Chapter 15

Lecture Outlines
Chapter 15
The Science behind the
4th Edition
© 2011 Pearson Education, Inc.
This lecture will help you understand:
• Water’s importance to
people and ecosystems
• Water’s distribution
• Use and alteration of
freshwater systems
• Problems of water supply
and solutions
• Problems of water quality
and solutions
• How wastewater is treated
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Gambling with water in the Colorado River
• 7 states share the Colorado river
• Droughts and overuse are
threatening supplies
• Las Vegas, Nevada, needs more
water than it is allotted
• Other states will let Las Vegas
drill for underground water
• Drilling threatens the area’s
ecology and people
• This issue will end up in Nevada’s
Supreme Court
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The Colorado River
• The Colorado River originates
in the Rocky Mountains
- Draining into the Gulf of
• Its waters chiseled the Grand
- But it has been reduced to a
mere trickle
• Dams provide flood control,
recreation, and hydroelectric
- 30 million people use the
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Freshwater systems
• Water may seem abundant, but drinkable water is rare
• Freshwater = relatively pure, with few dissolved
- Most is tied up in glaciers, ice caps, and aquifers
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Water is renewed and recycled
• As water is cycled it redistributes heat, erodes mountains,
builds river deltas, maintains ecosystems and organisms
- It also shapes civilizations and political conflicts
• Surface water = on Earth’s surface
- 1% of freshwater
• Runoff = water that flows over land
- Water merges in rivers and ends up in a lake or ocean
• Tributary = a smaller river slowing into a larger one
• Watershed (drainage basin) = the area of land drained
by a river system (river and its tributaries)
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Water is renewed and recycled as it moves
through the hydrologic cycle
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Water Cycle Scramble
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Rivers and streams wind through
• Rivers shape the landscape
• Braided river = an interconnected series of watercourses
that run through steep slopes
• Meandering river = rivers in flatter areas
- Water rounding a bend erodes soil from the outer bank
- Sediment is deposited on the inside of the bend
- Rivers become exaggerated oxbows
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Rivers shape the landscape
• Oxbows = areas where river
bends become exaggerated
• Oxbow lake = erosion cuts
off and isolates the oxbow
into a U-shaped water body
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A river may shift course over time
• Floodplain = areas nearest to the river’s course that are
flooded periodically
- Frequent deposition of silt makes floodplain soils
- Good areas for agriculture
• Riparian = riverside areas that are productive and
• Rivers and streams hosts diverse ecological communities
- Algae, insects, fish, amphibians, birds, etc.
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Lakes and ponds are ecologically diverse
• Lakes and ponds = bodies of open, standing water
• Littoral zone = region ringing the edge of a water body
- Rooted aquatic plants grow in this shallow part
• Benthic zone = extends along the bottom of the water
- Home to many invertebrates
• Limnetic zone = open portion of the lake or pond where
sunlight allows photosynthesis
• Profundal zone = water that sunlight does not reach
- Supports fewer animals because there is less oxygen
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A typical lake
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Lakes vary in their nutrients and oxygen
• Oligotrophic lakes and ponds = have low nutrient and
high oxygen conditions
• Eutrophic lakes and ponds = have high nutrient and low
oxygen conditions
• Eventually, water bodies fill completely in through the
process of succession
• The largest lakes are known as inland seas
- Great Lakes, The Caspian Sea
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Wetlands include marshes, swamps, bogs,
and seasonal pools
• Wetlands = the soil is saturated
with shallow standing water
• Freshwater marshes = shallow
- Plants grow above the surface
• Swamps = shallow water in
forested areas
- Can be made by beavers
• Bogs = ponds covered in thick
floating mats of vegetation
- A stage in aquatic succession
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Species in vernal
pools are adapted
to seasonal drying
Wetlands are valuable
• Wetlands are extremely valuable for wildlife
- They slow runoff, reduce flooding, recharge aquifers,
and filter pollutants
• People have drained wetlands, mostly for agriculture
- Southern Canada and the U.S. have lost over half of
their wetlands
• In 2006 the Supreme Court told the Army Corps of
Engineers it must create guidelines to determine when
wetlands are valuable enough to protect by law
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Groundwater plays a key role
• Groundwater = water beneath the surface held in pores
in soil or rock
- 20% of the Earth’s freshwater supply
• Aquifers = porous, sponge-like formations of rock,
sand, or gravel that hold water
- Zone of aeration = pore spaces are partly filled with
- Zone of saturation = spaces are filled with water
- Water table = boundary between the two zones
• Recharge zone = any area where water infiltrates Earth’s
surface and reaches aquifers
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A typical aquifer
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There are two categories of aquifers
• Confined (artesian) aquifer = water-bearing, porous
rocks are trapped between less permeable substrate (clay)
- Is under great pressure
• Unconfined aquifer = no upper layer to confine it
- Readily recharged by surface water
• Groundwater’s average age is 1,400 years
- It may be tens of thousands of years old
• Groundwater becomes surface water through springs or
human-drilled wells
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The Ogallala Aquifer
• The world’s largest
known aquifer
• Underlies the Great Plains
of the U.S.
