civ a.xml McGraw-Hill Dictionary of Environmental Science June 2, 2003 19:52
McGraw-Hill
Dictionary of
Environmental
Science
McGraw-Hill
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civ a.xml McGraw-Hill Dictionary of Environmental Science June 2, 2003 19:52
Contents
Preface v
Staff vi
How to Use the Dictionary vii
Fields and Their Scope ix
Pronunciation Key xii
A-Z Terms 1-465
Appendix 467
Base units of the International System 469
Derived units of the International System 470
Prefixes for units in the International System 472
Some common units defined in terms of SI units 473
Equivalents of commonly used units for the U.S.
Customary System and the metric system 474
Conversion factors for the U.S. Customary System,
metric system, and International System 475
The chemical elements 479
Periodic table 480
Classification of living organisms 481
Soil orders 490

dictionaries and glossaries; the McGraw-Hill Dictionary of Environmental Science,
however, aims to provide the user with the convenience of a single,
comprehensive reference. It is the editors’ hope that it will serve the needs of
scientists, engineers, students, teachers, librarians, and writers for high-quality
information, and that it will contribute to scientific literacy and communication.
Mark D. Licker
Publisher
v
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civ a.xml McGraw-Hill Dictionary of Environmental Science June 2, 2003 19:52
Staff
Mark D. Licker, Publisher—Science
Elizabeth Geller, Managing Editor
Jonathan Weil, Senior Staff Editor
David Blumel, Staff Editor
Alyssa Rappaport, Staff Editor
Charles Wagner, Digital Content Manager
Renee Taylor, Editorial Assistant
Roger Kasunic, Vice President—Editing, Design, and Production
Joe Faulk, Editing Manager
Frank Kotowski, Jr., Senior Editing Supervisor
Ron Lane, Art Director
Thomas G. Kowalczyk, Production Manager
Pamela A. Pelton, Senior Production Supervisor
Henry F. Beechhold, Pronunciation Editor
Professor Emeritus of English
Former Chairman, Linguistics Program
The College of New Jersey
Trenton, New Jersey
vi

also made from variant spellings, acronyms, abbreviations, and symbols.
aestivation See estivation.
ED
50
See effective dose 50.
PVC See polyvinyl chloride.
ALSO KNOWN AS . . . , etc. A definition may conclude with a mention of
a synonym of the term, a variant spelling, an abbreviation for the term, or
vii
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civ a.xml McGraw-Hill Dictionary of Environmental Science June 2, 2003 19:52
other such information, introduced by “Also known as ,”“Also spelled ,”
“Abbreviated ,”“Symbolized . . . ,” “Derived from ,”When a term has more
than one definition, the positioning of any of these phrases conveys the extent
of applicability. For example:
term [
ECOL] 1. Definition. Also known as synonym. 2. Definition.
Symbolized T.
In the above arrangement, “Also known as. . . ” applies only to the first definition;
“Symbolized. . . ” applies only to the second definition.
term [
ECOL] 1. Definition. 2. Definition. [GEN] Definition. Also known
as synonym.
In the above arrangement, “Also known as . . . ” applies only to the second field.
term [
ECOL] Also known as synonym. 1. Definition. 2. Defini-
tion. [
GEN] Definition.
In the above arrangement, “Also known as . . . ” applies only to both definitions
in the first field.

diversity, evolution, reproduction, and utilization of plants and their
interactions within the environment.
[
CHEM] chemistry—The scientific study of the properties, composition, and
structure of matter, the changes in the structure and composition of matter,
and accompanying energy changes; includes the fields of analytical chemistry,
inorganic chemistry, organic chemistry, physical chemistry, and spectro-
scopy.
[
CHEM ENG] chemical engineering—A branch of engineering whichinvolves the
design of chemicalproducts and processesfor a widerange of engineering fields,
including petroleum, materials science, agricultural, energy, environmental,
pharmaceutical, and biomedical.
[
CIV ENG
] civil engineering—The planning, design, construction, and main-
tenance of fixed structures and ground facilities for industry, for transportation,
for use and control of water, for occupancy, and for harbor facilities.
[
CLIMATOL] climatology—That branch of meteorology concerned with the
mean physical state of the atmosphere together with its statistical variations in
both space and time as reflected in the weather behavior over a period of many
years.
[
ECOL] ecology—The study of the interrelationships between organisms and
their environment.
[
ENG] engineering—The art and science by which the properties of matter
and the sources of power in nature are made useful to humans, for example,
in structures, machines, processes, and products; subfields include aerospace

