Rare earth elements Category: Mineral and other nonliving resources Where Found Mixtures of the rare earth elements are present, but only in small amounts, in most rocks of the Earth.. T
Trang 1ter the 1970’s, when fuel costs increased and
environ-mental concerns over pesticide use increased, brush
control practices were reduced considerably Modern
environmental concerns include rangeland
degrada-tion from livestock grazing, especially on riparian
veg-etation along streams, endangered animal and plant
species These issues have become controversial in
the United States
Rangelands as Ecosystems
Rangelands constitute natural ecosystems with
non-living environmental factors such as soil and
clima-tic factors, primary producers (grasses, forbs, and
shrubs), herbivores (livestock; big game animals such
as deer, bison, pronghorn antelope; and many
ro-dents and insects), carnivores and omnivores
(coy-otes, bears, weasels, eagles, spiders, and cougars), and
decomposers that break down organic matter into
el-ements that can be utilized by plants Plants convert
carbon dioxide and water into complex carbohydrates,
fats, and proteins that can be utilized by animals
feed-ing on the plants Individual chemical elements are
circulated throughout the various components Many
of these elements are present in the parent material
of the soil (for example, phosphorus, magnesium,
potassium, and sulfur) Nitrogen, on the other hand,
is present in large amounts in the atmosphere but
must be converted (fixed) into forms that can be
uti-lized by plants before it can be cycled
When chemicals are taken up by plant roots from
the soil solution, they are available to a wide group
of herbivores from small microbes to large
ungu-lates Eventually nutrients are passed on to higher
trophic groups (omnivores and carnivores) Both
plant and animal litter is eventually broken down by
decomposers—bacteria, fungi, and other small soil
organisms—and returned to the soil or, in the case of
nitrogen, given off to the atmosphere
Energy is fixed through the process of
photosyn-thesis and transformed to forms useful for the plants
themselves and animals that feed on the plants
How-ever, energy is degraded at each step along the way
and cannot be used again Energy is transferred but
not cycled Grazing animals on rangelands influence
plants by removing living tissue, by trampling, and by
altering competitive relations with other plants Large
grazing animals tend to compact the soil and reduce
infiltration and increase surface runoff Plants
fur-nish all the nutrients obtained by herbivores and
eventually by carnivores and omnivores as well
Rangeland Dynamics Rangelands vary considerably with time; they are not static Scientists are gaining a better understanding
of some factors related to rangeland change over time Pollen records and, in the southwestern United States, packrat middens have been used to recon-struct past climate and vegetational changes Some areas have become drier and others more mesic For-mation and retreat of glaciers have influenced range-lands, climatic patterns, and soil development A re-cent general trend in many rangelands of the world is
an increase in woody plants at the expense of grasses Many factors are probably responsible for these shifts, but fire control, excessive livestock grazing, climatic shifts, introduction of exotic species, and the influ-ence of native animals are likely causal agents Rangelands are threatened by encroachment from crop agriculture as human populations increase No-madic herders traditionally dealt with periodic drought conditions by moving to areas not impacted
by drought In modern society, with reductions of area available for livestock grazing and restrictions for political reasons, herders are often forced to maintain higher livestock numbers to support their growing families and others directly dependent on livestock Despite various kinds of disturbances and stresses on rangelands, these areas have supported many large grazing animals and people for centuries They are re-silient and will likely be sustained for many more cen-turies to come
Rex D Pieper
Further Reading
Anella, Anthony, and John B Wright Saving the Ranch: Conservation Easement Design in the American West Photographs by Edward Ranney Washington,
D.C.: Island Press, 2004
Heady, Harold F., and R Dennis Child Rangeland Ecology and Management Boulder, Colo.: Westview
Press, 1994
Holechek, Jerry L., Rex D Pieper, and Carlton H
Herbel Range Management: Principles and Practices.
5th ed Upper Saddle River, N.J.: Pearson/Prentice Hall, 2004
Johnson, Barbara H., ed Forging a West That Works—
An Invitation to the Radical Center: Essays on Ranching, Conservation, and Science Santa Fe, N.Mex.: Quivira
Coalition, 2003
Miller, G Tyler, Jr Resource Conservation and Manage-ment Belmont, Calif.: Wadsworth, 1990.
