Published on November 2, 2007
9: 9 Freshwater and marine resources This lecture will help you understand:: This lecture will help you understand: The hydrologic cycle and human interactions with it Freshwater ecosystems, distribution, depletion, and pollution Ocean currents Marine ecosystems Human impacts on marine environments Marine reserves and protected areas Central Case: Plumbing the Colorado River: Central Case: Plumbing the Colorado River The once-mighty Colorado River is now dammed. So much water is withdrawn that it barely reaches the sea. Western states apportion the water according to a pact, but California has long exceeded its share. In 2003 the U.S. government cut California’s flow. Months of wrangling followed until a deal was reached. Freshwater: Freshwater Water that is relatively pure, with very few dissolved salts Freshwater occurs in: Lakes, rivers, streams, groundwater, glaciers, rainwater, soil, water vapor in the atmosphere (In contrast, ocean water is salty because salts from land run into it and stay there as surface water evaporates.) Freshwater: Freshwater Figure 14.1 Only 2.5% of the planet’s water is freshwater, and only 1% of that exists on Earth’s surface. Only 1 part in 10,000 of water is easily accessible for drinking and irrigation. Hydrologic cycle: Colorado River: Hydrologic cycle: Colorado River Air rising over the Rocky Mountains. drops precipitation that feeds the Colorado River’s headwaters. The air depleted of moisture creates a dry rainshadow east of the mountains. Figure 14.2 Colorado River: Colorado River The river flows through arid country, nourishing ecosystems along its banks. It dumps into the Sea of Cortez, where a large estuary once flourished. Today so much water is withdrawn for irrigation and drinking supplies that the river barely makes it to the sea. Groundwater: Groundwater Water beneath Earth’s surface that did not evaporate, flow into rivers, or get taken up by organisms Plays key role in hydrologic cycle, and in meeting human needs 20% of all freshwater Groundwater is contained in aquifers. Aquifers: Aquifers Aquifer = a porous spongelike layer of rock, sand, or gravel that holds groundwater Confined or artesian aquifer = water under pressure, trapped within impermeable layers (often clay) Unconfined aquifer = water under less pressure; no overlying impermeable layer Aquifer recharge zone = geographic area where water infiltrates soil and recharges aquifer. Groundwater and aquifers: Groundwater and aquifers Figure 14.3 Freshwater distribution: Freshwater distribution Global freshwater distribution is very uneven. Rainfall varies from nearly zero up to 1,200 centimeters (470 inches)/year. Canada has 20 times as much water per citizen as does China. Available freshwater resources: Available freshwater resources Nations vary by more than a factor of 100 inches of water per capita. Figure 14.5a Available freshwater resources: Available freshwater resources Asia has lots of water but very little water per capita. Australia has lots of water per capita but little water overall. Figure 14.5b Freshwater ecosystems: Rivers and streams: Freshwater ecosystems: Rivers and streams Bodies of water that flow downhill, joining one another, shape the landscape. The beds of rivers move over time, depositing sediments over large areas of floodplain Figure 14.6a Freshwater ecosystems: Lakes and ponds: Freshwater ecosystems: Lakes and ponds Stationary bodies of water we call lakes and ponds also change slowly over time, through aquatic succession. Depending on nutrient input and other factors, these can be very productive and diverse ecosystems. Figure 14.6b Freshwater ecosystems: Wetlands: Freshwater ecosystems: Wetlands Wetlands include freshwater marshes, swamps, and bogs. Wet areas with lush vegetation, they are especially productive and valuable for wildlife. Yet they are often destroyed by human development, as they occur in flat areas that can be developed if drained. Figure 14.6d How we use water: How we use water Consumptive use = water is removed from an aquifer or surface body, and not returned. (most agricultural, industrial, and residential use) Nonconsumptive use = removal of water is only temporary. (passing water through a hydroelectric dam) How we use water: Agriculture: How we use water: Agriculture Agriculture = 87% of world’s consumptive use of water Global consumption has risen in tandem with irrigation. Figure 14.8 How we use water: Groundwater extraction: How we use water: Groundwater extraction 1 in 3 humans relies on groundwater for drinking. 