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Lecture Outlines Chapter 15 Environment: The Science behind the Stories 4th Edition Withgott/Brennan

Lecture Outlines Chapter 15 Environment: The Science behind the Stories 4th Edition Withgott/Brennan. This lecture will help you understand:. Water’s importance to people and ecosystems Water’s distribution Use and alteration of freshwater systems Problems of water supply and solutions

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Lecture Outlines Chapter 15 Environment: The Science behind the Stories 4th Edition Withgott/Brennan

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  1. Lecture Outlines Chapter 15 Environment:The Science behind the Stories 4th Edition Withgott/Brennan

  2. This lecture will help you understand: • Water’s importance to people and ecosystems • Water’s distribution • Use and alteration of freshwater systems • Problems of water supply and solutions • Problems of water quality and solutions • How wastewater is treated

  3. Gambling with water in the Colorado River basin • 7 states share the Colorado river • Droughts and overuse are threatening supplies • Las Vegas, Nevada, needs more water than it is allotted • Other states will let Las Vegas drill for underground water • Drilling threatens the area’s ecology and people • This issue will end up in Nevada’s Supreme Court

  4. The Colorado River • The Colorado River originates in the Rocky Mountains • Draining into the Gulf of California • Its waters chiseled the Grand Canyon • But it has been reduced to a mere trickle • Dams provide flood control, recreation, and hydroelectric power • 30 million people use the water

  5. Freshwater systems • Water may seem abundant, but drinkable water is rare • Freshwater = relatively pure, with few dissolved salts • Most is tied up in glaciers, ice caps, and aquifers

  6. Water is renewed and recycled • As water is cycled it redistributes heat, erodes mountains, builds river deltas, maintains ecosystems and organisms • It also shapes civilizations and political conflicts • Surface water = on Earth’s surface • 1% of freshwater • 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 • Watershed (drainage basin) = the area of land drained by a river system (river and its tributaries)

  7. Water is renewed and recycled as it moves through the hydrologic cycle

  8. Water Cycle Scramble

  9. Rivers and streams wind through landscapes • Rivers shape the landscape • Braided river = an interconnected series of watercourses that run through steep slopes • Meandering river = rivers in flatter areas • Water rounding a bend erodes soil from the outer bank • Sediment is deposited on the inside of the bend • Rivers become exaggerated oxbows

  10. Rivers shape the landscape • Oxbows = areas where river bends become exaggerated • Oxbow lake = erosion cuts off and isolates the oxbow into a U-shaped water body

  11. A river may shift course over time • Floodplain = areas nearest to the river’s course that are flooded periodically • Frequent deposition of silt makes floodplain soils fertile • Good areas for agriculture • Riparian= riverside areas that are productive and species-rich • Rivers and streams hosts diverse ecological communities • Algae, insects, fish, amphibians, birds, etc.

  12. Lakes and ponds are ecologically diverse • Lakes and ponds = 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 = extends along the bottom of the water body • Home to many invertebrates • Limnetic zone = open portion of the lake or pond where sunlight allows photosynthesis • Profundal zone = water that sunlight does not reach • Supports fewer animals because there is less oxygen

  13. A typical lake

  14. Lakes vary in their nutrients and oxygen • Oligotrophic lakes and ponds = have low nutrient and high oxygen conditions • Eutrophic lakes and ponds = have high nutrient and low oxygen conditions • Eventually, water bodies fill completely in through the process of succession • The largest lakes are known as inland seas • Great Lakes, The Caspian Sea

  15. Wetlands include marshes, swamps, bogs, and seasonal pools • Wetlands = the soil is saturated with shallow standing water • Freshwater marshes = shallow water • Plants 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 Species in vernal pools are adapted to seasonal drying

  16. Wetlands are valuable • Wetlands are extremely valuable for wildlife • They slow runoff, reduce flooding, recharge aquifers, and filter pollutants • People have drained wetlands, mostly for agriculture • Southern Canada and the U.S. have lost over half of their wetlands • In 2006 the Supreme Court told the Army Corps of Engineers it must create guidelines to determine when wetlands are valuable enough to protect by law

  17. Groundwater plays a key role • Groundwater = water beneath the surface held in pores in soil or rock • 20% of the Earth’s freshwater supply • Aquifers = porous, sponge-like formations of rock, sand, or gravel that hold water • Zone of aeration = pore spaces are 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

  18. A typical aquifer

  19. There are two categories of aquifers • Confined (artesian) aquifer = water-bearing, porous rocks are trapped between less permeable substrate (clay) layers • Is under great pressure • Unconfined aquifer = no upper layer to confine it • Readily recharged by surface water • Groundwater’s average age is 1,400 years • It may be tens of thousands of years old • Groundwater becomes surface water through springs or human-drilled wells

  20. The Ogallala Aquifer • The world’s largest known aquifer • Underlies the Great Plains of the U.S. Its water has allowed farmers to create the most bountiful grain-producing region in the world

  21. Water is unequally distributed across Earth • Water is unevenly distributed in space and time • Different areas possess different amounts of water • People erect dams to store water Many densely populated areas are water-poor and face serious water shortages

  22. Climate change may bring shortages • Climate change will cause • Altered precipitation patterns • Melting glaciers • Early season runoff • Intensified droughts • Flooding Lake Mead is already hurting from drought

  23. How we use water • We have achieved impressive engineering accomplishments to harness fresh water • 60% of the world’s largest 227 rivers have been strongly or moderately affected • Dams, dikes, and diversions • Consumption of water in most of the world is unsustainable • We are depleting many sources of surface water and groundwater

