Ch15 lecture 3e

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
PowerPoint® Slides prepared by
Jay Withgott and Heidi Marcum
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Ch 15
Freshwater Resources:
Natural Systems,
Human Impact, and
Conservation
Part 2: Environmental Issues
and the Search for Solutions

This lecture will help you understand:
• Water and the hydrologic cycle
• Water’s distribution on Earth
• Freshwater ecosystems
• Use and alteration of freshwater
systems
• Problems of water supply and
solutions
• Problems of water quality and
solutions
• How wastewater is treated

Plumbing the Colorado River
• The 2,330 km Colorado River begins in
the Rocky Mountains and trickles into
the Gulf of California
• Dams and irrigation provide water to
millions of people in 7 states
• Las Vegas, Nevada, is growing rapidly,
and needs more water
• The other states are allowing Las Vegas
to drill for underground water, even
though it threatens the area’s ecology
and people

Freshwater systems
• Water may seem abundant, but drinkable water is rare
• Freshwater = relatively pure, with few dissolved
salts
- Only 2.5% of Earth’s water is fresh
- Most freshwater is tied up in glaciers and ice caps

Rivers and streams wind through
landscapes
• Water from rain, snowmelt, or springs forms streams,
creeks, or brooks
• These merge into rivers, and eventually reaches the ocean
- Tributary = a smaller river slowing into a larger one
- Watershed = the area of land drained by a river and
its tributaries

Rivers shape the landscape
• If there is a large bend in the
river, the force of the water
cuts through the land
- Oxbow = an extreme
bend in a river
- Oxbow lake = the bend is
cut off and remains as an
isolated, U-shaped body
of water

A river may shift course
• Floodplain = areas nearest to the river’s course that are
flooded periodically
- Frequent deposition of silt makes floodplain soils
fertile
• Riparian = riverside areas that are productive and
species-rich
• Water of rivers and streams hosts diverse ecological
communities

Wetlands include marshes, swamps, and
bogs
• Wetlands = systems that combine
elements of freshwater and dry land
• Freshwater marshes = shallow
water allows plants to grow above
the water’s surface
• Swamps = shallow water that
occurs in forested areas
- Can be created by beavers
• Bogs = ponds covered in thick
floating mats of vegetation
- A stage in aquatic succession

Wetlands are valuable
• Wetlands are extremely valuable for wildlife
• They slow runoff
- Reduce flooding
- Recharge aquifers
- Filter pollutants
• People have drained wetlands, mostly for agriculture
- Southern Canada and the U.S. have lost more than half
of their wetlands

Lakes and ponds are ecologically diverse
• Lakes and ponds are bodies of open, standing water
• Littoral zone = region ringing the edge of a water body
• Benthic zone = extends along the entire bottom of the
water body
- Home to many invertebrates
• Limnetic zone = open portions of the lake or pond where
the sunlight penetrates the shallow waters
• Profundal zone = water that sunlight does not reach
- Supports fewer animals because there is less oxygen

A typical lake

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
• Inland seas = large lakes that hold so much water, their
biota is adapted to open water

Groundwater plays a key role
• Groundwater = any precipitation that does not evaporate,
flow into waterways, or get taken up by organisms
- Groundwater makes up one fifth of the Earth’s
freshwater supply
• Aquifers = Porous sponge-like formations of rock, sand, or
gravel that hold groundwater
• Zone of aeration = pore spaces are partially filled with water
• Zone of saturation = spaces are completely filled with water
• Water table = boundary between the two zones
• Aquifer recharge zone = any area where water infiltrates
Earth’s surface and reaches aquifers

A typical aquifer

There are two categories of aquifers
• Confined or artesian = water-bearing, porous rocks
are trapped between layers of less permeable
substrate (i.e., clay)
- Is under a lot of pressure
• Unconfined aquifer = no upper layer to confine it
- Readily recharged by surface water
• Groundwater becomes surface water through springs
or human-drilled wells
• Groundwater may be ancient: the average age is
1,400 years

