Environmental Encyclopedia
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Environmental Encyclopedia 3
Bikini atoll
At that time, 161 people belonging to 11 families lived
on Bikini. Since the Bikinians have no written history, little
is known about their background. According to their oral
tradition, the original home of their ancestors is nearby
Wotje Atoll. Until the early 1900s, they had relatively little
contact with strangers and were regarded with some disdain
even by other Marshall Islanders. After the arrival of mis-
sionaries early in the twentieth century, the Bikinians became
devout Christians. People lived on coconuts, breadfruits,
arrowroot, fish, turtle eggs, and birds, all available in abun-
dance on the atoll. The Bikinians were expert sailors and
fishermen. Land ownership was important in the culture,
and anyone who had no land was regarded as lacking in
dignity.
On January 10, 1946, President Truman signed an
order authorizing the transfer of everyone living on Bikini
Atoll to the nearly uninhabited Bongerik Atoll. The United
States Government asked the Bikinians to give up their
native land to allow experiments that would bring benefit
to all humankind. Such an action, the Americans argued,
would earn for the Bikinians special glory in heaven. The
islanders agreed to the request and, along with their homes,
church, and community hall, were transported by the United
States Navy to Rongerik.
In June and July of 1946, two tests of atomic bombs
were conducted at Bikini as part of “Operation Crossroads.”
More than 90 vessels, including captured German and Japa-
nese ships along with surplus cruisers, destroyers, subma-
rines, and amphibious craft from the United States Navy,
were assembled. Following these tests, however, the Navy
concluded that Bikini was too small and moved future experi-
ments to Eniwetok Atoll.
The testing of a nuclear fusion device in Operation
Castle marked the return of bomb testing to Bikini. The
most memorable test of that series took place in 1954 and
was code-named “Bravo.” Experts expected a yield of six
megatons from the hydrogen bomb used in the test, but
measured instead a yield of 15 megatons, 250% greater.
Bravo turned out to be the largest single explosion in all of
human history, producing an explosive force greater than all
of the bombs used in all the previous wars in history.
Fallout from Bravo was consequently much larger than
had been anticipated. In addition, because of a shift in wind
patterns, the fallout spread across an area of about 50,000
mi
2
(11.5 km
2
), including three inhabited islands—
Rongelap, Itrik, and Rongerik. A number of people living
on these islands developed radiation burns and many were
evacuated from their homes temporarily. Farther to the east,
a Japanese fishing boat which had accidentally sailed into
the restricted zone was showered with fallout. By the time
the boat returned to Japan, 23 crew members had developed
radiation sickness
. One eventually died of infectious hepa-
127
titis, probably because of the numerous blood transfusions
he received.
The value of Bikini as a test site ended in 1963 when
the United States and the Soviet Union signed the Limited
Test Ban Treaty which outlawed nuclear weapons testing
in the
atmosphere
, the oceans, and outer space. Five years
later, the United States government decided that it was safe
for the Bikinians to return home. By 1971, some had once
again take up residence on their home island. Their return
was short-lived. In 1978, tests showed that returnees had
ingested quantities of radioactive materials much higher than
the levels considered to be safe. The Bikinians were relocated
once again, this time to the isolated and desolate island of
Kili, 500 mi (804 km) from Bikini.
The primary culprit on Bikini was the radioactive
iso-
tope
cesium-137. It had become so widely distributed in
the
soil
, the water, and the crops on the island that no one
living there could escape from it. With a half life of 30 years,
the isotope is likely to make the island uninhabitable for
another century.
Two solutions for this problem have been suggested.
The brute-force approach is to scrape off the upper 12 in
(30 cm) of soil, transport it to some uninhabited island, and
bury it under concrete. A similar burial site, the “Cactus
Crater,” already exists on Runit Island. It holds radioactive
wastes removed from Eniwetok Atoll. The cost of clearing
off Bikini’s 560 acres (227 ha) and destroying all its vegeta-
tion (including 25,000 trees) has been estimated at more
then $80 million. A second approach is more subtle and
makes use of chemical principles. Since potassium replaces
cesium in soil, scientists hope that adding potassium-rich
fertilizers to Bikini’s soil will leach out the dangerous ce-
sium-137.
At the thirtieth anniversary of Bravo, the Bikinians
had still not returned to their home island. Many of the
original 116 evacuees had already died. A majority of the
1,300 Bikinians who then lived on Kili no longer wanted
to return to their native land. If given the choice, most
wanted to make Maui, Hawaii, their new home. But they
did not have that choice. The United States continues to
insist that they remain somewhere in the Marshall Islands.
The only place there they can’t go, at least within most of
their lifetimes, is Bikini Atoll.
[David E. Newton]
R
ESOURCES
P
ERIODICALS
Davis, J. “Paradise Regained?” Mother Jones 18 (March/April 1993): 17.
Delgado, J. P. “Operation Crossroads.” American History Illustrated 28
(May/June 1993): 50–59.
Environmental Encyclopedia 3
Bioaccumulation
Eliot, J. L., and B. Curtsinger. “In Bikini Lagoon Life Thrives in a Nuclear
Graveyard.” National Geographic 181 (June 1992): 70–83.
Lenihan, D. J. “Bikini Beneath the Waves.” American History Illustrated
28 (May/June 1993): 60–67.
Bioaccumulation
The general term for describing the accumulation of
chemi-
cals
in the tissue of organisms. The chemicals that bioaccu-
mulate are most often organic chemicals that are very soluble
in fat and lipids and are slow to degrade. Usually used in
reference to aquatic organisms, bioaccumulation occurs from
exposure to contaminated water (e.g., gill uptake by fish) or
by consuming food that has accumulated the chemical (e.g.,
food chain/web
transfer). Bioaccumulation of chemicals
in fish has resulted in public health consumption advisories
in some areas, and has affected the health of certain fish-
eating
wildlife
including eagles, cormorants, terns, and
mink.
