(8) Water

How Graphene Desalination could Increase Water Supplies

The State of the Planet's Fresh Water Supply

Water8

How Can We Increase Water Supplies?

Concept 11-2A Groundwater used to supply cities and grow food is being pumped from aquifers in some areas faster than it is renewed by precipitation.

Concept 11-2B Using dams, reservoirs, and transport systems to transfer water to arid regions has increased water supplies in those areas, but has disrupted ecosystems and displaced people.

Concept 11-2C We can convert salty ocean water to freshwater, but the cost is high, and the resulting salty brine must be disposed of without harming aquatic or terrestrial ecosystems

There Are Several Ways to Increase Freshwater Supplies

The most common ways to increase the supply of freshwater in a particular area are withdrawing groundwater, building dams and reservoirs to store runoff in rivers for release as needed, transporting surface water from one area to another, and converting saltwater to freshwater (desalination) (Concepts 11-2A, 11-2B, and 11-2C). Other important strategies discussed later in this chapter involve water conservation and better use of the natural hydrologic cycle.

We Are Withdrawing Groundwater Faster Than It Is Replenished in Some Areas

Most aquifers are renewable resources unless their water becomes contaminated or is removed faster than it is replenished by rainfall, as is occurring in many parts of the world. Aquifers provide drinking water for nearly half of the world’s people. In the United States, aquifers supply almost all of the drinking water in rural areas, one-fifth of that in urban areas, and 37% of irrigation water. Relying more on groundwater has advantages and disadvantages. Water tables are falling in many areas of the world because the rate of pumping water (mostly to irrigate crops) from aquifers exceeds the rate of natural recharge from rainfall and snowmelt (Concept 11-2A). The world’s three largest grain producers-India, China, and the United States-and several other countries such as Saudi Arabia, Mexico, and Pakistan are over pumping many of their aquifers. Currently, more than half a billion people are being fed by grain produced through the unsustainable use of groundwater, and this number is expected to grow. Worldwide, the unsustainable depletion of aquifers amounts to water that every day would fill a convoy of large tanker trucks stretching 480,000 kilometers (300,000 miles)-more than the distance to the moon. In the United States, groundwater is being withdrawn on average four times faster than it is replenished (Concept 11-2A). One of the most serious overdrafts is in the lower half of the Ogallala, the world’s largest known aquifer, which lies under eight Midwestern states from southern South Dakota to Texas. Although it is gigantic, the Ogallala is essentially a one-time deposit of liquid natural capital with a very slow rate of recharge. In some areas, farmers are withdrawing water from this aquifer as much as 40 times faster than nature replaces it. Such over drafting has lowered the water table more than 30 meters (100 feet) in some places. Unless water saving irrigation systems are used, most hydrologists predict that groundwater levels in much of this aquifer will drop to the point where using deep wells to pump the water out will cost more than the water is worth for growing crops and raising cattle. Serious groundwater depletion is also taking place in California’s Central Valley, which supplies half of the country’s fruit and vegetables.

Groundwater overdrafts near coastal areas can contaminate groundwater supplies by causing intrusion of saltwater into freshwater aquifers, which makes such water undrinkable and unusable for irrigation. This problem is especially serious in the U.S. coastal areas of Florida, California, South Carolina, Georgia, New Jersey, and Texas, as well as in coastal areas of Turkey, Manila in the Philippines, and Bangkok in Thailand. Rising sea levels from global warming will increase saltwater intrusion and can decrease the amount of groundwater available in heavily populated coastal areas.

If we don’t sharply slow the depletion of groundwater, an increasing number of the world’s people will have to live on rainwater and suffer from decreased food production.

With global water shortages looming, scientists are evaluating deep aquifers-found at depths of 0.8 kilometer (0.5 mile) or more-as future water sources. Preliminary results suggest that some of these aquifers hold enough water to support billions of people for centuries.

The quality of water in these aquifers may also be much higher than the quality of the water in most rivers and lakes. Assuming that the costs are not too high, there are two major concerns about tapping these nonrenewable deposits of water. First, little is known about the geological and ecological impacts of pumping water from deep aquifers. Second, some deep aquifers flow beneath several different countries, and there are no international water treaties that govern rights to such water. Without such treaties, conflicts could ensue over who has the right to tap into these valuable resources.

Large Dams and Reservoirs Have Advantages and Disadvantages

Large dams and reservoirs have both benefits and drawbacks. Their main purposes are to capture and store runoff and release it as needed to control floods, generate electricity, and supply water for irrigation and for towns and cities. Reservoirs also provide recreational activities such as swimming, fishing, and boating. Over the past 50 years, an average of two large dams at least 15 meters (49 feet) high have been constructed somewhere on the earth every day. As a result, reservoirs now hold 3 to 6 times more water than flows in the world’s natural rivers, many of which no longer reach the sea.

More than 45,000 large dams in the world (22,000 of them in China) have increased the annual reliable runoff available for human use by nearly one-third. But a series of dams on a river and withdrawals of river water for agricultural and urban uses, especially in arid areas, can reduce downstream flow to a trickle and prevent it from reaching the sea as a part of the hydrologic cycle. According to the World Commission on Water in the 21st century, more than half of the world’s major rivers go dry part of the year because of such flow reduction especially during drought years.

Worldwide, this engineering approach to river management has displaced 40–80 million people from their homes, flooded an area of mostly productive land roughly equal to the area of the U.S. state of California, and often impairs some of the important ecological services rivers provide (Concept 11-2B). According to water-resource expert Peter H. Gleck, at least a fourth of the world’s freshwater fish species are threatened or endangered, primarily because dams and water withdrawals have destroyed many free-flowing rivers.

Since 1960, the Colorado River, the largest river in the U.S. southwest, has rarely made it to the Gulf of California because of a combination of multiple dams, large-scale water withdrawal, and prolonged drought. Such withdrawals threaten the survival of species that spawn in the river, destroy estuaries that serve as breeding grounds for numerous aquatic species, and increase saltwater contamination of aquifers near the coast.

Climate change will heighten shortages of water in many parts of the world. Hundreds of millions of people in China, India, and other parts of Asia depend on river flows fed by melting glaciers in the Himalayas. Many of these glaciers in Asia and in parts of South America are receding and are projected to disappear during this century as the earth’s atmosphere continues to warm. Global warming also changes the timing of water flows into rivers from melting snow in mountainous areas. As temperatures rise, the melting snow will fill rivers earlier in spring and sharply reduce the supply needed to grow crops during the summer. Alterations in the patterns of precipitation and evaporation caused by climate change from global warming are still poorly understood, but there is general agreement that some areas will get drier and some will get wetter and that this will change where we can grow food.

California Transfers Massive Amounts of Water from Water-Rich Areas to Water-Poor Areas

Tunnels, aqueducts, and underground pipes can transfer stream runoff collected by dams and reservoirs from water-rich areas to water-poor areas, but they also create environmental problems (Concept 11-2B).

