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The Nitrogen Cycle

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Title: The Nitrogen Cycle


1
The Nitrogen Cycle
2
The Nitrogen Cycle
  • Represents one of the most important nutrient
    cycles found in terrestrial ecosystems. Model
    that describes the movement of nitrogen in its
    many forms between the hydrosphere, lithosphere,
    atmosphere, and biosphere.

3
The Hydrosphere
  • The hydrosphere describes the waters of the
    earth. Water exists on the earth in various
    stores, including the atmosphere, oceans, lakes,
    rivers, glaciers, snowfields, and groundwater.

4
Hydrosphere Continued
  • Water moves from one store to another by way of
    evaporation, condensation, precipitation,
    deposition, runoff, infiltration, sublimation,
    transpiration, and groundwater flow.

5
continued
  • The form and movement of nitrogen are greatly
    influenced by components of the hydrologic cycle,
    which is particularly important for agriculture
    and the environment.

6
The Lithosphere
  • Rigid outer layer of earth Includes crust and
    upper part of mantle.
  • Relatively strong layer in contrast to underlying
    asthenosphere.

7
Lithosphere Continued
  • The brittle most upper layer of the Earth that is
    broken up into a number of tectonic plates.
  • Consists of the heavy oceanic and lighter
    continental crusts and the upper part of the
    mantle.
  • The lithosphere rests on a soft layer called the
    asthenosphere, over which the plates of the
    lithosphere glide.

8
The Atmosphere
  • Life on earth is supported by the atmosphere,
    solar energy, and our planet's magnetic fields.
    The atmosphere absorbs the energy from the sun,
    recycles water and other chemicals, and works
    with the electrical and magnetic forces to
    provide a moderate climate.
  • The atmosphere
  • The atmosphere also protects us from high-energy
    radiation and the frigid vacuum of space.

9
Composition of Atmosphere
  • The atmosphere is primarily composed of nitrogen
    (N2, 78), oxygen (O2, 21), and argon (Ar, 1).
  • A number of other very influential components are
    also present the water (H2O, 0 - 7),
    "greenhouse" gases or ozone (O, 0 - 0.01),
    carbon dioxide (CO2, 0.01-0.1).

10
continued
  • Nitrogen, mostly in the form of ammonium and
    nitrate, reaches the Earth's surface as a result
    of atmospheric lightning, precipitation and
    industrial pollution.

11
The Biosphere
  • The biosphere is the life zone of the Earth and
    includes all living organisms, including man, and
    all organic matter that has not yet decomposed.
  • The biosphere is structured into a hierarchy
    known as the food chain whereby all life is
    dependent upon the first tier (i.e. mainly the
    primary producers that are capable of
    photosynthesis).

12
Biosphere Part 2
  • The biosphere can be divided into distinct
    ecosystems that represent the interactions
    between a group of organisms forming a trophic
    pyramid and the environment or habitat in which
    they live.

13
Continued
  • Animals consume nitrogen from plants
  • Plants consume nitrogen from the soil
  • Soil gets nitrogen from water or rain that
    contains nitrogen.

14
Nitrogen Cycle Continued
  • All life requires nitrogen-compounds, e.G.,
    Proteins and nucleic acids.
  • Air, which is 79 nitrogen gas (N2), is the major
    reservoir of nitrogen.
  • But most organisms cannot use nitrogen in this
    form.

15
  • Plants must secure their nitrogen in "fixed"
    form, i.E., Incorporated in compounds such as
    Nitrate ions (NO3-)
  • Ammonia (NH3)
  • Urea (NH2)2CO
  • Animals secure their nitrogen (and all other)
    compounds from plants (or animals that have fed
    on plants).

16
Nitrogen Fixation
  • Three processes are responsible for most of the
    nitrogen fixation in the biosphere are
  • atmospheric fixation by lightning
  • biological fixation by certain microbes - alone
    or in a symbiotic relationship with plants
  • industrial fixation

17
Atmospheric Fixation
  • The enormous energy of lightning breaks nitrogen
    molecules and enables their atoms to combine with
    oxygen in the air forming nitrogen oxides.
  • These dissolve in rain, forming nitrates, that
    are carried to the earth.
  • Atmospheric nitrogen fixation probably
    contributes some 5-8 of the total nitrogen fixed.

18
Biological Fixation
  • The ability to fix nitrogen is found only in
    certain bacteria.
  • Some live in a symbiotic relationship with
    plants of the legume family (e.g., soybeans,
    alfalfa).
  • Some establish symbiotic relationships with
    plants other than legumes (e.g., alders).

19
Continued
  • Some nitrogen-fixing bacteria live free in the
    soil.
  • Nitrogen-fixing cyanobacteria are essential to
    maintaining the fertility of semi-aquatic
    environments like rice paddies.

20
Industrial Fixation
  • Under great pressure, at a temperature of 600C,
    and with the use of a catalyst, atmospheric
    nitrogen and hydrogen (usually derived from
    natural gas or petroleum) can be combined to form
    ammonia (NH3).
  • Ammonia can be used directly as fertilizer, but
    most of its is further processed to urea and
    ammonium nitrate (NH4NO3).

