Final Paper---Pollution Prevention

Chapter 18

Botkin, D. B., & Keller, E. A. (2014). Environmental science: Earth as a living planet (9th ed.). Hoboken, NJ: John Wiley & Sons, Inc.

18.1 Water

To understand water as a necessity, as a resource, and as a factor in the pollution problem, we must first understand its characteristics, its role in the biosphere, and its part in sustaining life. Water is a unique liquid; without it, life as we know it is impossible. Consider the following:

• Compared with most other common liquids, water has a high capacity to absorb and store heat. Its capacity to hold heat has important climatic significance. Solar energy warms the oceans, storing huge amounts of heat. The heat can be transferred to the atmosphere, devel- oping hurricanes and other storms. The heat in warm oceanic currents, such as the Gulf Stream, warms Great Britain and western Europe, making these areas much more hospitable for humans than would otherwise be possible at such high latitudes.

• Water is the universal solvent. Because many natural waters are slightly acidic, they can dissolve a great vari- ety of compounds, ranging from simple salts to miner- als, including sodium chloride (common table salt) and calcium carbonate (calcite) in limestone rock. Water also reacts with complex organic compounds, including many amino acids found in the human body.

• Compared with other common liquids, water has a high surface tension, a property that is extremely important in many physical and biological processes that involve moving water through, or storing water in, small open- ings or pore spaces.

• Water is the only common compound whose solid form is lighter than its liquid form. (It expands by about 8% when it freezes, becoming less dense.) That is why ice floats. If ice were heavier than liquid water, it would sink to the bottom of the oceans, lakes, and rivers. If water froze from the bot- tom up, shallow seas, lakes, and rivers would freeze solid.

All life in the water would die because cells of living organ- isms are mostly water, and as water freezes and expands, cell membranes and walls rupture. If ice were heavier than water, the biosphere would be vastly different from what it is, and life, if it existed at all, would be greatly altered.5

• Sunlight penetrates water to variable depths, permitting photosynthetic organisms to live below the surface.

A Brief Global Perspective

In brief, the water supply problem we are facing is a grow- ing global water shortage that is linked to our food sup- ply. Increasing water demand due to population growth is projected to reduce the per capita available water resource by more than 30% in the next 50 years. More than 2 bil- lion people today live in countries with moderate to severe water stress (potential shortage of supply), and this num- ber may grow to exceed 4 billion people by 2025. Poorer countries with large populations and harsh climates along with unreliable water sources, combined with lack of ap- propriate technology and water experience, are most vul- nerable to future water problems.4,6,7

A review of the global hydrologic cycle, introduced in Chapter 7, is important here. The main process in the cy- cle is the global transfer of water from the atmosphere to the land and oceans and back to the atmosphere (Figure 18.3). Table 18.1 lists the relative amounts of water in the major storage compartments of the cycle. Notice that more than 97% of Earth’s water is in the oceans; the next largest storage compartment, the ice caps and glaciers, ac- counts for another 2%. Together, these sources account for more than 99% of the total water, and both are generally unsuitable for human use because of salinity (seawater) and location (ice caps and glaciers). Only about 0.001% of the total water on Earth is in the atmosphere at any one time. However, this relatively small amount of wa- ter in the global water cycle, with an average atmosphereresidence time of only about nine days, produces all our freshwater resources through the process of precipitation. Water can be found in liquid, solid, or gaseous form at a number of locations at or near Earth’s surface. De- pending on the specific location, the water’s residence time may vary from a few days to many thousands of years (see Table 18.1). However, as already mentioned, more than 99% of Earth’s water in its natural state is unavailable or unsuitable for beneficial human use. Thus, the amount of water for which all the people, plants, and animals on Earth compete is much less than 1% of the total.

As the world’s population and industrial production of goods increase, the use of water will also accelerate. The aver- age global per capita use of water (water footprint from 1996 to 2005) is shown in Figure 18.4. The lowest use of water per person is mostly in Central Africa and Asia, while high per capita use is mostly in North America, central South America, northern Africa, and some European countries.8

Compared with other resources, water is used in very large quantities. In recent years, the total mass (or weight) of water used on Earth per year has been approximate- ly 1,000 times the world’s total production of minerals, including petroleum, coal, metal ores, and nonmetals.

Where it is abundant and readily available, water is gener- ally a very inexpensive resource. In places where it is not abundant, such as the southwestern United States, the cost of water has been kept artificially low by government subsidies and programs.

Because the quantity and quality of water available at any particular time are highly variable, water shortages have occurred, and they will probably occur with increas- ing frequency, sometimes causing serious economic dis- ruption and human suffering.6,7 In the Middle East and northern Africa, scarce water has led to harsh exchanges and threats between countries and could even lead to war. The U.S. Water Resources Council estimates that water use in the United States by the year 2020 may exceed sur- face-water resources by 13%.6,7 Therefore, an important question is: How can we best manage our water resources, use, and treatment to maintain adequate supplies?

Groundwater and River/Stream Flow

Before moving on to issues of water supply and manage- ment, we introduce groundwater and surface water and the terms used in discussing them. You will need to be familiarwith this terminology to understand many environmental issues, problems, and solutions.

The term groundwater usually refers to the water be- low the water table, where saturated conditions exist. The upper surface of the groundwater is called the water table.

Rain that falls on the land evaporates, runs off the surface, or moves below the surface and is transported underground. Locations where surface waters move into (infiltrate) the ground are known as recharge zones. Places where groundwater flows or seeps out at the surface, such as springs, are known as discharge zones or discharge points.

Water that moves into the ground from the surface first seeps through pore spaces (empty spaces between soil particles or rock fractures) in the soil and rock known as the vadose zone. This area is seldom saturated (not all pore spaces are filled with water). The water then enters the groundwater system, which is saturated (all of its pore spaces are filled with water).

An aquifer is an underground zone or body of earth material from which groundwater can be obtained (from a well) at a useful rate. Loose gravel and sand with lots of pore space between grains and rocks or many open fractures generally make good aquifers. Groundwater in aquifers usually moves slowly at rates of centimeters or meters per day. When water is pumped from an aquifer, the water table is depressed around the well, forming a cone of depression. Figure 18.5 shows the major features of a groundwater and surface-water system.

Streams may be classified as effluent or influent. In an ef- fluent stream, the flow is maintained during the dry season by groundwater seepage into the stream channel from the subsurface. A stream that flows all year is called a perennial stream. Most perennial streams flow all year because they constantly receive groundwater to sustain flow. An influent stream is entirely above the water table and flows only in di- rect response to precipitation. Water from an influent stream seeps down into the subsurface. An influent stream is called an ephemeral stream because it doesn’t flow all year.

A given stream may have reaches (unspecified lengths of stream) that are perennial and other reaches that are ephemeral. It may also have reaches, known as intermit- tent, that have a combination of influent and effluent flow varying with the time of year. For example, streams flow- ing from the mountains to the sea in southern California often have reaches in the mountains that are perennial, supporting populations of trout or endangered southern steelhead, and lower intermittent reaches that transition to ephemeral reaches. At the coast, these streams may re- ceive fresh or salty groundwater and tidal flow from the ocean to become a perennial lagoon.

Interactions between Surface Water and Groundwater

Surface water and groundwater interact in many ways and should be considered part of the same resource. Nearly all natural surface-water environments, such as rivers and lakes, as well as human-made water environments, such as reser- voirs, have strong linkages with groundwater. For example, pumping groundwater from wells may reduce stream flow, lower lake levels, or change the quality of surface water.

