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Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures forBio logy, Seventh Edi t ion
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 54
Ecosystems
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Overview: Ecosystems, Energy, and Matter
An ecosystem consists of all the organismsliving in a community
As well as all the abiotic factors with whichthey interact
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Ecosystems can range from a microcosm, such
as an aquarium To a large area such as a lake or forest
Figure 54.1
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Regardless of an ecosystems size
Its dynamics involve two main processes:energy flow and chemical cycling
Energy flows through ecosystems
While matter cycles within them
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Concept 54.1: Ecosystem ecology emphasizes
energy flow and chemical cycling Ecosystem ecologists view ecosystems
As transformers of energy and processors ofmatter
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Ecosystems and Physical Laws
The laws of physics and chemistry apply to
ecosystems Particularly in regard to the flow of energy
Energy is conserved
But degraded to heat during ecosystemprocesses
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Trophic Relationships
Energy and nutrients pass from primary
producers (autotrophs) To primary consumers (herbivores) and then to
secondary consumers (carnivores)
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Energy flows through an ecosystem
Entering as light and exiting as heat
Figure 54.2
Microorganismsand other
detritivores
Detritus
Primary producers
Primary consumers
Secondaryconsumers
Tertiaryconsumers
Heat
Sun
Key
Chemical cycling
Energy flow
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Nutrients cycle within an ecosystem
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Decomposition
Decomposition
Connects all trophic levels
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Detritivores, mainly bacteria and fungi, recycleessential chemical elements By decomposing organic material and returning
elements to inorganic reservoirs
Figure 54.3
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Concept 54.2: Physical and chemical factors
limit primary production in ecosystems Primary production in an ecosystem
Is the amount of light energy converted tochemical energy by autotrophs during a giventime period
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Ecosystem Energy Budgets
The extent of photosynthetic production
Sets the spending limit for the energy budgetof the entire ecosystem
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The Global Energy Budget
The amount of solar radiation reaching the
surface of the Earth Limits the photosynthetic output of ecosystems
Only a small fraction of solar energy
Actually strikes photosynthetic organisms
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Gross and Net Primary Production
Total primary production in an ecosystem
Is known as that ecosystems gross primaryproduction (GPP)
Not all of this production
Is stored as organic material in the growingplants
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Net primary production (NPP)
Is equal to GPP minus the energy used by theprimary producers for respiration
Only NPP
Is available to consumers
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Different ecosystems vary considerably in their netprimary production And in their contribution to the total NPP on Earth
Lake and stream
Open oceanContinental shelf
Estuary
Algal beds and reefsUpwelling zones
Extreme desert, rock, sand, ice
Desert and semidesert scrubTropical rain forest
SavannaCultivated land
Boreal forest (taiga)
Temperate grassland
Tundra
Tropical seasonal forest
Temperate deciduous forestTemperate evergreen forest
Swamp and marsh
Woodland and shrubland
0 10 20 30 40 50 60 0 500 1,000 1,500 2,000 2,500 0 5 10 15 20 25
Percentage of Earths net primary production
Key
Marine
Freshwater (on continents)
Terrestrial
5.20.30.10.1
4.7
3.53.32.92.7
2.41.8
1.71.6
1.5
1.31.00.4
0.4
125360
1,500
2,500
5003.090
2,200
900600
800600
700
1401,600
1,2001,300
2,000250
5.61.20.9
0.1
0.040.9
22
7.99.1
9.6
5.4
3.50.6
7.1
4.93.8
2.30.3
65.0 24.4
Figure 54.4a c
Percentage of Earths surface area
(a) Average net primaryproduction (g/m 2 /yr)
(b) (c)
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Overall, terrestrial ecosystems
Contribute about two-thirds of global NPP andmarine ecosystems about one-third
Figure 54.5
180 120 W 60 W 0 60 E 120 E 180
North Pole
60 N
30 N
Equator
30 S
60 S
South Pole
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Primary Production in Marine and FreshwaterEcosystems
In marine and freshwater ecosystems Both light and nutrients are important in
controlling primary production
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L ight L imitation
The depth of light penetration
Affects primary production throughout thephotic zone of an ocean or lake
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Nutrient L imitation
More than light, nutrients limit primaryproduction
Both in different geographic regions of theocean and in lakes
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A limiting nutrient is the element that must beadded
In order for production to increase in aparticular area
Nitrogen and phosphorous Are typically the nutrients that most often limit
marine production
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Nutrient enrichment experiments Confirmed that nitrogen was limiting phytoplankton
growth in an area of the ocean
EXPERIMENT Pollution from duck farms concentrated nearMoriches Bay adds both nitrogen and phosphorus to the coastal wateroff Long Island. Researchers cultured the phytoplankton Nannochloris
atomus with water collected from several bays.