99% of the rural U.S. relies on groundwater for drinking. Extraction from aquifers is increasing, especially in developing nations whose agriculture intensified with green revolution. How we use water: Surface diversion: How we use water: Surface diversion Colorado River water is heavily diverted today from a series of dams, mostly for agriculture. Figure 14.10a How we use water: Flood control: How we use water: Flood control We build dikes and levees to prevent floods when river levels rise. Flood control has saved many towns and crops from ruin. But long term, flood control can be self-defeating: • Forces floodwater to stay in channel, creating risk of catastrophic overflow or dike break downstream • Deprives farmland of nutrients that floods bring; decreases soil productivity How we use water: Dams: How we use water: Dams We build dams blocking the flow of rivers in order to: • Prevent floods • Generate electricity • Provide drinking water • Provide irrigation 45,000 dams over 15 meters(49 feet) high have been built in the world. Few major rivers today are not dammed. Benefits and costs of dams: Benefits and costs of dams Figure 14.11 Benefits and costs of dams: Benefits and costs of dams BENEFITS: Electricity generation Fewer emissions from hydropower generation Crop irrigation Drinking water supply Flood control Shipping New recreational opportunities COSTS: Habitat alteration Native fisheries decline Population displacement Disruption of flood cycles Sediment capture Lost recreational opportunities Risk of catastrophic failure The biggest dam yet: The biggest dam yet China’s Three Gorges Dam across the Yangtze River is the world’s largest. Completed in 2003. Over 1 million people were displaced to build it. Farmland, archaeology, and habitat were submerged. Critics worry about sedimentation and water quality. Figure 14.12 Dam removal: Dam removal In the U.S., some smaller dams are now being removed. Removal proponents want many larger dams removed too, as their licenses come up for renewal. Dam removal helps: • Restore riparian ecosystems • Reestablish economically vital fisheries (e.g., salmon) • Reintroduce recreation (rafting, fly-fishing…) Viewpoints: Dams: Viewpoints: Dams Sara Nicholas Thomas Flint “Many dams are obsolete, providing no direct economic, safety, or social function. These should be considered for removal. All dams harm riparian environments. Once a dam has outlived its usefulness, it makes great sense to restore the river back to its original condition.” “Dams and reservoirs address the needs of a growing world by efficiently storing and regulating water for multiple uses. Our world relies on the benefits they bring—drinking water, flood control, power generation, irrigation, and recreation.” From Viewpoints Freshwater depletion: Aral Sea: Freshwater depletion: Aral Sea The Aral Sea, in central Asia, was the fourth largest freshwater body on Earth, but it could disappear completely! Overirrigation for cotton was responsible in 1960, 1999, and 2002 Figure 14.13c Freshwater depletion: Aral Sea: Freshwater depletion: Aral Sea Satellite photo: Deep water today Shallow water today Dry former lake bed Figure 14.13b Freshwater depletion: Aral Sea: Freshwater depletion: Aral Sea The Aral Sea’s depletion has been devastating to the local people and their economies. Hundreds of ships lie stranded in the sand, because water fell so fast. Figure 14.13a Groundwater depletion: Groundwater depletion Bigger threat than surface water depletion because aquifers recharge very slowly Water mining = withdrawing groundwater faster than it can be replenished Water tables in some areas are falling by 1–3 meters (3–9 feet)/year. The Ogallala Aquifer has lost the equivalent of yearly flow of 18 Colorado Rivers! Impacts of water mining: Impacts of water mining Figure 14.14 When water is mined, ground may suddenly collapse in sinkholes. Other impacts: Slow subsidence (Venice, Mexico City) Saltwater intrusion into drinking water Soil compaction Wetland destruction Irrigation: Irrigation Figure 14.15 Most irrigation practiced today is very inefficient. Only 45% ends up being used by crops. A future of water wars?: A future of water wars? “The wars of the 21st century will be fought over