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7
Environmental Systems and
Ecosystem Ecology
Chapter Objectives
This chapter will help students:
Describe the nature of environmental systems
Define ecosystems and evaluate how living and nonliving entities interact
in ecosystem-level ecology
Compare and contrast how carbon, phosphorus, nitrogen, and water cycle
through the environment
Explain how plate tectonics and the rock cycle shape the earth beneath
our feet
Lecture Outline
I. Central Case: The Gulf of Mexico’s “Dead Zone”
A. In 2002, the dead zone grew to its largest size ever—22,000 square
km (8,500 square miles).
B. The dead zone is a region in the Gulf of Mexico so depleted of
oxygen that it cannot support marine organisms, a condition called
hypoxia.
C. The change from productive fishery to dead zone has occurred in the
last 30 years. The spread of the hypoxic zone threatens the Gulf’s
fishing industry, one of the most productive fisheries in the United
States.
D. Scientists studying the dead zone have determined that fertilizer
runoff from midwestern farms is a major cause.
E. Other important causes include urban runoff, industrial discharge,
fossil fuel combustion, and municipal sewage.
II. Earth’s Environmental Systems
A. Systems show several defining properties.
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1. A system is a network of relationships among a group of parts,
elements, or components that interact with and influence one
another through the exchange of energy, matter, and/or
information.
2. Systems receive input, process it, and produce output.
3. Sometimes a system’s output can serve as input to that same
system in a circular process called a feedback loop.
a. In a negative feedback loop, output driving the system in
one direction acts as input that moves the system in the other
direction.
b. In a positive feedback loop, the output drives the system
further toward one extreme.
4. The inputs and outputs of a complex natural system often occur
simultaneously, keeping the system constantly active. If they are
in balance, it is called a dynamic equilibrium.
5. Processes in dynamic equilibrium contribute to homeostasis,
where the tendency of the system is to maintain stable internal
conditions.
6. It is difficult to fully understand systems by focusing on their
individual components because systems can show emergent
properties, characteristics that are not evident in the system’s
components.
7. Systems rarely have well-defined boundaries, so deciding where
one system ends and another begins can be difficult.
8. A closed system is isolated and self-contained, having no
interactions with other systems. This does not occur in nature
but is a useful way to begin considering a simple version of a
system.
9. An open system exchanges energy, matter, and information with
other systems. All systems on Earth are open systems.
B. Understanding the dead zone requires considering Mississippi River
and Gulf of Mexico systems together.
1. Hypoxia in the Gulf of Mexico stems from excess nitrogen from
the Mississippi River watershed.
2. Excess nutrients are present in runoff from fertilized agricultural
fields, animal manure, crop residues, sewage, and industrial and
automobile emissions.
3. The nutrients reach the Gulf, where they boost the growth of
microorganisms; this provides food for bacterial decomposers,
which flourish.
4. The decomposers use the oxygen in the water; other organisms,
such as fish and shrimp, suffocate and die.
5. The process of nutrient enrichment, algal bloom, bacterial
increase, and ecosystem deterioration is called eutrophication.
C. Environmental systems may be perceived in various ways.
1. The atmosphere is comprised of the air surrounding our planet.
2. The hydrosphere encompasses all water in surface bodies,
underground, and in the atmosphere.
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3. The lithosphere is everything that is solid earth beneath our
feet.
4. The biosphere consists of the sum total of all the planet’s living
organisms, or biotic components, and the abiotic portions of the
environment with which they interact.
III. Ecosystems
A. Ecosystems are systems of interacting living and nonliving entities.
1. An ecosystem describes all interacting organisms and abiotic
factors that occur in a particular place at the same time.
2. Energy for most ecosystems is input from the sun and is
converted to biomass by producers through photosynthesis. Net
Primary Production can be measured by the energy or the organic
matter stored by plants after they have metabolized enough for
their own maintenance.
3. Most materials cycle within an ecosystem.
4. Ecosystem outputs include energy (often as heat), water, and
waste products from plants and animals. Autotrophs (green
plants) produce food, while heterotrophs (animals) consume
plants and other animals.
5. Ecosystems that produce large amounts of biomass are
considered to have high net primary productivity.
