Chapter 20
Water Pollution
Chapter Outline
CORE CASE STUDY The Gulf of Mexico’s Annual Dead Zone
20-1 What Are the Causes and Effects of Water Pollution?
SCIENCE FOCUS Testing Water for Pollutants
20-2 What Are the Major Water Pollution Problems in Streams and Lakes?
CASE STUDY Pollution in the Great Lakes
20-3 What Are the Major Pollution Problems Affecting Groundwater?
CASE STUDY Arsenic in Drinking Water
CASE STUDY Is Bottled Water a Good Option?
20-4 What Are the Major Water Pollution Problems Affecting Oceans?
CASE STUDY Ocean Garbage Patches: There Is No Away
CASE STUDY The BP Deepwater Horizon Oil-Rig Spill
20-5 How Can We Deal with Water Pollution?
CASE STUDY U.S. Experience with Reducing Point-Source Pollution
Individuals matter Ashley Murray: Wastewater Engineer, Entrepreneur, and National Geographic
Emerging Explorer
SCIENCE FOCUS Treating Sewage by Working with Nature
TYING IT ALL TOGETHER Dead Zones and Sustainability
Key Concepts
20-1A Water pollution causes illness and death in humans and other species, and disrupts ecosystems.
20-1B The chief sources of water pollution are agricultural activities, industrial facilities, and mining, but
the growth of both the human population and our rate of resource use makes it increasingly worse.
20-2A Streams and rivers around the world are extensively polluted, but they can cleanse themselves of
many pollutants if we do not overload them or reduce their flows.
20-2B Adding excessive nutrients to lakes from human activities can disrupt their ecosystems, and
prevention of such pollution is more effective and less costly than cleaning it up.
20-3A Chemicals used in agriculture, industry, transportation, and homes can spill and leak into
groundwater and make it undrinkable.
20-3B There are both simple ways and complex ways to purify groundwater used as a source of drinking
water, but protecting it through pollution prevention is the least expensive and most effective strategy.
20-4A Most ocean pollution originates on land and includes oil and other toxic chemicals, as well as solid
waste, which threaten fish and wildlife and disrupt marine ecosystems.
20-4B The key to protecting the oceans is to reduce the flow of pollution from land and air and from
streams emptying into ocean waters.
20-5 Reducing water pollution requires that we prevent it, work with nature to treat sewage, and use
natural resources far more efficiently.
Key Questions and Concepts
CORE CASE STUDY: The Gulf of Mexico’s annual dead zone. Water draining into the Mississippi
River and its tributaries comes from farms, cities, and factories. Each spring and summer this huge input
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of nutrients overfertilizes coastal waters and results in an explosion of phytoplankton that eventually die
and fall to the seafloor. Oxygen consuming bacteria begin to decompose the phytoplankton and deplete
the oxygen in the Gulf’s bottom layer of water. Oxygen depleted zones represent a disruption of the
nitrogen cycle.
20-1 What Are the Causes and Effects of Water Pollution?
A. Water is polluted is any physical change in water quality that has a harmful effect on living
organisms or makes the water unfit for human uses.
B. Water pollution can come from a single source or from a variety of dispersed sources. Point
sources discharge pollutants at specific locations through drain pipes, ditches, or sewer lines into
bodies of surface water. Non-point sources are scattered and diffuse and can’t be traced to any
single site of discharge.
C. The leading sources of water pollution are agriculture, industries, and mining.
D. Common diseases are transmitted to humans through contaminated drinking water (Table 20-2).
The World Health Organization (WHO) estimates that 1.6 million people, most of whom are
children, die prematurely every year from infectious diseases spread by contaminated water or
lack of water for adequate hygiene.
SCIENCE FOCUS: Testing water for pollutants. Scientists monitor water quality by using
bacterial counts, chemical analysis, and indicator organisms.
20-2 What Are the Major Water Pollution Problems in Streams and Lakes?
A. Streams can recover from moderate levels of degradable water pollutants if the flows are not
reduced. A combination of dilution and biodegradation can allow recovery of stream pollution if
they are not overloaded, or have reduced flow due to damming, agricultural diversion, or
drought.
B. Most developed countries have reduced point source pollution, but toxic chemicals and pollution
from non-point sources are still problems.
C. Stream pollution in most developing countries is a serious and growing problem. Half of the
world’s 500 major rivers are heavily polluted and most of them run through developing
countries where waste treatment is minimal or nonexistent.
1. More than half of China’s population lives without sewage treatment.
D. Lakes have stratified layers and little flow and so are less effective at diluting pollutants that
enter them.
E. Human activities can overload lakes with plant nutrients that reduce dissolved oxygen and kill
some aquatic species. Nutrient enrichment of lakes from runoff is called eutrophication.
CASE STUDY: Pollution in the Great Lakes. The Great lakes constitute 95% of North America’s
fresh surface water. Less than 1% of the water entering the lakes flows out, so pollutants can take as
long as 100 years to flush. In the 1960’s the lakes suffered from cultural eutrophication. In 1972
Canada and the US signed the Great Lakes Water Quality Agreement, and the situation has
improved. However, the lakes still suffer from ongoing pollution problems, and lack of funding for
cleanup.
20-3 What Are the Major Pollution Problems Affecting Groundwater and Other Drinking Water
Sources?
A. Groundwater is vulnerable to contamination because it can’t effectively cleanse itself and dilute
or disperse pollutants. Contaminated water in the aquifer will slowly flow along and create a
plume of contaminated water. It can take hundreds of years to cleanse degradable wastes;
nondegradable wastes are there permanently.
B. The extent of groundwater contamination is generally unknown since there has been little
tracking and testing done on aquifers.
C. Prevention is the most effective and affordable way to protect groundwater from pollutants.
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D. Groundwater pollution can include human pollutants and natural pollutants such as Arsenic.
