Nature Recycles

All ecosystems consist of biotic (living) and abiotic (nonliving)
components. Interactions occurring between the biotic and abiotic parts of
an ecosystem are essential to make it function as one unit or system. As we
learned in Section 1.6, solar energy is an important abiotic component of
nearly every ecosystem.
Once the solar energy is converted to chemical energy, it may be used
for essential life processes. Much of it is lost as heat. Energy passes
through an ecosystem in much the same way that cars travel on a one-way
street. It travels in only one direction—from sun to producer to consumer.
The process of photosynthesis must constantly replace the energy that is
lost from the ecosystem.
Unlike energy, matter can be recycled within an ecod^stem. Matter
may be defined as anything that takes up space and h/sjnass. Matter
refers to all of the chemicals that make up the earth, the air and the
organisms in an ecosystem. The chemicals cannot be created or
destroyed, but they can be changed from one form to another.
O B J E C T I V E S
Compare the movement of
energy and the movement of
matter in an ecosystem.
Compare the movement of
matter in natural ecosystems and
human-made ecosystems.
Create models or illustrations
showing the relationships
between the biotic and abiotic
components of the
biogeochemical cycles.
Nature Recycles
Imagine an aquarium, that doesn't require someone to feed the fish. In a
closed ecosystem, matter is never gained nor lost. Working for NASA, Dr.
Joe Hanson developed a totally closed aquatic ecosystem. Dr. Hanson
carefully selected species of shrimp, algae and microorganisms, and then
he sealed them in glass containers. No one ever needs to feed the shrimp or
change the water in the aquarium.
With controlled light and temperature conditions, the sealed
ecosystems continue to function without the loss or gain of any matter. The
light provides the energy, and the microorganisms recycle the chemicals.
Most human-made ecosystems are not closed ecosystems. They usually
require huge inputs of matter and energy. Zoos are an excellent example of
an unnatural ecosystem where matter is not recycled within the system.
In natural ecosystems, some matter is gained or lost, but most matter
is recycled. Although it is unusual, meteors and debris from outer space
sometimes inject matter into an ecosystem. It is far more likely that matter
entering an ecosystem was removed from another ecosystem by wind or
water. Water sometimes removes large amounts of soil from an ecosystem
and deposits it in an aquatic ecosystem. Wind picks up and carries small
particles and gases great distances. Rain cleanses the air and deposits the
matter in a distant ecosystem.
Human activities sometimes disrupt the normal flow of matter and
threaten the continued existence of an ecosystem. The biogeochemical
cycles, the flow of chemicals between the environment and organisms in it,
are essential to the survival of all ecosystems. As you study each cycle, give
particular attention to the potential environmental impacts of technology.
Ecosphere — A totally enclosed
ecosystem.
A zoo is not a closed ecosystem
because it requires huge inputs of
resources.
The Carbon-Oxygen Cycle
Smokestacks at coal-burning power
plants and industries release huge
amounts of carbon dioxide and water
vapor into the atmosphere.
Plants use carbon dioxide (CO2) from the atmosphere in the process of
photosynthesis. Using light energy, plants combine carbon dioxide and water
to form sugar. The sugar is both a source of energy and a building block for
other compounds such as proteins, oils and starches. The compounds
produced by plants contain carbon and are called organic compounds.
Plants give off oxygen (O2) as a waste product. Although algae in the
ocean produce most of the oxygen in our atmosphere, trees are also an
important source. Plants, animals and microorganisms use oxygen in the
process of respiration. In respiration, the compounds containing
carbon—the organic compounds—are broken down, and carbon dioxide
is released. When respiration occurs without enough oxygen, the organic
chemicals are not completely broken down, and the organic compounds
released often have offensive odors.
The Carbon-Oxygen cycle is out of balance. There is more carbon
dioxide being released into the atmosphere than is being removed from it.