One of the world’s largest water transfer projects is the California Water Project. It uses a maze of giant dams, pumps, and aqueducts to transport water from water-rich northern California to water-poor southern California’s heavily populated, arid agricultural regions and cities. This project supplies massive amounts of water to areas that, without such water transfers, would be mostly desert.

For decades, northern and southern Californians have feuded over how the state’s water should be allocated under this project. Southern Californians want more water from the north to grow more crops and to support Los Angeles, San Diego, and other growing urban areas. Agriculture consumes three-fourths of the water withdrawn in California, much of it used inefficiently for water-thirsty crops such as rice and alfalfa growing in desert-like conditions.

Northern Californians counter that sending more water south degrades the Sacramento River, threatens fisheries, and reduces the flushing action that helps clean San Francisco Bay of pollutants. They also argue that much of the water sent south is wasted. They point to studies showing that making irrigation just 10% more efficient would provide enough water for domestic and industrial uses in southern California.

According to a 2002 study by a group of scientists and engineers, projected global warming will sharply reduce water availability in California (especially southern California) and other water-short states in the western United States even in the best-case scenario. Some analysts project that sometime during this century, many people living in arid southern California cities such as Los Angeles and San Diego, as well as farmers in this area, may have to move elsewhere for water.

Pumping more groundwater is not the answer because groundwater is already being withdrawn faster than it is replenished in much of central and southern California. It would be quicker and cheaper to improve irrigation efficiency, stop growing water-thirsty crops in arid areas, and increase the historically low price of water to reduce water waste.

The Aral Sea Disaster

The shrinking of the Aral Sea is the result of a large-scale water transfer project in an area of the former Soviet Union with the driest climate in central Asia. Since 1960, enormous amounts of irrigation water have been diverted from the inland Aral Sea and its two feeder rivers to create one of the world’s largest irrigated areas, mostly for raising cotton and rice. The irrigation canal, the world’s longest, stretches more than 1,300 kilometers (800 miles). This large-scale water diversion project, coupled with droughts and high evaporation rates due to the area’s hot and dry climate, has caused a regional ecological and economic disaster. Since 1961, the sea’s salinity has tripled and the average level of its water has dropped by 22 meters (72 feet). It has lost 90% of its volume of water and has split into two parts. Water withdrawal for agriculture has reduced the two rivers feeding the sea to mere trickles.

About 85% of the area’s wetlands have been eliminated and roughly half the local bird and mammal species have disappeared. In addition, a huge area of former lake bottom has been converted to a human-made desert covered with glistening white salt. The sea’s increased salt concentration-three times saltier than ocean water-caused the presumed extinction of 20 of the area’s 24 native fish species. This has devastated the area’s fishing industry, which once provided work for more than 60,000 people. Fishing villages and boats once located on the sea’s coastline now sit abandoned in the middle of a salt desert.

Winds pick up the sand and salty dust and blow it onto fields as far as 300 kilometers (190 miles) away. As the salt spreads, it pollutes water and kills wildlife, crops, and other vegetation. Aral Sea dust settling on glaciers in the Himalayas is causing them to melt at a faster than normal rate-a prime example of unexpected connections and unintended consequences. Shrinkage of the Aral Sea has also altered the area’s climate. The once-huge sea acted as a thermal buffer that moderated the heat of summer and the extreme cold of winter. Now there is less rain, summers are hotter and drier, winters are colder, and the growing season is shorter. The combination of such climate change and severe salinization has reduced crop yields by 20–50% on almost one-third of the area’s cropland. To raise yields, farmers have used more herbicides, insecticides, and fertilizers, which have percolated downward and accumulated to dangerous levels in the groundwater-the source of most of the region’s drinking water.

Many of the 45 million people living in the Aral Sea’s watershed have experienced increasing health problems-including anemia, respiratory illnesses, kidney disease, and various cancers-from a combination of toxic dust, salt, and contaminated water.

Since 1999, the United Nations and the World Bank have spent about $600 million to purify drinking water and upgrade irrigation and drainage systems. This has improved irrigation efficiency and flushed some salts from croplands. A new dike should raise the average level of the small Aral by 3 meters (10 feet). Some artificial wetlands and lakes have been constructed to help restore aquatic vegetation, wildlife, and fisheries.

The five countries surrounding the lake and its two feeder rivers have worked to improve irrigation efficiency and to partially replace water-thirsty crops with others requiring less irrigation water. As a result, the total annual volume of water in the Aral Sea basin has been stabilized. Nevertheless, experts expect the largest portion of the Aral Sea to continue shrinking.

Removing Salt from Seawater Is Costly, Kills Marine Organisms, and Produces Briny Wastewater

Desalination involves removing dissolved salts from ocean water or from brackish (slightly salty) water in aquifers or lakes for domestic use. It is another way to increase supplies of freshwater (Concept 11-2C). One method for desalinating water is distillation-heating saltwater until it evaporates, leaving behind salts in solid form, and condenses as freshwater. Another method is reverse osmosis (or microfiltration), which uses high pressure to force saltwater through a membrane filter with pores small enough to remove the salt. In effect, high pressure is used to push freshwater out of saltwater.

Today about 15,000 desalination plants operate in more than 125 countries, especially in the arid nations of the Middle East, North Africa, the Caribbean, and the Mediterranean. They meet less than 0.3% of the world’s demand for freshwater.

There are three major problems with the widespread use of desalination. One is the high cost, because it takes a lot of energy to desalinate water. A second problem is that pumping large volumes of seawater through pipes and using chemicals to sterilize the water and control algae growth kills many marine organisms. A third problem is that desalination produces large quantities of briny wastewater that contain lots of salt and other minerals. Dumping concentrated brine into a nearby ocean increases the salinity of the ocean water, threatening food resources and aquatic life in the vicinity.

Dumping it on land could contaminate groundwater and surface water. Some research is being carried out on the economic and ecological feasibility of building desalination plants offshore and pumping the freshwater to the shore. This could help dilute the resulting briny seawater.

Bottom line: Currently, significant desalination is practical only for water-short, wealthy countries and cities that can afford its high cost (Concept 11-2C).

The Aral Sea was once the world’s fourth largest freshwater lake. Since 1960, it has been shrinking and getting saltier because most of the water from the rivers that replenish it has been diverted to grow cotton and food crops.

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(7) Water

Stop Water Pollution! Save Our Mother Earth!

International Water Association (IWA)

Water7

How Can We Best Deal with Water Pollution

CONCEPT 11-5A Streams can cleanse themselves of many pollutants if we do not overload them.

CONCEPT 11-5B Preventing water pollution usually works better and costs less than trying to clean it up.

CONCEPT 11-5C Reducing water pollution requires preventing it, working with nature in treating sewage, cutting

Water Pollution Comes from Point and Nonpoint Sources

Water pollution is any chemical, biological, or physical change in water quality that harms living organisms or makes water unsuitable for desired uses. Water pollution can come from single, or point sources, or from larger and dispersed nonpoint sources. Point sources discharge pollutants at specific locations through drain pipes, ditches, or sewer lines into bodies of water. Examples include factories, sewage treatment plants (which remove some but not all pollutants), underground mines, and oil tankers.

