Go back 12 Glossary
Our liquid planet glows like a soft blue sapphire in the hardedged darkness of space. There is nothing else like it in the solar system. It is because of water. JOHN TODD
12-1 WATER'S IMPORTANCE AND UNIQUE PROPERTIES
Why Is Water So Important?
We live on the water planet, with a precious film of water-most of it salt water-covering about 71% of the earth's surface (Figure 3-12, p. 53). All organisms are made up mostly of water; a tree is about 60% water by weight, and you and most animals are about 50-65% water.
Each of us needs only about a dozen cupfuls of water per day to survive, but huge amounts of water are needed to supply us with food, shelter, and our other needs and wants. Water also plays a key role in (1) sculpting the earth's surface, (2) moderating climate, and (3) diluting pollutants.
What Are Some Important Properties of Water?
Water is a remarkable substance with a unique combination of properties:
. There are strong forces of attraction (called hydrogen bonds) between molecules of water. These attractive forces are the major factor determining water's unique properties.
. Water exists as a liquid over a wide temperature range because of the strong forces of attraction between water molecules. Its high boiling point of 100°C (212°F) and low freezing point of O°C (32°F) mean that water remains a liquid in most climates on the earth.
. Liquid water changes temperature very slowly because it can store a large amount of heat )without a large change in temperature. This high heat capacity (1) helps protect living organisms from temperature fluctuations, (2) moderates the earth's climate,.and (3) makes water an excellent coolant for car engine power plants, and heat-producing industrial processes.
. It takes a lot of heat to evaporate liquid water because of the strong forces of attraction between its molecules. Water absorbs large amounts of heat as it changes into water vapor and releases this heat as the vapor condenses back to liquid water. This is a primary factor in distributing heat throughout the world and thus plays an important role in determining the climates of various areas (Figure 11-5, p. 239). This property also makes water evaporation an effective cooling process, which is why you feel cooler when perspiration or bathwater evaporates from your skin.
. Liquid water can dissolve a variety of compounds. This enables it to (1) carry dissolved nutrients into the tissues of living organisms, (2) flush waste products out of those tissues, (3) serve as an all-purpose cleanser, and (4) help remove and dilute the water-soluble' wastes of civilization. Water's superiority as a solvent also means that water-soluble wastes pollute it easily. . Water molecules can break down (ionize) into hydrogen ions (H+) and hydroxide ions (OH-;; which help maintain a balance between acids and bases in cells, as measured by the pH of water solutions (Figure 9-4, p. 189).
. Water filters out wavelengths of ultraviolet radiation (Figure 2-6, p. 20) that would harm some aquatic organisms.
. The strong attractive forces between the molecules of liquid water cause its surface to contract (high surface tension) and to adhere to and coat a solid (high wetting ability). These cohesive forces pull water molecules at the surface layer together so strongly that it can support small insects. The combination of high surface tension and. wetting ability allow water to rise through a plant from the roots to the leaves (capillary action).
. Unlike most liquids, water expands when it freezes. This means that ice has a lower density (mass per unit of volume) than liquid water. Thus ice floats on water. Without this property, lakes and streams in cold climates would freeze solid and lose most of their current forms of aquatic life. Because water expands upon freezing, it can also (1) break pipes, (2) crack engine blocks (which is why we use antifreeze), (3) break up streets, and (4) fracture rocks (thus forming soil).
Water is the lifeblood of the biosphere. It connects us to one another, to other forms of life, and to the entire planet. Despite its importance, water is one of our most poorly managed resources. We waste it and pollute it. We also charge too little for making it available. This encourages still greater waste and pollution of this renewable resource, for which we have no substitute.
12-2 SUPPLY, RENEWAL, AND USE OF WATER RESOURCES
How Much Fresh Water Is Available?
Only a tiny fraction of the planet's abundant water is available to us as fresh water (Figure 12-1). About 97.4% by volume is found in the oceans and is too salty for drinking, irrigation, or industry (except as a coolant).
Most of the remaining 2.6% that is fresh water is (1) locked up in ice caps or glaciers or (2) in groundwater too deep or salty to be used.
Thus only about 0.014% of the earth's total volume of water is easily available to us as soil moisture, usable groundwater, water vapor, and lakes and streams (Figure 12-1). If the world's water supply were only 100 liters (26 gallons), our usable supply of fresh water would be only about 0.014 liter (2.5 teaspoons).
Some good news is that the available fresh water amounts to a generous supply. Moreover, this water is continuously collected, purified, recycled, and distributed in the solar-powered hydrologic cycle (Figure 2-24, p. 35) as long as we do not (1) overload it with slowly degradable and nondegradable wastes or (2) withdraw it from underground supplies faster than it is replenished. The bad news is that in parts of the world we are doing both.
Differences in average annual precipitation divide the world's countries and people into water haves and have-nots. For example, Canada, with only 0.5% of the world's population, has 20% of the world's fresh water, whereas China, with 21% of the world's people, has only 7% of the supply.
As population, irrigation, and industrialization increase, water shortages in already water-short regions will intensify and heighten tensions between and within countries. Global warming can (1) increase global rates of evaporation, (2) Shift precipitation patterns, and (3) disrupt water suppli s in unpredictable ways. Some areas will get more"frecipitation and some less. Some river flows will chi,ge.
What Is Surface Water?
Precipitation that does not infiltrate the ground or return to the atmosphere by evaporation (including transpiration) is called surface runoff, which flows into streams, lakes, wetlands, and reservoirs.
About two-thirds of the world's annual runoff is lost by seasonal floods and is not available for human use. The remaining one-third is reliable runoff, which generally we count on as a stable source of water from year to year.
A watershed, also called a drainage basin, is a region from which water drains into a stream, lake, reservoir, wetland, or other body of water.
What Is Groundwater?
Some precipitation infiltrates the ground and percolates downward through voids (pores, fractures, crevices, and other spaces) in soil and rock (Figure 12-2). The water in these voids is called groundwater.
Close to the surface, the voids have little moisture in them. However, below some depth, in the zone of saturation, the voids are completely filled with water. The water table is located at the top of the zone of saturation. It falls in dry weather and rises in wet weather.
Porous, water-saturated layers of sand, gravel, or bedrock through which groundwater flows are called aquifers (Figure 12-2). Aquifers are like huge elongated sponges through which groundwater seeps. Aquifers are recharged naturally by precipitation that percolates downward through soil and rock in what is called natural recharge, but some are recharged from the side by lateral recharge.
Groundwater normally moves from (1) points of high elevation and pressure to (2) points of lower elevation and pressure. This movement is quite slow, typically only a meter or so (about 3 feet) per year and rarely more than 0.3 meter (1 foot) per day.
Some aquifers get very little (if any) recharge and on a human time scale are nonrenewable resources. They are often found fairly deep underground and were formed tens of thousands of years ago. Withdrawals from such aquifers amount to water mining that, if kept up, will deplete these ancient deposits of water.
Figure 12-1 The planet's water budget. Only a tiny fraction by volume of the world's water supply is fresh water available for human use.
Figure 12-2 The groundwater system. An unconfined aquifer is an aquifer with a water table. A confined aquifer is bounded above and below by less permeable beds of rock. Groundwater in this type of aquifer is confined under pressure.
How Much of the World's Reliable Water Supply Are We Withdrawing?
Since 1900, global water use has increased about ninefold and per capita use has quadrupled, with irrigation accounting for the largest increase in water use (Figure 12-3). As a result, humans now withdraw about 35% of the world's reliable runoff. We leave another 20% of this runoff in streams to (1) transport goods by boats, (2) dilute pollution, and (3) sustain fisheries and wildlife.
Thus we directly or indirectly use more than half of the world's reliable runoff. Because of increased population growth and economic development, global withdrawal rates of surface water are projected to (1) at least double in the next two decades and (2) exceed the reliable surface runoff in a growing number of areas.
How Do We Use the World's Fresh Water?
Uses of withdrawn water vary from one region to another and from one country to another (Figure 12-4, p. 272). Worldwide, about 70% of all water withdrawn each year from rivers, lakes, and aquifers is used to (1) irrigate 18% of the world's cropland and (2) produce about 40% of the world's food.
Figure 12-3 Global water use, 1900-2000. Between 2000 and 2054, the world's population is expected to increase by about 3.3 billion people. (Data from World Commission on Water Use in the 21st Century)
Industry uses about 20% of the water withdrawn each year, and cities and residences use the remaining 10%. Agriculture and manufacturing use large amounts of water (Figure 12-5. p. 272).
Figure 12-4 Water use in the United States and China. The United States has the world's
highest per capita use of water,
amounting to an average of 4,800 liters (1,280 gallons) per person per day in 1999. Between 1980 and 1999, total water use in the United States decreased by 10% despite a 17% increase in population, mostly because of more efficient irrigation. (Data
from Worldwatch Institute and World Resources Institute)
Case Study: Freshwater Resources in the United States The United States has plenty of fresh water. However, much of it is (1) in the wrong place at the wrong time or (2) contaminated by agricultural and industrial practices. The eastern states usually have ample precipitation, whereas many western states have too little (Figure 12-6, left).
In the East, the largest uses for water are for energy production, cooling, and manufacturing. The largest use by far in the West is for irrigation (which accounts for about 85% of all water use).
In many parts of the eastern United States, the most serious water problems are (1)
flooding, (2) occasional urban shortages, and (3) pollution. For example, the 3 million
residents of Long Island, New York, get most of their water from an increasingly
contaminated aquifer. The major water problem in the arid and semiarid areas of the
western half of the country is a shortage of runoff, caused by (1) low precipitation
(Figure 12-6, left), (2) high evaporation, and (3) recurring prolonged drought. Water
tables in many areas are dropping rapidly as farmers and cities deplete aquifers faster
than they are recharged. Many U.S. urban centers (especially in the West and Midwest) are
located in areas that do not have enough water (Figure 12-6, right).
12-3 WATER RESOURCE PROBLEMS: TOO LITTLE WATER AND TOO MUCH WATER
What Causes Freshwater Shortages?
According to water expert Malin Falkenmark, the four causes of water scarcity are (1) a
dry climate (Figure 11-3, p. 237),
Figure 12-6 Average annual precipitation and major rivers (left) and water-deficit regions in the continental United States and their proximity to metropolitan areas having populations greater than 1 million (right). (Data from U.S. Water Resources Council and U.S. Geological Survey)
Figure 12-7 Stress on the world's major river basins, based on a comparison of the amount of water available with the amount used by humans. (Data from World Commission on Water Use in the 21st Century) (2) drought (a period of 21 days or longer in which precipitation is at least 70% lower and evaporation is higher than normal), (3) desiccation (drying of the soil because of such activities as deforestation and overgrazing by livestock), and (4) water stress (low per capita availability of water caused by increasing numbers of people relying on limited levels of runoff).
Figure 12-7 shows the degree of stress on the world's major river systems, based on a comparison of the amount of water available with the amount used by humans. A country is said to be water stressed when the volume of its reliable runoff per person drops to below about 1,700 cubic meters (60,000 cubic feet) per year.
According to the United Nations, currently about 500 million people live in countries that are waterscarce or water-stressed. By 2025, this figure is projected to be between 2.4-3.4 billion people.
Even when a plentiful supply of water exists, most of the 1.2 billion poor people living on less than $1 a day cannot afford a safe supply of drinking water. Most must collect water from unsafe sources or buy water (often coming from polluted rivers) from private vendors at high prices.
Since the 1970s, water scarcity intensified by prolonged drought has killed more than 24,000 people per year and created millions of environmental refugees. In water-short rural areas in developing countries, many women and children must walk long distances each day, carrying heavy jars or cans, to get a meager and sometimes contaminated supply of water.
Case Study: Water Conflicts in the Middle East
A number of analysts believe access to water resources, already a key foreign policy and environmental security issue for water-short countries, will become even more important over the next 10-25 years. Some 40% of the world's population already clashes over water, especially in the Middle East.
