Environmental Encyclopedia

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Environmental Encyclopedia 3

Biogeochemistry

include

carbon

nitrogen

phosphorus

, potassium, cal-

cium, magnesium, and sulfur. Some of these can occur vari-

ously as gases in the

atmosphere

, as ions dissolved in water,

in minerals in rocks and

soil

, and in a great variety of

organic chemicals in the living or dead biomass of organisms.

Ecologists study

nutrient

cycles by determining the quanti-

ties of the various chemical forms of nutrients in various

compartments of ecosystems, and by determining the rates

of transformation and cycling among the various compart-

ments.

The

nitrogen cycle

is particularly well understood,

and it can be used to illustrate the broader characteristics of

nutrient cycling. Nitrogen is an important nutrient, being

one of the most abundant elements in the tissues of organ-

isms and a component of many kinds of biochemicals, in-

cluding amino acids, proteins, and nucleic acids. Nitrogen

is also one of the most common limiting factors to

primary

productivity

, and the growth rates of plants in many ecosys-

tems will increase markedly if they are fertilized with nitro-

gen. This is a fairly common characteristic of terrestrial and

marine environments, and to a lesser degree of freshwater

ones.

Plants assimilate most of their nitrogen from the soil

environment, as nitrate (NO

) or ammonium (NH

) dis-

solved in the water that is taken up by roots. Some may also

be taken up as gaseous

nitrogen oxides

(such as NO or

) that are absorbed from the atmosphere. In addition,

some plants live in a beneficial

symbiosis

with

microorgan-

isms

that have the ability to fix atmospheric dinitrogen gas

) into ammonia (NH

), which can be used as a nutrient.

In contrast, almost all animals satisfy their nutritional needs

by eating plants or other animals and metabolically breaking

down the organic forms of nitrogen, using the products (such

as amino acids) to synthesize the necessary biochemicals of

the animal. When plants and animals die, microorganisms

active in the detrital cycle metabolize organic nitrogen in

the dead biomass into simpler compounds, ultimately to

ammonium.

The nitrogen cycle has always occurred naturally, but

in modern times some of its aspects have been greatly modi-

fied by human influences. These include the fertilization of

agricultural ecosystems, the dumping of nitrogen-containing

sewage into lakes and other waterbodies, the

emission

gaseous forms of nitrogen into the atmosphere, and the

cultivation of nitrogen-fixing legumes. In some cases, human

effects on nitrogen biogeochemistry result in increased pro-

ductivity of crops, but in other cases serious ecological dam-

ages occur.

Toxic Chemicals in Ecosystems

Some human activities result in the release of toxic

chemicals into the environment, which under certain condi-

tions can pose risks to human health and cause serious dam-

137

ages to ecosystems. These damages are called

pollution

whereas the mere presence of chemicals which cause no

damage in the environment is referred to as contamination.

Biogeochemistry is concerned with the emissions, transfers,

and quantities of these potentially toxic chemicals in the

environment and ecosystems.

Certain chemicals have a great ability to accumulate

in organisms rather than in the non-living (or inorganic)

components of the environment. This tendency is referred to

as bioconcentration. Chemicals that strongly bioconcentrate

include methylmercury and all of the persistent organochlo-

rine compounds, such as

dichlorodiphenyl-trichloroeth-

ane

(DDT),

pentachlorophenol

(PCBs), dioxins, and

fu-

rans

. Methylmercury bioconcentrates because it is rather

tightly bound in certain body organs of animals. The organo-

chlorines bioconcentrate because they are extremely insolu-

ble in water but highly soluble in fats and lipids, which are

abundant in the bodies of organisms but not in non-living

parts of the environment.

In addition, persistent organochlorines tend to occur

in particularly large concentrations in the fat of top predators,

that is, in animals high in the ecological food web, such as

marine mammals, predatory birds, and humans. This hap-

pens because these chemicals are not easily metabolized into

simpler compounds by these animals, so they accumulate in

increasingly larger residues as the animals feed and age.

This phenomenon is known as food-web magnification (or

biomagnification

). Food-web magnification causes chemi-

cals such as DDT to achieve residues of tens or more

parts

per million

(ppm) in the fatty tissues of top predators, even

though they occur in the inorganic environment (such as

water) in concentrations smaller than one part per billion

(ppb). These high body residues can lead to ecotoxicological

problems for top predators, some of which have declined in

abundance because of their exposure to

chlorinated hydro-

carbons

Because a few

species

of plants have an affinity for

potentially toxic elements, they may bioaccumulate them to

extremely high concentrations in their tissues. These plants

are genetically adapted ecotypes which are themselves little

affected by the residues, although they can cause toxicity to

animals that might feed on their biomass. For example, some

plants that live in environments in which the soil contains

a mineral known as serpentine accumulate

nickel

to concen-

trations which may exceed thousands of ppm. Similarly,

some plants (such as locoweed) growing in semi-arid envi-

ronments can accumulate thousands of ppm of selenium in

their tissues, which can poison animals that feed on the

plants.

[Bill Freedman Ph.D.]

Environmental Encyclopedia 3

Biogeography

ESOURCES

OOKS

Atlas, R.M., and R. Bartha. Microbial Ecology. Menlo Park, CA: Benjamin/

Cummings, 1987.

Freedman, B. Environmental Ecology, 2nd ed. San Diego, CA: Academic

Press, 1995.

Schlesinger, W. H. Biogeochemistry: An Analysis of Global Change. San

Diego, CA: Academic Press, 1991.

Smith, R. P. A Primer of Environmental Toxicology. Philadelphia, PA: Lea &

Febiger, 1992.

