Biogeochemical Cycles - 1
Class Lecture Goals
1. What are systems?
2. What are biogeochemical cycles?
3. Why are they important?
4. What is common about them?
5. Carbon and nitrogen cycles
6. Focus on the Water Cycle (Monday)
Today’s Topic: “Did Logging
Worsen Floods?”
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State Senate Committee
Weyerhaeuser Co.
State DNR
David Montgomery
Phil Mote
Ideas
– System: Watershed
– Cumulative effects
– Climate Change
What is a system?
• System: a collection of matter, parts, or
components which are included inside a specified,
often arbitrary, boundary. Example: Ecosystem
• Systems often have inputs and outputs.
• For dynamic systems, by definition, one or more
aspects of the system change with time.
– Example of a simple dynamic system: bathtub or your
‘bank’ account.
Flux
• The
boundary
Pool of a dynamic system is chosen for
convenient conceptual separation for the system
Carbon
dioxide
Sugar
C-pool
Night
Reading Assignments
• Examine this web page
(http://www.cses.washington.edu/cig/pnwc/cc.shtml)
Select the true statement from
below for the PNW: Climate
change will
1. Increase
precipitation &
snowpack
2. Increase
temperature &
snowpack
3. Increase
precipitation &
decrease
snowpack
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Answer Now!
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10
What are biogeochemical cycles?
• Earth system has four parts
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Atmosphere
Hydrosphere
Lithosphere
Biosphere
• Biogeochemical cycles: The chemical
interactions (cycles) that exist between
the atmosphere, hydrosphere,
lithosphere, and biosphere.
• Abiotic (physio-chemical) and biotic
processes drive these cycles
• Focus on carbon and water cycles (but
could include all necessary elements for
life). N - cycle weakly touched on!
What is common amongst them?
• Each compound (water, carbon, nitrogen)
typically exists in all four parts of the Earth
System
• There are
– ‘Pools’
– Fluxes in and out of pools
– Chemical or biochemical transformations
• Transformations
– are important
– can lead to positive & negative consequences
Transformations
Examples of Transformations
1. Carbon cycle: Organic compounds to CO2
(processes: respiration, decomposition, or fire)
2. Carbon cycle: CO2 to organic compounds (process:
photosynthesis)
3. Nitrogen cycle: N2 to NO3 (atmospheric nitrogen to
plant utilizable nitrate) (process: N-fixation)
4. Nitrogen cycle: N2 to NH3 (plant utilizable ammonia)
(process: Haber-Bosch Industrial N-fixation)
5. Water cycle: Liquid water to water vapor (process:
evaporation and evapo-transpiration)
6. Water cycle: Water vapor to liquid water (process:
condensation)
Carbon Cycle
5000
http://www.epa.gov/climatechange/kids/carbon_cycle_version2.html
Carbon Cycle Data
760
• Burning of fossil
fuels
• Land conversion
• Cement
• Role of Oceans
• Role of terrestrial
plants (trees &
soils)
Lithosphere
Changes in Atmospheric C02 - 1
Dr. Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/cgg/trends)
Changes in Atmospheric C02 - 2
http://www.whrc.org/resources/online_publications/warming_earth/scientific_evidence.htm
Key Aspects of the Carbon Cycle
• Carbon is the skeleton of all life.
• Carbon dioxide is a critical gas:
– Taken up by plants in photosynthesis
– Released by plants and animals in respiration
– Released during decomposition (and fires)
– Greenhouse gas (greenhouse effect - your car
in the sun)
Question: Photosynthesis is
an example of a pool
1. True
2. False
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Answer Now!
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Nitrogen Cycle
Forms of Nitrogen (N2)
1. N2 - inert gas, 78% of the atmosphere
2. NO, N20, NO2 - other gases of nitrogen, not directly
biologically important. Part of the gases found in
smog.
3. NO3- (nitrate) and NH4+ (ammonium) -- ionic forms of
nitrogen that are biologically usable.
http://soil.gsfc.nasa.gov/NFTG/nitrocyc.htm
Nitrogen Cycle
Forms & Sources of biologically available nitrogen (N2)
For plants
• NO3- (nitrate)
• NH4+ (ammonium)
• Sources: N-fixation by plants (N2 to NH3 and N2 to NO3),
lightening, bacteria decomposition of organic N (amino
acids & proteins)
For animals
• Organic forms: amino acids and proteins (from plants or
other animals)
http://soil.gsfc.nasa.gov/NFTG/nitrocyc.htm
Nitrogen Cycle
Losses of nitrogen from system
• In bogs, lakes (places of low oxygen), NO3- is converted
to N2 by bacteria (get their oxygen from the NO3)
• Volatilization of NH4+ (urea) to ammonia gas (NH3) warm, dry conditions.
• Leaching of NO3- (nitrate)
• Erosion
• Fire (combustion)
http://soil.gsfc.nasa.gov/NFTG/nitrocyc.htm
Nitrogen Sources over time
Nitrogen Cycle: Key Points
• Nitrogen is in the atmosphere as N2 (78%)
• N2 is an inert gas and cannot be used by
plants or animals
• N2 can be converted to a usable form via
– Lightening
– N-fixing plants and cyanobacteria
– Industrial process (energy intensive)
• Nitrogen limits plant growth
• Nitrogen is easily lost from biological
systems
Summary
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1. What are systems?
2. What are biogeochemical cycles?
3. Why are they important?
4. What is common about them?
5. Carbon and nitrogen cycles