Because point sources are located at specific places, they are fairly easy to identify, monitor, and regulate.

Most developed countries have laws that help control point-source discharges of harmful chemicals into aquatic systems. In most developing countries, there is little control of such discharges.

Nonpoint sources are scattered and diffuse and cannot be traced to any single site of discharge. Examples include runoff of chemicals and sediments into surface water from cropland, livestock feedlots, logged forests, urban streets, lawns, and golf courses. We have made little progress in controlling water pollution from nonpoint sources because of the difficulty and expense of identifying and controlling discharges from so many diffuse sources.

Agricultural activities are by far the leading cause of water pollution. Sediment eroded from agricultural lands is the largest source. Other major agricultural pollutants include fertilizers and pesticides, bacteria from livestock and food processing wastes, and excess salt from soils of irrigated cropland. Industrial facilities are another source of water pollution; they emit a variety of harmful inorganic and organic chemicals. Mining is the third biggest source. Surface mining creates major erosion of sediments and runoff of toxic chemicals.

Climate change from global warming can also affect water pollution. In a warmer world, some areas will get more precipitation and other areas will get less. Intense downpours will flush more harmful chemicals, plant nutrients, and microorganisms into waterways. Prolonged drought will reduce river flows that dilute wastes.

Major Water Pollutants Have Harmful Effects

The WHO estimates that 3.2 million people-most of them children younger than age 5-die prematurely every year by contracting infectious diseases spread by contaminated water or by having too little water for adequate hygiene. Each year, diarrhea alone kills about 1.9 million people-about 90% of them children under age 5-in developing countries. This means that diarrhea caused mostly by exposure to polluted water kills a young child every 17 seconds.

Streams Can Cleanse Themselves If We Do Not Overload Them

Rivers and streams can recover rapidly from pollution caused by moderate levels of degradable, oxygen demanding wastes and excess heat. They do so through a combination of dilution, biodegradation, and the presence of bacteria that break down the waste. But this natural recovery process does not work when streams become overloaded with pollutants or when drought, damming, or water diversion reduce their flows (Concept 11-5A). Likewise, these processes do not eliminate slowly degradable or nondegradable pollutants.

In a flowing stream, the breakdown of degradable wastes by bacteria depletes dissolved oxygen and creates an oxygen sag curve. This reduces or eliminates populations of organisms with high oxygen requirements until the stream is cleansed of wastes. Similar oxygen sag curves can be plotted when heated water from industrial and power plants is discharged into streams.

Water pollution control laws enacted in the 1970s have greatly increased the number and quality of wastewater treatment plants in the United States andmost other developed countries. Such laws also require industries to reduce or eliminate their point-source discharges of harmful chemicals into surface waters. This has enabled the United States to hold the line against increased pollution by disease-causing agents and oxygen-demanding wastes in most of its streams. It is an impressive accomplishment given the country’s increased economic activity, resource consumption, and population growth since passage of these laws.

But large fish kills and drinking water contamination still occasionally occur in parts of the United States and other developed countries. One cause of such problems is accidental or deliberate releases of toxic inorganic and organic chemicals by industries or mines.

Another is malfunctioning sewage treatment plants. A third cause is nonpoint runoff of pesticides and excess plant nutrients from cropland and animal feedlots. In most developing countries, stream pollution from discharges of untreated sewage and industrial wastes is a serious and growing problem. According to a 2003 report by the World Commission on Water in the 21st Century, half of the world’s 500 rivers are heavily polluted, most of them running through developing countries. Most of these countries cannot afford to build waste treatment plants and do not have, or do not enforce, laws for controlling water pollution.

Industrial wastes and sewage pollute more than two-thirds of India’s water resources and 54 of the 78 rivers and streams monitored in China. Only about 10% of the sewage produced in Chinese cities is treated and 300 million Chinese-an amount equal to the entire U.S. population-do not have access to drinkable water. In Latin America and Africa, most streams passing through urban or industrial areas suffer from severe pollution.

Major Water Pollutants and Their Sources

Type/Effects - Examples - Major Sources

Infectious agents cause diseases - Bacteria, viruses, parasites - Human and animal wastes Oxygen-demanding wastes deplete dissolved oxygen needed by aquatic species -  Biodegradable animal wastes and plant debris - Sewage, animal feedlots, food processing facilities, pulp mills

Plant nutrients cause excessive growth of algae and other species growth - Nitrates (NO3-) and phosphates (PO4 3-) - Sewage, animal wastes, inorganic  fertilizers.

Organic chemicals add toxins to aquatic system - Oil, gasoline, plastics, pesticides, cleaning solvents - Industry, farms, and households.

Inorganic chemicals add toxins to aquatic system - Acids, salts, metal compounds - Industry, households, surface runoff.

Sediments disrupt photosynthesis, food webs, and other processes - Soil, silt - Land erosion

Thermal pollution makes some species vulnerable to diseases- Heat - Electric power and industrial plants.

Low Water Flow and Too Little Mixing Makes Lakes Vulnerable to Water Pollution

In lakes and reservoirs, dilution of pollutants often is less effective than in streams for two reasons. First, lakes and reservoirs often contain stratified layers that undergo little vertical mixing. Second, they have little flow. The flushing and changing of water in lakes and large artificial reservoirs can take from 1 to 100 years, compared with several days to several weeks for streams.

As a result, lakes and reservoirs are more vulnerable than streams are to contamination by runoff or discharge of sediment, plant nutrients, oil, pesticides, and toxic substances such as lead, mercury, and selenium.

These contaminants can kill bottom life and fish and birds that feed on contaminated aquatic organisms. Many toxic chemicals and acids also enter lakes and reservoirs from the atmosphere.

Eutrophication is the name given to the natural nutrient enrichment of a shallow lake, estuary, or slow-moving stream, mostly from runoff of plant nutrients such as nitrates and phosphates from surrounding land. An oligotrophic lake is low in nutrients and its water is clear. Over time, some lakes become more eutrophic as nutrients are added from natural and human sources in the surrounding watersheds.

Near urban or agricultural areas, human activities can greatly accelerate the input of plant nutrients to a lake-a process called cultural eutrophication. It is mostly nitrate- and phosphate-containing effluents from various sources that cause this change. These sources include runoff from farmland, animal feedlots, urban areas, chemically fertilized suburban yards, and mining sites, and from the discharge of treated and untreated municipal sewage. Some nitrogen also reaches lakes by deposition from the atmosphere.

During hot weather or drought, this nutrient overload produces dense growths or “blooms” of organisms such as algae and cyanobacteria and thick growths of water hyacinth, duckweed, and other aquatic plants. These dense colonies of plant life can reduce lake productivity and fish growth by decreasing the input of solar energy needed for photosynthesis by the phytoplankton that support fish.

