited.

Where the annual precipitation exceeds about 20 inches (500

mm), there is usually adequate downward movement of salts

through

leaching

to prohibit the development of

saline

soil

. Occasionally salinization of soil will occur where there

has been an inundation of land by sea water. Some areas of

the world were once under sea water, but due to uplift the

land is now many feet above sea level. These lands are

common sources of “ancient salts” and may lead to the devel-

opment of saline waters as these soils are slowly leached.

Natural sources of salts in soil are primarily from the

decomposition

of rocks and minerals through the processes

of chemical

weathering

. With adequate amounts of mois-

ture present, hydrolysis, hydration, solution, oxidation, and

carbonation cause the minerals to decompose and release the

ionic constituents to form various salts. The more common

cations are sodium, calcium, and magnesium with lesser

amounts of potassium and boron. The common anions are

chloride and sulfate with lesser amounts of bicarbonate, car-

bonate, and occasionally nitrate.

Inherent factors of the landscape may also lead to

salinization of soils. One of the more common factors is the

restriction of water

drainage

within the soil, often referred

to as soil permeability. Soil becomes less

permeable

because

of genetic or inherited layers within the

soil profile

that

have relatively high amounts of clay. Because of the extremely

small sizes of the clay particles, the natural pore size is also

very small, frequently being less than 0.0001 mm average

diameter. The natural tortuosity and small size combine to

severely reduce the rate of water movement downward which

tends to increase salt buildup.

In addition, because of the soil pore size, saline waters

may be transported upward through the processes of capillary

action. While the rate of upward movement of water may

be relatively slow, the process can deliver saline water from

several inches below the surface of the land and create a

zone of highly saline soil at the surface of the earth.

1240

Salinization of soils has also occurred in areas where

irrigation

waters have been applied to lands that have not

been subject to long-term natural leaching by rainfall. In

several cases the application of relatively good quality water

to arid soils with poor internal drainage has caused the soil

to develop a higher

water table

which in turn has permitted

the salts within the soil to be carried to the surface by high

evaporation demand. In other cases water of relatively high

salt content has been applied to soils without proper drain-

age, resulting in the development of saline soils. As the water

is evaporated from the soil or the plant surfaces, the salts

are left to accumulate in the soil.

Because of the increasing demand for food and fiber,

many marginal lands are being brought into agronomic pro-

duction. Proper irrigation management and drainage deci-

sions must be considered on a worldwide and long-term

basis to avoid a deleterious influence on the ability to produce

on these soils and to determine the appropriate environmen-

tal considerations for disposal of salts from salinized soils.

See also Arable land; Nitrates and nitrates; Runoff; Soil con-

servation; Soil eluviation; Soil illuviation

[Royce Lambert]

ESOURCES

OOKS

Foth, H. D. Fundamentals of Soil Science. 7th ed. New York: Wiley, 1984.

Singer, M. J., and D. N. Munns. Soils: An Introduction. 5th ed. New York:

Macmillan, 2001.

THER

Richards, L. A., ed. Diagnosis and Improvement of Saline and Alkali Soils.

USDA Handbook 60. Washington, DC: U.S. Government Printing Of-

fice, 1964.

Salmon

Salmon is a popular fish for food and sport fishing. Five

species

of salmon live in the North Pacific Ocean: Pink,

Sockeye, Coho, Chum, and Chinook. One species, the At-

lantic salmon, lives in the North Atlantic Ocean. Two other

fish species that are also members of the Salmonidae fish

family—steelhead and sea-run cutthroat trout—live in the

Pacific Northwest. The Pacific Coast salmon populations

are being threatened with extirpation from much, if not all,

of their range.

At the heart of the Pacific salmon species’ range, and

perhaps indicative of the heart of its problems, is the Colum-

bia River basin. Covering parts of seven states and two

Canadian provinces, the Columbia River system contains

over 100

dams

, 56 of which are major structures, including

19 major generators of hydroelectric power. These structures

present an insurmountable obstacle for these migrating

Environmental Encyclopedia 3

Salmon

fishes. Adult salmon, after growing and maturing in the

ocean, return to the freshwater stream of their origin as they

swim upstream to spawn. The adults will die shortly after this

culmination of their arduous journey, and, after hatching,

the young salmon—called smolts—swim downstream to the

ocean to continue this life cycle.

About three-fourths of all of the population declines

of salmon are directly attributable to hydroelectric dams.