Bioaerosols
Bioaerosols are airborne particles derived from plants, ani-
mals or are living organisms, including viruses, bacteria,
fungi
, and mammal and bird antigens. Bioaerosols can range
in size from roughly 0.01 micrometer (
virus
) to 100 microm-
eter (pollen). These particles can be inhaled and can cause
many types of health problems, including allergic reactions
(specific activation of the immune system), infectious disease
(pathogens that invade human tissues), and toxic effects
(due to biologically produced chemical
toxins
). The most
common outdoor bioaerosols are pollens from grasses, trees,
weeds, and crops. The most common indoor biological pol-
lutants are animal dander (minute scales from hair, feathers,
or skin), dust mite and cockroach parts, fungi (molds), infec-
tious agents (bacteria and viruses), and pollen.
Bioassay
Bioassay refers to an evaluation of the toxicity of an
effluent
or other material on living organisms such as fish, rats,
insects, bacteria, or other life forms. The bioassay may be
used for many purposes, including the determination of: 1)
permissible
wastewater discharge
rates; 2) the relative
sensitivities of various animals; 3) the effects of physico-
chemical parameters on toxicity; 4) the compliance of dis-
charges with effluent guidelines; 5) the suitability of a drug;
6) the safety of an
environment
; and 7) possible synergistic
or antagonistic effects.
There are those who wish to reserve the term simply
for the evaluation of the potency of substances such as drugs
128
and vitamins, but the term is commonly used as described
above. Of course, there are times when it is inappropriate
to use bioassay and evaluation of toxicity synonymously, as
when the goal of the assay is not to evaluate toxicity.
Bioassays are conducted as static, renewal, or continu-
ous-flow experiments. In static tests, the medium (air or
water) about the test organisms is not changed, in renewal
tests the medium is changed periodically, and in continuous-
flow experiments the medium is renewed continuously.
When testing
chemicals
or wastewaters that are unstable,
continuous-flow testing is preferable. Examples of instability
include the rapid degradation of a chemical, significant losses
in
dissolved oxygen
, problems with volatility, and precipi-
tation.
Bioassays are also classified on the basis of duration.
The tests may be short-term or acute, intermediate-term,
or long-term, also referred to as chronic. In addition, aquatic
toxicologists speak of partial- or complete- life-cycle assess-
ments. The experimental design of a bioassay is in part
reflected in such labels as range-finding, which is used for
preliminary tests to approximate toxicity; screening for tests
to determine if toxicity is likely by using one concentration
and several replicates; and definitive, for tests to establish a
particular end point with several concentrations and repli-
cates).
The results of bioassays are reported in a number of
ways. Early aquatic toxicity data were reported in terms of
tolerance limits (TL). The term has been superseded by
other terms such as effective concentration (EC), inhibiting
concentration (IC), and lethal concentration (LC). The re-
sults of tests in which an animal is dosed (fed or injected)
are reported in terms of effective dosage (ED) or lethal
dosage (LD). When the potency of a drug is being studied,
a therapeutic index (TI) is sometimes reported, which is the
dose needed to cause a certain desirable effect (ED) divided
by the lethal dose (LD) or some other ED. Median doses,
the amount needed to affect 50% of the test population, are
not always used. Needless to say, an evaluation of the re-
sponse of a control population of organisms not exposed to
a test agent or solution during the course of an experiment
is very important.
Quality assurance and quality control procedures have
become a very important part of bioassay methods. For ex-
ample, the U.S.
Environmental Protection Agency
(EPA)
has very specifically outlined how various aquatic bioassay
procedures are to be performed and standardized to enhance
reliability,
precision
, and
accuracy
. Other agencies in the
United States and around the world have also worked very
hard in recent years to standardize and improve quality assur-
ance and control guidelines for the various bioassay tech-
niques.
[Gregory D. Boardman]
Environmental Encyclopedia 3
Bioassessment
R
ESOURCES
B
OOKS
Manahan, S. E. Toxicological Chemistry. 2nd ed. Ann Arbor, MI: Lewis,
1992.
Rand, G. M., and Petrocelli, S. R. Fundamentals of Aquatic Toxicology
Methods and Applications. Washington, DC: Hemisphere, 1985.
Bioassessment
According to the official definition of the United States
Environmental Protection Agency
(EPA), bioassessment
refers to the process of evaluating the biological condition
of a body of water using biological surveys (biosurveys) and
other direct measurements of the resident biota—those
organisms living in the surface water, including fish, insects,
algae, plants and others. Since 1972 when the
Clean Water
Act
was passed by Congress in order to clean up America’s
polluted waterways, the biological integrity of the nation’s
bodies of water has been the focus of professionals and
citizens in ensuring the success of reaching this goal.
The derivation of biocriteria emerges from the bioas-
sessment, and offers a narrative or numeric expression that
explains the life surviving in the water. The process of evalu-
ating biocriteria can be in “scores” using a method known
as the Ohio multimetric approach; or, reported in “clusters”
according to the Maine statistical approach.
Particularly in the study of
water pollution
, and the
examinination of ways to correct it, a bioassessment of a body
of water measures the composition, diversity, and functional
organization of the community living in it. Consequently it
lays the groundwork for the biocriteria in the determination
of the quality of the desired goal in regard to the condition
of the resource, and to what maximum level of management
that water can be maintained. The result is not how extensive
the pollutant level can be. The result of any bioassessment
should be that the unique members of this community of
living organisms thrive as they interact with the various
elements of their common home. Biocriteria must be main-
tained separately from any chemical evaluation, whose whole
effluent toxicity (WET) is a distinct measurement, and plays
a different role in water management, along with the physical
and toxicity factors also included in a complete
water qual-
ity
management program.
