54 Ecosystems

8/14/2019 54 Ecosystems

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Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

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 of matter


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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)



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



Nutrients cycle within an ecosystem



Decomposition

Decomposition

Connects all trophic levels



Detritivores, mainly bacteria and fungi, recycleessential chemical elements

By decomposing organic material and returningelements to inorganic reservoirs

Figure 54.3



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



Ecosystem Energy Budgets

The extent of photosynthetic production

Sets the spending limit for the energy budgetof the entire ecosystem



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



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 netprimary 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

5.61.2

0.90.1

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 54.4ac

Percentage of Earthssurface 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

30S

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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Light Limitation

The depth of light penetration

Affects primary production throughout thephotic zone of an ocean or lake


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Nutrient Limitation

More than light, nutrients limit primary

production Both in different geographic regions of the

ocean and in lakes


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A limiting nutrient is the element that must be

added In order for production to increase in a

particular area

Nitrogen and phosphorous

Are typically the nutrients that most often limitmarine production


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Nutrient enrichment experiments

Confirmed that nitrogen was limiting phytoplanktongrowth in an area of the ocean

EXPERIMENT Pollution from duck farms concentrated near Moriches Bay adds both nitrogen and phosphorus to the coastal water off 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.

L o n g I s

l a n d

G r e a t S o u

t h B a y

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 plantsand evaporated from a landscape

Is related to net primary production

Figure 54.8Actual 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 primaryproduction

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

d i ffi i


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Production Efficiency

When a caterpillar feeds on a plant leaf

Only about one-sixth of the energy in the leaf is used for secondary production

Figure 54.10

Plant materialeaten by caterpillar

Cellular respiration

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 d E l i l P id


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Trophic 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 i


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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 higher trophic 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

P id f N b


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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 of individual 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 tappingphotosynthetic 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 andare 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

materialsunavailableas nutrients

Coal, oil,peat

Inorganicmaterialsavailable

as nutrients

Inorganicmaterials

unavailableas 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 of water vapor by wind

Precipitationover ocean

Evaporationfrom ocean

Evapotranspirationfrom land

Precipitationover land

Percolationthroughsoil

Runoff andgroundwater

CO 2 in atmosphere

Photosynthesis

Cellular respiration

Burning of fossil fuelsand wood Higher-level

consumersPrimaryconsumers

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 of photosynthesis 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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The rates at which nutrients cycle in differentecosystems

Are extremely variable, mostly as a result of differences in rates of decomposition

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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In one experiment, the trees in one valley werecut down

And the valley was sprayed with herbicides

Figure 54.19b(b) One watershed was clear cut to study the effects of the loss

of vegetation on drainage and nutrient cycling.


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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 of tree 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 of ecosystems in most parts of the world


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Agriculture 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

Contamination of Aquatic Ecosystems


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q y

The critical load for a nutrient

Is the amount of that nutrient that can beabsorbed by plants in an ecosystem withoutdamaging it


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Sewage runoff contaminates freshwater ecosystems

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 containingnitric 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 byacid precipitation

Figure 54.22

Field pH 5.3

5.25.35.15.25.05.14.95.04.84.94.74.84.64.74.54.64.44.54.34.4< 4.3


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Environmental regulations and new industrialtechnologies

Have allowed many developed countries toreduce sulfur dioxide emissions in the past 30years

Toxins in the Environment


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Humans release an immense variety of toxicchemicals

Including thousands of synthetics previouslyunknown to nature

One of the reasons such toxins are so harmful Is that they become more concentrated in

successive trophic levels of a food web


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In biological magnification

Toxins concentrate at higher trophic levelsbecause 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 Atmospheric 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

How Elevated CO 2 Affects Forest Ecology: The


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FACTS-I Experiment

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

The Greenhouse Effect and Global Warming


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The greenhouse effect is caused byatmospheric CO 2

But is necessary to keep the surface of theEarth at a habitable temperature


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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 graduallythinning 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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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 causesCl2O 2 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

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