Chemical Cycles

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Chemical Cycles
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Outline
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Major cycles
TECTONIC Creation and destruction of earth's
crust
ROCK Produces rocks and soils
HYDROLOGIC Cycling of water
BIOGEOCHEMICAL Cycling of chemical elements
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Hydrologic cycle
DEFINITION Cycling of water through soil,
atmosphere, surface waters, ice caps, glaciers
WATER Exists as liquid, solid, or vapor
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Atmosphere (0.001)
Lakes (0.009)
Rivers (0.001)
Oceans (97.2)
Shallow Groundwater (0.03)
Hydrologic (Water) Cycle
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Land Precipitation
Evaporation and Transpiration
Ocean Precipitation
Ocean Evaporation
Hydrologic (Water) Cycle
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Biogeochemical cycles
DEFINITION Cycling of chemical elements
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What is an element?
Table 4.1
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Atoms
Comprised of protons, neutrons, and electrons
Protons and neutrons are about 1000 times more
massive than electrons
Protons positively charge, electrons negatively
charged, and neutrons neutrally charged What
does this mean?
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Where do elements come from?
SUPERNOVA Exploding stars Elements other than
H formed in stars Scattered when star
explodes Condense into planets Cycle within
planet (closed system)
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Elements cycling
Elements can form different compounds while
cycling
N2 (nitrogen gas)
NO3- (nitrate)
NH3 (ammonia)
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An example of cycling - carbon
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General cycle characteristics
Reservoir B
Reservoir A
Flux A ? B
Flux B ? A
FLUX RATE amount entering or leaving a reservoir
per unit time (high flux rate rapid cycling)
RESIDENCE TIME length of time material stays in
reservoir (short residence time rapid cycling)
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Rates of cycling
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Biogeochemical cycles
Cycling of materials through
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Why study them?
Human activities can affect the cycling of
materials
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What cycles are important?
Macronutrients
Elements needed in large quantities by living
things Ex. carbon, nitrogen, hydrogen, oxygen,
phosphorous
Micronutrients
Elements needed in small quantities by living
things Ex. copper, zinc
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Cycling within ecosystems
Cycling usually examined within ecosystems
african savanna
1 m2 of topsoil
Examples
lake
a puddle of water
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Cycling overview
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Biota and cycling
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Ignore units, focus on relative values
Atmosphere (720 3 per yr)
Soils (1500)
Land plants (560)
Shallow ocean (39,000)
Fossil fuels (4000)
Sedimentary rocks (100,000,000)
Carbon Storage
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Volcanoes (0.1 per yr)
Burning fossil fuels (5.4 per yr)
Land photosynthesis and respiration (120 per yr)
Ocean photosynthesis and respiration (107 per
yr)
Carbon Cycle
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Carbon Cycle in a lake
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Nitrogen cycle
Atmosphere (4,000,000,000)
Land plants (3,500)
Most organisms can't use nitrogen gas directly -
it must first be "fixed" into a solid form by
bacteria
Organic soils (9,500)
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Nitrogen fixation (bacteria)
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Nitrogen Fixation and Denitrification rates
Land Fixation (140 per yr)
Ocean Fixation (30 per yr)
Industrial Fixation (100 per yr)
Land denitrification (130 per yr)
Ocean denitrification (110 per yr)
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Phosphorous Cycle
Phosphorous has no gaseous phase it is a
limiting nutrient because of this (does not
cycle quickly)
Cycle has been greatly enhanced by mankind
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Sulfur Cycle
Necessary for some amino acids and sulfate esters
Naturally gets into the cycle by plants absorbing
it through the soil
Mankind has greatly enhanced this cycle by
burning sulfur-bearing coal
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Human effects on cycles
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Human impacts on cycling
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Water Human impacts
Transpiration (water release from photosynthesis)
by vegetation forms clouds
Tropical forests cleared
Tropical deforestation forests cleared less
transpiration water cycle affected
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Water Human impacts (?) Global temperature
increases
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Carbon Human impacts (?) Global warming
Burning fossil fuels more CO2 in
atmosphere note small contribution compared to
other cycle components may be sufficient to
alter carbon cycle
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Carbon Human impacts
Deforestation burning adds CO2 to
atmosphere less vegetation to take up CO2 uptake
from atmosphere carbon cycle disrupted
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Nitrogen Human impacts Industrial fixation
Fertilizers nitrogen historically
limiting industrial fixing - late 1800's allows
large-scale farming
Effects overwhelms denitrification
rates eutrophies waterways rapid population growth
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Feedback
Output from a system acts as input in order to
change the system
Ex. Microphone near the speaker
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Negative Feedback
Change that drives the system back to equilibrium

• Humans increase the amount of carbon dioxide in
  the atmosphereby burning fossil fuels.
• Increased carbon dioxide causes increase in plant
  life
• More plants means more carbon dioxide absorbed -gt
  lesscarbon dioxide in the air

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Positive Feedback
Change that drives a system away from equilibrium

• Humans increase the amount of carbon dioxide in
  the atmosphereby burning fossil fuels.
• Increased carbon dioxide causes atmospheric
  temperature increase
• Higher temperatures means oceans less able to
  hold carbondioxide -gt more carbon dioxide in the
  air