Its water has allowed farmers to create the most
bountiful grain-producing region in the world
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Water is unequally distributed across Earth
• Water is unevenly distributed in space and time
- Different areas possess different amounts of water
- People erect dams to store water
Many densely populated areas are water-poor
and face serious water shortages
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Climate change may bring shortages
• Climate change will cause
- Altered precipitation
- Melting glaciers
- Early season runoff
- Intensified droughts
- Flooding
Lake Mead is already
hurting from drought
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How we use water
• We have achieved impressive engineering
accomplishments to harness fresh water
- 60% of the world’s largest 227 rivers have been
strongly or moderately affected
- Dams, dikes, and diversions
• Consumption of water in most of the world is
- We are depleting many sources of surface water and
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Water supplies houses, agriculture, and
• Proportions of these three types of use vary dramatically
among nations
- Arid countries use water for agriculture
- Developed countries use water for industry
• Consumptive use = water is removed from an aquifer or
surface water body and is not returned
- Irrigation = the provision of water to crops
• Nonconsumptive use = does not remove, or only
temporarily removes, water
- Electricity generation at hydroelectric dams
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Why does agriculture use so much water?
• Rapid population growth requires more food and clothes
• The Green Revolution uses irrigation
- We use 70% more irrigation water than 50 years ago
• Irrigation can double crop yields
- 18% of land is irrigated but produces 40% of our crops
• Irrigation is highly inefficient
- Water evaporates in “flood and furrow” irrigation
• Overirrigation leads to waterlogging and salinization
- Reducing world farm income by $11 billion
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Governments subsidize irrigation
• Irrigation subsidies promote food self-sufficiency
- But irrigation uses up huge amounts of groundwater
for little gain
• Water in the Colorado River Valley is diverted for
cotton and other crops grown in the desert
Farmers in California’s
Imperial Valley pay
only 1 penny for 220
gallons of water
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We divert surface water for our needs
• People divert water to
farm fields, homes, and
The once mighty
Colorado River has
been extensively
diverted and used
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Water-poor regions take water from others
• Politically strong, water-poor areas forcibly take
water from weaker communities
• Los Angeles commandeered water from rural areas
- Turning the environment into desert, creating
dustbowls, and destroying the economy
• In 1941, L.A. diverted streams that fed Lake Mono
- Lake levels fell, salt concentrations doubled
• Las Vegas wants to import water from sparsely
populated eastern Nevada
- An ecologically sensitive area
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We build dikes and levees to control floods
• Flooding = a normal, natural process where water
spills over a river’s banks
- Spreading nutrient-rich sediments over large areas
• In the short term, floods damage property
• Dikes and levees (long, raised mounds of earth) along
the banks of rivers hold water in channels
- Levees make floods worse by forcing water to stay
in channels and then overflow
• Dams prevent flooding and change a river’s nature
- Releasing water periodically simulates flooding
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Levees increase flooding
• A major levee along the Mississippi River failed after
Hurricane Katrina, allowing parts of New Orleans to be
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We have erected thousands of dams
• Dam = any obstruction placed in a river or stream to
block the flow of water to prevent floods, provide
drinking water, allow irrigation, and generate