Figure 54.6
Coast of Long Island, New York. The numbers on the map indicatethe data collection stations.
Shinnecock
BayMoriches Bay
Atlantic Ocean
30 21
19
151154
2
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Figure 54.6
(a) Phytoplankton biomass and phosphorus concentration (b) Phytoplankton response to nutrient enrichment
GreatSouth Bay
MorichesBay
ShinnecockBay
Startingalgal
density
2 4 5 11 30 15 19 21
30
24
18
12
6
0
Unenriched control
Ammonium enrichedPhosphate enriched
Station number
P h y t o p
l a n
k t o n
( m i l l i o n s o f c e
l l s p e r m
L )
876543210
2 4 5 11 30 15 19 21
87
654
3210
I n o r g a n
i c p
h o s p
h o r u s
( g a
t o m s
/ L )
P h y t o p
l a n
k t o n
( m i l l i o n s o
f c e
l l s / m L )
Station number
CONCLUSION Since adding phosphorus, which was already in rich supply, had no effect onNannochloris growth, whereas adding nitrogen increased algal density dramatically, researchersconcluded that nitrogen was the nutrient limiting phytoplankton growth in this ecosystem.
Phytoplankton
Inorganicphosphorus
RESULTS Phytoplankton abundance parallels the abundance of phosphorus in the water (a). Nitrogen,however, is immediately taken up by algae, and no free nitrogen is measured in the coastal waters. Theaddition of ammonium (NH 4 ) caused heavy phytoplankton growth in bay water, but the addition of
phosphate (PO 43
) did not induce algal growth (b).
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Experiments in another ocean region
Showed that iron limited primary production
Table 54.1
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The addition of large amounts of nutrients tolakes
Has a wide range of ecological impacts
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In some areas, sewage runoff
Has caused eutrophication of lakes, which canlead to the eventual loss of most fish species fromthe lakes
Figure 54.7
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Primary Production in Terrestrial and WetlandEcosystems
In terrestrial and wetland ecosystems climaticfactors
Such as temperature and moisture, affect
primary production on a large geographic scale
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The contrast between wet and dry climates
Can be represented by a measure calledactual evapotranspiration
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Actual evapotranspiration Is the amount of water annually transpired by plants
and evaporated from a landscape
Is related to net primary production
Figure 54.8 Actual evapotranspiration (mm H 2O/yr)
Tropical forest
Temperate forest
Mountain coniferous forest
Temperate grassland
Arctic tundra
Desertshrubland
N e
t p r i m a r y p r o
d u c
t i o n
( g / m 2 / y r )
1,000
2,000
3,000
0500 1,000 1,5000
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On a more local scale A soil nutrient is often the limiting factor in primary
production
Figure 54.9
EXPERIMENT Over the summer of 1980, researchers addedphosphorus to some experimental plots in the salt marsh, nitrogento other plots, and both phosphorus and nitrogen to others. Someplots were left unfertilized as controls.
RESULTS
Experimental plots receiving justphosphorus (P) do not outproducethe unfertilized control plots.
CONCLUSION
L i v e ,
a b o v e - g r o u n
d b i o m a s s
( g d r y w
t / m
2 )
Adding nitrogen (N)boosts net primaryproduction.
300
250
200
150
100
50
0June July August 1980
N P
N only
Control
P only
These nutrient enrichment experimentsconfirmed that nitrogen was the nutrient limiting plant growth inthis salt marsh.
