Environmental Engineering Reference
In-Depth Information
Air capacity
The percentage of soil volume occupied by air spaces or pores.
Aklé
A wavy- or cuspate-edged transverse dune with the points of each cusp pointing
downwind.
Albedo
An index of the reflecting power of a surface. It is usually used of
short-wave
radiation
. Light-coloured surfaces such as ice have a high albedo.
Alkali
Said of a substance capable of liberating hydroxide ions in water, measured by a
pH
of more than 7·0, and possessing caustic properties; it can neutralize hydrogen
ions, with which it reacts to form a salt and water, and is an important agent in
rock
weathering
.
Allogenic successions
Plant successions affected by material originating from elsewhere
(seeds, sediment).
Alluvial fan
A fan-shaped spread of
alluvium
deposited where a tributary stream loses
power on entering a more gently sloping valley.
Alluvial toeslope
The lowest component of a hill slope bordering the valley floor, where
slope and channel processes interact.
Alluvium
A general term for unconsolidated, granular sediments deposited by rivers.
Alp
A high-altitude bench overlooking a glacial trough or the
alpine meadow
growing
there; sometimes used to describe a glaciated mountain in or resembling the European
Alps.
Alpha diversity
Diversity within a habitat measured by the number of species of a
specified taxonomic group in a specified area.
Alpine
Said of a rugged, steep and high mountain or mountainous region resembling the
European Alps; the region is likely to be a young
orogen
high enough to support
alpine glaciers
.
Alpine glacier
A temperate, warm-based mountain glacier characterized by vigorous
mass balance
, high flow velocities and confinement to rock-walled channels.
Alpine heath
A vegetation community with dominant dwarf woody shrubs adapted to
high-altitude conditions.
Alpine landsystem
A distinctive landsystem with integrated glacial,
cryonival
, mountain
slope and
ecosystem
elements dominated by cold climate processes on steep slopes.
Alpine meadow
A vegetation community characterized by grasses and flowering plants
adapted to high-altitude conditions.
Alteration compounds
Colloids (clays, iron oxides) formed by the weathering of rock
minerals.
Altiplanation
The combined processes of
frost shattering
and
solifluction
which
progressively level mountain summits, leaving residual rock platforms and
blockfields
.
Alumino-silicates
Silicate minerals in which aluminium substitutes for one or more
silicate cation.
Ammonification
The production of ammonia and ammonium-nitrogen through the
decomposition of organic nitrogen compounds in soil organic matter.
Ampferer subduction or A-subduction
The downward displacement of continental
crust, usually in an intercontinental collision zone, named after an Alpine geologist;
buoyancy prevents the granitic crust from being recycled into the mantle but it may
melt locally.