Future military wars between countries in the Middle East could be fought over water, not oil. Most water in this dry region comes from three shared river basins: the Nile, Jordan, and Tigris-Euphrates (Figure 12-8, p. 274). Water in much of this arid region is already in short supply.
Ethiopia, which controls the headwaters that feed 85% of the Nile's flow, plans to divert more of this water; so does Sudan. This could reduce the amount of water available to water-short Egypt, whose terrain is desert except for a green area of irrigated cropland running down its middle along the Nile and its delta. Between 2002 and 2050, Egypt's population is expected to increase from 71 million to 115 million, greatly increasing the demand for already scarce water.
Egypt's options are to (1) go to war with Sudan and Ethiopia to obtain more water, (2) cut population growth, (3) improve irrigation efficiency, (4) spend $2 billion to build the world's longest concrete canal and pump water out of Lake Nasser (the reservoir created from the Nile by the Aswan High Dam) to create more irrigated farmland in the middle of the desert, (5) import more grain to reduce the need for irrigation water, (6) work out water-sharing agreements with other countries, or (7) suffer the harsh human and economic consequences of extreme hydrological poverty.
Figure 12-8 The Middle East, whose countries have some of the highest population growth rates in the world. Because of the dry climate, food production depends heavily on irrigation. Existing conflicts between countries in this region over access to water may soon overshadow both long-standing religious and ethnic clashes and attempts to take over valuable oil supplies.
The Jordan Basin is by far the most water-short region, with fierce competition for its water among Jordan, Syria, Palestine (Gaza and the West Bank), and Israel (Figure 12-8). The combined populations of these already water-short countries are projected to more than double from 33 million to 69 million between 2002 and 2025. Some good news is that in 1994, Israel and Jordan signed a peace treaty that addressed their disputes over water from the Jordan River basin.
Syria plans to build dams and withdraw more water from the Jordan River, decreasing the downstream water supply for Jordan and Israel. Israel warns that it will consider destroying the largest dam that Syria plans to build.
Turkey, located at the headwaters of the Tigris and Euphrates Rivers, controls how much water flows downstream to Syria and Iraq before emptying into the Persian Gulf (Figure 12-8). Turkey is building 24 dams along the upper Tigris and Euphrates rivers to (1) generate huge quantities of electricity and (2) irrigate a large area of land.
If completed, these dams will reduce the flow of water downstream to Syria and Iraq by up to 35% in normal years and much more in dry years. Syria also plans to build a large dam along the Euphrates River to divert water arriving from Turkey. This will leave little water for Iraq and possibly lead to a war between Syria and Iraq.
Clearly, water distribution will be a key issue in any peace talks in this region. Resolving these problems will require a combination of (1) regional cooperation in allocating water supplies, (2) slowed population growth, (3) improved efficiency in water use, (4) increased water prices to encourage water conservation and improve irrigation efficiency, and (5) increased grain imports to reduce water needs.
What Are the Causes and Effects of 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 rapid melting of snow. This causes water in a stream to overflow its normal channel and flood the adjacent area, called a floodplain (Figure 12-9, left). Floodplains, which include highly productive wetlands, help (1) provide natural flood and erosion control, (2) maintain high water quality, and (3) recharge groundwater.
People settle on floodplains because of their many advantages, including (1) fertile soil, (2) ample water for irrigation, (3) flat land suitable for crops, buildings, highways, and railroads, and (4) availability of nearby rivers for transportation and recreation. In the United States, 10 million households and businesses with property valued at $1 trillion exist in flood-prone areas.
Floods are a natural phenomenon and have several benefits. They (1) provide the world's most productive farmland because they are regularly covered with nutrient-rich silt left after floodwaters recede, (2) recharge groundwater, and (3) refill wetlands.
However, each year floods kill thousands of people and cause tens of billions of dollars in property damage. Floods, like droughts, usually are considered natural disasters, but since the 1960s human activities have contributed to the sharp rise in flood deaths and damages. Three ways humans increase the severity of flood damage are by (1) removing water-absorbing vegetation, especially on hillsides (Figure 12-10, p. 276), (2) draining wetlands that absorb floodwaters and reduce the severity of flooding, and (3) living on floodplains (Connections, p. 275). Urbanization also increases flooding by replacing water-absorbing vegetation, soil, and wetlands with highways, parking lots, and buildings that cannot absorb rainwater.
In developed countries, people deliberately settle on floodplains and then expect dams, levees, and other devices to protect them from floodwaters. In many developing countries, the poor have little choice but to try to survive in flood-prone areas (Connections, p. 275).
Figure 12-9 Land in a natural floodplain (left) often is flooded after prolonged rains. When the floodwaters recede, deposits of silt are left behind, creating a nutrient-rich soil. To reduce the threat of flooding (and thus allow people to live in floodplains), rivers have been (1) dammed to create reservoirs that store and release water as needed, (2) narrowed and straightened (channelization), and (3) equipped with protective levees and walls (middle). These alterations can give a false sense of security to floodplain dwellers living in high-risk areas. In the long run, such measures can greatly increase flood damage because they can be overwhelmed by prolonged rains (right), as happened in the midwestern United States during the summer of 1993.
Bangladesh is one of the world's (1) most densely populated countries, with 134 million people packed into an area roughly the size of Wisconsin, and (2) poorest countries, with an average per capita GNP PPP of about $1,590, or $4.36 per day.
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 by receiving an annual deposit of eroded Himalayan soil.
However, excessive flooding can be disastrous. In the past, great floods occurred every 50 years or so, but since the 1970s they have come about every 4 years.
Bangladesh's increased flood problems begin in the Himalayan watershed. A combination of rapid population growth, deforestation, overgrazing, and unsustainable farming on steep, easily erodible mountain slopes has greatly diminished the soil's ability to absorb
water. Instead of being absorbed and released slowly, water from the monsoon rains runs off the denuded Himalayan foothills, carrying vital topsoil with it (Figure 12-10, p. 276).
This runoff, combined with heavier-than-normal monsoon rains, has increased the severity of flooding along Himalayan rivers and downstream in Bangladesh. For example, a disastrous flood in 1998 (1) covered two-thirds of Bangladesh's land area for 9 months, (2) leveled 2 million homes, (3) drowned at least 2,000 people, (4) left 30 million people homeless, (5) destroyed more than one-fourth of the country's crops, which caused thousands of people to die of starvation, and (6) caused at least $3.4 billion in damages.
Living on Bangladesh's coastal floodplain also carries dangers from storm surges and cyclones. Since 1961,17 devastating cyclones have slammed into Bangladesh. In 1970, as many as 1 million people drowned in one storm, and another surge killed an estimated 139,000 people in 1991.
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. This has led to more severe flooding because these coastal wetlands shelter Bangladesh's lowlying coastal areas from storm surges and cyclones. 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.
1. Bangladesh's population is growing rapidly and expected to increase from 134 million to 178 million between 2002 and 2025. How could slowing its rate of population growth help reduce poverty and the harmful impacts of excessive flooding?
2. How could reforestation in the upstream countries of Bhutan, China, India, and Nepal reduce flooding in those countries and in Bangladesh?
Figure 12-10 A hillside before and after deforestation. Once a hillside has been deforested for timber and fuelwood, livestock grazing, or unsustainable farming, water from precipitation (1) rushes down the denuded slopes, (2) erodes precious topsoil, and (3) floods downstream areas. A 3,000-year-old Chinese proverb says, "To protect your rivers, protect your mountains."
Solutions: How Can We Reduce Flood Risks?
We can reduce the risk from flooding by
. Straightening and deepening streams (channelization; Figure 12-9, middle). Channelization can reduce upstream flooding but the increased flow of water can (1) increase upstream bank erosion and downstream flooding and sediment deposition and (2) reduce habitats for aquatic wildlife by removing bank vegetation and increasing stream velocity.
. Building levees (Figure 12-9, middle). Levees contain and speed up stream flow but (1) increase the water's capacity for doing damage downstream and (2) do not protect against unusually high and powerful floodwaters, as occurred in 1993 when two-thirds of the levees built along the Mississippi River in the United States were damaged or destroyed.
. Building dams. A flood control dam built across a stream can reduce flooding by storing water in a reservoir and releasing it gradually. Dams have a number of advantages and disadvantages (Figure 6-17, p. 110).
. Restoring wetlands to take advantage of the natural flood control provided by floodplains.
. Identifying and managing floodplains to get people out of flood-prone areas. This prevention or precautionary approach is based on thousands of years of experience that can be summed up in one idea: Sooner or later the river (or the ocean) always wins.
12-4 SOLUTIONS: SUPPLYING MORE WATER
How Can We Increase Freshwater Supplies?
Six ways to increase the supply of fresh water in a particular area are to (1) build dams and reservoirs to store runoff, (2) bring in surface water from another area, (3) withdraw groundwater, (4) convert salt water to fresh water (desalination), (5) improve the efficiency of water use, and (6) import food to reduce irrigation.
In developed countries, people tend to live where the climate is favorable and then bring in water from another watershed. In developing countries, most people (especially the rural poor) must settle where the water is and try to capture and use the precipitation they need.
What Are the Advantages and Disadvantages of Large Dams and Reservoirs? Large dams and reservoirs have benefits and drawbacks (Figure 6-17, p. 110). Their main purpose is to capture and store runoff and release it as needed for (1) controlling floods, (2) producing hydroelectric power, and (3) supplying water for irrigation and for towns and cities. Reservoirs also provide recreational activities such as swimming, fishing, and boating.
Some good news is that the world's dams have increased the annual runoff available for human use by nearly one-third. Some bad news is that a series of dams on a river, 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, half of the world's major rivers (1) run dry part of the year or (2) have little water in them when they get to the sea. In addition to threatening the water supplies for 500 million people, this engineering approach to river management often impairs the important ecological services that rivers provide (Figure 12-11).
Case Study: China's Three Gorges Dam When completed, China's Three Gorges project on the mountainous upper reaches of the Yangtze River will be the world's largest hydroelectric dam and reservoir. According to Chinese officials, this superdam, with the electric output of 20 large coal-burning or nuclear power plants, will
. Generate almost 10% of China's electricity for use by industries and about 150 million people.
. Help China reduce its dependence on coal, which causes severe air pollution and releases enormous amqunts of the greenhouse gas carbon dioxide into the atmosphere.
. Hold back the Yangtze River's floodwaters, which have killed more than 500,000 people during the past 100 years. According to Chinese officials, the 400 million people living in the Yangtze River Valley will benefit from the dam. This greatly exceeds the 1.9 million people who will be relocated from the area to be flooded to form a gigantic 600-kilometer-Iong (370mile-long) reservoir behind the dam.
. Reduce flooding and silting of the river by eroded soil.
Figure 12-11 Some ecological services provided by rivers. Currently, the services are given little or no monetary value when the costs and benefits of dam and reservoir projects are assessed. According to environmental economists, attaching even crudely estimated monetary values to these ecosystem services would help sustain them.
Critics point to a number of drawbacks of the Yangtze dam and reservoir project:
. Forming the huge reservoir will (1) flood large areas of productive farmland and (2) displace about 1.9 million people from their homes.
. The region's entire ecosystem will be radically changed.
. Water pollution will increase because of the river's reduced water flow.
. If the reservoir fills up with sediment and overflows (especially if the reservoir is kept filled at a high level, as planned, to provide maximum hydroelectric power), half a million people will be exposed to severe flooding.
. Annual deposits of nutrient-rich sediments below the dam will be reduced.
. The reduced downstream water flow will promote saltwater intrusion into drinking water supplies near the mouth of the river.
What Are the Advantages and Disadvantages of Water Transfers?
The California Experience Tunnels, aqueducts, and underground pipes can transfer stream runoff collected by dams and reservoirs from water-rich areas to water-poor areas. Although such transfers have benefits, they also create environmental problems (Case Study, p. 279). Indeed, most of the world's dam projects and large-scale water transfers illustrate the important ecological principle that you cannot do just one thing.