6. The absence of one or more critical nutrient molecule or element
can limit net primary productivity.
B. Landscape ecologists study geographic areas with multiple
ecosystems.
1. Landscape ecology is the broad-scale study of how landscape
structure affects the abundance, distribution, and interactions of
organisms.
2. An ecotone is a transitional zone where two or more ecosystems
meet; it contains some elements from each ecosystem.
3. Landscapes are composed of an array of spatial units called
patches spread in a mosaic throughout the area. Depending on
an ecologist’s research focus, patches can be ecosystems,
communities, or habitat for specific species.
C. Energy is converted to biomass.
1. Autotrophs capture the sun’s energy through photosynthesis. This
is gross primary production.
2. After autotrophs use some of their acquired energy for their own
metabolism, the remainder is used to generate biomass. This
amount is the net primary production.
3. The rate at which biomass is generated is called productivity.
Ecosystems with rapid biomass production have high net
primary productivity.
D. Nutrients can limit ecosystem productivity.
1. Nutrients are elements and compounds that organisms consume
and require for survival.
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2. In natural ecosystems, some nutrients always run off land into
oceans. This nutrient input causes high primary productivity in
nearshore waters along continents.
3. When human activities, such as farms, cities, and industry,
increase this nutrient load, then eutrophication and hypoxia often
occur. This creates dead zones.
IV. Biogeochemical Cycles
A. Nutrients circulate through ecosystems in biogeochemical cycles.
1. Nutrients move through the environment in cycles called
nutrient cycles or biogeochemical cycles.
2. Most nutrients travel through the atmosphere, hydrosphere, and
lithosphere and from one organism to another, moving between
pools, or reservoirs, remaining in a reservoir for a residence
time.
3. Nutrient movement between reservoirs is called flux; the rates of
flux can change over time. Flux typically involves negative
feedback loops that promote dynamic equilibrium.
4. Human activity has changed some flux rates.
B. The carbon cycle circulates a vital organic nutrient.
1. Carbon is an ingredient in carbohydrates, fats, proteins, bones,
cartilage, and shells of all living things.
2. The carbon cycle describes the routes carbon takes through the
environment.
3. Through photosynthesis, producers pull carbon dioxide out of
the atmosphere to produce oxygen and carbohydrates.
4. During respiration, producers, consumers, and decomposers
break down carbohydrates to produce carbon dioxide and water.
C. Humans are shifting carbon from the lithosphere to the atmosphere.
1. As we mine fossil fuel deposits and cut or burn vegetation, we
remove carbon from reservoirs and increase the flux into the
atmosphere.
2. This ongoing flux of carbon into the atmosphere is a major force
behind global climate change.
3. Atmospheric scientists remain baffled by the “missing carbon
sink,” the roughly 1–2 billion metric tons of carbon unaccounted
for that we anticipate should be in the atmosphere due to fossil
fuel combustion and deforestation.
D. The phosphorus cycle involves mainly lithosphere and ocean.
1. The element phosphorus is a key component of DNA, RNA,
ATP, and cell membranes.
2. Phosphorus is primarily found in rocks, soil, sediments and
oceans; the weathering of rocks releases phosphates into water
at a very low rate of flux.
3. The phosphorus cycle has no appreciable atmospheric
component.
4. Concentrations of available phosphorus in the environment are
very low; this is often a limiting factor for producers.
E. We affect the phosphorus cycle.
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1. We mine rocks for phosphorus to make fertilizers, and our
sewage discharge and agricultural runoff are high in phosphates.
2. These additions to the available reservoir of phosphorus in water
and soil can cause rapid increases in biomass and eutrophication
and hypoxia in waterways.
F. The nitrogen cycle involves specialized bacteria.
1. Nitrogen makes up 78% of the atmosphere and is the sixth most
abundant element on Earth.
2. The nitrogen cycle involves chemically inert nitrogen gas, which
most living organisms cannot use. This makes the atmosphere the
major reservoir for nitrogen.
3. Lightning, highly specialized bacteria, and human technology are
the only ways to fix nitrogen into compounds usable by living
organisms.
4. Nitrogen is frequently a limiting factor for producers and
therefore limits populations of consumers, including humans.