Ogallala Aquifer

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

http://water.usgs.gov/wid/
FS_215-95/FS_215-95.html#WL9394

Water in the Ogallala Formation originates as precipitation or irrigation water at the land surface. Precipitation or
irrigation water that percolates through the root and unsaturated zones underlying irrigated fields may transport
fertilizer and pesticide residues to the formation. As more water percolates through the unsaturated zone, the ground
water is driven deeper into the formation; therefore, the older water is at the bottom of the formation and the younger
water is at the water table.
http://webserver.cr.usgs.gov/nawqa/hpgw/factsheets/PETEFIG3.html

Water is unequally distributed across Earth’s
surface
• Different regions possess vastly different amounts of
groundwater, surface water, and precipitation
• Many areas with high population density are water-
poor and face serious water shortages

Water is distributed unevenly in time, too
• Monsoon seasons bring concentrated storms
- Half a region’s annual rain may fall in a few hours
• People erect dams to store water

Climate change will cause water shortages
• Climate change will cause
- Altered precipitation patterns
- Melting glaciers
- Early season runoff
- Intensified droughts
- Flooding
• Increasing probability that there
will be still less water for more
people

How we use water
• We have achieved impressive engineering
accomplishments to harness freshwater sources
- 60 % of the world’s largest 227 rivers have been
strongly or moderately affected
- Dams, canals, and diversions
• Consumption of water in most of the world is
unsustainable
- We are depleting many sources of surface water and
groundwater

Water supplies houses, agriculture, and
industry
• Proportions of these three types of use vary
dramatically among nations
- Arid countries use water for agriculture
- Developed countries use water for industry

Different types of water use
• Consumptive use = water is removed from an aquifer or
surface water body, and is not returned
• Non-consumptive use = does not remove, or only
temporarily removes, water from an aquifer or surface
water
- Electricity generation at hydroelectric dams

We have erected thousands of dams
• Dam = any obstruction placed in a river or stream to
block the flow of water so that water can be stored in
a reservoir
- To prevent floods, provide drinking water, allow
irrigation, and generate electricity
- 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

A typical dam

China’s Three Gorges Dam
• The dam, on the Yangtze
River, is the largest in the
world
- 186 m (610 feet) high, 2
km (1.3 mi) wide
- Its reservoir stretches for
616 km (385 mi)
- Provides flood control,
passage for boats, and
electricity

Drawbacks of the Three Gorges Dam
• Cost $25 billion to build
• Is flooding 22 cities and the homes of
1.13 million people
• Submerging 10,000-year-old
archaeological sites
• Drowning farmland and wildlife habitat
• Tidal marshes at the Yangtze’s mouth
are eroding
• Pollutants will be trapped
• China will spend $5 billion to build
sewage treatment plants

Benefits and drawbacks of dams
• Benefits:
- Power generation
- Emission reduction
- Crop irrigation
- Drinking water
- Flood control
- Shipping
- New recreational
opportunities
• Drawbacks:
- Habitat alteration
- Fisheries declines
- Population
displacement
- Sediment capture
- Disruption of flooding
- Risk of failure
- Lost recreational
opportunities

Some dams are being removed
• Some people feel that the cost of dams outweighs their
benefits
- They are pushing to dismantle dams
• Rivers with dismantled dams
- Have restored riparian ecosystems
- Reestablished fisheries
- Revived river recreation
• 500 dams have been removed in the U.S.
- Property owners who opposed the removal change
their minds once they see the healthy river

Dikes and levees are meant to control floods
• Flooding is a normal, natural process
- Floodwaters spread nutrient-rich sediments over
large areas
• Floods also do tremendous damage to property
• Dikes and levees (long, raised mounds of earth) along
the banks of rivers hold rising waters in channels
- The U.S. Army Corps of Engineers has
constructed thousands of miles of levees
• Levees can make floods worse by forcing water to
stay in channels and overflow

We divert – and deplete – surface water
People have long
diverted water to farm
fields, homes, and
cities
The once mighty
Colorado River has
been extensively
dammed and diverted

The Colorado River is heavily diverted
- What water is left after all the diversions
comprises just a trickle into the Gulf of California
- On some days, water does not reach the gulf
- Diversion has drastically altered the river’s
ecology