[
GEOPHYS] geophysics—The branch of geology in which the principles and
practices of physics are used to study the earth and its environment, that is,
earth, air, and (by extension) space.
[
HYD] hydrology—The science dealing with all aspects of the waters on earth,
including their occurrence, circulation, and distribution; their chemical and
physical properties; and their reaction with the environment, including their
relation to living things.
[
MED] medicine—The study of the causes, effects, and treatment of human
diseases, including the subfields of immunology (the study of the native or
acquired resistance of higher animal forms and humans to infection with
microorganisms); pathology (the study of disease, including the biochemical
and microbiological examination of bodily substances and the study of
structural abnormalities of cells, tissues, and organs); and pharmacology (the
study of the action of drugs and other chemical substances on biological
systems).
x
civ a.xml McGraw-Hill Dictionary of Environmental Science June 2, 2003 19:52
[METEOROL] meteorology—The science concerned primarily with the
observation of the atmosphere and its phenomena, including temperature,
density, winds, clouds, and precipitation.
[
MICROBIO] microbiology—The study of organisms of microscopic size, such
as bacteria, viruses, and protozoa.
[
MYCOL] mycology—The branch of biological science concerned with the study
of fungi.
[

ZOO] zoology—The science that deals with the taxonomy, behavior, and mor-
phology of animal life, usually divided into vertebrate and invertebrate zoology.
xi
civ a.xml McGraw-Hill Dictionary of Environmental Science June 2, 2003 19:52
Pronunciation Key
Vowels
a asinbat, that
¯
a asinbait, crate
¨
a asinbother, father
e asinbet, net
¯
e asinbeet, treat
i asinbit, skit
¯
ı asinbite, light
¯
o asinboat, note
˙
o asinbought, taut
˙
u asinbook, pull
¨
u asinboot, pool
ə as in but, sofa
a
˙
u asincrowd, power
˙

n
indicates nasalization of
preceding vowel
ŋ as in ring,single
pasinpier, slip
rasinred, scar
sasinsign, post
sh as in sugar, shoe
tasintimid, cat
th as in thin, breath
th
as in then, breathe
vasinveil, weave
zasinzoo, cruise
zh as in beige, treasure
Syllabication
.
Indicates syllable boundary
when following syllable is
unstressed
xii
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civ a.xml McGraw-Hill Dictionary of Environmental Science June 9, 2003 20:8
A
aapamoor
[ECOL
] A moor with elevated areas or mounds supporting dwarf shrubs
and sphagnum, interspersed with low areas containing sedges and sphagnum, thus
forming a mosaic. {
¨

appearance of the first lifeform on earth. Also the discredited idea of spontaneous
generation. {
¯
a
b
¯
ı·
¯
o jen·ə·sis }
abioseston [OCEANOGR] A general term for deadorganicmatterfloating in ocean water.
{
¯
a
b
¯
ı·
¯
o ses·tə
n}
abiotic [BIOL] Referring to the absence of living organisms. { a b
¯
ı
¨
ad·ik }
abiotic environment [ECOL] All physical and nonliving chemical factors, such as soil,
water, and atmosphere,which influence living organisms. {
a b
¯
ı
¨

e·ə }
ablation cone
[HYD] A debris-covered cone of ice, firn, or snow formed by differential
ablation. {
ə bl
¯
a·shənk
¯
on }
ablation factor [HYD] The rate at which a snow or ice surface wastes away. { ə bl
¯
a·shən
fak·tər}
ablation form [HYD
] A feature onasnow or ice surface caused by meltingorevaporation.
{
ə bl
¯
a·sh
ənf
˙
orm }
abrade [GEOL] To wear away by abrasion or friction. { ə br
¯
ad }
Abraham’s tree [METEOROL] The popular name given to a form of cirrus radiatus
clouds, consisting of an assemblage of long feathers and plumes of cirrus that seems
to radiate from a single point on the horizon. {
¯
a·br