Trang 2Sayre, Nathan F The New Ranch Handbook: A Guide
to Restoring Western Rangelands Santa Fe, N.Mex.:
Quivira Coalition, 2001
White, Courtney Revolution on the Range: The Rise of a
New Ranch in the American West Washington, D.C.:
Island Press/Shearwater Books, 2008
See also: Conservation; Ecology; Farmland; Forests;
Land management; Livestock and animal husbandry;
Overgrazing; Public lands
Rare earth elements
Category: Mineral and other nonliving resources
Where Found
Mixtures of the rare earth elements are present, but
only in small amounts, in most rocks of the Earth The
rare earth elements are more concentrated in rocks
of the continents than in those of the ocean basins
The minerals monazite, a phosphate mineral, and
bastnäsite, a fluorine-carbonate mineral, form the
main ores for the rare earth elements with lower
atomic numbers Xenotime, another phosphate
min-eral, is mined for its concentration of the rare earth
elements with higher atomic numbers The largest
sources of rare earth elements are from bastnäsites
mined in China and the United States Monazite
deposits are found in Australia, Brazil, Chile, India,
Malaysia, South Africa, Sri Lanka, Thailand, and the
United States
Primary Uses
Mixtures of the rare earth elements are used for
breaking down hydrocarbons in petroleum to form
more gasoline, to remove impurities from iron and
steel, as polishing materials, for carbon arcs, and in
metallurgy Pure rare earth elements are used as
col-oring agents
Technical Definition
The rare earth elements (abbreviated REE), or
lantha-nide elements, are a group of elements from atomic
numbers 57 to 71 Their atomic weights range from
138.91 to 174.99 This large group of elements is
grouped together because they have similar chemical
properties The names of the rare earth elements,
from low to high atomic numbers, are lanthanum,
cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dyspro-sium, holmium, erbium, thulium, ytterbium, and lute-tium In addition, the elements scandium and yttrium (atomic numbers 21 and 30 respectively) are some-times included with the rare earth elements because they have chemical properties similar to those of the rare earth elements The density of the pure metals ranges from 5.23 to 9.84 grams per cubic centimeter Melting points for the metals range from 798° to 1,663° Celsius
Description, Distribution, and Forms The rare earth elements, because of their similar chemical properties, do not occur as separate indi-vidual elements in minerals Rather, they are frac-tionated in similar ways within or on the Earth The rare earth elements are not normally soluble in water,
so they are not transported in solution by natural waters
The rare earth elements are widely distributed in the rocks of the world The concentrations of some of the rare earth elements are as high as those of copper
or zinc For example, the dark, fine-grained rocks composing much of the ocean floor (called basalts) contain about 3 to 5 parts per million lanthanum, whereas igneous and sedimentary rocks on the conti-nents typically contain 20 to 100 parts per million lan-thanum The rare earth elements are lowest in con-centration in carbonate rocks such as limestone
History
A mineral now called gadolinite was discovered by Jo-han Gadolin, who subsequently separated an “ele-ment” called yttria from gadolinite in 1796 Later it was discovered that yttria actually consisted of a con-centration of the heavy rare earth elements Another
“element” called ceria was separated in the early nine-teenth century; ceria was later discovered to consist of
a concentration of the light rare earth elements
By the mid-nineteenth century, individual rare earth element oxides were separated from yttria and ceria by a series of chemical separations and identi-fied after analytical techniques such as the spectro-graph were developed
Obtaining Rare Earth Elements Monazite and the associated xenotime are mined from beach sands in Brazil, India, Australia, South Carolina, South Africa, and Russia Monazite is weakly
Trang 3magnetic and may be separated from the non-ore
minerals by magnetic separation Bastnäsite is mined
in Africa, China, and the United States It occurs in
large amounts at Mountain Pass in California mixed
with the non-ore minerals quartz, barite, and calcite
The ore is crushed, and bastnäsite is concentrated by
flotation The rare earth elements are further
concen-trated by heating and leaching with hydrochloric
acid Minor amounts of the rare earth elements are
also produced as by-products from other ore
process-ing, such as uranium production
Uses of Rare Earth Elements
Rare earth elements have a large variety of end uses,
in glass-polishing agents, ceramics, catalytic
convert-ers, computer monitors (phosphors), lighting, radar,
televisions, X-ray films, chemicals, petroleum-refining
catalysts, pharmaceuticals, magnets, metallurgy, and
laser and scintillator crystals
Pure europium mixed with yttrium oxides, for
ex-ample, produces an intense red fluorescence, so the
mixture is used in television screens Pure
lantha-num oxide is used to make quality glass for lenses The
rare earth elements are also used for X-ray screens,
high-quality magnets, artificial diamonds, and
super-alloys
Robert L Cullers
Further Reading
Delfrey, Keith N., ed Rare Earths: Research and
Applica-tions New York: Nova Science Publishers, 2008.