One of the world's largest watershed transfer projects is the California Water Project. The California Water Project uses a maze of giant dams, pumps, andaqueducts to transport water from water-rich northern California to heavily populated areas and to arid and semiarid agricultural regions, mostly in southern California (Figure 12-12, p. 278).
For decades, northern and southern Californians have been feuding over how the state's water should be allocated under this project. Southern Californians say they need more water from the north to support Los Angeles, San Diego, and other growing urban areas and to grow more crops. Agriculture uses 74% of the water withdrawn in California, much of it for waterthirsty crops.
Opponents in the north say that sending more water south would (1) degrade the Sacramento River, (2) threaten fisheries, and (3) reduce the flushing action that helps clean San Francisco Bay of pollutants. They also argue that (1) much of the water sent south is wasted unnecessarily, and (2) making irrigation just 10% more efficient would provide enough water for domestic and industrial uses in southern California. However, if water supplies in northern California and in the Colorado River basin drop sharply because of global warming, the amount of water delivered by the huge distribution system will plummet.
Pumping out more groundwater is not the answer because groundwater is already being withdrawn faster than it is replenished throughout much of California. To most analysts, quicker and cheaper solutions are (1) improving irrigation efficiency and (2) allowing farmers to sell their legal rights to withdraw certain amounts of water from rivers.
Figure 12-12 The California Water Project and the Central Arizona Project involve large-scale water transfers from one watershed to another. Arrows show the general direction of water flow.
What Are the Advantages and Disadvantages of Withdrawing Groundwater?
Pumping groundwater from aquifers has several advantages over tapping more erratic flows from streams. Groundwater (1) can be removed as needed year round, (2) is not lost by evaporation, and (3) usually is less expensive to develop than surface water systems.
Aquifers provide drinking water for almost onethird of the planet's people. In Asia alone, more than 1 billion people depend on groundwater for drinking. In the United States, water pumped from aquifers supplies about (1) 51 % of the drinking water (96% in rural areas and 20% in urban areas) and (2) 43% of irrigation water.
However, withdrawing groundwater from aquifers faster than it is replenished can cause or intensify several problems: (1) water table lowering, (2) aquifer depletion (Figure 12-13, top), (3) aquifer subsidence (sinking of land when groundwater is withdrawn; Figure 12-13, bottom), (4) intrusion of salt water into aquifers, (5) drawing of chemical contamination in groundwater toward wells, and (6) reduced stream flow because of diminished flows of groundwater into streams. Also, industrial and agricultural activities, septic tanks, and other sources can contaminate groundwater.
In the United States, groundwater is being withdrawn at four times its replacement rate. The most serious overdrafts are occurring (1) in parts of the huge Ogallala Aquifer, extending from southern South Dakota to central Texas (Case Study, p. 280), and (2) in parts of the arid southwestern United States (Figure 12-13, top), especially California's Central Valley, which supplies about half the country's vegetables and fruits.
Aquifer depletion also is a problem in (1) Saudi Arabia, (2) central and northern China, (3) northwest and southern India (where one-fourth of the country's grain is produced by unsustainable groundwater withdrawal), (4) northern Africa (especially Libya and Tunisia), (5) southern Europe, (6) the Middle East, and (7) parts of Mexico, Thailand, and Pakistan.
When fresh water from an aquifer near a coast is withdrawn faster than it is recharged, salt water intrudes into the aquifer (Figure 12-14, p. 281). Such intrusion can contaminate the drinking water of many towns and cities along coastal areas.
Figure 12-13 Areas of greatest aquifer depletion and groundwater contamination (top) and ground subsidence (bottom) in the continental United States. Aquifer depletion is also high in Hawaii and Puerto Rico (not shown on map). (Data from U.S. Water Resources Council and U.S. Geological Survey)
Once the world's fourth largest freshwater lake, the Aral Sea has been shrinking and getting saltier since 1960 because most of the water from the rivers that replenisl). it has been diverted to grow cotton and food crops. As the lake shrinks, it leaves behind a salty desert, economic ruin, increasing health problems, and severe ecological disruption.
The shrinking of the Aral Sea (see figure) is a 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 irrigate cotton, vegetable, fruit, and rice crops and create one of the world's largest irrigated areas. The irrigation canal, the world's longest, stretches over 1,300 kilometers (800 miles).
This water diversion project (coupled with droughts) as caused a regional ecological, economic, and health disaster. Problems caused by this massive water-diversion project include the following:
. Tripling of the sea's salinity.
. Decreasing the sea's surface area by 54% (see figure) and its volume by 75%.
. Reducing the sea's two supply rivers to mere trickles.
. Converting about 36,000 square kilometers (14,000 square miles) of former lake bottom to a human-made desert covered with glistening white salt.
. Causing the presumed extinction of 20 of the area's 24 native fish species as the salt concentrations in the sea's water have increased. This has devastated the area's fishing industry, which once provided work for more than 60,000 people. Fishing villages and boats once on the sea's coastline now are in the middle of a salt desert and have been abandoned.
. Eliminating 85% of the area's wetlands, which along with increased pollution has greatly reduced waterfowl populations.
. Disappearance of roughly half the area's bird and mammal species.
. Causing one of the world's worst salinization problems. Winds pick up the salty dust that encrusts the lake's now-exposed bed and blow it onto fields as far as 300 kilometers (190 miles) away. As the salt spreads, it kills wildlife, crops, and other vegetation and pollutes water.
. Increasing groundwater and surface water pollution. To raise yields, farmers have increased inputs of herbicides, insecticides, fertilizers, and irrigation water on some crops. Many of these chemicals have percolated downward and accumulated to dangerous levels in the groundwater, from which most of the region's drinking water comes.
. Alteration of 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. ow(l)thereisless rain, (2) summers are hotter and drier, (3) winters are colder, and (4) the growing season is shorter.
. Reduction of crop yields by 20-50% from a combination of climate change and severe salinization of almost a third of the area's cropland.
. Greatly increased health problems from a combination of toxic dust, salt, and contaminated water for a growing number of the 58 million people living in the Aral Sea's watershed.
Can the Aral Sea be saved, and can the area's serious ecological and human health problems be reduced? Since 1999, the United Nations and the World Bank have spent $600 million to (1) purify drinking water, (2) upgrade irrigation and drainage systems to improve irrigation efficiency, flush salts from croplands, and boost crop productivity, and (3) construct wetlands and artificial lakes to help restore aquatic vegetation, wildlife, and fisheries. However, this process will take decades and will not prevent the shrinkage of the Aral Sea into a few brine lakes.
What ecological and economic lessons can we learn from the Aral Sea tragedy?
The Ogallala, the world's largest known aquifer. If the water in this aquifer were above ground, it could cover all 50 states with 0.5 meter (1.5 feet) of water. Water withdrawn from this aquifer is used to grow crops, raise cattle, and provide cities and industries with water. As a result, this aquifer, renewed very slowly, is being depleted (especially at its thin southern end in parts of Texas, New Mexico, Oklahoma, and Kansas). (Data from U.S. Geological Survey)
Large amounts of water have been pumped from the Ogallala, the world's largest known aquifer (see figure). This has helped transform vast areas of arid high plains prairie land into one of the largest and most productive agricultural regions in the United States.
Mostly because of irrigated farming, this region produces 20% of U.S. agricultural output (including 40% of its feedlot beef), valued at $32 billion per year. This has brought prosperity to many farmers and mer chants in this region, but the hidden environmental 'and economic cost has been increasing aquifer depletion in some areas.
Although this aquifer is gigantic, it is essentially nonrenewable (stored during the retreat of the last ice age about 15,000-30,000 years ago) with an extremely slow recharge rate. In some areas, water is being pumped out of the aquifer 8-10 times faster than the aquifer's natural recharge rate.
The northernmost states (Wyoming, North Dakota, South Dakota, and parts of Colorado) still have ample supplies. However, supplies in parts of the southern states, where the aquifer is thinner (see figure), are being depleted rapidly, with about two thirds of the aquifer's depletion taking place in the Texas High Plains.
Water experts project that at the current rate of withdrawal, one-fourth of the aquifer's original supply will be depleted by 2020 and much sooner in areas where it is shallow. It will take thousands of years to replenish the aquifer.
Government subsidies designed to increase crop production also increase depletion of the Ogallala by (1), encouraging farmers to grow water-thirsty cotton in the lower basin, (2) providing crop-disaster payments, and (3) providing tax breaks in the form of groundwater depletion allowances, with larger breaks for heavier groundwater use.
Depletion of this essentially nonrenewable water resource can be delayed if farmers (1) use more efficient forms of irrigation (Figure 12-15, p. 282), (2) switch to crops that need less water, or (3) irrigate less land.
Cities using this groundwater can also implement policies and technologies to reduce their water use and waste. People enjoying the benefits of this aquifer can help by (1) installing water-saving toilets and showerheads and (2) converting their lawns to plants that can survive in an arid climate with little watering.
1. What are the pros and cons of giving government subsidies to farmers and ranchers using water withdrawn from the Ogallala to grow crops and raise livestock that need large amounts of water? How do you benefit from such subsidies?
2. Should these government subsidies be reduced or eliminated and replaced with subsidies that encourage farmers to use more efficient forms of irrigation and switch to crops that need less water? Explain.
Figure 12-14 Saltwater intrusion along a coastal region. When the water table is lowered, the normal interface (dotted line) between fresh and saline groundwater moves inland (solid line), making coastal drinking water supplies unusable.
Ways to prevent or slow groundwater depletion include (1) controlling population growth, (2) not planting water-intensive crops such as cotton and sugarcane in dry areas, (3) shifting to crops that need less water in dry areas, (4) developing crop strains that need less water and are more resistant to heat stress, (5) wasting less irrigation water, and (6) importing grain, with each imported metric ton of grain saving roughly 1,000 metric tons of water needed to produce the grain.
How Useful Is Desalination?
Removing dissolved salts from ocean water or from brackish (slightly salty) groundwater, called desalination, is another way to increase supplies of fresh water. The two most widely used methods are (1) distillation, which involves heating salt water until it evaporates (and leaves behind salts in solid form) and condenses as fresh water, and (2) reverse osmosis, in which salt water is pumped at high pressure through a thin membrane whose pores allow water molecules, but not dissolved salts, to pass through.
About 13,300 desalination plants in 120 countries (especially in the arid Middle East and parts of North Africa, the Carribean, and the Mediterranean) meet less than 0.2% of the world's water needs. Desalination would have to increase 25-fold just to supply 5% of current world water use.
This is unlikely because desalination has two major disadvantages:
. It is expensive because it takes large amounts of energy. Desalinating water costs 2-3 times as much as the conventional purification of fresh water.
. It produces large quantities of waste water (brine) containing high levels of salt and other minerals. Dumping the concentrated brine into the ocean near the plants increases the local salt concentration and threatens food resources in estuary waters. Dumping it on land could contaminate groundwater and surface water.
Scientists are working to develop new membranes for reverse osmosis that can separate water from salt more efficiently and under less pressure. If successful, this strategy could help bring down the cost of using desalinization to produce drinking water. However, desalinated water probably will not be cheap enough to irrigate conventional crops or meet much of the world's demand for fresh water unless (1) affordable solar-powered distillation plants can be developed and (2) someone can figure out what to do with the resulting mountains of salt.
12-5 SOLUTIONS: WASTING LESS WATER
What Are the Benefits of Reducing Water Waste?
Mohamed EI-Ashry of the World Resources Institute estimates that 65-70% of the water people use throughout the world is lost through evaporation, leaks, and other losses. The United States, the world's largest user of water, does slightly better but still loses about 50% of the water it withdraws. EI-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.
Accomplishing this will require greatly increased use of water-saving technologies and practices. It will (1) decrease the burden on wastewater plants, (2) reduce the need for expensive dams and water transfer projects that destroy wildlife habitats and displace people, (3) slow depletion of groundwater aquifers, and (4) save energy and money.
Why Do We Waste So Much Water?
