Nitrogen Cycle in Aquaponics
Nitrogen cycle
• Nitrogen is a fundamental element
that is necessary for all forms of life
on Earth. Nitrogen is an important
component in both plant and animal
cells.
• Organisms need nitrogen to produce
proteins, nucleic acids, and amino
acids. Although Nitrogen gas (N2) is
roughly 78% of the earth’s
atmosphere, it is unusable in this
form.
• The majority of organisms on earth
can only use nitrogen when it is
‘fixed’ – combined with carbon,
hydrogen or oxygen.
• The nitrogen cycle is the process by
which microorganisms convert the
nitrogen in the air and organic
compounds (such as within soil) into
a usable form.
Composition of Atmosphere
•
Nitrogen is the major gas in
the atmosphere.
• Why would nitrogen be
limiting if it makes up most
of the atmosphere?
Nitrogen
Cycle
• Unlike carbon or
oxygen, nitrogen is
not very available to
life.
• It’s conversion to a
useable form
requires biological
activity
• Cyclic conversions
from one form to
another are mainly
mediated by
bacteria.
Nitrogen cycle and Aquaponics
• The Nitrogen cycle is the most significant
process within aquaponics. It is
responsible for the conversion of fish
waste into nutrients for the plants.
• Without this process, the water quality
would deteriorate rapidly and become
toxic to both the fish and plants in the
system.
• The water therefore in aquaponics does
not need to be treated chemically to make
it ‘safe’ nor does it have to be replaced.
• In aquaponics, a system is said to have
‘cycled’ when there are sufficient
quantities of bacteria to convert all the
ammonia into an accessible form of
nitrogen for the plants.
• The bacteria will arrive naturally to a
system and colonize the water column and
biofilter (usually clay pebbles, gravel or
netting).
Why do plants need Nitrogen?
• Nitrogen is one of the main elements in
protein. Nitrogen is also a component of
nucleic acid, DNA, RNA, genes, chromosomes,
enzymes, chlorophyll, secondary metabolites
(alkaloids), and amino acids.
• Protein is essential for all living organisms, and
is required for growth and development.
• Nitrogen accounts for about 1 to 6 % of plant
dry matter, depending on the species and is
often the limiting factor in plant growth.
Bacteria in Aquaponics
• One of the most important
yet least understood
aspects of Aquaponics
is the bacteria that we rely
on and its function in the
nitrogen cycle.
• I know what you’re
thinking, bacteria (or
“GERMS” if you watch a lot
of
disinfectant commercials)
are meant to be bad, aren’t
they?
• The fact is that there is
good and bad in everything,
even down to bacteria. Life
wouldn’t be possible
without them.
Ammonia Toxicity
Fish excrete ammonia (NH4). In a
lake or ocean it’s all good because
the vast volume of water dilutes
this ammonia. When you’re
keeping fish at home or in an
aquaponics lab it needs to
be managed as it is very toxic
to the fish. Decomposing food also
creates ammonia.
Some of the effects of excessive ammonia
include:
• Extensive damage to tissues, especially the
gills and kidney
• Impaired growth
• Decreased resistance to disease
• Death
•
Keep below 1ppm
Ammonia  Nitrite  Nitrate
• Luckily natures got it all sorted! The
Nitrosomonas sp. Is a good little
bacterium that eats ammonia and
converts it to nitrite (NO2-).
• Now, nitrite is much less poisonous to
the fish than ammonia, but it’s by no
means a good thing. It stops the fish
from taking up oxygen (keep below
5ppm).
• Natures got it under control again,
with Nitrobacter sp. This good
bacterium eats nitrite and converts it
to nitrate (NO3-). Luckily nitrate
happens to be the favorite food of
plants. Also the fish will tolerate a
much higher level of nitrate than they
will ammonia or nitrite.