1. Populations and the use of Natural Resources
Chapter 27

2. Resources and Organisms
All organisms need particular natural resources such as air, food, water, and, in some cases, shelter to maintain life, grow, and reproduce.
Most organisms are adapted to their immediate environment; they live in a balance with the natural resources their environment provides.
Some organisms alter their environment to better meet their needs.

3. Resources and Population Growth
As any population increases, its demand for natural resources increases as well.
Exponential growth is a pattern of growth in which a population grows faster as it increases in size, resulting in a population explosion.

4. Resources and Population Growth
This graph shows a rapid increase over time in the population of bacteria after just a few individuals were added to a petri dish full of nutrients. Note the J-shaped curve of the graph.

5. Limits to Population Growth
Eventually, one or more limiting factors, such as the availability of food, water, or clean air, will cause a population to stop increasing.
Carrying capacity is the number of organisms that any given environment can support.
A population that is at the carrying capacity for its environment is in equilibrium and will remain so as long as natural resources are available.

6. Limits to Population Growth
Under normal conditions, populations usually reach an equilibrium with the resources available in the environment. From that point on, the population size will fluctuate around the carrying capacity.

7. Limits to Population Growth
Environmental Limits
Density-independent factors are environmental factors, such as storms, droughts, and pollution, that affect all populations that they come in contact with, regardless of population size.
Density-dependent factors are environmental factors, such as disease, parasites, and lack of food, that increasingly affect a population as the population’s size increases.

8. Human Population Growth
A graph of human population growth still shows a J-shaped curve.

9. Human Impact on Land Resources
Each year, a typical person in North America consumes resources equal to the renewable yield from approximately 5 ha (about acres) of forest and farmland.
Through our use of mineral resources, food, lumber, and living space, humans have a significant impact on Earth’s surface.

10. Extraction of Mineral Resources
Modern societies require huge amounts of land resources, including iron, aluminum, copper, sand, gravel, and limestone.
Finding a balance between the need for mineral resources and controlling the environmental change caused by extraction can be difficult.

11. Extraction of Mineral Resources
Underground Mining
Underground mining, also called subsurface mining, is used where mineral resources lie deep under the ground.
Underground mining is less disruptive to Earth’s surface than surface mining, but it still has impacts on the environment.

12. Extraction of Mineral Resources
Surface Mining
Mineral and ore deposits found just beneath Earth’s surface can be extracted by removing huge amounts of overlying soil and rock.
Mining in this way completely changes the landscape.
Reclamation is the process of restoring the land to its original contours and replanting vegetation.

13. Agriculture
Biodiversity refers to the biological diversity of an ecosystem, which is determined by the variety of species of plants and animals.
Ecosystems that have high biodiversity are more stable than those with fewer species.

14. Agriculture Monoculture
When land is cleared for food production, a biologically diverse ecosystem is often replaced with a single plant species, such as corn or wheat.
Monoculture is the planting of just one species in a field.
Growing a monoculture crop is an efficient farming method, but it is more susceptible to disease than other crops.

15. Agriculture Pesticides
Pesticides, including fungicides and insecticides, have played an important role in boosting food production worldwide by eliminating organisms that destroy crops.

16. Agriculture
Topsoil
It can take thousands of years for topsoil to form, and thus, once it is lost, it is hard to replace.
Erosion of topsoil occurs when forests or grasslands are cleared for the first time.
The addition of fertilizers helps replace some of the nutrients that are depleted by topsoil erosion, but they cannot provide all of the lost substances.
Methods used by farmers to selectively apply fertilizers where they will provide the greatest benefit include soil analysis, careful mapping of fields, and monitoring of plant growth.

17. Forestry
Worldwide, thousands of hectares of forests are cut down annually to meet the demand for firewood, charcoal, paper, and lumber.
Deforestation is the removal of trees from a forested area without adequate replanting.
Deforestation often involves clear-cutting, the complete removal of all the trees in an area.

18. Forestry
The negative environmental impacts of deforestation can be minimized through the practices of selective logging, and the retention of buffer zones of trees along streambeds.