Greenwood, N N., and A Earnshaw Chemistry of the
El-ements 2d ed Boston: Butterworth-Heinemann,
1997
Gschneidner, Karl A., ed Industrial Applications of Rare
Earth Elements: Based on a Symposium Sponsored by the
Division of Industrial and Engineering Chemistry at the
Second Chemical Congress of the North American
Conti-nent (180th ACS National Meeting), Las Vegas,
Ne-vada, August 25-26, 1981 Washington, D.C.:
Ameri-can Chemical Society, 1981
Kogel, Jessica Elzea, et al., eds “Rare Earth Elements.”
Industrial Minerals and Rocks: Commodities, Markets,
and Uses 7th ed Littleton, Colo.: Society for Mining,
Metallurgy, and Exploration, 2006
Krebs, Robert E “Lanthanide Series (Rare-Earth
Ele-ments): Period 6.” In The History and Use of Our
Earth’s Chemical Elements: A Reference Guide 2d ed
Il-lustrations by Rae Déjur Westport, Conn.:
Green-wood Press, 2006
Web Sites U.S Geological Survey Rare Earth Elements: Critical Resources for High Technology
http://pubs.usgs.gov/fs/2002/fs087-02 U.S Geological Survey
Rare Earths: Statistics and Information http://minerals.usgs.gov/minerals/pubs/
commodity/rare_earths See also: Alloys; Igneous processes, rocks, and min-eral deposits; Magnetic materials; Metals and metal-lurgy
Reclamation Act
Categories: Laws and conventions; government and resources
Date: Passed by Congress June 17, 1902
The Reclamation Act marked the beginning of active federal involvement in the development of irrigated ag-riculture in the western United States.
Background The Reclamation Act, passed by Congress in 1902, es-tablished a comprehensive federal program of agri-cultural water development for the western United States The Reclamation Act authorized the secretary
of the interior to undertake construction of dams, reservoirs, and diversion facilities to provide irriga-tion water to farmers in all sixteen states west of, and including, the tier of states from North Dakota down to Oklahoma These projects were to be funded from the newly created reclamation fund, which was
to be financed from the sale of public lands in the sixteen states and revenues from sale of irrigation water Consistent with a long tradition of nineteenth century federal public-lands policies that encouraged small-scale farming, the Reclamation Act restricted the sale of irrigation water to farms of less than 65 hectares
Provisions Passage of the Reclamation Act was the culmina-tion of a decade-long political struggle over how the arid regions of the western United States were to
Trang 4be reclaimed By the late nineteenth century,
irriga-tion was taking hold throughout the West In 1890,
the U.S Census of Agriculture counted more than
1.5 million irrigated hectares spread over fifty-four
thousand farms in the sixteen western states
How-ever, increasing costs of water development, greater
need for storage of surplus water, and the
increas-ingly interstate character of water development all
stimulated western demand for federal involvement
in reclamation This demand intensified in 1893
when economic depression struck, making it much
more difficult for states and private entities to
de-velop water on their own However, enactment of
federal reclamation was delayed by political
resis-tance from many eastern quarters and by divisions
within the West over the desirability of federal
in-volvement Resistance within the West was overcome
when provisions were inserted that ensured that
recla-mation benefits would be spread throughout the West
and that existing water rights would be respected
In addition, federal reclamation was given a strong
boost after President Theodore Roosevelt took office,
as Roosevelt was an active supporter of western
irri-gation The Reclamation Act passed handily through
a coalition of western interests and congressional
Democrats
Impact on Resource Use
Within a month of passage of the Reclamation Act,
Secretary of the Interior Ethan Hitchcock had
cre-ated the Reclamation Service (later the Bureau of
Reclamation) and charged it with carrying out the
federal reclamation program The Reclamation
Ser-vice quickly went to work, with Hitchcock approving
five major projects within a year However, as its work
progressed, the Reclamation Service soon
encoun-tered difficulties in securing payment from farmers,
particularly during times of economic distress This
led Congress in 1914 to increase the time period over
which payments were due from ten to twenty years
Subsequent congressional legislation passed in 1926
and 1939 made repayment terms increasingly
favor-able to farmers The result has been a federal
recla-mation program that has heavily subsidized western
farmers, though this was not the intent of the original
Reclamation Act
Mark Kanazawa
See also: Bureau of Reclamation, U.S.; Department
of the Interior, U.S.; Irrigation; Water
Recycling
Categories: Environment, conservation, and resource management; pollution and waste disposal
The debate over dumping trash versus recycling its re-usable components has existed since the beginning of technology New technologies have made the issues dif-ferent and more complex, but they are nevertheless es-sentially housekeeping issues affecting every material and product used in society Recycling can save re-sources, reduce toxic wastes in the ecosystem, and save space in landfills.