water.” — Ismail Serageldin, Chairman of the World Water Commission Already, scarcity has caused or exacerbated conflict in arid areas: Colorado River states in southwest U.S. Israel and Palestinian Territories Solutions for depletion: Desalination: Solutions for depletion: Desalination Desalination or desalinization = removal of salt from seawater to create freshwater Perfecting this technology would mean the oceans could provide us with unlimited freshwater. But so far, it is expensive! Most of the world’s 7,500 desalination plants are in wealthy oil states of the Middle East, where water is scarce enough to make desalination economically feasible. Solutions for depletion: Reducing demand: Solutions for depletion: Reducing demand In AGRICULTURE: Use high-efficiency irrigation techniques Line irrigation canals to prevent leaks Level fields to reduce runoff Choose crops appropriate to climate Eliminate government subsidies of inappropriate crops and methods New GM crops? Solutions for depletion: Reducing demand: Solutions for depletion: Reducing demand In the INDUSTRIAL and MUNICIPAL sectors: Shift to processes that save water (and thus money) Invest in repairing pipe leaks Recycle “gray” wastewater Solutions for depletion: Reducing demand: Solutions for depletion: Reducing demand In the RESIDENTIAL sector (what YOU can do): Install low-flow faucets and appliances Use automatic dishwashers Replace lawns with native vegetation If you keep lawns, water them at night Recycle “gray” wastewater Freshwater pollution: Freshwater pollution Over half of the world’s major rivers are “seriously depleted and polluted, degrading and poisoning the surrounding ecosystems, threatening the health and livelihood of people who depend on them.” —World Commission on Water, 1999 Groundwater pollution is extensive but invisible, a “covert crisis.” Indicators of water quality: Indicators of water quality Scientists use chemical properties to measure water quality: • pH: water’s acidity or alkalinity • Hardness: hard water has high concentrations of salts • Dissolved oxygen content: indicates suitability for life. High D.O. generally good for organisms. • Taste and odor: can show presence of certain chemical contaminants Indicators of water quality: Indicators of water quality Scientists use physical properties to measure water quality: • Turbidity: density of suspended particles. Water with sediments from erosion is turbid. • Color: indicates tannins and other chemicals • Temperature: aquatic organisms sensitive to temperature; warm water holds less dissolved oxygen Indicators of water quality: Indicators of water quality Scientists use biological properties to measure water quality: • Presence of pathogens: disease-causing organisms may be present, making water risky for drinking. Water pollution: point and non-point sources: Water pollution: point and non-point sources Figure 14.17 Types of pollution: Pathogens: Types of pollution: Pathogens Waterborne disease from viruses, bacteria, etc., contributes to 5 million deaths per year. • Diarrhea: 4 billion cases/year, 2.2 million deaths • Intestinal worms: 1 in 10 people in developing world • Blindness from trachoma: 6 million people • Schistosomiasis from blood flukes: 200 million people Types of pollution: Eutrophication: Types of pollution: Eutrophication Excess runoff of nutrients like nitrogen and phosphorus leads to blooms of algae or phytoplankton… … and then microbial decay that sucks oxygen from the water (e.g., the hypoxic zone in the Gulf of Mexico) Eutrophication: Eutrophication Excess nutrients promote algal growth… and its decay depletes water of oxygen needed by fish. Figure 14.18a Eutrophication: Eutrophication Figure 14.18b,c Oligotrophic water body Eutrophic water body Types of pollution: Synthetic chemicals: Types of pollution: Synthetic chemicals Many thousands of chemicals we manufacture find their way into our water, where some have toxic effects. • Pesticides • Petroleum products • Arsenic, lead, mercury, other metals • Acids from mining runoff and acid precipitation Types of pollution: Sediment: Types of pollution: Sediment Erosion of soil from mining, clear-cutting, real estate development, and farming puts sediment into waterways. There it alters conditions and can kill organisms. Types of pollution: Heat and cold: Types of pollution: Heat and cold Yes, even heat and cold can pollute! Organisms