5. There are two ways that inert nitrogen gas becomes “fixed” so
that plants can use it—nitrogen fixation and nitrification.
a. Nitrogen fixation occurs through lightning or nitrogenfixing bacteria that live in mutualistic relationships with
many leguminous plants.
b. Nitrification occurs through specialized free-living bacteria.
c. Denitrifying bacteria converts nitrates in soil or water to
gaseous nitrogen.
G. Humans have greatly influenced the nitrogen cycle.
1. Nitrogen fixation has always been a bottleneck, limiting the flux
of nitrogen out of the atmospheric reservoir.
2. The Haber-Bosch process allows humans to synthesize
ammonia, accelerating its flux into other reservoirs within the
cycle.
3. Burning forests and fields and fossil fuels all increase the
amount of atmospheric nitrogen, as does bacterial decomposition
of animal wastes from feedlots.
4. Strategies to limit the amount of damage caused by excess
nutrients in the waterways are not successful at this time.
H. The hydrologic cycle influences all other cycles.
1. The oceans are the main reservoir, holding 97% of all water on
Earth. Less than 1% of planetary water is usable by humans.
2. Water moves into the atmosphere via evaporation and
transpiration. It returns to the surface as precipitation, most of
which flows into water bodies as runoff.
3. Some precipitation and surface water soaks down to recharge
underground reservoirs known as aquifers. This is
groundwater, and its depth underground is the water table.
I. Our impacts on the hydrologic cycle are extensive.
1. We have dammed rivers and created reservoirs, increasing
evaporation.
2. We have changed vegetation patterns, increasing runoff and
erosion and decreasing recharge.
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3. Irrigation, industry, and other human uses have depleted aquifers
and increased evaporation.
4. Atmospheric pollutants have changed the chemical nature of
precipitation.
5. Water shortages are giving rise to conflicts throughout the world
and are predicted to increase.
V. Geological Systems: How Earth Works
A. The rock cycle is a fundamental environmental system.
1. Over geological time, rocks are heated, cooled, broken down,
and reassembled in the rock cycle.
2. Rocks that form when magma cools are called igneous rock.
When magma is spewed from a volcano, it is known as lava.
3. Sedimentary rock is formed when dissolved minerals seep
through sediment layers and crystallize and bind particles
together in the process called lithification.
4. When great heat or pressure is exerted on rock, it is transformed
into metamorphic rock; marble and slate are examples.
5. Understanding the rock cycle helps us appreciate soil formation
and conservation, and conservation of fossil fuels and other
natural resources.
B. Plate tectonics shapes Earth’s geography.
1. Earth’s surface consists of the crust, mantle, and core. Earth’s
internal heat causes the mantle to flow, pushing rock up and
down.
2. In the distant past all the landmasses on the plates joined into a
supercontinent called Pangaea.
3. New crust is formed where two plates are pushed apart at
divergent plate boundaries.
4. When two plates meet, they may slip and grind alongside one
another, forming a transform plate boundary.
5. When two plates collide at convergent plate boundaries, uplift
or subduction can result.
VI. Conclusion
A. Approaching questions holistically by taking a systems approach is
helpful in environmental science.
B. The case of the Gulf of Mexico’s hypoxic zone provides evidence
that systems thinking can lead the way to solutions.
C. Renewable solar energy, nutrient recycling, dynamic equilibrium,
and negative feedback loops are all hallmarks of unperturbed
ecosystems that have survived the test of time.
D. Our industrialized civilization is very young in comparison; we
should consider taking lessons in sustainability from these older,
successful ecosystems.
Key Terms
aquifer
atmosphere
biogeochemical cycles
biomass
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carbon cycle
closed cycle
convergent plate boundary
core
crust
denitrifying bacteria
divergent plate boundary
dynamic equilibrium
ecotone
emergent properties
eutrophication
evaporation
feedback loop
gross primary production
groundwater
Haber-Bosch process
homeostasis
hydrologic cycle
hydrosphere
hypoxia
igneous rock
landscape ecology
lava
lithification
lithosphere
magma
mantle
metamorphic rock
negative feedback loop
net primary production
net primary productivity
nitrification
nitrogen cycle
nitrogen fixation
nitrogen-fixing bacteria
nutrient cycles
nutrients
open system
phosphorus cycle
plate tectonics
positive feedback loop
precipitation
productivity
rock cycle
runoff
secondary production
sediment
sedimentary rock
subduction
system
transform plate boundary
transpiration
water table
Teaching Tips
1. Illustrate the relative size of the lithosphere and the atmosphere by making a
comparison with an apple. The skin of the apple represents the atmosphere,
while the flesh and core of the apple represent the lithosphere.