Reducing effluent stream flow by lowering the ground- water level may change a perennial stream into an inter- mittent influent stream. Similarly, withdrawing surface water by diverting it from streams and rivers can deplete groundwater or change its quality. Diverting surface waters that recharge groundwaters may increase concentrations of dissolved chemicals in the groundwater because dissolved chemicals in the groundwater will no longer be diluted by infiltrated surface water. Finally, pollution of groundwater may result in polluted surface water, and vice versa.9

Selected interactions between surface water and groundwater in a semiarid urban and agricultural environ- ment are shown in Figure 18.6. Urban and agricultural runoff increases the volume of water in the reservoir. Pump- ing groundwater for agricultural and urban uses lowers the groundwater level. The quality of surface water and ground- water is reduced by urban and agricultural runoff, which adds nutrients from fertilizers, oil from roads, and nutrients from treated wastewaters to streams and groundwater.

18.2 Water Resources

The common sources of water are surface water and ground- water. Additional sources are desalination and treated waste- water. Conservation of water is also a source of water. Which sources are used at a particular place depends on factors such as location, water quality, water availability, technology available, water demand, and in some cases preferences.

Surface Runoff

The water supply at any particular point on the land sur- face depends on several factors in the hydrologic cycle, including the rates of precipitation, evaporation, tran- spiration (water in vapor form that directly enters the atmosphere from plants through pores in leaves and stems), stream flow, and subsurface flow. A concept use- ful in understanding water supply is the water budget (Figure 18.7). A water budget balances the inputs, outputs, and storage of water in a system such that water inflow mi- nus outflow equals the change in water storage.6 Water sys- tems include lakes, rivers, or aquifers. Simple annual water budgets (precipitation – evaporation 5 runoff) for North America and other continents are shown in Table 18.2. The total average annual water yield (runoff) from Earth’s rivers is approximately 47,000 km3 (1.2 3 1016 gal), but its distribution is far from uniform (see Table 18.2). Some runoff occurs in relatively uninhabited regions, such as Ant- arctica, which produces about 5% of Earth’s total runoff.

South America, which includes the relatively uninhabited Amazon basin, provides about 25% of Earth’s total runoff. Total runoff in North America is about two-thirds that of South America. Unfortunately, much of the North Ameri- can runoff occurs in sparsely settled or uninhabited regions, particularly in the northern parts of Canada and Alaska.

In developing water budgets for water resources management, it is useful to consider annual precipitation and runoff patterns. Potential problems with water sup- ply can be predicted in areas where average precipitation and runoff are relatively low, such as the arid and semi- arid parts of the southwestern and Great Plains regions of the United States. Surface-water supply can never be as high as the average annual runoff because not all runoff can be successfully stored, due to evaporative losses from river channels, ponds, lakes, and reservoirs. Water short- ages are common in areas that have naturally low precipi- tation and runoff, coupled with strong evaporation. In such areas, rigorous conservation practices are necessary to help ensure an adequate supply of water.6,7

Groundwater Resources

Nearly half the people in the United States use ground- water as a primary source of drinking water. It accounts for approximately 20% of all water used. Fortunately, the total amount of groundwater available in the United States is enormous. In the contiguous United States, the amount of shallow groundwater within 0.8 km (about 0.5 mi) of the surface is estimated at 125,000 to 224,000 km3 (3.3 3 1016 to 5.9 3 1016 gal). To put this in perspective, the lower estimate of the amount of shallow groundwa- ter is about equal to the total discharge of the Mississippi River during the last 200 years. However, the high cost of pumping limits the total amount of groundwater that can be economically recovered.6,7

Groundwater Overdraft:

In many parts of the country, groundwater withdrawal from wells exceeds natural inflow. In such cases of overdraft, we can think of water as a nonrenewable resource that is be- ing mined. This can lead to a variety of problems, including damage to river ecosystems and land subsidence. Groundwa- ter overdraft is a serious problem in the Texas–Oklahoma– High Plains area (which includes much of Kansas and Nebraska and parts of other states), as well as in California, Arizona, Nevada, New Mexico, and isolated areas of Loui- siana, Mississippi, Arkansas, and the South Atlantic region.

In the Texas–Oklahoma–High Plains area, the over- draft amount per year is approximately equal to6the natural flow of the Colorado River for the same period. The Ogal- lala Aquifer (also called the High Plains Aquifer), which is composed of water-bearing sands and gravels that underlie an area of about 400,000 km2 from South Dakota into Tex- as, is the main groundwater resource in this area. Although the aquifer holds a tremendous amount of groundwater, it is being used in some areas at a rate up to 20 times higher than the rate at which it is being naturally replaced. As a result, the water table in many parts of the aquifer has de- clined in recent years (Figure 18.8), causing yields from wells to decrease and energy costs for pumping the water to rise. The most severe water depletion problems in the Ogal- lala Aquifer today are in locations where irrigation was first used in the 1940s. There is concern that eventually a signifi- cant portion of land now being irrigated will be returned to dryland farming as the resource is used up.

Some towns and cities in the High Plains are also start- ing to have water supply problems. Along the Platte River in northern Kansas there is still plenty of water, and ground- water levels are high (Figure 18.8). Farther south, in south- west Kansas and the panhandle in western Texas, where water levels have declined the most, supplies may last only another decade or so. In Ulysses, Kansas (population 6,000), and Lubbock, Texas (population 200,000), the situation is already getting serious. South of Ulysses, Lower Cimarron Springs, which was a famous water hole along a dry part of the Santa Fe Trail, dried up decades ago due to pumping groundwater. It was a symptom of what was coming. Both Ulysses and Lubbock are now facing water shortages and will need to spend millions of dollars to find alternative sources.

Water Reuse as a Water Resource

Water recycling and reuse, in locations where water is be- coming scarce, is a growing source of water for both urban areas and agriculture. From Florida to California, numer- ous communities reuse treated wastewater for a variety of noncontact uses. In some more limited cases, treated wastewater is highly treated by natural flow through the ground and high-technology filtration to reclaim water for all desired uses, including human consumption. For example, Singapore (see the opening case study) treats all wastewater, and it is used again. We will return to wastewa- ter treatment and water reuse in Chapter 19.

Water Conservation as a Water Source

When we conserve water, we save water for other uses. Thus, conservation may be considered a water resource. For example, when an agricultural operation saves water through improved irrigation, the saved water may be made available for urban uses or use by ecosystems. We will dis- cuss water conservation as a major subject in Section 18.4.

Desalination as a Water Resource

Seawater is about 3.5% salt; that means each cubic meter of seawater contains about 40 kg (88 lb) of salt. Desalination, a technology that removes salt from water, is being used at several hundred plants around the world to produce water with reduced salt. To be used as a freshwater resource, the salt content must be reduced to about 0.05%. Large desalina- tion plants produce 20,000–30,000m3 (about 5–8 million gal) of water per day. Today, more than 15,000 desalination plants in over 100 countries are in operation; improving technology is significantly lowering the cost of desalination.

Even so, desalinated water costs several times as much as traditional water supplies in the United States. Desalinated water has a place value, which means that the price rises quickly with the transport distance and the cost of moving water from the plant. Because the various processes that re- move the salt require large amounts of energy, the cost of the water is also tied to ever-increasing energy costs. For these reasons, desalination will remain an expensive process, used only when alternative water sources are not available.