not adapted to the new temperature conditions can suffer or die. • Warm water from power plants decreases dissolved oxygen. • Clearing streamside vegetation also warms water. • Cold water is released below dams, harming native fish. Groundwater pollution: Groundwater pollution Worse than surface water pollution, because it is longer lasting (e.g., persistent toxicants get washed out of rivers, but remain in groundwater until they break down.) Groundwater pollution: Groundwater pollution Sources are both natural and anthropogenic. NATURAL SOURCES: Arsenic Aluminum Fluoride Nitrates Sulfates HUMAN SOURCES: Leaky underground storage tanks (oil, gas, industrial chemicals, septic waste) Nitrates from fertilizers Pesticides Pathogens from wells and feedlots Contamination from underground hazardous waste disposal Industrial chemical waste Compounds from military sites Groundwater pollution: Thousands of wells dug by international aid workers for the benefit of Bangladesh’s citizens turned out to be poisoned with natural sources of arsenic. From The Science behind the Stories Mapped arsenic concentrations; red is highest Groundwater pollution Solutions for freshwater pollution: Solutions for freshwater pollution In AGRICULTURE: Reduce erosion to minimize sediment pollution Use fewer or less toxic pesticides Use fewer fertilizers Properly treat animal waste Solutions for freshwater pollution: Solutions for freshwater pollution In the INDUSTRIAL and MUNICIPAL sectors: Shift to processes that produce less waste Shift to less-toxic chemicals and products Invest in reducing leaks Properly treat wastewater Restrict use of pollutants over aquifers Follow government regulations for health and safety Solutions for freshwater pollution: Solutions for freshwater pollution In the RESIDENTIAL sector (what YOU can do): Buy phosphorus-free detergents and other “environmentally friendly” products Dispose of hazardous waste properly, not down a drain Get involved in monitoring your local watershed; join or start a grassroots “riverwatch” group Press politicians to support clean water Success stories: Success stories Many water pollution problems have decreased since the 1960s and 1970s, due to legislation: Clean Water Act of 1977 in the U.S. Similar acts in other nations The Great Lakes: Canadian and U.S. governments decreased PCBs, DDE, fertilizers, etc., by 70–90%. Fish and bird populations are now recovering. Marine Systems: Marine Systems Oceans cover 71% of Earth’s surface. Oceans contain 97.2% of the planet’s surface water. The one world ocean: The one world ocean The world’s oceans are connected in one vast water body. Figure 13.2 Ocean water composition: Ocean water composition The oceans consist of (by mass): 96.5% water 3.0% sodium and chlorine ions (table salt, Na+ and Cl–) 0.5% other salts Figure 13.3 Ocean currents: Ocean currents Currents = vast river-like flows in the surface waters of the ocean Driven by density differences, sunlight, wind Can be cool or warm Vary in size and speed Influence climate Figure 13.5b Major surface currents of the world’s oceans: Major surface currents of the world’s oceans Figure 13.5a Vertical movement of ocean water: Vertical movement of ocean water Ocean water can move up or down due to wind, heating, or density differences. Upwelling = cold deep water comes to surface Occurs where currents diverge Brings nutrients to surface; promotes fisheries Downwelling = warm surface water moves downward Occurs where currents converge Brings dissolved oxygen to deep-water life Upwelling: Upwelling Water along the California coast moves away from shore, allowing upwelling that nourishes biodiversity in surface waters. Figure 13.6 Bathymetry: Bathymetry Underwater topography reveals several major features: Gently sloping continental shelves underlie shallow waters around continents. The topographys drops down along continental slopes and continental rises to abyssal plains. Volcanic activity may create a trench where one plate is subducted beneath another. Magma erupting from plate boundaries may create mountains that break the water’s surface to become islands. Bathymetry: Bathymetry Figure 13.8 Pelagic zone = open water between surface and seafloor Benthic zone = ocean floor Marine ecosystems: Open ocean: Marine ecosystems: Open ocean Surface waters of the pelagic zone are variable in their biology. Many areas are scarce in life, but