Measuring biological integrity is accomplished most
successfully when researchers utilize the Rapid Bioassessment
Protocols (RBPs) established originally in the 1980s by the
EPA, and revised and reissued in 1999. The concept at
the core of these protocols according to the official EPA
information are:
O
Cost-effective, scientifically valid procedures for biological
surveys
129
O
Provisions for multiple site investigations in a field season
O
Quick turn-around of results for management decisions
O
Scientific reports easily translated to management and the
public
These RBPs resulted from those methods already in
use by several state agencies. They are useful in the following
areas of study:
O
Determining if a stream is supporting a designated aquatic
life use specified in state water quality standards
O
Characterizing the existence and severity of impppairment
to the water resource
O
Helping to identify the sources and causes of impairment
O
Evaluating the effectiveness of control actions and restora-
tion activities
O
Supporting use attainability studies an cumulative impact
assessment
O
Characterizing regional biotic attributes of reference condi-
tions.
Not only are current living conditions key factors in
studying this aquatic life. Physical and biological elements
known as stressors are those that exert a negative or adverse
effect on the organisms. How those stressors might have
affected the organisms over a long period of time is crucial
to understanding what actions will be necessary to improve
the
ecology
of the waterbody.
Centers and groups for bioassessment are active in
each state throughout the United States, and throughout
the world. They operate with scientifical professionals such
as biologists, as well as include trained citizen groups who
participate by volunteering their time to monitor local water
conditions. In one such program begun in California in
1998, trained citizen groups throughout the state under the
training and guidance of a water biologist with the California
Department of Fish and Game (CDFG) track the abun-
dance and diversity of macroinvertebrates in order to assess
the effects of
pollution
. This method was considered one
of the best ways to monitor the health of streams and lakes
due to the fact that each
species
is adapted to thrive in a
particular habitat—along with an examination of bugs,
whose various reactions to different types of pollutions have
been monitored and well-established for years.
In an article written for the EPA Journal, in 1990,
“Measuring Environmental Success,” Steve Glomb noted
that, “Biological community interactions are probably the
most difficult goals to measure, Many scientists, however,
think that these interactions are the most important factors
to assess.” Those interactions are often subtle, such as the
example of invertebrates living in the mud on the floor of
coastal waters, as Glomb mentioned. “Because they don’t
move much,” he observed, “they can be used as an indication
of problems over time.” In determining past and current
Environmental Encyclopedia 3
Biochemical oxygen demand
living conditions, bioassessment has proved an invaluable
tool in implementing the goals of clean water for all life,
including humans.
[Jane E. Spear]
R
ESOURCES
P
ERIODICALS
California Aquatic Bioassessment Workgroup. Mission Statement<:http://
www.dfg.ca.gov/>
Central Plains Center for BioAssessment. Home Page. http://www.cpcb.u-
kans.edu/>
Glomb, Steve. “Measuring Environmental Success.” EPA Journal 16 (Nov/
Dec 1990): 57.
Levy, Sharon. “Using Bugs to Bust Polluters.” Bioscience 48 (May 1998): 342.
U.S. Environmental Protection Agency. Biocriterial. http://www.epa.gov/
ost/>
Yosemite National Park/U.S. Environmental Protection Agency. Water.
http://www.yosemite.epa.gov/>
O
RGANIZATIONS
California Aquatic Bioassessment Workgroup, Department of Fish and
Game, 1416 Ninth Street, Sacramento, CA United States 95814 (916)445-
0411, Fax: (916)653-1856, <www.dfg.ca.gov>
Central Plains Center for BioAssessment, 2021 Constant Avenue,
Lawrence, KA United States 66047-3729 (785)864-7729, Email:
dbaker@ukans.edu, <www.cpcb.ukans.edu>
U. S. Environmental Protection Agency, 1200 Pennsylvania Avenue, NW,
Washington, D.C. United States 20460 (202) 260-2090, , <www.epa.gov>
Biocentrism
see
Environmental ethics
Biochemical oxygen demand
The biochemical oxygen demand (BOD) test is an indirect
measure of the
biodegradable
organic matter in an aqueous
sample. The test is indirect because oxygen used by
microbes
as they degrade organic matter is measured, rather than the
depletion of the organic materials themselves. Generally, the
test is performed over a five-day period (BOD
5
) at 68°F
(20°C) in 10 fl oz (300 ml) bottles incubated in the dark to
prevent interference from algal growth.
Dissolved oxygen
(DO) levels (in mg/l) are measured on day zero and at the
end of the test. The following equation relates how the
BOD
5
of a sample is calculated:
(Do
initial
-DO
after 5 days
)
BOD
5
,mg/L =
mL sample
Note that in the above equation “ml sample” refers to
the amount of sample that is placed in a 300 ml BOD bottle.
This is critical in doing a test because if too much sample
is added to a BOD bottle, microbes will use all the DO
130
in the water (i.e., DO
after 5 days
=0) and a BOD
5
cannot be
calculated. Thus, the DO uptake at various dilutions of a
given sample are made. One way of making the dilutions is
to add different amounts of sample to different bottles. The
bottles are then filled with dilution water which is saturated
with oxygen, contains various nutrients, is at a neutral
pH
,
and is very pure so as not to create any interference. Research-
ers attempt to identify a dilution which will provide for a
DO uptake of greater than or equal to 2 mg/l and a DO
residual of greater than or equal to 0.5–1.0 mg/l.
In some cases compounds or ions may be present in
a sample that will inhibit microbes from degrading organic
materials in the sample, thereby resulting in an artificially
low or no BOD. Other times, the right number and/or types
of microbes are not present, so the BOD is inaccurate.
Samples may be “seeded” with microbes to compensate for
these problems. The absence of a required
nutrient
will also
make the BOD test invalid.
Thus, a number of factors can influence the BOD,
and the test is known to be rather imprecise (i.e., values
obtained vary by 10–15% of the actual value in a good test).