Desalination also has environmental impacts. Discharge of very salty water from a desalination plant into another body of water, such as a bay, may locally increase salinity and kill some plants and animals. The discharge from desalina- tion plants may also cause wide fluctuations in the salt con- tent of local environments, which may damage ecosystems.

18.3 Water Use

In discussing water use, it is important to distinguish be- tween off-stream and in-stream uses. Off-stream use refers to water removed from its source (such as a river or reservoir) for use. Much of this water is returned to the source after use; for example, the water used to cool industrial processes may go to cooling ponds and then be discharged to a river, lake, or reservoir. Consumptive use is an off-stream use in which water is consumed by plants and animals or used in indus- trial processes. The water enters human tissue or products or evaporates during use and is not returned to its source.

In-stream use includes the use of rivers for naviga- tion, hydroelectric power generation, fish and wildlife habitats, and recreation. These multiple uses usually cre- ate controversy because each requires different conditions. For example, fish and wildlife require certain water lev- els and flow rates for maximum biological productivity. These levels and rates will differ from those needed for hydroelectric power generation, which requires large fluc- tuations in discharges to match power needs. Similarly, in- stream uses of water for fish and wildlife will likely conflict with requirements for shipping and boating. Figure 18.9 demonstrates some of these conflicting demands on a graph that shows optimal discharge for various uses throughout the year. In-stream water use for navigation is optimal at a constant fairly high discharge. Some fish, however, prefer higher flows in the spring for spawning.6,7

One problem for off-stream use is how much water can be removed from a stream or river without damag- ing the stream’s ecosystem. This is an issue in the Pacific Northwest, where fish, such as steelhead trout and salm- on, are on the decline partly because diversions for agri- cultural, urban, and other uses have reduced stream flow to the point where fish habitats are damaged.

The Aral Sea in Kazakhstan and Uzbekistan provides a wake-up call regarding the environmental damage that can be caused by diverting water for agriculture. Diverting water from the two rivers that flow into the Aral Sea has transformed one of the larg- est bodies of inland water in the world from a vibrant ecosystem into a dying sea. The present shoreline is surround- ed by thousands of square kilometers of salt flats that formed as the sea’s sur- face area shrank about 90% in volume in the past 50 years (Figure 18.10). The volume of the sea was reduced by about 70%, and the salt content increased to more than twice that of seawater, causing fish kills, including sturgeon, an important component of the economy. Dust raised by winds from the dry salt flats is producing a regional air-pollution problem, and the climate in the region has changed as the moderating effect of the sea has been reduced. Winters have grown colder and summers warmer. Fishing centers, such as Muynak in the south and Aralsk to the north that were once on the shore of the sea, are now many kilometers inland (Figure 18.11). Loss of fishing, along with a decline in tourism, has damaged the local economy. 4,10

Restoration of the small northern port of the Aral Sea is ongoing. In 2005 a low, long dam was constructed across the lakebed just south of where the Syr Darya River enters the lake, and another dam further north is scheduled for completion in 2013. Conservation of water and the con- struction of the dam are producing and will continue to produce dramatic improvements to the northern port of the lake, and some fishing is returning there. The future of the lake has improved, but great concern remains.4,10

Transport of Water

In many parts of the world, demands are being made on rivers to supply water to agricultural and urban areas. This is not a new trend—ancient civilizations, including the Romans and Native Americans, constructed canals and aqueducts to transport water from distant rivers to where it was needed. In our modern civilization, as in the past, water is often moved long distances from areas with abundant rainfall or snow to areas of high use (usually agricultural areas). For instance, in California, two-thirds of the state’s runoff occurs north of San Francisco, where there is a surplus of water. However, two-thirds of the water use in California occurs south of San Francisco, where three-fourths of the people in the state live and there is a deficit of water. In recent years, canals of the California Water Project have moved great quantities of water from the northern to the southern part of the state, mostly for agricultural uses, but increasingly for urban uses as well.

On the opposite coast, New York City has imported water from nearby areas for more than 100 years. Wa- ter use and supply in New York City show a repeating pattern. Originally, local groundwater, streams, and the Hudson River itself were used. However, as the popula- tion increased and the land was paved over, surface waters were diverted to the sea rather than percolating into the soil to replenish groundwater. Furthermore, what water did infiltrate the soil was polluted by urban runoff. Water needs in New York exceeded local supply, and in 1842 the first large dam was built.

As the city rapidly expanded from Manhattan to Long Island, water needs increased. The shallow aquifers of Long Island were at first a source of drinking water, but this water was used faster than the infiltration of rainfall could replenish it. At the same time, the groundwater be- came contaminated with urban and agricultural pollut- ants and from saltwater seeping in underground from the ocean. (The pollution of Long Island groundwater is ex- plored in more depth in the next chapter.) Further expan- sion of the population created the same pattern: initial use of groundwater, pollution, salinization, and overuse of the resource. A larger dam was built in 1900 about 50 km (30 mi) north of New York City at Croton-on-Hudson (Fig- ure 18.12), and later new, larger dams were built farther and farther upstate in forested areas.

From a broader perspective, the cost of obtaining water for large urban centers from far-off sources, along with competition for available water from other sources and users, will eventually place an upper limit on the wa- ter supply of New York City. As with other resources, as the water supply shrinks and demand for water rises, so does the price. As shortages develop, stronger conserva- tion measures are implemented, and the cost of water in- creases. If the price goes high enough, costlier sources may be developed—for example, pumping from deeper wells or desalinating.

Transfer of Water: Real and Virtual

Here we consider transfer of water to be different from transport of water in canals and pipes discussed above. Water has been transferred long distances in containers for hundreds of years—for example, water bags on camels crossed the deserts in ancient caravans. Ice has also been harvested from frozen lakes, rivers, and glaciers (and still is) to be sold. Water stored in crops has also been used throughout human history, and those crops may be used in a place far away from where they were grown.

Real Water

The transfer of water through its export in plastic and glass bottles grew very rapidly beginning in 1960, increas- ing from about 5 billion liters in 1960 to 27 billion liters in 2000. Bottled water costs about 1,000 to 5,000 times more than tap water. A major complaint is that plastic wa- ter bottles are discarded routinely by users, a practice that pollutes the environment. When recycled, plastic bottles are a resource for other plastic production. (Typically, only about one-third are recycled.) Some universities and other places are discouraging bottled water by providing free dispensing units of purified water that people can use to fill their water bottles.4

Some people believe tap water is less pure than bottled water or take exception to the common practice of adding fluoride to municipal water as a means of reducing dental cavities. They believe that bottled water is safer (even pro- viding a health benefit) than tap water and better tasting. The taste of chlorine in some tap water is a major reason people turned to bottled water. Depending on your loca- tion and local water supply, bottled water may be better tasting. However, it is not always safer.4

Bottled water is very useful following emergencies such as floods and earthquakes when local water supplies may be damaged or polluted. It may be stored with oth- er emergency supplies to be quickly taken to where it is needed. 4

Virtual Water

Virtual water is water embodied in goods and crops. It is measured as the volume of virtual water imported or exported to other regions or countries.