2. Ask students to conduct Internet research on the Gulf of Mexico “dead
zone.” What is the current status of the dead zone? Has it increased or
decreased in size since 2002? What is being done to address the problem?
3. Describe human activities that are affecting the flux rates in each of the
major biogeochemical cycles. Divide students into small groups and have
each group take one of the cycles, either on land, in freshwater, or in the
oceans, and research the human effects. Depending on the size of the class,
you may need to divide them further; you might do so by industrialized
countries, emerging economies, and nonindustrialized countries or by
continent. Groups could present their findings as written reports, posters,
web pages, or oral presentations.
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4. Have students make a table to compare and contrast the major
biogeochemical cycles, their reservoirs, which is the sink and which is the
source, time frames for flux, and other pertinent information. This could be
done in groups or individually and during a lab period or for homework.
5. Consider having students make a miniature biosphere as a lab project. They
have to consider producers, consumers, detritivores, nutrient cycling, water
cycles, energy input, and waste heat. Small aquariums covered with glass or
plastic sheeting can be used if you have space for such a long-term project.
Otherwise, see the ideas listed at www.bottlebiology.org, a website
maintained by the University of Wisconsin-Madison through an NSF grant.
Some ideas there are very simplistic, but students can create a fairly
sophisticated biosphere using the techniques. These biospheres have the
advantages of being very inexpensive and taking up very little space in a
classroom or lab.
6. Model-making involves whole-brain thinking. Each state typically has a
Geological Survey division. This office compiles records of the state’s
geologic past. Create an assignment where students will research the state’s
geologic history, be it glacial, cataclysmic flooding, earthquakes, or
volcanism. The map that will be most helpful is the state’s landforms. Have
students use the landform map to create a three-dimensional model of their
state. This works most effectively as a group project. Innovative models have
used ceramics, ice sculptures, and even fruit to represent recent and ancient
glacial advances.
Learning about landforms and geology gives students a deeper understanding
and appreciation for present-day plant communities, soil regimes, and
waterflow patterns.
Additional Resources
Websites
1. Mississippi River Basin Gulf of Mexico, U.S. Environmental Protection
Agency (www.epa.gov/msbasin/mexico.htm)
This website provides background information about the Gulf of Mexico and
describes the Gulf of Mexico Program and its accomplishments.
2. National Centers for Coastal Ocean Science Gulf of Mexico Hypoxia
Assessment, NOAA’s National Ocean Service
(www.nos.noaa.gov/products/pubs_hypox.html)
This website provides an integrated assessment of hypoxia in the Gulf of
Mexico.
3. Water Resources of the United States, USGS (http://water.usgs.gov)
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This website is the gateway to data, reports, and educator’s resources on
water science.
4. USGS Rocks and Images, USGS Learning Web Explorer
(http://interactive2.usgs.gov/learningweb/explorer/topic_rocks.htm)
This website provides an introduction to geology and descriptions of the
rock types.
5. This Dynamic Earth: The Story of Plate Tectonics, USGS
(http://pubs.usgs.gov/publications/text/dynamic.html)
This online publication describes plate tectonics with images and maps.
Audiovisual Materials
1. Strange Days on Planet Earth, National Geographic
(http://shop.nationalgeographic.com/index.jsp)
This two-DVD set follows scientists as they try to solve a series of
mysteries.
2. World’s Last Great Places, National Geographic
(http://shop.nationalgeographic.com/index.jsp)
This 11-part series examines specific locations to illustrate biome
characteristics.
3. Planet Earth: Living Machine, Teacher’s Video Company
(www.teachersvideo.com)
This video in the Planet Earth series describes the theory of plate tectonics.
4. Rock Cycle, Teacher’s Video Company (www.teachersvideo.com)
This video explains how minerals become rocks and is available in both DVD
and VHS formats.