However, the test continues to be a primary index of how
well waters need to be treated or are treated and of the
quality of natural waters. If wastes are not treated properly
and contain too much BOD, the wastes may create serious
oxygen deficits in environmental waters. The saturation con-
centration of oxygen in water varies somewhat with tempera-
ture and pressure but is often only in the area of 8–10 mg/
l or less. To serve as a reference, the BOD
5
of raw, domestic
wastewater
ranges from about 100–300 mg/l. The demand
for oxygen by the sewage is therefore clearly much greater
than the amount of oxygen that water can hold in a dissolved
form. To determine allowable BOD levels for a wastewater
discharge
, one must consider the relative flows/volumes of
the wastewater and receiving (natural) water, temperature,
reaeration of the natural water, biodegradation rate, input
of other wastes, influence of benthic deposits and algae, DO
levels of the wastewater and natural water, and condition/
value of the receiving water.
[Gregory D. Boardman]
R
ESOURCES
B
OOKS
Corbitt, R. A. Standard Handbook of Environmental Engineering. New York:
McGraw-Hill, 1990.
Davis, M. L., and D. A. Cornwell. Introduction to Environmental Engi-
neering. New York: McGraw-Hill, 1991.
Tchobanoglous, G., and E. D. Schroeder. Water Quality. Reading, MA:
Addison-Wesley, 1985.
Viessman Jr., W., and M. J. Hammer. Water Supply and Pollution Control.
5th ed. New York, Harper Collins, 1993.
Environmental Encyclopedia 3
Biodiversity
Bioconcentration
see
Biomagnification
Biodegradable
Biodegradable substances are those that can be decomposed
quickly by the action of biological organisms, especially
mi-
croorganisms
. The term is a process by which materials or
compounds are broken down to smaller components, and
all living organisms participate to some degree. Foods, for
instance, are degraded by living creatures to release energy
and chemical constituents for growth. In the sense that
the term is usually used, however, it has a more restricted
meaning. It refers specifically to the breakdown of undesir-
able toxic and waste materials or compounds to harmless or
tolerable ones. When breakdown results in the destruction
of useful objects, it is referred to as biodeterioration.
Although the term has been in common use for only
two or three decades, processes of biodegradation have been
known and used for centuries. Some of the most familiar
are
sewage treatment
of human wastes,
composting
of
kitchen, garden and lawn wastes, and spreading of
animal
waste
on farm fields. These processes, of course, all mitigate
problems with common and ubiquitous byproducts of civili-
zation. The variety of objectionable wastes has greatly in-
creased as human society has become more complex. The
waste stream
now includes items such as plastic bottles,
lubricants, and foam packaging. Many of the newer products
are virtually non-biodegradable, or they degrade only at a
very slow rate. In some instances biodegradability can be
greatly enhanced by minor changes in the chemical composi-
tion of the product. Biodegradable containers and packaging
have been developed that are just as functional for many
purposes as their non-degradable counterparts.
Advances in the science of microbiology have greatly
expanded the potential for biodegradation and have in-
creased public interest. Examples of new developments in-
clude the discovery of hitherto unknown microorganisms
capable of degrading crude oil,
petroleum hydrocarbons
,
diesel fuel,
gasoline
, industrial solvents, and some forms
of synthetic polymers and
plastics
. These discoveries have
opened new approaches for cleansing the
environment
of
the accumulating
toxins
and debris of human society. Un-
fortunately, the rate at which the new organisms attack exotic
wastes is sometimes quite slow, and dependent on environ-
mental conditions. Presumably, microorganisms have been
exposed to common wastes of a very long time and have
evolved efficient and rapid ways to attack and use them as
food. On the other hand, there has not been sufficient time
to develop equally efficient means for degrading the newer
wastes.
131
Research continues on the surprising capabilities of
the new
microbes
emphasizing opportunities for genetic
control and manipulation of the unique metabolic pathways
that make the organisms so valuable. The potential for bio-
degradation can be improved by increasing the rates at which
wastes are attacked, and the range of environmental condi-
tions in which degrading organisms can thrive. The advan-
tages of biological cleanup agents are several. Non-biological
techniques are often difficult and expensive. The traditional
way of removing petroleum wastes from
soil
, for instance,
has been to collect and incinerate it at high temperatures.
This is very costly and sometimes impossible. The prospect
of accomplishing the same thing by treating the
contami-
nated soil
with microorganisms without removing it from
its location has much appeal. It should have less destructive
impact on the contaminated site and be much less expensive.
[Douglas C. Pratt]
R
ESOURCES
B
OOKS
King, R. B., G. M. Long and J. K. Sheldon. Practical Environmental
Bioremediation. Boca Raton, Florida: CRC Press, Inc., 1992.
Sharpley, J. M. and A. M. Kaplan. Proceedings of the Third International
Biodegradation Symposium. London: Applied Science Publishers, 1976.
Biodiversity
Biodiversity is an ecological notion that refers to the richness
of biological types at a range of hierarchical levels, including:
(1) genetic diversity within
species
, (2) the richness of spe-
cies within communities, and (3) the richness of communi-
ties on landscapes. In the context of environmental studies,
however, biodiversity usually refers to the richness of species
in some geographic area, and how that richness may be
endangered by human activities, especially through local or
global
extinction
.
Extinction represents an irrevocable and highly regret-
table loss of a portion of the biodiversity of Earth. Extinction
can be a natural process, caused by: 1) random catastrophic
events; 2) biological interactions such as
competition
, dis-
ease, and predation; 3) chronic stresses; or 4) frequent distur-
bance. However, with the recent ascendance of human activi-
ties as a dominant force behind environmental changes, there
has been a dramatic increase in rates of extinction at local,
regional, and even global levels.
The recent wave of
anthropogenic
extinctions in-
cludes such well-known cases as the
dodo
,
passenger pi-
geon
, great auk, and others. There are many other high-
profile species that humans have brought to the brink of
extinction, including the plains buffalo,
whooping crane
,
eskimo curlew,
ivory-billed woodpecker
, and various ma-
Environmental Encyclopedia 3
Biodiversity
rine mammals. Most of these instances were caused by an
insatiable over-exploitation of species that were unable to
sustain a high rate of
mortality
, often coupled with an
intense disturbance of their
habitat
.