It is useful to consider the amount of water necessary to produce a product, such as an automobile, or a crop, such as rice.11–14 This content is measured at the place where the product is produced or the crop is grown.12

The amount of water necessary to produce crops and animals may be surprisingly large and variable. A few years ago, the question of how much water is required to produce a cup of coffee was asked. The answer is not trivial. Coffee is an important crop for many countries and the major social drink in much of the world. Many a romance has been initiated with the question, “Would you like a cup of coffee?”

How much water is necessary to produce a cup of coffee requires knowing how much water is necessary to produce the coffee berries (that contain the bean) and the roasted coffee. The question is complicated by the fact that water used to raise coffee varies from location to lo- cation, as does the yield of berries. Much of the water in coffee-growing areas is free; it comes from rain. However, that doesn’t mean the water has no value. People are usu- ally surprised to learn that it takes about 140 L (40 gal) of water to produce one cup of coffee. The amount of water that is needed to produce a ton of a crop varies from a low of about 175 m3 for sugarcane to 1,300 m3 for wheat, 3,400 m3 for white rice, and 21,000 m3 for roasted coffee. For the meat we eat, the amount per ton is 3,900 m3 for chicken, 4,800 m3 for pork, and 15,500 m3 for beef.12

The United States produces food that is exported around the world (as discussed in Chapter 11). As a result, people consuming imported U.S. crops in western Europe directly affect the regional water resources of the United States. Similarly, our consumption of imported foods— such as cantaloupes grown in Mexico or blueberries in Chile—affects the regional water supply and groundwater resources of the countries that grew and exported them.

The amount of water required to produce a crop of domestic animals is useful in water resource planning from the local to global scale. A country with an arid cli- mate and restricted water resources can choose between developing those resources for agriculture or for other water uses—for example, to support wetland ecosystems or a growing human population. Since the average global amount of water necessary to produce a ton of white rice is about 3,400 m3 (nearly 900,000 gal), growing rice in countries with abundant water resources makes sense. For countries with a more arid environment, it might be prudent to import rice and save local and regional water resources for other purposes. Jordan, for example, imports about 7 billion m3 of water per year by importing foods that require a lot of water to produce. As a result, Jordan withdraws only about 1 billion m3 of water per year from its own water resources. Egypt, on the other hand, has the Nile River and imports only about one-third as much water stored in food and goods it imports as it withdraws from its own domestic supply. Egypt has a goal of water independence and is much less dependent on water im- ported in food and goods (often called virtual water with units in volume of water per year).12

Another way to think of this is that Jordon derives a higher percentage of its water needs (water to produce food and goods) from other countries than does Egypt. In the United States, California (with a need for more water resources in the future as its population increases) grows rice, and that uses a lot of water. If the United States imported more rice from countries with abundant water resources, the California water used to grow rice could be conserved for other uses.

Examination of global water resources and potential global water conservation is an important part of sustain- ing our water supply. For example, by trading virtual wa- ter, the international trade markets reduce agriculture’s global water use by about 5%.12 Figure 18.13 shows net virtual water budgets (balances) for major trades. The balance is determined by import minus export in km3 of virtual water, where 1 km3 is 109 (one billion) m3. For ex- ample, when the United States and Canada export wheat and other products to Mexico and eastern Europe, a lot of virtual water is exported, explaining the negative balance for the United States and Canada, both of which export more virtual water than they import. In contrast, coun- tries that import a lot of food and other products have a positive balance because their imports of virtual water exceed their exports.

The concept of virtual water has three major uses for society and the world:14

• It promotes efficient use of water from a local to global scale. Trading virtual water can conserve global water resources by producing products that require a lot of water in places where water is abundant and can be efficiently used. When those products are exported to places where water is scarce or difficult to use efficiently, water is conserved and real water savings are realized.

• It offers countries and regions an opportunity to enjoy greater water security. Virtual water can be thought of as an alternative, additional water supply that, from a political point of view, can increase security and help solve geopolitical problems between nations.

• It helps us to understand relationships between water- consumption patterns and their environmental, eco- nomic, and political impacts. Knowing the virtual water content of the products we produce and where and how they are produced increases our awareness of water de- mand and ways to realize water savings.

Water Footprint

A water footprint is the total volume of fresh water used to produce the products and services used by an individual, community, country, or region. The footprint is a multi- dimensional indicator of the use of water resources (all water use from local and regional supply to virtual water). It is generally expressed as the volume of water used per year and is divided into three components:12

• Precipitation that contributes to water stored in soils. This is the water consumed by crops (consumptive use) that evaporates or transpires from plants we cultivate.

• Surface and groundwater. This is used to produce our goods and services (consumptive use).

• Water polluted by the production of goods and services and rendered not available for other uses. The volume water use has been estimated by calculating the amount of water required to dilute pollutants to the point that the water quality is acceptable and consistent with wa- ter-quality standards.

The concept of virtual water, when linked to the wa- ter footprint, provides a new tool to better manage water resources sustainably. An objective is to work toward wa- ter conservation and, ultimately, water self-sufficiency.

Some Trends in Water Use

Trends in freshwater withdrawals and human population for the United States from 1950 to 2005 (the most re- cent data available) are shown in Figure 18.14. You can see that during that period, withdrawal of surface water far exceeded withdrawal of groundwater. In addition, withdrawals of both surface water for human uses and groundwater increased between 1950 and 1980, reaching a total maximum of approximately 375,000 million gal/ day. However, after 1980, water withdrawals decreased and leveled off. It is encouraging that water withdrawals decreased after 1980, while the U.S. population contin- ued to increase. This suggests that we have improved our water management and water conservation.

Trends in freshwater withdrawals by water-use cat- egories for the United States from 1950 to 2005 (most recent data available) are shown in Figure 18.15. Exami- nation of this graph suggests the following:

1. The major uses of water were for irrigation and the thermoelectric industry. Excluding thermoelectric use, agri- culture accounted for 65% of total withdrawals in 2005.

2. The use of water for irrigation by agriculture increased about 68% from 1950 to 1980. It decreased and leveled off from about 1985 to 2005, due in part to better

irrigation efficiency, crop type, and higher energy costs.

3. Water use by the thermoelectric industry decreased slightly, beginning in 1980, and has stabilized since 1985 due to recirculating water for cooling in closed- loop systems. During the same period, electrical genera- tion from power plants increased by more than 10 times.

4. Use of water for public and rural supplies continued to increase through the period 1950–2005, presumably due to the increase in human population.15,16

18.4 Water Conservation

Water conservation is the careful use and protection of water resources. It involves both the quantity of water used and its quality. Conservation is an important com- ponent of sustainable water use. Because the field of wa- ter conservation is changing rapidly, it is expected that a number of innovations will reduce the total withdrawals of water for various purposes, even though consumption will continue to increase.6,7

Agricultural Use—Suggestions

Improved irrigation (Figure 18.16) could reduce agricul- tural withdrawals by 20 to 30%. Because agriculture is the biggest water user, this would be a huge savings. Sugges- tions for agricultural conservation include the following:

• Price agricultural water to encourage conservation (subsidizing water encourages overuse).

• Use lined or covered canals that reduce seepage and evaporation.

• Use computer monitoring and schedule release of water for maximum efficiency.

• Integrate the use of surface water and groundwater to more effectively use the total resource. That is, irrigate with surplus surface water when it is abundant, and also use surplus surface water to recharge groundwater aqui- fers, using specially designed infiltration ponds or injec- tion wells. When surface water is in short supply, use more groundwater.

• Irrigate when evaporation is minimal, such as at night or in the early morning.

