CHAPTER 9
WATER RESOURCES AND WATER POLLUTION
THINKING
Objectives
1.List six unique qualities of water. Explain the significance of these qualities for the role water plays in the environment.
2.Briefly describe the earth's water supply. Compare amounts of saltwater and freshwater. Compare amounts of frozen freshwater and water available for human use. Distinguish between surface water and groundwater. Describe how groundwater moves and is recharged. Summarize trends in water use since 1950.
3.Briefly describe three major water problems. Evaluate which of these problems is of most concern in the United States and the region where you live.
4.Evaluate increasing the water supply through use of dams and water transfer projects. Compare the advantages and disadvantages of increasing the water supply through use of groundwater, desalination, and cloud seeding.
5.State how much water is wasted. Briefly describe measures that can be taken to reduce water losses through irrigation, industry, and home use.
6.List eight common types of water pollutants and give an example of each. Distinguish between point and nonpoint sources of pollution. Summarize the availability of clean drinking water for human populations.
7.Draw an oxygen sag curve to illustrate what happens to dissolved oxygen levels in streams below points where degradable oxygen-demanding wastes are added.
8.Compare problems of lake water pollution to those of stream pollution. List three ways to prevent cultural eutrophication and three ways to clean up cultural eutrophication. Summarize the state of the Great Lakes.
9.Compare freshwater pollution to ocean pollution. List three ways to protect coastal waters. List the major pollutants of groundwater and three ways to control groundwater pollution.
10.Briefly describe and distinguish among septic tanks, primary, secondary, and advanced sewage treatment. Describe Arcata, California's approach to sewage treatment. Summarize how drinking water is purified.
11.Briefly describe two major laws that protect water quality in the United States.
Key Terms (Terms are listed in the same font style as they appear in the text.)
1
Water Resources and Water Pollution
hydrologic cycle (p. 171)
surface runoff (p. 171)
watershed (p. 171)
drainage basin (p. 171)
reliable runoff (p. 172)
groundwater (p. 172)
zone of saturation (p. 172)
water table (p. 172)
aquifers (p. 172)
natural recharge (p. 172)
lateral recharge (p. 172)
water mining (p. 173)
water hot spots (p. 173)
hydrological poverty (p. 174)
floodplain (p. 175)
channelization (p. 177)
levees (p. 177)
dams (p. 177)
wetlands (p. 177)
managing floodplains (p. 177)
California Water Project (p. 179)
distillation (p. 182)
reverse osmosis (p. 182)
flood irrigation (p. 183)
center-pivot low-pressure sprinklers (p. 184)
low-energy precision application
(LEPA) sprinklers (p. 184)
soil moisture detectors (p. 184)
drip irrigation systems (p. 184)
microirrigation systems (p. 184)
xeriscaping (p. 184)
blue revolution (p. 185)
water pollution (p. 186)
point sources (p. 186)
nonpoint sources (p. 186)
oxygen sag curve (p. 188)
eutrophication (p. 189)
cultural eutrophication (p. 189)
degradable wastes (p. 190)
nondegradable wastes (p. 190)
integrated coastal management (p. 193)
crude petroleum (p. 194)
refined petroleum (p. 194)
crude oil (p. 194)
refined oil (p. 194)
Federal Water Pollution Control Act (p. 195)
Water Quality Act (p. 195)
discharge trading policy (p. 195)
septic tank (p. 196)
sewage treatment plants (p. 196)
primary sewage treatment (p. 196)
secondary sewage treatment (p. 196)
bleaching (p. 197)
disinfection (p. 197)
chlorination (p. 197)
composting toilet systems (p. 197)
living machines (p. 197)
1
Water Resources and Water Pollution
Outline
9-1Water’s Importance, Use, and Renewal
A.Water is important for several reasons.
1.It keep us alive; most organisms are more than half water.
2.It sculpts the earth’s surface and moderates the climate.
3.Water removes and dilutes wastes and pollutants.
B.The management of water’s supply, renewal, and use is a huge, twenty-first century challenge. Only about 0.01% of the earth’s supply of water is available as freshwater in soil, usable groundwater, water vapor, lakes, and streams.