Beyond these tragic cases of extinction or endanger-
ment of large, charismatic vertebrates, the earth’s biota is
experiencing an even more substantial loss of biodiversity
caused by the loss of habitat. In part, this loss is due to the
conversion of large areas of tropical ecosystems, particularly
moist forest, to agricultural or otherwise ecologically de-
graded habitats. A large fraction of the biodiversity of tropi-
cal biomes is comprised of rare, endemic (i.e., with a local
distribution) species. Consequently the conversion of
tropi-
cal rain forest
to habitats unsuitable for these specialized
species inevitably causes the extinction of most of the locally
endemic biota. Remarkably, the biodiversity of tropical for-
ests is so large, particularly in insects, that most of it has
not yet been identified taxonomically. We are therefore faced
with the prospect of a
mass extinction
of perhaps millions
of species before they have been recognized by science.
To date, about 1.7 million organisms have been identi-
fied and designated with a scientific name. About 6% of
identified species live in boreal or polar latitudes, 59% in
the temperate zones, and the remaining 35% in the tropics.
The knowledge of the global richness of species is very
incomplete, particularly in the tropics. If a conservative esti-
mate is made of the number of unidentified tropical species,
the fraction of global species that live in the tropics would
increase to at least 86%.
Invertebrates comprise the largest number of described
species, with insects making up the bulk of that total and
beetles (Coleoptera) comprising most of the insects. Biologists
believe that there still is a tremendous number of undescribed
species of insects in the tropics, possibly as many as another
30 million species. This remarkable conclusion has emerged
from experiments conducted by the entomologist Terry Er-
win, in which scientists “fogged” tropical forest canopies and
then collected the “rain” of dead arthropods. This research
suggests that: (1) a large fraction of the insect biodiversity
of tropical forests is undescribed; (2) most insect species are
confined to a single type of forest, or even to particular plant
species, both of which are restricted in distribution; and (3)
most tropical forest insects have a very limited dispersal
ability.
The biodiversity and endemism of other tropical forest
biota are better known than that of arthropods. For example,
a plot of only 0.2 acres (0.1 ha) in an Ecuadorian forest had
365 species of vascular plants. The richness of woody plants
in tropical
rain forest
can approach 300 species per hectare,
compared with fewer than 12–15 tree species in a typical
temperate forest, and thirty to thirty-five species in the Great
132
Smokies of the United States, the richest temperate forest
in the world.
There have been few systematic studies of all of the
biota of particular tropical communities. In one case, D. H.
Janzen studied a savanna-like, 67-mi
2
(108-km
2
) reserve of
dry tropical forest in Costa Rica for several years. He esti-
mated that the site had at least 700 plant species, 400 verte-
brate species, and a remarkable 13,000 species of insect,
including 3,140 species of moths and butterflies.
Why should one worry about the likelihood of extinc-
tion of so many
rare species
of tropical insects, or of many
other rare species of plants and animals? There are three
classes of reasons why extinctions are regrettable:
(1) There are important concerns in terms of the ethics
of extinction. Central questions are whether humans have
the “right” to act as the exterminator of unique and irrevoca-
ble species of
wildlife
and whether the human existence is
somehow impoverished by the tragedy of extinction. These
are philosophical issues that cannot be scientifically resolved,
but it is certain that few people would applaud the extinction
of unique species.
(2) There are utilitarian reasons. Humans must take
advantage of other organisms in myriad ways for sustenance,
medicine, shelter, and other purposes. If species become
extinct, their unique services, be they biological, ecological,
or otherwise, are no longer available for exploitation.
(3) The third class of reasons is ecological and involves
the roles of species in maintaining the
stability
and integrity
of ecosystems, i.e., in terms of preventing
erosion
and con-
trolling
nutrient
cycling, productivity, trophic dynamics, and
other aspects of
ecosystem
structure and function. Because
we rarely have sufficient knowledge to evaluate the ecological
“importance” of particular species, it is likely that an extraor-
dinary number of species will disappear before their ecologi-
cal roles are understood.
There are many cases where research on previously
unexploited species of plants and animals has revealed the
existence of products of great utility to humans, such as
food or medicinals. One example is the rosy periwinkle
(Catharantus roseus), a plant native to
Madagascar
. During
a screening of many plants for possible anti-cancer proper-
ties, an extract of rosy periwinkle was found to counteract
the reproduction of
cancer
cells. Research identified the
active ingredients as several alkaloids, which are now used
to prepare the important anti-cancer drugs vincristine and
vinblastine. This once obscure plant now allows treatment
of several previously incurable cancers and is the basis of a
multi-million-dollar economy.
Undoubtedly, there is a tremendous, undiscovered
wealth of other biological products that are of potential use
to humans. Many of these natural products are present in
Environmental Encyclopedia 3
Biodiversity
the biodiversity of tropical species that has not yet been
“discovered” by taxonomists.
It is well known that extinction can be a natural pro-
cess. In fact, most of the species that have ever lived on
Earth are now extinct, having disappeared “naturally” for
some reason or other. Perhaps they could not cope with
changes in their inorganic or biotic
environment
, or they
may have succumbed to some catastrophic event, such as a
meteorite impact.
The rate of extinction has not been uniform over geo-
logical time. Long periods characterized by a slow and uni-
form rate of extinction have been punctuated by about nine
catastrophic events of mass extinction. The most intense
mass extinction occurred some 250 million years ago, when
about 96% of marine species became extinct. Another exam-
ple occurred 65 million years ago, when there were extinc-
tions of many vertebrate species, including the reptilian or-
ders Dinosauria and Pterosauria, but also of many plants
and invertebrates, including about one half of the global
fauna
that existed then.
In modern times, however, humans are the dominant
force causing extinction, mostly because of: (1) overharvest-
ing; (2) effects of introduced predators, competitors, and
diseases; and (3) habitat destruction. During the last 200
years, a global total of perhaps 100 species of mammals, 160
birds, and many other taxa are known to have become extinct
through some human influence, in addition to untold num-
bers of undescribed, tropical species.