When the algae die, they are decomposed by swelling populations of aerobic bacteria, which deplete dissolved oxygen in the surface layer of water near the shore and in the bottom layer. This can kill fish and other aerobic aquatic animals. If excess nutrients continue to flow into a lake, anaerobic bacteria take over and produce gaseous products such as smelly, highly toxic hydrogen sulfide and flammable methane.

According to the U.S. EPA, about one-third of the 100,000 medium to large lakes and 85% of the large lakes near major population centers in the United States have some degree of cultural eutrophication. According to the International Water Association, more than half of the lakes in China suffer from cultural eutrophication. There are several ways to prevent or reduce cultural eutrophication. We can use advanced (but expensive) waste treatment to remove nitrates and phosphates before wastewater enters lakes. We can also use a preventive approach by banning or limiting the use of phosphates in household detergents and other cleaning agents and employing soil conservation and land-use control to reduce nutrient runoff.

There are also several ways to clean up lakes suffering from cultural eutrophication. We can mechanically remove excess weeds, control undesirable plant growth with herbicides and algicides, and pump air through lakes and reservoirs to prevent oxygen depletion, all of which are expensive and energy-intensive methods.

As usual, pollution prevention is more effective and usually cheaper in the long run than cleanup (Concept 11-5B). The good news is that if excessive inputs of plant nutrients stop, a lake usually can recover from cultural eutrophication.

Water in many of central China’s rivers is greenish-black from uncontrolled pollution by thousands of factories. Water in some rivers is too toxic to touch, much less drink. The cleanup of some modernizing Chinese cities such as Beijing and Shanghai is forcing polluting refineries and factories to move to rural areas where two-thirds of China’s population resides. Liver and stomach cancer, linked in some cases to water pollution, are among the leading causes of death in the countryside. Farmers too poor to buy bottled water must often drink polluted well water.

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(6) Water

 

CAUGHT ON CAMERA: Seaside town's pier ripped up by 'Violent Waves' at Aberystwyth

Water6

How Can We Reduce the Threat of Flooding?

CONCEPT 11-4 We can improve flood control by protecting more wetlands and natural vegetation in watersheds and by not building in areas subject to frequent flooding.

Some Areas Get Too Much Water from Flooding

Whereas some areas have too little water, others sometimes have too much because of natural flooding by streams, caused mostly by heavy rain or rapidly melting snow. A flood happens when water in a stream overflows its normal channel and spills into the adjacent area, called a floodplain. Floodplains, which usually include highly productive wetlands, help to provide natural flood and erosion control, maintain high water quality, and recharge groundwater. People settle on floodplains because of their many advantages, including fertile soil, ample water for irrigation, and availability of nearby rivers for transportation and recreation. Floodplains provide flat land suitable for crops, buildings, highways, and railroads.

To reduce the threat of flooding and thus to allow people to live in floodplains, rivers have been narrowed and straightened (channelized), equipped with protective levees and walls, and dammed to create reservoirs that store and release water as needed. But in the long run, such measures can greatly increase flood damage because they can be overwhelmed by prolonged rains, as happened along the Mississippi River in the Midwestern United States during the summer of 1993.

Floods provide several benefits. They have created the world’s most productive farmland by depositing nutrient-rich silt on floodplains. They also recharge groundwater and help refill wetlands. But floods kill thousands of people each year and cause tens of billions of dollars in property damage. Indeed, floods annually affect more people than the combined numbers affected by drought, tropical cyclones, famine, earthquakes, tsunamis, and volcanic eruptions. Floods usually are considered natural disasters. Since the 1960s, however, human activities have contributed to the sharp rise in flood deaths and damages.

One such activity is removal of water-absorbing vegetation, especially on hillsides, and replacing that vegetation with farm fields, pastures, pavement, or buildings that cannot absorb rainwater. Another is draining wetlands that normally absorb floodwaters and building on the land. For example, Hurricane Katrina struck the Gulf Coast of the United States in August 2005 and flooded the city of New Orleans and surrounding areas. The damage was intensified because of the degradation and removal of coastal wetlands that had historically buffered the land from storm surges. Living on floodplains increases the threat of damage from flooding. Many poor people have little choice but to live in such risky areas, as discussed in the following

CASE STUDY

Living Dangerously on Floodplains in Bangladesh

Bangladesh is one of the world’s most densely populated countries, with 147 million people packed into an area roughly the size of the U.S. state of Wisconsin. It is very flat, only slightly above sea level, and it is one of the world’s poorest countries. The people of Bangladesh depend on moderate annual flooding during the summer monsoon season to grow rice and help maintain soil fertility in the delta basin. The annual floods deposit eroded Himalayan soil on the country’s crop fields.

In the past, great floods occurred every 50 years or so. But since the 1970s, they have come roughly every 4 years. Bangladesh’s flooding problems begin in the Himalayan watershed, where rapid population growth, deforestation, overgrazing, and unsustainable farming on steep and easily erodible slopes have increased flows of water during monsoon season. Monsoon rains now run more quickly off the denuded Himalayan foothills, carrying vital topsoil with them. This increased runoff of soil, combined with heavier-than-normal monsoon rains, has increased the severity of flooding along Himalayan rivers and downstream in Bangladesh. In 1998, a disastrous flood covered two-thirds of Bangladesh’s land area for 9 months, drowned at least 2,000 people, and left 30 million people homeless. It also destroyed more than one-fourth of the country’s crops, which caused thousands of people to die of starvation. In 2002, another flood left 5 million people homeless and flooded large areas of rice fields. Yet another major flood occurred in 2004.

Living on Bangladesh’s coastal floodplain at sea level means coping with storm surges, cyclones, and tsunamis, such as the one in 2004 caused by earthquakes under the Indian Ocean. In 1970, as many as 1 million people drowned as a result of one tropical cyclone. Another cyclone in 2003 killed more than a million people and left tens of millions homeless. In their struggle to survive, the poor in Bangladesh have cleared many of the country’s coastal mangrove forests for fuelwood, farming, and aquaculture ponds for raising shrimp. The result: more severe flooding, because these coastal wetlands had sheltered Bangladesh’s low-lying coastal areas from storm surges, cyclones, and tsunamis. Damages and deaths from cyclones in areas of Bangladesh still protected by mangrove forests have been much lower than in areas where the forests have been cleared.

A 3,000-year-old Chinese proverb says, “To protect your rivers, protect your mountains.”

THINKING ABOUT

Bangladesh

What are three things that could be done to help reduce the threat of flooding in Bangladesh?

We Can Reduce Flood Risks

To improve flood control, we can rely less on engineering devices such as dams and levees and more on nature’s systems such as wetlands and natural vegetation in watersheds. Straightening and deepening streams (channelization) reduces upstream flooding. But it also eliminates aquatic habitats, reduces groundwater discharge, and results in a faster flow, which can increase downstream flooding and sediment deposition. In addition, channelization encourages human settlement in floodplains, which increases the risk of damages and deaths from major floods.

