The Nitrogen Cycle

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The Nitrogen Cycle
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Nitrogen

• Nitrogen (N) is an essential component of DNA,
  RNA, and proteins, the building blocks of life.
• All organisms require nitrogen to live and grow.
• The majority (78) of the Earths atmosphere is
  N2.

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Have you ever started a fishtank?

• Why must you wait
• to add a bunch of fish?
• Like all living creatures, fish give off waste
  products (pee and poo). These nitrogenous waste
  products break down into ammonia (NH3), which is
  highly toxic to most fishes.

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Nitrogens triple bond

• Although the majority of the air we breathe is
  N2, most of the nitrogen in the atmosphere is
  unavailable for use by organisms.
• This is because the strong triple bond between
  the N atoms in N2 molecules makes it relatively
  inert (like a noble gas).

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How can we use N2?

• In order for plants and animals to be able to use
  nitrogen, N2 gas must first be converted to more
  a chemically available form such as ammonium
  (NH4) or nitrate (NO3-).

WE CANT!
But BACTERIA can
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Nitrogen Fixation (N2 --gt NH3 or NH4)
Nitrogen Fixation (N2 --gt NH3 or NH4)

• HOW? Biological or Environmental or Humans
• BIOLOGICAL Bacteria (called Nitrogen-fixing
  bacteria)These bacteria form symbiotic
  relationships with host plants. The bacteria
  live in nodules found in the roots of the legume
  family of plants (e.g. beans, peas, and clover)

• HOW? Biological or Environmental or Humans
• BIOLOGICAL Bacteria (called Nitrogen-fixing
  bacteria)These bacteria form symbiotic
  relationships with host plants. The bacteria
  live in nodules found in the roots of the legume
  family of plants (e.g. beans, peas, and clover)

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Nitrogen Fixation (N2 --gt NH3 or NH4)

• How?BIOLOGICAL
• In aquatic environments (like fishtanks),
  blue-green algae (cyanobacteria) is an
  important free-living nitrogen fixer.

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Nitrogen Fixation (N2 --gt NH3 or NH4)

• ENVIRONMENTAL
• High-energy natural events which break the bond
  N2
• Exampleslightningforest fireshot lava flows

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Nitrogen Fixation N2 --gt NH3 or NH4

• How?
• HUMAN IMPACT
• Burning fossil fuels,
• using synthetic nitrogen fertilizers,
• and cultivation of legumes
• all fix nitrogen.

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Nitrogen Fixation Atmospheric Nitrogen is broken
into useable nitrogen (NH3 or NH4)
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Nitrogen Mineralizationalso called
AmmonificationOrganic N --gt NH4

• Decay of dead things, manure, etc.
• Done by decomposers (bacteria, fungi, etc.)
• During this process, a significant amount of the
  nitrogen contained within the dead organism is
  converted to ammonium (NH4).

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Nitrification NH3 or NH4 --gt NO2- --gt NO3-

• (Nitrifying) Bacteria add oxygen to nitrogen in
  two steps

• STEP 1 Bacteria take in NH3 or NH4 make NO2-
  nitrite

• Step 2Bacteria take in NO2- make NO3-
  nitrate

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Nitrification
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Nitrogen Uptake

• The ammonia (NH3) produced by nitrogen-fixing
  bacteria is usually quickly incorporated into
  protein and other organic nitrogen compounds
  (organisms!).
• Its either absorbed by a plant, by the bacteria
  itself, or by another soil organism.
• Organisms at the top of the food chain (like us!)
  eat and grow, uptaking nitrogen (that has already
  been fixed).

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DenitrificationNO3- --gt N2

• (Denitrifying) Bacteria do it.
• Denitrification removes nitrogen from ecosystems,
  and converts it back to atmospheric N2.

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Human Impact

• FERTILIZERS!
• Extra nitrogen fertilizer can runoff, where it
  contaminates surface water or infiltrates into
  ground water.
• In drinking water, excess nitrogen can lead to
  cancer in humans and respiratory distress in
  infants.

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Human Impact

• In surface waters, extra nitrogen can lead to
  nutrient over-enrichment.
• This leads to
• fish-kills,
• harmful algal blooms,
• and species shifts in aquatic and land
  ecosystems.

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Human Impact

• Some forms of nitrogen (like NO3- and NH4) can
  also enter the atmosphere to become
• smog- nitric oxide (NO)
• Greenhouse gas- nitrous oxide (N2O)
• Acid Rain- (nitrogen oxides)

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Nitrogen Cycle Pictures

• Good pictures of the nitrogen cycle have these
  processes
• Nitrogen fixation (N2 bonds are broken)
• Nitrification (oxygen is added to form nitrogen
  oxides)
• Denitrification (N2 is put back into the air)
• It is also helpful to have
• Ammonification (mineralization/waste conversion
  by decomposers)
• Assimilation (intake by producers)

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• Yellow arrows indicate human sources of nitrogen
  to the environment. Red arrows indicate bacterial
  transformations of nitrogen. Blue arrows indicate
  physical forces acting on nitrogen. And green
  arrows indicate natural, non-microbial processes
  affecting the form and fate of nitrogen.

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