- 45,000 large dams have been erected in more than
140 nations
• Only a few major rivers remain undammed
- In remote regions of Canada, Alaska, and Russia
• Dams are great engineering feats
- Many stand hundreds of feet tall
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A typical dam
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China’s Three Gorges Dam
• The dam, on the Yangtze
River, is the largest in the
- 186 m (610 feet) high, 2.3
km (1.4 mi) wide
- Its reservoir stretches for
616 km (385 mi)
- Provides flood control,
passage for boats, and
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Drawbacks of the Three Gorges Dam
• Cost $39 billion to build
• Flooded 22 cities and the
homes of 1.24 million people
• Submerged 10,000-year-old
archaeological sites
• Drowned farmland and
wildlife habitat
• Tidal marshes at the Yangtze’s
mouth are eroding
• Pollutants will be trapped
It will cost $5 billion to
build sewage treatment
plants to treat water
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Some dams are being removed
• Some people feel that the costs of dams outweigh their
- They are pushing to dismantle dams
• The Federal Energy Regulatory Commission (FERC)
renews licenses for dams
- If dam costs exceed benefits, the license may not be
• 400 dams have been removed in the U.S.
- Property owners who opposed the removal change
their minds once they see the healthy river
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We are depleting surface water
• In many places, we are withdrawing water at
unsustainable rates
- Reduced flow drastically changes the river’s ecology,
plant community, and destroys fish and invertebrates
The Colorado River
often does not reach
the Gulf of California
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The Aral Sea
• Once the fourth-largest lake on Earth
- It lost 80% of its volume in 45
• The two rivers leading into the Aral
Sea were diverted to irrigate cotton
• 60,000 fishing jobs are gone
• Pesticide-laden dust from the lake
bed is blown into the air
• Cotton cannot save the region’s
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Can the Aral Sea be saved?
People have begun
saving the northern
part of the Aral Sea
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Irrigation wastes water
• 15–35% of water withdrawals for irrigation are
• Water mining = withdraws water faster than it can be
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The world is losing wetlands
• Wetlands are being lost as we divert and withdraw water
- Channelize rivers, build dams, etc.
• As wetlands disappear, we lose ecosystem services
- Filtering pollutants, wildlife habitat, flood control, etc.
• Many are trying to protect and restore them
• The Ramsar Convention on Wetlands of International
Importance (1971)
- Seeks the conservation and wise use of wetlands in the
context of sustainable development
- 1,900 sites covering 185 million ha are protected
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We are depleting groundwater
• Groundwater is easily depleted
- Aquifers recharge slowly
- Used by one-third of all people
• As aquifers are mined, water tables
- Salt water intrudes in coastal areas
• Sinkholes = areas where ground gives
way unexpectedly
- Aquifers can’t recharge
• Wetlands dry up
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Can we quench our thirst for bottled water?
• Groundwater is being withdrawn for bottled water
- An average American drinks 29 gallons/year
• People drink bottled water for portability, convenience
- They think it tastes better or is healthier
• Bottled water is no better than tap water
- It is heavily packaged and travels long distances using
fossil fuels
- Bottles are not recycled
- Corporations move in, deplete water, and move away
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Bottled water is popular but problematic
• Bottled water is popular but it has several problems
Energy costs of bottled water are 1,000–2,000
times greater than those of tap water
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Will we see a future of water wars?