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Concept 54.3: Energy transfer between trophiclevels is usually less than 20% efficient
The secondary production of an ecosystem
Is the amount of chemical energy inconsumers food that is converted to their ownnew biomass during a given period of time
P d i Effi i
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Production Efficiency
When a caterpillar feeds on a plant leaf
Only about one-sixth of the energy in the leafis used for secondary production
Figure 54.10
Plant materialeaten by caterpillar
Cellularrespiration
Growth (new biomass)
Feces 100 J
33 J
200 J
67 J
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The production efficiency of an organism
Is the fraction of energy stored in food that isnot used for respiration
T hi Effi i dE l i lP id
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Tr ophic Efficiency and Ecological Pyramids
Trophic efficiency
Is the percentage of production transferredfrom one trophic level to the next
Usually ranges from 5% to 20%
P id f P d ti
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Pyramids of Production
This loss of energy with each transfer in a food chain
Can be represented by a pyramid of net production
Figure 54.11
Tertiaryconsumers
Secondaryconsumers
Primaryconsumers
Primaryproducers
1,000,000 J of sunlight
10 J
100 J
1,000 J
10,000 J
P id f Bi
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Pyramids of Biomass
One important ecological consequence of lowtrophic efficiencies
Can be represented in a biomass pyramid
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Most biomass pyramids
Show a sharp decrease at successively highertrophic levels
Figure 54.12a
(a) Most biomass pyramids show a sharp decrease in biomass atsuccessively higher trophic levels, as illustrated by data froma bog at Silver Springs, Florida.
Trophic level Dry weight
(g/m2
)
Primary producers
Tertiary consumers
Secondary consumers
Primary consumers
1.5
11
37809
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Certain aquatic ecosystems
Have inverted biomass pyramids
Figire 54.12b
Trophic level
Primary producers (phytoplankton)
Primary consumers (zooplankton)
(b) In some aquatic ecosystems, such as the English Channel,a small standing crop of primary producers (phytoplankton)supports a larger standing crop of primary consumers (zooplankton).
Dry weight(g/m 2)
21
4
Pyramids of Numbers
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Pyramids of Numbers
A pyramid of numbers
Represents the number of individualorganisms in each trophic level
Figure 54.13
Trophic level Number ofindividual organisms
Primary producers
Tertiary consumers
Secondary consumers
Primary consumers
3
354,904
708,624
5,842,424
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The dynamics of energy flow throughecosystems
Have important implications for the humanpopulation
Eating meat Is a relatively inefficient way of tapping
photosynthetic production
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Worldwide agriculture could successfully feedmany more people
If humans all fed more efficiently, eating onlyplant material
Figure 54.14
Trophic level
Secondaryconsumers
Primaryconsumers
Primaryproducers
The Green World Hypothesis
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The Green World Hypothesis
According to the green world hypothesis
Terrestrial herbivores consume relatively littleplant biomass because they are held in checkby a variety of factors
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Most terrestrial ecosystems
Have large standing crops despite the largenumbers of herbivores
Figure 54.15
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The green world hypothesis proposes severalfactors that keep herbivores in check Plants have defenses against herbivores Nutrients, not energy supply, usually limit
herbivores Abiotic factors limit herbivores Intraspecific competition can limit herbivore
numbers Interspecific interactions check herbivore
densities
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Concept 54.4: Biological and geochemicalprocesses move nutrients between organic andinorganic parts of the ecosystem
Life on Earth
Depends on the recycling of essential chemicalelements