Biogeography

Biogeography is the study of the spatial distribution of plants

and animals, both today and in the past. Developed during

the course of nineteenth century efforts to explore, map,

and describe the earth, biogeography asks questions about

regional variations in the numbers and kinds of

species

Where do various species occur and why? What physical

and biotic factors limit or extend the range of a species? In

what ways do species disperse (expand their ranges), and

what barriers block their dispersal? How has species distribu-

tion changed over centuries or millennia, as shown in the

fossil record? What controls the makeup of a

biotic commu-

nity

(the combination of species that occur together)? Bioge-

ography is an interdisciplinary science: many other fields,

including paleontology, geology, botany, oceanography, and

climatology, both contribute to biogeography and make use

of ideas developed by biogeographers.

Because physical and biotic environments strongly in-

fluence species distribution, the study of

ecology

is closely

tied to biogeography. Precipitation, temperature ranges,

soil

types, soil or water

salinity

, and insolation (exposure to the

sun) are some elements of the physical

environment

that

control the distribution of plants and animals. Biotic limits

to distribution, constraints imposed by other living things,

are equally important. Species interact in three general ways:

competition

with other species (for space, sunlight, water,

or food), predation (e.g., an owl species relying on rodents

for food), and

mutualism

(e.g., an insect pollenizing a plant

while the plant provides nourishment for the insect). The

presence or absence of a key plant or animal may function as

an important control on another species’ spatial distribution.

Community ecology

, the ways in which an assemblage of

species coexist, is also important. Biotic communities have

a variety of niches, from low to high trophic levels, from

generalist roles to specialized ones. The presence or absence

of species filling one of these roles influences the presence

or survival of a species filling another role.

Two other factors that influence a region’s biotic

composition or the range of a particular species are dis-

persal, or spreading, of a species from one place to another;

138

and barriers, environmental factors that block dispersal.

In some cases a species can extend its range by gradually

colonizing adjacent, hospitable areas. In other cases a

species may cross a barrier, such as a mountain range, an

ocean, or a

desert

, and establish a colony beyond that

barrier. The cattle egret (Bubulcus ibis) exemplifies both

types of movement. Late in the nineteenth century these

birds crossed the formidable barrier of the Atlantic Ocean,

perhaps in a storm, and established a breeding colony in

Brazil. During the past one hundred years this small egret

has found suitable

habitat

and gradually expanded its

range around the coast of South America and into North

America, so that by 1970 it had been seen from southern

Chile to southern Ontario.

The study of dispersal has special significance in

island

biogeography

. The central idea of island biogeography,

proposed in 1967 by R. H. MacArthur and

Edward O.

Wilson

, is that an island has an equilibrium number of

species that increases with the size of the land mass and its

proximity to other islands. Thus species diversity should

be extensive on a large or nearshore island, with enough

complexity to support large carnivores or species with very

specific food or habitat requirements. Conversely, a small

or distant island may support only small populations of a

few species, with little complexity or

niche

specificity in the

biotic community.

Principles of island biogeography have proven useful

in the study of other “island” ecosystems, such as isolated

lakes, small mountain ranges surrounded by deserts, and

insular patches of forest left behind by clearcut

logging

In such threatened areas as the Pacific Northwest and the

Amazonian rain forests, foresters are being urged to leave

larger stands of trees in closer proximity to each other so

that species at high trophic levels and those with specialized

food or habitat requirements (e.g., Northern spotted owls

and Amazonian monkeys) might survive. In such areas as

Yellowstone National Park

, which national policy desig-

nates as an insular unit of habitat, the importance of adjacent

habitat has received increased consideration. Recognition

that clearcuts and farmland constitute barriers has led some

planners to establish forest corridors to aid dispersal, enhance

genetic diversity, and maintain biotic complexity in unsettled

islands of natural habitat.

[Mary Ann Cunningham Ph.D.]

ESOURCES

OOKS

Brown, J. H., and A. C. Gibson. Biogeography. St. Louis: Mosby, 1983.

MacArthur, R. H., and E. O. Wilson. The Theory of Island Biogeography.

Vol. 1, Monographs in Population Biology. Princeton: Princeton University

Press, 1967.

Environmental Encyclopedia 3

Bioindicator

Biohydrometallurgy

Biohydrometallurgy is a technique by which

microorgan-

isms

are used to recover certain metals from ores. The tech-

nique was first used over 300 years ago to extract

copper

from low-grade ores. In recent years, its use has been ex-

tended to the recovery of

uranium

and gold, and scientist

believe that it will eventually be applied to the recovery of

other metals such as

lead

nickel

, and zinc.

In most cases, biohydrometallurgy is employed when

conventional mining procedures are too expensive or ineffec-

tive in recovering a metal. For example, dumps of unwanted

waste materials are created when copper is mined by tradi-

tional methods. These wastes consist primarily of rock,

gravel, sand, and other materials that are removed in order

to reach the metal ore itself. But the wastes also contain

very low concentrations (less than 0.5%) of copper ore.

Until recently, the concentrations of copper ore in a

dump were too low to have any economic value. The cost

of collecting the ore was much greater than the value of the

copper extracted. But, as richer sources of copper ore are

used up, low grade reserves (like dumps) become more attrac-

tive to mining companies. At this point, biohydrometallurgy

can be used to leach out the very small quantities of ore

remaining in waste materials.

The extraction of copper by means of biohydrometal-

lurgy involves two types of reactions. In the first, microorgan-

isms operate directly on compounds of copper. In the second,

microorganisms operate on metallic compounds other than

those of copper. These metallic compounds are then con-

verted into forms which can, in turn, react with copper ores.