areas like nutrient-rich upwellings teem with life. Plankton (photo) are the base of the food chain. Figure 13.10 Marine ecosystems: Deep ocean: Marine ecosystems: Deep ocean Deep waters are devoid of sunlight, so ecosystems cannot rely on plant growth. Animals here (few and far between) scavenge detritus from above, or prey on each other, or have symbiotic microbes that produce food for them. Figure 13.11 The anglerfish is one of many bizarre-looking deep-sea creatures. The luminescent projection on its forehead attracts curious fish, which it eats. Marine ecosystems: Kelp forests: Marine ecosystems: Kelp forests Kelp (large brown algae or seaweed) grows up to 60 meters (200 feet) tall from the continental shelves. It creates “forests” that harbor and feed many other organisms. Figure 13.12 Marine ecosystems: Coral reefs: Marine ecosystems: Coral reefs Corals (photo) = tiny invertebrate animals that occur in huge numbers together. As they die, skeletons build coral reefs out of calcium carbonate. Reefs provide habitat, protection, and food for many other animals. Coral reefs are a key ecosystem for biodiversity. Figure 13.13 Marine ecosystems: Intertidal zones: Marine ecosystems: Intertidal zones Intertidal or littoral ecosystems occur along rocky beaches. Tides cover organisms most of each day, and leave them exposed to air or bathed in tidepools part of the day. High biodiversity: Starfish, crabs, sea urchins, algae, etc. Must endure extreme fluctuating conditions Figure 13.15b Marine ecosystems: Salt marshes: Marine ecosystems: Salt marshes Grassy salt marshes cover intertidal areas with sandy or silty substrate in temperate regions. They have high primary productivity, but people often drain for coastal development. Figure 13.16 Marine ecosystems: Mangrove forests: Marine ecosystems: Mangrove forests In tropical and subtropical regions, sandy/silty beaches host forests of mangroves, bushy trees adapted to salt water. Many animals find homes among the root networks. These forests are often lost to human development. Figure 13.17 Marine ecosystems: Estuaries: Marine ecosystems: Estuaries Many salt marshes and mangrove forests occur near estuaries, areas where rivers flow into the ocean and mix fresh with salt water. Biologically very productive: fish, birds, invertebrates Human use of oceans: Human use of oceans Transportation routes—early exploration; modern shipping Commercial fishing Mining minerals Energy sources, e.g., offshore oil Recreation Ocean pollution: Debris: Ocean pollution: Debris Garbage that litters the ocean doesn’t merely look ugly on beaches. It can kill marine life. Turtles die from eating plastic bags that look like jellyfish. Discarded fishing nets tangle seals and drown them. Plastic 6-pack rings strangle birds. Ocean pollution: Oil: Ocean pollution: Oil We get much of our petroleum from seafloor deposits drilled from offshore platforms. Some pollution results, but natural seeps in such areas also spurt oil into the ocean. Oil spills from tankers transporting oil are what grab headlines. Though rare, these can cause great damage locally. Figure 13.18 Ocean pollution: Oil: Ocean pollution: Oil Better prevention and response are beginning to reduce amounts of oil spilled into the oceans in major tanker spill events. BUT most oil entering the ocean is runoff coming from numerous minor sources on land. The oil leaking from your car finds its way to the sewer system, rivers, and, eventually, the ocean. Figure 13.19 Ocean pollution: Algal blooms: Ocean pollution: Algal blooms Excess nutrient runoff (as from fertilizers) can spur out-of-control growth of algae that kill fish and other organisms. These harmful algal blooms are also called red tides because some types color water red. Figure 13.20 Pollution solutions: Pollution solutions All these problems can be addressed: • Reduce plastic waste by reusing bags, buying less packaging, cutting 6-pack rings, etc. • Strengthen regulations on oil tankers further to minimize major spills. • Reduce oil runoff by disposing of hazardous waste safely. • Reduce fertilizer use to lessen chance of red tides. Emptying the oceans: Emptying the oceans As bad as some pollution problems may be, the oceans today suffer most from overfishing. Oceans are vulnerable to the “tragedy of the commons.” Depletion is not a new problem: For centuries people approached fishing as if “there’s always more