Nutrient circuits that cycle matter through anecosystem Involve both biotic and abiotic components and
are often called biogeochemical cycles
A General Model of Chemical Cycling
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A General Model of Chemical Cycling
Gaseous forms of carbon, oxygen, sulfur, andnitrogen
Occur in the atmosphere and cycle globally
Less mobile elements, including phosphorous,potassium, and calcium Cycle on a more local level
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A general model of nutrient cycling
Includes the main reservoirs of elements andthe processes that transfer elements betweenreservoirs
Figure 54.16
Organicmaterialsavailable
as nutrients
Livingorganisms,detritus
Organic
materialsunavailable as nutrients
Coal, oil,peat
Inorganicmaterialsavailable
as nutrients
Inorganicmaterials
unavailable as nutrients
Atmosphere,soil, water
Mineralsin rocksFormation of
sedimentary rock
Weathering,erosion
Respiration,decomposition,excretion
Burningof fossil fuels
Fossilization
Reservoir a Reservoir b
Reservoir c Reservoir d
Assimilation,photosynthesis
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All elements
Cycle between organic and inorganicreservoirs
Biogeochemical Cycles
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Biogeochemical Cycles
The water cycle and the carbon cycle
Figure 54.17
Transportover land
Solar energy
Net movement ofwater vapor by wind
Precipitationover ocean
Evaporationfrom ocean
Evapotranspirationfrom land
Precipitationover land
Percolationthroughsoil
Runoff andgroundwater
CO 2 in atmosphere
Photosynthesis
Cellularrespiration
Burning offossil fuelsand wood
Higher-levelconsumersPrimary
consumers
DetritusCarbon compoundsin water
Decomposition
THE WATER CYCLE THE CARBON CYCLE
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Water moves in a global cycle
Driven by solar energy
The carbon cycle
Reflects the reciprocal processes ofphotosynthesis and cellular respiration
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The nitrogen cycle and the phosphorous cycle
Figure 54.17
N2 in atmosphere
Denitrifyingbacteria
Nitrifyingbacteria
Nitrifyingbacteria
Nitrification
Nitrogen-fixingsoil bacteria
Nitrogen-fixingbacteria in rootnodules of legumes
Decomposers
Ammonification
Assimilation
NH3 NH4+
NO 3
NO 2
Rain
Plants
Consumption
Decomposition
Geologicuplift
Weatheringof rocks
Runoff
SedimentationPlant uptakeof PO 43
Soil
Leaching
THE NITROGEN CYCLE THE PHOSPHORUS CYCLE
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Most of the nitrogen cycling in naturalecosystems
Involves local cycles between organisms andsoil or water
The phosphorus cycle Is relatively localized
Decomposition and Nutrient Cycling Rates
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Decomposition and Nutrient Cycling Rates
Decomposers (detritivores) play a key role
In the general pattern of chemical cycling
Figure 54.18
Consumers
Producers
Nutrientsavailable
to producers
Abioticreservoir
Geologicprocesses
Decomposers
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Vegetation and Nutrient Cycling: The Hubbard
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Vegetation and Nutrient Cycling: The HubbardBrook Experimental Forest
Nutrient cycling Is strongly regulated by vegetation
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Long-term ecological research projects
Monitor ecosystem dynamics over relativelylong periods of time
The Hubbard Brook Experimental Forest
Has been used to study nutrient cycling in aforest ecosystem since 1963
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The research team constructed a dam on thesite
To monitor water and mineral loss
Figure 54.19a
(a) Concrete dams and weirs built across streams atthe bottom of watersheds enabled researchers tomonitor the outflow of water and nutrients from theecosystem.
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Net losses of water and minerals were studied And found to be greater than in an undisturbed area
These results showed how human activity Can affect ecosystems
Figure 54.19c(c) The concentration of nitrate in runoff from the deforested watershed was 60 times
greater than in a control (unlogged) watershed.