C.The hydrologic cycle collects, purifies, recycles, and distributes the world’s freshwater supply.
D.Overloading the earth’s water systems with slowly degradable and nondegradable wastes and withdrawing underground water faster than it is replenished is compromising the hydrologic cycle.
E.Some countries have more water than they need; some countries have far less. Poor people have less access and less availability to water, just as to food supplies.
F.Water that flows across the earth and empties into rives, streams, lakes, etc., that does not infiltrate the ground or evaporate into the atmosphere, is called surface runoff.
1.A watershed/drainage basin is that region where surface water drains into a body of water.
2.Reliable runoff is the runoff that is stable from one year to the next.
3.Water that percolates down through the ground and is stored in pores, crevices, etc. is groundwater, an important freshwater source.
a.An aquifer consists of porous, water-saturated layers of sand, gravel, or bedrock. Groundwater flows through it, usually from high elevation to lower elevation.
1)An aquifer with a water table is an unconfined aquifer.
2)A confined aquifer is bound by less permeable beds of rock.
b.In the zone of saturation, the spaces in the ground are filled with water.
c.The water table is located at the top of the zone of saturation.
d.A natural recharge replenishes an aquifer through the precipitation that percolates down through soil and rock.
e.Lateral recharge is replenished from the side of nearby streams.
f.Water mining withdraws water from deep underground, ancient deposits of water that are not generally recharged.
G.The world’s demand for water now requires 54% of the world’s reliable runoff of surface water. In some places usage rates are exceeding the reliable runoff available.
1.70% of the water we withdraw from surface water/aquifers is to irrigate crops that account for 40% of the world’s food.
2.Industries use 20% of such water.
3.Cities and residencies use 10% of reliable runoff.
4.The U.S., unlike many other countries, has enough freshwater, but its availability is influenced by difference in climate.
9-2Water Resource Problems: Too Little Water and Too Much Water
Water resource problems rest on too little water and too much water in the wrong places.
A.Water scarcity arises from a dry climate, drought, dry soil, and too many people straining the water supply.
1.A drought occurs when precipitation is at least 70% lower than usual and evaporation is higher than normal for more than 21 days.
2.Desiccation occurs when the soil dries out because of deforestation and overgrazing.
3.Increasing numbers of people relying on limited runoff produces a low per capita availability of water, creating water stress. Water stress comes when the volume of reliable runoff per capita drops to below 60,000 cubic feet/year.
4.Water scarcity occurs when per capita water availability falls below 35,000 cubic feet per year.
B.Almost 42% of the world’s population lives in river basins, which suffer from either water stress or water scarcity.
1.A United Nations study found that one of six people do not have access to adequate, affordable, and clean water.
2.Poor people live in hydrological poverty—they have no access and/or cannot afford clean water at a reasonable cost.
3.Water resources for the Middle East are especially limited, and populations in many of these countries continue to soar.
a.Ethiopia, the Sudan, and Egypt rely on the Nile River for their water. Egypt is last in line for this support.
b.The Jordan Basin has competition from Jordan, Syria, Palestine, and Israel for water in the world’s most water-starved region.
4.Conflicts over water will require regional cooperation to allocate water supplies, slow population growth, improve efficiency in water use, raise water prices to improve irrigation methods, and increase grain imports.
C.Natural flooding causes some areas to have too much water.
1.When water overflows its normal channel and floods adjacent areas, the area flooded is called the floodplain.
2.Floodplains and their highly productive wetlands provide flood and erosion control, maintain high water quality, and recharge groundwater.
3.People have tried to reduce flooding dangers near floodplains with these methods:
a.Rivers are narrowed and straightened/channelized.
b.Rivers have been equipped with walls and protective levees.
c.Rivers have been dammed to create reservoirs.
4.People live on floodplains because of these advantages:
a.The soil is fertile because of silt deposits left after flooding.
b.There is plenty of water for irrigation.
c.The near-by river is convenient for transportation and recreation.
d.Flat land makes crops, building, highways, and railroads easier to support.