Most of the carbon dioxide is produced during the process of burning—
combustion. When compounds containing carbon (coal, oil, or wood) are
burned, the carbon is chemically combined with oxygen, and carbon
dioxide is released. In a short period of time, combustion releases carbon
dioxide into the atmosphere. The use of carbon dioxide by plants during
photosynthesis is a much slower process. As a result of the imbalance
between these two processes, the level of carbon dioxide in the
atmosphere is increasing. In Unit 2, pages 111, 119, and 124, we will
examine the possible effects of the increasing levels of carbon dioxide.
When organisms die, decomposers break down the carbon compounds
in their bodies, and carbon dioxide is returned to the atmosphere. During
decomposition (decay), other chemicals are also returned to the soil or
released into the air. One of these chemicals is nitrogen.
380
Algae, such as this seaweed clinging to
the rocks and microscopic algae
(phytoplankton), produce most of the
oxygen in the atmosphere.
310
1955
1965
1975
1985
1995
2005
YEAR
The increasing level of carbon dioxide over time is due to the burning of fossil fuels.
Carbon-Oxygen Cycle
Oxygen
Respiration
Photosynthesis
Combustion
in most cells
in green plants and algae
burning of fuel
Algae, Fungi, Plants,
Animals, Bacteria, Protists
Vehicles, Furnaces, Factories,
Volcanoes, Forest Fires, Power Plants
Carbon Dioxide
The Nitrogen Cycle
Without plants and decomposers, the carbon—oxygen cycle would stop.
Plants and decomposers are also important in the nitrogen cycle, but a
certain group of bacteria is essential to this cycle—the nitrogen "fixers."
Plants and animals need nitrogen to make protein. The air is about 78%
nitrogen, but plants and animals cannot use nitrogen (N2) directly from the
atmosphere.
Special bacteria, in the soil and water, must change or "fix" nitrogen
gas (N2) into nitrogen fertilizers (nitrate ions (NOj) or ammonium ions
(NH^)} that plants can use. These bacteria are called nitrogen fixers. Most
nitrogen-fixing bacteria live in little houses, or nodules, on the roots of
plants called legumes. Legumes are members of a large family of plants
that includes peas, beans, alfalfa, clover, vetches, and locust trees. The
plants provide food and cover for the bacteria, and the bacteria convert
nitrogen gas into fertilizer for the plant.
Animals get nitrogen from plants or from other plant-eating animals,
in the form of protein. The nitrogen is recycled by special bacteria that
break down the nitrogen compounds (proteins) in dead plants and
animals, and in animal wastes. If plants do not use the nitrogen
compounds as fertilizer, special forms of bacteria may recycle it. These
bacteria convert the unused fertilizer into nitrogen gas and release it into
the atmosphere. All natural ecosystems depend upon bacteria to keep the
nitrogen cycle going.
Lightning plays a small role in the nitrogen cycle. The huge amount
of electrical energy, called lightning, combines nitrogen and oxygen in the
atmosphere. Dissolved in the rain, the "fixed" nitrogen enters the soil
where bacteria convert it into nitrate fertilizer. But nature is no longer in
total control of the nitrogen cycle. Human activities are dramatically
increasing the nitrogen available to ecosystems.
To grow crops that require large amounts of nitrogen, farmers add
commercial fertilizers. Fertilizer manufacturers take nitrogen from the air
UIUJUI
For information on the
global carbon cycle, visit
www.whrc.org/carbon/carbon.htm.
Crown vetch has been planted along
highways to control erosion. It needs
no fertilizer because bacteria on its
roots can "fix" nitrogen from the air.
Nitrogen Cycle
Nitrogen
Gas
Blue-Green
Bacteria
Lightning
Nitrogen Oxides
LegufrfeVwith
Nitrogen-Fixing
Bacteria
jRoots
Fertilizer
Bacteria in the nodules on the roots
of soybeans and other legumes can
"fix" or change nitrogen gas into
fertilizers.
and hydrogen from natural gas and combine them in a high-pressure,
high-temperature environment. Since this process is very expensive,
farmers often plant legume crops to take advantage of their natural
abilities to fix nitrogen. There is also a large demand for some legume
crops such as soybeans.