Background
A number of factors led to the recycling programs ini-tiated in the 1970’s and 1980’s Throughout history, waste disposal schemes have generally assumed that there was infinite sky and ocean to dilute wastes until they became undetectably faint Then rivers began to catch fire, mercury was discovered in tuna caught at sea, forests in Scandinavia suffered from sulfur diox-ide coming from British smokestacks, and people in the fishing village of Minamata, Japan, were poisoned
by a vinyl factory that was dumping wastes into their bay Many such instances finally led to the realization that the natural world was not an infinite sink and that humankind might be fouling its own nest Hence, be-ginning in the 1970’s, ecology became a major politi-cal issue A related concern was that fuels and certain key minerals might be exhausted in the near future because of the ever-expanding consumption of non-renewable resources These fears were strongly pre-sented in 1970 in “The First Report to the Club of
Rome,” published as The Limits to Growth, based on a
computer projection of population, food production, industry, resources, and pollution
The “landfill crisis” in the United States began
in the 1970’s when environmental regulations re-stricted open dumps, backyard burning, and burning
in apartment-sized incinerators Restricted burning cleared the air but increased the burden on dumps Other new regulations required greater use of sani-tary landfills, in which trash is covered daily Because trash in sanitary landfills has less environmental dete-rioration from fires, rain, and vermin, it requires as much as three times the volume of old dumps
Trang 5Waste Streams
Wastes can be defined in a number of ways Municipal
solid waste (MSW), or trash, is the most commonly
considered object of recycling MSW is an almost
in-finitely varied mixture of newspapers, grass clippings,
beverage containers, aerosol cans, old clothes, kitchen
wastes, small appliances, and hundreds of other types
of items Calculations from the Environmental
Pro-tection Agency for 2007 listed roughly 254 million
metric tons of municipal solid waste in the United
States—approximately 2 kilograms per person per
day However, the numbers are more complicated than that They do not include construction and demoli-tion debris (about 155 million metric tons) composed
of bricks, wood, concrete, and fixtures taken when old structures are razed They also do not include the liner and covering materials for the landfill Finally, they do not include sewage sludge, composed of both food garbage that is ground up in garbage disposals and human wastes With those additions, the average daily weight produced per person nearly doubles Other complications in figuring the waste stream
United States Environmental Protection Agency, 2007.
Source:
23.7
Percentage Recovered
70 60
50 40
30 20
10 Yard trimmings
Other nonferrous
materials
Aluminum
Ferrous metals
Glass
Plastics
Rubber and
leather
Other wastes
22.6
33.2
26.9
66.3
5.8
12.2
51.7
27.0
54.5
Paper and
paperboard
42.8
2000 2007
33.8
21.8
69.3
14.7
64.1
31.9 6.8
Percentages of Recovered Municipal Solid Wastes, 2000 and 2007
Trang 6come from good news Automobiles and appliances
are now rare in landfills because they are recycled for
the metal Beginning in the second half of the
twenti-eth century, steel “mini-mills” allowed more
profit-able recycling of such items because the mini-mills are
less susceptible to “poisoning” by metals other than
iron Corrugated paper boxes (cardboard) would be
a much larger percentage of the waste stream than
they are, but retailers smash, bale, and return large
numbers to the manufacturers
There are other, much larger, waste streams than
municipal waste, including manufacturing and
sludges; agricultural wastes, such as corn cobs and
ma-nure; and mine tailings However, municipal waste
takes priority as far as recycling goes; one reason is
that, if buried in landfills, some of these materials
(paint, radioactive elements of smoke alarms,
insecti-cide, nickel-cadmium batteries, and the mercury in
fluorescent light tubes) could create toxic messes
centuries in the future
Repurposing Waste
Recycling, or reusing materials for other purposes,
re-duces trash, energy use, and the consumption of
min-eral resources For example, aluminum cans that are
melted and made into new cans do not go to a landfill;
they require no aluminum ore and much less energy
than smelting new aluminum A society with a “total
recycling” program could conceivably function with
little mining of nonfuel minerals (assuming a neutral
population growth)
Recycling increased greatly beginning in the 1970’s,
and governments have begun favoring recycled
prod-ucts over those made from virgin materials In some
European countries, manufacturers are held
respon-sible for the eventual scrapping of their products,
which results in designs favoring quick disassembly
and recycling of standard materials
Technological Innovations
Every waste stream is a potential resource stream
Many waste streams are already composed of liquids
or small particles for easier processing Thus there are
myriad technologies for recycling and great prospects
for improvement, depending on the money and
ef-fort that a society is willing to expend
Many companies have profited from the