According to water resource experts, the major causes of water waste are (1) government subsidies of water supply projects such as large dams and large-scale water transfer schemes that create artificially low water prices and (2) lack of subsidies for improving water efficiency. 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 water subsidies argue that they (1) promote settlement and agricultural production in arid and semiarid areas, (2) stimulate local economies, and (3) help lower prices of food and manufactured goods for consumers.
Solutions: How Can We Waste Less Water in Irrigation?
Much of the irrigation water applied throughout the world does not reach the targeted crops. Most irrigation systems distribute water from a groundwater well or a surface water source and allow it to flow by gravity through unlined ditches in crop fields so the water can be absorbed by crops (Figure 12-15, left). This flood irrigation method (1) delivers far more water than needed for crop growth and (2) typically allows only 60% of the water to reach crops because of evaporation, seepage, and runoff.
Some good news is that more efficient and environmentally sound irrigation technologies exist that could reduce water demands and waste on farms by up to 50%. Here are some examples:
. Center-pivot low-pressure sprinklers (Figure 12-15, right), which typically allow 80% of the water input to reach crops and reduce water use over conventional gravity flow systems by 20-25%.
. Low-energy precision application (LEPA) sprinklers. This form of center-pivot irrigation allows 90-95% of the water input to reach crops by spraying it closer to the ground and in larger droplets than the centerpivot,low-pressure system. LEPA sprinklers use 20-30% less energy than low-pressure sprinklers and typically use 37% less water than conventional gravity flow systems.
. Using surge or time-controlled valves on conventional gravity flow irrigation systems (Figure 12-15, left). These valves send water down irrigation ditches in pulses instead of in a continuous stream, which can raise irrigation efficiency to 80% and reduce water use by 25%. . Using soil moisture detectors to water crops only when they need it. For example, some farmers in Texas bury a $1 cube of gypsum, the size of a lump of sugar, at the root zone of crops. Wires embedded in the gypsum are run back to a small portable meter that indicates soil moisture. Farmers using this technique can use 33-66% less irrigation water.
. Drip irrigation systems (Figure 12-15, center, and Solutions, p. 283), which can raise water efficiency to 90-95% and reduce water use by 37-70%.
Other ways to reduce water waste in irrigating crops are listed in Figure 12-16. Since 1950, water-short Israel has used many of these techniques to slash irrigation water waste by about 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 (1) gradually removed most government water subsidies to raise the price of irrigation water to one of the highest in the world, (2) imports most of its waterintensive wheat and meat, and (3) concentrates on growing fruits, vegetables, and flowers that need less water.
Many of the world's poor farmers cannot afford to use most of the modern technological methods for increasing irrigation and irrigation efficiency. These farmers increase irrigation by using small-scale and low-cost traditional technologies such as (1) pedal powered treadle pumps to move water through irrigation ditches (widely used in Bangladesh), (2) animalpowered irrigation pumps, (3) buckets with holes for drip irrigation, (4) small dams, ponds, and tanks to col
Figure 12-16 Methods for reducing water waste in irrigation.
The development of inexpensive, weather-resistant, and flexible plastic tubing after World War II paved the way for a new form of microirrigation called drip irrigation (Figure 12-15, middle). It consists of a network of perforated plastic tubing, installed at or below the ground surface. The small holes or emitters in the tubing deliver drops of water at a slow and steady rate close to plant roots.
This technique, developed in Israel in the 1960s and now used by half of the country's farmers, has a number of advantages, including the following:
. Adaptability. The tubing system can easily be fitted to match the patterns of crops in a field and left in place or moved to different locations.
. Efficiency, with 90-95% of the water input reaching crops.
. Lower operating costs because 37-70% less energy is needed to pump this water at low pressure, and less labor is needed to move sprinkler systems.
. Ability to apply fertilizer solutions in precise amounts, which reduces (1) fertilizer use and waste, (2) salinization, and (3) water pollution from fertilizer runoff.
. An increase in crop yields of20-90% by getting more crop growth per drop of water.
. Healthier plants and higher yields because plants are neither underwatered nor overwatered.
Despite these advantages, drip irrigation is used on less than 1 % of the world's irrigated area. The capi tal cost of conventional drip irrigation systems is too high for most poor farmers and for use on lowvalue row crops. However, drip irrigation is economically feasible for high-profit fruit, vegetable, and orchard crops and for home gardens.
Some good news is that the capital cost of a new drip irrigation system is one-tenth as much per hectare as conventional drip systems. Another innovation is DRiWATER@, called "drip irrigation in a box." It consists of I-liter (1.1-quart) packages of gelencased water that is released slowly into the soil after being buried near plant roots. It wastes almost no water and lasts about 3 months. Egypt is using it to help grow 17 million trees in a desert community.
These and other low-cost drip irrigation systems could bring about a revolution in more sustainable irrigated agriculture that would (1) increase food yields, (2) reduce water use and waste, and (3) lessen some of the environmental problems associated with agriculture (Figure 9-17, p. 203).
Should governments provide subsidies to farmers who use drip irrigation based on how much water they save? Explain.
Figure 12-17 Methods for reducing water waste in industries, homes, and businesses. person as Las Vegas, a desert city with much less rainfall and less emphasis on water conservation (Spotlight, right).
See the website for this chapter for ways you can reduce your personal water use and waste.
12-6 TYPES, EFFECTS, AND SOURCES OF WATER POLLUTANTS
What Are the Major Types and Effects of Water Pollutants?
Water pollution is any chemical, biological, or physical change in water quality that (1) has a harmful effect on living organisms or (2) makes water unsuitable for desired uses. Table 12-1 lists the major classes of water pollutants along with their major human sources and harmful effects.
How Do We Measure Water Quality?
Scientists measure water quality using a variety of methods:
. Measuring the number of colonies of coliform bacte
ria present in a lOa-milliliter (O.l-quart) sample of water. The WHO recommends a coliform bacteria count of a colonies per 100 milliliters for drinking water, and the U.S. Environmental Protection Agency (EPA) recommends a maximum level for swimming water of 200 colonies per 100 milliliters.
. Measuring the level of dissolved oxygen to determine water pollution from oxygen-demanding wastes and plant nutrients.
. Measuring the biological oxygen demand (BOD) to determine the quantity of oxygen-demanding wastes in water.
. Using chemical analysis to determine the presence and concentrations of most inorganic and organic chemicals that pollute water.
. Using living organisms as indicator species to monitor water pollution. For example, scientists can remove aquatic plants such as cattails and analyze them to determine pollution in areas contaminated with fuels, solvents, and other organic chemicals.
What Are Point and Nonpoint Sources of Water Pollution?
Point sources discharge pollutants at specific locations through pipes, ditches, or sewers into bodies of surface water (Figure 12-18, p. 286). Examples include (1) factories, (2) sewage treatment plants (which remove some but not all pollutants), for repair, fish and other organisms adapted to a particular temperature range can be killed by the abrupt change in water temperature-known as thermal shock.
(3) active and abandoned underground mines, and (4) oil tankers. Because point sources are at specific places, they are fairly easy to identify, monitor, and regulate. Most developed countries control point source discharges of many harmful chemicals into aquatic systems, whereas there is little control of such discharges in most developing countries.
Nonpoint sources cannot be traced to any single site of discharge (Figure 12-18, p. 286). They are usually large land areas or airsheds that pollute water by runoff, subsurface flow, or deposition from the atmosphere. Examples include (1) acid deposition (Figure 11-26, p. 258) and (2) runoff of chemicals into surface water from croplands, livestock feedlots, logged forests, urban streets, lawns, golf courses, and parking lots. There has been little progress in controlling nonpoint water pollution because of the difficulty and expense of identifying and controlling discharges from so many diffuse sources.
Las Vegas, Nevada, located in the Mojave Desert, is an artificial aquatic wonderland of large trees, green lawns and golf courses, waterfalls, and swimming pools. The city is also one of the fastest growing cities in the United States, with its population more than doubling from 550,000 in 1985 to 1.4 million in 2001. The city is estimated to use more water per person than any city in the world.
Tucson, Arizona, in the Sonora Desert, is a model of water conservation. It began a strict water conservation program in 1976, including raising water rates 500% for some residents.
In contrast, Las Vegas, which gets one-third less rainfall than Tucson, only recently started to encourage water conservation by (1) raising water rates sharply (but they are still less than half those in Tucson) and (2) encouraging replacement of lawns with rocks and native plants that survive on little water.
Water experts project that even if these recent water conservation efforts are successful, the city should begin running short of water by 2007.
1. If you were an elected official in charge of Las Vegas, what three actions would you take to improve water conservation? What might be the political implications of instituting such a program?
2. If water shortages by 2007 limit the growth of the area's population, would you consider this outcome good or bad? Explain.
Table 19-1 Major Categories of Water Pollutants
INFECTIOUS AGENTS Examples: Bacteria, viruses, protozoa, and parasitic worms
Major Human Sources: Human and animal wastes Harmful Effects: Disease
Examples: Organic waste such as animal manure and plant debris that can be decomposed by aerobic (oxygen-requiring) bacteria
Major Human Sources: Sewage, animal feedlots, paper mills, and food processing facilities
Harmful Effects: Large populations of bacteria decomposing these wastes can degrade water quality by depleting water of dissolved oxygen. This causes fish and other forms of oxygen-consuming aquatic life to die.
INORGANIC CHEMICALS Examples: Water-soluble (1) acids, (2) compounds of toxic metals such as lead (Pb), arsenic (As), and selenium (Se), and (3) salts such as NaCI in ocean water and fluorides (F-) found in some soils
Major Human Sources: Surface runoff, industrial effluents, and household cleansers
Harmful Effects: Can (1) make freshwater unusable for drinking or irrigation, (2) cause skin cancers and crippling spinal and neck damage (F-), (3) damage the nervous system, liver, and kidneys (Pb and As), (4) harm fish and other aquatic life, (5) lower crop yields, and (6) accelerate corrosion of metals exposed to such water.
ORGANIC CHEMICALS Examples: Oil, gasoline, plastics, pesticides, cleaning solvents, detergents
Major Human Sources: Industrial effluents, household cleansers, surface runoff from farms and yards
Harmful Effects: Can (1) threaten human health by causing nervous system damage (some pesticides), reproductive disorders (some solvents), and some cancers (gasoline, oil, and some solvents) and (2) harm fish and wildlife
PLANT NUTRIENTS Examples: Water-soluble compounds containing nitrate (NO3-), phosphate (POi-), and ammonium (NH4+) ions Major Human Sources: Sewage, manure, and runoff of agricultural and urban fertilizers
Harmful Effects: Can cause excessive growth of algae and other aquatic plants, which die, decay, deplete water of dissolved oxygen, and kill fish. Drinking water with excessive levels of nitrates lowers the oxygen-carrying capacity of the blood and can kill unborn children and infants ("bluebaby syndrome").
Examples: Soil, silt
Major Human Sources: Land erosion
Harmful Effects: Can (1) cloud water and reduce photosynthesis, (2) disrupt aquatic food webs, (3) carry pesticides, bacteria, and other harmful substances, (4) settle out and destroy feeding and spawning grounds of fish, and (5) clog and fill lakes, artificial reservoirs, stream channels, and harbors.
RADIOACTIVE MATERIALS Examples: Radioactive isotopes of iodine, radon, uranium, cesium, and thorium
Major Human Sources: Nuclear power plants, mining and processing of uranium and other ores, nuclear weapons production, natural sources
Harmful Effects: Genetic mutations, miscarriages, birth defects, and certain cancers
HEAT (THERMAL POLLUTION)
Examples: Excessive heat Major Human Sources: Water cooling of electric power plants (Figure 6-33, p. 122) and some types of industrial plants. Almost half of all water withdrawn in the United States each year is for cooling electric power plants.
Harmful Effects: Lowers dissolved oxygen levels and makes aquatic organisms more vulnerable to disease, parasites, and toxic chemicals. When a power plant first opens or shuts down
Is the Water Safe to Drink? About one-fifth of the people in developing countries do not have access to clean drinking water. Only 6 of China's 27 largest cities provide drinking water that meets government standards. In Russia, half of all tap water is unfit to drink. In Africa, some 290 million people-about equal to the entire U.S. population-do not have access to safe drinking water.
