Science of Water : Concepts and Applications

402 The Science of Water: Concepts and Applications
Aquaculture The science of farming organisms that live in water, such as fi sh, shellfi sh, and
algae.
Aquatic Living or growing in or on water.
Aquatic guidelines Specifi c levels of water quality, which, if reached, may adversely affect
aquatic life. These are nonenforceable guidelines issued by a governmental agency or
other institution.
Aquifer A geologic formation, group of formations, or part of a formation that contains suffi
cient saturated permeable material to yield signifi cant quantities of water to springs and
wells.
Arroyo A small, deep, fl at-fl oored channel or gully of an ephemeral or intermittent stream, usually
with nearly vertical banks cut into unconsolidated material.
Artifi cial recharge Augmentation of natural replenishment of groundwater storage by some
method of construction, spreading of water, or by pumping water directly into an
aquifer.
Atmospheric deposition The transfer of substances from the air to the surface of the Earth,
either in wet form (rain, fog, snow, dew, frost, hail) or in dry form (gases, aerosols,
particles).
Atmospheric pressure The pressure exerted by the atmosphere on any surface beneath or
within it; equal to 14.7 lb/in 2 at sea level.
Average discharge As used by the U.S. Geological Survey, the arithmetic average of all complete
water years of record of surface water discharge whether consecutive or not. The
term “average” generally is reserved for average of record and “mean” is used for averages
of shorter periods, namely, daily, monthly, or annual mean discharges.
B
Background concentration A concentration of a substance in a particular environment that is
indicative of minimal infl uence by human (anthropogenic) sources.
Backwater A body of water in which the fl ow is slowed or turned back by an obstruction such
as a bridge or dam, an opposing current, or the movement of the tide.
Bacteria Single-celled microscopic organisms.
Bank The sloping ground that borders a stream and confi nes the water in the natural channel
when the water level, or fl ow, is normal.
Bank storage The change in the amount of water stored in an aquifer adjacent to a surface water
body resulting from a change in stage of the surfacewater body.
Barrier bar An elongate offshore ridge, submerged at least at high tide, built up by the action
of waves or currents.
Base fl ow The sustained low fl ow of a stream, usually groundwater infl ow to the stream channel.
Basic The opposite of acidic; water that has a pH greater than 7.
Basin and range physiography A region characterized by a series of generally north-trending
mountain ranges separated by alluvial valleys.
Bed material Sediment comprising the streambed.
Bed sediment The material that temporarily is stationary in the bottom of a stream or other
watercourse.
Bedload Sediment that moves on or near the streambed and is in almost continuous contact
with the bed.
Bedrock A general term used for solid rock that underlies soils or other unconsolidated
material.
Benthic invertebrates Insects, mollusks, crustaceans, worms, and other organisms without a
backbone that live in, on, or near the bottom of lakes, streams, or oceans.