ap environmental science mr. grant lesson 75

© 2011 Pearson Education, Inc.

AP Environmental Science

Mr. GrantLesson 75

How We Use Water

&

Solutions to Depletion of Fresh Water


Objectives:

• Define the term sinkhole.• Discuss how we use water and alter freshwater systems.• Assess problems of water supply and propose solutions to

address depletion of fresh water.• 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.


Sinkhole: A depression in the land formed from the collapse or erosion of the underlying rock or soil.

Define the term sinkhole.


Discuss how we use water and alter freshwater systems.• We use water for agriculture, industry, and residential

use. Globally 70% is used for agriculture.

• We divert water with canals and irrigation ditches to bring water to where it is desired.

• We attempt to control floods with dikes and levees.

• We have dammed most of the world’s rivers. Dams bring a diversity of benefits and costs. Some dams are now being removed.

• We pump water from aquifers and surface water bodies, sometimes at unsustainable rates.


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 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

• 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


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


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


We divert surface water for our needs

• People divert water to farm fields, homes, and cities

The once mighty Colorado River has been extensively diverted and used


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


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


Levees increase flooding

• A major levee along the Mississippi River failed after Hurricane Katrina, allowing parts of New Orleans to be flooded


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 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• Dams are great engineering feats

- Many stand hundreds of feet tall


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, 2.3

km (1.4 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 $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


Some dams are being removed

• Some people feel that the costs of dams outweigh their benefits- 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

renewed• 400 dams have been removed in the U.S.

- Property owners who opposed the removal change their minds once they see the healthy river


Assess problems of water supply and propose solutions to address depletion of fresh water.• Surface water extraction has caused rives to run dry and water bodies to

shrink.

• Many wetlands have been lost, and we are now trying to restore some.

• Water tables are dropping in many areas from unsustainable groundwater extraction.

• Some of our water extraction now goes to bottled water, which is hugely popular despite being no healthier than tap water and creating substantial plastic waste.

• Political tensions over water may heighten in the future.

• Desalination increases water supply, but is expensive and energy intensive.

• Solutions to reduce demand include technology, market-based approaches, and consumer products that increase efficiency in agriculture, industry, and the home.

• Privatization of water supplies is a much-debated issue.


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


The Aral Sea• 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 from the lake

bed is blown into the air• Cotton cannot save the region’s

economy


Can the Aral Sea be saved?

People have begun saving the northern part of the Aral Sea


Irrigation wastes water• 15–35% of water withdrawals for irrigation are

unsustainable

• Water mining = withdraws water faster than it can be replenished


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


We are depleting groundwater

• Groundwater is easily depleted - Aquifers recharge slowly- Used by one-third of all people

• As aquifers are mined, water tables drop- Salt water intrudes in coastal areas

• Sinkholes = areas where ground gives way unexpectedly- Aquifers can’t recharge

• Wetlands dry up


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


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


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- They sign water-sharing treaties


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 elsewhere

• 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


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

East- It is expensive, requires fossil fuels, kills aquatic life,

and produces salty waste


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 cost-effective way


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


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/dayXeriscaping uses plants adapted to arid conditions


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

plumbing• Audit industries• Promote conservation/education


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 suffer

• 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


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)

http://www.ted.com/speakers/anupam_mishra.html

ap environmental science mr. grant lesson 75

Documents

irrigation water

diversionsconsumption

provision of water

gallons of water

depletion of fresh water

surface water bodies

sources of surface water

surface water body