The United Nations estimates it would cost about $23 billion a year over 8-10 years to bring low-cost safe water and sanitation to the 1.1 billion people who do not have access to clean drinking water. These expenditures could prevent many of the (1) 3.4 million deaths (including 2 million children under age 5) and (2) 3.4 billion cases of illness caused each year by unsafe water. Currently, the world is spending about $16 billion a year on clean water efforts. The $7 billion shortfall is about equal to what the world spends every 4 days for military purposes.
12-7 POLLUTION OF FRESHWATER STREAMS, LAKES, AND AQUIFERS
What Are the Water Pollution Problems of Streams?
Flowing streams, including large ones called rivers, can recover rapidly from degradable, oxygen-demanding wastes and excess heat through a combination of dilution and bacterial decay. This natural recovery process works as long as (1) pollutants do not overload the streams, and (2) drought, damming, or diversion for agriculture and industry do not reduce their flow. However, these natural dilution and biodegradation processes do not eliminate slowly degradable and nondegradable pollutants.
In a flowing stream, the breakdown of degradable wastes by bacteria depletes dissolved oxygen, which reduces or eliminates populations of organisms with high oxygen requirements until the stream is cleansed of wastes. The depth and width of the resulting oxygen sag curve (Figure 12-19) determine the time and distance needed for a stream to recover. This recovery time depends on the volume of incoming degradable wastes and the stream's (1) volume, (2) flow rate, (3) temperature, and (4) pH level (Figure 9-4, p. 189). Similar oxygen sag curves can be plotted when heated water from industrial and power plants is discharged into streams.
What Is the Good News About Stream Pollution?
Here is some good news about stream pollution cleanup in parts of the world. Water pollution control laws enacted in the 1970s have (1) greatly increased the number and quality of wastewater treatment plants in the United States and many other developed countries and (2) required industries to reduce or eliminate point-source discharges into surface waters. These efforts have enabled the United States to hold the line against increased pollution of most of its streams by disease-causing agents and oxygen-demanding wastes. This is an impressive accomplishment given the rise in economic activity and population since passage of these laws.
The cleanup of Ohio's Cuyahoga River is one success story. This river was so polluted that in 1959 and again in 1969 it caught fire and burned for several days as it flowed through Cleveland. The highly publicized image of this burning river prompted city, state, and federal officials to (1) enact laws limiting the discharge of industrial wastes into the river and sewage systems and (2) appropriate funds to upgrade sewage treatment facilities. Today the river has made a comeback and is widely used by boaters and anglers.
What Is the Bad News About Stream Pollution?
Despite progress in improving stream quality in most developed countries, large fish kills and drinking water contamination still occur. Most of these disasters are caused by (1) accidental or deliberate releases of toxic inorganic and organic chemicals by industries or mines, (2) malfunctioning sewage treatment plants, and (3) nonpoint runoff of pesticides and nutrients (eroded soil, fertilizer, and animal waste) from cropland or animal feedlots (Individuals Matter, p. 289).
Figure 12.19 Dilution and decay of degradable, oxygen-demanding wastes and heat, showing the oxygen sag curve and the oxygen demand curve. Depending on flow rates and the amount of pollutants, streams recover from oxygen-demanding wastes and heat if they are given enough time and are not overloaded.
Available data indicate that stream pollution from discharges of sewage and industrial wastes is a serious and growing problem in most developing countries, where waste treatment is practically nonexistent. Numerous streams in the former Soviet Union and in eastern European countries are severely polluted. Industrial wastes and sewage pollute more than twothirds of India's water resources. Untreated sewage and industrial wastes severely pollute 54 of the 78 streams monitored in China. In Latin America and Africa, most streams passing through urban or industrial areas suffer from severe pollution.
What Are the Pollution Problems of Lakes?
In lakes, reservoirs, and ponds, dilution often is less effective than in streams because
. Lakes and reservoirs often contain stratified layers (Figure 3-17, p. 56) that undergo little vertical mixing.
. They have little flow. For example, 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.
. Ponds contain small volumes of water.
Consequently, lakes, reservoirs, and ponds are more vulnerable than streams to contamination by
(1) plant nutrients, (2) oil, (3) pesticides, and (4) toxic substances such as lead, mercury, and selenium. These contaminants can kill (1) bottom life and fish and (2) birds that feed on contaminated aquatic organisms. Many toxic chemicals and acids (Figure 11-26, p. 258) also enter lakes and reservoirs from the atmosphere.
Lakes receive inputs of nutrients and silt eroded and running off from the surrounding land basin. Eutrophication is the name given to this natural nutrient enrichment of lakes. Over time, some lakes become more eutrophic (Figure 3-18, bottom, p. 57), but others do not because of differences in the surrounding drainage basin.
Near urban or agricultural areas, human activities can greatly accelerate the input of plant nutrients to a lake, which results in a process known as cultural eutrophication. Such a change is caused mostly by nitrate- and phosphate-containing effluents from various sources (Figure 12-20, p. 288).
During hot weather or drought, this nutrient overload produces dense growths of organisms such as algae, cyanobacteria, water hyacinths, and duckweed. When the algae die, their decomposition by aerobic bacteria depletes dissolved oxygen in the surface layer of water near the shore and in the bottom layer. This oxygen depletion can kill fish and other aerobic aquatic animals. If excess nutrients continue to flow into a lake, anaerobic bacteria (1) take over and (2) produce gaseous decomposition products such as smelly, highly toxic hydrogen sulfide and flammable methane.
Figure 12-20 Principal sources of nutrient overload causing cultural eutrophication in lakes and coastal areas. The amount of nutrients from each source varies according to the types and amounts of human activities occurring in each airshed and watershed. Levels of dissolved oxygen drop when enlarged populations of algae and plants (stimulated by increased nutrient input) die and are decomposed by aerobic bacteria. Lowered oxygen levels can (1) kill fish and other aquatic life and (2) reduce biodiversity and the aesthetic and recreational value of the lake.
According to the EPA, about one-third of the 100,000 medium to large lakes and about 85% of the large lakes near major population centers in the United States have some degree of cultural eutrophication. One-fourth of the lakes in China suffer from cultural eutrophication.
Ways to prevent or reduce cultural eutrophication include (1) advanced (but expensive) waste treatment to remove nitrates and phosphates before wastewater enters lakes, (2) bans or limits on phosphates in household detergents and other cleaning agents, and (3) soil conservation and land-use control to reduce nutrient runoff.
Major cleanup methods are (1) removing excess weeds, (2) controlling undesirable plant growth with herbicides and algicides, and (3) pumping air through lakes and reservoirs to avoid oxygen depletion (an expensive and energy-intensive method).
As usual, pollution prevention is more effective and usually cheaper in the long run than cleanup. If excessive inputs of plant nutrients stop, a lake usually can return to its previous state.
Case Study: Chemical Pollution in the Great Lakes
The five interconnected Great Lakes contain at least 95% of the fresh surface water in the United States and 20% of the world's fresh surface water. The Great Lakes basin is home for about 38 million people-about 30% of the Canadian population and 14% of the u.s. population.
Despite their enormous size, these lakes are vulnerable to pollution from point and nonpoint sources because less than 1% of the water entering the Great Lakes flows out to the St. Lawrence River each year. In addition to land runoff, these lakes receive large quantities of acids, pesticides, and other toxic chemicals by deposition from the atmosphere (often blown in from hundreds or thousands of kilometers away).
By the 1960s, many areas of the Great Lakes were suffering from severe (1) cultural eutrophication,
JoAnn M. Burkholder is professor of aquatic biology and marine science at North Carolina State University. She knows what it is like to be sickened by a newly identified fishkilling microbe and to experience the political heat when you go public with your research to alert peo. pIe about a potentially serious health threat.
In 1986, Burkholder investigated why a colleague's laboratory research fish were dying mysteriously and discovered the culprit was a new microbe so tiny that dozens could fit on the head of a pin. She and her codiscoverer named it Pfiesteria piscida (pronounced "fee-STEER-e-ah pis-SEED-uh"), but some biologists call it the cell from hell.
She and her colleagues discovered this complex microscopic organism can assume at least 24 guises in its lifetime. Without suitable prey, the microbe can masquerade as a plant or lie dormant for years. Then under certain conditions these microbes can change from algae eaters into fish-killing dinoflagellates that release neurotoxins that stun fish in rivers and coastal estuaries and usually kill them within 10 minutes to several hours.
The neurotoxin can also form an aerosol above the water. In 1993, Burkholder and her chief research aide breathed toxic fumes released in tanks of fish dying from Pfiesteria attacks. They experienced (1) nausea, (2) burning eyes and cramps, (3) weakness, (4) slow-healing sores, (5) difficulty breathing, and (6) severe loss of memory and mental powers. Eventually they recovered but still suffer from shortness of breath after strenuous exercise.
Since then, more than 100 researchers, anglers, and water skiers in North Carolina, Virginia, and Maryland have experienced one or more of these symptoms when exposed to water or air presumably contaminated by Pfiesteria toxins.
In 1995, Burkholder and her colleagues detected a second species of fish-eating Pfiesteria in North Carolina's New River after a major spill from a hog-waste lagoon. These two species of single-cell organisms live in waters from the Chesapeake Bay to the Gulf Coast of Florida and Alabama, and each year they cause more than $60 million in losses to U.S. fisheries and tourism.
Through lab and field research, Burkholder and others developed evidence that connected outbreaks or blooms of Pfiesteria with excessive levels of nitrogen (as nitrates) and phosphorus (as phosphates) in rivers and estuaries. High levels of such nutrients occur in runoff from fertilized croplands, industrial development, and feedlots (especially those used to raise hogs and chickens) into rivers flowing into coastal estuaries.
In 1991, Burkholder went public with her findings and urged North Carolina state legislators to put curbs on hog farming and enact much tougher laws to reduce the flow of nutrients and other pollutants into the state's rivers. Hog farmers, developers, farming interests, fishing industry officials (worried about whether it is safe to eat fish and shellfish from affected rivers and estuaries), tourist industry officials (alarmed about a negative image of the state's huge coastal recreational industry), and some state officials reacted negatively to her political activism.
Some challenged her character and competence and accused her of using the results of preliminary research to push for questionable policies. She also received some anonymous death threats.
Burkholder has not backed down, and she continues to criticize state health officials and legislators for not taking her concerns about public health seriously enough. Under the glare of state and national publicity, * the state now supports research on the problem and since 1997 has declared had a moratorium on construction of new hog farms and is looking for better ways to deal with hog waste.
Research by other scientists has confirmed the link between Pfiesteria outbreaks and nutrient overloading of rivers. Since 1997, a number of federal and state environmental, health, and agricultural agencies have set up a coordinated research effort to learn more about what triggers outbreaks of the organism and how they affect humans and other organisms.
*For a popularized description of her research and political battle to alert the public and elected officials to the dangers posed by this microbe, see Rodney Barker's And the Waters Turned to Blood: The Ultimate Biological Threat (New York: Simon & Schuster, 1997).
(2) huge fish kills, and (3) contamination from bacteria and a variety of toxic industrial wastes. The impact on Lake Erie was particularly intense because it is the shallowest of the Great Lakes and has the highest concentrations of people and industrial activity along its shores. Many bathing beaches had to be closed, and by 1970 the lake had lost nearly all its native fish (Figure 12-21, left, p. 290).
Here is some good news. Since 1972, a $20 billion Great Lakes pollution control program has been car
ried out jointly by Canada and the United States. This program has (1) significantly decreased levels of phosphates, coliform bacteria, and many toxic industrial chemicals, (2) decreased algae blooms, (3) increased dissolved oxygen levels and sport and commercial fishing catches (Figure 12-21, right), and (4) allowed most swimming beaches to reopen.
