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Biology
A Guide to the Natural World
Chapter 36 • Lecture Outline
An Interactive Living World 3: Ecosystems and Biomes
Fifth Edition
David Krogh
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36.1 The Ecosystem
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The Ecosystem
• An ecosystem is a community of organisms
and the physical environment with which
these organisms interact.
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36.2 Nutrient and Water Cycling
in the Ecosystem
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The Cycling of Ecosystem
Resources
• The approximately 30 chemical elements
that are vital to life are known as nutrients.
• Along with water, nutrients move back and
forth between abiotic (nonliving) and biotic
(living) domains on Earth in a process
called biogeochemical cycling.
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The Cycling of Ecosystem
Resources
• Nutrients can be stored in living things,
transferred between them, or transferred
between them and the abiotic domain.
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The Carbon Cycle
• Carbon comes into the living world through
the plants, algae, and bacteria that take in
atmospheric carbon dioxide to perform
photosynthesis.
• Animals obtain their carbon from these
photosynthesizing organisms.
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The Carbon Cycle
• The carbon cycle is completed when carbon
moves back into the atmosphere in the form
of carbon dioxide, which is produced
naturally through two processes:
• the respiration of living things
• the decomposition of them following their
death
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The Carbon Cycle
atmospheric CO2
The carbon cycle
1. Plants and other
photosynthesizing organisms
take in atmospheric carbon
dioxide (CO2) and convert or
“fix” it into molecules that
become part of the plant.
1 photosynthesis
2. The physical functioning or
respiration of organisms
converts the carbon in their
tissues back into CO2.
respiration
5 burning
of fossil
fuels
2 respiration
plants
animals
decomposition
by bacteria and
fungi
4
fossil fuels
3
dead organisms
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3. Plants and animals die and
are decomposed by fungi and
bacteria. Some CO2 results,
which moves back into the
atmosphere.
4. Some of the carbon in the
remains of dead organisms
becomes locked up in
carbon-based compounds
such as coal or oil.
5. The burning of these fossil
fuels puts this carbon into
the atmosphere in the form
of CO2.
Figure 36.1
The Carbon Cycle
• Carbon dioxide makes up a small but
critical proportion of the Earth’s
atmosphere.
• It is vital to life and greatly affects global
temperature.
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The Carbon Cycle
Animation 36.1: The Carbon Cycle
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The Nitrogen Cycle
• Prior to the twentieth century, nitrogen
entered the biotic domain mostly through
the action of certain bacteria that have the
ability to convert atmospheric nitrogen into
forms that can be taken up and used by
living things.
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The Nitrogen Cycle
• Other bacteria have the ability to convert
this organic nitrogen back into atmospheric
nitrogen, thus completing the nitrogen
cycle.
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The Nitrogen Cycle
The nitrogen cycle
atmospheric N2
bacteria
in root
nodules
of plants
and in soil
1 nitrogen fixation
assimilation
into animals
2 assimilation
into plants
animal waste
dead organisms
5 denitrifying
bacteria
ammonia (NH3)
ammonium (NH4+)
3 decomposition
by bacteria and fungi
1. Nitrogen-fixing bacteria convert N2
into ammonia (NH3), which converts in
water into the ammonium ion (NH4+).
The latter is a compound that plants
can assimilate into tissues. In the
diagram, bacteria living symbiotically
in plant root nodules have produced
NH4+, which their plant partners have
taken up and used. Meanwhile,
free-standing bacteria living in the soil
have likewise produced NH4+.
2. Other plants take up NH4+ that has
been produced by soil-dwelling
bacteria and assimilate it. Animals
eat plants and assimilate the
nitrogen from the plants.
3. Animal waste and the tissues of dead
animals are decomposed by fungi
and by other bacteria, which turn
organic nitrogen back into NH4+.
4. Other “nitrifying” bacteria convert
NH4+ into nitrate (NO3–), which
likewise can be assimilated by plants.
4 nitrifying
bacteria
5. Some nitrate, however, is converted
by “denitrifying” bacteria back into
atmospheric nitrogen, completing
the cycle.
nitrate (NO3–)
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Figure 36.2
Nitrogen as Fertilizer
• Early in the twentieth century, an industrial
process was invented for producing a
biologically useful form of nitrogen—one
that can be applied to agricultural crops as
fertilizer.
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Nitrogen as Fertilizer
• With this step, human beings became
important participants in the Earth’s
nitrogen cycle.
• Nitrogen runoff from agriculture can be a
form of nutrient pollution that can harm
both small and large aquatic ecosystems.