The use of biohydrometallurgical techniques on a cop-

per ore waste dump typically begins by spraying the dump

with dilute sulfuric

acid

. As the acid seeps into the dump,

it creates an

environment

favorable to the growth of acid-

loving microorganisms that attack copper ores. As the micro-

organisms metabolize the ores, they convert copper from an

insoluble to a soluble form. Soluble copper is then leached

out of the dump with sulfuric acid. It is recovered when the

solution is pumped out to a recovery tank.

A second reaction occurs within the dump. Microor-

ganisms also convert ferrous iron (Fe

) in ores such as pyrite

(FeS

) to ferric iron (Fe

). The ferric iron, in turn, oxidizes

copper in the dump from an insoluble to a soluble form.

The mechanism described here is a highly efficient

one. As microorganisms act on copper and iron compounds,

they produce sulfuric acid as a by-product, thus enriching

the environment in which they live. Ferric iron reduces and

oxidizes copper at the same time, making the copper available

for attack by microorganisms once again.

A number of microorganisms have been used in biohy-

drometallurgy. One of the most effective for the

leaching

139

of copper is Thiobacillus ferrooxidans. Research is now being

conducted on the development of genetically engineered

microorganisms that can be used in the recovery of copper

and other metals.

The two other metals for which biohydrometallurgy

seems to be most useful are uranium and gold. Waste dumps

in South Africa and Canada have been treated to convert

insoluble forms of uranium to soluble forms, allowing recov-

ery by a method similar to that used with copper. In the

treatment of gold ores, biohydrometallurgy is used in a pre-

treatment step prior to the conventional conversion of the

metal to a cyanide-complex. The first commercial plants for

the biohydrometallurgical treatment of gold ores are now in

operations in South Africa and Zimbabwe.

[David E. Newton]

ESOURCES

OOKS

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

McGraw-Hill, 1992.

Rossi, G. Biohydrometallurgy. New York: McGraw-Hill, 1990.

Bioindicator

A bioindicator is a plant or animal

species

that is known

to be particularly tolerant or sensitive to

pollution

. Based

on the known association of an organism with a particular

type or intensity of pollution, the presence of the organism

can be used as a tool to indicate polluted conditions relative

to unimpacted reference conditions. Sometimes a set of spe-

cies or the structure and function of an entire

biological

community

may function as a bioindicator. In assessing the

impacts of pollution, bioindicators are frequently used to

evaluate the “health” of an impacted

ecosystem

relative to

a reference area or reference conditions. Field-based, site-

specific environmental evaluations based on the bioindicator

approach generally are complemented with laboratory stud-

ies of toxicity testing and

bioassay

experiments.

The use of individual species or a community structure

as bioindicators involves the identification, classification and

quantification of biota in the affected area. While many

species are in use, the most widely used biological communi-

ties are the benthic macroinvertebrates. These are the seden-

tary and crawling worms and insect larvae that reside in the

bottom sediments of aquatic systems such as lake and river

bottoms. The bottom sediments usually contain most of the

pollutants introduced into an aquatic system. Since these

macroinvertebrates have limited mobility, they are continu-

ally exposed to the highest concentrations of pollutants in

the system. Therefore, this benthic community is an ideal

Environmental Encyclopedia 3

Biological community

bioindicator: stationary, localized and exposed to maximum

pollutant concentrations within a specific location.

Often, alterations in community structure due to pol-

lution include a change from a more diverse to a less diverse

community with fewer species or taxa. The indicator com-

munity may also be composed mostly of species that are

tolerant of or adapted to polluted conditions and pollution-

sensitive species that are present upstream may be absent in

the impacted zones. However, depending on the type of

pollutant, the abundance of the pollution-tolerant species

may be very high and, therefore, the size of the benthic

community may be similar to or exceed the reference com-

munity upstream. This is common in cases where pollution

from sewage discharges adds organic matter that provides

food for some of the tolerant benthic species. In the case of

toxic chemical (e.g.,

heavy metals

, organic compounds)

pollution, the benthic community may show an overall re-

duction both in diversity and abundance.

Tubificid worms are an example of pollution-tolerant

indicator organisms. These worms live in the bottom sedi-

ments of streams and lakes and are highly tolerant of the

kind of pollution that results from sewage discharges. In a

river polluted by

wastewater discharge

from a

sewage

treatment

plant, it is common to see a large increase in

the number of tubificid worms in the stream sediments

immediately downstream of the discharge. Upstream of the

discharge, the number of these worms is much lower, re-

flecting the cleaner conditions. Further downstream, as the

discharge is diluted, the number of tubificid worms again

decreases to a level similar to the upstream portions of the

river. Large populations of these worms dramatically demon-

strate that pollution is present, and the location of these

populations may also indicate the general area where the

pollution enters the

environment

Alternatively, pollution-intolerant organisms can also

be used to indicate polluted conditions. The larvae of may-

flies live in stream sediments and are known to be particularly

sensitive to pollution. In a river receiving wastewater dis-

charge, mayflies show a pattern opposite to that of the tubi-

ficid worms. The mayfly larvae are normally present in large

numbers above the discharge point, decrease or disappear at

the discharge point (just where the tubificid worms are most

abundant) and reappear further downstream as the effects

of the discharge are diluted. In this case, the mayflies are

pollution-sensitive indicator organisms and their absence

serves as the indication of pollution. Similar examples of

indicator organisms can be found among plants, fishes and

other biological groups. Giant reedgrass (Phragmites austra-

lis) is a common marsh plant that is typically indicative of

disturbed conditions in

wetlands

. Among fish, disturbed

conditions may be indicated by the disappearance of sensitive

species like trout which require clear, cold waters to thrive.