19. Urban Development
An estimated 5 billion people worldwide will be living in cities and towns by the year 2025.
The development of land for the growth of urban areas has many impacts on the environment.
Natural habitats are lost as forests are cleared and wetlands are filled to provide land.
During construction, erosion of topsoil often increases until new landscaping can be established.

20. Urban Development
Concrete and asphalt coverage prevents groundwater supplies from being recharged and increases flooding.
Increasing urbanization produces large volumes of solid waste which is often buried in landfills.
Contamination of soil and groundwater with heavy metals and poisonous chemicals occurs as a result of industrial processes.

21. Urban Development
This graph shows the percentage of solid waste generated by various users of natural resources in the United States annually. Municipal wastes are those wastes contributed by homes and businesses.

22. Urban Development Solutions
Most environmental problems that urban development creates can be solved.
Barriers can be placed around construction sites to catch sediment from increased erosion.
In the United States, wetlands are now recognized as valuable ecosystems and are protected from development.
Modern landfills are carefully designed to minimize leakage of toxic liquids.

23. Urban Development Solutions
Several methods are available for cleaning up industrial toxic-waste sites.
Contaminated soil can be removed and incinerated at temperatures high enough to destroy the toxic chemicals.
Bioremediation, which has been especially useful for contamination caused by spilled gasoline and oil, is the use of organisms to clean up toxic wastes.

24. Human Impact on Air Resources
Smog is a photochemical haze caused by the action of solar radiation on an atmosphere polluted with hydrocarbons and nitrogen oxides mostly from automobile exhaust systems.
Ozone (O3), the major chemical in smog, is a gas molecule made up of three oxygen atoms.
Ozone is beneficial in the upper atmosphere because it absorbs and filters out harmful ultraviolet (UV) radiation.
Ground-level ozone irritates the eyes, noses, throats, and lungs of humans, and it also has harmful effects on plants.

25. Human Impact on Air Resources
Air pollution also occurs in the form of particulate matter ranging in size from microscopic bits to large grains.
Particulates can lodge in lung tissues and cause breathing difficulties and lung disease.

26. Global Impacts of Air Pollution
Global Warming
The greenhouse effect is a natural phenomenon in which Earth’s atmosphere traps heat in the troposphere to warm Earth.
Global warming, a phenomenon related to the greenhouse effect, is an increase in Earth’s average surface temperature.
Human activities, especially the burning of fossil fuels, are largely responsible for increased levels of carbon dioxide, which is the main greenhouse gas that causes global warming.

27. Global Impacts of Air Pollution
Global Warming
The amount of atmospheric carbon dioxide has increased greatly since the 1850s.

28. Global Impacts of Air Pollution
Global Warming
Earth’s mean surface temperature has risen about 0.5°C in the last century.
Some scientists predict it may rise by 1 to 3.5°C in the next 100 years as a result of global warming.
Other scientists argue that the increase in Earth’s temperature could be part of a natural pattern of climatic change.

29. Global Impacts of Air Pollution
Ozone Depletion
The ozone layer serves as a protective shield as it absorbs and filters out harmful UV radiation.
Chlorofluorocarbons (CFCs), which were previously used in refrigerators, cleaning agents, and as propellants in aerosol cans, used to contribute to ozone destruction in the upper atmosphere.

30. Global Impacts of Air Pollution
Ozone Depletion
Since the mid-1980s, atmospheric studies have detected a thinning of the ozone layer, including an “ozone hole” over Antarctica.
Ozone depletion is entirely a result of human activity.
The Montreal Protocol, which 186 countries had signed by 2003, calls for a phase-out in the production and use of most ozone-destroying chemicals by developed countries by the year 2005 and developing countries by the year 2015.
Based on current trends in data, the return to pre-1980 ozone amounts over Antarctica is expected by the middle of this century.

31. Global Impacts of Air Pollution
Acid Precipitation
Acid precipitation is precipitation with a pH of less than 5.0.
Acid precipitation forms when sulfur dioxide and nitrogen oxides combine with atmospheric moisture to create sulfuric acid and nitric acid.
Although volcanoes and marshes add sulfur gases to the atmosphere, 90 percent of the sulfur emissions in eastern North America are of human origin.