The dams simply do not allow a majority of these fish

to successfully complete their

migration

, and many salmon

die as they swim, or are swept, directly into the turbines.

Fish ladders, stepped pools intended as an aid for fish

to bypass the dams, enable some salmon to continue their

journey, but many do not find their way through. As

they move downstream, the smolts are slowed or stopped

by the reservoirs created by the dams. Here they are

exposed to larger populations of predators than in their

natural riverine

habitat

. They are exposed to a wide

variety of pathogens as well as a physical

environment

of warmer, slow moving waters, to which they are only

moderately tolerant. Only 20% of the downstream migrants

ever make it to the Pacific. Poor

water quality

and

nutrient

deficits in many stretches of the Columbia River

also takes a toll on the young smolts.

Overfishing

, both offshore and along the rivers, con-

tributes to the decline of salmon populations. Fishery biolo-

gists have attempted to offset these losses of native stocks

by releasing hatchery-raised salmon. However, interbreeding

reduces the genetic hardiness of these fish. They also weaken

the genetic lines of wild fish when they breed with them.

Historically, when hatchery programs have increased the

mixed stock fish population (i.e., wild and farmed) dramati-

cally, fishing activity increases and a further depletion of

wild salmon results.

To address overfishing issues, in 1996 Washington

State began using a mass-marking program designed to en-

able fishermen to more easily identify hatchery chinook and

coho salmon. Fish bred in a hatchery have their adipose fin

(a small tail fin) removed before they are released. Anyone

who catches a marked hatchery fish may keep it; wild salmon

that are unmarked must be released back into the wild.

Realizing the need for a more balanced management

plan for the Columbia River basin, Congress passed the

Northwest Power Act in 1980. This act established the

Northwest Power Planning Council (NWPPC), which was

charged with the task of balancing long-term hydroelectric

energy needs with minimizing the negative impact of dams

on native salmon populations. However, despite modifica-

tions to water flow along the Snake and Columbia Rivers

instituted by the NWPPC, the native salmon population

continued to decline throughout the 1980s.

1241

In 1991, the National Marine Fisheries Service

(NMFS) began an extensive study of salmon populations in

the northwestern United States. The NMFS found that

52 distinct populations (termed Evolutionarily Significant

Units, or ESUs) of Pacific salmon have been identified in

west coast states. That same year, Snake River stocks of

sockeye salmon were first listed under the

Endangered Spe-

cies Act

(ESA) as endangered. Twenty-six salmon ESUs

are now listed as threatened or endangered status.

In June 2000, the NMFS adopted a rule prohibiting

the killing or injuring of 14 ESUs of Pacific salmon and

steelhead classified as threatened under the Endangered

Species Act (ESA). This “take” rule was adopted under

section 4(d) of the ESA. The rule does allow for the

removal of ESA-listed salmon in association with approved

programs such as scientific research and tribal fishing

rights.

Various species of salmon have been added to the ESA

list in the past several decades. As of May 2002, Atlantic

salmon were included on the ESA with an endangered status,

while chum and coho were listed as threatened. Dual status

ESA species (endangered in one part of their range and

threatened in another) include chinook salmon, sockeye

salmon, and steelhead.

In late 2001, a U.S. district court ruled that the

NMFS listing of Oregon coast coho salmon as endangered

was “arbitrary and capricious” (Alsea Valley Alliance v.

Evans). The court determined that excluding hatchery

stock from the population assessment of this species, as

NMFS had done, was inappropriate. This ruling could

have far-reaching implications for other salmon stocks

listed as endangered or threatened; after the Alsea ruling,

six delisting petitions were filed by farming

irrigation

groups and other agencies requesting the removal of addi-

tional ESUs from endangered status. As of May 2002,

NMFS was appealing the Alsea decision, but had also

announced status reviews on fourteen endangered salmon

ESUs. The Oregon coho remains on the endangered list

pending the decision of the appeal.

Long-term, sustained population recovery for these

ecologically, as well as economically, important salmon pop-

ulations will depend on changes in both habitat and human

behavior. More water is needed downstream to aid migra-

tion. This would mean less water for irrigation and for

hydroelectric-generated power. Increased water flow

through releases from reservoirs and spillway openings in

the hydroelectric dam system has been shown to improve

salmon survival rates in the Snake River. Balancing the power

requirements of the Pacific Northwest with the habitat needs

of salmon species will be a key part of ensuring their contin-

ued survival.