140

The usefulness of indicator organisms is unquestion-

able but limited. While their presence or absence provides

a reliable general picture of polluted conditions, it is often

difficult to identify clearly the exact sources of pollution,

especially in areas with multiple sources of pollution. In the

sediments of New York Harbor, for example, pollution-

tolerant insect larvae are overwhelmingly dominant. How-

ever, it is impossible to attribute the large larval populations

to just one of the numerous possible sources of pollution

in this area which include ship traffic, sewage discharge,

industrial discharge, and

storm runoff

. As more is learned

about the physiology and life-history of an

indicator orga-

nism

and its response to different types of pollution, it may

be possible to draw more specific conclusions.

Although the two terms are sometimes used inter-

changeably, indicator organisms should not be confused with

monitor organisms (also called biomonitors) which are

organisms that bioaccumulate toxic substances present in

trace amounts in the environment. For example, when it is

difficult to measure directly the low concentrations of a

pollutant in water, chemical analysis of shellfish tissues from

that location may show much higher, easily detected concen-

trations of that pollutant. In this case, the shellfish is used

to monitor the level of the long-term presence of that pollut-

ant in the area.

In the environmental field, bioindicators are com-

monly used in field investigations of contaminated sites to

document impacts on the biological community and ecosys-

tem. These studies are then followed up with focused labora-

tory tests to pinpoint the source of toxicity or stress. After

clean-up and remedial actions have been implemented at a

site, bioindicators are also used to track the effectiveness of

the

remediation

activity. In the future, bioindicators may

be used more widely as investigative and decision-making

tools from the initial pollution and impact assessment stage

to the remediation and post-remediation monitoring stages.

[Usha Vedagiri]

ESOURCES

OOKS

Connell, D. W., and G. J. Miller. Chemistry and Ecotoxicology of Pollution.

New York: Wiley-Interscience, 1984.

Biological community

A biological community is an association or assemblage of

populations of organisms living in a localized area or

habitat

The community is a level of organization incorporating indi-

vidual organisms,

species

, and populations. A population

is an assemblage of one species, and the community is a

collage of one or more populations. Communities may be

Environmental Encyclopedia 3

Biological methylation

large or small, ranging from the microscopic to the level of

biome

and

biosphere

“Community,” as contrasted conceptually to

ecosys-

tem

, does not necessarily include consideration of the

physical

environment

or the habitat of a particular group

of organisms, though it is of course impossible to under-

stand fully the dynamics of a community without reference

to the resources on which it exists. The term ecosystem

was coined to incorporate study of a community together

with its physical environment. Still, communities are adap-

tive systems, inseparable from and evolving in response

to changing environmental conditions. So, the supply and

availability of resources in the environment and also time

are considerations in the dynamics of community structure

and relationships. Individual communities may be relatively

stable or in constant flux. Actual equilibrium may never

exist but, even in approximation, it must be viewed as a

dynamic state—the community in constant, subtle flux

and change.

Biological communities are “interactional fields” char-

acterized by a complicated set of interactions among

complex assemblages, both within the locale and from

without—including trophic relationships, the “who eats

who” of energy exchanges. Interactions may be proximal

or between locales (close by or quite widely separated),

including intensive, extensive, or limited exchanges with

the outside world. Organisms in communities interact both

functionally and spatially or locationally, both “horizontally”

and “vertically,” interactions often independent of each

other and not reducible to one or the other. Not all

organisms necessarily interact with all the others, some

may be almost totally uncoupled from some of the others

and coexist relatively independently.

Most questions in

community ecology

focus on

the “existence, importance, looseness, transience, and

contingency of interactions.” The degree to which these

interactions result in meaningful biological patterns is

still an open question—though particular communities

are usually identified by some pattern of interactions, if

only to set them off from others for the purposes of

scientific study.

[Gerald L. Young]

ESOURCES

OOKS

Roughgarden, J. The Structure and Assembly of Communities. In Perspectives

in Ecological Theory, edited by J. Roughgarden, R. M. May, and S. A.

Levin. Princeton: Princeton University Press, 1989.

Strong, D. R., Jr., et. al., eds. Ecological Communities: Conceptual Issues and

the Evidence. Princeton: Princeton University Press, 1984.

141

Taylor, P. J. “Community.” In Keywords in Evolutionary Biology, edited by

E. Keller and E. Lloyd. Cambridge: Harvard University Press, 1991.

ERIODICALS

Drake, J. A. “The Mechanics of Community Assembly and Succession.”

Journal of Theoretical Biology 147 (1990): 213–233.

Richardson, J. L. “The Organismic Community: Resilience of an Embattled

Ecological Concept.” BioScience 30 (1988): 465–471.

Biological fertility

The number of offspring produced by a female organism.

In a population, biological fertility is measured as the general

fertility rate (the birth rate multiplied by the number of

sexually productive females) or as the total fertility rate (the

lifetime average number of offspring per female). General

dictionaries list fertility and

fecundity

as synonyms for re-

productive fruitfulness. In

population biology

, biological

fertility refers to the number of offspring actually produced,

while fecundity is merely the biological ability to reproduce.

Fecund individuals that fail to mate do not produce offspring

(that is, are not biologically fertile), and do not contribute

population growth

Biological integrity

see

Ecological integrity

Biological magnification

see

Biomagnification

Biological methylation

The process by which a methyl radical (-CH

) is chemically

combined with some other substance through the action of a

living organism. One of the most environmentally important

examples of this process is the

methylation

mercury

the sediments of lakes, rivers, and other bodies of water.

Elementary mercury and many of its inorganic compounds

have relatively low toxicity because they are insoluble. How-

ever, in sediments, bacteria can convert mercury to an organic

form, methylmercury, that is soluble in fat. When ingested

by animals, methylmercury accumulates in body fat and ex-

erts highly toxic, sometimes fatal, effects.