Even pre-industrial human societies caused extinc-
tions. Stone-age humans are believed to have caused the
extinctions of large-animal fauna in various places, by the
unsustainable and insatiable
hunting
of vulnerable species
in newly discovered islands and continents. Such events of
mass extinction of large animals, co-incident with human
colonization events, have occurred at various times during
the last 10–50,000 years in Madagascar, New Zealand,
Aus-
tralia
, Tasmania, Hawaii, North and South America, and
elsewhere.
In more recent times,
overhunting
has caused the
extinction of other large, vulnerable species, for example the
flightless dodo (Raphus cucullatus) of Mauritius. Some North
American examples include Labrador duck (Camptorhynchus
labradorium), passenger pigeon (Ectopistes migratorius), Car-
olina parakeet (Conuropsis carolinensis), great auk (Pinguinus
impennis), and Steller’s sea cow (Hydrodamalis stelleri). Many
other species have been brought to the brink of extinction
by overhunting and loss of habitat. Some North American
examples include eskimo curlew (Numenius borealis), plains
bison
(Bison bison), and a variety of marine mammals, in-
cluding manatee (Trichechus manatus), right
whales
(Euba-
133
laena glacialis), bowhead whale (Balaena mysticetus), and blue
whale (Balaenoptera musculus).
Island biotas are especially prone to both natural and
anthropogenic extinction. This syndrome can be illustrated
by the case of the
Hawaiian Islands
, an ancient volcanic ar-
chipelago in the Pacific Ocean, about 994 mi (1,600 km) from
the nearest island group and 2,484 mi (4,000 km) from the
nearest continental landmass. At the time of colonization by
Polynesians, there were at least 68
endemic species
of Ha-
waiian birds, out of a total richness of land birds of 86 species.
Of the initial 68 endemics, 24 are now extinct and 29 are peril-
ously endangered. Especially hard hit has been an endemic
family, theHawaiian honeycreepers (Drepanididae), of which
13 species are believed extinct, and 12 endangered. More than
50 alien species of birds have been introduced to the Hawaiian
Islands, but this gain hardly compensates for the loss and en-
dangerment of specifically evolved endemics. Similarly, the
native
flora
of the islands is estimated to have been comprised
of 1,765–2,000 taxa of angiosperm plants, of which at least
94% were endemic. During the last two centuries, more than
100 native plants have become extinct, and the survival of at
least an additional 500 taxa is threatened or endangered, some
now being represented by only single individuals. The most
important causes of extinction of Hawaiian biota have been
the conversion of natural ecosystems to agricultural and urban
landscapes, the introduction of alien predators, competitors,
herbivores, and diseases, and to some extent, aboriginal over-
hunting of some species of bird.
Overhunting has been an important cause of extinc-
tion, but in modern times habitat destruction is the most
important reason for the event of mass extinction that Earth’s
biodiversity is now experiencing. As was noted previously,
most of the global biodiversity is comprised of millions of as
yet undescribed taxa of tropical insects and other organisms.
Because of the extreme endemism of most tropical biota, it
is likely that many species will become extinct as a result of
the clearing of natural tropical habitats, especially forest, and
its conversion to other types of habitat.
The amount and rate of
deforestation
in the tropics
are increasing rapidly, in contrast to the situation at higher
latitudes where forest cover is relatively stable. Between the
mid 1960s and the mid 1980s there was little change (less
than 2%) in the forest area of North America, but in Central
America forest cover decreased by 17%, and in South
America by 7% (but by a larger%age in equatorial countries
of South America). The global rate of clearing of tropical
rain forest in the mid 1980s was equivalent to 6–8% of that
biome
per year, a rate that if projected into the future would
predict a biome
half-life
of only nine to 12 years. Some of the
cleared forest will regenerate through secondary
succession
,
which would ultimately produce another mature forest. Little
is known, however, about the rate and biological character
Environmental Encyclopedia 3
Biofilms
of succession in tropical rainforests, or how long it would
take to restore a fully biodiverse ecosystem after disturbance.
The present rate of disturbance and conversion of
tropical forest predicts grave consequences for global biodiv-
ersity. Because of a widespread awareness and concern about
this important problem, much research and other activity
has recently been directed towards the
conservation
and
protection of tropical forests. As of 1985, several thousand
sites, comprising more than 640,000 mi
2
(1 million km),
had received some sort of “protection” in low-latitude coun-
tries. Of course the operational effectiveness of the protected
status varies greatly, depending on the commitment of gov-
ernments to these issues. Important factors include: (1) polit-
ical stability; (2) political priorities; (3) finances available to
mount effective programs to control
poaching
of animals
and lumber and to prevent other disturbances; (4) the support
of local peoples and communities for biodiversity programs;
(5) the willingness of relatively wealthy nations to provide
a measure of debt relief to impoverished tropical countries
and thereby reduce their short term need to liquidate
natural
resources
in order to raise capital and provide employment;
and (6) local
population growth
, which also generates ex-
treme pressures to over exploit natural resources.
The biodiversity crisis is a very real and very important
aspect of the global environmental crisis. All nations have
a responsibility to maintain biodiversity within their own
jurisdictions and to aid nations with less economic and scien-
tific capability to maintain their biodiversity on behalf of
the entire planet. The modern biodiversity crisis focuses on
species-rich tropical ecosystems, but the developed nations
of temperate latitudes also have a large stake in the outcome
and will have to substantially subsidize global conservation
activities if these are to be successful. Much needs to be
done, but an encouraging level of activity in the conservation
and protection of biodiversity is beginning in many countries,
including an emerging commitment by many nations to the
conservation of threatened ecosystems in the tropics.
[Bill Freedman Ph.D.]
R
ESOURCES
B
OOKS
Ehrlich, P. R., and A. H. Ehrlich. Extinction: The Causes and Consequences
of the Disappearance of Species. New York: Ballantyne Books, 1981.