Levees or floodwalls along the sides of streams contain and speed up stream flow, but they increase the water’s capacity for doing damage downstream. They also do not protect against unusually high and powerful floodwaters, such as those occurring in 1993 when two-thirds of the levees built along the Mississippi River in the United States were damaged or destroyed. Dams can reduce the threat of flooding by storing water in a reservoir and releasing it gradually, but they also have a number of disadvantages. Another way to reduce flooding is to preserve existing wetlands and restore degraded wetlands to take advantage of the natural flood control they provide in floodplains.

On a personal level, we can use the precautionary approach to think carefully about where we live. Many poor people live in flood-prone areas because they have nowhere else to go. Most people, however, can choose not to live in areas especially subject to flooding or to water shortages caused by climate factors, increased population, and economic development.

THINKING ABOUT

Where to Live

Do you now live in a flood-prone area? Have you thought about moving to or away from such an area? Do the attractions of living there outweigh the risks for you?

SOLUTIONS

Reducing Flood Damage

Prevention

Preserve forests on watersheds

Preserve and restore wetlands in floodplains

Tax development on floodplains

Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry

Control

Strengthen and deepen streams (channelization)

Build levees or floodwalls along streams

Build dams

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(5) Water

World Water Day: UN urges sustainable use of Earth's most critical resource

Water5

 How Can We Use Water More Sustainably

 CONCEPT 11-3 We can use water more sustainably by cutting water waste, raising water prices, slowing population growth, and protecting aquifers, forests, and other ecosystems that store and release water.

 Reducing Water Waste Has Many Benefits

Mohamed El-Ashry of theWorld Resources Institute estimates that 65-70% of the water people use throughout the world is lost through evaporation, leaks, and other losses, and global warming is expected to increase evaporation in many parts of the world. The United States does slightly better but still loses about half of the water it withdraws.

 El-Ashry believes it is economically and technically feasible to reduce such water losses to 15%, thereby meeting most of the world’s water needs for the foreseeable future.

 This win–win solution would decrease the burden on wastewater plants and reduce the need for expensive dams and water transfer projects that destroy wildlife habitats and displace people. It would also slow depletion of groundwater aquifers and save both energy and money.

 According to water resource experts, the main cause of water waste is that we charge too little for water. Such under pricing is mostly the result of government subsidies that provide irrigation water, electricity, and diesel fuel for farmers to pump water from rivers and aquifers at below-market prices.

 Because these subsidies keep water prices low, users have little or no financial incentive to invest in water saving technologies. According to water resource expert Sandra Postel, “By heavily subsidizing water, governments give out the false message that it is abundant and can afford to be wasted-even as rivers are drying up, aquifers are being depleted, fisheries are collapsing, and species are going extinct.”

 However, farmers, industries, and others benefiting from government water subsidies argue that the subsidies promote settlement and farming of arid, unproductive land, stimulate local economies, and help keep the prices of food, manufactured goods, and electricity low.

 Most water resource experts believe that when water scarcity afflicts many areas in this century, governments will have to make the unpopular decision to raise water prices. China did so in 2002 because it faced water shortages in most of its major cities with rivers running dry and water tables falling in key agricultural areas.

Higher water prices encourage water conservation but make it difficult for low-income farmers and city dwellers to buy enough water to meet their needs.

 When South Africa raised water prices, it established lifeline rates that give each household a set amount of free or low-priced water to meet basic needs. When users exceed this amount, the price rises as water use increases-a user-pays approach.

 The second major cause of water waste is too few government subsidies for improving the efficiency of water use. A basic rule of economics is that you get more of what you reward. Withdrawing subsidies that encourage water waste and providing subsidies for efficient water use would sharply reduce water waste. There should be two goals: greatly improve the efficiency of irrigation that accounts for 70% of the world’s water use and use inexpensive means to collect rainwater and pipe it to where it is needed.

 We Can Greatly Cut Water Waste in Irrigation

About 60% of the irrigation water applied throughout the world does not reach the targeted crops. Most irrigation systems obtain water from a groundwater well or a surface water source. The water then flows by gravity through unlined ditches in crop fields so the crops can absorb it. This flood irrigation method delivers far more water than is needed for crop growth and typically loses 40% of the water through evaporation, seepage, and runoff. This wasteful method is used on 97% of China’s irrigated land.

More efficient and environmentally sound irrigation technologies can greatly reduce water demands and water waste on farms by delivering water more precisely to crops-a more-crop-per-drop strategy. For example, the center-pivot, low-pressure sprinkler uses pumps to spray water on a crop. Typically, it allows 80% of that water to reach crops. Low-energy, precision application (LEPA) sprinklers, another form of center pivot irrigation, put 90–95% of the water where crops need it.

Drip or trickle irrigation, also called micro irrigation, is the most efficient way to deliver small amounts of water precisely to crops. It consists of a network of perforated plastic tubing installed at or below the ground level. Small pinholes in the tubing deliver drops of water at a slow and steady rate, close to the roots of individual plants.

Current drip irrigation systems are costly but they drastically reduce water waste, with 90–95% of the water input reaching the crops, and they increase crop yields by 20–90% over conventional gravity flow systems.

By using less water, they also reduce the amount of salt that irrigation water leaves in the soil. Increased use of an inexpensive drip irrigation system developed by the nonprofit International Development Enterprises (IDE) will raise crop yields in water-short areas and help lift poor families out of poverty.

Drip irrigation is used on just over 1% of the world’s irrigated crop fields and 4% of those in the United States. This percentage rises to 90% in Cyprus, 66% in Israel, and 13% in California. If water were priced closer to the value of the ecological services it provides and if government subsidies that encourage water waste were reduced or eliminated, water experts say that drip irrigation would quickly be used to irrigate most of the world’s crops.

 RESEARCH FRONTIER

Developing more efficient and affordable irrigation systems is other ways to reduce water waste in irrigating crops. Since 1950, Israel has used many of these techniques to slash irrigation water waste by 84% while irrigating 44% more land. Israel now treats and reuses 30% of its municipal sewage water for crop production and plans to increase this to 80% by 2025.

The government also gradually eliminated most water subsidies to raise Israel’s price of irrigation water to one of the highest in the world. Israelis also import most of their wheat and meat and concentrate on growing fruits, vegetables, and flowers that need less water.

Irrigation systems do not have to be complex and expensive. Many of the world’s poor farmers use small-scale and low-cost traditional technologies such as human-powered treadle pumps to pump groundwater close to the earth’s surface through irrigation ditches.

Rainwater harvesting is another simple and inexpensive way to provide water for drinking and growing crops throughout most of the world. It involves using pipes from rooftops and mini-reservoirs to catch rainwater.

In southern Australia, more than 40% of households use rainwater stored in tanks as their main source of drinking water. In Germany, half a million households and buildings harvest rainwater.

Poor farmers can also capture rainfall that would otherwise run off the land and store it in shallow aquifers, ponds, and water tanks for use during dry spells. According to a 2006 report by the U.N. Environment Programme (UNEP), harvesting rainfall in Africa and other parts of the world is an underused and cheap way to provide water compared to the costs of building dams or systems for piping drinking water to homes.