  24. Water supplies houses, agriculture, and industry • Proportions of these three types of use vary dramatically among nations • Arid countries use water for agriculture • Developed countries use water for industry • Consumptive use = water is removed from an aquifer or surface water body and is not returned • Irrigation = the provision of water to crops • Nonconsumptive use = does not remove, or only temporarily removes, water • Electricity generation at hydroelectric dams

  25. Why does agriculture use so much water? • Rapid population growth requires more food and clothes • The Green Revolution uses irrigation • We use 70% more irrigation water than 50 years ago • Irrigation can 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

  26. Governments subsidize irrigation • Irrigation subsidies promote food self-sufficiency • But irrigation uses up huge amounts of groundwater for little gain • Water in the Colorado River Valley is diverted for cotton and other crops grown in the desert Farmers in California’s Imperial Valley pay only 1 penny for 220 gallons of water

  27. We divert surface water for our needs • People divert water to farm fields, homes, and cities The once mighty Colorado River has been extensively diverted and used

  28. Water-poor regions take water from others • 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, L.A. diverted streams that fed Lake Mono • Lake levels fell, salt concentrations doubled • Las Vegas wants to import water from sparsely populated eastern Nevada • An ecologically sensitive area

  29. We 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 • Dikes and levees (long, raised mounds of earth) along the banks of rivers hold water in channels • Levees make floods worse by forcing water to stay in channels and then overflow • Dams prevent flooding and change a river’s nature • Releasing water periodically simulates flooding

  30. Levees increase flooding • A major levee along the Mississippi River failed after Hurricane Katrina, allowing parts of New Orleans to be flooded

  31. We have erected thousands of dams • Dam = any obstruction placed in a river or stream to block the flow of water to prevent floods, provide drinking water, allow irrigation, and generate electricity • 45,000 large dams have been erected in more than 140 nations • Only a few major rivers remain undammed • In remote regions of Canada, Alaska, and Russia • Dams are great engineering feats • Many stand hundreds of feet tall

  32. A typical dam

  33. China’s Three Gorges Dam • The dam, on the Yangtze River, is the largest in the world • 186 m (610 feet) high, 2.3 km (1.4 mi) wide • Its reservoir stretches for 616 km (385 mi) • Provides flood control, passage for boats, and electricity

  34. Drawbacks of the Three Gorges Dam • 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 • Tidal marshes at the Yangtze’s mouth are eroding • Pollutants will be trapped It will cost $5 billion to build sewage treatment plants to treat water

  35. Some dams are being removed • Some people feel that the costs of dams outweigh their benefits • They are pushing to dismantle dams • 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 U.S. • Property owners who opposed the removal change their minds once they see the healthy river

  36. We are depleting surface water • In many places, we are withdrawing water at unsustainable rates • Reduced flow drastically changes the river’s ecology, plant community, and destroys fish and invertebrates • The Colorado River often does not reach the Gulf of California

  37. The Aral Sea 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 from the lake bed is blown into the air Cotton cannot save the region’s economy

  38. Can the Aral Sea be saved? People have begun saving the northern part of the Aral Sea

  39. Irrigation wastes water • 15–35% of water withdrawals for irrigation are unsustainable • Water mining = withdraws water faster than it can be replenished

  40. The world is losing wetlands • Wetlands are being lost as we divert and withdraw water • Channelize rivers, build dams, etc. • As wetlands disappear, we lose ecosystem services • Filtering pollutants, wildlife habitat, flood control, etc. • Many are trying to protect and restore them • The Ramsar Convention on Wetlands of International Importance (1971) • Seeks the conservation and wise use of wetlands in the context of sustainable development • 1,900 sites covering 185 million ha are protected

  41. We are depleting groundwater • Groundwater is easily depleted • Aquifers recharge slowly • Used by one-third of all people • As aquifers are mined, water tables drop • Salt water intrudes in coastal areas • Sinkholes = areas where ground gives way unexpectedly • Aquifers can’t recharge • Wetlands dry up

  42. Can we quench our thirst for bottled water? • Groundwater is being withdrawn for bottled water • An average American drinks 29 gallons/year • 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 • Bottles are not recycled • Corporations move in, deplete water, and move away

  43. Bottled water is popular but problematic • Bottled water is popular but it has several problems Energy costs of bottled water are 1,000–2,000 times greater than those of tap water

  44. Will we see a future of water wars? • 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 • Many nations have cooperated with neighbors to resolve disputes • They sign water-sharing treaties

  45. Solutions can address supply or demand • We can either increase supply or reduce demand • Increasing supply through intensive extraction • Diversions increase supply in one area but decrease it elsewhere • 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

  46. Desalinization “makes” more 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 • Desalinization facilities operate mostly in the arid Middle East • It is expensive, requires fossil fuels, kills aquatic life, and produces salty waste

  47. The world’s largest reverse osmosis plant • Near Yuma, Arizona • Intended to remove salt from irrigation runoff • Too expensive to operate and closed after 8 months • Engineers are trying to re-open it in a cost-effective way

  48. Agricultural demand can be reduced • Line irrigation canals • 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 • Selective breeding and genetic modification to produce crops that require less water • Eat less meat

  49. Residential demand can be reduced • Install low-flow faucets, showerheads, washing machines, and toilets • Rainwater harvesting = capturing rain from roofs • Gray water = wastewater from showers and sinks • Water lawns at night • We can save hundreds or thousands of gallons/day Xeriscaping uses plants adapted to arid conditions

  50. Industrial demand can be reduced • Shift to processes that use less water • Wastewater recycling • Use excess surface water runoff to recharge aquifers • Patch leaky pipes and retrofit homes with efficient plumbing • Audit industries • Promote conservation/education

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