Another major source of nitrogen comes from burning fossil fuels.
The atmosphere contains 78% nitrogen and nearly 21% oxygen. The high
temperatures created during combustion cause nitrogen and oxygen to
combine creating nitrogen oxides (NOx). Motor vehicles, factories, power
plants, forest fires, fireplaces and even grills are all sources of nitrogen
oxides. The gases dissolve in the rain and are carried to an ecosystem
somewhere downwind from where they were created. While their
fertilizing effect may benefit some crops, there are some disadvantages.
These are discussed in Unit 2, page 123.
The Mineral Cycle
At Mammoth Springs in Yellowstone
National Park, hot water evaporates
leaving behind an impressive deposit
of minerals.
b.
Most of the minerals (such as calcium and phosphorus) in an ecosystem are
stored in rocks. They are released from the rocks by the action of wind,
water and changes in temperature. The process of physical and chemical
forces releasing minerals from rocks is called weathering.
Wind sometimes acts as a sand-blaster, breaking off small particles of
the rock. Rocks are broken into smaller pieces when water freezes and
thaws. Rocks are also broken by the action of the roots. Plant roots exert a
great amount of force as they grow. This can be seen when walking along a
sidewalk on a tree-lined street. The tree roots often cause sections of
concrete to crack. The foundations of buildings and underground pipes are
sometimes cracked by the growth of tree roots. This is physical weathering.
Chemical weathering occurs when acidic rain dissolves minerals in
the rocks. Roots also produce chemicals that dissolve minerals in the
rocks. The trees absorb some of the minerals. Others are carried away by
water moving through the soil. This process is known as leaching.
Phosphate and Other
Minerals are Released by:
I) Weathering
Mineral Cycle
To Ocean
2' Ac: dnfcf F int Roots
3) Mining
To City and Farm
Ecosystems
Due to leaching and mining, the mineral cycle is a leaky cycle.
Mining is the process of removing a natural substance from an ecosystem
faster than it is replaced. Humans mine many ores for the minerals they
contain—aluminum, zinc, lead, gold and phosphorus. You can think of
others. We often remove these materials for use in our human-made
ecosystems. Some of the minerals will be recycled and used over and over
again. Others will be discarded in a landfill.
Mineral particles are also removed from an ecosystem by the action of
wind and water. This process is called erosion. The mineral particles
carried away by the flowing water may become a part of a sand bar in a
large river or they may be deposited in the ocean. Whether they are
removed from the cycle by leaching, mining or erosion, the minerals are
no longer available to the ecosystem.
The Hydrologic Cycle
"Hydro" means water. The hydrologic or water cycle describes the
movement and storage of water on planet earth. The total amount of water
doesn't change. Its movement is influenced by the earth's surface. Winds
transport water vapor in the atmosphere and influence climate. The sun
provides the energy for the water cycle.
Water re-enters the atmosphere by one of two processes—evaporation
or transpiration. Water is lost from the soil and all surface water—rivers,
lakes, streams and oceans—through the process of evaporation. Since the
oceans cover more than 70% of the earth's surface, most water enters the
atmosphere through the process of evaporation. Evaporation occurs
when the sun's energy heats the water, changing it from its liquid state
into its gaseous state known as water vapor.
Water taken up by the roots of plants travels to the leaves. Some of
these water molecules move by the process of osmosis through the cell
membranes and into the microscopic spaces within the leaf. The water
vapor then diffuses out of the leaf through openings called stomata. This
loss of water vapor from the leaves of plants is called transpiration.
During the growing season, as many as 500,000 gallons (2 million L] of
What forces will cause weathering of
the rocks shown in this picture?
UIUIIU
For information on the
hydrologic cycle, visit
www.epa.gov/seahome/
groundwater/src/cycle.htm and
utility.co.Dinellas.fl. us/hydro.html.