• Use improved irrigation systems, such as sprinklers or drip irrigation, which apply water to crops more effectively.

• Improve land preparation for water application—that is, improve the soil so that more water sinks in and less runs off. Where applicable, use mulch to help retain wa- ter around plants.

• Encourage the development of crops that require less water or are more salt-tolerant, so that less periodic flooding of irrigated land is necessary to remove accu- mulated salts in the soil.

Public Supply and Domestic Use

Domestic use of water accounts for only about 12% of total national water withdrawals. However, because public supply water use is concentrated in urban areas, it may pose major local problems in areas where water is periodi- cally or often in short supply. (See the opening case study about Singapore.)

The population of the United States continues to grow, and many urban areas in the United States are ex- periencing or will experience the impact of population growth on water supply. For example:

• Southern California, in particular San Diego and Los Angeles, is growing rapidly, and its water needs are quickly exceeding local supplies. As a result, the city of San Diego has negotiated with farmers to the east, in the Imperial Valley, to purchase water for urban areas. The city is also building desalination plants and consid- ering raising the height of dams so that more water can be stored for urban uses. Southern California has long imported water from the Sierra Nevada to the north. If climate change brings less snow and more rain, that supply may become more variable because snow melts slowly and thus serves as a water source for a longer time than rain, which quickly runs off. In the expectation of more rain than snow, plans for what is called the Inland Feeder Project include a series of large-diameter tunnels to quickly deliver large volumes of water from north- ern California to southern California during periods of rapid runoff. They will be used to fill local reservoirs and groundwater basins, providing water during dry periods and emergencies.

• In Denver, city officials, fearing future water shortages, are proposing strict conservation measures that include limits on water use for landscaping and the amount of grass that can be planted around new homes.

• Chicago, one of the fastest-growing urban areas in the United States, reports groundwater-depletion problems. The city is located on the shores of Lake Michigan, one of the largest sources of fresh water in the world. Water shortages in outlying urban areas may become apparent by 2020.

• Tampa, Florida, fearing shortages of fresh water because of its continuing growth, recently began operating a de- salination plant that produces approximately 25 million gallons of water daily.

• Atlanta, Georgia, another fast-growing urban area in the United States, expects increased demand on its wa- ter supplies as a result of growth and is exploring ways to meet that demand.

• New York City, which imports water from the upstate Catskill Mountains, periodically has water shortages during droughts. The city placed water restrictions on its more than 9 million citizens in 2002.

About 14 million m2 (million ft2) of lawn for homes and golf courses (land adjacent to fairways and greens) has been replaced with desert plants, saving about 160 million m3 (42 billion gal) of water per year.

What is clear from these examples is that while there is no shortage of water in the United States, there are lo- cal and regional shortages, particularly in large, growing urban areas in the semiarid western and southwestern part of the country.17

Most water in homes is used in the bathroom and for washing laundry and dishes. Domestic water use can be substantially reduced at a relatively small cost by the fol- lowing measures:

• In semiarid regions, replace lawns with decorative gravel and native plants.

• Use more efficient bathroom fixtures, such as low-flow toilets that use 1.6 gallons or less per flush (rather than the standard 5 gallons) and low-flow showerheads that still deliver sufficient water.

• Flush toilets only when really necessary. • Turn off water when not absolutely needed for washing,

brushing teeth, shaving, and so on.

• Fix all leaks quickly. Dripping pipes, faucets, toilets, or garden hoses waste water. A small drip can waste several liters per day; multiply this by millions of homes with a leak, and a large volume of water is lost.

• Purchase dishwashers and laundry machines that mini- mize water use.

• Take a long bath rather than a long shower.

• Don’t hose sidewalks and driveways; sweep them.

• Consider using gray water (from showers, bathtubs, sinks, and washing machines) to water vegetation. The gray water from laundry machines is easiest to use, as it can be easily diverted before entering a drain.

• Water lawns and plants in the early morning, late after- noon, or at night to reduce evaporation.

• Use drip irrigation and place water-holding mulch around garden plants.

• Plant drought-resistant vegetation that requires less water.

• Learn how to read the water meter to monitor for un- observed leaks and record your conservation successes.

• Use reclaimed water. (See the opening case study and A Closer Look 18.1.)

In addition, local water districts should encourage wa- ter pricing policies that make water use more expensive for those who exceed some baseline amount determined by the number of people in a home and the size of the property.

Industry and Manufacturing Use

Water conservation by industry can be improved. For instance, water use for steam generation of electricity could be reduced 25 to 30% by using cooling towers that require less or no water (as has often been done in the United States). Manufacturing and industry could curb water use by increasing in-plant treatment and recycling water and by developing new equipment and processes that require less water.6,7

18.5 Sustainability and Water Management

Because water is essential to sustain life and maintain ecological systems necessary for human survival, it plays important roles in ecosystem support, economic develop- ment, cultural values, and community well-being. Man- aging water use for sustainability is thus important in many ways.

Sustainable Water Use

From a supply and management perspective, sustainable water use can be defined as use of water resources in a way that allows society to develop and flourish for an indefi- nite future without degrading the various components of the hydrologic cycle or the ecological systems that depend on it. Some general criteria for water-use sustainability are as follows.4,18

• Develop enough water resources to maintain human health and well-being.

• Provide sufficient water resources to guarantee the health and maintenance of ecosystems.

• Ensure basic standards of water quality for the various users of water resources.

• Ensure that people do not damage or reduce the long- term renewability of water resources.

• Promote the use of water-efficient technology and practice.

• Gradually eliminate water-pricing policies that subsi- dize inefficient use of water.

The concept of sustainability, by definition, implies a long-term perspective. With groundwater resources, effec- tive management for sustainability requires an even lon- ger time frame than for other renewable resources. Surface waters, for example, may be replaced over a relatively short time, whereas replacement of groundwater may take place slowly over many years. The effects of pumping ground- water faster than it is being replenished—drying up of springs, weaker stream flow—may not be noticed until years after pumping begins. The long-term approach to sustainability with respect to groundwater is basically not to take out more than is going in, continuing to monitor input and to adjust output accordingly.19

Water Management

Maintaining a water supply is a complex issue that will become more difficult as demand for water increases in the coming years. The problem will be especially challeng- ing in the southwestern United States and other semiarid and arid parts of the world where water is in short supply or soon will be. Options for minimizing problems include finding alternative water supplies and managing existing supplies better. In some areas, finding new supplies is so unlikely that people are seriously considering some liter- ally far-fetched water sources, such as towing icebergs to coastal regions where fresh water is needed. It seems ap- parent that water will become much more expensive in the future, and if the price is right, many innovative pro- grams are possible.

A number of municipalities are using the variable- water-source approach. The city of Santa Barbara, Califor- nia, for example, has developed a variable-water-source approach that uses several interrelated measures to meet present and future demand. Details of the plan include importing state water, developing new sources, using re- claimed water, and instituting a permanent conservation program. In addition, there is a desalination plant near the ocean that is in long-term storage but could be brought online if needed. In essence, this seaside community has developed a master water plan.

Water Management and the Environment

Many agricultural and urban areas depend on water de- livered from nearby (and in some cases not-so-nearby) sources. Delivering the water requires a system for water storage and routing by way of canals and aqueducts from reservoirs. As a result, dams are built, wetlands may be modified, and rivers may be channelized to help control flooding—all of which usually generates a good deal of controversy.