5. Rockin’ World of Geology 1 & 2, Teacher’s Video Company
(www.teachersvideo.com)
A variety of basic geological topics are presented in a language all students
can understand, with colorful graphics and lively skits.
Weighing the Issues: Facts to Consider
Ecosystems Where You Live
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Facts to consider: When describing ecosystems, one needs to include the
interdependent biotic and abiotic components (e.g., temperature,
precipitation, latitude, and elevation, as well as water table, soil type, and
nutrient flow). Because all ecosystems are part of a set of contiguous
ecosystems, what flows into one ecosystem has flowed out of at least one
other ecosystem. If one ecosystem is disturbed, ecosystems that are
“downstream” will suffer a loss of materials (such as water) or be
susceptible to damage from any artificial additions at the disturbed site (such
as petroleum or fertilizers). Flora and fauna of the disturbed area will be
greatly affected, possibly also affecting those in nearby systems. Invasive
species, which are better competitors in stressful environments, may
establish themselves in the disturbed ecosystems, forcing native species to
disappear through local extinction or through migration to more favorable
habitats.
Nitrogen Pollution and Its Financial Impacts
Facts to consider: This is a political question with no clear right or wrong
answer. When the interests of different regions are at odds, the advantage of
working out their differences themselves is that they know the problems and
needs and may be able to reach an agreement that satisfies all sides.
However, federal intervention should take into account the problems and
needs of all possible affected parties to attempt a fair compromise. This is a
cost-benefit analysis, where agriculture’s benefit to the nation is to be
weighed against the value of the Gulf fisheries and the massive
environmental impact in the agricultural lands and waters. The health of the
Gulf’s waters should be taken into consideration, as well as the impacts on
human health in the decades to come.
Your Water
Facts to consider: It is important to consider all aspects of the hydrologic
cycle when looking at water quality and quantity issues, as well as how
hydrologic cycles will differ from region to region. A good answer will refer
to precipitation, infiltration, and recharge while discussing the relationship
between surface water and groundwater. Regional information about water
quantity and quality issues can be found at the United States Geological
Survey’s website (http://water.usgs.gov).
Here are some guiding questions to help students find out about their
regional water issues: What is the water source? How many users are there?
Is the population growing? Has the depth of the water table changed? Is the
economic base changing (i.e., becoming more particular about the water
quality while at the same time producing more hazardous waste from
facilities such as computer chip factories)? What happens to sewage, storm
runoff, and hazardous waste?
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Geology and Topography
Facts to consider: Land forms are usually created by wind, water,
temperature, and/or large-scale earth movements/changes. Each type of force
leaves behind specific characteristics. Wind and water erode and pick up
sediments and deposit them elsewhere. Sediments can also be used by wind
and water to abrade rock. Precipitation can cause chemical reactions and
weather rock through cycles of freezing and warming. The movement of the
Earth’s crust produces underground forces and tension that cause
earthquakes and volcanoes. Earthquakes deform land surfaces through smalland large-scale uplift, subsidence, and horizontal movement. Volcanoes are
involved in mountain building and alteration of landforms by addition of
igneous rock material such as lava or ash. Earthquake and volcanic effects
take place over short or long periods of time and over small and large areas.
Information about recent earthquakes and volcanic eruptions can be found at
the Earthquake Hazards Program (http://earthquake.usgs.gov) and the
Volcanoes Hazards Program (http://volcanoes.usgs.gov).
The Science behind the Stories: Thinking Like
a Scientist
Biosphere 2
Observation: In 1992, oxygen levels in Biosphere 2, an attempt to create a
closed ecosystem in the Arizona desert, began dropping rapidly, leaving the
eight biospherians inside gasping for breath.
Hypothesis: Microbes in Biosphere 2’s unusually rich soils were consuming
oxygen and emitting carbon dioxide, and the carbon dioxide, which should
have been reconverted to oxygen by the project’s abundant vegetation, was
instead being deposited in the soil or elsewhere in Biosphere 2.
Experiment: The amount of organic matter, microbial life, and carbon
dioxide in the soil was measured. Holes were drilled into Biosphere 2’s
exposed concrete to measure deposits of calcium carbonate, the product of a
reaction between concrete and carbon dioxide.