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Gulf of Mexico “Dead Zone”
(a) Runoff from the Atchafalaya and Mississippi Rivers...
Des Moines
Chicago
IA
MO
IL
St. Louis
KS
Nitrogen runoff from the
enormous Mississippi
watershed runs down the
river to the Gulf of Mexico.
TN
OK
(b) ... is given a wide distribution westward in the Gulf of Mexico.
Memphis
AR
AL
New Orleans
MS
TX
mouth of
Atchafalaya
River
LA
dead zone
Mississippi
River delta
New Orleans
dead zone
direction of prevailing wind
sediment
Gulf of
Mexico
sediment and/or algae
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Figure 36.3
The Nitrogen Cycle
Animation 36.2: The Nitrogen Cycle
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The Cycling of Water
• As with carbon or nitrogen, all of Earth’s
water either is being cycled or is being
stored—in such forms as glaciers or polar
ice.
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The Cycling of Water
• As little as 0.5 percent of Earth’s water is
available as fresh, liquid water.
• About 25 percent of this is groundwater,
which generally is stored in geological
formations called aquifers.
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The Hydrologic Cycle
water
vapor
90%
precipitation
over ocean
10%
precipitation
over land
evaporation
transpiration,
evaporation
surface
runoff
groundwater
ocean
groundwater
runoff
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Figure 36.4
The Cycling of Water
• Fresh, sanitary water is a scarce commodity
even for human beings, despite the fact that
civilization now uses more than half the
world’s accessible water.
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source of
water for
confined
aquifer
source of water for
unconfined aquifer
wells
unconfined aquifer
impermeable
rock layers
confined aquifer
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Figure 36.6
Enormous Stores of Underground Water
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Figure 36.7
The Cycling of Water
• The scarcity of water can be traced in
significant part to the inefficient ways in
which humans use it.
• Human diversion of water from natural
environments is having harmful impacts on
species such as fish.
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The Hydrologic Cycle
Animation 36.3: The Hydrologic Cycle
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36.3 How Energy Flows
through Ecosystems
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Trophic Levels
• Plants and other photosynthesizers are an
ecosystem’s producers, while the organisms
that eat plants are its consumers.
• Every ecosystem has a number of feeding or
trophic levels, with producers forming the
first trophic level and consumers forming
several additional levels.
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Trophic Levels
4
tertiary consumers
(carnivore predators)
3
Trophic levels:
1
2
secondary consumers
(herbivore predators)
primary consumers
(plant predators)
producers
(photosynthesizers)
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Figure 36.10
Detritivores
• A detritivore is a class of consumer that
feeds on the remains of dead organisms or
cast-off material from living organisms.
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Detritivores
Chain of Detritivores
long-horned
beetle
bark
beetle
carpenter
ant
termite
dry rot
fungus
intact
fallen
tree
tree
reduced
to powder
decomposer
nutrients returned to soil
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Figure 36.12
Detritivores
• A decomposer is a special kind of
detritivore that breaks down dead or cast-off
organic material into its inorganic
components, which can then be recycled
through an ecosystem.
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Energy-Flow Model
• The energy-flow model of ecosystems
provides ecologists with a powerful
analytical tool; it measures energy as it is
used by and transferred among different
members of an ecosystem.
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Absorption and Use of Solar Energy
by Plants
heat
2% of available solar
energy is assimilated
in photosynthesis
gross
primary production
(total material
produced through
photosynthesis)
15-70%
30-85%
cellular
respiration
(“overhead”)
net primary
production
(amount of
material plant
accumulates)
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Figure 36.13
Energy Loss
• Very little of the energy that a given trophic
level receives is passed along to the next
trophic level.
• A rule of thumb in ecology is that for each
jump up in trophic level, the amount of
available energy drops by 90 percent.
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Energy Loss
• This explains why large, predatory animals
are rare.
• The makeup of given ecosystems can
also be affected by the consumption of
second-level herbivores by third-level
carnivores.
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Energy Pyramid
tertiary consumer
secondary consumer
primary consumer
primary producer
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Figure 36.14
36.4 Earth’s Physical Environment
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Earth’s Atmosphere
• The atmosphere is the layer of gases
surrounding the Earth.
• The lowest layer of the atmosphere, the
troposphere, contains the bulk of the
atmosphere’s gases.
