Environmental Systems and Ecosystem Ecology

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.

IG-88 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. 3. The lithosphere is everything that is solid earth beneath our feet.

IG-89 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. 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.

IG-90 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. 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.

IG-91 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 nitrogen- fixing 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. 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.

IG-92 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 emergent properties atmosphere eutrophication biogeochemical cycles evaporation biomass feedback loop carbon cycle gross primary production closed cycle groundwater convergent plate boundary Haber-Bosch process core homeostasis crust hydrologic cycle denitrifying bacteria hydrosphere divergent plate boundary hypoxia dynamic equilibrium igneous rock ecotone landscape ecology

IG-93 lava phosphorus cycle lithification plate tectonics lithosphere positive feedback loop magma precipitation mantle productivity metamorphic rock rock cycle negative feedback loop runoff net primary production secondary production net primary productivity sediment nitrification sedimentary rock nitrogen cycle subduction nitrogen fixation system nitrogen-fixing bacteria transform plate boundary nutrient cycles transpiration nutrients water table open system 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.

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.

IG-94 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)

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)

IG-95 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

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.

IG-96 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?

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 small- and 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).

IG-97 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.

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

IG-98 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 Location Topic Region Sea Lions Hit by High Levels of Acid Poison in Los Angeles, California CA Toxicology California An Island Wilderness and Alligator Kingdom in Bulls Island, South South Carolina SC Conservation Carolina Saving Wildlife in Zambia, and Raising Human Prospects Zambia Conservation Zambia A Plan to Curb Farm-to- Watershed Pollution of Chesapeake Bay Pennsylvania Agriculture Pennsylvania Videos Location Topic Region New York, Sustainable No Impact Man NY Solutions 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

IG-99 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 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

IG-100 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

Number of Pounds of Fertilizer application lawns nitrogen To your 1/3-acre lawn 1 15 To the lawns of your Answers will Answers will classmates vary vary To the lawns of all your Answers will Answers will schoolmates vary vary To all the lawns in your Answers will Answers will hometown vary vary To all the lawns in your Answers will Answers will state vary vary To all the lawns in the United States 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.

IG-101 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