The Biosphere – Chapter 56

Key terms

Weather / Rivers
Climate / Ponds
Trophosphere / Wetlands
Stratosphere / Plankton
Rain shadow effect / Nekton
Upwelling / Hydrothermal vents
Biome / Limnetic zone
Savanna / Profundal zone
Tropical rain forest / Epilimnion
Temperate rain forest / Hypolimnion
Desert / Thermocline
Boreal forest / Turnover
Taiga / Eutrophic
Temperate deciduous forest / Oligotrophic
Tundra / Cultural eutrophication
Tropical seasonal forest / Kyoto Protocol
Grassland / Milpa or swidden agriculture
Regional climate / Genetically modified organisms (GMOs)
Mediterranean climate / Integrated Pest Management (IPM)
Photic zone / Selective cutting
Aphotic zone / Clear cutting
Neritic zone / Salinization
Benthic zone / Industrial timber
Pelagic zone / Fuelwood
Littoral zone / Endocrine disrupters
Intertidal zone / Urbanization
Abyssal zone / Urban sprawl
Barrier islands / Smart growth
Estuaries / Pollution
Mangrove swamps / Pesticide
Lakes / Point source
Ozone hole / Non-point source
Clean Air Act / Primary pollutant
Oxygen demanding wastes / Secondary pollutant
Infectious agents / Particulate matter
Harmful algal blooms / Photochemical oxidants
Sedimentation / Bioaccumulation
Clean Air Act / Biomagnification
Clean Water Act

Key concepts

Factors affecting temperature and precipitation

Climate and other effects of El Niño

Defining and distinguishing biomes

Cause and effects of global climate change

Stratospheric ozone depletion

Nutrient enrichment in aquatic and marine ecosystems

Outline of topics

56.1 Climate shapes the character of ecosystems.

Effects of the Sun and Atmospheric Circulation
• The tropics are warmer than temperate regions because the sun's rays arrive almost perpendicular to equatorial regions. (p. 1204)
• High temperatures near the equator encourage evaporation and create warm, moist air, causing large amounts of precipitation near the equator. (p. 1205)
• When the air masses reach about 30° north and south latitude, the cool, dry air sinks, forming areas of low precipitation (deserts). (p. 1205)

Atmospheric Circulation, Precipitation, and Climate
• The rain shadow effect helps create deserts at places other than 30° north and south latitude, as mountain ranges intercept moisture-laden winds and cause most of the precipitation to fall on the windward side of the range, blocking moisture from the leeward side. (p. 1206)
• Unique regional climates such as Mediterranean climates are also formed due to prevailing winds such as the westerlies and the trade winds. (p. 1206)
• Temperature tends to vary according to latitude -- warm in the tropics, and cooler as you move away -- and according to elevation, with temperature decreasing as elevation increases. (p. 1207)

Effects of Oceans on Climates
• Oceans move heat energy around the globe and moderate climates.
• When the east-west trade winds in the Pacific Ocean slacken, warm water begins to move back across the ocean from the coast of South America, causing a phenomenon called El Niño, which widely influences the world's weather systems. (p. 1213)

56.2 Biomes are widespread terrestrial ecosystems.

The Major Biomes
• Biomes are major communities of organisms with a characteristic appearance that are distributed over areas defined by temperature and precipitation differences. (p. 1208)
• Eight of the major biomes are tropical rain forest, seasonal tropical forest, savanna, desert, temperate rainforest, grassland, temperate deciduous forest, boreal forest, taiga, and tundra. (p. 1208)

• Each biome has a unique set of characteristics that define them.

• All biomes on earth are threatened by human activity.

56.3 Aquatic ecosystems cover much of the earth.

Marine Ecosystems
• The marine environment consists of three major habitats: the neritic zone (shallow water containing most of the world's major fisheries), the pelagic zone (water above the ocean floor), and the benthic zone (ocean floor). (p. 1214)
• Approximately 40% of all photosynthesis on earth is performed by photosynthetic plankton in the oceans. (p. 1215)

