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© 2011 Pearson Education, Inc.
AP Environmental Science
Mr. Grant
Lesson 72
Human Activities Affect Waterways
© 2014 Pearson Education, Inc.
Mastery Check
Compare and contrast the main types of freshwater ecosystems. Name and describe the major zones of a typical pond or lake.
© 2011 Pearson Education, Inc.
Objectives:
• Define the term sinkhole.
• Discuss how we use water and alter freshwater systems.
• TED - With wisdom and wit, Anupam Mishra talks about the amazing feats of engineering built centuries ago by the people of India's Golden Desert to harvest water. These structures are still used today -- and are often superior to modern water megaprojects.
© 2011 Pearson Education, Inc.
Discuss how we use water and alter freshwater systems.• Water is a renewable but limited resource, so we must manage it
sustainably.
• We use water for agriculture, industry, and residential use. Globally 70% is used for agriculture.
• We pump water from aquifers and surface water bodies, sometimes at unsustainable rates.
• Some of our water extraction now goes to bottled water, which is hugely popular even though it is no healthier than tap water and creates substantial plastic waste.
• We attempt to control floods with dikes and levees.
© 2011 Pearson Education, Inc.
Discuss how we use water and alter freshwater systems, con’t.
• We divert water with canals and irrigation ditches to bring water to where it is desired.
• We have dammed most of the world’s rivers. Dams bring a diversity of benefits and costs.
• Some dams are now being removed.
• Many wetlands have been lost, and we are now trying to restore some.
© 2014 Pearson Education, Inc.
Human Activities Affect Waterways
Water is crucial for human health as well as farms and factories
Water is a limited but renewable resource Withdrawal of water in most of the world is
unsustainable We are depleting many sources of surface water and
groundwater
One-third of the world’s people are affected by water shortages
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Human Activities Affect Waterways We have achieved impressive engineering
accomplishments to harness fresh water 60% of the world’s largest 227 rivers have been
strongly or moderately affected by dams, dikes, and diversions
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Fresh water and human populations are unevenly distributed across Earth Different areas possess different amounts of water
People are not distributed in accordance with water availability
Asia has the most water of any continent but the least water available per person
Densely populated nations like Pakistan, Iran, India, and Egypt face serious water shortages
Fresh water is also unevenly distributed in time Seasonal rains lead to differences in water availability India can receive half of its rain in a single monsoon Dams are used to store water for dry times
© 2014 Pearson Education, Inc.
Fresh water and human populations are unevenly distributed across Earth
Climate change will worsen conditions in many region Altered precipitation patterns
Melting glaciers causing early season runoff
Intensified droughts and flooding
One-third of the world’s major rivers experienced reduced flow from 1948 to 2004 Attributed largely to climate change
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Water supplies households, industry, and especially agriculture Globally, 70% of water is used for agriculture, 20%
for industry, and 10% for residential and municipal use Arid countries use more water for agriculture Developed countries use more water for industry
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Water supplies households, industry, and especially agriculture Consumptive use = when water is removed from
an aquifer or surface water body and is not returned Nonconsumptive use = does not remove, or only
temporarily removes, water
Irrigation = is the water applied to crops
Electricity generation at hydroelectric dams
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Water supplies households, industry, and especially agriculture Rapid population growth requires more food and clothes
We use 70% more irrigation water than 50 years ago
Irrigation can more than 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
Farmers in California’s Imperial Valley pay only 1 penny for 220 gallons of water
Water use for agriculture is subsidized by governmentsFarmers have little incentive to conserve
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Excessive water withdrawals can drain rivers and lakes
In many places, we are withdrawing water at unsustainable rates
Many of the world’s major rivers regularly run dry before reaching the sea The Colorado River often does not reach the Gulf of
California, threatening the future of cities and farms that rely on its water
Reduced flow drastically changes the river’s ecology and plant community and destroys fish and invertebrates
© 2014 Pearson Education, Inc.