N i t r a t e
c o n c e n
t r a
t i o n
i n r u n o f f
( m g
/ L )
Deforested
Control
Completion oftree cutting
1965 1966 1967 1968
80.060.040.020.0
4.03.02.01.0
0
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Concept 54.5: The human population isdisrupting chemical cycles throughout thebiosphere
As the human population has grown in size
Our activities have disrupted the trophicstructure, energy flow, and chemical cycling ofecosystems in most parts of the world
Nutrient Enrichment
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In addition to transporting nutrients from onelocation to another
Humans have added entirely new materials,some of them toxins, to ecosystems
Agricul ture and Nitrogen Cycling
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g g y g
Agriculture constantly removes nutrients fromecosystems
That would ordinarily be cycled back into the soil
Figure 54.20
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Nitrogen is the main nutrient lost throughagriculture
Thus, agriculture has a great impact on thenitrogen cycle
Industrially produced fertilizer is typically usedto replace lost nitrogen
But the effects on an ecosystem can be
harmful
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When excess nutrients are added to anecosystem, the critical load is exceeded
And the remaining nutrients can contaminategroundwater and freshwater and marineecosystems
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Sewage runoff contaminates freshwaterecosystems
Causing cultural eutrophication, excessivealgal growth, which can cause significant harmto these ecosystems
Acid Precipitation
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Combustion of fossil fuels
Is the main cause of acid precipitation
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North American and European ecosystemsdownwind from industrial regions Have been damaged by rain and snow containing
nitric and sulfuric acid
Figure 54.21
4.6
4.64.3
4.14.3
4.6
4.64.3
Europe
North America
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By the year 2000 The entire contiguous United States was affected by
acid precipitation
Figure 54.22
Field pH5.3
5.2 5.35.1 5.25.0 5.14.9 5.04.8 4.94.7 4.84.6 4.74.5 4.64.4 4.54.3 4.4
4.3
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Environmental regulations and new industrialtechnologies
Have allowed many developed countries toreduce sulfur dioxide emissions in the past 30years
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In biological magnification Toxins concentrate at higher trophic levels
because at these levels biomass tends to be lower
Figure 54.23
C o n c e n
t r a
t i o n o
f P C B s
Herringgull eggs124 ppm
Zooplankton0.123 ppm
Phytoplankton0.025 ppm
Lake trout4.83 ppm
Smelt1.04 ppm
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In some cases, harmful substances
Persist for long periods of time in anecosystem and continue to cause harm
Atmospheric Carbon Dioxide
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One pressing problem caused by humanactivities
Is the rising level of atmospheric carbondioxide
Rising Atmospher ic CO 2
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Due to the increased burning of fossil fuels andother human activities
The concentration of atmospheric CO 2 has beensteadily increasing
Figure 54.24
C O
2 c o n c e n
t r a
t i o n
( p p m
)
390
380
370
360
350
340
330
320
310
3001960 1965 1970 1975 1980 1985 1990 1995 2000 2005
1.05
0.90
0.75
0.60
0.45
0.30
0.15
0
0.15
0.30
0.45
T e m p e r a
t u r e v a r i a
t i o n
( C )
Temperature
CO 2
Year
H ow El evated CO 2 Affects F orest Ecology: The
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F ACTS-I Exper iment
The FACTS-I experiment is testing how elevated CO 2
Influences tree growth, carbon concentration in soils,and other factors over a ten-year period
Figure 54.25
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Increased levels of atmospheric CO 2 aremagnifying the greenhouse effect
Which could cause global warming andsignificant climatic change
Depletion of Atmospheric Ozone
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Life on Earth is protected from the damagingeffects of UV radiation
By a protective layer or ozone moleculespresent in the atmosphere
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Satellite studies of the atmosphere Suggest that the ozone layer has been gradually
thinning since 1975
Figure 54.26
O z o n e
l a y e r
t h i c k n e s s
( D o b s o n u n
i t s
)
Year (Average for the month of October)
350
300
250
200
150
100
50
01955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
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Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The destruction of atmospheric ozone
Probably results from chlorine-releasingpollutants produced by human activity
Figure 54.27
1
2
3
Chlorine from CFCs interacts with ozone (O 3),forming chlorine monoxide (ClO) andoxygen (O 2).
Two ClO moleculesreact, formingchlorine peroxide (Cl 2O 2).
Sunlight causesCl2O2 to breakdown into O 2 and freechlorine atoms.The chlorineatoms can beginthe cycle again.
Sunlight
Chlorine O 3
O 2
ClO
ClO
Cl2O 2
O 2
Chlorine atoms
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Scientists first described an ozone hole
Over Antarctica in 1985; it has increased insize as ozone depletion has increased
(a) October 1979 (b) October 2000