21
Decay
  • Proteins made by plants enter and pass through
    food webs just as carbohydrates do.
  • At each trophic level, their metabolism produces
    organic nitrogen compounds that return to the
    environment, chiefly in excretions.

22
Continued
  • The final beneficiaries of these materials are
    microorganisms of decay. They break down the
    molecules in excretions and dead organisms into
    ammonia.

23
Nitrification
  • Ammonia can be taken up directly by plants -
    usually through their roots.
  • Most of the ammonia produced by decay is
    converted into nitrates. This is accomplished in
    two steps
  • Bacteria of the genus Nitrosomonas oxidize NH3 to
    nitrites(NO2-).
  • Bacteria of the genus Nitrobacter oxidize the
    nitrites to nitrates (NO3-).

24
Continued
  • These two groups or autotrophic bacteria are
    called nitrifying bacteria. Through their
    activities (which supply them with all their
    energy needs), nitrogen is made available to the
    roots of plants.

25
Assimilation
  • Plant roots absorb inorganic ammonia, ammonium
    ions, and nitrate ions. Formed by nitrification
    and nitrogen fixation.
  • Ions are used to make nitrogen containing organic
    molecules such as
  • DNA
  • Amino Acids
  • Proteins

26
Dentrification
  • The three processes above remove nitrogen from
    the atmosphere and pass it through ecosystems.
  • Denitrification reduces nitrates to nitrogen gas,
    thus replenishing the atmosphere.
  • Bacteria are the agents. They live deep in soil
    and in aquatic sediments where conditions are
    anaerobic. They use nitrates as an alternative to
    oxygen for the final electron acceptor in their
    respiration.

27
Human Influence
  • German chemist of WWII, Fritz Haber developed a
    chemical process in which nitrogen and hydrogen
    gas combine to form gaseous ammonia.
  • Coupled with irrigation, this input of nitrogen
    into the soil revolutionized agriculture by
    increasing crop yields

28
Ways Humans Intervene 1
  • We emit a large amount of nitrogen into the
    atmosphere when we burn fuel

29
2
  • We emit heat-trapping nitrous oxide gas into the
    atmosphere through anaerobic bacteria on
    livestock wastes and commercial inorganic
    fertilizers applied to the soil
  • Emission of this gas rise and account for few
    greenhouse gases that can cause global warming
  • When it reaches the stratosphere, it depletes
    some of the ozone layer

30
3
  • We remove nitrogen from the earth's crust when we
    mine nitrogen-containing materials for
    fertilizers
  • Deplete nitrogen from soil by harvesting
    nitrogen-rich crops
  • Leach water-soluble nitrate ions from soil by
    irrigation

31
4
  • Remove nitrogen from soil when we burn grasslands
    and clear forests before planting crops

32
5
  • Add excess nitrogen compounds to aqautic systems
    in agricultural runoff, sewage, and deposition of
    nitrogen compounds from the atmosphere
  • Stimulates excess growth of algae and other
    aquatic plants
  • Breakdown of dead algae by aerobic decomposers
    deplete water of dissolved oxygen and disrupt
    aquatic systems and reduce aquatic biodiversity

33
6
  • Add excess nitrogen compounds to terrestrial
    ecosystems through atmospheric deposition

34
Atmospheric Deposition
  • The movement of reactive nitrogen compounds, such
    as nitric acid, nitrogen dioxide, from the
    atmosphere onto plant leaves and other surfaces

35
6 (continued)
  • The nitrogen becomes available for plant and
    microbial growth, and can lead to weeds which can
    better use nitrogen for growth,
    outgrowing/eliminating other plants that cant use
    nitrogen as well.
  • THUS our excessive inputs of nitrogen into the
    atmosphere can reduce terrestrial biodiversity

36
Works Cited
  • http//liftoff.msfc.nasa.gov/academy/space/atmosph
    ere.html
  • http//www.geog.ouc.bc.ca/physgeog/contents/images
    /lithosphere.gif
  • http//www.oilandgas.org.uk/issues/images/z0002409
    .gif
  • http//www.webref.org/geology/1/lithosphere.htm
  • http//www.bartleby.com/65/li/lithosph.html
  • http//www.elmhurst.edu/chm/onlcourse/chm110/outl
    ines/nitrogencycle.html
  • http//users.rcn.com/jkimball.ma.ultranet/BiologyP
    ages/N/NitrogenCycle.html

37
Continued
  • http//web.geology.ufl.edu/Biosphere.html
  • http//www.cas.muohio.edu/mbi-ws/biogeochemicalcy
    cles/Nitrogen/nitrogen.htmAss
  • http//www.marietta.edu/biol/102/ecosystem.htmlT
    heNitrogenCycle12
  • Living in the Environment/Eleventh Edition/G
    Tyler Miller, Jr.
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