Abbreviated abs. {
ab·s
ə
l
¨
ut }
absolute drought
[METEOROL] In Britain, aperiodof at least 15 consecutive daysduring
which no measurable daily precipitation has fallen. {
ab·sə l
¨
ut dra
˙
ut }
absolute instability [METEOROL] The state of a column of air in the atmosphere when it
has a superadiabatic lapse rate of temperature, that is, greater than the dry-adiabatic
lapse rate. Also known as autoconvective instability; mechanical instability. {
ab·sə
l
¨
ut in·stə bil·ə·d
¯
e}
absolute stability [
METEOROL] The state of a column of air in the atmosphere when
its lapse rate of temperature is less than the saturation-adiabatic lapse rate. {
ab·sə
l
¨
ut st

or·bər pl
¯
at }
absorption
[HYD] Entrance of surface water into the lithosphere. { əb
s
˙
orp·sh
ən}
absorption spectrum [
CHEM
] A plot of how much radiation a sample absorbs over a
range of wavelengths;the spectrum can be aplot of either absorbance ortransmittance
versus wavelength, frequency, or wavenumber. {
əb s
˙
orp·shən spek·trəm}
abstraction [HYD] 1. The draining of water from a stream by another having more rapid
corroding action.
2. The part of precipitation that does not become direct runoff.
{ab
strak·sh
ən}
abundance [GEOCHEM] The relative amount of a given element among other elements.
{
ə bə
n·də
ns }
abyssal [OCEANOGR] Pertaining to the abyssal zone. { ə bis·əl}
abyssal-benthic

civ a.xml McGraw-Hill Dictionary of Environmental Science June 9, 2003 20:8
accumulated temperature
acanthocheilonemiasis [MED] A parasitic infection of humans caused by the filarial
nematode Acanthocheilonema perstans. {
ə kan·thə k
¯
ı·lə·ne m
¯
ı·ə·səs}
acaricide [AGR] A pesticide used to destroy mites on domestic animals, crops, and
humans. Also known as miticide. {
ə kar·ə s
¯
ıd }
Acaridiae [ZOO] A group of pale, weakly sclerotized mites in the suborder Sarcopti-
formes, including serious pests of stored food products and skin parasites of warm-
blooded vertebrates. {
a·kə rid·
¯
e
¯
e}
acarophily [ECOL
] A symbiotic relationship between plants and mites. {
a·kə·r
¯
o fil·
¯
e}
acarpous [BOT] Not producing fruit. {

ses·ə·r
¯
e pig·məns }
accident [HYD] An interruption in a river that interferes with, or sometimes stops, the
normal development of the river system. {
ak·s
ə
dent }
accidental species
[ECOL] Species that are not characteristic of a particular habitat
type and occur there only by chance. {
ak·sə den·təl sp
¯
e·sh
¯
ez }
acclimated microorganism [ECOL] Any microorganism that is able to adapt to
environmental changes such as a change in temperature, or a change in the quantity
of oxygen or other gases. {
ə kl
¯
ım·əd·əd m
¯
ı·kr
¯
o
˙
or·g
ə·niz·əm}
acclimation See acclimatization. { ak·lə m

indicating that the coast has been built seaward. {
ə kr
¯
e·shən er·
¯
e rij }
accretion tectonics [GEOL] The bringing together, or suturing, of terranes; regarded by
many geologists as an important mechanism of continental growth. Also known as
accretion. {
ə kr
¯
e·shən tek t
¨
an·iks }
accumulated dose [MED
] The total amount of radiation absorbed by an organism as a
result of exposure to radiation. {
ə
ky
¨
u·my
ə
l
¯
ad·
əd
d
¯
os }
accumulated temperature [METEOROL] A value based on the integrated product of the