“indus-trial ecology” of using waste streams from one area as
resource streams for another For instance, the ashes
from burning coal have always been available as a raw
material for making cement, but pilot projects to do
so were only started in the 1980’s when environmental pressures increased Likewise, manure can be spread back on fields or biologically digested to yield natural gas and concentrated fertilizer The energy crisis of the 1970’s and 1980’s led to increased use of cogener-ation, in which food-processing plants burn waste products such as corn cobs and shells from nuts for both process heat and generation of electricity Even asphalt and concrete can be ground up and reused Some of the most likely improvements to munici-pal waste recycling include automated sorting, elec-tronic monitoring of the liquid trash in sewers, charg-ing for eventual disposal, and use of materials on-site Automated sorting lowers labor costs, allows sorting at any time, and allows a finer sorting For instance, a manual trash “disassembly line” has stations for sepa-rating aluminum, iron, brass, all other metals, plas-tics, wood, and glass, but an automated facility can separate many types of plastics, metals, glass, and or-ganic matter Separating out nonoror-ganic materials
Workers sort through recyclable materials at a waste management site in San Francisco, a city that uses innovative recycling tech-niques to sort paper, plastics, glass, concrete, wood, and metal.
(Getty Images)
Trang 7lows processing the remaining material into
some-thing usable and nontoxic Piles of damp organic
material naturally compost into soil through the
ac-tion of bacteria Hot diluted acid breaks the woody
cellulose of organic materials into sugars that can be
fermented into fuel alcohol
Using materials on-site includes composting of yard
wastes and kitchen scraps Just as cities run
compost-ing operations, gardeners have composted for
centu-ries to fertilize their gardens Meanwhile, trash
collec-tion agencies are spared the colleccollec-tion and landfill
costs of burying dirt Another method is plumbing
houses so that wastewater from showers and hand
washing (“gray water”) can be recycled for watering
ornamental plants
Monitoring of sewers allows the use of an old
recy-cling method, spreading processed sewage sludge on
fields as fertilizer for nonfood crops Unfortunately,
sewage sludge can be easily tainted by industrial wastes,
such as metal ions or solvents These wastes could
poi-son the soil indefinitely Until the early 1990’s there
was no cost-effective way to monitor the sewers Then
cellular phones became widespread, and development
began on computer-chip-sized sensors Together these
two technologies allow waste-management officals to
monitor wastes in sewer lines in real-time so that
ille-gal wastes can be detected immediately
The Economics of Recycling
Recycling saves material, and it often reduces energy
consumption However, collection and processing use
energy and require labor as well as storage areas for
the materials being recycled Successful recycling must
balance those profits and costs Historically, recycling
was feasible and widely practiced because labor was
cheap and materials were expensive Rag pickers
col-lected old cloth for making paper Polite wealthy
diners left some food on their plates so that it could be
given to the poor Communist China provides a
mod-ern example that shows the drawbacks of intensive
re-cycling: During the period of revolutionary fervor
that existed from the 1950’s through the 1970’s, one
program involved returning and repairing lightbulbs
Unfortunately, each worker in a light-bulb assembly
factory averaged production of hundreds of bulbs per
hour, while a repair technician only fixed several
Such labor-intensive recycling cannot compete in the
modern world
A second factor is that some materials favor
recy-cling more than others Glass containers are initially
cheaper than aluminum ones, but glass is heavy (pos-sessing low value per unit weight) to recycle back to collection points; moreover, tiny amounts of the wrong color ruin the color in remelted batches, and glass shards are dangerous Meanwhile, the primary raw material for new glass is as common as sand on the beach
Like aluminum, plastic has a high value in recy-cling because of light weight and great energy advan-tages However, just as glass has many colors, plastics include many formulas Mixing different kinds of plastics may degrade the performance of the recycled product Worse, metals in inks on plastic containers may degrade performance or make the recycled plas-tic unsuitable for uses near food Successful plasplas-tics recycling requires methods to sort or separate differ-ent kinds of plastics and, ideally, would include prohi-bitions against toxic inks
Paper box beverage containers with just one-stop recycling have several advantages over both glass and aluminum They are initially cheaper They are lighter and pack more product in a given storage volume, saving energy in transportation and storage Finally, they can be crushed into a renewable fuel roughly equivalent to brown coal in heating value (Once again, this is a low unit value, applicable only with au-tomated sorting to remove metals that would make the ash toxic.)
