Transcript Nitrogen Cycle - Ms Kim`s Biology Class

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.
 Fish eat food and excrete organic waste matter in the form of urea from
digesting the 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, 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.
Why do plants need Nitrogen?
 Nitrogen is one of the main elements in
protein.
 Nitrogen is 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.
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 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 their energy
by oxidizing NH3 or NH4, while
using CO2 as a source of carbon
to synthesize organic compounds.
 Plants take up NO3 to make
proteins
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 cycling
 Nitrogen Fixation
 Nitrogen equilibria
 Decay
 Toxicity
 Nitrification
 Denitrification