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50
Stratosphere
(contains ozone layer)
25
20
30
ozone layer (O3)
15
20
10
transitional zone
10
Troposphere
contains most of
atmospheric gases
Mount
Everest
Mount
Everest
sea level
0
sea level
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Altitude (miles)
Altitude (kilometers)
40
30
5
0
Figure 36.16
Earth’s Atmosphere
• Nitrogen and oxygen make up 99 percent of
the troposphere, with carbon dioxide and
small amounts of such gases as argon and
methane making up the rest.
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Earth’s Atmosphere
• The gas called ozone exists primarily in a
layer of the atmosphere called the
stratosphere.
• It screens out 99 percent of the sun’s
potentially harmful ultraviolet radiation.
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Ozone Depletion
• Human-made compounds such as
chlorofluorocarbons (CFCs), used in
various consumer and industrial products,
can destroy ozone.
• International action taken on this issue in
the 1980s seems to be bringing the ozone
layer back to health.
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36.5 Global Warming
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Global Warming
• The Earth’s atmospheric temperature is
increasing through the phenomenon known
as global warming.
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Global Warming
• Between 1906 and 2005, Earth’s surface
temperature increased by 1.3°F
• The planet may warm by more than this amount
in the coming decades as a result of human
activities:
• Deforestation
• Emission of carbon dioxide
• Methane emissions
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Growing Concentration of
Atmospheric CO2
Global temperature (oF)
58.5
380
360
58.0
340
57.5
320
300
57.0
280
56.5
Carbon dioxide concentration
(parts per million)
400
260
1880
1900
1920
1940
1960
1980
2000
Year
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Figure 36.17
The Greenhouse Effect
greenhouse gases
heat trapped
reflection of
low-energy
radiation (heat)
high-energy
sun rays
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Figure 36.19
Global Warming
• All of the long term consequences of global
warming cannot be predicted because such
consequences will vary with the amount of
greenhouse gases emitted in the coming years
• Certain consequces:
• Rise in sea levels
• Change in rainfall patterns
• Alteration in the mix of species in different
geographical regions.
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Global Warming
• Recent scientific calculations indicate that
societies may have a short time frame in
which to take action if the phenomenon of
dangerous climate change is to be avoided.
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36.6 Earth’s Climate
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Earth’s Tilt and the Seasons
• Earth is tilted at an angle of 23.5° relative
to the plane of its orbit around the sun, a
fact that dictates much about climate on
Earth, which in turn dictates much about
life on Earth.
• Sunlight strikes the equatorial region of the
Earth more directly than the polar regions.
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Earth’s Tilt and the Seasons
23.5°
Northern
Hemisphere
vernal equinox
(March 21–22)
sun
Southern
Hemisphere
winter solstice
(December 21–22)
summer solstice
(June 21–22)
autumnal equinox
(September 22–23)
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Figure 36.21
Circulation Cells
• The differential warming that results
produces a set of enormous interrelated
circulation cells of moving air, each existing
all the way around the globe at its latitude.
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cold desert
wet rising air
(drops rain as it rises)
60° N
forest
falling air (dry)
hot desert
30° N
forest
equator
wet rising
air (drops
rain as it
rises)
30° S
hot desert
forest
60° S
cold desert
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Figure 36.22
Circulation Cells
• Each of these circulation cells drops rain on
the Earth where the moving air rises but
dries the Earth where it descends.
• This is why some regions of the Earth get so
much more rainfall than others.
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Circulation Cells and Precipitation
60° N
30° N
equator
30° S
60° S
under 25 cm annual rainfall
over 150 cm annual rainfall
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Figure 36.23
Importance of Climate to Life
• A climate is an average weather condition
in a given area.
• Large vegetative formations essentially are
defined by climate regions.
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Line of Transition
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Figure 36.25
36.7 Earth’s Biomes
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Earth’s Biomes
• Biomes are large terrestrial regions of the
Earth that have similar climates and hence
similar vegetative formations.
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Types of Biomes
• Six types of biomes are recognized at a
minimum:
•
•
•
•
•
•
tundra
taiga
temperate deciduous forest
temperate grassland
desert
tropical rain forest
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Distribution of Biomes
ice
tundra
taiga
temperate forest
chaparral
grassland
desert
tropical savanna
tropical rainforest
mountains
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Figure 36.26
Types of Biomes
• Polar ice and mountains often are
recognized as separate biomes, as are the
tropical grasslands called tropical savannas
and the dry, shrub-dominated formations
called chaparral.
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Tundra
• Tundra is the biome of the far north, frozen
much of the year but with a seasonal
vegetation formation of low shrubs, mosses,
lichens, grasses, and the grass-like sedges.