These improvements occurred mainly because of (1) new or upgraded sewage treatment plants, (2) better treatment of industrial wastes, and (3) banning of phosphate detergents, household cleaners, and water conditioners.
Figure 12-21 Generalized view of progress in cleaning up Lake Erie since 1969.
Here is some bad news:
. Less than 3% of the lakes' shoreline is clean enough for swimming or for supplying drinking water.
. Nonpoint land runoff of pesticides and fertilizers from urban sprawl has surpassed industrial pollution as the greatest threat to the lakes.
. Forty-three toxic hot spots remain heavily polluted.
. About half of the input of toxic compounds comes from (1) atmospheric deposition of pesticides, (2) mercury from coal-burning plants, and (3) other toxic chemicals from as far as Mexico and Russia.
. Toxic chemicals such as PCBs have (1) built up in food chains and webs, (2) contaminated many types of sport fish, and (3) depleted populations of birds, river otters, and other animals feeding on contaminated fish.
. A survey by Wisconsin biologists revealed that one fish in four taken from the Great Lakes is unsafe for human consumption.
Why Is Groundwater Pollution Such a Serious Problem? According to many scientists, a serious threat to human health is the out-of-sight pollution of groundwater, a prime source of water for drinking and irrigation.
Studies indicate that groundwater pollution comes from numerous sources (Figure 12-22). Groundwater is also contaminated by people who dump or spill gasoline, oil, and paint thinners and other organic solvents onto the ground.
Although experts rate groundwater pollution as a low-risk ecological problem, they consider pollutants in drinking water (much of it from groundwater) a high risk health problem (Figure 10-7, left, p. 231). When groundwater becomes contaminated, it cannot cleanse itself of degradable wastes as flowing surface water does (Figure 12-19). This happens because groundwater (1) flows so slowly (usually less than 0.3 meters or 1 foot per day) that contaminants are not diluted and dispersed effectively, (2) has much smaller populations of decomposing bacteria, and (3) has cold temperatures that slow down the chemical reactions that decompose wastes.
Thus it can take hundreds to thousands of years for contaminated groundwater to cleanse itself of degradable wastes. On a human time scale, nondegradable wastes (such as toxic lead, arsenic, and fluoride) are there permanently.
What Is the Extent of Groundwater Pollution? The answer is that we do not know because few countries go to the great expense of locating, tracking, and testing aquifers. However, scientific studies in scattered parts of the world indicate the following:
. According to the EPA and the U.S. Geological Survey, one or more organic chemicals contaminate about 45% of municipal groundwater supplies in the United States. In New Jersey every major aquifer is contaminated.
. An EPA survey found that (1) one-third of 26,000 industrial waste ponds and lagoons in the United States have no liners to prevent toxic liquid wastes from seeping into aquifers, and (2) one-third of these sites are within 1.6 kilometers (1 mile) of a drinking water well.
. The EPA estimates that at least 100,000 underground tanks storing gasoline, diesel fuel, home heating oil, and toxic solvents are leaking their contents into groundwater in the United States (Figure 12-21).
During this century, scientists expect many of the millions of such tanks installed around the world in recent decades to corrode, leak, contaminate groundwater, and become a major global health problem.
. Toxic arsenic (As) contaminates drinking water through the drilling of tubewells into aquifers where soils and rock are naturally rich in arsenic. In India's state of West Bengal and parts of Bangladesh, 28-57 milbon people are drinking water with arsenic levels 5-100 times the WHO limit. In the United States, the standards for arsenic in drinking water are controversial (Spotlight, p. 292).
. In coastal areas, excessive pumping of water from aquifers can lead to contamination of drinking water by saltwater intrusion (Figure 12-14).
Solutions: How Can We Protect Groundwater? Contaminated aquifers are almost impossible to clean because of their (1) enormous volume, (2) inaccessibility, and (3) slow movement. Pumping polluted groundwater to the surface, cleaning it up, and returning it to the aquifer is extremely expensive. Thus preventing contamination is the only effective way to protect groundwater resources. Ways to do this include
. Monitoring aquifers near landfills and underground tanks.
. Requiring leak detection systems for underground tanks used to store hazardous liquids.
. Banning or more strictly regulating disposal of hazardous wastes in deep injection wells and landfills.
. Storing hazardous liquids above ground in tanks with systems that detect and collect leaking liquids.
12-8 OCEAN POLLUTION
How Much Pollution Can the Oceans Tolerate? The oceans are the ultimate sinks for much of the waste matter we produce. Oceans can dilute, disperse, and degrade large amounts of raw sewage, sewage sludge, oil, and some types of degradable industrial waste, especially in deep-water areas. Some forms of marine life have been more resilient than originally expected. Consequently, some scientists suggest it is safer to dump sewage sludge and most other hazardous wastes into the deep ocean than to bury them on land or burn them in incinerators.
Other scientists disagree, pointing out we know less about the deep ocean than we do about outer space. They add that dumping waste in the ocean would (1) delay urgently needed pollution prevention and (2) promote further degradation of this vital part of the earth's life-support system.
Arsenic is a naturally occurring element in various rocks and can be released into groundwater and surface water from the natural weathering of minerals in deep soils and rocks. In addition, arsenic can be released into the air and water from (1) coal burning, (2) copper and lead smelting, (3) municipal trash incinerators, (4) wood-preserving treatments, (5) leaching from landfills containing arsenic-laden ash produced by coal-burning power plants, and (6) use of certain arsenic-containing pesticides.
According to a 1999 report by the U.s. National Academy of Sciences, long-term exposure to arsenic in drinking water can (1) cause cancer of the skin, bladder, and lungs, (2) possibly cause kidney and liver cancer, (3) cause skin lesions and hardening of the skin (keratosis), and (4) be linked to adult-onset diabetes, cardiovascular disease, anemia, and disorders of the immune, nervous, and reproductive systems. In 2001, researchers at the Dartmouth Medical School reported that arsenic is also a potent endocrine disrupter
The acceptable level of arsenic in U.S. drinking water has been 50 parts per billion (50 ppb) since 1942. This is five times the international standard of 10 ppb adopted in 1993 by the WHO and in 1998 by the IS-member European Union.
In 1962, the U.s. Public Health Service proposed lowering the US drinking water standard for arsenic from 50 ppb to 10 ppb. After more than 25 years of scientific reviews, including a 1999 study by the National Academy of Sciences, the EP A proposed that the U.s. drinking water standard for arsenic be reduced to the international standard of 10 ppb.
According to the WHO scientists, even the 10 ppb standard is not safe. Based on health concerns, many scientists call for lowering the standard to 3-5 ppb. A 2001 study by the u.s. National Academy of Sciences found that routinely drinking water with arsenic levels of even 3 ppb poses a 1 in 1,000 risk of developing bladder or lung cancer.
Running drinking water through activated aluminia can absorb arsenic. Reverse osmosis also removes arsenic, but it is an expensive process.
According to the EPA, implementing the 10 ppb standard would (1) require about 3,000 communities with high levels of arsenic in groundwater (see figure) to improve their drinking water treatment at an average annual cost of about $12 per person, (2) cost about $181 million per year, (3) make drinking water safer for at least 11 million Americans, and (4) provide annual benefits of $140-198 million from reduction of arsenic-related bladder and liver cancers.
Mining, coal, and lumber products and other arsenicproducing companies (that could face tougher regulations) oppose the 10 ppb standard and say the estimated costs are too low. In addition, some small communities contend they cannot afford to implement the new standard. For example, for affected communities with 500 or fewer homes, the annual water bill could increase by $162-327 per household. However, the federal government could subsidize some or all treatment costs for small systems.
In March 2001, President George W. Bush (under lobbying pressure from mining interests, coal companies, the wood products industry, and other arsenic producers) withdrew implementation of the new EP A standard, arguing it would cost too much to implement. Health scientists and environmentalists were outraged and accused the Bush administration of caving to the demands of industries whose activities release toxic levels of arsenic into drinking water supplies. That same month, the EPA reversed its controversial earlier decision and lowered the acceptable concentration of arsenic from 50 ppb to 10 ppb, to take effect in 2006.
Do you believe the drinking standard for arsenic in U.s. drinking water should be lowered from 50 ppb to (a) 10 ppb or (b) 3ppb? Explain. If you lived in a community affected by such a standard, how much more per year would you be willing to pay on your water bill to implement the standard?
How Do Pollutants Affect Coastal Areas?
Coastal areas-especially wetlands and estuaries, coral reefs, and mangrove swamps-bear the brunt of our enormous inputs of wastes into the ocean (Figure 12-23, p. 294). This is not surprising because (1) about 40% of the world's population lives on or within 100 kilometers (160 miles) of the coast, (2) 14 of the world's15 largest metropolitan areas, each with 10 million people or more, are near coastal waters (Figure 5-14, p. 87), and (3) coastal populations are growing more rapidly than the global population.
In most coastal developing countries (and in some coastal developed countries), municipal sewage and industrial wastes are dumped into the sea without treatment. For example, about 85% of the sewage from large cities along the Mediterranean Sea, which has a coastal population of 200 million people during tourist season, is discharged into the sea untreated. This causes widespread beach pollution and shellfish contamination.
Runoff of sewage and agricultural wastes into coastal waters and acid deposition from the atmosphere (Figure 11-26, p. 258) introduce large quantities of nitrate (NO3 -) and phosphate (pal-) plant nutrients, which can cause explosive growth of harmful algae. These algal blooms are called red, brown, or green tides, depending on their color. They can (1) release waterborne and airborne toxins that damage fisheries, (2) kill some fish-eating birds, (3) reduce tourism, and (4) poison seafood. Death and decompo ition of the algae deplete dissolved oxygen in coastal waters and cause the deaths of a variety of marine species.
Case Study: The Chesapeake Bay
The Chesapeake Bay, the largest estuary in the United States, is in trouble because of human activities. Between 1940 and 2001, the number of people living in the Chesapeake Bay area grew from 3.7 million to 17 million, and within a few years its population may reach 18 million.
The estuary receives wastes from point and nonpoint sources scattered throughout a huge drainage basin that includes 9 large rivers and 141 smaller streams and creeks in parts of six states (Figure 12-24, p. 294). The bay has become a huge pollution sink because it is quite shallow, and only 1% of the waste entering it is flushed into the Atlantic Ocean.
Phosphate and nitrate levels have risen sharply in many parts of the bay, causing algae blooms and oxygen depletion (Figure 12-24). Studies have shown that point sources, primarily sewage treatment plants, account for about 60% by weight of the phosphates. Nonpoint sources-mostly runoff of fertilizer and animal wastes from urban, suburban, and agricultural land and deposition from the atmosphere-account for about 60% by weight of the nitrates.
Large quantities of pesticides also run off cropland and urban lawns, and industries discharge large amounts of toxic wastes (often in violation of their discharge permits). Commercial harvests of oysters, crabs, and several important fish have fallen sharply since 1960 because of a combination of overfishing, pollution, and disease.
Figure 12-23 How residential areas, factories, and farms contribute to the pollution of coastal waters and bays.
Figure 12-24 Chesapeake Bay, the largest estuary in the United States, is severely degraded as a result of water pollution from point and non point sources in six states and from deposition of air pollutants.
In 1983, the Chesapeake Bay Program, the country's most ambitious attempt at integrated coastal management, was implemented. Between 1985 and 2000, phosphorus levels declined 27% and nitrogen levels dropped 16%, a significant achievement given the increasing population in the watershed and the fact that nearly 40% of the nitrogen inputs come from the atmosphere.
Reaching the declared goal of a 40% reduction in nutrient levels and a significant improvement in habitat water quality throughout the bay will be difficult because of projected population growth. There is still a long way to go, but the Chesapeake Bay Program shows what can be done when diverse interested parties work together to achieve goals that benefit both wildlife and people.
Case Study: Effects of Oil on Ocean Life
Crude petroleum (oil as it comes out of the ground) and refined petroleum (fuel oil, gasoline, and other processed petroleum products; Figure 6-24, p. 115) are accidentally or deliberately released into the environment from a number of sources.