Freedman, B. Environmental Ecology. San Diego, CA: Academic Press,
1989.
Peters, R. L., and T. E. Lovejoy. Global Warming and Biological Diversity.
New Haven, CT: Yale University Press, 1992.
Wilson, E. O. Biodiversity. Washington, DC: National Academy Press,
1988.
———. Biophilia: The Human Bond With Other Species. Cambridge, MA:
Harvard University Press, 1984.
134
P
ERIODICALS
Janzen, D. H. “Insect Diversity in a Costa Rican Dry Forest: Why Keep
It, and How.” Biological Journal of the Linnaean Society 30 (1987): 343–356.
Biofilms
Marine microbiology began with the investigations of marine
microfouling by L. E. Zobell and his colleagues in the 1930s
and 1940s. Their interests focused primarily on the early
stages of settlement and growth of
microorganisms
, pri-
marily bacteria on solid substrates immersed in the sea. The
interest in the study of marine microfouling was sporadic
from that time until the early 1960s when interest in marine
bacteriology began to increase. Since 1970 the research on
the broad problems of bioadhesion and specifically the early
stages of microfouling has expanded tremendously.
The initial step in marine fouling is the establishment
of a complex film. This film, which is composed mainly of
bacteria and diatoms plus secreted extracellular materials and
debris, is most commonly referred to as the “primary film” but
may also be called the “bacterial fouling layer,” or “slime layer.”
The latter name is aptly descriptive since the film ultimately
becomes thick enough to feel slippery or slimy to touch. In
addition to the bacteria and diatoms that comprise most of the
biota, the film may also include yeasts,
fungi
, and protozoans.
The settlement sequence in the formation of primary
films is dependent upon a number of variables which may
include the location of the surface, season of the year, depth,
and proximity to previously fouled surfaces and other physio-
chemical factors.
Many studies have demonstrated the existence of some
form of ecological
succession
in the formation of fouling
communities, commencing with film forming microorgan-
isms and reaching a climax community of macrofouling
organisms such as barnacles, tunicates, mussels, and sea-
weeds.
Establishment of primary films in marine fouling has
two functions: (a) to provide a surface favoring the settlement
and adhesion of animal larvae and algal cells, and (b) to
provide a
nutrient
source that could sustain or enhance the
development of the fouling community.
Formation of a primary film is initiated by a phenome-
non known as “molecular fouling” or “surface conditioning.”
The formation of this molecular film was first demonstrated
by Zobell in 1943 and since has been confirmed by many
other investigators. The molecular film forms by the
sorp-
tion
to solid surfaces of organic matter dissolved or sus-
pended in seawater. The sorption of this dissolved material
creates surface changes in the surface of the substrate which
are favorable for establishing biological settlement. These
dissolved organic materials originate from a variety of sources
Environmental Encyclopedia 3
Biofiltration
such as end-products of bacterial decay, excretory products,
dissolution from seaweeds, etc., and consist principally of
sugars, amino acids, urea, and fatty acids.
This molecular film has been observed to form within
minutes after any clean, solid surface is immersed in natural
seawater. The role of this film in
biofouling
has been shown
to modify the “critical surface tension” or wetability of the
immersed surface which than facilitates the strong bonding
of the microorganisms through the agency of mucopolysac-
charides exuded by film-forming bacteria.
Bacteria have been found securely attached to sub-
strates immersed in seawater after just a few hours. Initial
colonization is by rod-shaped bacteria followed by stalked
forms within 24–72 hours. As many as 40–50
species
have
been isolated from the surface of glass slides immersed in
seawater for a few days.
Following the establishment of the initial film of bac-
teria and their secreted extracellular polymer on a solid sub-
strate, additional bacteria and other microorganisms may
attach. Most significant in this population are benthic dia-
toms but there are also varieties of filamentous microorgan-
isms and protozoans. These organisms, together with debris
and other organic particular matter that adhere to the surface
create an intensely active biochemical
environment
and
form the primary stage in the succession of a typical mac-
rofouling community.
Considering the enormous economic consequences of
marine fouling it is not at all surprising that there continues
to be intense interest in the results of recent research, particu-
larly in the conditions and processes of molecular film for-
mation.
[Donald A. Villeneuve]
R
ESOURCES
B
OOKS
Corpe, W. A. “Primary Bacterial Films and Marine Microfouling.” In
Proceedings of the 4th International Congress of Marine Corrosion and Fouling,
edited by V. Romansky. 1977.
P
ERIODICALS
Zobell, L. E., and E. C. Allen. “The Significance of Marine Bacteria in
the Fouling of Submerged Surfaces.” Journal of Bacteriology 29 (1935):
239–251.
Biofiltration
Biofiltration refers to the removal and oxidation of organic
gases (i.e., volatile organic compounds, or VOCs) from con-
taminated air by vapor phase biodegradation in beds (biofilt-
ers) of compost,
soil
, or other materials such as municipal
waste, sand, bark peat, volcanic ash, or diatomaceous earth.
As contaminated air (such as air from a soil vapor extraction
135
process) flows through the biofilter, the VOCs sorb onto
surfaces of the pile and are degraded by
microorganisms
.
Nutrient
blends or exogenous microbial cultures can be
added to a biofilter to enhance its performance. Moisture
needs to be continually supplied to the biofilter to counteract
the drying effects of the gas stream. The stationary support
media that make up the biofiltration bed should be porous
enough to allow gas flow through the biofilter and should
provide a large surface area with high wetting and sorptive
capacities. This support media should also provide adequate
buffering capacity and may also serve as a source of inorganic
nutrients. Biofilters, also used to treat odors as well as organic
contaminants, have been used in Europe for over twenty
years. Compared to
incineration
and
carbon adsorption
,
biofilters do not require landfilling of residuals or regenera-
tion of spent materials.
