Lecture Outlines. Chapter 15. Freshwater Systems and Resources. Withgott/Laposata Fifth Edition Pearson Education, Inc.

Transcription

1 Lecture Outlines Chapter 15 Freshwater Systems and Resources Withgott/Laposata Fifth Edition

2 This lecture will help you understand: Water s distribution and types of freshwater ecosystems Use and alteration of freshwater systems Problems of water supply and solutions Classes of water pollution and solutions How drinking water and wastewater are treated

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4 Central Case Study: Starving the Louisiana Coast of Sediment Louisiana loses 65 km 2 (25 mi 2 ) of coastal wetlands each year These ecosystems support a diversity of animals Protect coastal cities from damaging storms Created by sediments deposited at the end of the Mississippi River The river accumulates material from water flowing off of its 3.2 million km 2 (1.2 million mi 2 ) watershed The wetlands naturally compact, sink, and would vanish New sediment is naturally added to maintain them

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6 Case Study: Starving the Louisiana Coast of Sediment The Mississippi River has been extensively modified River s basin contains nearly 2000 dams The dams slow the water, and the sediment drops out Levees confine the river, making it deeper and faster Sediments shoot out rather then settle in the wetlands Oil and gas extraction has increased the rate of soil compaction Solution: allow water from the Mississippi into the coastal wetlands rather than shooting it into the Gulf This approach is rebuilding the Atchafalaya delta

7 Freshwater Systems Water may seem abundant, but drinkable water is rare Fresh water = water that is relatively pure, with few dissolved salts only 2.5% of total water Most is tied up in glaciers, ice caps, and aquifers One part in 10,000 is easily available for our use

8 Freshwater Systems Water is renewed and recycled as it moves through the water cycle Precipitation sinks into the ground or runs off into rivers to form lakes or enter oceans Rivers interact with ponds, wetlands, and coasts Groundwater exchanges with rivers and ponds Water moves organisms, sediments, and chemicals

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11 Groundwater plays key roles in the hydrologic cycles Surface water = water located atop Earth s surface Groundwater = water beneath the surface held in pores in soil or rock 20% of the Earth s freshwater supply Aquifers = porous, spongelike formations of rock, sand, or gravel that hold water Zone of aeration = pore spaces partly filled with water Zone of saturation = spaces are filled with water Water table = boundary between the two zones Recharge zone = any area where water infiltrates Earth s surface and reaches aquifers

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13 Groundwater plays key roles in the hydrologic cycles Confined (artesian) aquifer = water-bearing, porous rocks are trapped between less permeable substrate (clay) layers Water here is under great pressure Unconfined aquifer = no upper layer to confine it Readily recharged by surface water Groundwater s average age is 1400 years It may be tens of thousands of years old The Ogallala Aquifer is the world s largest known aquifer Current water use for irrigation is not sustainable

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15 Surface water converges in river and stream ecosystems Surface water accounts for just 1% of fresh water Vital for us and Earth s ecological systems Runoff = water that flows over land Water merges in rivers and ends up in a lake or ocean Tributary = a smaller river slowing into a larger one

16 Surface water converges in river and stream ecosystems Watershed (drainage basin) = the area of land drained by a river system (river and its tributaries) Surface water becomes groundwater through infiltration Groundwater becomes surface water through springs or human-drilled wells 1.9 trillion L (492 billion gal) each day in the United States

17 Hydrologic Cycle Major Aspects Right-click/Select Play

18 Hydrologic Cycle Crossword Puzzle Right-click/Select Play

19 Surface water converges in river and stream ecosystems Rivers shape the landscape Braided river = an interconnected series of watercourses that run through steep slopes Meandering river = river in flatter areas Water rounding a bend erodes soil from the outer bank Sediment is deposited on the inside of the bend Rivers form oxbows, areas where river bends become exaggerated Oxbow lake = water body formed when erosion cuts off and isolates the oxbow into a U-shape

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21 Surface water converges in river and stream ecosystems Floodplain = areas nearest to a river s course that are flooded periodically Frequent deposition of silt makes floodplain soils fertile Good areas for agriculture Riparian = describing riverside areas that are productive and species-rich Damming prevents large floods and river meanders Rivers and streams host diverse ecological communities Algae, insects, fish, amphibians, birds, etc.