The Colorado River Basin

The Colorado River
• Colorado River Compact of 1922
- Total flow of river apportioned
- Legal entitlements exceed actual distribution
• Destruction of downstream habitat
- California Delta
• Lots of Dams and channels
• Starting to understand importance of natural flow of
rivers and discharge

Glen Canyon Dam

The Aral Sea
• Once the fourth-largest lake on Earth
- It has lost more than 80% of its
volume in just 45 years
- The two rivers leading into the
Aral Sea were diverted to
irrigate cotton fields
• Consequences of a shrinking sea
- 60,000 fishing jobs are gone
- Pesticide-laden dust from the
lake bed is blown into the air
- The cotton cannot bring back the
region’s economy

Can the Aral Sea be saved?
People may have
begun saving the
northern part of the
Aral Sea

Inefficient irrigation wastes water
• Today, 70% more water is withdrawn for irrigation
than in 1960
- The amount of irrigated land has doubled
- Crop yields can double

Most irrigation is highly inefficient
• Only 45% of water is absorbed by crops via “flood
and furrow” irrigation
• Overirrigation leads to waterlogging, salinization, and
lost farming income
• Most national governments subsidize irrigation
• Water mining = withdrawing water faster than it can
be replenished

Areas where water use exceeds supply

We are depleting groundwater
• Groundwater is easily depleted
- Aquifers recharge slowly
- 1/3 of world population relies on groundwater
• As aquifers become depleted
- Water tables drop
- Salt water intrudes in coastal areas
- Sinkholes = areas where ground gives way unexpectedly
- Some cities (Venice, Mexico City) are slowly sinking
- Wetlands dry up

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
disputes

Solutions can address supply or demand
• We can either increase supply or reduce demand
• Lowering demand
- Politically difficult in the short term
- Offers better economic returns
- Causes less ecological and social damage
• Increasing supply
- Water can be transported through pipes and aqueducts
- It can be forcibly appropriated from weak
communities

Desalinization “makes” more water
• Desalinization = the removal of salt from seawater or
other water of marginal quality
- Distilling = hastens evaporation and condenses the
vapor
- Reverse osmosis = forces water through membranes
to filter out salts
• Desalinization facilities operate mostly in the arid Middle
East
• It is expensive, requires fossil fuels, and produces
concentrated salty water

The world’s largest reverse osmosis plant
• Near Yuma, Arizona
• Intended to reduce the
salinity of irrigation
runoff
• Too expensive to operate
and closed after 8 months

Agricultural demand can be reduced
• Look first for ways to decrease agricultural demand
- Lining irrigation canals
- Low-pressure spray irrigation that spray water
downward
- Drip irrigation systems that target individual plants
- Match crops to land and climate
- Selective breeding and genetic modification to raise
crops that require less water

Residential demand can be reduced
• Install low-flow faucets,
showerheads, washing
machines, and toilets
• Water lawns at night, when
evaporation is minimal
• Eat less meat
• Xeriscaping = landscaping
using plants adapted to arid
conditions

Industrial demand can be reduced
• Shift to processes that use less water
- Wastewater recycling
- Excess surface water runoff used for recharging
aquifers
- Patching leaky pipes
- Auditing industries
- Promoting conservation/education

Economic approaches to water conservation
• End government subsidies of inefficient practices
- Let the price of water reflect its true cost of extraction
• Industrial uses are more profitable than agricultural
- Less developed countries suffer
• Privatization of water supplies
- May improve efficiency
- Firms have little incentive to provide access to the
poor
• Decentralization of water control may conserve water
- Shift control to the local level

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
- Threaten the health and livelihood of people
• The invisible pollution of groundwater has been called a
“covert crisis”

Nutrient pollution
• Pollution = the release of matter or energy into the
environment that causes undesirable impacts on the
health and well-being of humans or other organisms
• Nutrient pollution from fertilizers, farms, sewage,
lawns, golf courses
- Leads to eutrophication
• Solutions
- Phosphate-free detergents
- Planting vegetation to increase nutrient uptake
- Treat wastewater
- Reduce fertilizer application