Waste gases are moved through the units by induced
or forced draft. Biofilters are capable of handling rapid air
flow rates (e.g., up to 90,000 cubic ft (2,700 cubic m) per
minute (cfm) in
filters
up to 20,000 sq ft (1,800 sq m) in
wetted area) and VOC concentrations greater than 1,000
ppm. However, biofiltration removal of more highly haloge-
nated compounds such as trichloroethylene (TCE) or carbon
tetrachloride, which biodegrade very slowly under
aerobic
conditions, may require very long residence times (i.e., very
large biofilters) or treatment of very low flow rates of air
containing the contaminants.
The soil-type biofilter is similar in design to a soil
compost pile. Fertilizers are preblended into the compost
pile to provide nutrients for indigenous microorganisms,
which accomplish the biodegradation of the VOCs. In the
treatment bed type of biofilter, the waste air stream is humid-
ified as it is passed through one or more beds of compost,
municipal waste, sand, diatomaceous earth or other materi-
als. Another type of biofilter is the disk biofilter, which
consists of a series of humidified, compressed disks placed
inside a reactor shell. These layered disks contain activated
charcoal, nutrients, microbial cultures, and compost material.
The waste air stream is passed through the disk system.
Collected water condensate from the process is returned to
the humidification system for
reuse
.
[Judith L. Sims]
R
ESOURCES
B
OOKS
Baker, K. H., and D. S. Herson. Bioremediation. New York: McGraw-
Hill, 1994.
King, B. R., G. M. Long, and J. K. Sheldon. Practical Environmental
Bioremediation. Boca Raton, FL: Lewis Publishers, 1992.
Stoner, D. L., ed. “Organic Waste Forms and Treatment Strategies.” Bio-
technology for the Treatment of Hazardous Waste. Boca Raton, FL: Lewis
Publishers, 1994.
Environmental Encyclopedia 3
Biofouling
Biofouling
The term fouling, or more specifically biofouling, is used to
describe the growth and accumulation of living organisms
on the surfaces of submerged artificial structures as opposed
to natural surfaces. Concern over and interest in fouling
arises from practical considerations including the enormous
costs resulting from fouling of ships, buoys, floats, pipes,
cables and other underwater man-made structures.
From its first immersion in the sea, an artificial struc-
ture or surface changes through time as a result of a variety
of influences including location, season and other physical
and biological variables. Fouling communities growing on
these structures are biological entities and must be under-
stood developmentally. The development of a fouling com-
munity on a bare, artificial surface immersed in the sea
displays a form of
succession
, similar to that seen in terres-
trial ecosystems, which culminates in a community which
may be considered a climax stage. Scientists have identified
two distinct stages in fouling community development: 1)
the primary or microfouling stage, and 2) the secondary or
macrofouling stage.
Microfouling: When a structure is first submerged in
seawater,
microorganisms
, primarily bacteria and diatoms,
appear on the surface and multiply rapidly. Together with
debris and other organic
particulate
matter, these microor-
ganisms form a film on the surface. Although the evidence
is not conclusive, it appears that the development of this
film is a prerequisite to initiation of the fouling succession.
Macrofouling: The animals and plants that make up
the next stages of succession in fouling communities are
primarily the attached or sessile forms of animals and plants
that occur naturally in shallow waters along the local coast.
The development of fouling communities in the sea depends
upon the ability of locally-occurring organism to live success-
fully in the new artificial
habitat
. The first organisms to
attach to the microfouled surface are the swimming larvae
of
species
present at the time of immersion. The kinds of
larvae present vary with the season. Rapidly growing forms
that become established first may ultimately be crowded out
by others which grow more slowly. A comprehensive list of
species making up fouling communities recorded from a
wide variety of structures identified 2,000 species of animals
and plants. Although the variety of organisms identified
seems large it actually represents a very small proportion of
the known marine species. Further, only about 50 to 100
species are commonly encountered in fouling, including bi-
valve mollusks (primarily oysters and mussels), barnacles,
aquatic invertebrates in the phylum Bryozoa, tubeworms
and other organisms in the class Polychaeta, and green and
brown algae.
136
Control of fouling organisms has long been a formi-
dable challenge resulting in the development and applica-
tion of a wide variety of toxic paints and greases, or the
use of metals which give off toxic ions as they corrode.
However, none of the existing methods provide permanent
control. Furthermore, the recognition of the potential
environmental hazards attendant with the use of materials
that leach
toxins
into the marine
environment
has led
to the ban of some of the most widely used materials.
This has stimulated efforts to develop alternative materials
or methods of controlling biofouling that are environmen-
tally safe.
[Donald A. Villeneuve]
R
ESOURCES
B
OOKS
Workshop on Preservation of Wood in the Marine Environment. Marine
Borers, Fungi and Fouling Organisms of Wood. Paris: Organization for Eco-
nomic Cooperation and Development, 1971.
Melo, L. F., et al, eds. Fouling Science and Technology. Norwell, MA: Kluwer
Academic, 1988.
Woods Hole Oceanographic Institution. Marine Fouling and Its Prevention.
Annapolis, MD: U. S. Naval Institute, 1952.
Biogeochemistry
Biogeochemistry refers to the quantity and cycling of
chemi-
cals
in ecosystems. Biogeochemistry can be studied at vari-
ous spatial scales, ranging from communities, landscapes
(or seascapes), and over Earth as a whole. Biogeochemistry
involves the study of chemicals in organisms, and also in
non-living components of the
environment
.
An important aspect of biogeochemistry is the fact
that elements can occur in various molecular forms that
can be transformed among each other, often as a result of
biological reactions. Such transformations are an especially
important consideration for nutrients, i.e., those chemicals
that are required for the healthy functioning of organisms.
As a result of biogeochemical cycling, nutrients can be used
repeatedly–nutrients contained in dead
biomass
can be re-
cycled through inorganic forms, back into living organisms,
and so on. Biogeochemistry is also relevant to the movements
and transformations of potentially toxic chemicals in ecosys-
tems, such as metals, pesticides, and certain gases.
Nutrient Cycles
Ecologists have a good understanding of the biogeo-
chemical cycling of the most important nutrients. These