[Eugene C. Beckham and Paula A. Ford-Martin]

Environmental Encyclopedia 3

Henry S. Salt

ESOURCES

OOKS

Lichatowich, Jim. Salmon Without Rivers: A History of the Pacific Salmon.

Washington, DC: Island Press, 2001.

Taylor, Joseph. Making Salmon: An Environmental History of the Northwest

Fisheries Crisis. Seattle, WA: University of Washington Press, 2001.

ERIODICALS

Curtis, S. “Power Plan Trumps Salmon Recovery.” Field & Stream 106,

no.1 (May 2001): 16.

Gresh, Ted, J. Lichatowich, and P. Schoonmaker. “An Estimation of

Historic and Current Levels of Salmon Production in the Northeast Pacific

Ecosystem.” Fisheries 25, no.1 (January 2000): 15–21.

THER

Northwest Fisheries Science Center, National Marine Fisheries Service.

Salmonid Travel Time and Survival Related to Flow in the Columbia River

Basin. March 2000 [cited May 2002]. <http://www.nwfsc.noaa.gov/pubs/

nwfscpubs.html>.

Northwest Salmon Recovery Planning. [cited May 31, 2002]. <http://re-

search.nwfsc.noaa.gov/cbd/trt/index.html>.

RGANIZATIONS

Northwest Fisheries Science Center, NMFS, NOAA, 2725 Montlake

Blvd. E, Seattle, WA USA 98112 (206) 860-3200, Email:

NWFSC.Webmaster@noaa.gov, <http://www.nwfsc.noaa.gov/>

Henry S. Salt (1851 – 1939)

English writer and reformer

Although he is probably best known as the vegetarian author

of Animals’ Rights Considered in Relation to Social Progress

(1892), Henry Salt was a man with many roles—teacher,

biographer, literary critic, and energetic advocate of causes he

grouped under the title of humanitarianism. These included

pacifism and socialism as well as

vegetarianism

, anti-vivi-

sectionism, and other attempts to promote the welfare of

animals. Late in his life, Salt also advocated efforts to con-

serve the beauties of

nature

, especially wildflowers and

mountain districts.

Salt was born in India in 1851, the son of a colonel

in the Royal Bengal Artillery. When his parents separated

a year later, Salt’s mother moved to England, and he spent

much of his childhood at the home of her well-to-do parents.

Educated at Eton and Cambridge, he embarked on an appar-

ently comfortable career when he returned to Eton as an

assistant master. While teaching at Eton, however, Salt met

some of the leading radicals and reformers of the day, includ-

ing William Morris, John Ruskin, and George Bernard

Shaw, with whom he formed a lasting friendship. During

this period Salt became a vegetarian. He also read

Henry

David Thoreau’s

Walden, which inspired Salt and his wife

to leave Eton and move to a country cottage in 1885 to lead

a simple, self-sufficient life. For Salt, the simple life was far

from dull. He became a prolific writer, although his efforts

brought little financial profit. In addition to Animals’ Rights,

1242

his works include a biography of Thoreau, studies of Shelley

and Tennyson, a translation of Virgil’s Aeneid, and an autobi-

ography, Seventy Years Among Savages (1921), in which he

examined English life as if he were an anthropologist study-

ing a primitive tribe. Another book, A Plea for Vegetarianism,

came to the attention of

Mohandas Karanchand Gandhi

when he was a student in London. Gandhi, who was raised

a vegetarian, later wrote in his Autobiography that Salt’s book

made him “a vegetarian by choice.” Salt apparently met

Gandhi in 1891, then corresponded with him in 1929 during

Gandhi’s nonviolent struggle for the independence of In-

dia—a struggle inspired, in part, by Thoreau’s essay, “Civil

Disobedience.”

Perhaps the best statement of Salt’s views is the address

he wrote to be read at his funeral. Declaring himself “a

rationalist, socialist, pacifist, and humanitarian,” Salt disa-

vowed any belief “in the present established religion,” but

acknowledged “a very firm religious faith” in “a Creed of

Kinship:” “a belief that in years yet to come there will be a

recognition of the brotherhood between man and man, na-

tion and nation, human and sub-human, which will trans-

form a state of semi-savagery...into one of civilization, when

there will be no such barbarity as warfare, or the robbery of

the poor by the rich, or the ill-usage of the lower animals

by mankind.”