• Freshwater depletion leads to shortages, which can lead
to conflict
- 261 major rivers cross national borders
• Water is a key element in hostilities among Israel,
Palestinians, and neighboring countries
• Many nations have cooperated with neighbors to resolve
- They sign water-sharing treaties
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Solutions can address supply or demand
• We can either increase supply or reduce demand
• Increasing supply through intensive extraction
- Diversions increase supply in one area but decrease it
• Reducing demand is harder politically in the short term
- International aid agencies are funding demand-based
solutions over supply-based solutions
- Offers better economic returns
- Causes less ecological and social damage
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Desalinization “makes” more water
• Desalination (desalinization) = the removal of salt from
seawater or other water of marginal quality
- Distilling = evaporates and condenses ocean water
- Reverse osmosis = forces water through membranes to
filter out salts
• Desalinization facilities operate mostly in the arid Middle
- It is expensive, requires fossil fuels, kills aquatic life,
and produces salty waste
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The world’s largest reverse osmosis plant
• Near Yuma, Arizona
• Intended to remove salt
from irrigation runoff
• Too expensive to operate
and closed after 8 months
- Engineers are trying to
re-open it in a costeffective way
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Agricultural demand can be reduced
• Line irrigation canals
• Level fields to reduce runoff
• Use efficient irrigation methods
- Low-pressure spray irrigation sprays water downward
- Drip irrigation systems target individual plants
• Match crops to land and climate
• Eliminate water subsidies
• Selective breeding and genetic modification to produce
crops that require less water
• Eat less meat
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Residential demand can be reduced
• Install low-flow faucets,
showerheads, washing
machines, and toilets
• Rainwater harvesting =
capturing rain from roofs
• Gray water = wastewater
from showers and sinks
• Water lawns at night
• We can save hundreds or
thousands of gallons/day
Xeriscaping uses plants
adapted to arid conditions
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Industrial demand can be reduced
• Shift to processes that use less water
- Wastewater recycling
• Use excess surface water runoff to recharge aquifers
• Patch leaky pipes and retrofit homes with efficient
• Audit industries
• Promote conservation/education
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Market-based approaches to conservation
• End government subsidies of inefficient practices
- Let the price of water reflect its true cost of extraction
- But since industrial uses are more profitable than
agricultural uses, poorer, less developed countries
• Privatize water supplies: construction, maintenance,
management, and ownership
- May improve efficiency
- There is little incentive to provide access to the poor
• Decentralization of water control may conserve water
- Shift control to the local level
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Freshwater pollution and its control
• Water for human consumption and other organisms
needs to be:
- Disease-free
- Nontoxic
• Half of the world’s major rivers are seriously depleted
and polluted
- They poison surrounding ecosystems
- Threatening the health and livelihood of people
• The invisible pollution of groundwater has been called a
“covert crisis”
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Point and nonpoint sources of pollution
• Pollution = the release of matter or energy that causes
undesirable impacts on the health and well-being of
humans or other organisms
• Point sources = discrete locations of water pollution
- Factories, sewer pipes
- Addressed by the U.S. Clean Water Act
• Nonpoint sources = pollution arises from multiple inputs
over larger areas (farms, city streets, neighborhoods)
- The major source of U.S. water pollution
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Freshwater pollution sources
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Nutrient pollution
• Nutrient pollution from fertilizers, farms, sewage, lawns,
golf courses leads to eutrophication
- Fertilizers add phosphorus to water, which boosts
algal and aquatic plant growth
- Spreading algae cover the surface, decreasing sunlight
- Bacteria eat dead algae, reducing dissolved oxygen
- Fish and shellfish die
• Solutions include treating wastewater
- Reducing fertilizer application
- Using phosphate-free detergents
- Planting vegetation to increase nutrient uptake
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Eutrophication is a natural process, but…
• Human activities dramatically increase the rate at which it
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Pathogens and waterborne diseases
• Enter water supplies through inadequately treated human
waste and animal waste from feedlots
• Fecal coliform bacteria indicate fecal contamination
- They are not pathogenic organisms
- But the water may also hold other disease-causing
pathogens (e.g., giardiasis, typhoid, hepatitis A)
• Bacterial pollution causes more human health problems
than any other type of water pollution
- Conditions are improving
- 86% of people now have safe water
