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Glossary
Acid – A substance characterized by the ability to react with bases or alkalis in water
to form salts. An acid releases hydrogen ions upon dissociation in water, having a
pH of less than seven.
AC/DC – A type of electrical device that can function both with alternating current
(AC), such as that from a wall socket, and direct current (DC), such as that from
a battery. Usually used in regard to battery-based backup systems for aerators and
water pumps.
Aerobic – A condition or process where gaseous oxygen is present or required. Aerobic
organisms obtain energy for growth from aerobic respiration.
Alkalinity – Amount of alkaline minerals (acid binding) that a solution has in the water
to neutralize hydrogen ions. It is usually expressed as SBV units (abbreviation of
the German term Säurebindungsvermögen) or equivalents of calcium carbonate
under the conversion factor of 1 SBV = 50 mg eq. CaCO3/litre. Alkalinity is
measured by using methyl orange as an indicator, whose variation in colour at pH
4.2–4.4 indicates, by definition, the complete depletion of alkali.
Anaerobic – Referring to a condition or process where gaseous oxygen is not present
or not necessary.
Autosiphon – A device that automatically floods and drains a water tank without a
timer or moving parts. Incoming water fills the tank in question until it reaches the
critical height set by the siphon; this starts pulling water out of the tank with an
outflow faster than the inflow, which eventually empties the tank and lets air enter
the device to break the draining and allow the tank to refill.
Base – A substance characterized by the ability to react with acids or hydrogen ions in
water to form salts. A base releases hydroxide ions upon dissociation in water and
has a pH of higher than seven.
Balance – A state of dynamic equilibrium in an integrated agricultural system, such
as aquaponics, where the various biological and chemical processes remain stable
over time.
Biofouling – Accumulation of organisms on wet surfaces that can affect their
functioning.
Biological filter (biofilter) – The component of the treatment units of an aquaculture
system in which organic pollutants are decomposed (mainly oxidized) as a result
of microbiological activity. The most important processes are the degradation of
nitrogen metabolites by heterotrophic bacteria and the oxidation of ammonia via
nitrite to nitrate.
Biomass ratio – The optimal balance between the fish and plants to obtain good
fish and vegetable growth. It is expressed as the plant growing area that can be
supported given a certain feeding rate.
Buffering (acid binding capacity) – The capacity of a solution containing a weak base
and its conjugated acid to resist falls in pH when small quantities of an acid are
added. The buffering occurs within a specific pH range and capacity that depends
on the amount of alkali present in the solution. In aquaponics, the buffering occurs
with carbonate or bicarbonate ions binding hydrogen ions from nitric acid until
they all become saturated into carbonic acid, their weak conjugated acid form.
Carnivore – An animal that feeds mainly on the tissues of other animals.
Clarifier – A sedimentation tank built to remove suspended solids from the water by
means of settling or separation from the aqueous media.
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Chelate – A molecular association of a metal ion and a larger ligand, typically making
the ion more soluble and biologically available.
Denitrification – The biochemical reduction of nitrate via the intermediate nitrite to
molecular (gaseous) nitrogen and carbon dioxide through microbiological activity.
In aquaculture: a necessary water treatment process in recycling systems from
nitrogen buildup with little or no water exchange; also occurs in settling tanks,
suspended solid traps and water storage tanks.
Feed rate ratio – The ratio that helps balance an aquaponics system, relating the
amount of feed added to the amount of plant growing area.
Flood and drain – A method controlling the water flow in a hydroponic or aquaponic
grow bed where the media is alternatively submerged and drained with water,
which ensures both adequate aeration of the plant roots and bacterial colonies
while distributing water and nutrients equally. Also known as ebb and flow.
Footprint – A resource-measuring tool to determine the amount of land or water
needed to support with resources a community or an activity and to assimilate
the waste produced. Higher sustainability is obtained when a smaller footprint is
required to obtain the same product by using a different technology or to support
a community by adopting more sound management.
Granulometry – A description of the size classes in a group of granular material with
implications for surface area to volume ration.
Hardness – Measure of the concentrations of dissolved ions of calcium and magnesium
in the water. Hardness is expressed as equivalent of calcium carbonate in milligrams
per litre (mg/litre). Hardness can be also expressed as milliequivalent per litre,
German hardness (°dH) or mg/litre of calcium oxide (CaO) according to the
following conversion factor: 50 mg/litre CaCO3 = 1 meq/litre = 2.805 (°dH) =
28 mg/litre CaO.
Head, head pressure – In hydraulics: the measurement of pressure of water expressed
in height at which water is held or can rise to, allowing it to flow to lower levels,
push through pipes, etc.
Header tank – A water tank kept at a height for supplying water to lower rearing units,
for example hatchery incubators and nursery tanks.
Herbivore – An animal that feeds mainly on plant material.
Hydroponics – A form of soil-less agriculture where plants are provided a nutrient
solution containing all essential macronutrients and micronutrients necessary
for growth, either through irrigation of inert media or directly within tanks of
nutrient solution.