Biological oxygen demand

see

Biochemical oxygen demand

Environmental Encyclopedia 3

Biological Resources Division

Created to assess, monitor, and research biological resources

in United States, the Biological Resources Division (BRD)

of the United States

Geological Survey

(USGS) is the

non-regulatory biological research component of the United

States Department of the Interior. First created in 1994 as

the National Biological Survey (NBS), an independent

agency within the

U.S. Department of the Interior

, the

NBS was merged with the USGS (also part of the Interior

Department) in 1996.

The BRD is the principal biological research and mon-

itoring agency of the federal government. It is responsible

for gathering, analyzing, and disseminating biological infor-

mation in order to support sound management and steward-

ship of nation’s biological and

natural resources

. It is also

directed to foster understanding of biological systems and

their benefits to society, and to make biological information

available to the public. Although it was created mainly on

the impetus of environmental and scientific organizations,

the BRD also supports commercial and economic interests

in that it seeks to identify opportunities for sustainable re-

source use. Agriculture and

biotechnology

are among the

industries that stand to benefit from BRD research on new

sources of food, fiber, and medicines.

Because it is independent of regulatory agencies—

which are responsible for enforcing laws—the BRD has

no formal regulatory, management, or enforcement roles.

Therefore the BRD does not enforce laws such as the

Endan-

gered Species Act

. Instead the BRD is responsible for gath-

ering data that are scientifically sound and unbiased. The

BRD also fosters public-private cooperation. For example,

it worked with the International Paper Company in Alabama

to develop a management plan for two

species

of pitcher

plants found on company land that were candidates for the

Endangered Species

List. If it succeeds, this management

plan will both preserve the pitcher plant populations—pre-

venting the legal complications of having it listed as a feder-

ally endangered species—and allow continued judicious use

of the land and resources.

The Biological Resources Division of the USGS was

created in 1994 as an independent agency with the name

National Biological Survey. The Survey was established on

November 11, 1994, on the recommendations of President

Bill Clinton and Interior Secretary Bruce Babbit. Renamed

the National Biological Service (NBS) shortly after its cre-

ation, the agency was created by combining the biological

research, inventory, and monitoring programs of seven agen-

cies within the Department of the Interior. Built on the

model of the Geological Survey, the NBS was established

to provide accurate baseline data about ecosystems and spe-

cies in United States territory. The mission of the NBS

142

was to provide information to support sound stewardship of

natural resources on public lands under the administration

of the Department of the Interior. Part of its mission was

also to foster cooperation among other entities involved in

managing, monitoring, and researching natural resources.

On October 1, 1996, the NBS was renamed the Biological

Resources Division and merged with the United States Geo-

logical Survey. The USGS-BRD retains the research and

information provision mandates of the NBS. Appointed as

the first NBS/BRD director was H. Ronald Pulliam, a pro-

fessor and research ecologist from of the Institute of Ecology

and the University of Georgia in Athens.

The National Biological Service had a predecessor in

the Bureau of Biological Survey, which operated as part

of the Department of Agriculture from 1885–1939. The

Bureau’s first director, C. Hart Merriam, revolutionized bio-

logical collection techniques and in 15 years nearly quadru-

pled the number of known American mammal species. In

1939, the Bureau was transferred to the Department of the

Interior, where it was the predecessor to the

Fish and Wild-

life Service

. After its transfer to the Department of the

Interior, the Bureau of Biological Survey’s baseline data gath-

ering and survey functions gradually diminished. The Fish

and Wildlife Service now has regulatory and management

responsibilities as well as research programs.

In recent years the need for a biological survey, and

especially for the production of reliable baseline data, has

resurfaced. The resurgence of interest in baseline data results

in part from an interest in managing ecosystems, with a

focus on stewardship and

ecosystem

restoration, in place

of previous emphasis on individual species management.

Managing and restoring ecosystems requires basic data and

information on biological indicators, which are often un-

available. Interest in threatened and endangered species, and

public participation in environmental organizations probably

also contributed to the widespread support for establishing

a biological survey.

The BRD is important because it is the only federal

agency whose principal mission is to perform basic scientific,

biological, and ecological research. As an explicitly scientific

research body, the BRD works to incorporate current ecolog-

ical theory in its research and monitoring programs. Central

to the BRD’s mission are ideas such as long-term steward-

ship of resources, maintaining

biodiversity

, identifying eco-

logical services of biological resources, anticipating

climate

change, and restoring populations and habitats. Because of

its emphasis on basic research the BRD can address current

scientific themes that pertain to public policy such as fire

ecology,

endocrine disruptors

(

chemicals

such as penta-

chlorophenols [PCBs] that interfere with endocrine and re-

productive functions in animals), ecological roles of

wet-

lands

, and

habitat

restoration. The primary purpose of

Environmental Encyclopedia 3

Bioluminescence

this research activity is to provide land managers, especially

within the Department of the Interior, with sound informa-

tion to guide their management policies.

The BRD has two broad categories of research activi-

ties. One focus is on species for which the Department

of Interior has trust responsibilities, including endangered

species, marine mammals, migratory birds, and anadromous

fish such as

salmon

. Research on these organisms involves

studies of physiology, behavior, population dynamics, and

mortality

. The second general focus is on ecosystems. This

class of research is directed at using experimentation,

model-

ing

, and observation to produce practical information con-

cerning the complex interactions and functions of ecosys-

tems, as well as human-induced changes in ecosystems.

In addition to these ecological research questions, the

BRD is mandated to perform basic classification, mapping,

and description functions. The division is responsible for

classifying and mapping species within the United States,

as well as prospecting for new species. It is also directed to

develop a standard classification system for ecological units,

biological indicators for

ecosystem health

, protocols for

managing

pollution

, and guidelines for ecosystem resto-

ration.