The days of developing large projects in the United States without environmental and public review have passed. Resolving water development issues now involves input from a variety of government and public groups that may have very different needs and concerns. These range from agricultural groups that see water development as critical for their livelihood to groups primarily concerned with wildlife and wilderness preservation, wetlands, dams, channelization, and flooding.

18.6 Wetlands

Wetlands is a comprehensive term for landforms such as salt marshes, swamps, bogs, prairie potholes, and vernal pools (shallow depressions that seasonally hold water). Their common feature is that they are wet at least part of the year and, as a result, have a particular type of vegeta- tion and soil. Figure 18.18 shows several types of wetlands.

Wetlands may be defined as areas inundated by water or saturated to a depth of a few centimeters for at least a few days per year. Three major characteristics in identify- ing wetlands are hydrology, or wetness; type of vegetation; and type of soil. Of these characteristics, hydrology is of- ten the most difficult to define because some freshwater wetlands may be wet for only a few days a year. The dura- tion of inundation or saturation must be sufficient for the development of wetland soils, which are characterized by poor drainage and lack of oxygen, and for the growth of specially adapted vegetation.

Natural Service Functions of Wetlands

Wetland ecosystems may serve a variety of natural service functions for other ecosystems and for people, including the following:

• Freshwater wetlands are a natural sponge for water. Dur- ing high river flow, they store water, reducing down- stream flooding. Following a flood, they slowly release the stored water, nourishing low flows.

• Many freshwater wetlands are important as areas of groundwater recharge (water seeps into the ground from a prairie pothole, for instance) or discharge (water seeps out of the ground in a marsh fed by springs).

• Wetlands are one of the primary nursery grounds for fish, shellfish, aquatic birds, and other animals. It has been estimated that as many as 45% of endangered animals and 26% of endangered plants either live in wetlands or depend on them for their continued existence.20

• Inland and coastal wetlands are extensively used by migrating birds.

• Wetlands are natural filters that help purify water; plants in wetlands trap sediment and toxins.

• Wetlands are often highly productive and are places where many nutrients and chemicals are naturally cycled.

• Coastal wetlands buffer inland areas from storms and high waves.

• Wetlands are an important storage site for organic car- bon; carbon is stored in living plants, animals, and rich organic soils.

• Wetlands are aesthetically pleasing to people.

Freshwater wetlands are threatened in many areas. An estimated 1% of the nation’s total wetlands are lost every two years, and freshwater wetlands account for 95% of this loss. Wetlands such as prairie potholes in the midwestern United States and vernal pools in southern California are particularly vulnerable because their hydrology is poorly understood and establishing their wetland status is more difficult.21 Over the past 200 years, over 50% of the wet- lands in the United States have disappeared because they have been diked or drained for agriculture or filled for urban or industrial development. Perhaps as much as 90% of the freshwater wetlands have disappeared.4

Although most coastal marshes are now protected in the United States, the extensive salt marshes at many of the na- tion’s major estuaries, where rivers entering the ocean wid- en and are influenced by tides, have been modified or lost. These include deltas and estuaries of major rivers, such as the Mississippi, Potomac, Susquehanna (Chesapeake Bay), Delaware, and Hudson. The San Francisco Bay estuary, considered the estuary most modified by human activity in the United States today, has lost nearly all its marshlands to leveeing and filling. Modifications result not only from fill- ing and diking but also from loss of water. The freshwater inflow has been reduced by more than 50%, dramatically changing the hydrology of the bay in terms of flow charac- teristics and water quality. As a result of the modifications, the plants and animals in the bay have changed as habitats for fish and wildfowl have been eliminated.22

The delta of the Mississippi River includes some of the major coastal wetlands of the United States and the world. Historically, coastal wetlands of southern Louisi- ana were maintained by the flooding of the Mississippi River, which delivered water, mineral sediments, and nu- trients to the coastal environment. The mineral sediments contributed to the vertical accretion (building up) of wet- lands. The nutrients enhanced growth of wetland plants, whose coarse, organic components (leaves, stems, roots) also accreted. These accretion processes counter processes that naturally submerge the wetlands, including a slow rise in sea level and subsidence (sinking) due to compac- tion. If the rates of submergence of wetlands exceed the rates of accretion, then the area of open water increases, and the wetlands are reduced.

Today, levees line the lower Mississippi River, con- fining the river and directing floodwaters, mineral sedi- ments, and nutrients into the Gulf of Mexico, rather than into the coastal wetlands. Deprived of water, sediments, and nutrients, in a coastal environment where the sea level is rising, the coastal wetlands are being lost. The global sea level is rising about 3 mm/ yr (0.12 in/yr) as a result of processes that began at the end of the last ice age: the melting of glaciers and expansion of ocean waters as they warm. Regional and local subsidence in the Mississippi delta region combines with the global rise in sea level to produce a relative sea level rise of about 12 mm/yr. To keep the coastal wetlands from declining, the rate of ver- tical accretion would thus need to be about 13 mm/yr.

Currently, natural vertical accretion is only about 5 to 8 mm/yr.23

Most people agree that wetlands are valuable and pro- ductive for fish and wildlife. But wetlands are also valued as potential lands for agriculture, mineral exploitation, and building sites. Wetland management is drastically in need of new incentives for private landowners (who own the majority of several types of wetlands in the United States) to preserve wetlands rather than fill them in and develop the land.21 Management strategies must also include careful planning to maintain the water quantity and quality necessary for wetlands to flourish or at least survive. Unfortunately, although laws govern the filling and draining of wetlands, no national wetland policy for the United States is in place. Debate continues as to what constitutes a wetland and how property owners should be compensated for preserving wetlands.20,24

Restoration of Wetlands

A related management issue is wetlands restoration. A number of projects have attempted to restore wetlands, with varied success. The most important factor to be con- sidered in most freshwater marsh restoration projects is the availability of water. If water is present, wetland soils and vegetation will likely develop. The restoration of salt marshes is more difficult because of the complex interac- tions among the hydrology, sediment supply, and vegeta- tion that allow salt marshes to develop. Careful studies of relationships between the movement of sediment and the flow of water in salt marshes are providing information crucial to restoration, which makes successful reestablish- ment of salt-marsh vegetation more likely. The restoration of wetlands has become an important topic in the United States because of the mitigation requirement related to en- vironmental impact analysis, as set forth in the Nation- al Environmental Policy Act of 1969. According to this requirement, if wetlands are destroyed or damaged by a particular project, the developer must obtain or create ad- ditional wetlands at another site to compensate.20 Unfortu- nately, the state of the art of restoration is not adequate to ensure that specific restoration projects will be successful.25

Constructing wetlands (an example of ecological engineering) for the purpose of cleaning up agricultural runoff is an idea being implemented in areas with exten- sive agricultural runoff. Wetlands have a natural ability to remove excess nutrients, break down pollutants, and cleanse water. A series of wetlands are being created in Florida to remove nutrients (especially phosphorus) from agricultural runoff and thus help restore the Everglades to more natural functioning. The Everglades are a huge wetland ecosystem that functions as a wide, shallow riv- er flowing south through southern Florida to the ocean. Fertilizers applied to farm fields north of the Everglades make their way directly into the Everglades by way of agricultural runoff, disrupting the ecosystem. (Phospho- rus enrichment causes undesired changes in water quality and aquatic vegetation; see the discussion of eutrophica- tion in the next chapter.) The human-made wetlands are designed to intercept and hold the nutrients so that they do not enter and damage the Everglades.26

