1. © 2011 Pearson Education, Inc. AP Environmental Science Mr. Grant Lesson 75 How We Use Water & Solutions to Depletion of Fresh Water

2. © 2011 Pearson Education, Inc. 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.

3. © 2011 Pearson Education, Inc. Sinkhole: A depression in the land formed from the collapse or erosion of the underlying rock or soil. Define the term sinkhole.

4. © 2011 Pearson Education, Inc. 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.

5. © 2011 Pearson Education, Inc. 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

6. © 2011 Pearson Education, Inc. 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

7. © 2011 Pearson Education, Inc. 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

8. © 2011 Pearson Education, Inc. 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

9. © 2011 Pearson Education, Inc. 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

10. © 2011 Pearson Education, Inc. 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

11. © 2011 Pearson Education, Inc. 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

12. © 2011 Pearson Education, Inc. Levees increase flooding A major levee along the Mississippi River failed after Hurricane Katrina, allowing parts of New Orleans to be flooded

13. © 2011 Pearson Education, Inc. 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

14. © 2011 Pearson Education, Inc. A typical dam

15. © 2011 Pearson Education, Inc. 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

16. © 2011 Pearson Education, Inc. 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

17. © 2011 Pearson Education, Inc. 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

18. © 2011 Pearson Education, Inc. 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.

19. © 2011 Pearson Education, Inc. 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

20. © 2011 Pearson Education, Inc. 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

21. © 2011 Pearson Education, Inc. Can the Aral Sea be saved? People have begun saving the northern part of the Aral Sea

22. © 2011 Pearson Education, Inc. Irrigation wastes water 15–35% of water withdrawals for irrigation are unsustainable Water mining = withdraws water faster than it can be replenished

23. © 2011 Pearson Education, Inc. 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

24. © 2011 Pearson Education, Inc. 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

25. © 2011 Pearson Education, Inc. 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

26. © 2011 Pearson Education, Inc. 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

27. © 2011 Pearson Education, Inc. 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

28. © 2011 Pearson Education, Inc. 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

29. © 2011 Pearson Education, Inc. 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

30. © 2011 Pearson Education, Inc. 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

31. © 2011 Pearson Education, Inc. 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

32. © 2011 Pearson Education, Inc. 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

33. © 2011 Pearson Education, Inc. 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

34. © 2011 Pearson Education, Inc. 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

35. © 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)