ə·ky
¨
u·myə l
¯
a·shən z
¯
on }
accumulator plant [BOT] A plant or tree that grows in a metal-bearing soil and
accumulates an abnormal content of the metal. {
ə ky
¨
u·myə l
¯
ad·ər plant }
accustomization [
ENG] The process of learning the techniques of living with a
minimum of discomfort in an extreme or new environment. {
ə
kəs·tə·mə z
¯
a·shən}
acephate [CHEM
]C
4
H
10
NO
3
PS A white solid with a melting point of 72–80
˚

acetate into methane and carbon dioxide. {
a·sə·t
¯
o klas·təs}
acetogenic bacteria [BIOL] Anaerobic bacteria capable of reducing carbon dioxide to
acetic acid or converting sugars into acetate. {
a·sə·t
¯
o jen·ik bak tir·
¯
e·ə }
acetone cyanohydrin [CHEM] (CH
3
)
2
COHCN A colorless liquid obtained from conden-
sation of acetone with hydrocyanic acid; used as an insecticide or as an organic
chemical intermediate. {
as·ə t
¯
on s
¯
ı ə·n
¯
o h
¯
ıd·r
ən}
acetylacetone
[CHEM

oil pə r
¨
ak s
¯
ıd }
acetyl-CoA pathway [BIOL] A pathway of autotrophic carbon dioxide fixation. { a sed·
əl k
¯
o
¯
a
path w
¯
a}
acheb [ECOL] Short-lived vegetation regions of the Sahara composed principally of
mustards (Cruciferae) and grasses (Gramineae). {
ə cheb }
acicular ice [HYD] Fresh-water ice composed of many long crystals and layered hollow
tubes of varying shape containing air bubbles. Also known as fibrous ice; satin ice.
{
ə sik·y
ə·l
ər
¯
ıs }
acid clay [GEOL] A type of clay that gives off hydrogen ions when it dissolves in water.
{
as·ə
d
kl

acid rain [METEOROL] Precipitation in the form of water drops that incorporates
anthropogenic acids and acid materials. {
as·əd r
¯
an }
acid soil
[GEOL] A soil with pH less than 7; results from presence of exchangeable
hydrogen and aluminum ions. {
as·əd s
˙
oil }
acid soot [ENG] Carbon particles that have absorbed acid fumes as a by-product of
combustion; hydrochloric acidabsorbed on carbon particulates isfrequently the cause
of metal corrosion in incineration. {
as·əd s
˙
ut }
acidulous water
[HYD] Mineral water either with dissolved carbonic acid or dissolved
sulfur compounds such as sulfates. {
ə
sij·ə·l
əs
w
˙
od·ər}
acid-water pollution [ENG] Industrial wastewaters that are acidic; usually appears in
effluent from the manufacture of chemicals, batteries, artificial and natural fiber,
fermentation processes (beer), and mining. {
as·əd w

¨
us·tik n
˙
oiz }
acoustic shielding [PHYS] A sound barrier that prevents the transmission of acoustic
energy. {
ə k
¨
us·tik sh
¯
eld·iŋ }
acquired [BIOL
] Not present at birth, but developed by an individual in response to the
environment and not subject to hereditary transmission. {
ə
kw
¯
ırd }
acquired immune deficiency syndrome [MED] A disease that is caused by the human
immunodeficiency virus (HIV) and compromises the competency of the immune
system; characterized by persistent lymphadenopathy, opportunistic infections, and
malignancies. HIV infection is transmitted by sexual intercourse, by blood and blood
products, and perinatally from infected mother to child (prepartum, intrapartum, and
postpartum via breast milk). {
ə kw
¯
ırd ə my
¨
un də fish·ən·s
¯