[Richard K. Dagger]

ESOURCES

OOKS

Hendrick, G., and W. Hendrick, eds. The Savour of Salt: A Henry Salt

Anthology. Fontwell, Sussex: Centaur Press, 1989.

ERIODICALS

Jolma, D. J. “Henry Salt and 100 Years of Animal Rights.” The Animals’

Agenda (November–December 1992): 30–2.

Salt marsh

see

Wetlands

Salt (road)

While several

chemicals

are available for deicing winter

roads, common salt (NaCl) is most frequently used. Approxi-

mately 20 billion lb (9 billion kg) of salt are used each year

in the United States for treating ice and snow on roads.

Calcium chloride (CaCl

), potassium chloride (KCl), and

urea are also available but used in smaller quantities. Com-

mon salt is preferred because it is cheaper per pound and

more effective. While the price per pound of salt is cheap,

about 1.5 billion dollars are spent per year on the enormous

quantity used, and its distribution and application.

Environmental Encyclopedia 3

Salt water intrusion

Salt in its solid form does not melt ice. It first must

go into solution to form a brine, and the brine effects a

melting of ice and snow. Ordinarily, snow is packed on the

road surface by vehicular traffic; known as the “hard-pack,” it

forms a bond with the underlying pavement that is frequently

impossible to remove with snowplows. Salt melts through

the hard-pack and breaks the ice-pavement bonding. Traffic

breaks the loosened ice, and snowplows are then able to

remove the broken ice and packed snow. Deicing facilitates

traffic movement after a snow fall and it is thought to make

winter driving safer.

But there are hidden costs in the use of salt. It corrodes

steel, and it is estimated that about three billion dollars is

spent annually to protect vehicles from rust with corrosion-

resistant coatings. Some have added to this estimate the

costs of frequent washings to save vehicles from rust. The

expense of salt deicing does not stop, however, with motor

vehicle protection and damage. The United States has about

500,000 bridges, of which an estimated 40% are currently

considered deficient. Damage to bridges comes from a vari-

ety of causes, but many experts consider the most significant

agent for premature deterioration is deicing salt. It is esti-

mated that repair and protection to damaged bridges in the

United States in the next decade will cost between one-half

and two-thirds of a billion dollars. Salt damage is also causing

bridges in Great Britain to deteriorate more rapidly than

expected and is believed to be the principal cause of bridge

damage with an anticipated cost of repair in the next decade

of a half billion pounds.

Salt damages roadside vegetation, and it has been

shown that waters downstream from a deiced highway con-

tain significantly more (in one case 31 times as much) chlo-

ride than waters in the same rivers upstream. Well water

can similarly become contaminated with salt, and both Mas-

sachusetts and Connecticut have large numbers of

wells

with a sodium content in excess of 20 mg per liter, which

is considered to be the upper limit for individuals who must

control sodium intake. One area of Massachusetts has quit

using deicing salt because of concern for sodium in their

drinking water.

It would be useful to develop a deicer that has less

impact on the economy and the

environment

. One such

alternative is calcium magnesium acetate (CME) which,

while initially far more costly than salt, is believed to have

less potential for damaging the environment. See also Auto-

mobile; Groundwater pollution; Salinity; Salinization

[Robert G. McKinnell]

ESOURCES

ERIODICALS

Boice, L. P. “Environmental Management: CMA, An Alternative to Road

Salt?” Environment 28 (1985): 45.

1243

Saltwater intrusion into a coastal aquifer due

to depletion of the freshwater in the aquifer.

(Illustration by Hans & Cassidy.)

“Deicing Agents: A Primer.” Public Works (July 1991): 50–51.

Dunker, K. F., and B. G. Rabbat. “Why America’s Bridges Are Crumbling.”

Scientific American 268 (March 1993): 66–72.

“Highway Deicing: Comparing Salt and Calcium Magnesium Acetate.”

TR News 163 (November–December 1992): 17–19.

Reina, P. “Salt Breaks the Back of Motorway Bridges.” New Scientist (April

29, 1989): 30.

