BELLRINGER 1. Write out the word for each chemical formula NO3
NH3 NO2 N2 2.Why is the nitrogen cycle important to
aquaponics?
Slide 2
Aquatic Nitrogen Cycle The most important concept for
Aquaponics!
Slide 3
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?
Slide 4
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?
Slide 5
When the nitrite levels reach a certain point, nitrite-
oxidizing 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.
Slide 6
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.
Slide 7
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?
Slide 8
Nitrogen Cycle Unlike carbon or oxygen, nitrogen is not very
available to life. Its conversion to a useable form requires
biological activity Cyclic conversions from one form to another are
mainly mediated by bacteria.
Slide 9
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
Slide 10
Process 1: Fixation Nitrogen fixation refers to the conversion
of nitrogen gas to either NH 3 or NH 4 by bacteria. Terrestrial
systems: soil bacteria in root nodules of legumes. Aquatic systems:
blue green algae. N 2 NH 3
Slide 11
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 NH 3 or
NH 4 to NO 2 or NO 3 Plants take up NO 3 to make proteins NH 3 NO 2
NO 3 Process 2: Nitrification
Slide 12
Process 3: Decay 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 (NH 3 ). Proteins NH 3
Slide 13
By this process, NO 3 in soil or water is converted into N 2
gas. This must occur under anaerobic conditions (anaerobic
respiration). Again, mediated by bacteria. Should not happen in an
aquaponics system! Process 4: Denitrification NO 3 N 2
Slide 14
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! Process 5: Dissimilation NO 3 NO 2 NH 3
Slide 15
Simplified diagram of the nitrogen cycle that is established in
an aquatic system
Slide 16
Conversion of ammonia (NH 3 ) to nitrate (NO 3 - ) is via
chemoautotrophic bacteria. First step (NH 3 NO 2 ) by Nitrosomonas
sp. second step(NO 2 NO 3 ) by Nitrospira sp. Both steps/reactions
use NH 4 + and NO 2 - as an energy source, CO 2 as a carbon source.
This is a non-photosynthetic type of growth. Aquatic Nitrogen
Cycling
Slide 17
Reaction runs best at pH 7-8 and 25-30 o C. However; under low
Dissolved Oxygen, it runs in reverse. NO 3 - is converted to NO 2 =
and other forms. Can go all the way backwards to NH 3. Aquatic
Nitrogen Cycling
Slide 18
Ammonia Toxicity Fish excrete ammonia (NH4). When youre 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 dont 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
Slide 19
Nitrite Toxicity Now, nitrite is much less poisonous to the
fish than ammonia. But its by not good either. It stops the fish
from taking up oxygen. Keep below 5 ppm