How do ecosystems work? Part 2!
Chapter 41
How does increased CO2 cause
global warming?
 Greenhouse effect:
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Certain gases in the atmosphere
(water vapor, methane, CO2 )
absorb heat.
More greenhouse gases  more
trapped heat
 Earth does need some
greenhouse gases!

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Without any heat-absorbing
molecules, the earth would be
too cold for life!
But we are now overheating the
earth…
Some potential impacts of global warming
 Melting of ice  sea level rise

Some low-lying islands have already been inundated
 Changes in weather patterns

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Droughts in some places, floods in others
Shift in agricultural centers (loss of some, gain of others)
 Increased hurricane intensity
 Shifts in species distribution

Example 1: Mosquitoes that carry Plasmodium (the malaria
parasite)


How have they shifted? (Think about logically, considering they are
found in warm climates…)
Example 2: Penguins in the Antarctic
Focus: Antarctic penguins
Gentoo penguins
(Photo: B. Grunewald)
Chinstrap penguin
(Photo: Shir Goldberg
Adelie penguins
(Photo: K. Haberman)
Shift in penguin species on the Antarctic Peninsula
What can you do???

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Overall, reduce use of fossil fuels.
Buy energy efficient appliances.
Line dry your clothes.
BUY LOCALLY!

Shipping of products around the world uses a great
deal of fossil fuels.
 Buy certified organic food (minimal use of
fertilizers that use fossil fuels to make.)
 Invest in alternative, renewable energy.
 Vote wisely…
Nitrogen cycle (preview)
Nitrogen cycle: Nitrogen fixation
 The atmosphere is earth’s major nitrogen reservoir

N2 gas not directly usable by producers
 Nitrogen fixation converts N2 to usable nitrogen
forms (ammonia and nitrate)

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Lightning fixes nitrogen
Bacteria fix nitrogen
Humans fix nitrogen via chemical processing to make
fertilizers or by burning fossil fuels.
Nitrogen cycle: Cycling through food webs
 Primary producers
take up ammonia and
nitrate

Convert to organic
nitrogen (part of protein
& DNA molecules)
 Consumers feed on
producers

Gain organic molecules
with nitrogen
 Bacteria decompose
dead organisms

Convert back into
inorganic forms that can
be taken up by producers
Nitrogen cycle: Denitrification
 Denitrifying
bacteria convert
nitrates and
ammonia back
into atmospheric
nitrogen
Nitrogen cycle (review)
Phosphorous cycle (preview)
Phosphorous cycle: How does phosphorous
enter ecosystems?
 Phosphorous comes
from rocks (reservoir
for phosphorous)
 Weathering of rocks
and runoff moves
phosphorous into
ecosystems
 Human-synthesized
phosphorous (as
phosphates) are also
applied to crops
Phosphorous cycle: Cycling through food webs
 Primary producers take
up phosphorous

Convert inorganic
phosphates to organic
phosphorous (part of
protein, lipid & DNA
molecules)
 Consumers feed on
producers (arrow
missing in diagram!)

Gain organic molecules
with phosphorous
 Bacteria decompose
dead organisms

Convert back into
inorganic forms that can
be taken up by producers
Phosphorous cycle: Loss of phosphorous from
ecosystems
 Phosphorous ends up
in aquatic sediments
(such as deep ocean)

Will only be
reintroduced with
uplifting of mountains!
Phosphorous cycle (review)
Phosphorous and aquatic ecosystems
 Agricultural and domestic
runoff puts excessive
amounts of phosphorous into
aquatic ecosystems

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Intense blooms of phytoplankton
Often these are toxic species
Why?
Dead zones: Too much
phytoplankton at once  All dies
at once bacterial decomposition
of excess phytoplankton reduces
oxygen  animals die…
 Clean Water Act (1977)

Reduction of phosphate-based
detergents has decreased this
problem in some places