Saving rainwater can also save poor women and children from having to spend hours a day fetching water.

Africa is generally viewed as a dry continent but overall it has more water resources per capita than Europe. The UNEP estimates that Kenya has enough rainfall each year to supply 6 or 7 times its current population of 34 million. Increased rainwater harvesting in Ethiopia, where half of its 77 million people suffer from hunger and malnutrition, could supply 520 million people a year with water.

 We Can Cut Water Waste in Industry and Homes

The chemical, paper and pulp, oil, coal, primary metals, and food processing industries use almost 90% of the water used by industry in the United States. Some of these industries recapture, purify, and recycle water to reduce their water use and water treatment costs.

However, most industrial processes could be redesigned to use much less water. Flushing toilets with water (most of it clean enough to drink) is the single largest use of domestic water. Since 1992, U.S. government standards require new toilets to use no more than 6.1 liters (1.6 gallons) of water per flush. Models that use 4.8 liters (1.28 gallons) are available. William McDonough has designed a toilet with a bowl so smooth that nothing sticks to it, including bacteria. Only a light mist is needed to flush it. Low-flow showerheads can cut shower water flow in half, save about 19,000 liters (5,000 gallons) per person each year, and reduce water bills.

According to U.N. studies, 40–60% of the water supplied in nearly all of the world’s megacities in developing countries is lost mostly through leakage of water mains, pipes, pumps, and valves. Even in advanced industrialized countries such as the United States these losses average 10–30%. Water experts say that fixing these leaks should be a high government priority that would cost less than building dams or importing water.

Many homeowners and businesses in water-short areas are using drip irrigation and are copying nature by replacing green lawns with native vegetation. This win–win approach, called Xeriscaping (pronounced “ZEER-i-scaping”), reduces water use by 30–85% and sharply reduces needs for labor, fertilizer, and fuel. It also reduces water and air pollution and yard wastes.

About 50–75% of the slightly dirtied water from bathtubs, showers, sinks, dishwashers, and clothes washers in a typical house could be stored in a holding purifies water by recycling, and thus follows one of the four scientific principles of sustainability.

A major cause of excessive water use and waste in homes and industries is under pricing (Concept 11-3). Many water utility and irrigation authorities charge a flat fee for water use and some charge less for the largest users of water. About one-fifth of all U.S. public water systems do not have water meters and charge a single low rate for almost unlimited use of high-quality water. Also, many apartment dwellers have little incentive to conserve water because water use charges are included in their rent. When the U.S. city of Boulder, Colorado, introduced water meters, water use per person dropped by 40%. GREEN

 CAREER: Water conservation specialist

Currently, we use large amounts of freshwater good enough to drink to flush away industrial, animal, and household wastes. According to the FAO, if current trends continue, within 40 years we will need the world’s entire reliable flow of river water just to dilute and transport the wastes we produce. We could save much of this water by using systems that mimic the way nature deals with wastes. One way to do this would be to return the nutrient rich sludge produced by conventional waste treatment plants to the soil as a fertilizer, instead of using freshwater to transport it. Banning the discharge of industrial toxic wastes into municipal sewer systems would make this feasible. Another way is to rely more on waterless composting toilets that convert human fecal matter to a small amount of dry and odorless soil-like humus material that can be removed from a composting chamber every year or so and returned to the soil as fertilizerWe

 Need to Use Water More Sustainably

Sustainable water use is based on the commonsense principle stated in an old Inca proverb: “The frog does not drink up the pond in which it lives.” lists ways to implement this principle by using water more sustainably (Concept 11-3).

Each of us can help bring about such a blue revolution by using and wasting less water. As with other problems, the solution starts with thinking globally and acting locally.

 SOLUTIONS

 Reducing Irrigation Water Waste

 Line canals bringing water to irrigation ditches

 Irrigate at night to reduce evaporation

 Monitor soil moisture to add water only when necessary

 Grow several crops on each plot of land (polyculture)

 Encourage organic farming

 Avoid growing water-thirsty crops in dry areas

 Irrigate with treated urban waste water

 Import water-intensive crops and meat

  * Methods for reducing water waste in irrigation.

 Question: Which two of these solutions do you think are the most important? Why?

  SOLUTIONS

 Reducing Water Waste

 Redesign manufacturing processes to use less water

 Recycle water in industry

 Landscape yards with plants that require little water

 Use drip irrigation

 Fix water leaks

 Use water meters

 Raise water prices

 Use waterless composting toilets

 Require water conservation in water-short cities

 Use water-saving toilets, showerheads, and front-loading clothes washers

 Collect and reuse household water to irrigate lawns and nonedible plants

 Purify and reuse water for houses, apartments, and office buildings

 * Methods for reducing water waste in industries, homes, and businesses.

 Question: Which three of these solutions do you think are the most important? Why?

  SOLUTIONS

 Sustainable Water Use

 Waste less water and subsidize water conservation

 Do not deplete aquifers

 Preserve water quality

 Protect forests, wetlands, mountain glaciers, watersheds, and other natural systems that store and release water

 Get agreements among regions and countries sharing surface water resources

 Raise water prices

 Slow population growth

  * Methods for achieving more sustainable use of the earth’s water resources (Concept 11-3). Question: Which two of these solutions do you think are the most important? Why?

  WHAT CAN YOU DO?

 Water Use and Waste

 Use water-saving toilets, showerheads, and faucet aerators.

 Shower instead of taking baths, and take short showers.

 Repair water leaks.

 Turn off sink faucets while brushing teeth, shaving, or washing.

 Wash only full loads of clothes or use the lowest possible water-level setting for smaller loads.

 Use recycled (gray) water for watering lawns and houseplants and for washing cars.

 Wash a car from a bucket of soapy water, and use the hose for rinsing only.

 If you use a commercial car wash, try to find one that recycles its water.

 Replace your lawn with native plants that need little if any watering.

 Water lawns and yards in the early morning or evening.

 Use drip irrigation and mulch for gardens and flowerbeds.

  * Individuals matter: ways in which you can reduce your use and waste of water. Visit www.h2ouse.org  for an array of water-saving tips from the EPA and the California Urban Water Conservation Council that can be used anywhere.

Question: Which four of these actions do you think are the most important? Why?

 

 

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(4) Water

Water Supply Video

Water4

 How Can We Increase Water Supplies?

CONCEPT 11-2A Groundwater used to supply cities and grow food is being pumped from aquifers in some areas faster than it is renewed by precipitation.

 CONCEPT 11-2B Using dams, reservoirs, and transport systems to transfer water to arid  regions has increased water supplies in those areas, but has disrupted ecosystems and displaced people.

 CONCEPT 11-2C We can convert salty ocean water to freshwater, but the cost is high, and the resulting salty brine must be disposed of without harming aquatic or terrestrial ecosystems.