In southern Louisiana, restoration of coastal wetlands includes the application of treated wastewater, which adds nutrients, nitrogen, and phosphorus to accelerate plant growth. As plants grow, organic debris (stems, leaves, and so forth) builds up on the bottom and causes the wetland to grow vertically. This growth helps offset a relative rise in sea level, maintaining and restoring the wetland.23

18.7 Dams and the Environment

Dams and their reservoirs generally are designed to be multifunctional. People who propose the construction of dams and reservoirs point out that they may be used for recreational activities and for generating electricity, as well as for providing flood control and ensuring a more stable water supply. However, it is often difficult to recon- cile these various uses at a given site. For example, water demands for agriculture might be high during the sum- mer, resulting in a drawdown of the reservoir and leav- ing extensive mudflats or an exposed bank area subject to erosion. Recreational users find the low water level and the mudflats aesthetically displeasing. Also, high demand for water may cause quick changes in lake levels, which could interfere with wildlife (particularly fish) by dam- aging or limiting spawning opportunities. Another con- sideration is that dams and reservoirs tend to give a false sense of security to those living below them. Dams may fail. Flooding may originate from tributary rivers that en- ter the main river below a dam, and dams cannot be guar- anteed to protect people against floods larger than those for which they have been designed.

The environmental effects of dams are considerable and include the following:

• Loss of land, cultural resources, and biological resources in the reservoir area.

• Potentially serious flood hazard, should larger dams and reservoirs fail.

• Storage behind the dam of sediment that would other- wise move downstream to coastal areas, where it would supply sand to beaches. The trapped sediment also reduces water storage capacity, limiting the life of the reservoir.

• Downstream changes in hydrology and in sediment transport that change the entire river environment and the organisms that live there.

• Fragmentation of ecosystems above and below a dam.

• Restricted movement upstream and downstream of organic material, nutrients, and aquatic organisms.

For a variety of reasons—including displacement of people, loss of land, loss of wildlife, and permanent, ad- verse changes to river ecology and hydrology—many peo- ple today are vehemently opposed to turning remaining rivers into a series of reservoirs with dams. In the United States, several dams have been removed, and the disman- tling of others is being considered because of the envi- ronmental damage they are causing. In contrast, China recently constructed the world’s largest dam. The Three Gorges Dam, on the Yangtze River (Figure 18.19), has drowned cities, farm fields, important archaeological sites, and highly scenic gorges and has displaced approximately 2 million people from their homes. In the river, rare fresh- water dolphins called Baiji (by legend, the reincarnated 3rd-century Chinese princess who symbolizes peace, pros- perity, and love) are functionally extinct. A few may still exist, but scientists believe recovery is not possible. On land, habitats were fragmented and isolated as mountain- tops became islands in the reservoir.

The dam, which is approximately 185 m (607 ft) high and more than 1.6 km wide (1 mi), produces a reservoir nearly 600 km (373 mi) long. Raw sewage and industrial pollutants that are discharged into the river are deposited in the reservoir, and there is concern that the reservoir will become seriously polluted. Since the reservoir has been filling for several years, the banks are becoming saturated, increasing the landslide hazard. Large ships make matters worse by generating waves that increase shoreline erosion and cause the rock slopes and shoreline homes to vibrate and shake. Some older homes are thought to be unsafe due to the landslide hazard that has evidently increased since the reservoir began filling. In addition, the Yangtze River has a high sediment load, and it is feared that dam- age to deep water shipping harbors will eventually occur at the upstream end of the reservoir, where sediments now being deposited are producing shallower water.

The dam may also mislead people living down- stream into thinking they are secure. Should the dam fail, downstream cities, such as Wushan, with a popula- tion of several million people, might be submerged, with catastrophic loss of life.27 The dam may also encourage further development in flood-prone areas, which will be damaged or lost if the dam and reservoir are unable to hold back floods in the future. If this happens, loss of property and life from flooding may be greater than if the dam had not been built. Contributing to this prob- lem is the dam’s location in a seismically active region where earthquakes and large landslides have been com- mon in the past.

A positive attribute of the giant dam and reservoir is its capacity to produce about 18,000 MW of electric- ity, the equivalent of about 18 large coal-burning power plants. As pointed out in earlier discussions, pollution from coal burning is a serious problem in China. Some of the dam’s opponents have pointed out, however, that a series of dams on tributaries to the Yangtze River could have produced similar electric power without causing en- vironmental damage to the main river.28

The Glen Canyon Dam on the Colorado River was completed in 1963. From a hydrologic viewpoint, the Colorado River has been changed by the dam. The river has been tamed. The higher flows have been reduced, the average flow has increased, and the flow changes often because of fluctuating needs to generate electrical power. Changing the hydrology of the river has also changed other aspects, including the rapids, the distribution of sediments that form sandbars (called beaches by rafters), and the vegetation near the water’s edge.29 The sandbars, valuable wildlife habitats, shrank in size and number fol- lowing construction of the dam because sediment that would have moved downstream to nourish them was trapped in the reservoir. All these changes affect the Grand Canyon, which is downstream from the dam. In an effort to restore part of the sand flow and maintain sandbars, releases from the dam are periodically increased to more closely match natural pre-dam flows.30,31 The higher flows have helped maintain sandbars by mobiliz- ing sand but cannot be expected to restore the river to pre-dam conditions.

If our present water-use practices continue, we will very likely need additional dams and reservoirs, and some existing dams will be heightened to increase water storage. However, there are few acceptable sites for new dams, and conflicts over the construction of additional dams and res- ervoirs are bound to occur. Water developers may view a canyon dam site as a resource for water storage, whereas others may view that canyon as a wilderness area and rec- reation site for future generations. The conflict is common because good dam sites are often sites of high-quality sce- nic landscape.

Dams also have an economic aspect: They are expen- sive to build and operate, and they are often constructed with federal tax dollars in the western United States, where they provide inexpensive subsidized water for agriculture. This has been a point of concern to some taxpayers in the eastern United States, who do not have the benefit of fed- erally subsidized water. Perhaps a different pricing struc- ture for water would encourage conservation, and fewer new dams and reservoirs would be needed.

Removal of Dams

Many dams in the United States have outlived their origi- nal purposes or design lives. These are generally small structures that now are viewed as a detriment to the ecological community of the river. The dams fragment river ecosystems by producing an upstream-of-dam en- vironment and a downstream environment. Often, the structure blocks upstream migration of threatened or endangered fish species (for example, salmon in the Pa- cific Northwest). The perceived solution is to remove the dam and restore the river’s more natural hydrology and ecological functions. However, removal must be carefully planned and executed to ensure that the removal doesn’t itself cause ecological problems, such as sudden release of an unacceptable amount of sediment to the river or con- taminated sediment.32

A large number of U.S. dams (mostly small ones) have been removed or are in the planning stages for removal. The Edwards Dam near Augusta, Maine, was dismantled in 1999, opening about 29 km (18 mi) of river habitat to migrating fish, including Atlantic salmon, striped bass, shad, alewives, and Atlantic sturgeon. The Kennebec Riv- er came back to life as millions of fish migrated upstream for the first time in 160 years.33

The Marmot Dam on the Sandy River in northwest Oregon was removed in 2007 (Figure 18.20). The dam was about 15 m (49 ft) high, 50 m (164 ft) wide, and was filled with 750,000 cubic3 of sand and gravel. The removal was a scientific experiment and provided useful information for future removal projects. Salmon again swim up the river and spawn and people are kayaking in stretches where the river hadn’t been run by a boat in almost 100 years.34

The Elwha and Glines Canyon Dams, constructed in the early 18th century on the Elwha River in Wash- ington State’s Puget Sound (Figure 18.21), are also being removed. As of 2011, the two dams had trapped about 18 million cu3 of sediment. Up to two-thirds of the sedi- ment consists of fine grains (clay, silt, sand), with the rest being gravel and cobbles. The dams keep sediment from reaching the sea and nourishing beaches. Denied sediment, beaches at the river’s mouth have eroded, caus- ing the loss of clam beds. Within two to three years after removal, about one-third of the stored sediment will be transported downstream to the sea.