Results: The soil was found to contain extraordinarily high levels of
oxygen-consuming bacteria, and calcium carbonate deposits were found as
deep as 6 inches into the concrete walls. The exposed concrete was covered
with paint to prevent the formation of further deposits, and more than 23
tons of pure oxygen were injected into Biosphere 2 to compensate for what
had been lost.
Hypoxia and the Gulf of Mexico “Dead Zone”
Observation: Spots in the northern Gulf of Mexico appeared to “die” each
summer because of low oxygen levels, or hypoxia.
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Hypothesis: The hypoxia was not isolated or rare, and it represented a
growing environmental problem.
Experiments: Long-term, widespread oxygen monitoring; water sampling
for nitrogen and other substances; dives to observe sea life; measurements of
current and historical levels and sources of nitrogen in the Mississippi River.
Results: The Gulf’s dead zone covered thousands of square miles and
reappeared each summer, fed by rivers polluted from farm runoff. The
hypoxia stunned, drove away, or killed sea life. The U.S. government is
instituting new policies to control river pollution and shrink the dead zone.
Causes and Consequences
The following answers for the Causes and Consequences features are examples, and
are not intended to represent a comprehensive list. In addition, the sequence of items
is not meant to connote relative importance.
Issue: Dead Zones
Causes:
nutrient runoff from agricultural fertilizers
nutrient input from factories, air pollution, etc.
wetland destruction
river channelization
Consequences:
death of aquatic organisms that cannot escape
emigration of organisms from hypoxic areas
economic impacts on fisheries and coastal communities
Solutions:
steps to decrease nutrient pollution from farms
steps to decrease nutrient runoff from other sources
restore wetlands and natural filtration capacity
de-channelize sections of river
Unintended consequences:
Regulation of fertilizer use could hurt farmers economically.
…and New solutions:
Consider compensating farmers hurt by mandated fertilizer reductions,
perhaps with funds from areas benefiting from the recovery of dead zones.
InvestigateIt Case Studies and Videos
Case Studies
Sea Lions Hit by High
Levels of Acid Poison in
California
An Island Wilderness and
Location
Topic
Region
Los Angeles,
CA
Bulls Island,
Toxicology
Conservation
California
South
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Alligator Kingdom in
South Carolina
Saving Wildlife in Zambia,
and Raising Human
Prospects
A Plan to Curb Farm-toWatershed Pollution of
Chesapeake Bay
Videos
No Impact Man
SC
Carolina
Zambia
Conservation
Zambia
Pennsylvania
Location
New York,
NY
Agriculture
Topic
Sustainable
Solutions
Pennsylvania
Region
New York
Answers to End-of-Chapter Questions
Testing Your Comprehension
1. Negative feedback loops are most common in nature, whereas positive loops
sometimes result from human actions. When they do, they tend to move
systems away from their homeostatic condition.
2. Excess nutrients in runoff from the land fertilize phytoplankton in the coastal
marine ecosystem. This results in rapid growth of the phytoplankton
population. Dead phytoplankton and waste products then accumulate on the
bottom, where bacterial decomposition consumes most of the available
oxygen, causing hypoxia.
3. An ecosystem includes both the biotic community and its abiotic
environment. A community includes only the populations of living
organisms in a given area.
4. Typically, energy moves through an ecosystem from its source (the sun) to
plants or other photosynthetic primary producers. They are then consumed
by a variety of organisms, which in turn are consumed by others. At each
step, some energy is passed along to the consumer and some is lost as waste
heat. Matter is also transferred up the food chain as organisms eat organisms
on lower trophic levels, but matter from organisms’ waste and from dead
organisms is consumed and broken down by detritivores and decomposers,
returning matter to the soil so that it can be recycled through the food web.
5. Cars release significant amounts of CO2 into the atmosphere from the
combustion of oil. Photosynthesis is the process by which plants remove
CO2 from the atmosphere and store the carbon as sugar. The oceans are
home to a large volume of phytoplankton which can remove CO2 from the
air by photosynthesis; CO2 also dissolves in seawater, is incorporated into
carbonate minerals, and collects as sediment on the ocean floor. The
sediments eventually can become part of the Earth’s crust. This carbon
returns to the atmosphere when the crustal plates are themselves recycled
along plate boundaries, and some of the plate material is melted and erupts
volcanically.