22 Lakes and ponds are ecologically diverse systems Lakes and ponds are bodies of open, standing water Littoral zone = region ringing the edge of a water body Rooted aquatic plants grow in this shallow part Benthic zone = the entire bottom of the water body Home to many invertebrates Limnetic zone = open portion of the lake or pond where sunlight allows photosynthesis that produces oxygen Supports phytoplankton and zooplankton Profundal zone = water that sunlight does not reach Supports fewer animals because there is less oxygen

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24 Lakes and ponds are ecologically diverse systems Ponds and lakes may change over time Oligotrophic lakes and ponds have low-nutrient and high-oxygen conditions Eutrophic lakes and ponds have high-nutrient and low-oxygen conditions Eutrophication may result from human pollution Eventually, water bodies may fill completely in through the process of succession The largest lakes are known as inland seas Great Lakes, the Caspian Sea, Lake Baikal

25 Freshwater wetlands include marshes, swamps, bogs, and vernal pools Wetlands = systems in which the soil is saturated with shallow standing water with vegetation Freshwater marshes = shallow water with plants that grow above the surface Swamps = shallow water in forested areas Can be made by beavers Bogs = ponds covered in thick floating mats of vegetation A stage in aquatic succession Vernal pools = pools that form in spring then dry up

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27 Freshwater wetlands include marshes, swamps, bogs, and vernal pools Wetlands are extremely valuable for wildlife Louisiana s coastal wetlands host 1.8 million migratory birds each year They provide valuable ecosystem services They slow runoff, reduce flooding, recharge aquifers, and filter pollutants People have drained wetlands, mostly for agriculture Southern Canada and the United States have lost over half of their wetlands Wetlands are affected when we withdraw water, build dams and levees, and introduce pollution

28 Human Activities Affect Waterways Water is crucial for human health as well as farms and factories Water is a limited but renewable resource Withdrawal of water in most of the world is unsustainable We are depleting many sources of surface water and groundwater One-third of the world s people are affected by water shortages

29 Human Activities Affect Waterways We have achieved impressive engineering accomplishments to harness fresh water 60% of the world s largest 227 rivers have been strongly or moderately affected by dams, dikes, and diversions

30 Fresh water and human populations are unevenly distributed across Earth Different areas possess different amounts of water People are not distributed in accordance with water availability Asia has the most water of any continent but the least water available per person Densely populated nations like Pakistan, Iran, India, and Egypt face serious water shortages Fresh water is also unevenly distributed in time Seasonal rains lead to differences in water availability India can receive half of its rain in a single monsoon Dams are used to store water for dry times

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32 Fresh water and human populations are unevenly distributed across Earth Climate change will worsen conditions in many region Altered precipitation patterns Melting glaciers causing early season runoff Intensified droughts and flooding One-third of the world s major rivers experienced reduced flow from 1948 to 2004 Attributed largely to climate change

33 Water supplies households, industry, and especially agriculture Globally, 70% of water is used for agriculture, 20% for industry, and 10% for residential and municipal use Arid countries use more water for agriculture Developed countries use more water for industry Consumptive use = when water is removed from an aquifer or surface water body and is not returned Irrigation = is the water applied to crops Nonconsumptive use = does not remove, or only temporarily removes, water Electricity generation at hydroelectric dams

34 Water supplies households, industry, and especially agriculture Rapid population growth requires more food and clothes We use 70% more irrigation water than 50 years ago Irrigation can more than double crop yields 18% of land is irrigated but produces 40% of our crops Irrigation is highly inefficient Water evaporates in flood and furrow irrigation Overirrigation leads to waterlogging and salinization Reducing world farm income by $11 billion Water use for agriculture is subsidized by governments Farmers have little incentive to conserve

35 Excessive water withdrawals can drain rivers and lakes In many places, we are withdrawing water at unsustainable rates Many of the world s major rivers regularly run dry before reaching the sea The Colorado River often does not reach the Gulf of California, threatening the future of cities and farms that rely on its water Reduced flow drastically changes the river s ecology and plant community and destroys fish and invertebrates