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Pathogens cause human health problems
• 1 billion are still without safe water
• 2.6 billion have inadequate sewer or sanitary facilities
- Mostly rural Asians and Africans
• Health impacts kill 5 million people per year
• Solutions:
- Disinfect drinking water
- Treat sewage
- Public education to encourage personal hygiene
- Government enforcement of regulations protecting
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Toxic chemicals
• Pesticides, petroleum products, synthetic chemicals
- Arsenic, lead, mercury, acid rain, acid drainage from
• Effects include poisoned animals and plants, altered
aquatic ecosystems, and decreased human health
• Solutions:
- Issue and enforce more stringent regulations of
- Modify industrial processes
- Modify our purchasing decisions
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Sediment pollution
• Sediment in rivers can impair aquatic ecosystems
• Clear-cutting, mining, clearing land for housing, and
cultivating farm fields expose soil to erosion
• It dramatically changes aquatic habitats
- Fish may not survive
• Solutions:
- Better management of farms and forests
- Avoid large-scale disturbance of vegetation
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Thermal pollution
• Water that is too warm causes problems
- Warmer water holds less oxygen
- Dissolved oxygen decreases as temperature increases
- Industrial cooling heats water
- Removing streamside cover raises water temperature
• Water that is too cold also causes problems
- Water at the bottom of reservoirs behind dams is
- When water is released, downstream water
temperatures drop suddenly, killing aquatic organisms
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Indicators of water quality
• Scientists measure properties of water to characterize
its quality
- Biological indicators: presence of fecal coliform
bacteria, disease-causing organisms, algae, etc.
- Chemical indicators: nutrient concentrations, pH,
taste, odor, hardness, dissolved oxygen
- Physical indicators: color, temperature, turbidity
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Groundwater pollution is a difficult problem
• Groundwater is increasingly contaminated
- But is hidden from view and difficult to monitor
- “Out of sight, out of mind”
• Groundwater pollution is hard to address
- It retains contaminants for decades and longer
- It takes longer for contaminants to break down because
of lower sunlight, microbes, and dissolved oxygen
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Sources of groundwater pollution
• Some toxic chemicals occur
- Aluminum, fluoride,
• Pollution from human
causes wastes leach through
- Pathogens enter through
improperly designed
- Leaking underground
storage and septic tanks
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So far, the EPA has
cleaned up 388,000
leaking tanks
Agriculture and industry pollute
• Agricultural pollution comes from several sources
- Pesticides are in most of the shallow aquifers tested
- Nitrates from fertilizers have caused cancer,
miscarriages, and “blue-baby” syndrome
- Pathogens like Escherichia coli (E. coli)
• Manufacturing industries and military sites have been
heavy polluters
- By-products seep into water from miles around
- Radioactive wastes will contaminate water for 750,000
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It is best to prevent pollution
• It is far better to prevent pollution than use “end-of-pipe”
treatment and cleanup
• Other options are not as good:
- Removing just one herbicide from water in the U.S.
Midwest costs $400 million/year
- Pumping, treating, and re-injecting it takes too long
• Consumers can purchase sustainably made products
- Become involved in local “riverwatch” projects
- Urge government to pursue policies to fight pollution
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Legislative efforts reduce pollution
• Water pollution was worse decades ago
- Citizen activism and government response resulted in
legislation during the 1960s and 1970s
- The situation is much better now
• The Federal Water Pollution Control Act (1972)
- Renamed the Clean Water Act in 1977
- It is illegal to discharge pollution without a permit
- Sets standards for industrial wastewater
- Funded sewage treatment plants
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Enforcement of water quality is decreasing
• Underfunded and understaffed state and federal
regulatory agencies were pressured by industries and
• Violations of the Clean Water Act have risen to over
100,000 documented violations/year
- 10% of Americans are unknowingly exposed to unsafe
drinking water
- The new EPA administrator has promised to improve
• Citizens pushed politicians to improve the Great Lakes
- The water quality of the lakes has dramatically
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We treat our drinking water
• Technology and government regulation have improved
our pollution control
- Treated drinking water is widespread and successful in
developed nations
• Before water reaches the user, it is chemically treated,
filtered, and disinfected
• The EPA sets standards for over 90 drinking water
- Local governments and private water suppliers must
meet these standards
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We treat our wastewater
• Wastewater = water people have used in some way
- Household, manufacturing, stormwater runoff, etc.