E. The technology exists to purify wastewater to be used as drinking water, but it is expensive and
faces public opposition.
F. Fifty-four countries have standards for safe drinking water. The U.S. Safe Drinking Water Act of
1974 requires the EPA to establish minimum contaminant levels for pollutants that may adversely
affect human health.
CASE STUDY: Is bottled water a good option? The United States has the world’s cleanest
drinking water, yet its people consume the most bottled water of any nation. Use of bottled water is
energy intensive and creates a lot of waste. Currently, there is a growing back-to-the-tap movement.
20-4 What Are the Major Water Pollution Problems Affecting Oceans?
A. Oceans can disperse and break down large quantities of degradable pollutants if they are not
overloaded.
B. Pollution of coastal water near heavily populated areas is a serious problem. About 40% of the
world’s population lives on or within 62 miles of the coast, and this puts a tremendous burden on
the wetlands, estuaries, coral reefs and mangrove swamps found along the coast.
C. Runoff of sewage and agricultural waste increases nitrate and phosphate levels and can lead to
algal blooms. These then cause oxygen-depleted zones.
CASE STUDY: Ocean garbage patches: there is no away. There are two floating islands of
garbage in the Pacific Ocean. Tiny particles of plastic in these patches can be harmful to birds and
other wildlife.
D. Most ocean pollution comes from human activities on land such as changing and dumping motor
oil.
E. Oil pollution can have a number of harmful ecological and economic effects, but most disappear
within 3 to 20 years.
CASE STUDY: The BP Deepwater Horizon oil-rig spill. In 2010, the rig Deepwater Horizon in
the Gulf of Mexico experienced an accident that lead to the spill of about 4.9 million barrels of crude
oil. The spill disrupted coastal ecosystems and livelihoods of people that work on the coast.
20-5 How Can We Best Deal with Water Pollution?
A. Reduce non-point pollution by preventing it from reaching bodies of surface water. Reduce soil
erosion and the amount of fertilizer that runs off.
B. The Federal Water Pollution Control Act of 1972, the Clean Water Act of 1977, and the 1987
Water Quality Act are the basis of pollution control of surface waters in the U.S.
CASE STUDY: The U.S. experience with reducing point-source pollution. The Clean Water Act
led to improvements that include more community water systems meeting federal health standards,
more streams being fishable and swimmable, a greater portion of the populations served by sewage
treatment plants, and reduced wetland losses. There is still need for improvement and some
scientists call for strengthening the Clean Water Act.
C. Septic tanks and various levels of sewage treatment can reduce point-source water pollution.
D. In urban areas, sewage and runoff flow to wastewater treatment plants, where waters undergo
primary (a physical process) and secondary (a biological process) treatment.
E. Preventing toxic chemicals from reaching sewage treatment plants would eliminate these from
sludge and water that is discharged.
F. Natural and artificial wetlands and other ecological systems can be used to treat sewage.
SCIENCE FOCUS: Treating sewage by working with nature. Some communities and individuals
are experimenting with using various organisms to purify water in holding tanks. Others use natural
or artificially-created wetlands to this end.
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Teaching Tips:
Large Lecture Courses:
Start the class with five bottles of water from around the world. Have a handful of students taste the
bottles and pick their favorite. One bottle should be filled with tap water. When the students have voted
on a favorite, show the prices of the water on a per liter basis compared to other products such as
gasoline. Use the comparison to start students thinking about the irony of assuming drinking imported
water is very safe water versus what is available from a tap, and as a counterpoint mention statistics on
worldwide access to safe drinking water.
Smaller Lecture Classes:
Borrow or buy several camping water filters from the college outdoor center or a local store. Go through
how the filters work and what types of chemicals and size of filtration units are used in each filter. Have
students choose different filters for different places on the planet. For example, have students pick a filter
that would be best for drinking water out of an irrigation ditch in Iowa. This particular filter should handle
dissolved ions like nitrate as well as organic compounds such as pesticides and herbicides. Other
examples would be for use while camping in the Congo (water borne viruses) or near an organic farm
(bacterial contamination more likely with organic fertilizers).
Key Terms
cultural eutrophication
eutrophication
nonpoint sources
point sources
primary sewage treatment
secondary sewage treatment
septic tank
water pollution
Term Paper Research Topics
1.
Water pollution: animal feedlot wastes; electric power plants and thermal pollution; pesticides; deepwell disposal and groundwater contamination; sanitary landfills and groundwater contamination;
hazardous storage and disposal problems; leaking underground gasoline tanks; salinity problems in
irrigated areas.
2.
Water pollution and human health: waterborne disease-causing agents and their control; waterborne
disease problems in developing countries.
3.
Case studies in water pollution: the fight to save Lake Erie; Lake Baikal; James River kepone spill;
Chesapeake Bay; ocean dumping in the New York Bight; Exxon Valdez oil spill.
4.
How responsible are upstream communities for ensuring that high-quality water is delivered to
downstream communities?
5.
Is the public ready for water recycling? What are some examples of this approach in use in the U.S.?
6.
Would privatization of water resources lead to improved water quality? Why or why not?
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7.
National policy: the Safe Drinking Water Act of 1974; protection of groundwater; the Clean Water
Act; problems in enforcing water quality standards; the role of the Environmental Protection Agency
in water quality management; the Toxic Substances Control Act; the National Eutrophication
Survey; the Coastal Barrier Resources Act; water-rights battles in the West.
8.
International policy: UN Conference on the Law of the Sea.
9.
Chesapeake Bay: What is the problem, what are the causes, and what work is underway to fix these
problems?
10. Non-point source pollution and the Gulf of Mexico dead zone. What are the problems and causes,
and why is this so difficult to address?
Water Pollution