Eutrophication is a natural process, but…
• Human activities dramatically increase the rate at which it
occurs

Pathogens and waterborne diseases
• Enters water supply via inadequately treated human
waste and animal waste via feedlots
• Causes more human health problems than any other type
of water pollution
• Fecal coliform bacteria indicate fecal contamination of
water
- The water can hold other pathogens, such as giardiais,
typhoid, hepatitis A

Pathogens cause massive human health
problems
• Currently, 1.1 billion people are without safe drinking
water
• 2.4 billion have no sewer or sanitary facilities
- Mostly rural Asians and Africans
• An estimated 5 million people die per year
• Solutions:
• Treat sewage
• Disinfect drinking water
• Public education to encourage personal hygiene
• Government enforcement of regulations

Toxic chemicals
• From natural and synthetic sources
- Pesticides, petroleum products, synthetic chemicals
- Arsenic, lead, mercury, acid rain, acid drainage from mines
• Effects include: poisoning animals and plants, altering aquatic
ecosystems, and affecting human health
• Solutions:
• Legislating and enforcing more stringent regulations of
industry
• Modify industrial processes
• Modify our purchasing decisions

Sediment pollution
• Sediment can impair aquatic ecosystems
- Clear-cutting, mining, poor cultivation practices
- Dramatically changes aquatic habitats, and fish may
not survive
- Solutions: better management of farms and forests;
avoid large-scale disturbance of vegetation

Thermal pollution
• Warmer water holds less oxygen
- Dissolved oxygen decreases as temperature increases
- Industrial cooling heats water
- Removing streamside cover also raises water
temperature
• Water that is too cold causes problems
- Water at the bottom of reservoirs is colder
- When water is released, downstream water
temperatures drop suddenly and may kill aquatic
organisms

Point and nonpoint source water pollution
• Point source water pollution = discrete locations of pollution
- Factory or sewer pipes
• Nonpoint source water pollution = pollution from multiple
cumulative inputs over a large area
- Farms, cities, streets, neighborhoods
• The U.S. Clean Water Act
- Addressed point sources
- Targeted industrial discharge
• In the U.S., nonpoint sources have a greater impact on quality
- Limit development on watershed land surrounding reservoirs

Freshwater pollution sources

Indicators of water quality
• Scientists measure properties of water to characterize
its quality
- Biological indicators: presence of fecal coliform
bacteria and other disease-causing organisms
- Chemical indicators: pH, nutrient concentration,
taste, odor, hardness, dissolved oxygen
- Physical indicators: turbidity, color, temperature

Groundwater pollution is a serious problem
• Groundwater is increasingly contaminated, but is hidden
from view
- Difficult to monitor
- Out of sight, out of mind
- Retains contaminants for decades and longer
- Takes longer for contaminants to breakdown in
groundwater because of the lower dissolved oxygen
levels

Sources of groundwater pollution
• Some toxic chemicals occur
naturally
- Aluminum, fluoride, sulfates
• Pollution from human causes
- Wastes leach through soils
- Pathogens enter through
improperly designed wells
- Hazardous wastes are pumped
into the ground
- Underground storage septic
tanks may leak

Agriculture and industries pollute
groundwater
• Agricultural pollution
- Nitrates from fertilizers
- Pesticides were detected in more than half of the
shallow aquifers tested
• Manufacturing industries and military sites have been
heavy polluters

Legislative efforts reduce pollution
• Federal Water Pollution Control Act (1972)
- Renamed the Clean Water Act in 1977
- Illegal to discharge pollution without a permit
- Standards for industrial wastewater
- Funded sewage treatment plants
• Because of legislation, the situation is much better than it
was
• Other nations have also reduced pollution

We treat our drinking water
• Technology has improved our pollution control
• The EPA sets standards for more than 80 drinking water
contaminants
- Local governments and private water suppliers must
meet
• Before water reaches the user
- It is chemically treated, filtered, and disinfected