By spring of 2012, the 33 m (108 ft) high Elwha Dam had been removed. The Elwha headwater is in Olympic National Park, and prior to the dam’s construc- tion, it supported large salmon and steelhead runs. De- nied access to almost their entire spawning habitat, fish populations there have declined greatly. Large runs of fish had also brought nutrients from the ocean to the river and landscape. Bears, birds, and other animals used to eat the salmon and transfer nutrients to the forest ecosystem. Without the salmon, both wildlife and forest suffer.

The largest of the two, the Glines Canyon Dam (about 70 m [230 ft] high), will be the highest dam ever removed.35 It is being removed in stages to minimize downstream im- pacts from the release of sediment. With the Elwah Dam now removed, the river flows freely for the first time in a century (some fish returned in 2012). When removal of the upstream Glines Canyon Dam is completed (expected by summer 2013), it is hoped that the ecosystem will further recover and that the fish will return in greater numbers.35,36

The perception of dams as permanent edifices, similar to the pyramids of Egypt, has clearly changed. What is learned from studying the removal of the Edwards Dam in Maine, the Marmot Dam in Oregon, and the Elwah and Glines Canyon Dams in Washington will be useful in planning other dam removal projects. The studies will also provide important case histories to evaluate ecological restoration of rivers after removal of dams. In sum, remov- ing dams is simple in concept, but it involves complex problems relating to sediment and water. It provides an opportunity to restore ecosystems, but with that opportu- nity comes responsibility.34

18.8 Global Water Shortage linked to Food Supply

As a capstone to this chapter, we present the hypothesis that we are facing a growing water shortage linked to our food supply. This is potentially a very serious problem. In the past few years, we have begun to realize that iso- lated water shortages are apparently indicators of a global pattern.37 At numerous locations on Earth, both surface water and groundwater are being stressed and depleted:

• Groundwater in the United States, China, India, Pakistan, Mexico, and many other countries is being mined (used faster than it is being renewed) and is, therefore, being depleted.

• Large bodies of water—for example, the Aral Sea—are drying up (see Figure 18.10).

• Large rivers, including the Colorado in the United States and the Yellow in China, do not deliver any wa- ter to the ocean in some seasons or years. Others, such as the Nile in Africa, have had their flow to the ocean greatly reduced.

• Water demand during the past half-century has tripled as the human population more than doubled. In the next half-century, the human population is expected to grow by another 2 to 3 billion. There is growing con- cern that there won’t be enough water to grow the food to feed the 8–9 billion people expected to inhabit the planet by the year 2050. Therefore, a food shortage linked to water resources seems a real possibility. The problem is that our increasing use of groundwater and surface water for irrigation has allowed for increased food production—mostly crops such as rice, corn, and soybeans. These same water resources are being deplet- ed, and as water shortages for an agricultural region oc- cur, food shortages may follow. Water is also linked to energy because irrigation water is often pumped from groundwater. As the cost of energy rises, so does the cost of food and the difficulty of purchasing food, especially in poor countries. This scenario in 2007–2008 resulted in a number of food riots in more than 30 countries, including Haiti, Mexico, and West Bengal.

• Serious drought in countries that grow much of the world’s grains, such as the United States, Canada, Russia, and India, will result in lower crop yields and higher prices. A 2012 drought in the midwestern United States caused a drop in corn yields that resulted in higher prices of meat. (Corn is a main component of livestock feed.) Similarly, a drought in West Texas in 2011 caused ponds and streams to go dry, forcing the sale of cattle at a low price to the rancher. One town in West Texas lost the reservoir that was its water supply and was forced to quickly build a pipeline to another area to obtain groundwater. Droughts are mostly natu- ral events caused by ocean circulation that causes high pressure to linger over regions, as was the case with the 2012 drought in the U.S. Midwest. There is some evi- dence that droughts are more intense with a warming planet. Drought is fairly common in West Texas, and ranchers have experienced droughts in past decades. However, the consequences to people, animals, and natural ecosystems from extreme droughts increase as demands grow for dwindling surface and groundwater supplies necessary to feed a growing population.

The way to avoid food shortages caused by wa- ter resource depletion is clear: We need to control hu- man population growth and conserve and sustain water resources. In this chapter, we have outlined a number of ways to conserve, manage, and sustain water. The good news is that a solution is possible—but it will take time, and we need to be proactive, taking steps now before sig- nificant food shortages develop. For all the reasons dis- cussed, one of the most important and potentially serious resource issues of the 21st century is water supply and management.

SUMMARY

• Water is a liquid with unique characteristics that have made life on Earth possible.

• Although it is one of the most abundant and impor- tant renewable resources on Earth, more than 99% of Earth’s water is unavailable or unsuitable for beneficial human use because of its salinity or location.

• The pattern of water supply and use at any particular point on the land surface involves interactions and link- ages among the biological, hydrological, and rock cycles. To evaluate a region’s water resources and use patterns, a water budget is developed to define the natural vari- ability and availability of water.

• It is expected that during the next several decades, the total water withdrawn from streams and groundwater in the United States will decrease slightly, but that the consumptive use will increase because of greater de- mands from our growing population and industry.

• Water withdrawn from streams competes with in- stream needs, such as maintaining fish and wildlife hab- itats and navigation, and may therefore cause conflicts.

• Groundwater use has led to a variety of environmen- tal problems, including loss of vegetation along water- courses and land subsidence.

• Because agriculture is the biggest user of water, conser- vation of water in agriculture has the most significant effect on sustainable water use. However, it is also im-

portant to practice water conservation at the personal level in our homes and to price water in a way that en- courages conservation and sustainability.

• There is a need for a new philosophy in water resource management that considers sustainability and uses cre- ative alternatives and variable sources. A master plan must include normal sources of surface water and groundwater, conservation programs, and use of re- claimed water.

• Development of water supplies and facilities to move water more efficiently may cause considerable environ- mental degradation; construction of dams and reservoirs should be considered carefully in light of potential en- vironmental impacts.

• Removal of dams as a way to reconnect river ecosystems is becoming more common.

• The concepts of virtual water and the water footprint are becoming important in managing water resources at the regional to global level.

• Wetlands serve a variety of functions at the ecosystem level that benefit other ecosystems and people.

• We are facing a growing global water shortage linked to the food supply.

• Water supply and management is one of the major re- source issues of the 21st century.

Botkin, D. B., & Keller, E. A. (2014). Environmental science: Earth as a living planet (9th ed.). Hoboken, NJ: John Wiley & Sons, Inc.