Excessive water withdrawals can drain rivers and lakes
The Aral Sea in in present day Uzbekistan and Kazakhstan was once the fourth-largest lake on Earth It lost 80% of its volume in 45 years
The two rivers leading into the Aral Sea were diverted to irrigate cotton fields
60,000 fishing jobs are gone
Pesticide-laden dust is blown into the air
Little cotton can grow on the salty soil
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Excessive water withdrawals can drain rivers and lakes Worldwide, 15%–35% of water withdrawals for agriculture are
unsustainable
Water mining = withdrawing water faster than it is replenished
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Groundwater can also be depletedGroundwater is more easily depleted than surface water
Aquifers recharge slowly
Used by one-third of all people
As aquifers are mined, water tables drop
In many areas, water tables are falling 1–3 m/year Salt water
intrudes in coastal areas, making water undrinkable
Land above the aquifers subsides
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Groundwater can also be depleted
Sinkholes = areas where ground gives way suddenly Once the soil is compacted, aquifers can’t recharge
Wetlands that get their water from groundwater dry up
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Groundwater supplies our bottled water
Groundwater is being withdrawn for use as bottled water An average American drinks 29 gallons/year
Sales topped $15 billion in the United States in 2012
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
Energy costs of bottled water are 1000–2000 times greater than those of tap water
Only 25% of bottles are recycled in the United States
© 2011 Pearson Education, Inc.
Bottled water is popular but problematic
Energy costs of bottled water are 1,000–2,000 times greater than those of tap water
© 2014 Pearson Education, Inc.
People 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
Levees (or dikes) are the long, raised mounds of earth along the banks of rivers that hold water in channels Stop flooding from most rains
May make floods worse by forcing water to stay in channels, build energy, 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 flooded
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We divert surface water to suit our needs
People divert water to farm fields, homes, and cities Water from the Colorado River is diverted to Denver, Las
Vegas, Los Angeles, and elsewhere
In China, $62 billion is being spent to move water from the Yangtze to the Yellow River
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, it diverted streams that fed Mono Lake
Lake levels fell; salt concentrations doubled
© 2011 Pearson Education, Inc.
We divert surface water for our needs
The once mighty Colorado River has been extensively diverted and used
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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
They create reservoirs = artificial lakes Dams are built to prevent floods, provide drinking
water, allow irrigation, and generate electricity 45,000 large dams have been erected in more than
140 nations
Tens of thousands of smaller dams have been built
Only a few major rivers remain undammed in remote regions of Canada, Alaska, and Russia
© 2014 Pearson Education, Inc.
We have erected thousands of dams Dams produce a mix of benefits and costs The dam on the Yangtze River is the largest in the
world Its reservoir stretches for 616 km (385 mi)
It provides flood control, passage for boats, and huge amounts of electricity
© 2014 Pearson Education, Inc.
We have erected thousands of dams
However, it 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
The tidal marshes at the Yangtze’s mouth are eroding
Pollutants may be trapped, making the water undrinkable
© 2014 Pearson Education, Inc.
Some dams are being removed Some people feel that the costs of dams outweigh their benefits
and are pushing to dismantle dams
Removing dams will restore riparian ecosystems, reestablish fisheries, and revive river recreation
The Federal Energy Regulatory Commission (FERC) renews licenses for dams
If dam costs exceed benefits, the license may not be renewed
400 dams have been removed in the United States
Some property owners who opposed the removal changed their minds once they saw the healthy river
© 2014 Pearson Education, Inc.
Wetlands are affected by human manipulations of waterways Wetlands are being lost as we divert and withdraw water,
channelize rivers, build dams, etc.
Wetlands have also been widely drained for agriculture
As wetlands disappear, we lose ecosystem services
Filtering pollutants, wildlife habitat, flood control, etc.
Many are trying to protect and restore them
© 2014 Pearson Education, Inc.
Wetlands are affected by human manipulations of waterways
The Ramsar Convention on Wetlands of International Importance (1971) seeks the conservation and wise use of wetlands in the context of sustainable development 1900 sites covering 185 million ha are protected
© 2014 Pearson Education, Inc.
Solutions to Depletion of Fresh Water
Our use of fresh water has doubled over the last 50 years
We can either increase supply or reduce demand Increasing supply through intensive extraction is
only a temporary fix Diversions increase supply in one area but decrease
it elsewhere
© 2011 Pearson Education, Inc.
TED Video
To promote smart water management, Anupam Mishra works to preserve rural India’s traditional rainwater harvesting techniques.
"In [him] lives a spirit, of quiet service, that once existed freely in our politics and our activism, a spirit that has been completely excised from one sphere and remains gravely threatened in the other."
Ramachandra Guha, in The Hindu
Anupam Mishra: The ancient ingenuity of water harvesting (17:15)
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