Tanker accidents and blowouts at offshore drilling rigs (when oil escapes under high pressure from a borehole in the ocean floor) get most of the publicity because of their high visibility. However, more oil is released (1) during normal operation of offshore wells, (2) from washing tankers and releasing the oily water, and (3) from pipeline and storage tank leaks.
Natural oil seeps also release large amounts of oil into the ocean at some sites, but most ocean oil pollution comes from activities on land. Almost half (some experts estimate 90%) of the oil reaching the oceans is waste oil dumped, spilled, or leaked onto the land or into sewers by cities, industries, and people changing their own motor oil. Worldwide, about 10% of the oil that reaches the ocean comes from the atmosphere, mostly from smoke emitted by oil fires.
Volatile organic hydrocarbons in oil immediately kill a number of aquatic organisms, especially in their vulnerable larval forms. Some other chemicals in oil form tarlike globs that float on the surface and coat the feathers of birds (especially diving birds) and the fur of marine mammals. This oil coating destroys their natural insulation and buoyancy, causing many of them to drown or die of exposure from loss of body heat.
Heavy oil components that sink to the ocean floor or wash into estuaries can (1) smother bottom-dwelling organisms such as crabs, oysters, mussels, and clams or (2) make them unfit for human consumption. Some oil spills have killed reef corals.
Research shows that most (but not all) forms of marine life recover from exposure to large amounts of crude oil within 3 years. However, recovery from exposure to refined oil, especially in estuaries, can take 10 years or longer. Oil slicks that wash onto beaches can have a serious economic impact on coastal residents, who lose income from fishing and tourist activities.
If they are not too large, oils spills can be partially cleaned up by mechanical, chemical, fire, and natural methods. Mechanical methods include using (1) floating booms to contain the oil spill or keep it from reaching sensitive areas, (2) skimmer boats to vacuum up some of the oil into collection barges, and (3) absorbent pads or large mesh pillows filled with feathers or hair to soak up oil on beaches or in waters too shallow for skimmer boats.
Chemical methods include using (1) coagulating agents to cause floating oil to clump together for easier pickup or to sink to the bottom, where it usually does less harm, and (2) dispersing agents to break up oil slicks. However, these agents can damage some types of organisms. Fire can burn off floating oil, but crude oil is hard to ignite nd this approach produces air pollution.
These methods remove only part of the oil, and none work well on a large spill. Scientists estimate that current methods can recover no more than 12-15% of the oil from a major spill. This explains why preventing oil pollution is the most effective and in the long run the least costly approach.
Solutions: How Can We Protect Coastal Waters? Analysts have suggested various ways to prevent and reduce excessive pollution of coastal waters (Figure 12-25). The key to protecting oceans is to reduce the flow of pollution from the land and from streams emptying into the ocean. Scientists call for integrating such efforts with those to prevent and control air pollution because an estimated 33% of all pollutants entering the ocean worldwide comes from air emissions from land-based sources.
Figure 12-25 Methods for preventing and cleaning up excessive pollution of coastal waters.
12-9 SOLUTIONS: PREVENTING AND REDUCING SURFACE WATER POLLUTION
What Can We Do About Water Pollution from Nonpoint Sources?
Ways to help control nonpoint water pollution, most of it from agriculture, include the following:
. Reduce fertilizer runoff into surface waters and leaching into aquifers by using slow-release fertilizer and using none on steeply sloped land.
. Plant buffer zones of vegetation between cultivated fields and nearby surface water.
. Reduce pesticide runoff by applying pesticides only when needed and using biological control or integrated pest management (p. 215).
. Control runoff and infiltration of manure from animal feedlots by (1) improving manure control, (2) planting buffers, and (3) not locating feedlots and animal waste storage lagoons on steeply sloped land near surface water and in flood zones.
. Reduce soil erosion and flooding by reforesting critical watersheds.
What Can We Do About Water Pollution from Point Sources?
The Legal Approach Developed countries purify most wastes from point sources to some degree. In the United States, the Federal Water Pollution Control Act of 1972 (renamed the Clean Water Act when it was amended in 1977) and the 1987 Water Quality Act are used to help control pollution of the country's surface waters.
In 1995, the EPA developed a discharge trading policy designed to use market forces to reduce water pollution (as has been done with sulfur dioxide for air pollution control, p. 263). This policy allows a water pollution source, such as an industrial plant or a sewage treatment plant, to sell credits for its excess reductions to another facility that cannot reduce its discharges as cheaply.
Here is some good news. The Clean Water Act of 1972 led to the following improvements in U.S. water quality between 1972 and 1998: (1) The percentage of US. rivers and lakes tested that are fishable and swimmable increased from 36% to 62%, (2) the amount of
. topsoil lost through agricultural runoff was cut by about 1.1 billion metric tons (1 billion tons) annually, (3) the proportion of the U.S. population served by sewage treatment plants increased from 32% to 74%, and (4) annual wetland losses decreased by 83%.
Here is some bad news: (1) About 44% of lakes, 38% of rivers (up from 26% in 1984), and 32% of tested estuaries in the United States are still unsafe for fishing, swimming, and other recreational uses, (2) hog, poul
try, and cattle farm runoff pollutes 70% of US. rivers, (3) large quantities of toxic industrial wastes are illegally dumped into U.S. rivers each year, (4) fish caught in more than 1,400 different waterways are unsafe to eat because of high levels of pesticides and other toxic substances, and (5) a 2001 study by the National Academy of Sciences found thatthe area of wetlands in the United States is continuing to fall, despite a government goal of "no net loss" in the area and function of wetlands.
Should We Strengthen or Weaken the U.S. Clean Water Act? Some environmentalists and a 2001 report by the EP A's inspector general call for the Clean Water Act to be strengthened by (1) increasing funding and authority to control nonpoint sources of pollution, (2) increasing monitoring of state programs to see that pollution permits are not allowed to expire, (3) strengthening programs to prevent and control toxic water pollution, (4) providing more funding and authority for integrated watershed and airshed planning to protect groundwater and surface water from contamination, (5) requiring states to do a better job of monitoring and enforcing water pollution laws, and (6) expanding the rights of citizens to bring lawsuits to ensure that water pollution laws are enforced. The National Academy of Sciences also calls for (1) halting the loss of wetlands, (2) higher standards for restoration, and (3) creating new wetlands before filling any natural wetlands.
Many people oppose these proposals, contending that the Clean Water Act's regulations and government wetlands regulations are already too restrictive and costly. Farmers and developers (1) see the law as a curb on their rights as property owners to fill in wetlands and (2) believe they should be compensated for property value losses because of federal wetland protection regulations. State and local officials want more discretion in testing for and meeting water quality standards. They argue that in many communities it is unnecessary and too expensive to test for all the water pollutants required by federal law.
What Can We Do About Water Pollution from Point Sources?
The Technological Approach In rural and suburban areas with suitable soils, sewage from each house usually is discharged into a septic tank (Figure 12-26). About 25% of all homes in the United States are served by septic tanks, which should be cleaned out every 3-5 years by a reputable contractor so they will not contribute to groundwater pollution.
Figure 12-26 Septic tank system used for disposal of domestic sewage and wastewater in rural and suburban areas. This system traps greases and large solids and discharges the remaining wastes over a large drainage field. As these wastes percolate downward, the soil filters out some potential pollutants, and soil bacteria decompose biodegradable materials. To be effective, septic tank systems must be (1) properly installed in soils with adequate drainage, (2) not placed too close together or too near well sites, and (3) pumped out when the settling tank becomes full.
In U.S. urban areas, most waterborne wastes from homes, businesses, factories, and storm runoff flow through a network of sewer pipes to wastewater treatment plants. When sewage reaches a treatment plant, it typically undergoes one or both of the following levels of purification:
. Primary sewage treatment: a mechanical process that uses screens to filter out debris such as sticks, stones, and rags and allows suspended solids to settle out as sludge in a settling tank (Figure 12-27).
. Secondary sewage treatment: a biological process in which aerobic bacteria are used to remove up to 90% of biodegradable, oxygen-demanding organic wastes (Figure 12-27).
Figure 12-27 Primary and secondary sewage treatment.
Because of the Clean Water Act, most U.S. cities have combined primary and secondary sewage treatment plants (Figure 12-27). However, government studies have found that (1) at least two-thirds of these plants have violated water pollution regulations, (2) 500 cities have failed to meet federal standards for sewage treatment plants, and (3) 34 East Coast cities simply screen out large floating objects from their sewage before discharging it into coastal waters.
Before discharge, water from primary and secondary sewage treatment undergoes (1) bleaching to remove water coloration and (2) disinfection to kill disease-carrying bacteria and some but not all viruses. The usual method for doing this is chlorination. However, chlorine can react with organic materials in water to form small amounts of chlorinated hydrocarbons, some of which cause cancers in test animals and may damage the human nervous, immune, and endocrine systems (Connections, p. 224). Use of other disinfectants, such as ozone and ultraviolet light, is increasing but they cost more and their effects do not last as long as chlorination.
How Can We Treat Sewage by Working with Nature?
Some communities and individuals are seeking better ways to purify contaminated water by working with nature. Ecologist John Todd designs, builds, and operates innovative ecological wastewater treatment systems called living machines. They look like aquatic botanical gardens and are powered by the sun in greenhouses or outdoors, depending on the climate.
This ecological purification process begins when sewage flows into a passive solar greenhouse or outdoor sites containing rows of large open tanks populated by an increasingly complex series of organisms. In the first set of tanks, algae and microorganisms decompose organic wastes, with sunlight speeding up the decomposition process. Water hyacinths, cattails, bulrushes, and other aquatic plants growing in the tanks take up the resulting nutrients.
After flowing though several of these natural purification tanks, the water passes through an artificial marsh of sand, gravel, and bulrush plants to filter out algae and remaining organic waste. Some of the plants also absorb (sequester) toxic metals such as lead and mercury and secrete natural antibiotic compounds that kill pathogens.
Next, the water flows into aquarium tanks. There snails and zooplankton consume microorganisms and are in turn consumed by crayfish, tilapia, and other fish that can be eaten or sold as bait. After 10 days, the clear water flows into a second artificial marsh for final filtering and cleansing.
The water can be made pure enough to drink by using ultraviolet light or passing the water through an ozone generator, usually immersed out of sight in an attractive pond or wetland habitat. Selling the ornamental plants, trees, and baitfish produced as byproducts of such living machines helps reduce costs. Operating costs are about the same as for a conventional sewage treatment plant.
Some communities use nearby natural wetlands to treat sewage, and others create artificial wetlands for such purposes (Solutions, p. 299). Mark Nelson has developed a small, low-tech, and inexpensive artificial wetland system to treat raw sewage from hotels, restaurants, and homes in developing countries (Figure 12-28). This wastewater garden system removes 99.9% of fecal coliform bacteria and more than 80% of the nitrates and phosphates from incoming sewage that in most developing countries is often dumped untreated into the ocean or into shallow holes in the ground. The water flowing out of such systems can be 1.lsed to (1) irrigate gardens or fields or (2) flush toilets and thus helps save water.
How Is Drinking Water Purified?
Treatment of water for drinking by city dwellers is much like wastewater treatment. Areas that depend on surface water usually store it in a reservoir for several days. This improves clarity and taste by increasing dissolved oxygen content and allowing suspended matter to settle. Next the water is pumped to a purification plant and treated to meet government drinking water standards. Before disinfection, the water is usually run through sand filters and activated charcoal. In areas with very pure groundwater sources, little treatment is necessary. In tropical countries without centralized water treatment systems, the WHO is urging people to purify their own drinking water by exposing a plastic bottle filled with contaminated water to the sun.
Figure 12-28 Wastewater garden. This small, artificial, gravity-fed wetland system for treating sewage uses only 1.9-3.8 square meters (20-30 square feet) of space per person.
How Is the Quality of Drinking Water Protected?