Salt water intrusion

Aquifers in coastal areas where fresh

groundwater

is dis-

charged into bodies of salt water such as oceans are subject

to salt water intrusion. Intrusion occurs when water usage

lowers the level of freshwater contained in the

aquifer

. The

natural gradient sloping down toward the ocean is changed,

resulting in a decrease or reversal of the flow from the aquifer

to the salt water body, which causes salt water to enter and

penetrate inland. If salt water travels far enough inland well

fields supplying freshwater can be ruined and the aquifer

can become so contaminated that it may take years to remove

the salt, even with fresh groundwater available to flush out

the saline water.

Salt water intrusion can also develop where there is

artificial access to salt water, such as sea level canals or

drainage

ditches. On the coastal perimeter of the United

States there are a number of areas with such intrusion prob-

lems. There are five methods available to control intrusion:

1) the reduction or rearrangement of the pumping draw-

down; 2) direct recharge; 3) the development of a pumping

trough adjacent to the coast; 4) maintenance of a freshwater

ridge above sea level along the coast; and 5) construction of

artificial subsurface barriers.

Environmental Encyclopedia 3

Sand dune ecology

Developing a pumping trough or maintaining a pres-

sure ridge are methods that do not solve the basic problem:

the overdraft or excessive withdrawal of water from the

aquifer. Only when this problem is solved by reducing draw-

down, or isolated by the subsurface barrier method, can the

intrusion be stopped or reversed. In some areas, it is simply

not economically feasible to control intrusion.

Oceanic islands, such as Hawaii, have unique problems

with salt water intrusion. Most islands consist of sand, lava,

coral, or limestone; they are relatively

permeable

, so fresh-

water is in contact with salt water on all sides. Because fresh

water is supplied entirely by rainfall in these places, only a

limited amount is available. A freshwater lens is formed by

movement of the freshwater toward the coast. Depth to salt

water at any location is a function of rainfall recharge, the

size of the island, and permeability. Tidal and seasonal fluc-

tuations may form a transition zone between freshwater and

salt water.

The close proximity of salt water in oceanic islands can

introduce saline water into fresh groundwater even without

excessive overdraft. An island well pumping at a rate high

enough to lower the

water table

disturbs the fresh-salt

water equilibrium, and salt water then rises as a cone within

the well. To avoid this condition, island

wells

are designed

for minimum drawdown, and they skim freshwater from the

top of the aquifer. In general, drawdowns of a few inches

to a few feet provide plentiful water supplies.

[James L. Anderson]

ESOURCES

ERIODICALS

Gorrie, P. “Water From the Ground.” Canadian Geographic 112 (Septem-

ber–October 1992): 68–77.

Wagman, D. “Protecting Hidden Assets: Many American Cities and Coun-

ties Are Designing Groundwater Regulations to Protect Underground Aq-

uifers.” American City and County 105 (March 1990): 38–41.

Sand dune ecology

Dunes

are mounds of sand that have been piled by the action

of winds. The sand is usually composed of bits of minerals

that have been eroded from rocks, picked up by water or

winds, and then re-deposited somewhere else. Typically, the

sand is deposited behind some object that is a barrier to the

movement of air currents, which causes the windspeed to

slow suddenly so that the load of sand particles can no longer

be contained against the force of gravity, and it falls to the

ground. If there is a suitable source of sand, dunes may

deposit along the edges of oceans, large lakes, rivers, and

even in inland locations.

1244

The mineralogical composition of sand in dunes varies

greatly from place to place. The most common minerals are

quartzitic (this is a silica sand), but other minerals may also

be mixed in, and they may dominate the composition of the

sand in some places. The White Sands National Monument

in New Mexico, for example, is characterized by a sand of

gypsum (calcium sulfate). The grain size of sands varies

depending on the strength of the winds that delivered the

sand to the location where the dune has formed—the greater

the typical windspeed, the larger the sand grains can be.

Once deposited to the surface, unconsolidated sand

tends to be moved about and shifted by the winds. In fact,

dunes tend to “migrate” in the direction of the prevailing

winds, with sand being picked up at the windward side of

the dune, and deposited on the leeward side. Because of the

mechanical instability of their surface young dunes initially

provide rather precarious habitats for the establishment of

vegetation. However, if plants do manage to establish a

foothold on a dune, the progressive development of vegeta-

tion over time will help to stabilize the surface, allowing an

ecosystem

to develop through the process of

succession

Some of the most extensive dune systems in the world

occur in deserts, including parts of the Sahara

Desert

northern Africa, the Gobi Desert of eastern Asia, and the

Great Western Desert of the United States and Mexico.

