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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Chapter 38. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. Why has the harvest of large predatory fish like swordfish and shellfish like the white abalone been in decline for the past 40 years?
  2. When land is transformed what does it become?
  3. How does the current amount of wetlands in your state compare to the amount present in 1780?
  4. What is a synthetic chemical and why are organisms so poorly able to deal with them?
  5. If nitrogen is a limiting resource, why have increased levels of nitrogen caused environmental problems?
  6. What were the results of the Montreal Protocol?
  7. In addition to carbon dioxide, what other greenhouse gasses represent serious environmental concerns?
  8. Why is the conclusion that global temperatures are rising so controversial?

A Guide to the Reading

When exploring the content in Chapter 38 for the first time, the following concepts typically give students the most difficulty. For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas.

A Worldwide Change in the Environment

Human activity has substantially changed the biosphere in the past 1,000 years. Collectively, these changes are referred to as land transformations, when the land surface has changed, and water transformations, when aquatic biomes are affected. Abundant evidence documents these changes, and the total area affected is surprisingly large. Ecologists estimate that humans have substantially altered one-third to one-half of the Earth’s land surface. Water transformation has been more difficult to document, but declines in the worldwide harvest of fish and shellfish are unprecedented in modern times. Ecosystems within these transformed areas have been dramatically affected. In the United States, wetland acreage, for example, has been in a continuous decline in every state for the past 200 years. When not directly lost, many ecosystems have become extensively modified to produce the goods and services needed by a growing human population. Humans are currently estimated to control 30 to 35 percent of the world’s net primary productivity. Diverting such a significant portion of an ecosystem’s NPP greatly reduces the amount of land and resources available to other species.

For more information on this concept, be sure to focus on:

  • Section 38.1, Land and Water Transformation

Global Changes in Nutrients

The benefit of supplementing soil nutrients has been long known.  In modern agriculture, the application of both synthetic chemicals, such as pesticides, and natural chemicals, such as phosphorus and nitrogen, has reached alarming proportions. Although composing almost 80 percent of the atmosphere, atmospheric nitrogen cannot be used directly by producers. The conversion to a useable form, called nitrogen fixation, is performed by certain species of bacteria. Currently, the amount of nitrogen fixation accomplished by human activities exceeds that of all natural sources combined. The consequences of changing the nitrogen cycle are far-reaching. When nitrogen is a limiting factor, NPP increases dramatically. Not all members of the ecosystem benefit, however. Those able to use the extra nitrogen may outcompete other species. One of the most common outcomes of nutrient enrichment is an eventual reduction in the number of species within the ecosystem. This is of concern because ecosystems are most stable when the number of species is greatest.

For more information on this concept, be sure to focus on:

  • Section 38.2, Changes in the Chemistry of Earth
  • Section 38.3, Changes in the Global Nitrogen Cycle
  • Figure 38.4, Human Effects on the Global Nitrogen Cycle

Global Warming

Atmospheric scientists around the world are uniformly concerned about the increases in atmospheric carbon dioxide. Beginning in the 1700s, Earth’s atmospheric levels of carbon dioxide have increased to levels that have not occurred naturally for the past 420,000 years. Carbon dioxide is transparent to the solar energy that reaches the earth, but reacts strongly with the heat energy released from the Earth’s surface. Acting just like the glass windows in a car on a cold clear day, the heat energy is trapped, warming either the car’s interior or the Earth itself. Average global temperatures have been slowly increasing for as long as reliable records are available. In Chapter 33 you learned that temperature and rainfall provide the primary influences that dictate biome development. As global temperatures change, so will the patterns of atmospheric circulation and rainfall. Climatologists wonder if the new patterns of rainfall will continue to support agriculture in the areas where it now occurs. The soils that make agriculture possible have developed with thousands of years of climatic influence. There is a significant possibility that rainfall patterns might shift to areas with unsuitable soils. The potential for human impact alone is tremendous.

For more information on this concept, be sure to focus on:

  • Section 38.4, Changes in the Global Carbon Cycle
  • Figure 38.7, Atmospheric CO2 Levels Are Rising Rapidly
  • Section 38.5, Global Warming

Tying it all together

Several concepts presented in this chapter build upon concepts presented in previous chapters and are also revisited and discussed in greater detail in subsequent chapters, including:

A Worldwide Change in the Environment

  • Chapter 34 – Section 34.6, Human Population Growth: Surpassing the Limits?
  • Chapter 36 – Section 36.3, Recovery from Disturbances
  • Chapter 37 – in Section 37.2, Human activities can increase or decrease NPP

Global Changes in Nutrients

  • Chapter 37 – Section 37.3, Nutrient Cycles

Global Warming

  • Chapter 33 - Section 33.3, Climate Has a Large Effect on the Biosphere
  • In Interlude G, Individual actions can have a ripple effect

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