There are levels of recycling Returnable bottles, simply washed and reused, represent the highest level
A lesser recycling level is remelting material to make new containers Lesser yet, but still useful, is using glass and plastic as aggregate for paving Lastly, simply burning the organic material can be used to produce energy, and it greatly reduces landfilling
E-Waste Electronic waste (or “e-waste”) has become an in-creasingly important part of the waste stream since the 1990’s These wastes include consumer electron-ics such as computers, their accessories (mice, moni-tors, keyboards), cell phones, and televisions The toxic contents of some of the components of e-waste require that they be recycled properly, by experts in the proper disposal and repurposing of hazardous wastes Some of the components can be reused For example, cell phones and televisions can be donated
to prolong their lives, and the materials (plastics, met-als, glass) can be retrieved and reused On average, however, in the United States only about 15 percent of
Trang 8these wastes are recycled annually, the rest finding
their way to landfills Even e-wastes that are
conscien-tiously transported to hazardous waste centers can
find their way to salvage yards, where their toxins can
leak into groundwater It is estimated that a large
por-tion of e-waste resides in consumers’ closets and
ga-rages, where it sits while owners are deciding how to
rid themselves of it Although some enterprising
indi-viduals have started businesses based on recycling
these wastes, the problem of mounting e-waste
contin-ues to grow
Social and Political Aspects
Almost everyone wants some trash to be recycled, and
as cheaply as possible The first responses to the
envi-ronmental movement were additions to labels that
cost little (“Dispose of this container properly!”) and
did not produce significant results Until container
deposit taxes were instituted, it was feared that North
America would be buried under empty aluminum
cans
Likewise, other types of recycling can work only if
there are financial incentives These incentives might
be like the “green dot” program in Europe, which
holds manufacturers responsible for the ultimate
dis-posal of the product This program has led companies
to design for eventual disassembly The previously
mentioned waste deposit taxes repay people for
re-turning sorted items
Trash taxes, rules, and limits on individuals have a
limited value If too harsh, they simply give people
an incentive to rebel against them Similarly, detailed
sets of rules on how things should be done are
proba-bly counterproductive Industrial ecology has worked
better in Europe than in the United States because
in-dustry could simply be ordered to reduce wastes In
the United States, certain materials are categorized as
toxic wastes and treated under the Resource
Conser-vation and Recovery Act of 1976 (Public Law 94-580),
one of the most complex sets of regulations ever
de-vised Recycling of many of these materials is
forbid-den, but the problem of how to reuse remains For
this reason, the Environmental Protection Agency’s
Web site not only describes how to recycle or dispose
of wastes but also urges conservation
Roger V Carlson
Further Reading
Alexander, Judd H In Defense of Garbage Westport,
Conn.: Praeger, 1993
Cothran, Helen, ed Garbage and Recycling: Opposing Viewpoints San Diego, Calif.: Greenhaven Press,
2003
Leverenz, Harold, George Tchobanoglous, and David
B Spencer “Recycling.” In Handbook of Solid Waste Management, edited by Tchobanoglous and Frank
Kreith New York: McGraw-Hill, 2002
Lund, Herbert F., ed The McGraw-Hill Recycling Hand-book 2d ed New York: McGraw-Hill, 2001.
