The Nitrogen Cycle

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The Nitrogen Cycle
http//www.nitrousoxide.org/images/fig2.gif
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Learning Targets

• Explain the importance of nitrogen to living
  things
• Trace the movement of nitrogen through the
  nitrogen cycle including
• Sources of nitrogen
• Processes and organisms that convert nitrogen
• Spheres involved
• Form used by plants
• Explain how humans impact the nitrogen cycle and
  the how excess nitrogen affects human health and
  the environment

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Importance of Nitrogen (N)

• N is an essential plant nutrient (N, P, K)
• All living things need nitrogen for amino acids,
  proteins and nucleic acids (DNA and RNA)
• Concentrations of N are important indicators of
  water quality.
• Excess N also affects air quality and human
  health

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http//extension.missouri.edu/p/WQ252
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Forms of Nitrogen

• Nitrogen exists in all four spheres
• The atmosphere is 78 N2 gas
• Nitrogen exists in several forms, organic and
  inorganic
• Organic means it is part of living organisms or
  the biosphere
• Examples - amino acids, proteins, DNA and RNA all
  contain Nitrogen
• Inorganic forms in soil (geosphere) and water
  (hydrosphere) include
• Nitrate (NO3), nitrite (NO2), and ammonium (NH4)

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Plants cant use N2

• Plants cannot absorb the Nitrogen gas from the
  atmosphere
• It must be fixed in the soil or water for them
• Meaning changed to a useable form
• Plants use ammonium or nitrate nitrogen

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Nitrogen Fixation

• Lightning makes nitrate and rain carries it into
  the soil
• Bacteria living in root nodules of legumes
  (soybeans, clover) convert N2 to ammonia
• Humans manufacture fertilizers and burn fossil
  fuels
• Cyanobacteria (blue-green algae) fix nitrogen in
  water

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Decomposers produce ammonia

• Ammonium ion is in waste products from animals
  (sewage) and produced from bacterial
  decomposition of dead plants and animals

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Denitrification by anaerobic bacteria (without
oxygen)

• Converts ammonia to nitrite and nitrate and N
• Gases are released into the air

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Human impact

• Over last 100 years weve more than doubled the
  amount of N entering the cycle
• 60 of N entering the cycle comes from commercial
  inorganic fertilizers
• Burning fossil fuels adds nitrates to the air
  which forms nitric acid in our atmosphere and
  contributes to acid deposition and global warming
• Nitrous oxide, N20 from anaerobic bacteria
  working on livestock waste and fertilizer
  contributes to global warming and ozone loss.
• Discharge of municipal sewage also add N to lakes
• Excess nitrates enters ground water and can harm
  young children and pregnant mothers (blue-baby
  syndrome)

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Cultural Eutrophication

• Excess nutrients (nitrogen and/or phosphorus)
  stimulate
• plant growth (algal bloom)
• When these plants die, decomposers use up the
  available oxygen during decomposition

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http//zolushka4earth.wordpress.com/tag/oligotroph
ic/
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This can lead to Dead Zones
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Learning Target Check

• Explain the importance of nitrogen to living
  things
• Trace the movement of nitrogen through the
  nitrogen cycle including
• What are the sources of nitrogen?
• What are processes and organisms that fix
  nitrogen in soil/water?
• What are the processes and organisms that release
  nitrogen to the atmosphere?
• What spheres contain nitrogen, and in what form?
• What form of nitrogen is used by plants?
• How do humans impact the nitrogen cycle and the
  how excess nitrogen affects human health, water
  quality/aquatic ecosystems, and air quality?