Geochemical Cycles

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Geochemical Cycles

• Carbon Cycle
• Nitrogen Cycle
• Hydrologic Cycle

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The Carbon Cycle

• 1. What is the difference between an organic and
  inorganic molecule?
• Organic molecules contain carbon and inorganic do
  not.
• All living organisms are made of carbon.

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2. Why do all living organisms need carbon?

• Carbon molecules are used for cellular structure,
  and as a source of energy.
• Humans are about ½ carbon molecules.

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3. What is the carbon cycle?Define and diagram.

• The carbon cycle is the movement of carbon
  between the atmosphere, oceans, biosphere and
  geosphere.

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Diagrams!
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4. What is the difference between a net carbon
sink and a net carbon source?

• In a net carbon sink, more carbon enters the pool
  than leaves.
• In a net carbon source, more carbon leaves the
  pool than enters.
• (A pool is a location where carbon is stored)

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5. What are the two main components of the global
carbon cycle?

• The geological cycle.
• The biological cycle.
• Geo means?
• Bio means?

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6. Explain how carbon can move from the Earths
crust to the ocean floor.

• Carbonic acid combines with minerals at the
  surface. (carbonic acid is weak acid rain)
• Due to weathering, carbonates are created.
• By erosion, carbonates are washed into the ocean
  and settle on the bottom.

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7. Explain how carbon on the ocean floor can be
returned to the atmosphere.

• Ocean crust can be subducted under continental
  plates. This melts the rock.
• Magma rises to surface and CO2 is released into
  the atmosphere.

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8. Explain the role of photosynthesis in the
carbon cycle.

• Photosynthesis absorbs atmospheric CO2 and uses
  it to make sugars (food).
• Requires sunlight to occur
• Occurs in all green plants

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9. Equation for photosynthesis.

• energy (sunlight) 6CO2 6H2O ---? C6H12O6
  6O2

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10. Explain the role of respiration in the carbon
cycle.

• Respiration in a process that occurs in cells of
  all living organisms (plants and animals ). It
  produces energy.
• Respiration releases CO2 into the atmosphere.

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11. Equation for respiration.

• Cellular Respiration
• C6H12O6 6O2 ? 6CO2
• 6 H2O energy

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12. Why do atmospheric levels of CO2 rise during
the winter months in the northern hemisphere?

• The green leaves in which photosynthesis occurs
  fall off so photosynthesis stops.
• This causes CO2 levels to rise during that time.
• Do plants still undergo respiration during this
  time?
• What happens to levels when spring arrives?

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13. How do limestone formation and fossil fuel
formation play a role in the carbon cycle?

• Limestone contains carbonates originally formed
  on the ocean floor.
• The carbon was in the ocean water, used to make
  shells of aquatic animals, shells are deposited
  on the ocean floor and eventually turned to rock
  (limestone).

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Fossil fuel formation . . .

• Organic matter (trees, plants etc.) is buried and
  forms coal and oil over a long period of time.
• Carbon is in the organic matter and is eventually
  changed into fuel. Fuels are burned and carbon
  is put back into the atmosphere.

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14. What human activities are contributing to
the increase in CO2 levels?

• Burning of fossil fuels releases carbon faster
  than it can be removed by natural processes.
• Deforestation removes trees that help reduce CO2
  from the atmosphere. Fewer trees more CO2 in
  the atmosphere.

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15. What effects do higher levels of CO2 have on
the earth?

• Global warming.
• Warmer climate melts ice, increasing sea level.
• Glacial retreat will occur
• Species ranges will shift
• Plant growth patterns may change world wide.

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16. What methods do scientists use to understand
how climate has changed in the past?

• Analyze gas bubbles trapped in glacial ice.
• Analyze tree rings
• Analyze ocean and lake floor sediments.
• Data shows levels have been high during
  interglacial periods (like now) and low during
  glacial periods.

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17. What doesIPCC mean?

• Intergovernmental Panel on Climate Change
• Climate experts worldwide that work together to
  report on climate change.

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18. What is the Kyoto Protocol?Does the United
States participate?

• This is a multilateral treaty aimed at averting
  the negative impacts associated with
  human-induced climate change.
• The U.S. has declined to participate.
• The U.S. currently produced about ¼ of global
  carbon dioxide emissions.

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The Nitrogen Cycle

• 1. Why do living organisms need nitrogen?
• Nitrogen is an essential part of DNA and RNA. It
  is also part of proteins.
• Most of the air we breathe in N2.

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2. In order for living organisms to utilize N2,
is must be converted into . .

• Must be converted in a chemically available form
  (its strong triple bond makes in relatively
  inert)
• Ammonium NH4
• Nitrate NO3
• Organic nitrogen such as urea (NH3)2CO

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3. Describe the Nitrogen cycle.Define and
diagram.