Part of this basic assessment function is a series of

National Status and Trends Reports, to be released by the

BRD every two years. These reports are to assess the health

of biological resources and to report trends in their decline

or improvement. The first two National Status and Trends

Reports were released in 1995 and 1997. The 1995 report

included more than 200 contributions on monitoring and

population trends for plant, invertebrate, and vertebrate spe-

cies, as well as summaries on the status of several biological

communities and ecosystems. The 1997 report, published

in two volumes, discusses factors such as natural processes,

harvest exploitation, contaminants,

land use

, water use,

nonindigenous species, and climate change that affect eco-

systems in the United States. This status report also includes

a major section discussing marine biological resources.

The USGS-BRD also provides a nationwide coordi-

nated research agenda and a set of priorities for biological

research. For example, it has undertaken a set of coordinated

regional studies of the wide-ranging biological and ecological

impacts of wetland distributions in Colorado, California,

Texas, and other regions of the United States. Collectively

these studies can provide a picture of nationwide trends and

conditions, as well as producing coordinated information

on restoration techniques, biodiversity issues, and biological

indicators, at the same time as regional wetland problems

are being addressed. Similar sets of coordinated studies have

begun concerning the effects of endocrine-disrupting chemi-

cals in the

environment

and on the use of prescribed fire

as a management technique in a variety of ecosystems.

143

One of the principal mandates of the BRD is to distrib-

ute information. Free sharing of information is intended to

maximize the usefulness of research findings. Part of the

information sharing program includes substantial use of the

Internet to distribute publications. Even the book-size Na-

tional Status and Trends Reports are being published online

to facilitate easy public access to their findings.

In addition to performing its own research the BRD

provides coordination and a network of communication be-

tween federal agencies, state governments, universities, mu-

seums, and private

conservation

organizations. The Na-

tional Partnership for Biological Survey, coordinated by the

BRD, provides a network for sharing information and tech-

nology between federal, state, and other agencies. Partici-

pants in the Partnership include the United States

Forest

Service

, the Natural Resources Conservation Service, the

National Oceanic and Atmospheric Administration

, the

Environmental Protection Agency

, the National Science

Foundation, the Department of Defense, and the

Army

Corps of Engineers

, as well as the Natural Heritage data

centers and programs maintained by many states. The net-

work of Natural Heritage programs is coordinated by

The

Nature Conservancy

, a private organization dedicated to

preserving habitat and species diversity. Also included in the

Partnership are museums and universities nationwide that

serve as repositories of information on biological resources

and that conduct biological research, a range of non-govern-

mental organizations, international conservation and re-

search groups, Native American groups, private land holders,

and resource user groups.

[Mary Ann Cunningham Ph.D.]

ESOURCES

THER

Biological Resources Division. Biological Resources Strategic Science Plan.

Washington, D.C.: Government Printing Office, 1996.

National Biological Service. Our Living Resources. Washington, DC: Gov-

ernment Printing Office, 1995.

RGANIZATIONS

US Geological Survey (USGS), Biological Resources Division (BRD),

Western Regional Office (WRO), 909 First Ave., Suite #800, Seattle, WA

USA 98104 (206) 220-4600, Fax: (206) 220-4624, Email:

brd_wro@usgs.gov, <http://biology.usgs.gov>

Biological treatment

see

Bioremediation

Bioluminescence

Bioluminescence ("living light") is the production of light

by living organisms through a biochemical reaction. The

Environmental Encyclopedia 3

Biomagnification

general reaction involves a substrate called luciferin and an

enzyme

called luciferase, and requires oxygen. Specifically,

luciferin is oxidized by luciferase and the chemical energy

produced is transformed into light energy. In

nature

, biolu-

minescence is fairly widespread among a diverse group of

organisms such as bacteria,

fungi

, sponges, jellyfish, mol-

lusks, crustaceans, some worms, fireflies, and fish. It is totally

lacking in vertebrate animals. Fireflies are probably the most

commonly recognized examples of bioluminescent organ-

isms, using the emitted light for mate recognition.

Biomagnification

The

bioaccumulation

chemicals

in organisms beyond

the concentration expected if the chemical was in equilibrium

between the organism and its surroundings. Biomagnifica-

tion can occur in both terrestrial and aquatic environments,

but it is generally used in relation to aquatic situations. Most

often, biomagnification occurs in the higher trophic levels

of the

food chain/web

, where exposure to chemicals takes

place mostly through food consumption rather than water

uptake.

Biomagnification is a specific case of bioaccumulation

and is different from bioconcentration. Bioaccumulation de-

scribes the accumulation of contaminants in the tissue of

organisms. Typical examples of this include the elevated

levels of many chlorinated pesticides and

mercury

in fish

tissue. Bioconcentration is used to describe the concentration

of a chemical in an organism from water uptake alone. This

is quantitatively described by the bioconcentration factor, or

BCF, which is the chemical concentration in tissue divided

by the chemical concentration in water, expressed in equiva-

lent units, at equilibrium. The vast majority of chemicals that

bioaccumulate are aromatic organic compounds, particularly

those with

chlorine

substituents. For organic compounds,

the mechanism of bioaccumulation is thought to be the

partitioning or solubilization of chemical into the lipids of

the organism. Thus the BCF should be proportional to

the lipophilicity of the chemical, which is described by the

octanol-water partition coefficient, Kow. The latter is a

physical-chemical property of the compound describing its

relative solubility in an organic phase and is the ratio of its

solubility in octanol to its solubility in water at equilibrium.