36 Excessive water withdrawals can drain rivers and lakes The Aral Sea in in present day Uzbekistan and Kazakhstan was once the fourth-largest lake on Earth It lost 80% of its volume in 45 years The two rivers leading into the Aral Sea were diverted to irrigate cotton fields 60,000 fishing jobs are gone Pesticide-laden dust is blown into the air Little cotton can grow on the salty soil

37 Excessive water withdrawals can drain rivers and lakes Worldwide, 15% 35% of water withdrawals for agriculture are unsustainable Water mining = withdrawing water faster than it is replenished

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40 Groundwater can also be depleted Groundwater is more easily depleted than surface water Aquifers recharge slowly Used by one-third of all people As aquifers are mined, water tables drop In many areas, water tables are falling 1 3 m/year Salt water intrudes in coastal areas, making water undrinkable Land above the aquifers subsides

41 Groundwater can also be depleted Sinkholes = areas where ground gives way suddenly Once the soil is compacted, aquifers can t recharge Wetlands that get their water from groundwater dry up

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43 Groundwater supplies our bottled water Groundwater is being withdrawn for use as bottled water An average American drinks 29 gallons/year Sales topped $15 billion in the United States in 2012 People drink bottled water for portability, convenience They think it tastes better or is healthier Bottled water is no better than tap water It is heavily packaged and travels long distances using fossil fuels Energy costs of bottled water are times greater than those of tap water Only 25% of bottles are recycled in the United States

44 People build dikes and levees to control floods Flooding = a normal, natural process where water spills over a river s banks Spreading nutrient-rich sediments over large areas In the short term, floods damage property Levees (or dikes) are the long, raised mounds of earth along the banks of rivers that hold water in channels Stop flooding from most rains May make floods worse by forcing water to stay in channels, build energy, and then overflow Dams prevent flooding and change a river s nature Releasing water periodically simulates flooding

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46 We divert surface water to suit our needs People divert water to farm fields, homes, and cities Water from the Colorado River is diverted to Denver, Las Vegas, Los Angeles, and elsewhere In China, $62 billion is being spent to move water from the Yangtze to the Yellow River Politically strong, water-poor areas forcibly take water from weaker communities Los Angeles commandeered water from rural areas, turning the environment into desert, creating dustbowls, and destroying the economy In 1941, it diverted streams that fed Mono Lake Lake levels fell; salt concentrations doubled

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48 We have erected thousands of dams Dam = any obstruction placed in a river or stream to block the flow of water They create reservoirs = artificial lakes Dams are built to prevent floods, provide drinking water, allow irrigation, and generate electricity 45,000 large dams have been erected in more than 140 nations Tens of thousands of smaller dams have been built Only a few major rivers remain undammed in remote regions of Canada, Alaska, and Russia

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50 We have erected thousands of dams Dams produce a mix of benefits and costs The dam on the Yangtze River is the largest in the world Its reservoir stretches for 616 km (385 mi) It provides flood control, passage for boats, and huge amounts of electricity

51 We have erected thousands of dams However, it cost $39 billion to build Flooded 22 cities and the homes of 1.24 million people Submerged 10,000-year-old archaeological sites Drowned farmland and wildlife habitat The tidal marshes at the Yangtze s mouth are eroding Pollutants may be trapped, making the water undrinkable

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53 Some dams are being removed Some people feel that the costs of dams outweigh their benefits and are pushing to dismantle dams Removing dams will restore riparian ecosystems, reestablish fisheries, and revive river recreation The Federal Energy Regulatory Commission (FERC) renews licenses for dams If dam costs exceed benefits, the license may not be renewed 400 dams have been removed in the United States Some property owners who opposed the removal changed their minds once they saw the healthy river

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55 Wetlands are affected by human manipulations of waterways Wetlands are being lost as we divert and withdraw water, channelize rivers, build dams, etc. Wetlands have also been widely drained for agriculture As wetlands disappear, we lose ecosystem services Filtering pollutants, wildlife habitat, flood control, etc. Many are trying to protect and restore them

56 Wetlands are affected by human manipulations of waterways The Ramsar Convention on Wetlands of International Importance (1971) seeks the conservation and wise use of wetlands in the context of sustainable development 1900 sites covering 185 million ha are protected