5.The positive values of floods are:
a.Floods recharge groundwater and refill wetlands.
b.The farmland is very productive.
6.Human activities increase the damage of flooding.
a.Humans remove water-absorbing vegetation, especially from hills.
b.Humans drain the wetlands, which traditionally absorb floodwaters, and thereby reduce the severity of flooding.
c.Floods denude slopes, erode topsoil, and flood areas downstream.
d.Bangladesh’s flooding is caused by deforestation of mountain slopes and clearing of mangrove forests on the coastal floodplains.
1)Previous forests that acted as sponges during monsoon rains are gone.
2)Topsoil floats away and monsoon rains destroy houses and people.
3)Storm surges and cyclones have increased in severity because the previous mangrove swamps are no longer buffers to the surges and cyclones.
7.Several techniques can be used to reduce the risk of floods.
a.Control river water flow through channelization, which straightens and deepens streams. Levees and floodwalls along streams and dams can be built.
b.Preserve and restore wetlands.
c.Identify and manage flood-prone areas.
d.Discourage and choose not to live in flood-prone areas.
9-3Supplying More Water
A.Water supplies can be increased by getting more water and wasting less.
1.Build dams, bring water in from somewhere else, withdraw groundwater, and convert saltwater to freshwater, a process called desalination.
2.We can waste less water and import food, rather than using water to grow it.
B.Dams and reservoirs capture and store runoff water.
1.The water is released to control floods, generate electricity, and irrigate.
2.Reservoirs also provide for swimming, fishing, and boating.
3.However, dam and reservoir construction displaces people and floods productive land.
4.The ecological services that rivers provide is given no value when building dams/reservoirs.
5.The Three Gorges Dam on the Yangtze River (in China) will be the largest hydroelectric dam and reservoir in the world.
a.1.3 million people are being relocated on some land that will not grow food.
b.The dam will reduce China’s dependence on coal and hold back the Yangtze’s floodwaters.
c.Large cargo-carrying ships will be able to go into China’s interior and thus reduce current transportation costs.
C.Water transfer has proven controversial; for example, transferring water from northern California to southern California.
1.Tunnel, aqueducts, and underground pipes can move water from dams and reservoirs in water-rich areas to water-poor areas.
2.Such movement of water can encourage water waste, threaten fisheries, and degrade rivers and streams from which the water is removed.
3.Water diverted from the Aral Sea for irrigation created a major ecological, economic, and health disaster.
a.The sea has gotten smaller and therefore saltier.
b.Most of the area’s wetlands have been eliminated; 50% of the bird and mammal species have disappeared.
c.A huge area of the former lake bottom has become a desert of salt; this salt concentration appears to have caused the extinction of 20 of the 24 native fish species.
d.The fishing industry has disappeared; salty dust from the exposed seabed blows onto fields as much as 190 miles away. Chemicals used to raise crop yields are poisoning the groundwater.
e.The reduction in the size of the sea has changed the area’s climate for the worse.
f.Health problems from the toxic dust, salt, and contaminated water plague the people.
D.The advantages of withdrawing groundwater are that it is a fairly cheap process if the withdrawal rate does not exceed the recharge rate and if the aquifer does not become contaminated.
E.Disadvantages of withdrawing groundwater are falling water tables, land sinking below the aquifers, and saltwater intrusion into the aquifers in coastal areas.
1.There are ways to prevent/slow groundwater depletion (Figure 9-16).
2.Withdrawing water from deep aquifers is being investigated.
a.The geological and ecological impacts of pumping water from these aquifers are unknown.
b.There are no treaties/agreements that indicate who has rights or ownership of water under several different countries.
F.A different method of producing freshwater is to desalinate it. Desalination removes salt from ocean or brackish groundwaters.
1.One desalination method is distillation, which heats saltwater until it evaporates and condenses as freshwater; the salts are left behind as solids.
a.Desalination is very expensive because of the amount of energy used.
b.Desalination produces large amounts of wastewater that must be disposed of.
9-4Reducing Water Waste
A.65–70% of water that we now use is lost through evaporation, leaks, and other losses.