Porter, Richard C The Economics of Waste Washington,
D.C.: Resources for the Future, 2002
Rathje, William L., and Cullen Murphy Rubbish! The Archaeology of Garbage New York: HarperCollins,
1992 Reprint Tucson: University of Arizona Press, 2001
Royte, Elizabeth Garbage Land: On the Secret Trail of Trash New York: Little, Brown, 2005.
Strasser, Susan Waste and Want: A Social History of Trash New York: Metropolitan Books, 1999 Tierney, John “Recycling Is Garbage.” The New York Times Magazine, June 20, 1996, p 24.
Web Site U.S Environmental Protection Agency Recycling
http://www.epa.gov/wastes/conserve/rrr/
recycle.htm See also: Aluminum; Cogeneration; Hazardous waste disposal; Incineration of wastes; Landfills; Paper; Superfund legislation and cleanup activities; Waste management and sewage disposal; Water supply sys-tems
Reforestation
Category: Environment, conservation, and resource management
The growth of new trees in an area that has been cleared of trees for commercial forestry or for agricul-ture is known as reforestation Reforestation can occur naturally or be initiated by people Many areas of the eastern United States, such as the New England re-gion, reforested naturally as farmland was abandoned and allowed to lie fallow for decades in the nineteenth and early twentieth centuries.
Trang 9Some form of reforestation to replace trees removed
for commercial purposes has been practiced in
West-ern Europe since the late Middle Ages English
mon-archs, including Queen Elizabeth I, realized that
forests were a vanishing resource and established
plantations of oaks and other hardwoods to ensure a
supply of ship timbers Similarly, the kings of Sweden
created a corps of royal foresters to plant trees and
watch over existing woodlands These early efforts at
reforestation were inspired by the threatened
disap-pearance of a valuable natural resource, but by the
mid-nineteenth century it was widely understood that
the removal of forest cover contributes to soil erosion,
water pollution, and the disappearance of many
spe-cies of wildlife Water falling on hillsides made barren
by clear-cutting timber washes away topsoil and causes
rivers to choke with sediment, killing fish and
inter-fering with navigation Without trees to slow the flow
of water, rain can also run off slopes too quickly,
caus-ing rivers to flood
Safeguarding Timber Resources
After an area has been logged, both environmentalists
and the commercial forest industry advocate planting
trees rather than waiting for natural regrowth,
be-cause the process of natural regeneration can be slow
as well as unpredictable In natural regeneration, the
mixture of trees in a naturally reforested area may
dif-fer significantly from the forest that preceded it For
example, when nineteenth century loggers clear-cut
the white pine forests of the Great Lakes region, many
logged-over tracts grew back primarily in mixed
hard-woods
In addition, land that has been damaged by
indus-trial pollution or agricultural practices may have lost
the ability to support natural reforestation In some
regions of Africa, soils exposed by slash-and-burn
agri-culture often contain high levels of iron or aluminum
oxide Without a protective cover of vegetation, even
under cultivation soil may undergo a process known as
laterization and become rock-hard Rather than
un-dergoing natural reforestation, such abandoned
farm-land is more likely to remain barren of almost all plant
life for many years In areas where industrial pollution
exists, such as former mining districts, native trees may
not be able to tolerate the toxins in the soil; in such
cases more tolerant species must be introduced
Reforestation differs from tree farming in that the
goal of reforestation is not merely to provide
wood-lands for future harvest Although tree farming is a type of reforestation in that trees are planted to re-place those that have been removed, in tree farming generally only one species of tree is planted with the explicit intention that it be harvested later The trees are seen first as a crop and only incidentally as wildlife habitat or a means of erosion control As foresters have become more knowledgeable about the com-plex interactions within forest ecosystems, however, tree-farming methods have begun to change Rather than monocropping (planting only one variety of tree) on plantations, the commercial forest industry has begun planting mixed stands Trees once consid-ered undesirable weed trees because they possessed
no perceived commercial value are now recognized as nitrogen fixers necessary for the healthy growth of other species In addition to providing woodlands for possible use in commercial forestry, reforestation in-cludes goals such as wildlife habitat restoration and the reversal of environmental degradation
Ecological and Environmental Aspects Scientists did not clearly establish the vital role that trees, particularly those in tropical rain forests, play