fish in the sea.” Fishing had already taken a toll on marine ecosystems many decades before ecologists began studying them. Collapsing stocks: Collapsing stocks Overfished stocks (orange) increased tenfold, 1950-1994. Collapsing stocks hurt fishing communities as well as fish. Figure 13.23 Fishing practices: Fishing practices Many marine fishing practices are not specifically targeted to the species fishermen want to catch. Instead, they catch lots of nontarget species. This is the by-catch. By-catch accounts for deaths of many thousands of sharks, seals, dolphins, turtles, and birds each year. Fishing practices: Fishing practices Driftnetting catches and drowns many seals, dolphins, birds, turtles. Longlining kills albatrosses and other seabirds, as well as turtles and sharks. Bottom-trawling destroys whole ecosystems. Nets and bars dragged across the bottom flatten benthic structure, devastating habitat for marine organisms. Figure 13.24 Traditional fisheries management: Traditional fisheries management Based on maximum sustainable yield (MSY): Allow maximal harvests of particular populations while keeping fish available for the future Managers regulate catch with limits, quotas, seasons, etc. Many marine conservation biologists today say MSY has failed. Instead of single-species MSY, we need to manage for entire ecosystems: Set aside no-fishing areas to protect whole systems. MPAs and marine reserves: MPAs and marine reserves Many marine protected areas (MPAs) have been established—over 200 in U.S. waters alone. But these do not fully protect resources. Plenty of fishing and other activities can go on in MPAs. Marine reserves are no-fishing zones where absence of human impact allows fish to live and breed without interference. These “no-take” areas should preserve whole ecosystems and increase fish populations for fisheries. Fishermen have opposed marine reserves: Fishermen have opposed marine reserves Understandably, many fishermen reject the idea of no-take zones where fishing is banned. Conservationists are trying to convince them that no-take marine reserves HELP fishing by restoring fish populations inside the reserve, allowing young fish to populate areas outside the reserve that CAN be fished. They say reserves are a win-win proposition. Do marine reserves work?: Do marine reserves work? A review of marine reserves showed that within 1–2 years they: • Increased density of organisms 91% • Increased biomass of organisms 192% • Increased size of organisms 31% • Increased species diversity 23% How best to design reserves?: Small reserve: Fish wander out of reserve, are not protected. No gain for anyone. Medium reserve: Big enough to conserve fish. Small enough to let some out for fishermen to catch. Good balance of benefits for everyone. Large reserve: Good preservation, but too few fish leave reserve to be caught. Not acceptable to fishermen. Figure 13.25 How best to design reserves? Do marine reserves work?: Do marine reserves work? A study in the Caribbean showed biomass increasing more in areas that were made reserves, relative to those that weren’t. From The Science behind the Stories Conclusions: Challenges: Conclusions: Challenges Coastal ecosystems like coral reefs, mangroves, salt marshes, and estuaries are hard hit by human impact. Several types of pollution affect the oceans. Fishing stocks are seriously depleted, and many are nearing collapse. Several fishing practices cause substantial by-catch. Marine reserves have met opposition from fishermen. Conclusions: Challenges: Conclusions: Challenges The uneven distribution of water creates potential for scarcity and conflict as populations grow. Freshwater ecosystems have been greatly degraded by depletion and pollution of water. We are depleting surface and groundwater sources. Dams create many problems as well as benefits. Pollution of surface and groundwater sources is having health and ecological impacts. Conclusions: Solutions: Conclusions: Solutions Coastal residents need to be made aware of the ecological and economic importance of saving local ecosystems. Marine pollution can be reduced through citizen action and consumer behavior as well as through laws and regulations. Unless traditional MSY is greatly strengthened, no-take reserves appear necessary to restore fisheries. Methods to reduce by-catch are being developed, such as colored flags on longlines that warn seabirds