B.Being more careful with water use will provide water for a long, long time.
C.Reasons for water waste are underpricing and not rewarding conservation.
1.Government subsidies support farmers’ energy costs for obtaining water.
2.Lifeline water pricing gives each household an amount of water for basic needs; excess usage means higher prices.
3.The government does not support improving water efficiency.
D.Improved irrigation techniques could save water.
1.Use center-pivot low-pressure sprinkler irrigation that sprays water directly on a crop rather than flood irrigation, which provides water flowing in ditches in crop fields.
2.Low-energy precision application (LEPA) sprinklers spray water closer to the ground than the center-pivot low-pressure sprinkler, using less energy and less water.
3.Surge/time-controlled values on conventional gravity flow irrigation systems send water down irrigation ditches in pulses, rather than in a continuous stream. This can increase efficiency to 80% and reduce water use by 25%.
4.Use soil moisture detectors to water crops only when they need it.
5.Drip irrigation/microirrigation systems are the most efficient ways to move small amounts of water to crops. Small holes in a network of perforated plastic tubing deliver drops of water at a slow and steady pace to plant roots.
a.It is very efficient with water input reaching crops.
b.Drip systems cost one-tenth as much per hectare as conventional drip systems.
6.DRiWATER consists of one-liter packages of gel-encased water that is planted near plant roots. The water is released slowly into the soil—“drip irrigation in a box.”
7.Poor farmers use pedal-powered treadle pumps to move water into irrigation ditches and buckets/tanks with holes for irrigation.
E.In order to waste less water in industries, homes, and businesses, we can:
1.Replace green lawns and ornamental shrubbery with vegetation that needs little water; this is called xeriscaping.
2.Use drip irrigation.
3.Raise water prices.
4.Fix leaks.
5.Mimic nature in dealing with wastes.
6.Use water-saving toilets and like appliances.
7.Discontinue dumping industrial toxic wastes into municipal sewer systems.
F.We must use water more sustainably across the globe and reduce demand for water.
1.We must discontinue wasting water.
2.Raising water prices would cause less use.
3.We must preserve forests on water basins.
4.The world needs to slow population growth.
G.A blue revolution to conserve water would include several components:
1.Use technology to irrigate more efficiently and to save water.
2.Apply economic and political realities, and remove subsidies that underprice water while guaranteeing low prices for low-income consumers. Subsidize reducing water waste with rewards.
3.Develop new waste production and treatment systems that accept only nontoxic materials, use less/no water to treat wastes, return nutrients in waste to the soil, and mimic nature’s decomposition and recycling processes.
9-5Types, Effects, and Sources of Water Pollution
A.Water pollution is a chemical, biological, or physical change in water quality that harms living organisms or makes water unsuitable for desired uses.
1.Infectious bacteria, inorganic and organic chemicals, and excess heat pollute water.
2.Water quality is monitored through bacterial counts, chemical analysis, and indicator organisms.
a.One method to determine water quality is to measure the number of colonies of fecal coliform bacteria present in a water sample.
b.The amount of dissolved oxygen in a water sample relates to the oxygen-demanded wastes and plant nutrients in a water sample.
c.The presence and concentration of inorganic and organic chemicals in water can be determined through chemical analysis.
d.Living organisms can be counted and serve as indicator species.
B.Water pollution can come from point and nonpoint sources.
1.Point sources discharge pollutants at specific locations in pipes, ditches, or sewers into bodies of surface water. Such sources include factories, sewage treatment plants, and oil tankers.
2.Nonpoint sources cannot be traced to a single discharge site. Examples include deposits from the atmosphere, runoff of chemicals from croplands, feedlots, logged forests, lawns, golf courses, etc.
3.20% of the world’s people in developing countries do not have access to safe drinking water.
9-6Pollution of Freshwater Streams, Lakes, and Aquifers
Water pollution is widespread in streams, lakes, and aquifers.
A.If streams are not overloaded and their flows are not reduced, they can recover from degradable water pollutants. The wastes are diluted and biodegraded by bacteria.