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Tundra
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Figure 36.27
Taiga
• Taiga is another biome of the north.
• It includes the enormous expanse of
coniferous trees that lies south of the tundra
at northern latitudes.
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Taiga
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Figure 36.28
Taiga
• The taiga exhibits a great deal of species
uniformity, with only a few types of trees—
spruce, fir, and pine—serving as ecological
dominants.
• The region supports large populations of
fur-bearing animals.
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Temperate Deciduous Forests
• Temperate deciduous forests grow in
regions of greater warmth and rainfall than
is the case with tundra or taiga.
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Temperate Deciduous Forests
• These forests exist over much of the eastern
United States.
• They are composed of an abundance of
trees such as maple and oak, complemented
by a robust understory of woody and
herbaceous plants.
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Temperate Deciduous Forests
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Figure 36.29
Temperate Grassland
• Temperate grassland goes by several names
around the world, including prairie and
steppes.
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Temperate Grassland
• This biome is characterized by less rainfall
than that of temperate forest and by grasses
as the dominant vegetation formation.
• Such regions can be very fertile agricultural
land.
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Temperate Grassland
• Chaparral is a biome dominated by
evergreen shrub vegetation.
• It is found in a few, relatively small regions
of the world that have a Mediterranean
climate, among them parts of coastal
California.
• These regions have mild, rainy winters and
very dry summers.
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Temperate Grassland
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Figure 36.30
Desert
• Deserts are characterized by both low
rainfall and water evaporation rates that are
high relative to rainfall.
• Deserts may be hot, cold, or temperate, but
all desert life is shaped by the need to
collect and conserve water.
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Desert
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Figure 36.31
Tropical Rain Forest
• The tropical rain forest biome is
characterized by warm, stable temperatures,
abundant moisture, great biological
productivity, and great species diversity.
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Tropical Rain Forest
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Figure 36.32
Tropical Rain Forest
• Rain forest productivity is concentrated
above the forest floor, often in the canopy
high above ground.
• Found in Earth’s equatorial region, tropical
rain forests are being greatly reduced in size
through cutting and burning.
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36.8 Life in the Water:
Aquatic Ecosystems
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Marine Ecosystems
• Ocean or marine ecosystems are most
biologically productive near the coasts, with
the deep open oceans having a productivity
that can be less than that of deserts.
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Marine Ecosystems
• Coastal areas benefit from wave actions that
bring in nutrients, carry away wastes, and
expose more of the surface area of
photosynthesizers to sunlight.
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Ocean Zones
coastal zone
open sea
photic zone
high
continental shelf
abundance
of life
pelagic zone
low
benthic
zone
benthic
zone
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Figure 36.33
Marine Ecosystems
• There is relatively more ocean life toward
the poles, with this concentration decreasing
as one moves toward the equator.
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Diversity in Ocean Life
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Figure 36.34
Marine Ecosystems
• The food webs in the oceans surrounding
Antarctica are based on photosynthesizing
phytoplankton.
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Marine Ecosystems
• Coral reefs are warm-water marine structures
composed of the piled-up remains of
generations of coral animals and their
associated algae.
• Coral reefs provide a habitat that results in a
rich species diversity.
• The health of many coral reefs is imperiled by
human activities.
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Freshwater Ecosystems
• Freshwater ecosystems, which include
inland lakes, rivers, and other running
water, cover only about 2.1 percent of
Earth’s surface.
• Freshwater lakes are most productive near
their shores and near their surface.
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Zones in a Lake
photic zone
profundal zone
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littoral
zone
Figure 36.35
Freshwater Ecosystems
• Lakes can be naturally eutrophic, meaning
nutrient rich, or oligotrophic, meaning
nutrient poor.
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Too Many Nutrients
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Figure 36.36
Estuaries
• Estuaries are areas where streams or rivers
flow into the ocean.
• They are characterized by high biological
productivity because of the constant
movement of water, which stirs up
nutrients.
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N
Maryland
Baltimore
Delaware
Bay
Washington D.C.
Delaware
Atlantic
Ocean
Virginia
Richmond
freshwater
slightly salty
water
moderately
salty water
0
10
20
30
Norfolk
miles
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very salty water
(approaching
ocean levels)
Figure 36.37
Wetlands
• Wetlands, also known as swamps or
marshes, are lands that are wet for at least
part of the year.
• Wetland soil may merely be waterlogged
for part of the year or under a permanent,
relatively deep cover of water.
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Wetlands
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Figure 36.38
Wetlands
• Wetlands are very productive and are
important habitats for migratory birds.
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