57 Solutions to Depletion of Fresh Water Our use of fresh water has doubled over the last 50 years We can either increase supply or reduce demand Increasing supply through intensive extraction is only a temporary fix Diversions increase supply in one area but decrease it elsewhere

58 Solutions to Depletion of Fresh Water Reducing demand is harder politically in the short term International aid agencies are funding demand-based solutions over supply-based solutions Offers better economic returns Causes less ecological and social damage

59 Desalinization makes more fresh water Desalination (desalinization) = the removal of salt from seawater or other water of marginal quality Distilling = evaporates and condenses ocean water Reverse osmosis = forces water through membranes to filter out salts Over 2000 desalinization facilities operate around the world, but there are problems with it Is expensive Requires large energy inputs (usually fossil fuels) Kills aquatic life at the water intakes Generates a concentrated salty waste

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61 Agricultural demand can be reduced Agriculture uses the largest amount of water of any use, but a number of measures can be taken to reduce waste Line irrigation canals to prevent leaks Level fields to reduce runoff Use efficient irrigation methods Low-pressure spray irrigation sprays water downward Drip irrigation systems target individual plants Match crops to land and climate Eliminate water subsidies Use selective breeding and genetic modification to produce crops that require less water

62 We can lower residential and industrial water use Residential water use can be cut in a number of ways Install low-flow faucets, toilets, etc. Rainwater harvesting = capturing rain from roofs Gray water = wastewater from showers and sinks that can be used to water lawns Xeriscaping = using plants adapted to arid conditions Industries and municipalities can save water Shift to processes that use less water Recycle wastewater Use surface water runoff to recharge aquifers Find and patch leaky pipes

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64 Market-based approaches to water conservation are being debated End government subsidies of inefficient practices Let the price of water reflect its true cost of extraction But since industrial uses are more profitable than agricultural uses, poorer, less developed countries suffer Privatize water supplies: construction, maintenance, management, and ownership May improve efficiency Little incentive to provide access to the poor Decentralization of water control may conserve water Shift control to the local level

65 Nations often cooperate to resolve water disputes Freshwater depletion leads to shortages, which can lead to conflict 261 major rivers cross national borders Water is a key element in hostilities among Israel, Palestinians, and neighboring countries Conflicts also exist between states in the United States Many nations have cooperated with neighbors to resolve disputes India has agreements to co-manage rivers with Pakistan, Bangladesh, Bhutan, and Nepal European nations on the Rhine and Danube signed treaties

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67 Freshwater Pollution and Its Control People affect aquatic ecosystems and human health when we introduce toxic substances and diseases Half of the world s major rivers are seriously depleted and polluted They degrade and poison surrounding ecosystems, threatening the health and livelihood of people 55% of U.S. streams and rivers are in poor condition The invisible pollution of groundwater has been called a covert crisis Preventing pollution is easier and more effective than mitigating it later

68 Water pollution comes from point and nonpoint sources Pollution = the release of matter or energy that causes undesirable impacts on the health and well-being of humans or other organisms Water pollution comes in many forms and causes diverse impacts Point sources = discrete locations of water pollution Factories, sewer pipes Addressed by the U.S. Clean Water Act Non-point sources = sources of pollution arising from multiple inputs over larger areas (farms, city streets, neighborhoods) The major source of U.S. water pollution

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70 Water pollution takes many forms Toxic chemicals: waterways have become polluted with toxic organic chemicals of our own making Pesticides, petroleum products, synthetic chemicals; arsenic, lead, mercury, acid rain, acid Effects include poisoned animals and plants, altered aquatic ecosystems, and decreased human health

71 Water pollution takes many forms Scientists measure a range of water characteristics to assess water quality (color, ph, temperature, etc.) Solutions: Issue and enforce more stringent regulations Modify industrial processes and our purchasing decisions to rely less on these substances

72 Pathogens and waterborne diseases Viruses, protists, and bacteria enter water supplies through inadequately treated human waste and animal waste from feedlots Fecal coliform bacteria indicate fecal contamination Usually are not pathogenic organisms Indicate that the water may hold other diseasecausing pathogens (e.g., giardiasis, typhoid, hepatitis A)