Ion – An atom or radical with an electrical charge that is positive (cation) or negative
(anion) as a result of having lost or gained electrons.
Molecular nitrogen – An odourless gaseous element that makes up 78 percent of the
Earth’s atmosphere, and is a constituent of all living tissue. It is almost inert in its
gaseous form.
New tank syndrome – A common condition in newly installed aquaculture and
aquarium systems with insufficient or immature biofiltration capabilities resulting
in accumulation of toxic ammonia and nitrite, causing fish stress and ultimate
death.
Nitrification – The aerobic bacterial conversion (oxidation) of ammonia and organic
nitrogen to stable salts (nitrates), via bacteria, often Nitrosomonas spp. and
Nitrobacter spp.
Nitrogen-fixation – The process by which certain bacteria and cyanobacteria are able
to convert atmospheric nitrogen into combined forms into the soil, making them
available to plants.
Glossary
Nutrient cycle (nitrogen cycle) – Biogeochemical cycle, in which inorganic nutrients
move through the soil, living organisms, air and water. In agriculture, it refers to
the return back to the soil of nutrients absorbed by plants from the soil. Nutrient
cycling can take place through leaf fall, root exudation (secretion), residue
recycling, incorporation of green manures, etc.
Nutrient lockout (pH-dependent nutrient availability) – An effect of pH and soil
chemistry on the bioavailability of nutrients to be absorbed by plants, especially
important in hydroponics and aquaponics. Each nutrient has a pH range in which
it is available, but outside this range the plants will not be able to use the nutrients
despite their presence in the nutrient solution.
Omnivore – An animal that consumes both plant and animal material.
Oxidation – Type of chemical reaction, always coupled with reduction, in which the
molecule in question loses an electron, often binding with oxygen. Examples
include the burning of wood or the rusting of iron.
Photoperiodism – The physiological response of plants and animals to the seasonal
length of days and nights. In plants, the presence of photoreceptors informs
the plants of the optimal period to flower. Photoperiodic plants can start their
flowering either with long or short days depending on the species. In animals,
photoperiodism together with temperature regulate the physiological changes in
sexual behaviour, migration and hibernation.
Reduction – Type of chemical reaction, always coupled with oxidation, in which the
molecule in question gains an electron, often losing an oxygen molecule, atom or
ion.
Soil-less agriculture (hydroponics) – The growing of plants without soil. Plants are
fed with an aerated solution of nutrients, and the roots are either supported within
an inert matrix, or are freely floating in the nutrient solution.
Soil tiredness – A condition in soils that lead to a progressive reduction in yields after
repeated cultivation of the same crop on the same area. The condition is due to
a combination of nutrient depletion, exploitation of soil structure (low organic
matter), accumulation of pathogens (parasites, pests, bacteria, fungi) specifically
targeting the crop, selection of species-specific weeds and accumulation of
inhibiting root exudates.
Soluble – The ability of a substance to be dissolved in water or other liquid media,
typically dependent on the charge and size of its molecules and the charge of the
liquid. The more uncharged and the larger the molecules are, the less soluble in
water is the substance.
Specific surface area – A metric to describe how much surface area is exposed for
each unit of volume of an object alone or in a set. The value provides an indirect
reading of porosity and granulometry of an object and is especially important for
chemical reaction and biological activity, with a high ratio providing more area for
the action in question.
Stocking density – Usually an expression of the number of fish per unit area or weight
of fish per unit of volume of water at stocking.
Stress – The sum of biological reactions to any adverse stimuli (physical, internal or
external) that disturb the organism’s optimum operating status and may reduce its
chances of survival.
Sustainable development – Management and conservation of the natural resource base,
and the orientation of technological and institutional change in such a manner as
to ensure the attainment of continued satisfaction of human needs for present and
future generations. Such sustainable development conserves land, water, plants
and animal genetic resources, is environmentally non-degrading, technologically
appropriate, economically viable and socially acceptable.
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System cycling – Initial development of a biofilter within an aquaculture or aquarium
system as the tank and biofilter material are colonized by ammonia-oxidizing
bacteria and nitrite-oxidizing bacteria. These groups of bacteria oxidize the
original source of ammonia into nitrite and nitrate, respectively. It usually takes
between one and six weeks depending on temperature, water quality and ammonia
source. Adequate system cycling reduces the effects of new tank syndrome.
Turnover rate – In culture systems such as tanks, raceways, ponds and other units,
this term refers to the real water exchange rate over a period of time defined as the
inverse of residence time: Q (water quantity, in m3/h) / V (unit volume, in m3).
Ultraviolet – Non-visible electromagnetic waves, which follow at the end of the violet
end of the light spectrum. That part of the solar radiation spectrum between
40 nm and 400 nm wavelength. Used in aquaculture to disinfect water and prevent
diseases caused by pathogenic microorganisms.