Because of the aridity of those environments only a very

limited amount of ecological development is possible. In

places with a more moderate

climate

, however, sand dunes

can be colonized by vegetation and succession can proceed

to the development of tall, mixed-species forests. This type

of succession is typical of many dune systems along the

coasts of the oceans and many large lakes and rivers of North

America.

Environmental conditions

Sandy soils are generally free-draining, so that even

in regions with abundant rainfall sand-dune habitats can be

quite

arid

. The dry

soil

conditions are made worse by the

frequently windy conditions in dune habitats, a factor that

speeds the evaporation of water from plant foliage and the

soil surface. Droughty conditions are especially important

on the higher parts of dunes; in low places the

water table

may come to the surface, creating locally moist or wet condi-

tions, which are sometimes referred to as dune slacks.

In addition, most sands contain few nutrients, so they

provide rather infertile conditions for plant growth. Sandy

soils are also lacking in organic matter, which prevents them

from holding much water or nutrients for later uptake by

plants. In fact, some sand-dune habitats can be referred to

as ombrotrophic, or “fed from the clouds,” which means that

atmospheric deposition

is the principal source of

nutrient

inputs in support of plant productivity. In addition, the low

levels of calcium concentrations make sandy soils highly

Environmental Encyclopedia 3

Sand dune ecology

Moving sand dunes are slowly engulfing a forest in Nags Head, North Carolina. (Photograph by Jack Dermid. National

Audubon Society Collection/Photo Researchers Inc. Reproduced by permission.)

vulnerable to

acidification

, a condition that can be stressful

to some

species

of plants.

Vegetation of sand dunes

The species of plants that grow on sand dunes vary

depending on the climate, the

stability

of the dunes, soil

chemistry, and

biogeography

. Dunes of the deserts of

southern California, southwestern Arizona, and nearby

Mexico are sparsely vegetated with a mixture of perennial

grasses, such as Pleuraphis rigida, perennial herbs such as

the sand sagebrush (Artemisia filifolia), and species of shrubs,

including ephedra (Ephedra trifurca), daleas (Dalea spp.),

Colorado desert buckwheat (Eriogonum deserticola), and mes-

quite (Propsis spp.). During occasional rainy periods these

sandy deserts can bloom prolifically with showy annual herbs,

such as species of Allionia, Boerhavia, Euphorbia, Oenothera,

and Pectis. Areas of gypsum-rich sand have other species

that are specific to that soil type, including yucca (Yucca

elata), ephedra (Ephedra torreyana), onion blanket (Gaillardia

multiceps), and grasses such as Bouteloua breviseta.

In more humid climatic regimes of North America,

younger sand-dune systems are initially colonized by species

1245

of dune-grasses, such as American beach grass (Ammophila

breviligulata), sea oats (Uniola paniculata), sand rye (Elymus

mollis), and beach grass (Calamovilfa longifolia). As the dunes

stabilize, other species invade the community. These may

form a

prairie

with interspersed shrub- and tree-dominated

nuclei, which may eventually coalesce to form continuous

forest (see the next section on dune succession). Some dune-

rich areas of the east coast of the United States support forests

of pines (Pinus spp.), oaks (Quercus spp.), and magnolia

(Magnolia virginiana). Older dunes in the

Great Lakes

region tend to be covered by mixed stands of oaks, pines,

and tulip-tree (Liriodendron tulipifera). The inland sand hills

of northern Alberta are commonly occupied by stands of

jack pine (Pinus banksiana).

Primary succession on sand dunes

Succession on recently formed sand dunes is a type of

primary succession. This is because the sandy substrate that

is newly exposed for ecological development has no pre-

existing biological capability to initiate the succession. Suc-

cession can not begin until

microbes

, plants, and animals

have invaded the site from existing ecosystems somewhere

Environmental Encyclopedia 3

Sanitary sewer overflows

else. (Secondary succession occurs after a disturbance, but

one that has allowed some of the original biota to survive,

so they can play a prominent role in ecological recovery.)

Some classic studies of primary succession have in-

volved sand-dune ecosystems. In North America, the most

famous studies were conducted on systems of dune ridges

at several places on Lake Michigan and Lake Huron. Dune

ridges are actively developing in those places to this day.

This occurs as sand is piled up onto the beach by wave

action, to be moved inland by the prevailing on-shore winds

and mostly deposited on the dune closest to the edge of the

lake, on its leeward, or building side. This process of dune-

building is an ancient phenomenon, and it has been actively

occurring in the region since deglaciation, more than twelve

thousand years ago.