• The nitrogen cycle is how nitrogen moves through
  the atmosphere, biosphere and geosphere in
  different forms.

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Diagrams!
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4. Name the 5 main processes that cycle nitrogen
through the biosphere.

• Nitrogen fixation
• Nitrogen uptake (growth)
• Nitrogen mineralization (decay)
• Nitrification
• Denitrification

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5. For each process in 4, do the following

• Process Nitrogen fixation
• a. N2 ? NH4
• b. N2 is converted into ammonium often by
  symbiotic relationships between plants and
  bacteria
• c. Is done by nitrogen fixing organisms such as
  certain bacteria and Blue Green Algae.

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Other forms of natural nitrogen fixation

• Lightning
• Forest fires
• Hot lava flows
• All these provide enough energy to break the
  triple bond but only fix small amounts of
  nitrogen.

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Human activities that fix nitrogen

• Burning fossil fuels
• Using synthetic fertilizers
• Cultivation of legumes (plants such as soybeans
  and alfalfa that fix nitrogen)
• These activities more than double the amounts of
  fixed nitrogen put into the biosphere every year.

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Process Nitrogen uptake

• a. NH4 ? Organic N
• b. Ammonia in the soil is used for plant growth.
• c. Any organism that takes nutrients from the
  soil OR any organism that eats the plants (like
  us!)

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Process Nitrogen Mineralization

• a. Organic N ? NH4
• b. The conversion of organic nitrogen back into
  inorganic nitrogen. We call this decay.
  Decomposers convert it as a part of the process.
• c. Bacteria and fungi are decomposers

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Process Nitrification

• a. NH4 ? NO3-
• b. Ammonium produced by decomposition is
  converted to nitrate. This only occurs in oxygen
  rich environments.
• c. Nitrifying bacteria.

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Process Denitrification

• a. NO3- ? N2 N2O
• b. Nitrate and nitrite are converted into
  dinitrogen (N2) and other forms of nitrogen.
  Most N2 is lost to the atmosphere. This is the
  only process that removes nitrogen from
  ecosystems.
• c. Certain bacteria

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6. How have synthetic nitrogen fertilizers
affected the following

• a. Groundwater
• Normal levels of nitrates should be 10mg /L (as
  set by the EPA)
• Runoff from fields can increase the levels of
  nitrates above this

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6 b c. Coastal Areas, Lakes

• Inflow from polluted rivers can cause
  eutrophication (over-enrichment) which leads to
  fish kill, harmful algal blooms and species
  shifts.

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7. How does reactive nitrogen affect our
atmosphere?

• Can enter the atmosphere as NO (nitrous oxide)
  which is a component of smog.
• NO is also a significant part of acid rain

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8. How can acid rain affect vegetation? Give an
example.

• Higher levels of acid rain have been blamed for
  forest death and decline
• Where? In the Northeast U.S. and Europe

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The Hydrologic Cycle

• 1. Has the amount of H2O on Earth always been
  constant? How do you know?
• Yes, the amount of water on Earth is constant.
  It just changes form. It exists in the
  atmosphere, in resevoirs and on land.

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2. What is the hydrologic cycle?

• The hydrologic cycle is a process by which water
  is constantly cycling through resevoirs (oceans,
  atmosphere, land).

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3. 97 of Earths water is in ___.

• The oceans.
• 4. 3 of Earths water is ______.
• Freshwater.

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5. Where is most freshwater found?

• 78 of freshwater in contained in glaciers.

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6. What process returns water vapor to the
atmosphere? Explain.
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7. How is water vapor returned to the surface?
Explain.

• By the process of condensation. Water vapor
  turns into liquid water when the air reaches the
  dew point.

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8. What factors determine if precipitation will
soak into the soil?

• The amount and intensity of the rain
• The prior condition of the soil
• The slope of the landscape
• Presence of vegetation

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9. Explain the role of transpiration in the water
cycle.

• Transpiration is the process by which plants lose
  water by evaporation from the surface of their
  leaves. This puts water vapor back into the
  atmosphere.

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TRANSPIRATION
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10. What is an aquifer?

• An aquifer is a resevoir of water that exists
  below the surface in rocks that are saturated.
• Ogallala
• Aquifer

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11. How can changes in the hydrologic cycle
affect us? (3 ways)

• Changes in the circulation of water within the
  atmosphere and oceans can result in major climate
  shifts.
• If warming trend continues, more glacial ice will
  melt, raising sea level
• More evaporation will lead to more precip. This
  may cause more severe weather events

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11. continued

• Freshwater resources are being used faster than
  they can be recharged naturally. Main cause is
  irrigation of farmland.
• Surface water contamination by human and animal
  waste
• Any change affects the entire cycle.

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Hydrologic Cycle Website

• http//ga.water.usgs.gov/edu/watercycle.html