3630 cubic feet. Abbreviated acre-in. {
¯
a·k
ər inch }
acre-yield [GEOL] The average amount of oil, gas, or water taken from one acre of a
reservoir. {
¯
a·k
ər y
¯
eld }
acrodomatia [ECOL] Specialized structures on certain plants adapted to shelter mites;
relationship is presumably symbiotic. {
ak·rə·də m
¯
ash·
¯
e·ə }
5
civ a.xml McGraw-Hill Dictionary of Environmental Science June 9, 2003 20:8
acrodynia
acrodynia [MED] A childhood syndrome associated with mercury ingestion and
characterized by periods of irritability alternating with apathy, anorexia, pink itching
hands and feet, photophobia, sweating, tachycardia, hypertension, and hypotonia.
{
ak·r
¯
o din·
¯
e·

ıd }
actinochemistry [CHEM] A branch of chemistry concerned with chemical reactions
produced by light or other radiation. {
ak·tə·n
¯
o kem·ə·str
¯
e}
Actinomyces [MICROBIO] The type genus of the family Actinomycetaceae; anaerobic to
facultatively anaerobic; includes human and animal pathogens. {
ak·tə·n
¯
o m
¯
ı·s
¯
es }
actinomycosis [MED] An infectious bacterial disease caused by Actinomyces bovis in
cattle, hogs, and occasionally in humans. Also known as lumpy jaw. {
ak·tə·n
¯
o m
¯
ı
k
¯
o·səs}
activate [PHYS] To induce radioactivity through bombardment by neutrons or by other
types of radiation. {
ak·tə v

a·sh
ən}
active front
[METEOROL] A front, or portion thereof, which produces appreciable
cloudiness and, usually, precipitation. {
ak·tiv fr
ənt }
active glacier [HYD] A glacier in which some of the ice is flowing. { ak·tiv gl
¯
a·shər}
active immunity
[MED
] Disease resistance in an individual due to antibody production
after exposure to a microbial antigen following disease, inapparent infection, or
inoculation. {
ak·tiv im y
¨
u·nət·
¯
e}
active layer
[GEOL] That part of the soil which is within the suprapermafrost layer
and which usually freezes in winter and thaws in summer. Also known as frost zone.
{
ak·tiv l
¯
a·ər}
active permafrost [GEOL] Permanently frozenground (permafrost) which, afterthawing
by artificial or unusual natural means, reverts to permafrost under normal climatic
conditions. {

[MED
] A complex of symptoms involving the intestinal
tract, blood-forming organs, and skin following whole-body irradiation. {
ə ky
¨
ut
r
¯
ad·
¯
e a·shən sin dr
¯
om }
acute rhinitis [MED] Inflammation of the nasal mucous membrane due to either
infection or allergy. {
ə
ky
¨
ut r
¯
ı n
¯
ıd·ə
s}
acute yellow atrophy
[MED] Rapid liver destruction following viral hepatitis, toxic
chemicals, or other agents. {
ə ky
¨
ut yel·

a·shənz }
adaptive value [GEN] The property of a given genotype that confers fitness to an
organism in a given environment. {
ə
dap·tiv val·y
¨
u}
Adenoviridae [MICROBIO] A family of double-stranded DNA viruses with icosahedral
symmetry; usually found in the respiratory tract of the host species and often
associated with respiratory diseases. Also known as adenovirus. {
ad·ən·
¯
o v
¯
ır·ə d
¯
e}
adenovirus See Adenoviridae. { ad·ə
n
o v
¯
ı·r
əs}
adequate contact [MED] The degree of contact required between an infectious and a
susceptible individual to cause infection of the latter. {
ad·ə·kwət k
¨
an takt }
adfluvial [
BIOL] Migrating between lakes and rivers or streams. { ad