About 54 countries, most of them in North America and Europe, have safe drinking water standards. The U.5. Safe Drinking Water Act of 1974 requires the EP A to establish national drinking water standards, called maximum contaminant levels, for any pollutants that may have adverse effects on human health.
Privately owned wells are not required to meet federal drinking water standards, primarily because of (1) the costs of testing each well regularly (at least $1,000) and (2) some home owners' opposition to mandatory testing and compliance.
Is Bottled Water the Answer?
Despite some problems, experts say the United States has some of the world's cleanest drinking water. Yet about half of all Americans worry about getting sick from tap water contaminants, and many drink bottled water or install expensive water purification systems. Studies indicate that many of these consumers are being cheated and in some cases may end up drinking water dirtier than much cheaper water they can get from their taps.
Bacteria contaminate an estimated one-third of the bottled water purchased in the United States. To be safe, consumers purchasing bottled water should determine whether the bottling company belongs to the International Bottled Water Association (IBWA) and adheres to its testing requirements.* Some companies pay $2,500 annually to obtain more stringent certification by the National Sanitation Foundation, an independent agency that tests for 200 chemical and biological contaminants.
Before drinking expensive bottled water and buying costly home water purifiers, health officials suggest that consumers have their water tested by local health authorities or private labs (not companies trying to sell water purification equipment) to (1) identify what contaminants, if any, must be removed and (2) recommend the type of purification needed to remove such contaminants. Independent experts contend that unless tests show otherwise, for most urban and suburban Americans served by large municipal drinking water systems, home water treatment systems are not worth the expense and maintenance hassles.
Buyers should check out companies selling water purification equipment and be wary of claims that the EPA has approved a treatment device. Although the EPA does register such devices, it neither tests nor approves them.
'Check for the IBWA seal of approval on the bottle, or contact the International Bottled Water Association (1700 Diagonal Road, Suite 650, Alexandria, VA 22314; telephone: 703-683-5213; information hotline: 1-800-WATER-ll; website: www.bottledwater.org) for a member list.
Waste treatment is one of the important ecological services provided by wetlands. More than 150 cities and towns in the United States now use natural and artificial wetlands to treat sewage as a low-tech, lowcost alternative to expensive waste treatment plants.
Some communities have created artificial wetlands to treat their water, as the residents of Arcata, California, did, led by Humboldt State University professors Robert Gearheart and George Allen.
In this coastal town of 17,000, some 63 hectares (155 acres) of wetlands has been created between the town and the adjacent Humboldt Bay. The marshes, developed on land that was once a dump, ' act as an inexpensive natural waste treatment plant. The project cost less than half the estimated cost of a conventional treatment plant.
Here is how it works. First, sewage goes to sedimentation tanks, where the solids settle out as sludge that is removed and processed for use as fertilizer. The liquid is pumped into oxidation ponds, where remaining wastes are broken down by bacteria. After a month or so, the water is released into the artificial marshes, where plants and bacteria carry out further filtration and cleansing.
Although the water is clean enough for direct discharge into the bay, state law requires it first be chlorinated. The town chlorinates the water and then dechlorinates it before sending it into the bay, where oyster beds thrive.
The marshes and lagoons also serve as an Audubon Society bird sanctuary and provide habitats for thousands of otters, seabirds, and marine animals. The town even celebrates its natural sewage treatment system with an annual "Flush with Pride" festival.
List some possible drawbacks to creating artificial wetlands to treat sewage. Do these drawbacks outweigh the benefits? Explain.
12-10 SOLUTIONS: ACHIEVING A MORE SUSTAINABLE WATER FUTURE
How Can We Use and Manage 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." Figure 12-29 lists ways to implement this principle.
The challenge in developing such a blue revolution is to implement a mix of strategies built around (1) irrigating crops more efficiently, (2) using water-saving technologies in industries and homes, and (3) improving and integrating management of water basins and groundwater supplies.
Accomplishing such a revolution in water use and management will be difficult and controversial. However, water experts contend that not developing such strategies will eventually lead to (1) economic and health problems, (2) increased environmental degradation and loss of biodiversity, (3) heightened tensions and perhaps armed conflicts over water supplies, (4) larger numbers of environmental refugees, and (5) threats to national and global military, economic, and environmental security.
How Can We Reduce Water Pollution?
Individuals Matter As with air pollution, it is encouraging that since 1970 most of the world's developed countries have enacted laws and regulations that have significantly reduced point sources of water pollutionmostly because of political pressure by individuals and organized groups of individuals on elected officials. However, little has been done to reduce water pollution in most developing countries
Figure 12-29 Methods for achieving more sustainable use of the earth's water resources.
To environmentalists the next step is to increase efforts to reduce and prevent water pollution in developed and developing countries by asking the question:. "How can we not produce water pollutants in the first place?" Ways to accomplish this goal include the following:
. Greatly reducing poverty.
. Putting much greater emphasis on keeping groundwater from being contaminated.
. Putting much more emphasis on preventing nonpoint pollution from the runoff of fertilizers, pesticides, and other pollutants from farms, animal feedlots, lawns, and urban developments.
. Reducing the toxicity or volume of pollutants. For example, organic solvent-based inks and paints can be replaced with water-based materials.
. Recycling pollutants. An example is cleaning up and recycling contaminated solvents for reuse instead of discharging them.
. Working with nature to treat sewage (p. 297).
. Integrating government policies for water pollution with policies for air pollution, agriculture, energy, solid and hazardous wastes, climate change, land use, and population.
Like the earlier shift to controlling water pollution between 1970 and 2000, this new shift to preventing water pollution will not take place without political pressure on elected officials by individual citizens and groups of such citizens. See the web site material for this chapter for some actions you can take to help reduce water pollution.
[tis not until the well runs dry that we know the worth ofwater. BENJAMIN FRANKLIN
1. Define the boldfaced terms in this chapter.
2. List nine unique properties of water, and explain the
importance of each property.
3. What percentage of the earth's total volume of water is available for use by us? How might global warming alter the hydrologic cycle?
4. Distinguish among surface runoff, reliable runoff, watershed, groundwater, zone of saturation, water table, aquifer, recharge area, and natural recharge; Explain how the water in some aquifers can be depleted.
5. Since 1900, how much has the total use and per capita use of water by humans increased? About what percentage of the world's reliable surface runoff is used by humanity? About what percentage of the water we withdraw each year is used for (a) irrigation, (b) industry, and (c) residences and cities?
6. What are the major water uses and problems of (a) the eastern United States and (b) the western United States?
7. List four causes of water scarcity. What is water stress?
8. Explain why there is a danger of water wars in the Middle East, and list five ways to avoid such events.
9. What is afloodplain? What three major services do floodplains provide? List four reasons why so many people live on floodplains.
10. List the major benefits and disadvantages of floods. List three ways in which humans increase the damages from floods. Describe the nature and causes of the flooding problems in Bangladesh.
11. List the pros and cons of trying to reduce flood risks by (a) stream channelization, (b) building levees, (c) building dams, and (d) managing floodplains.
12. List six ways to increase the supply of fresh water in a particular area.
13. List the major advantages and disadvantages of building large dams and reservoirs to supply fresh water. List the advantages and disadvantages of China's Three Gorges dam project. List seven ecological services that rivers provide.
14. List the major advantages and disadvantages of supplying water by transferring it from one watershed to another. List the advantages and disadvantages of (a) the Aral Sea water transfer project in Central Asia and (b) the California Water Project.
15. List the advantages and disadvantages of supplying more water by withdrawing groundwater. Summarize the problems of withdrawing groundwater from the Ogallala Aquifer in the United States. List six ways to prevent or slow groundwater depletion.
16. What is saltwater intrusion, and what harm does it cause?
17. List the advantages and disadvantages of increasing supplies of fresh water by desalination of salt water.
18. What percentage of the water used by people throughout the world is wasted? List four benefits of conserving water. List two major causes of water waste.
19. List ways to reduce water waste in (a) irrigation and (b) industry, homes, and businesses. List six advantages of drip irrigation, and explain how it could help bring about a revolution in improving water efficiency.
20. What is water pollution? What are eight types of water pollutants, and what are the major sources and effects of each type? List five ways to measure water quality.
21. Distinguish between point and nonpoint sources of water pollution, and give two examples of each type. Which type is easier to control? Why?
22. What are the major water pollution problems of streams? Explain how streams can handle some loads of biodegradable wastes, and explain the limitations of this approach.
23. Summarize the good and bad news about attempts to prevent or control stream pollution. Describe problems caused by pfiestera cells.
24. What are the major water pollution problems of lakes? List two reasons why dilution of pollution often is less effective in lakes and reservoirs than in streams.
25. Distinguish between eutrophication and cultural eutrophication. What are the major causes of cultural eutrophication? List three methods for (a) preventing cultural eutrophication and (b) cleaning up cultural eutrophication.
26. Summarize the good and bad news about attempts to reduce water pollution in the Great Lakes.
27. List five major sources of groundwater contamination. List three reasons why groundwater pollution is such a serious problem.
28. List three examples indicating the seriousness of groundwater pollution. List four ways to prevent groundwater contamination. Describe the controversy over reducing levels of arsenic in drinking water.
29. List the major pollution problems of the oceans. Why are most of these problems found in coastal areas?
30. Summarize (a) the major pollution problems of the Chesapeake Bay in the United States and (b) the progress made in dealing with these problems.
31. Summarize the major effects of oil pollution on ocean systems. What are the three major sources of oil pollution in the world's oceans? List five ways to prevent and help clean up oil pollution.
32. List seven ways to help (a) prevent pollution of coastal waters and (b) clean up pollution of coastal waters.
33. List five ways to help prevent water pollution from nonpoint sources.
34. Explain how the United States and most developed countries have reduced water pollution from point sources by enacting laws, and summarize the good and bad news about such efforts. List (a) six ways in which environmentalists believe water pollution control laws in the United States should be strengthened, and (b) two reasons why there is opposition to such changes.
35. Distinguish among septic tanks, primary sewage treatment, and secondary sewage treatment as ways to reduce water pollution.
36. Describe three ways to treat sewage based on working with nature.
37. How is drinking water purified? How is the quality of drinking water protected in the United States? How successful have these efforts been? List the pros and cons of drinking bottled water.
38. List three ways to use the world's water more sustainably.
39. List seven ways to shift the emphasis from cleanup to prevention of water pollution.
1. How do human activities increase the harmful effects of prolonged drought? How can we reduce these effects?
2. How do human activities contribute to flooding and flood damage? How can these effects be reduced?
3. Do you believe the projected benefits of China's Three Gorges dam and reservoir project on the Yangtze River will outweigh its potential drawbacks? Explain. What are the alternatives?
4. What role does population growth play in water supply problems?
5. Should the prices of water for all uses be raised sharply to include more of its environmental costs and to encourage water conservation? Explain. What harmful and beneficial effects might this have on (a) business and jobs, (b) your lifestyle and the lifestyles of any children or grandchildren you might have, (c> the poor, and (d) the environment?
6. How can a stream cleanse itself of oxygen-demanding wastes? Under what conditions will this natural cleansing system fail?
7. Which one or ones of the eight categories of pollutants listed in Table 12-1 are most likely to originate from
(a) point sources and (b) nonpoint sources?
8. Congratulations! You are in charge of managing the world's water resources. What are the three most important actions you would take?
9. Congratulations! You are in charge of sharply reducing water pollution throughout the world. What are the three most important things you would do?
Try to find the following articles:
1. Postel, S. 1999. When the world's wells run dry. World Watch 12: 30. Keywords: "aquifer" and "depletion." This article represents a good summary of groundwater-use issues, including sustainability, conservation, and government policy.
2. Rabalais, N. N., R. E. Turner, and D. Scavia. 2002. Beyond science into policy: Gulf of Mexico hypoxia and the Mississippi River. Bioscience 52: 129. Keywords: "Gulf of Mexico" and "hypoxia." Hypoxia (reduced oxygen levels) and cultural eutrophication are serious problems in the northern Gulf of Mexico. Is there a solution?
Go back Go top