  There Are Several Ways to Increase Freshwater Supplies

 The most common ways to increase the supply of freshwater in a particular area are withdrawing groundwater, building dams and reservoirs to store runoff in rivers for release as needed, transporting surface water from one area to another, and converting saltwater to freshwater (desalination) (Concepts 11-2A, 11-2B, and 11-2C). Other important strategies discussed later in this chapter involve water conservation and better use of the natural hydrologic cycle.

  We Are Withdrawing Groundwater Faster Than It Is Replenished in Some Areas

Most aquifers are renewable resources unless their water becomes contaminated or is removed faster than it is replenished by rainfall, as is occurring in many parts of the world. Aquifers provide drinking water for nearly half of the world’s people. In the United States, aquifers supply almost all of the drinking water in rural areas, one-fifth of that in urban areas, and 37% of irrigation water. Relying more on groundwater has advantages and disadvantages. Water tables are falling in many areas of the world because the rate of pumping water (mostly to irrigate crops) from aquifers exceeds the rate of natural recharge from rainfall and snowmelt (Concept 11-2A). The world’s three largest grain producers-India, China, and the United States-and several other countries such as Saudi Arabia, Mexico, and Pakistan are over pumping many of their aquifers. Currently, more than half a billion people are being fed by grain produced through the unsustainable use of groundwater, and this number is expected to grow. Worldwide, the unsustainable depletion of aquifers amounts to water that every day would fill a convoy of large tanker trucks stretching 480,000 kilometers (300,000 miles)-more than the distance to the moon. In the United States, groundwater is being withdrawn on average four times faster than it is replenished (Concept 11-2A). One of the most serious overdrafts is in the lower half of the Ogallala, the world’s largest known aquifer, which lies under eight Midwestern states from southern South Dakota to Texas. Although it is gigantic, the Ogallala is essentially a one-time deposit of liquid natural capital with a very slow rate of recharge. In some areas, farmers are withdrawing water from this aquifer as much as 40 times faster than nature replaces it.

Such over drafting has lowered the water table more than 30 meters (100 feet) in some places. Unless water saving irrigation systems are used, most hydrologists predict that groundwater levels in much of this aquifer will drop to the point where using deep wells to pump the water out will cost more than the water is worth for growing crops and raising cattle. Serious groundwater depletion is also taking place in California’s Central Valley, which supplies half of the country’s fruit and vegetables.

 Groundwater overdrafts near coastal areas can contaminate groundwater supplies by causing intrusion of saltwater into freshwater aquifers, which makes such water undrinkable and unusable for irrigation. This problem is especially serious in the U.S. coastal areas of Florida, California, South Carolina, Georgia, New Jersey, and Texas, as well as in coastal areas of Turkey, Manila in the Philippines, and Bangkok in Thailand. Rising sea levels from global warming will increase saltwater intrusion and can decrease the amount of groundwater available in heavily populated coastal areas.

 If we don’t sharply slow the depletion of groundwater, an increasing number of the world’s people will have to live on rainwater and suffer from decreased food production. Figure 11-10 lists ways to prevent or slow groundwater depletion by using this potentially renewable resource more sustainably. With global water shortages looming, scientists are evaluating deep aquifers-found at depths of 0.8 kilometer (0.5 mile) or more-as future water sources.

 Preliminary results suggest that some of these aquifers hold enough water to support billions of people for centuries. The quality of water in these aquifers may also be much higher than the quality of the water in most rivers and lakes.

Assuming that the costs are not too high, there are two major concerns about tapping these nonrenewable deposits of water. First, little is known about the geological and ecological impacts of pumping water from deep aquifers. Second, some deep aquifers flow beneath several different countries, and there are no international water treaties that govern rights to such water. Without such treaties, conflicts could ensue over who has the right to tap into these valuable resources.

  Large Dams and Reservoirs Have Advantages and Disadvantages

Large dams and reservoirs have both benefits and drawbacks. Their main purposes are to capture and store runoff and release it as needed to control floods, generate electricity, and supply water for irrigation and for towns and cities. Reservoirs also provide recreational activities such as swimming, fishing, and boating. Over the past 50 years, an average of two large dams at least 15 meters (49 feet) high have been constructed somewhere on the earth every day. As a result, reservoirs now hold 3 to 6 times more water than flows in the world’s natural rivers, many of which no longer reach the sea.

More than 45,000 large dams in the world (22,000 of them in China) have increased the annual reliable runoff available for human use by nearly one-third.

But a series of dams on a river and withdrawals of river water for agricultural and urban uses, especially in arid areas, can reduce downstream flow to a trickle and prevent it from reaching the sea as a part of the hydrologic cycle. According to the World Commission on Water in the 21st century, more than half of the world’s major rivers go dry part of the year because of such flow reduction especially during drought years.

 THINKING ABOUT

  Dams and Egypt

 Upstream dams and diversions of water from the Nile River by Ethiopia and Sudan will reduce the water available to Egypt, which cannot exist without such water. Which one or more of the options discussed in the Core Case Study do you think Egypt should pursue? Explain.

Worldwide, this engineering approach to river management has displaced 40-80 million people from their homes, flooded an area of mostly productive land roughly equal to the area of the U.S. state of California, and often impairs some of the important ecological services rivers provide (Concept 11-2B). According to water-resource expert Peter H. Gleck, at least a fourth of the world’s freshwater fish species are threatened or endangered, primarily because dams and water withdrawals have destroyed many free-flowing rivers.

Since 1960, the Colorado River, the largest river in the U.S. southwest, has rarely made it to the Gulf of California because of a combination of multiple dams, large-scale water withdrawal, and prolonged drought. Such withdrawals threaten the survival of species that spawn in the river, destroy estuaries that serve as breeding grounds for numerous aquatic species, and increase saltwater contamination of aquifers near the coast Climate change will heighten shortages of water in many parts of the world. Hundreds of millions of people in China, India, and other parts of Asia depend on river flows fed by melting glaciers in the Himalayas. Many of these glaciers in Asia and in parts of South America are receding and are projected to disappear during this century as the earth’s atmosphere continues to warm.

Global warming also changes the timing of water flows into rivers from melting snow in mountainous areas. As temperatures rise, the melting snow will fill rivers earlier in spring and sharply reduce the supply needed to grow crops during the summer. Alterations in the patterns of precipitation and evaporation caused by climate change from global warming are still poorly understood, but there is general agreement that some areas will get drier and some will get wetter and that this will change where we can grow food. California Transfers Massive Amounts of Water from Water-Rich Areas to Water-Poor Areas Tunnels, aqueducts, and underground pipes can transfer stream runoff collected by dams and reservoirs from water-rich areas to water-poor areas, but they also create environmental problems (Concept 11-2B).

One of the world’s largest water transfer projects is the California Water Project (Figure 11-13). It uses a maze of giant dams, pumps, and aqueducts to transport water from water-rich northern California to water-poor southern California’s heavily populated, arid agricultural regions and cities. This project supplies massive amounts of water to areas that, without such water transfers, would be mostly desert.