adiabatic chart See Stuve chart. { ad·
¯
e·ə bad·ik ch
¨
art }
adiabatic condensation pressure See condensation pressure. { ad·
¯
e·ə bad·ik k
¨
an
den s
¯
a·shən presh·ər}
7
civ a.xml McGraw-Hill Dictionary of Environmental Science June 9, 2003 20:8
adiabatic condensation temperature
adiabatic condensation temperature See condensation temperature. { ad·
¯
e·ə bad·ik
k
¨
an den s
¯
a·shən tem·prə·chər}
adiabatic equilibrium [METEOROL] A vertical distribution of temperature and pressure
in an atmosphere in hydrostatic equilibrium such that an air parcel displaced
adiabatically will continue to possess the same temperature and pressure as its
surroundings, so that no restoring force acts on a parcel displaced vertically. Also
known as convective equilibrium. {
ad·

ə
bad·ik sach·
ə r
¯
a·shən presh·ər}
adiabatic saturation temperature See condensation temperature. { ad·
¯
e·ə bad·ik
sach·ə r
¯
a·shən tem·prə·chər}
adiabatic system [SCI TECH] A body or system whose condition is altered without
gaining heat from or losing heat to the surroundings. {
ad·
¯
e·ə bad·ik sis·təm}
adjacent sea
[GEOGR] A sea connected with the oceans but semienclosed by land;
examples are the Caribbean Sea and North Polar Sea. {
ə
j
¯
as·ənt s
¯
e}
adjusted stream [HYD] A stream which flows mostly parallel to the strike and as little
as necessary in other courses. {
ə jəs·təd str
¯
em }

channel that may reach base level at its mouth. {
ad·əl es·ənt str
¯
em }
adret [ECOL
] The sunny (usually south) face of a mountain featuring high timber and
snow lines. {
ad·r
ət}
advance [HYD] The forward movement of a glacier. { əd vans }
advanced sewage treatment
See tertiary sewage treatment. { əd
vanst s
¨
u·ij tr
¯
et·
m
ənt }
advection [METEOROL] The process of transport of an atmospheric property solely by
the mass motion of the atmosphere. [
OCEANOGR] The process of transport of water,
or of an acqueous property, solely by the mass motion of the oceans, most typically
via horizontal currents. {
ad vek·sh
ən}
advectional inversion [METEOROL] An inverted temperature gradient in the air
resulting from a horizontal inflow of colder air into an area. { ad
vek·shən·əlinvər·
zh

r
¨
ut }
adventive [BIOL] 1. An organism that is introduced accidentally and is imperfectly
naturalized; not native.
2. See adventitious. { ad ven·tiv }
aelophilous
[BOT] Describing a plant whose disseminules are dispersed by wind.
{
¯
e
l
¨
a·fə·l
əs}
aeolian See eolian. {
¯
e
¯
ol·
¯
e·
ən}
aeration [ENG
] 1. Exposing to the action of air.
2.
Causing air to bubble through.
3. Introducing air into a solution by spraying, stirring, or similar method. 4. Supplying
or infusing with air, as in sand or soil. { e
r

ut }
aeroallergen
[MED] Any airborne particulate matter that can induce allergic responses
in sensitive persons. {
e·r
¯
o al·ər·jən}
aerobe [
BIOL
] An organismthat requires air orfree oxygen to maintainits life processes.
{
e r
¯
ob }
aerobic-anaerobic interface [CIV ENG] That point in bacterial action in the body of a
sewage sludge or compost heap where both aerobic and anaerobic microorganisms
participate, and the decomposition of the material goes no further. { e
r
¯
ob·ik an·ə
r
¯
ob·ik in·t
ər
f
¯
as }
aerobic-anaerobic lagoon [CIV ENG] A pond in which the solids from a sewage plant
are placed in the lower layer; the solids are partially decomposed by anaerobic
bacteria, while air or oxygen is bubbled through the upper layer to create an aerobic