32. Global Impacts of Air Pollution
Acid Precipitation
Automobiles are the greatest source of the nitrogen oxides that cause acid precipitation. Electrical utilities produce most of the sulfur dioxide.

33. Global Impacts of Air Pollution
Acid Precipitation
Coal-burning power plants in the midwestern United States release large amounts of sulfur dioxide because the coal they burn contains high amounts of sulfur.
When acids are carried into wet weather, they become part of the rain, snow, or fog that falls to the ground in areas far from their source.

34. Reducing Air Pollution
Solving air pollution problems requires cooperation between multiple governments because pollution travels across borders.
There has been an international effort to reduce global air pollution caused by carbon dioxide and CFCs.
In the United States, the 1990 Clean Air Act set specific reduction goals and enforcement policies for many types of air pollution.

35. Reducing Air Pollution
The Clean Air Act of 1972 was an attempt to reduce the amount of air pollution in the United States. This graph tracks the emission rates of six major air pollutants over a 30-year period.

36. Reducing Air Pollution
Many coal-burning power plants have installed a device such as the wet scrubber to reduce emissions of particulate matter and sulfur dioxide.

37. Reducing Air Pollution
Removing older, highly polluting vehicles from roadways is the most effective way to reduce air pollution.
It is estimated that just 10 percent of the motor vehicles in operation produce 50 to 60 percent of the air pollution generated by gasoline-powered engines.

38. Human Impact on Water Resources
In 1995, the United States consumed 378 billion L of water per day.
Freshwater use has nearly doubled since 1960 and the demand is expected to continue to increase.
When water supplies are limited, conflicts occur between the needs of people and the needs of other users, including wildlife.

39. Human Impact on Water Resources
This graph illustrates the percentage of total water supplies used for various purposes in the United States.

40. Water Pollution
Water-pollution sources are grouped into two main types.
Point sources generate pollution from a single point of origin, such as a sewage-treatment plant or an industrial site.
Nonpoint sources generate pollution from widely spread areas.

41. Water Pollution Point Sources
Common point sources of water pollution include:
Bacteria and viruses that enter water systems through improper disposal of sewage.
Toxic wastes that enter streams from both illegal dumping and accidental spills.

42. Water Pollution Nonpoint Sources
Common nonpoint sources of water pollution include:
Rainwater that has absorbed air pollutants or has become acidic.
Dissolved pesticides and fertilizers from farms and lawns.
Runoff from roads and parking lots that includes oil, gasoline, and other chemicals.

43. Water Pollution Pollution of Groundwater
A wide variety of pollutants can seep into the ground and foul underground water supplies.
Once groundwater is contaminated, the pollutants can be very difficult to remove.

44. Water Pollution Pollution in the Oceans
Since nearly 50 percent of the U.S. population lives near coastlines, pollutants from cities often end up in estuaries and other near-shore regions.
Sewage water is a major source of near-shore pollution around coastal areas due to high levels of nitrogen and phosphorus that can create blooms of cyanobacteria.
Untreated sewage, sometimes disposed of by pumping it through pipelines that extend far out into the ocean, can create large dead zones on the ocean floor where there are no living organisms.

45. Reducing Water Pollution
Two major laws have been passed in the United States to combat water pollution:
The Safe Drinking Water Act of 1974 was designed to ensure that everyone in the United States has access to safe drinking water.
The Clean Water Act of 1972, the primary federal law that protects our nation’s waters, was created to eliminate discharge of pollutants into waterways, lakes, and wetlands, and to restore water quality to levels that allow for recreational uses of waters.
Two-thirds of the nation’s waters are now safe for recreation, compared to only one-third in 1972.

46. Water Conservation
Water conservation, versus developing new supplies, is the most common solution to excessive demand.
Utilizing efficient irrigation methods reduces water usage.
Industries can develop ways to recycle cooling water and wastewater.
Manufacturing processes often can use recycled water, or be redesigned to conserve water.
Charging for public water that households use encourages people to fix leaks and conserve water.