It is constant at a given temperature. If one assumes that a

chemical’s solubility in octanol is similar to its solubility in

lipid, then we can approximate the lipid-normalized BCF

as equal to the Kow. This assumption has been shown to

be a reasonable first approximation for most chemicals accu-

mulation in fish tissue.

144

However, animals are exposed to contaminants by

other routes in addition to passive partitioning from water.

For instance, fish can take up chemicals from the food they

eat. It has been noted in field collections that for certain

chemicals, the observed fish-water ratio (BCF) is signifi-

cantly greater than the theoretical BCF, based on Kow. This

indicates that the chemical has accumulated to a greater

extent than its equilibrium concentration. This is defined as

biomagnification. This condition has been documented in

aquatic animals, including fish, shellfish,

seals and sea

lions

whales

, and otters, and in birds, mink, rodents, and

humans in both laboratory and field studies.

The biomagnification factor, BMF, is usually de-

scribed as the ratio of the observed lipid-normalized BCF

to Kow, which is the theoretical lipid-normalized BCF.

This is equivalent to the multiplication factor above the

equilibrium concentration. If this ratio is equal to or less

than one, then the compound has not biomagnified. If the

ratio is greater than one, then the chemicals biomagnified

by that factor. For instance, if a chemical’s Kow were

100,000, then its lipid normalized BCF should be 100,000

if the chemical were in equilibrium in the organism’s lipids.

If the fish tissue concentration (normalized to lipids) were

500,000, then the chemical would be said to have biomagni-

fied by a factor of five.

Biomagnification in the aquatic food chain often leads

to biomagnification in terrestrial food chains, particularly in

the case of bird and

wildlife

populations that feed on fish.

Consider the following example that demonstrates the re-

sults of biomagnification. The concentrations of the insecti-

cide dieldrin in various trophic levels are determined to be

the following: water, 0.1 ng/L;

phytoplankton

, 100 ng/g

lipid;

zooplankton

, 200 ng/g lipid; fish, 600 ng/g lipid;

terns, 800 ng/g lipid. If the Kow were equal to one million,

then the phytoplankton would be in equilibrium with the

water, but the zooplankton would have magnified the com-

pound by a factor of 2, the fish by a factor of 6, and the

terns by a factor of 8.

The mechanism of biomagnification is not completely

understood. To achieve a concentration of a chemical greater

than its equilibrium value indicates that the elimination rate

is slower than for chemicals that reach equilibrium. Transfer

efficiencies of the chemical would affect the relative ratio of

uptake and elimination. There are many factors that control

the uptake and elimination of a chemical from the consump-

tion of contaminated food, and these include factors specific

to the chemical as well as factors specific to the organism.

The chemical properties include solubility, Kow, molecular

weight and volume, and diffusion rates between organism

gut, blood, and lipid pools. The organism properties include

the feeding rate, diet preferences, assimilation rate into the

gut, rate of chemical’s

metabolism

, rate of egestion, and

Environmental Encyclopedia 3

Biomass

Biomagnification of the pesticide DDT in the

food chain. DDT travels from runoff up through

the food chain, accumulating in all exposed

species. (McGraw-Hill Inc. Reproduced by permission.)

rate of organism growth. It is thought that the chemical’s

properties control whether biomagnification will occur, and

that it is the transfer rate from lipid to blood that allows

the chemical to attain a lipid concentration greater than its

equilibrium value. Thus it follows that the chemicals that

biomagnify have similar properties. They typically are or-

ganic; they have molecular weights between 200 and 600

daltons; they have Kows between 10,000 and 10 million;

they are resistant to metabolism by the organism; they are

non-ionic, neutral compounds; and they have molecular vol-

umes between 260 and 760 cubic angstroms, a cross sectional

width of less than 9.5 angstoms and a molecular surface

area between 200 and 460 square angstroms. The latter

dimensions allow them to more easily pass through lipid

bilayers into cells but perhaps do not allow them to leave

the cell easily due to their high lipophilicity. Since this dis-

equilibrium would occur at each

trophic level

, it results in

more and more biomagnification at each higher trophic level.

Because humans occupy a very high trophic level, we are

particularly vulnerable to adverse health effects as a result

of exposure to chemicals that biomagnify.

[Deborah L. Swackhammer]

145

ESOURCES

OOKS

Connell, D. W. Bioaccumulation of Xenobiotic Compounds. Boca Raton:

CRC Press, 1990.

ERIODICALS

Bierman Jr., V. J. “Equilibrium Partitioning and Biomagnification of Or-

ganic Chemicals in Benthic Animals.” Environmental Science and Technology

24 (September 1990); 1407–12.

Sijm, D., W. Seinen, and A. Opperhuizen. “Life Cycle Biomagnification

Study in Fish.” Environmental Science and Technology 26 (November 1992):

2162–74.

Biomass

Biomass is a measure of the amount of biological substance

minus its water content found at a given time and place on

the earth’s surface. Although sometimes defined strictly as

living material, in actual practice the term often refers to

living organisms, or parts of living organisms, as well as waste

products or non-decomposed remains. It is a distinguishing

feature of ecological systems and is usually presented as

biomass density in units of dry weight per unit area. The

term is somewhat imprecise in that it includes autotrophic

plants, referred to as phytomass, heterotrophic

microbes

and animal material, or zoomass. In most settings, phytomass

is by far the most important component. A square meter of

the planet’s land area has, on average, about 22.05 – 26.46

lb (10 – 12 kg) of phytomass, although values may vary

widely depending on the type of

biome

. Tropical rain forests

average about 45 kg/m

while a

desert

biome may have a

value near zero. The global average for heterotrophic biomass

is approximately 0.1 kg/m

, and the average for human bio-

mass has been estimated at 0.5 g/m

if permanently glaciated

areas are excluded.