Freshwater Ecosystems
• Freshwater habitats are much more limited in area than marine habitats. (p. 1216)
• Photosynthetic organisms are limited to the upper photic zone of ponds and lakes. (p. 1216)
• Ponds and lakes have three zones where organisms are found, which are distributed according to the distance from shore: the littoral, limnetic, and profundal zones. (p. 1216)
• Thermal stratification is characteristic of larger lakes in temperate regions and seasonal turnovers occur. (p. 1216)
• Eutrophic lakes contain an abundant supply of organic matter, while organic matter and nutrients are relatively scarce in oligotrophic lakes. (p. 1217)
• Human activities can lead to the eutrophication of oligotrophic waters, a phenomenon known as cultural eutrophicantion. (p. 1217)
• Wetlands are often very productive ecosystems that filter out pollutants and also serve as water storage basins helping to moderate flooding. (p. 1217)

56.4 Human activity is placing the biosphere under increasing stress.

Carbon Dioxide and Global Warming
• The greenhouse effect is caused when carbon dioxide and other gases allow short-wavelength solar radiation into the atmosphere, but trap longer-wavelength heat radiation from escaping, thus warming the earth's atmosphere. (p. 1222)
• In the 1990s, the scientific community reached a consensus that the earth's average temperature is increasing, and human-related greenhouse gases are the major cause of the increase. (p. 1222)
• The effects of global warming on natural ecosystems may include the shifting of the geographic distribution of organisms tracking environmental conditions, as well as life cycle changes to adapt to changing environmental conditions. (p. 1223)
• Continued global warming may also influence human conditions due to rising sea levels, effects on agriculture, and human health issues. (p. 1224)

Destruction of Forests
• More than half of the world's human population lives in the tropics. This percentage is increasing, placing greater stress on tropical forests, areas of very high biodiversity. (p. 1220)
• Rain forests grow on poor soil, thus they can become hard to regenerate once they are cleared. (p. 1220)

• Milpa or swidden agriculture is a sustainable land use provided that rotation times between crops is 12-15 years.
• Increasingly, larger numbers of people moving into tropical areas are clearing larger areas of rain forest. (p. 1220)

• Half of the world’s forest resources are used for industrial timber while half is used for fuelwood. Most of the production of industrial timber occurs in the developed world, while most of the production occurs in the developing world.

• Clearcutting is very efficient and easy to implement, yet is less sustainable than selective cutting. Sustainable forestry allows use of forest resources at a rate no faster than they can be regenerated.

Agriculture

•Widespread modern agriculture introduces large amounts of new chemicals into the global ecosystem, including pesticides, herbicides, energy and fertilizers. (p. 1218)

• Genetically modified organisms contain DNA from an unrelated organism and can increase agricultural production. There are still concerns about the use of GMOs.

• Pesticides, while increasing yields, can have negative impacts through effects on non-target organisms, evolution of pesticide resistance, and contamination of the environment.

• Biological control, natural pesticides, integrated pest management and sustainable agriculture provide solutions to the negative impacts of synthetic pesticides.

Urbanization

• Over the course of history, humans have moved from rural areas to urban areas, a process known as urbanization.

• In the developing world, urban sprawl is the leading problem with urbanization, as housing tracts consume valuable farmland. The problems with urban sprawl include reliance on the automobile and loss of livable cities, as well as economicand racial segregation.

• Smart growth provides a solution to urban sprawl, allowing compatible use of land for environmental protection and human habitation.

Pollution
• Air pollutants, such as sulfur, particulate matter, nitrogen oxides, heavy metals, and ozone have negative environmental impacts and can be carried long distances.

• Stable, long-lasting chlorinated hydrocarbons such as DDT can become increasingly concentrated in an ecosystem due to bioaccumulation followed by biological magnification or biomagnification. (p. 1218)

• Industrial pollution contains many chemicals. For example, sulfur, when introduced into the upper atmosphere, can combine with water vapor to produce sulfuric acid, which can fall to the ground in many forms, including snow and rain. (p. 1219)
• Precipitation with an acidic pH can cause many environmental problems, including lake acidificationand forest damage. (p. 1219)
• Industrial chlorofluorocarbons (CFCs) released into the atmosphere for many decades have led to a thinning of the earth's stratospheric ozone layer, which shields the planet from harmful ultraviolet radiation. (p. 1221)

• Infectious diseases, oxygen demanding wastes, nutrient enrichment and sedimentation are causes of water pollution.

• The Clean Air Act and Clean Water Act are two pieces of legislation that seek to improve environmental quality, with a focus on human health.