water, water everywhere and not a drop to drink! 3.6 water resources
TRANSCRIPT
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Water, water everywhere and not a drop to drink!
3.6 Water Resources
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Connections between water resources and food resources
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Earth’s water budgetOnly about 3% of the water on our planet is
fresh water (97% salt water)69% of fresh water is in polar ice caps and
glaciers 30% is ground waterThe remaining 1% is lakes rivers swamps
and in the atmosphere
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Human Uses for Fresh waterDomestic water ( drinking, washing,
cleaning)IrrigationIndustry (manufacturing, mining, andagriculture)Hydroelectric powerTransportation (ships on lakes/rivers)Boundaries (states and nations)
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Water Usage Pie Chart
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Problems related to freshwater use• Low water levels in rivers, streams and lakes• Slow water flow• Underground aquifers become exhausted • Irrigation causes much of the water to
evaporate before it can be used. • Fertilizer and pesticides and industries
pollute streams • Industries release warm water into rivers,
causes dissolved oxygen to decrease (warm water contains less Oxygen).
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Solutions• Reduce domestic use of fresh water (shorter
showers/wash cars less…)• Irrigation: Drought resistant crops- Closed
pipes instead of open canals• Reduce farming contamination (pesticides and
fertilizers). • Force industry to remove pollutants from
wastewater
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Case Study: The Colorado River: An Over tapped Resource
1,429 miles through 7 U.S. statesSupplies water and electricity ~30 million people
in USA and MexicoHeavily dammed for electricity and agriculture
(14 dams)80% used for irrigation and cattle ranchingDownstream (in Mexico) can dry up completely
some years and lead to droughts.Salinity problems prevent irrigation in MexicoDried river causes loss of biodiversity
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The Colorado River Basin
Fig. 13-1, p. 317
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Aerial View of Glen Canyon Dam Across the Colorado River and Lake Powell
Fig. 13-2, p. 317
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A Closer Look at the Over tapped Colorado River Basin
Current rate of river withdrawal is not sustainable
Much water used for agriculture that is inefficient with water use: cotton, alfalfa, riceWater use subsidized by government
ReservoirsLeak water into ground belowLose much water through evaporationFill up with silt load of river, depriving deltaCould eventually lose ability to store water and
create electricityStates must conserve water, control population,
and slow urban development
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Water Shortages Will GrowDry climatesDroughtToo many people using a normal supply of
waterWasteful use of water30% earth’s land area experiences severe
droughtPotential conflicts/wars over water
Refugees from arid landsIncreased mortality
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Fig. 13-5, p. 322
Washington
OregonMontana
North Dakota
Idaho South DakotaWyoming
NevadaNebraska
Utah Colorado Kansas
California Oklahoma
ArizonaNew Mexico
Texas
Highly likely conflict potential
Substantial conflict potential
Moderate conflict potential
Unmet rural water needs
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Natural Capital Degradation: Stress on the World’s Major River Basins
Fig. 13-6, p. 323
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Is Extracting Groundwater the Answer? Groundwater is Being Withdrawn Faster Than It Is
ReplenishedMost aquifers are renewableAquifers provide drinking water for half the worldWater tables are falling in many parts of the world,
primarily from crop irrigation
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Water: A Replenishable ResourceIndia, China, and the United States
Three largest grain producersOver pumping aquifers for irrigation of cropsSmall farmers drilling tube wells Effect on water table
Saudi ArabiaAquifer depletion and irrigation
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Fig. 13-7, p. 325
Trade-Offs
Withdrawing Groundwater
Advantages Disadvantages
Useful for drinking and irrigation
Aquifer depletion from overpumping
Exists almost everywhere
Sinking of land from over pumping
Renewable if not overpumped or contaminated
Pollution of aquifers lasts decades or centuries
Deeper wells are nonrenewable
Cheaper to extract than most surface waters
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Is Building More Dams the Answer?
Main goal of a dam and reservoir systemCapture and store runoffRelease runoff as needed to control:
FloodsGenerate electricitySupply irrigation waterRecreation (reservoirs)
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Advantages and Disadvantages of Dams
AdvantagesReduce floodingZero emissions electricity production
DisadvantagesDisplaces people with reservoir Impaired ecological services of riversLoss of plant and animal speciesCan cause other streams and lakes to dry up
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Fig. 13-13a, p. 328
Provides irrigation water above and below dam
Flooded land destroys forests or cropland and displaces people
Large losses of water through evaporation
Provides water for drinking
Deprives downstream cropland and estuaries of nutrient-rich silt
Reservoir useful for recreation and fishing
Risk of failure and devastating downstream flooding
Can produce cheap electricity (hydropower)
Reduces down-stream flooding of cities and farms
Disrupts migration and spawning of some fish
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Is irrigation the answer? Case Study: The Aral Sea DisasterLarge-scale water transfers for irrigation
stops flow of water into the Aral SeaLess Water = Increase in salinityFish population declinesWater pollutionRestoration efforts
More efficient irrigationDam built to help raise lake level
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Natural Capital Degradation: The Aral Sea, Shrinking Freshwater Lake
Fig. 13-17, p. 332
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Is Desalination the Answer? Desalination- Removing Salt from
Seawater Distillation: evaporate water, leaving salts
behindReverse osmosis, microfiltration: use high
pressure to remove saltsProblems: Very Costly, Kills Organisms,
Creates Briny Wastewater14,450 plants in 125 countries
Saudi Arabia: highest number
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The Search for Improved Desalination Technology
Desalination on offshore shipsSolar or wind energy
Use ocean waves for powerBuild desalination plants near electric power
plants
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Deforestation Above China’s Yangtze River Contribute to Erosion and Floods
Fig. 13-26, p. 341
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Fig. 13-25a, p. 340
Diverse ecological habitat
Evapotranspiration
Trees reduce soil erosion from heavy rain and wind
Agricultural land
Tree roots stabilize soil
Vegetation releases water slowly and reduces floodingForested Hillside
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Fig. 13-25b, p. 340
Tree plantation
Roads destabilize hillsides Overgrazing accelerates soil
erosion by water and wind
Evapotranspiration decreases
Winds remove fragile topsoil
Agricultural land is flooded and silted up
Gullies and landslides
Heavy rain erodes topsoil
Silt from erosion fills rivers and reservoirs Rapid runoff causes flooding
After Deforestation
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Three Big Ideas1. One of the world’s major environmental problems is
the growing shortage of freshwater in many parts of the world.
2. We can increase water supplies in water-short areas in a number of ways, but the most important way is to reduce overall water use and waste by using water more sustainably.
3. We can use water more sustainably by cutting water waste, raising water prices, slowing population growth, and protecting aquifers, forests, and other ecosystems that store and release water.