Did
The average water molecule
;
resides in the atmosphere for 10
days where it may travel
thousands of miles before
returning to the earth as
precipitation.
The tiny water droplets in these
clouds are formed by the process of
condensation.
Did You Know
Morning dew is formed when (f
the night air is cooled below a
temperature called the "dew
point." The water vapor in the air
condenses into tiny droplets.The
droplets form on the surface of
the soil, and on plant leaves and
stems. These droplets of
condensed water vapor are called
dew.They will remain on plant
surfaces until the warmth of the
sun evaporates them.You may
want to check the newspaper's
daily weather report for further
information.
water vapor may re-enter the atmosphere through transpiration from one
acre (0.4 ha) of corn.
As warm humid air rises, it loses energy. As the air cools, the water
vapor collects on small particles in the atmosphere called condensation
nuclei. The tiny droplets that form on the surface of these particles form
clouds. This process of water vapor changing into its liquid form is called
condensation. When the water droplets become too heavy to remain in
the atmosphere they begin to fall. The temperature of the air determines
the form of moisture—rain, snow, sleet or hail. All moisture falling from
the atmosphere is collectively called precipitation.
Some precipitation falling through a warmer mass of air will reevaporate before it reaches the earth's surface. Since most of the earth's
surface is covered by water, most precipitation falls into the oceans or
into other bodies of water. If the precipitation falls on land, it may enter
the soil or flow over the surface as runoff. The runoff flows into streams
or lakes where the water may begin its journey back to the ocean. Along
the way it may evaporate or be withdrawn for many uses.
Infiltration is the process of precipitation entering the ground. Plants
may take up water that enters the soil, or it may move or percolate
through the soil and rocks until it reaches a layer of impermeable rock or
clay. This layer of water is called groundwater. The layer of permeable
(porous) rock where the water is stored is an aquifer. Seepage occurs
when groundwater flows naturally from the ground at a spring. More
often it is pumped from a well drilled into the aquifer.
The amount of precipitation is an important factor in determining the
type of ecosystem and the populations of organisms it can support. Unit
4 investigates the role of water in much more detail.
Transpiration
^
Think About It
What happens when you take a
soda can from the refrigerator on a
hot summer day? Can you explain
what actually happens when the
can "sweats"? What process in the
hydrologic cycle is occurring on the
surface of the can?
Evaporation
iljifi It ration!
,*P
!•
•Percolation]
^•k
Runoff
(Fed by
Underground Springs)
1.7
QUESTIONS FOR STUDY AND DISCUSSION:
1. Define the following terms: ( VOCABULARY )
abiotic /
erosion
aquifer "
, evaporation
biogeochemical cycles V groundwater"^/
biotic
infiltration v
combustion
leaching % /
condensation
legumes \/
condensation nuclei
matter
2. Compare the flow of matter and energy through
an ecosystem.
Nature Recycles
3. How did Dr. Hanson's ecosystems differ from
most human-made and natural ecosystems?
4. Compare the recycling of matter in natural
ecosystems and in human-made ecosystems.
The Carbon-Oxygen Cycle
5. What process uses carbon dioxide and
produces oxygen?
6. What kind of organism produces most of the
world's oxygen supply?
7. What two processes produce carbon dioxide?
What process produces most of the carbon
dioxide in the atmosphere?
8. By what process do decomposers return carbon
dioxide to the atmosphere?
The Nitrogen Cycle
9. What kinds of organisms are essential for the
nitrogen cycle?
mining
nitrogen fixers
nodules «y'
organic compounds **
photosynthesis
precipitation
respiration
runoff
seepage
spring
stomata v
transpiration -^/
water vapor
weathering
10. Identify plants that are legumes and explain
how they are important to the nitrogen cycle.
11. In what way is lightning important to the
nitrogen cycle?
12. Why do farmers plant legume crops?
The Mineral Cycle
13. How are minerals removed from rocks?
14. Identify three processes that create "leaks" in
the mineral cycle.
