Environmental Science: Toward a Sustainable Future Richard T' Wright

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Environmental Science Toward a Sustainable
Future Richard T. Wright
Chapter 7

• Water Hydrologic Cycle and Human Use
• PPT by Clark E. Adams

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Water Hydrologic Cycle and Human Use

• Water a vital resource
• Hydrologic cycle natural cycle, human impacts
• Water a resource to manage, a threat to control
• Water stewardship public-policy challenges

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Water A Vital Resource
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Hydrologic Cycle Natural Cycle, Human Impacts

• Evaporation, condensation, purification
• Precipitation
• Groundwater
• Pools and fluxes in the cycle
• Human impacts on the hydrologic cycle

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Polarity in H2O The Water Molecule
covalent bond
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Condensation
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Temperature Determines Whether Water Is a

• Gas steam
• Liquid running water
• Solid ice
• Why does ice float?

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The Water Cycle
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Water Cycle Review
B
A
D
C
E
F
H
G
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Condensation
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Precipitation

• Adiabatic cooling warm air rises, expands and
  cools
• 100 relative humidity cooling clouds
• Increasing condensation water droplets

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Global Precipitation

• Global precipitation distribution depends on
  patterns of rising and falling air currents
• Two main factors
• global convection currents
• rain shadow effect

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Global Air Circulation
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Rain Shadow Effect
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Water Balance in the Hydrologic Cycle
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Pools and Fluxes in the Cycle
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Human Impacts on the Water Cycle

• Changing the Earths surface
• Floods
• Climate change
• Atmospheric pollution
• Withdrawing water supplies

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Groundwater

• Decreased infiltration
• Increased runoff
• Decreased groundwater recharge

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Human Impacts on the Hydrologic Cycle
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Water A Resource to Manage, A Threat to Control

• Uses and sources
• Surface waters

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Water Uses
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Water Uses
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Municipal Water Use and Treatment
What is your communitys water source?
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Surface Waters

• Dam impacts (see Fig. 7-15)
• Ecological effects of changing salinity in
  estuaries
• Increased salinity
• Loss of native species
• Invasive species increase

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Consequences of Overdrawing Groundwater

• Falling water tables
• Diminishing surface waters (wetlands)
• Land subsidence (see Fig. 7-17)
• Saltwater intrusion

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Aquifer Exploitation

• Groundwater use exceeds aquifer recharge
• Many remaining aquifers are heavily polluted

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Saltwater Intrusion
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Water Stewardship Public-Policy Challenges

• Obtaining more water
• Groundwater
• Using less water
• Public-policy challenges

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Dams

• Three Gorges Dam
• Largest in world
• Controls deadly floods
• Displaced 1.2 million people including farms,
  cities, homes, and factories
• 370-mile-long reservoir

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Dams Disrupt Integrity of River System

• Above the dam
• Flooding
• Sediment deposition
• Loss of functional floodplain
• Below the dam
• Loss of normal river flow patterns
• Loss of river biota
• Loss of functional floodplain

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Using Less Water

• Irrigation
• Surge flow
• Drip irrigation
• Municipal uses
• Incentives and regulations limiting water use
• Gray water

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Desalting Seawater

• Reverse osmosis
• Distillation

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Public-Policy Challenges
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National Water Policy

• Promote water efficiency
• Reduce or eliminate water subsidies
• Charge polluters
• Add watershed management to pricing of water

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National Water Policy

• United States must respond to global water crisis
• United States must reduce emission of greenhouse
  gases
• Need more data for informed policy decisions

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End of Chapter 7