The dune building is, however, superimposed upon

another geological process—the slow rebounding in eleva-

tion of the regional ground surface, a phenomenon that is

known as isostasy. This slow, uplifting process is still oc-

curring in response to the long-ago melting of the continen-

tal glaciers that once covered virtually all of northern North

America; when the glaciers were present, their enormous

weight actually depressed crustal bedrocks beneath them into

Earth’s plastic mantle. The surface has been rebounding

since deglaciation released the crust from the weight of the

gigantic glaciers, at a fairly steady rate of about 1 yd (1 m)

per century. Because of isostatic rebound, ancient shorelines

of the Great Lakes are now higher in elevation than they

used to be, and in some flatter areas well-defined dune

systems formed on ancient shores can be found miles inland

of the present shoreline of the lakes. These circumstances

mean that dunes located further inland are older than dunes

occurring closer to the modern lake shores. Because the ages

of the various dunes can be dated, ecologists are able to

study a series of dunes of various age and their associated

communities. This so-called chronosequence technique

allows the ecologists to reconstruct the basic elements of the

successional process.

The first plants to colonize the embryonic dunes are

annual and biennial plants of shoreline habitats, such as the

American searocket (Cakile edentula), Russian thistle (Salsola

kali), orache (Atriplex patula), and a small euphorb (Eurphor-

bia polygonifolia). Although buffeted by severe weather, these

plants help in the initial stages of dune stabilization. The

next invaders of the site are several species of dune grasses,

particularly Ammophila breviligulata and Calamovilfa longi-

folia. The extensive roots and rhizomes of these grasses are

important in binding the sandy substrate, and in stabilizing

the lakeward dune ridges and allowing them to grow larger.

Once these grasses take hold, some other foredune plants

can establish and begin to grow, including the beach pea

(Lathyrus maritimus) and evening primrose (Oenothera

1246

biennis). With time, a tall grass prairie develops, dominated

by various species of grasses and broad-leaved herbs. The

prairie becomes invaded by shade-intolerant shrub and tree

species, which form forest nuclei. Eventually a climax forest

develops that is dominated by oaks, pines, and tulip-tree.

[Bill Freedman Ph.D.]

ESOURCES

OOKS

Barbour, M. G., and W. D. Billings. North American Terrestrial Vegetation.

Cambridge, UK: Cambridge University Press, 1988.

Ranwell, D. S. Ecology of Salt Marshes and Sand Dunes. Chapman and Hall,

London, 1972.

ERIODICALS

Morrison, R. G., and G. A. Yarranton. “Diversity, Richness, and Evenness

during a Primary Sand Dune Succession at Grand Bend, Ontario,” Canadian

Journal of Botany 51 (1973): 2401–2411.

Olson, J. S. “Rates of Succession and Soil Changes on Southern Lake

Michigan Sand Dunes.” Botanical Gazette 119 (958): 125–170.

Sanitary landfill

see

Landfill

Sanitary sewer overflows

Sanitary sewer overflows (Ssos) are discharges of untreated

sewage from municipal sanitary sewer systems that were

not designed to carry storm-water

runoff

. Almost all sewer

systems experience at least occasional Ssos and they occur

frequently in some systems. Ssos are a major source of

water

pollution

in lakes, rivers, and streams. Although they are

illegal under the

Clean Water Act

, the U.S.

Environmental

Protection Agency

(EPA) estimates that at least 40,000

Ssos occur annually nationwide.

Of the approximately 50 trillion gal (189 trillion l) of

raw sewage that flow daily through about 19,500 sewer sys-

tems in the United States, it is estimated that about 1.2

billion gal (4.5 billion l) were released in Ssos in 2000. This

raw sewage is discharged from manholes, bypassing pump

stations and treatment plants. It flows into basements, lawns,

streets, parks, streams, swimming areas, and drinking water.

It is estimated that sewers back up into basements 400,000

times a year in the United States.

Ssos pose a serious threat to human health and to the

environment

. Raw sewage can introduce disease-causing

organisms into drinking water and swimming and fishing

areas. People may swallow contaminated water or eat con-

taminated fish or shellfish. Diseases also can be contracted

by breathing in organisms from sewage or by

absorption

through the skin. Although most such illnesses are mild