The Hydrologic Cycle
15. Identify the two processes that return water to
the atmosphere. Most water enters the
atmosphere by which of these processes?
16. What is the process in which water vapor
collects to form tiny droplets?
17. What is the term that describes all forms of
moisture leaving the atmosphere?
18. What term describes the layer of porous rock
which is filled with water? What two processes
are necessary to maintain water in this layer.
^) Target Reading Skill Sequencing Refer to
your cycle diagram about the water cycle as you
answer Question 1.
Reviewing Key Concepts
1. a. Defining Name and define the three
major processes that occur during the
water cycle.
b. Making Generalizations Defend this
statement: The sun is the driving force
behind the water cycle.
2. a. Reviewing Which two substances are
linked in one recycling process?
b. Comparing and Contrasting What role
do producers play in the carbon and
oxygen cycles? What role do consumers
play in these cycles?
c. Developing Hypotheses How might the
death of all the producers in a community
affect the carbon and oxygen cycles?
3. a. Reviewing Why do organisms need nitrogen?
b. Sequencing Outline the major steps in the
nitrogen cycle.
c. Predicting What might happen in a community
if all the nitrogen-fixing bacteria died?
Writing in Science
Comic Strip Choose one of the cycles
discussed in this section. Then draw a comic
strip with five panels that depicts the
important events in the cycle. Remember that
the last panel must end with the same event
that begins the first panel.
1. Describe the two processes of the carbon cycle.
2. Describe how the burning of fossil fuels affects the
carbon cycle.
3. Explain how the excessive use of fertilizer affects the
nitrogen cycle and the phosphorus cycle.
4. Explain why the phosphorus cycle occurs more slowly
than both the carbon cycle and the nitrogen cycle.
CRITICAL THINKING
5. Making Comparisons Write a short paragraph
that describes the importance of bacteria in the carbon, nitrogen, and phosphorus cycles. What role do
bacteria play in each cycle?
6. Applying Ideas What is one way that a person can
help to reduce the level of carbon dioxide in the
atmosphere? Can you think of more than one way?
Lesson Review
1. Explain the sequence of events in the
cycle that moves carbon from the soil,
through living organisms, and then
directly back into soil.
4. Will Earth ever run out of water?
Explain your answer.
2. Summarize the ways in which human
activity is affecting the carbon cycle.
6. Explain why nitrogen is important to
living things.
3. Explain the importance of carbon for
living organisms.
7. Why is nitrogen fixation a necessary part
of the nitrogen cycle?
5. Describe the role of plants in the water
cycle. Describe the role of the sun.
Salve
Nutrient Cycling
in an Ecosystem
The soil in each ecosystem contains nutrients.
These nutrients—nitrogen, phosphorus,
potassium—are taken up by plants, make their
way through the ecosystem food web, and then
return to the soil after the death and decay of
plants and animals. Of course, not every bit of
these nutrients enters plants. When it rains,
for example, some nutrients leave the ecosystem
as runoff.
The graphs at right show the amount
of nitrate that a forest ecosystem loses as a
result of runoff at various stages in its history.
At each stage, the forest is in a different
condition.
Use the graphs and your knowledge of
ecosystems, nutrient cycles, and human activities
in forests to answer the questions below.
STAGE 1
— Time —
STAGE 2
Questions
1. Infer which graph shows the loss of nitrate
in a forest ecosystem in which many trees
are being cut down. Explain your answer.
•Time-
STAGE 3
2. Infer which graph shows a forest ecosystem
that was heavily logged several years
before but in which the plant community
is growing back. Explain your answer.
3. Infer which graph shows nitrate loss in
an intact, stable forest ecosystem. Explain
your answer.
4. Describe how the graph that shows
nutrient loss in a stable forest ecosystem
could be different if the area experienced
drought for a long period.
• Time •
Figure 6.15 Forests lose different amounts of
nitrate as a result of runoff at various stages in
their history.