Download Nitrogen Cycle in Aquaponics

BELLRINGER
• 1. Write out the word for each chemical
formula
– NO3
– NH3
– NO2
– N2
• 2. Why is the nitrogen cycle important to
aquaponics?
Aquatic Nitrogen Cycle
The most important concept for Aquaponics!
Why is the aquatic nitrogen cycle
important to aquaponics?
• Arguably, the nitrogen cycle is the most important concept to be understood
about aquaponics because, without it, there is no aquaponics.
• The fish eat food and excrete organic waste matter in the form of urea, uric acid
arising from the digestion of their food. They also emit ammonia as part of the
gaseous exchange that occurs through respiration.
• The ammonia compounds are toxic to fish and plants cannot absorb ammonia.
• What would happen if the system was left this way?
Why is the aquatic nitrogen cycle
important to aquaponics?
 What allows the fish and plants to survive and thrive?
 When ammonia levels in the fish tank reach a certain level,
bacteria (Nitrosomonas) begin to colonize the system.
 As the bacteria build up, the ammonia is converted to nitrite. As
the ammonia levels dip, the nitrite levels increase.
 The nitrites (like ammonia) are toxic to fish. 
Why is the aquatic nitrogen cycle
important to aquaponics?
 When the nitrite levels reach a certain point, nitriteoxidizing bacteria (nitrospira) colonize the system and
convert the nitrites to nitrates.....which become plant
food.
 The plants take up the nitrates (and other compounds)
and as they grow and are harvested, nitrogen is
removed from the system.
 Eventually, the system reaches the point where the
various aspects of the nitrogen cycle happen
simultaneously. As long as the fish are fed (and things
remain in balance), the cycle continues.
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.
Composition of Atmosphere
•
Nitrogen is the major gas in
the atmosphere.
• But it is often the limiting
factor in plant growth
• 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.
Cycling of Nitrogen
Five processes participate in
the cycling of nitrogen through
the biosphere:
1) Nitrogen fixation
2) Decay
3) Nitrification
4) Denitrification
5)Dissimilation
Microorganisms play major
roles in these processes
Process 1: Fixation
N2  NH3
• Nitrogen fixation refers to the
conversion of nitrogen gas to
either NH3 or NH4 by bacteria.
• Terrestrial systems: soil
bacteria in root nodules of
legumes.
• Aquatic systems: blue green
algae.
Process 2: Nitrification
NH3  NO2  NO3
 The term nitrification refers
to the conversion of
ammonium or ammonia to
nitrate
 Responsible: nitrifying
bacteria known as
chemoautotrophs.
 These bacteria gain energy
by converting NH3 or NH4 to
NO2 or NO3
 Plants take up NO3 to make
proteins
Process 3: Decay
Proteins  NH3
 Proteins pass through food webs just as
carbohydrates do.
 At each trophic level, organic nitrogen
compounds are returned to the environment
in waste excretions.
 Final beneficiaries of these materials are
microorganisms of decay.
 They breakdown the molecules in excretions
and dead organisms into ammonia (NH3).
Process 4: Denitrification
NO3  N2
 By this process, NO3 in soil or
water is converted into N2 gas.
 This must occur under
anaerobic conditions (anaerobic
respiration).
 Again, mediated by bacteria.
 Should not happen in an
aquaponics system!
Process 5: Dissimilation
NO3  NO2  NH3
• By this process, nitrates in soil
or water is converted back to
nitrites and ammonia
• This must occur under
anaerobic conditions.
• Again, mediated by bacteria.
• Should not happen in an
aquaponics system!
Simplified diagram of the nitrogen
cycle that is established in an
aquatic system
Aquatic Nitrogen Cycling
 Conversion of ammonia (NH3) to nitrate (NO3-) is via
chemoautotrophic bacteria.
 First step (NH3  NO2) by Nitrosomonas sp.
 second step(NO2  NO3) by Nitrospira sp.
 Both steps/reactions use NH4+ and NO2- as an energy
source, CO2 as a carbon source.
 This is a non-photosynthetic type of growth.
Aquatic Nitrogen Cycling
 Reaction runs best at pH 7-8 and 25-30oC.
 However; under low Dissolved Oxygen, it runs in
reverse.
 NO3- is converted to NO2= and other forms.
 Can go all the way backwards to NH3.
Ammonia Toxicity
• Fish excrete ammonia (NH4). 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, so don’t overfeed fish!
• 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 1 ppm
Nitrite Toxicity
 Now, nitrite is much less
poisonous to the fish
than ammonia.
 But it’s by not good
either. It stops the fish
from taking up oxygen.
 Keep below 5 ppm
Today, we discussed Nitrogenous
Compounds
Nitrogen cycle
Nitrogen Fixation
Decay
Nitrification
Denitrification
Nitrogen cycling
Nitrogen equilibria
Toxicity
Exit Slip-September 17, 2014
• Explain the role of:
– Nitrosomonas sp.
– Nitrospira sp.
• Draw a cycle/picture that includes:
– Fish, waste, ammonia, nitrite, nitrate, plants,
Nitrosomonas sp and nitrospira sp.