The nature of biomass varies widely. Density of fresh

material ranges from a low of 0.14 g/cm

for floats of aquatic

plants to values greater that 1 g/cm

for very dense hardwood.

The water content of fresh material may be as low as 5% in

mature seeds or as high as 95% in fruits and young shoots.

Water levels for living plants and animals run from 50 to

80%, depending on the

species

, season, and growing condi-

tions. To insure a uniform basis for comparison, biomass

samples are dried at 221°F (105°C) until they reach a con-

stant weight.

Organic compounds typically constitute about 95% by

weight of the total biomass, and nonvolatile residue, or ash,

about 5%.

Carbon

is the principle element in biomass and

usually represents about 45% of the total. An exception

occurs in species that incorporate large amounts of inorganic

elements such as silicon or calcium, in which case the carbon

content may be much lower and nonvolatile residue several

times higher. Another exception is found in tissues rich in

Environmental Encyclopedia 3

Biomass fuel

lipids (oil or fat), where the carbon content may reach values

as high as 70%.

Photosynthesis

is the principle agent for biomass

production. Light energy is used by chlorophyll-containing

green plants to remove (or fix)

carbon dioxide

from the

atmosphere

and convert it to energy rich organic com-

pounds or biomass. It has been estimated that on the face

of the earth approximately 200 billion tons of carbon dioxide

are converted to biomass each year. Carbohydrates are usually

the primary constituent of biomass, and cellulose is the single

most important component. Starches are also important and

predominate in storage organs such as tubers and rhizomes.

Sugars reach high levels in fruits and in plants such as sugar

cane and sugar beet. Lignin is a very significant non-carbohy-

drate constituent of woody plant biomass.

[Douglas C. Pratt]

ESOURCES

OOKS

Lieth, H. F. H. Patterns of Primary Production in the Biosphere. Stroudsburg,

PA: Dowden, Hutchinson, and Ross, distributed by Academic Press, 1978.

Smil, V. Biomass Energies: Resources, Links, Constraints. New York: Plenum

Press, 1983.

Biomass fuel

biomass

fuel is an energy source derived from living

organisms. Most commonly it is plant residue, harvested,

dried and burned, or further processed into solid, liquid, or

gaseous fuels. The most familiar and widely used biomass

fuel is wood. Agricultural waste, including materials such as

the cereal straw, seed hulls, corn stalks and cobs, is also a

significant source. Native shrubs and herbaceous plants are

potential sources.

Animal waste

, although much less abun-

dant overall, is a bountiful source in some areas.

Wood accounted for 25% of all energy used in the

United States at the beginning of this century. With in-

creased use of

fossil fuels

, its significance rapidly declined.

By 1976, only 1–2% of United States energy was supplied

by wood, and burning of tree wastes by the forest products

industry accounted for most of it. Although the same trend

has been evident in all industrialized countries, the decline

has not been as dramatic everywhere. Sweden, for instance,

still meets 8% of its energy needs with wood, and Fin-

land, 15%.

Globally, it is estimated that biomass supplies about 6

or 7% of total energy, and it continues to be a very important

energy source for many developing countries. In the last 15–

20 years, interest in biomass has greatly increased even in

countries where its use has drastically declined. In the United

States rising fuel prices led to a large increase in the use of

146

wood-burning stoves and furnaces for space heating. Im-

pending fossil fuel shortages have greatly increased research

on its use in the United States and elsewhere. Because bio-

mass is a potentially renewable resource, it is recognized as

a possible replacement of

petroleum

and

natural gas

Historically, burning has been the primary mode for

using biomass, but because of its large water content it must

be dried to burn effectively. In the field, the energy of the

sun may be all that is needed to sufficiently lower its water

level. When this is not sufficient, another energy source may

be needed.

Biomass is not as concentrated an energy source as

most fossil fuels even when it is thoroughly dry. Its density

may be increased by milling and compressing dried residues.

The resulting briquettes or pellets are also easier to handle,

store, and transport. Compression has been used with a

variety of materials including crop residues, herbaceous na-

tive plant material, sawdust, and other forest wastes.

Solid fuels are not as convenient or versatile as liquids

or gases, and this is a drawback to the direct use of biomass.

Fortunately, a number of techniques are known for con-

verting it to liquid or gaseous forms.

Partial

combustion

is one method. In this procedure,

biomass is burned in an

environment

with restricted oxygen.

Carbon monoxide

and

hydrogen

are formed instead of

carbon dioxide

and water. This mixture is called synthetic

gas or “syngas.” It can serve as fuel although its energy

content is lower than natural gas (

methane

). Syngas may

also be converted to

methanol

, a one carbon-alcohol that

can be used as a

transportation

fuel. Because methanol is

a liquid, it is easy to store and transport.

Anaerobic digestion

is another method for forming

gases from biomass. It uses

microorganisms

, in the absence

of oxygen, to convert organic materials to methane. This

method is particularly suitable for animal and human waste.

Animal

feedlots

faced with disposal problems may install

microbial gasifiers to convert waste to gaseous fuel used to

heat farm buildings or generate electricity.

For materials rich in starch and sugar, fermentation

is an attractive alternative. Through

acid

hydrolysis or enzy-

matic digestion, starch can be extracted and converted to

sugars. Sugars can be fermented to produce

ethanol

, a liquid

biofuel with many potential uses.

Cellulose is the single most important component of

plant biomass. Like starch, it is made of linked sugar compo-

nents that may be easily fermented when separated from the

cellulose polymer. The complex structure of cellulose makes

separation difficult, but enzymatic means are being devel-

oped to do so. Perfection of this technology will create a

large potential for ethanol production using plant materials

that are not human foods.