For decades, northern and southern Californians have feuded over how the state’s water should be allocated under this project. Southern Californians want more water from the north to grow more crops and to support Los Angeles, San Diego, and other growing urban areas. Agriculture consumes three-fourths of the water withdrawn in California, much of it used inefficiently for water-thirsty crops such as rice and alfalfa growing in desert-like conditions.

Northern Californians counter that sending more water south degrades the Sacramento River, threatens fisheries, and reduces the flushing action that helps clean San Francisco Bay of pollutants. They also argue that much of the water sent south is wasted. They point to studies showing that making irrigation just 10% more efficient would provide enough water for domestic and industrial uses in southern California. According to a 2002 study by a group of scientists and engineers, projected global warming will sharply reduce water availability in California (especially southern California) and other water-short states in the western United States even in the best-case scenario. Some analysts project that sometime during this century, many people living in arid southern California cities such as Los Angeles and San Diego, as well as farmers in this area, may have to move elsewhere for water.

Pumping more groundwater is not the answer because groundwater is already being withdrawn faster than it is replenished in much of central and southern California. It would be quicker and cheaper to improve irrigation efficiency, stop growing water-thirsty crops in arid areas, and increase the historically low price of water to reduce water waste.

CASE STUDY

 The Aral Sea Disaster

The shrinking of the Aral Sea is the result of a large-scale water transfer project in an area of the former Soviet Union with the driest climate in central Asia. Since 1960, enormous amounts of irrigation water have been diverted from the inland Aral Sea and its two feeder rivers to create one of the worlds largest irrigated areas, mostly for raising cotton and rice. The irrigation canal, the world’s longest, stretches more than 1,300 kilometers (800 miles).

This large-scale water diversion project, coupled with droughts and high evaporation rates due to the area’s hot and dry climate, has caused a regional ecological and economic disaster. Since 1961, the sea’s salinity has tripled and the average level of its water has dropped by 22 meters (72 feet). It has lost 90% of its volume of water and has split into two parts. Water withdrawal for agriculture has reduced the two rivers feeding the sea to mere trickles.

About 85% of the area’s wetlands have been eliminated and roughly half the local bird and mammal species have disappeared. In addition, a huge area of former lake bottom has been converted to a human-made desert covered with glistening white salt. The sea’s increased salt concentration-three times saltier than ocean water-caused the presumed extinction of 20 of the area’s 24 native fish species. This has devastated the area’s fishing industry, which once provided work for more than 60,000 people. Fishing villages and boats once located on the sea’s coastline now sit abandoned in the middle of a salt desert.

Winds pick up the sand and salty dust and blow it onto fields as far as 300 kilometers (190 miles) away. As the salt spreads, it pollutes water and kills wildlife, crops, and other vegetation. Aral Sea dust settling on glaciers in the Himalayas is causing them to melt at a faster than normal rate-a prime example of unexpected connections and unintended consequences. Shrinkage of the Aral Sea has also altered the area’s climate. The once-huge sea acted as a thermal buffer that moderated the heat of summer and the extreme cold of winter. Now there is less rain, summers are hotter and drier, winters are colder, and the growing season is shorter. The combination of such climate change and severe salinization has reduced crop yields by 20–50% on almost one-third of the area’s cropland.

To raise yields, farmers have used more herbicides, insecticides, and fertilizers, which have percolated downward and accumulated to dangerous levels in the groundwater-the source of most of the region’s drinking water.

Many of the 45 million people living in the Aral Sea’s watershed have experienced increasing health problems-including anemia, respiratory illnesses, kidney disease, and various cancers-from a combination of toxic dust, salt, and contaminated water.

Since 1999, the United Nations and the World Bank have spent about $600 million to purify drinking water and upgrade irrigation and drainage systems. This has improved irrigation efficiency and flushed some salts from croplands. A new dike should raise the average level of the small Aral by 3 meters (10 feet). Some artificial wetlands and lakes have been constructed to help restore aquatic vegetation, wildlife, and fisheries. The five countries surrounding the lake and its two feeder rivers have worked to improve irrigation efficiency and to partially replace water-thirsty crops with others requiring less irrigation water. As a result, the total annual volume of water in the Aral Sea basin has been stabilized. Nevertheless, experts expect the largest portion of the Aral Sea to continue shrinking.

 Removing Salt from Seawater Is Costly, Kills Marine Organisms, and Produces Briny Wastewater

Desalination involves removing dissolved salts from ocean water or from brackish (slightly salty) water in aquifers or lakes for domestic use. It is another way to increase supplies of freshwater (Concept 11-2C). One method for desalinating water is distillation-heating saltwater until it evaporates, leaving behind salts in solid form, and condenses as freshwater. Another method is reverse osmosis (or microfiltration), which uses high pressure to force saltwater through a membrane filter with pores small enough to remove the salt. In effect, high pressure is used to push freshwater out of saltwater.

Today about 15,000 desalination plants operate in more than 125 countries, especially in the arid nations of the Middle East, North Africa, the Caribbean, and the Mediterranean. They meet less than 0.3% of the world’s demand for freshwater.

There are three major problems with the widespread use of desalination. One is the high cost, because it takes a lot of energy to desalinate water. A second problem is that pumping large volumes of seawater through pipes and using chemicals to sterilize the water and control algae growth kills many marine organisms. A third problem is that desalination produces large quantities of briny wastewater that contain lots of salt and other minerals. Dumping concentrated brine into a nearby ocean increases the salinity of the ocean water, threatening food resources and aquatic life in the vicinity.

 Dumping it on land could contaminate groundwater and surface water. Some research is being carried out on the economic and ecological feasibility of building desalination plants offshore and pumping the freshwater to the shore. This could help dilute the resulting briny seawater.

 Bottom line: Currently, significant desalination is practical only for water-short, wealthy countries and cities that can afford its high cost (Concept 11-2C).

 RESEARCH FRONTIER

 Developing better and more affordable desalination technologies.

 

 

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(3) Water

UN Secretary-General message "International Year of Water Cooperation

Power-Water

Most of the freshwater we withdraw is used to irrigate crops

Worldwide, we use 70% of the water we withdraw each year from rivers, lakes, and aquifers to irrigate cropland. Industry uses another 20% of the water withdrawn each year, and cities and residences use the remaining 10%.

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(2) Water

Our liquid planet glows like a soft blue sapphire in the hard-edged darkness of space. There is not nothing else like it in the solar system. It is because of water.

John Tod

Water Conflicts in the Middle East: A Preview of the Future?

Many countries in the Middle East face water shortages and rising tensions over water sources they must share. Most water in this dry region comes from three river basins: the Nile, the Jordan, and the Tigris–Euphrates.

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(1) Water

DRINKING WATER & HEALTH - WHO

饮用水

AGUA POTABLE

WATER & HEALTH - WHO

AGUA

 

Water pollution can hurt our ability to use water in our homes, for recreation, and in commerce. It also harms other forms of life. We work to protect water in all its forms: on the ground, underground, and coming out of the tap.

Our main topics it will be:

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