of the lines. Scientists are compiling more data showing that marine reserves help fisheries and are talking with fishermen. Conclusions: Solutions: Conclusions: Solutions Although future “water wars” threaten, many nations have already entered into treaties to share water. Freshwater ecosystems (like the Great Lakes) can be restored if citizens push governments to take action. Many solutions exist for agriculture, industry, government, and consumers to conserve water. Dams with more costs than benefits can be removed. Many solutions exist for agriculture, industry, government, and consumers to reduce water pollution. QUESTION: Review: QUESTION: Review In regions of upwelling… ? a. Warm water moves upward, displacing cold water. b. Cold water transports dissolved gases upward. c. Nutrients are brought upward by cold water. d. Warm water moves upward and then along the coast. QUESTION: Review: QUESTION: Review Where might you find a kelp forest? a. In the Mississippi River Valley b. On the abyssal plain of the Atlantic Ocean c. On the continental shelf off the California coast d. Near a hydrothermal vent off British Columbia e. In the pelagic portion of the Indian Ocean QUESTION: Review: QUESTION: Review Which statement about coral is NOT true? a. Their skeletons help build reefs. b. They feed by swimming in areas of upwelling. c. They feed by using stinging tentacles. d. Creatures living inside them provide nutrition via photosynthesis. e. They provide habitat for other creatures. QUESTION: Review: QUESTION: Review What is meant by “fishing down the food chain”? a. Catching herbivorous fish species b. Catching species that are producers c. Using high-tech equipment to find large individuals d. Catching species on lower trophic levels, after depletion of other species e. Using producer species to catch consumer species QUESTION: Weighing the Issues: QUESTION: Weighing the Issues Almost 4% of U.S. land area is designated wilderness, but far less than 1% of coastal waters are protected in reserves. Why has it taken so long for the preservation ethic to reach the oceans? a. The oceans need preservation less than terrestrial systems. b. Fewer environmentalists care about the oceans than about the land. c. Because people don’t generally look underwater, we were unaware until recently what bad shape the oceans were in. QUESTION: Interpreting Graphs and Data: QUESTION: Interpreting Graphs and Data Figure 13.23 Which statement is correct? a. Undeveloped fisheries have increased over time. b. Senescent fisheries have increased over time. c. Fully developed fisheries have decreased over time. d. In 1967 there were more senescent fisheries than developing fisheries. QUESTION: Review: QUESTION: Review Which of the following is NOT true about aquifers? a. They hold surface water. b. They can be “confined” or “unconfined.” c. They can become polluted by numerous toxic substances. d. They generally are very slow to recharge. QUESTION: Review: QUESTION: Review Which water body would contain many nutrients and low oxygen levels? a. An oligotrophic lake b. A eutrophic lake c. A pristine fast-flowing mountain stream d. The deep ocean e. All of the above QUESTION: Review: QUESTION: Review Which of the following is NOT true about dams and their associated reservoirs? a. They alter riparian habitat. b. They can capture sediment. c. They can provide irrigation, hydropower, flood control, and drinking water. d. They can never be removed once built. e. They promote some types of recreation and inhibit others. QUESTION: Review: QUESTION: Review Which is a possible effect of groundwater depletion? a. Subsidence and sinkholes b. Sediment capture c. Saltwater intrusion into aquifers d. Both (a) and (b) e. Both (a) and (c) QUESTION: Weighing the Issues: QUESTION: Weighing the Issues As cities of the arid U.S. southwest grow and water becomes scarce, what should these metropolises do? a. Pull as much water as they can from the Colorado River b. Build desalination plants c. Regulate industry and agriculture more heavily to restrict water waste d. Promote conservation measures through education and market incentives QUESTION: Viewpoints: QUESTION: Viewpoints Should we remove dams? a. Yes; they have more costs than benefits. b. Sometimes; we should judge them on a case-by-case basis. c. No; they have more benefits than costs. No; money and resources are best spent on other things.