73 Pathogens and waterborne diseases Bacterial pollution causes more human health problems than any other type of water pollution Conditions are improving, but 800 million people lack reliable access to safe water Treating wastewater and personal hygiene reduce risks

74 Nutrient pollution Nutrient pollution from fertilizers, farms, sewage, lawns, golf courses leads to eutrophication Fertilizers add phosphorus to water, which boosts algal and aquatic plant growth Spreading algae cover the surface, decreasing sunlight Bacteria eat dead algae, reducing dissolved oxygen Fish and shellfish die

75 Nutrient pollution Areas of low oxygen can become dead zones Solutions include treating wastewater Reducing fertilizer application Using phosphate-free detergents Planting vegetation to increase nutrient uptake

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77 Biodegradable Wastes and Sediment Introducing large amounts of biodegradable waste into water decreases dissolved oxygen Wastewater = water affected by human activities; can be a source of biodegradable wastes Sediment is the eroded material carried by rivers

78 Biodegradable wastes and Sediment Clear-cutting, mining, clearing land for housing, and cultivating farm fields expose soil to erosion It dramatically changes aquatic habitats Fish may not survive Solutions: Better management of farms and forests Avoid large-scale disturbance of vegetation

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80 Thermal pollution Water that is too warm causes problems Warmer water holds less oxygen Dissolved oxygen decreases as temperature increases Industrial cooling heats water Removing streamside cover raises water temperature Water that is too cold also causes problems Water at the bottom of reservoirs behind dams is colder When water is released, downstream water temperatures drop suddenly, favoring cold-loving invasive fish

81 Groundwater pollution is a difficult problem Most pollution control efforts focus on surface water Groundwater is increasingly contaminated but is hidden from view and difficult to monitor Out of sight, out of mind Groundwater pollution is harder to address than surface water pollution Rivers flush pollutants out, but groundwater retains contaminants for decades and longer It takes longer for contaminants to break down because of lower sunlight, microbes, and dissolved oxygen

82 There are many sources of groundwater pollution Some toxic chemicals occur naturally Aluminum, fluoride, sulfates Pollution from human causes is widespread Industrial wastes can leach through soil Pathogens enter through improperly designed wells Leaking underground storage tanks are a source of carcinogenic pollutants from solvents and gasoline EPA has confirmed leaks from 510,000 tanks and cleaned up 430,000 of them over the last 15 years

83 There are many sources of groundwater pollution Leaking radioactive waste also pollutes groundwater In 2013, officials revealed that five underground storage tanks at the Hanford Nuclear Reservation in Washington were leaking radioactive waste Billions of dollars have been spent on remediation Agricultural pollution comes from several sources Pesticides are in most of the shallow aquifers tested Nitrates from fertilizers have caused cancer, miscarriages, and blue-baby syndrome Pathogens such as Escherichia coli (E. coli) can cause illness

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85 Legislative and regulatory efforts have helped to reduce pollution Water pollution was worse decades ago Citizen activism and government response resulted in legislation during the 1960s and 1970s Rivers and lakes are cleaner now The Federal Water Pollution Control Act (1972) Renamed as the Clean Water Act in 1977 Made it illegal to discharge pollution without a permit Set standards for industrial wastewater Funded sewage treatment plants

86 Legislative and regulatory efforts have helped to reduce pollution Underfunded and understaffed state and federal regulatory agencies succumbed to pressure by industries and politicians who received money from them Violations of the Clean Water Act have risen to over 100,000 documented violations/year 10% of Americans are unknowingly exposed to unsafe drinking water Government action was taken to help the Great Lakes The water quality of the lakes has dramatically improved Recent Supreme Court decisions removed enforcement powers of the EPA over many waterways

87 We treat our drinking water Technology and government regulation have improved our pollution control Treated drinking water is widespread and successful in developed nations Before water reaches the user, it is chemically treated, filtered, and disinfected The EPA sets standards for over 90 drinking water contaminants Local governments and private water suppliers must meet these standards