- It is treated before being released into the environment
• Septic systems = the most popular method of wastewater
disposal in rural areas
- Underground septic tanks separate solids and oils from
- The water drains into a drain field, where microbes
decompose the pollutants
- Solid waste is periodically pumped out and landfilled
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Municipal sewer systems
• In populated areas, sewer systems carry wastewater to
treatment locations
• Primary treatment = physically removes contaminants
in settling tanks (clarifiers)
• Secondary treatment = water is stirred and aerated
- Aerobic bacteria degrade organic pollutants
- Water treated with chlorine (and/or ultraviolet light) is
piped into rivers or the ocean
• Reclaimed water is used for lawns, irrigation, or industry
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A typical wastewater treatment facility
• Sludge = solid material
resulting from treatment
- Is decomposed
- Then landfilled,
incinerated, or used as
fertilizer on cropland
• Methane-rich gas created
by decomposition can be
burned to generate
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Artificial wetlands clean wastewater
• After primary treatment at a
conventional facility
- Water is pumped into the wetland
- Microbes decompose the
remaining pollutants
• Cleansed water is released into
- Or percolates underground
• They are havens for wildlife
and areas for human recreation
The U.S. has over 500 artificially constructed or
restored wetlands
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• Obtaining future supplies of freshwater requires citizen
action, legislation and regulation, technology, economic
incentives, and education
• With expanding population and increasing water usage,
we are approaching conditions of widespread scarcity
• Water pollution is already harming health, economies,
and societies of both rich and poor nations
• Better regulation has improved water quality in the U.S.
and other developed nations
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The picture shows a(n):
Braided river
Meandering river
River delta
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The area of a lake that rings the edge and contains rooted
plants is called the _______ zone.
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An unconfined aquifer is defined as:
a) An aquifer that traps porous rocks between layers of
less permeable substrate
b) An aquifer that traps porous rocks under one layer of
less permeable substrate
c) An aquifer with porous rocks resting on bedrock
d) An aquifer with no upper layer
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Why do governments subsidize irrigation?
It promotes food self-sufficiency.
Governments have to or food could not be grown.
Governments want to lower water tables.
Governments do not subsidize irrigation.
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Which of the following statements is NOT true
about dams?
They change habitat.
They generate electrical power.
They have created more farmland upstream.
Pollutants are trapped in reservoirs.
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Which of the following is a point source of water
A factory
Agricultural fields
All are point sources
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Which of the following type of water pollution causes
the most severe human health problems?
Nutrient pollution
Toxic chemicals
Sediment pollution
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Which statement is NOT correct regarding using
artificial wetlands to treat wastewater?
Water first undergoes primary treatment.
Microbes decompose pollutants.
Cleansed water cannot be released into waterways.
They are good areas for wildlife.
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QUESTION: Interpreting Graphs and Data
In this figure of a wastewater treatment facility, what is the
first step in treatment?
a) Physical screening to
remove large debris
b) Aeration in basins
c) Secondary
d) Piping the treated
water into a river
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QUESTION: Viewpoints
During times of drought, conflicts erupt between
farmers (who need water for irrigation) and ecologists
(who want water left in rivers to protect wildlife).
Who should have the highest priority?
a) Farmers - they need the water for their crops.
b) Wildlife - animals will die without water.
c) Farmers should be paid subsidies to withdraw
water from other places.
d) Farmers should be paid to plant different crops
that do not require so much water.
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QUESTION: Weighing the Issues
Should cities in dry areas, such as Las Vegas, be allowed
to increase their populations, so that they will require
more water?
a) Yes; it’s un-American to limit what cities can do.
b) Yes; but make the people pay the true cost of water.
c) Yes; but only if the people are required to use drastic
conservation measures.
d) No; enough is enough, and cities in arid
environments simply cannot continue growing.
© 2011 Pearson Education, Inc.

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