in removing carbon dioxide from the atmosphere through the process of photosynthesis until the mid-twentieth century Carbon dioxide is a greenhouse gas: It helps trap heat in the Earth’s atmosphere As forests disappear, the risk of global warming—caused
in part by an increase in the amount of carbon diox-ide in the atmosphere—becomes greater For many years, soil conservationists advocated reforestation as
a way to counteract the ecological damage caused by erosion Beginning in the 1980’s, scientists and envi-ronmental activists concerned about global warming joined foresters and soil conservationists in urging that for every tree removed anywhere, whether to clear land for development or to harvest timber, re-placement trees be planted As the area covered by tropical rain forests shrinks in size, the threat of irre-versible damage to the global environment becomes greater In 1988, American Forests, an industry group, began the Global ReLeaf program to encourage re-forestation efforts in an attempt to combat global warming By the end of 2006, this program had planted
25 million trees
Reforestation Programs
In addition to supporting reforestation efforts by gov-ernment agencies, corporations, and environmental
Trang 10organizations, Global ReLeaf and similar programs
encourage individuals to practice reforestation in their
own neighborhoods Trees serve as a natural climate
control, helping to moderate extremes in
tempera-ture and wind Trees in a well-landscaped yard can
re-duce homeowners’ energy costs by providing shade in
the summer and serving as a windbreak during the
winter Global ReLeaf is only one of many programs
that support reforestation efforts
Arbor Day, an annual day devoted to planting trees
for the beautification of towns or the forestation of
empty tracts of land, was established in the United
States in 1872 The holiday originated in Nebraska, a
prairie state that seemed unnaturally barren to
home-steaders used to eastern woodlands, and initially it
emphasized planting trees where none had existed
before Arbor Day is observed in public schools to
ed-ucate young people about the importance of forest
preservation, and in some states it is a legal holiday
Organizations such as the Arbor Day Foundation
pro-vide saplings (young trees) to schools and other
orga-nizations for planting in their own neighborhoods
Nancy Farm Männikkö
Further Reading
Berger, John J Forests Forever: Their Ecology, Restoration,
and Protection Chicago: Center for American
Places at Columbia College, 2008
Cherrington, Mark Degradation of the Land New York:
Chelsea House, 1992
Gradwohl, Judith, and Russell Greenberg Saving the
Tropical Forests Illustrated by Lois Sloan
Washing-ton, D.C.: Island Press, 1988
Küchli, Christian Forests of Hope: Stories of Regeneration.
Stony Creek, Conn.: New Society, 1997
Lamb, David, and Don Gilmour Rehabilitation and
Res-toration of Degraded Forests Gland, Switzerland:
IUCN, 2003
Lipkis, Andy, and Katie Lipkis The Simple Act of
Planting a Tree: A Citizen Forester’s Guide to Healing
Your Neighborhood, Your City, and Your World Los
An-geles: J.P Tarcher, 1990
Mansourian, Stephanie, Daniel Vallauri, and Nigel
Dudley Forest Restoration in Landscapes: Beyond
Planting Trees New York: Springer, 2005.
Rietbergen-McCracken, Jennifer, Stewart Maginnis,
and Alastair Sarre, eds The Forest Landscape
Restora-tion Handbook London: Earthscan, 2007.
Weiner, Michael A Plant a Tree: A Working Guide to
Regreening America New York: Macmillan, 1975.
Web Sites American Forests Global Releaf http://www.americanforests.org/global_releaf Arbor Day Foundation
Replanting Our National Forests http://www.arborday.org/replanting See also: Clear-cutting; Deforestation; Forest man-agement; Forests; Maathai, Wangari; Rain forests; Slash-and-burn agriculture; Timber industry
Refrigeration See Canning and
refrigeration of food
Remote sensing
Categories: Obtaining and using resources;
scientific disciplines
The use of technology to acquire images and data about distant objects—including Earth—has ex-panded humans’ ability to understand the location, availability, and nature of resources on Earth.
Background Remote sensing is the use of technology to extract in-formation from objects or areas distant from the ob-server It is the act of gathering information about a subject of interest without being in contact with the subject This technology often collects energy beyond the sensitivity of human eyes and ears, utilizing the en-tire range of energy of the electromagnetic spectrum, particles, or fields Remote-sensing technology is a successful tool for the discovery, inventory, and man-agement of resources, both natural and human-made These techniques make possible the collection of data beyond the range of human senses Moreover, the large-scale perspective remote sensing affords accel-erates our ability to map and identify change over time
Several areas in the sciences utilize remote-sensing techniques Astronomy has perhaps the longest his-tory of gathering information from a distance, but there are other fields that do so, such as geophysics