1. Sustainability is the careful use of natural resources in a way that does not deplete them for future use.
45.2 The Air
2. Pollution is any change in the environment that harms living organisms.
3. Air pollutants include heavy metals, particulates, and emissions from fossil fuel combustion in automobiles and industries. Some of these pollutants react in light to form photochemical smog.
4. Acid deposition forms when nitogen and sulfur oxides react with water in the upper atmosphere to form nitric and sulfuric acids. These acids return to earth as dry particles or in precipitation. Acidification of lakes changes aquatic communities. In terrestrial ecosystems, acid deposition kills leaves and releases toxic aluminum from soils.
5. The Clean Air Act improved air quality in the United States.
6. Use of chlorofluorocarbon compounds has thinned the stratospheric ozone layer, which protects life from ultraviolet radiation.
7. The greenhouse effect results from CO2 and other gases trapping heat near Earth’s surface. Agriculture, burning fossil fuels, and destruction of tropical rain forests generate greenhouse gases. The greenhouse effect may contribute to global warming. Shifting vegetation patterns, species ranges, and egg-laying schedules are responses to global warming.
45.3 The Land
8. Deforestation is the destruction of tree cover from forested areas. Subsistence-level agriculture contributes to the removal of tropical rain forests.
9. Draining lakes to irrigate crops and cattle grazing cause and hasten desertification, the expansion of desert into surrounding areas.
45.4 The Waters
10. Organic and inorganic toxins, sediments, heat, heavy metals, and excessive nutrient levels pollute aquatic ecosystems. Water quality in the United States has improved in recent decades.
11. Dams and levees alter river ecosystems.
12. Preserving estuaries is important because they are breeding grounds for many species.
13. Fishing with cyanide and dynamite, excessive nutrients, and hurricanes threaten coral reefs.
14. Loss of coastal habitat and overharvest contribute to declines of populations of valuable ocean species.
15. Plastic and oil contaminate surface waters.
16. Human activities and climatic fluctuations contribute to the spread of infectious disease among many ocean inhabitants.
45.5 Loss of Biodiversity
17. The diversity-stability hypothesis proposes that an ecosystem with many diverse species is better able to survive stresses than a species-poor ecosystem.
18. Reduction of the biosphere to similar ecosystem remnants may put Earth on the brink of a mass extinction.
19. After habitat destruction, biological invasion is the top cause of decreasing biodiversity as nonnative species displace native organisms.