88 We treat our wastewater Wastewater includes water that carries sewage and that from households, manufacturing, stormwater runoff, etc. It is treated before being released into the environment Septic systems = the most popular method of wastewater disposal in rural areas Underground septic tanks separate solids and oils from wastewater The water drains into a drain field, where microbes decompose the pollutants Solid waste is periodically pumped out and landfilled

89 We treat our wastewater In populated areas, sewer systems carry wastewater to treatment locations Primary treatment = physically removes contaminants in settling tanks (clarifiers) Secondary treatment = water is stirred and aerated Aerobic bacteria degrade organic pollutants Water is treated with chlorine (and/or ultraviolet light) to kill pathogens This water, called effluent, is piped into rivers or oceans Reclaimed water is used for lawns, irrigation, or industry

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91 We treat our wastewater Sludge = solid material resulting from treatment of wastewater Is decomposed microbially in digesters Resulting biosolids are dried then landfilled, incinerated, or used as fertilizer on cropland Methane-rich gas created by decomposition can be burned to generate electricity Six million dry tons of sludge are generated in the United States each year

92 Constructed wetlands can aid treatment Natural wetlands have long filtered and purified water Human-constructed wetlands can do the same thing After primary treatment at a conventional facility water is pumped into the wetland Microbes decompose the remaining pollutants

93 Constructed wetlands can aid treatment Cleansed water is released into waterways or percolates underground They are havens for wildlife and for human recreation The United States has over 500 artificially constructed or restored wetlands Released effluent has helped rebuild coastal wetlands along the Gulf Coast

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95 Conclusion Obtaining future supplies of fresh water requires citizen action, legislation and regulation, technology, economic incentives, and education With expanding population and increasing water usage, we are approaching conditions of widespread scarcity Water pollution is already harming health, economies, and societies of both rich and poor nations Better regulation has improved water quality in the United States and other developed nations

96 QUESTION: Review The picture shows a(n) a) braided river. b) meandering river. c) oxbow. d) river delta.

97 QUESTION: Review The area of a lake that rings the edge and contains rooted plants is called the zone. a) littoral b) benthic c) limnetic d) profundal

98 QUESTION: Review An unconfined aquifer is defined as a) an aquifer that traps porous rocks between layers of less permeable substrate. b) an aquifer that traps porous rocks under one layer of less permeable substrate. c) an aquifer with porous rocks resting on bedrock. d) an aquifer with no upper layer.

99 QUESTION: Review Why do governments subsidize irrigation? a) It promotes food self-sufficiency. b) Governments have to or food could not be grown. c) Governments want to lower water tables. d) Governments do not subsidize irrigation.

100 QUESTION: Review Which of the following statements about dams is NOT true? a) They change habitat. b) They generate electrical power. c) They have created more farmland upstream. d) Pollutants are trapped in reservoirs.

101 QUESTION: Review Which of the following is a point source of water pollution? a) A factory b) Roads c) Agricultural fields d) All are point sources.

102 QUESTION: Review Which of the following types of water pollution causes the most severe human health problems? a) Nutrient pollution b) Pathogens c) Toxic chemicals d) Sediment pollution

103 QUESTION: Review Which statement regarding using artificial wetlands to treat wastewater is NOT correct? a) Water first undergoes primary treatment. b) Microbes decompose pollutants. c) Cleansed water cannot be released into waterways. d) They are good areas for wildlife.

104 QUESTION: Viewpoints During times of drought, conflicts erupt between farmers (who need water for irrigation) and ecologists (who want water left in rivers to protect wildlife). Who should have the highest priority? a) Farmers; they need the water for their crops. b) Wildlife; animals will die without water. c) Farmers should be paid subsidies to withdraw water from other places. d) Farmers should be paid to plant different crops that do not require so much water.

105 QUESTION: Weighing the Issues Should cities in dry areas, such as Las Vegas, be allowed to increase their populations, so that they will require more water? a) Yes; it s un-american to limit what cities can do. b) Yes, but make the people pay the true cost of water. c) Yes, but only if the people are required to use drastic conservation measures. d) No; enough is enough, and cities in arid environments simply cannot continue growing.

106 QUESTION: Interpreting Graphs and Data Which nation has the largest desalination capacity? a) Japan b) Russia c) Saudi Arabia d) United States