It is better to prevent pollution
• It is far better to prevent groundwater contamination than
correct it
• Other options are not as good:
- Removing just one herbicide from water costs $400
million
- Pumping, treating, and re-injecting it takes too long
- Restricting pollutants above aquifers would shift
pollution elsewhere
• Consumers can purchase environmentally friendly
products
- Become involved in local “river watch” projects

Treating wastewater
• Wastewater = water that has been used by people in
some way
- Sewage, showers, sinks, manufacturing, storm water
runoff
• Septic systems = the most popular method of wastewater
disposal in rural areas
- Underground septic tanks separate solids and oils from
wastewater
- The water drains into a drain field, where microbes
decompose the water
- Solid waste needs to be periodically pumped and
landfilled

Municipal sewer systems
• In populated areas, sewer systems carry wastewater
- Physical, chemical, and biological water treatment
• Primary treatment = the physical removal of
contaminants in settling tanks (clarifiers)
• Secondary treatment = water is stirred and aerated
so aerobic bacteria degrade organic pollutants
- Water treated with chlorine is piped into rivers or
the ocean
- Some reclaimed water is used for irrigation,
lawns, or industry

A typical wastewater treatment facility

Artificial wetlands
• Natural and artificial wetlands can cleanse wastewater
- After primary treatment at a conventional facility,
water is pumped into the wetland
- Microbes decompose the remaining pollutants
- Cleansed water is released into waterways or
percolated underground
• Constructed wetlands serve as havens for wildlife and
areas for human recreation
- More than 500 artificially constructed or restored
wetlands exist in the U.S.

Conclusion
• Obtaining future supplies of freshwater will be an
environmental challenge
• With expanding population and increasing water usage,
we are approaching conditions of widespread scarcity
• Water pollution is already harming freshwater around the
world
• New approaches can help this situation

QUESTION: Review
The picture shows a(n) … ?
a) Estuary
b) Wetland
c) Oxbow lake
d) River delta

QUESTION: Review
The area of a lake that contains open water that does not
receive sunlight is called the _______zone.
a) Littoral
b) Benthic
c) Limnetic
d) Profundal

QUESTION: Review
A confined 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

QUESTION: Review
Arid countries tend to use their water mostly for…?
a) Developing industries
b) Agriculture
c) Households
d) Export to rich countries

QUESTION: Review
Which of the following statements is not a benefit of
dams?
a) Habitat alteration
b) Power generation
c) Crop irrigation
d) Shipping

QUESTION: Review
Pollution is defined as “the release of matter or energy
into the environment that causes ______”?
a) Undesirable impacts on human health
b) Undesirable impacts on other organisms
c) Undesirable impacts on human well-being
d) All of the above are included in the definition

QUESTION: Review
Which of the following is a nonpoint source of water
pollution?
a) A factory
b) Sewer pipes
c) Agricultural fields
d) All are nonpoint sources

QUESTION: Review
Primary treatment of wastewater includes…?
a) Treating water with chemicals
b) Stirring and aerating water
c) Degradation of wastes by bacteria
d) Physical removal of contaminants

QUESTION: Interpreting Graphs and Data
What is the relationship between water consumption and
the amount of land that is irrigated?
a) Irrigation has grown more
slowly than demand
b) Irrigation and demand
have both increased
c) Growth of demand and
irrigation will slow
d) The U.S. does not follow
this graph

QUESTION: Interpreting Graphs and Data
Which conclusion can you draw from this graph?
From The Science behind the Stories
a) It is more water efficient to
produce vegetables
b) It is more water efficient to
produce meat
c) Vegetable and meat production
are relatively alike in water
consumption
d) There is little correlation
between water consumption and
our diet

QUESTION: Viewpoints
In 2001, angry farmers disobeyed a federal order to
divert irrigation water downstream to save
endangered species of fish. What should happen to
the farmers?
a) Nothing; they need the water for their crops
b) They should be fined for breaking the law
c) They should be paid subsidies so they can
continue farming
d) They should be paid to plant different crops
that do not require so much water

QUESTION: Viewpoints
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 not the American way to limit what cities can do
b) Yes, but the people will have to 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

Ch15 lecture 3e

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