¯
o·bik p
¨
and }
aerobic process [BIOL] A process requiringthe presence of oxygen. { e r
¯
ob·ik pr
¨
as·əs}
9
civ a.xml McGraw-Hill Dictionary of Environmental Science June 9, 2003 20:8
aerobiology
aerobiology [BIOL] The study of the atmospheric dispersal of airborne fungus spores,
pollen grains, and microorganisms; and, more broadly, of airborne propagules of algae
and protozoans, minute insects such as aphids, and pollution gases and particles
which exert specific biologic effects. {
e·r
¯
o b
¯
ı
¨
al·
ə·j
¯
e}
aerobioscope
[MICROBIO
] An apparatus for collecting and determining the bacterial
content of a sample of air. {

or·ə n
¯
a·shən}
AERO code
[METEOROL] An international code used to encode for transmission, in
words five numerical digits long, synoptic weather observations of particular interest
to aviation operations. {
e·r
¯
o k
¯
od }
aerofilter [CIV ENG
] A filter bed for sewage treatment consisting of coarse material and
operated at high speed, often with recirculation. {
e·r
¯
o fil·tər}
aerogenerator [ENG] A generator that is driven by the wind, designed to utilize wind
power on a commercial scale. {
e·r
¯
o jen·ə r
¯
ad·ər}
aerogeography [GEOGR] The geographic study of earth features by means of aerial
observations and aerial photography. {
e·r
¯
o·j

aerology [METEOROL] The study of the free atmosphere throughout its vertical extent,
as distinguished from studies confined to the layer of the atmosphere near the earth’s
surface. { e
r
¨
a·lə·j
¯
e}
aeronautical climatology [METEOROL] The application of the data and techniques of
climatology to aviation meteorological problems. { e·r
ə n
˙
od·ə·kəl kl
¯
ı·mə t
¨
al·ə·je }
aeronautical meteorology
[METEOROL] The study of the effects of weather upon
aviation. { e·r
ə n
˙
od·ə·kəl m
¯
ed·
¯
e·ə r
¨
al·ə·j
¯

¯
as }
10
civ a.xml McGraw-Hill Dictionary of Environmental Science June 9, 2003 20:8
aged shore
aerotaxis [BIOL] The movement of an organism, especially aerobic and anaerobic
bacteria, with reference to the direction of oxygen or air. {
e·r
¯
o tak·səs}
aerotolerant [MICROBIO] Able to survive in the presence of oxygen. { e·r
¯
o t
¨
al·
ə·rənt }
aerotropism
[BOT] A response in which the growth direction of a plant component
changes due to modifications in oxygen tension. {
e·r
¯
o tr
¯
o piz·əm}
aestivation See estivation.
afforestation [FOR
] Establishment of a new forest by seeding or planting on non-
forested land. { a
f
¨

African swine fever See hog cholera. { af·ri·kən sw
¯
ın f
¯
ev·ər}
afterglow [METEOROL] A broad, high arch of radiance or glow seen occasionally in the
western sky above the highest clouds in deepening twilight, caused by the scattering
effect of very fine particles of dust suspended in the upper atmosphere. {
af·tər gl
¯
o}
afterripening [BOT] A period ofdormancy after a seed isshed during which thesynthetic
machinery of the seed is prepared for germination and growth. {
af·tər r
¯
ı·pən·iŋ }
agar [BOT
] A gelatinous product extracted from certain red algae and used chiefly as a
gelling agent in culture media. {
¨
ag·
ər}
agarophyte
[BOT
] Any seaweed that yields agar. {
ə
gar·ə f
¯
ıt }
Agassiz trawl [OCEANOGR] A dredge consisting of a net attached to an iron frame with

¯
a·j
əd}
age determination [GEOL] Identification of the geologic age of a biological or
geological specimen byusing the methods of dendrochronologyor radiometric dating.
{
¯
aj di
t
ər·mə
n
¯
a·sh
ən}
age distribution [ECOL] The proportions of a population falling into different age
groups {
¯
aj dis·tr
ə by
¨
u·shən}
aged shore [GEOL] A shore long established at a constant level and adjusted to the
waves and currents of the sea. {
¯
a·j
əd sh
˙
or }
11