6. Nitrogen-fixing bacteria convert N2 gas into a usable form for plants.
Denitrifying bacteria convert nitrates back into N2 gas.
7. Human activity has accelerated the release of CO2 into the atmosphere from
the combustion of fossil fuels and cement production, as well as
deforestation. High CO2 concentrations in the atmosphere contribute to the
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greenhouse effect. We mine rocks containing phosphorus for use as
fertilizer, and then allow excess phosphates to run into waterways, causing
eutrophication. We also fix more nitrogen now by the Haber-Bosch process
than is fixed naturally. This also can cause eutrophication, as well as some
health effects on humans and other animals consuming nitrate-contaminated
drinking water.
8. Evaporation is the conversion of water from its liquid to gaseous form.
Transpiration is the special case of evaporation and release of water vapor
from the leaves of plants. The water cycle impacts the other nutrient cycles
because these nutrients all have water-soluble forms: CO2 dissolved as
bicarbonate ions; nitrogen in the form of ammonia, nitrates, or nitrites; and
phosphorus as phosphates.
9. Igneous rocks form when molten rock cools and solidifies. Sedimentary
rocks form when sediments (which derive from the weathering, erosion, and
deposition of other rocks and from biological sources) are compressed
sufficiently to bind together. Greatly increased pressures can modify the
mineral structures of either igneous or sedimentary rocks, thereby forming
metamorphic rocks.
10. When crustal plates collide, they may be forced upward to form mountains.
If one plate slides under another (subduction), the plate being subducted will
melt, and the molten rock may be ejected through cracks to the surface in a
volcanic eruption, potentially forming mountains. When plates are sliding
past one another, force may be built up over time and then released suddenly
as the plates lurch past one another—an earthquake. Plate tectonics was most
likely not discovered sooner because the processes are on such a large scale
yet are largely hidden from direct observation, and occur so slowly as to be
almost imperceptible on the timescale of human lifetimes.
Interpreting Graphs and Data
1. Control: aboveground is approximately 380 g C/m2; belowground is
approximately 9,600 g C/m2; total is approximately 10,000 g C/m2. Fertilized
treatment: aboveground is approximately 620 g C/m2; belowground is
approximately 7,400 g C/m2;.total is approximately 8,000 g C/m2.
2. There was more aboveground C in the fertilized treatment than in the control
(625 g C/m2 for the fertilized treatment and only 375 g C/m2 for the control).
This suggests that the fertilizer did stimulate more aboveground plant
growth. The decrease in belowground biomass may have been caused by
either increased rates of decay or decreased rates of root growth.
3. The hypothesis is not supported—fertilization resulted in a net release of
about 2,000 g C/m2. Instead, fertilization may stimulate more decomposition
as well as more plant growth (see Fig. 7.12, which shows the carbon cycle).
Based on this study, one may predict that global climate change may cause
an increase in the atmospheric concentration of CO2.
Calculating Ecological Footprints
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Fertilizer application
To your 1/3-acre lawn
To the lawns of your
classmates
To the lawns of all your
schoolmates
To all the lawns in your
hometown
To all the lawns in your
state
To all the lawns in the
United States
Number of
lawns
Pounds of
nitrogen
1
Answers will
vary
Answers will
vary
Answers will
vary
Answers will
vary
15
Answers will
vary
Answers will
vary
Answers will
vary
Answers will
vary
60,000,000
900,000,000
1. Inorganic nitrogen-based fertilizer results from human production via the
Haber-Bosch process. Much of the nitrogen is taken up by the grass, but
much of it runs off and ends up in local waterways.
2. Overuse of fertilizers can have many of the environmental impacts discussed
in this chapter (e.g., on p. 193). The production, transport, and application of
fertilizer also involves use of fossil fuels, which themselves have
environmental impacts.
3. One clear step for an individual to take is to reduce use of nitrogen
fertilizers. Because much of this use is on large industrialized farms, farmers
will have the most impact in this regard. Individuals can also indirectly
affect nitrogen pollution by advocating with policymakers for restoration of
natural habitats in key areas and for investment in better wastewater
treatment processes and facilities.
IG-102