Chapter 17 Water: Resources and Pollution

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Chapter 17 Water Resources and Pollution
"Water will be more important than oil this
century. - Former U.N. Secretary General Boutros
Boutros Gali
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Ch 17 Outline

• Hydrologic Cycle
• Major Water Compartments
• Water Availability and Use
• Types of Water Use
• Freshwater Shortages
• Dams and Diversions
• Increasing Water Supplies

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Objectives

• 17.1 Explain why water is a precious
  resource and why shortages occur.
• 17.2 Compare major water compartments.
• 17.3 Summarize water availability and use.
• 17.4 Investigate freshwater shortages.
• 17.5 Illustrate the benefits and problems of
  dams and diversions.
• 17.6 Understand how we might increase water
  supplies.

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Why is Water Important?

• Necessary for all life to exist.
• Next to antibiotics, single biggest increase in
  human life span is due to having access to clean
  water.
• Diseases/toxins transmitted by contaminated
  water
• Intestinal disease (cholera/dysentery)
• Arsenic poisoning
• Mercury poisoning

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Average Annual Precipitation
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Hydrologic Cycle

• The water on earth is continually recycled.
• The hydrologic cycle describes this circulation
• Water evaporates from wet land, lakes, or oceans
  and transpires from plants as they dry up.
• Enters the atmosphere, which is much colder,
  condenses and falls as precipitation.
• Moves underground by infiltration or runs off
  into rivers, lakes, or the ocean.

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Hydrologic Cycle

• Solar energy drives the hydrologic cycle by
  evaporating surface water.
• Evaporation - changing liquid to a vapor below
  its boiling point
• Sublimation - changing water between solid and
  gaseous states without ever becoming liquid

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Hydrologic Cycle

• Humidity - amount of water vapor in the air
• Saturation point - when a volume of air contains
  as much water vapor as it can hold at a given
  temperature
• Relative humidity - amount of water vapor in the
  air expressed as a percentage of the maximum
  amount that can be held at that temperature

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Hydrologic Cycle

• Dew point - temperature at which condensation
  occurs for a given amount of water vapor
• Condensation nuclei - tiny particles that
  facilitate condensation
• Smoke, dust, sea salt, spores
• A cloud is an mixture of condensed water vapor in
  droplets or ice crystals. When droplets become
  large enough, gravity overcomes air currents and
  precipitation occurs.

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Regions of Plenty and Regions of Deficit

• Three principal factors control global water
  deficits and surpluses
• Global atmospheric circulation
• Proximity to water sources
• Topography

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Regions of Plenty and Regions of Deficit

• Mountains act as cloud formers and rain catchers.
• Air sweeps up the windward side of a mountain,
  pressure decreases, and the air cools.
• Eventually saturation point is reached, and
  moisture in the air condenses.
• Rain falls on the mountaintop.
• Cool, dry air descends and warms, absorbing
  moisture from other sources (Rain shadow).

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Rain Shadow Hawaiian style
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Earths Water Budget
All water
Oceans and saline lakes 97.4
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Earths Water Budget
All water
Oceans and saline lakes 97.4
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Earths Water Budget
All water
Fresh water
Readily accessible fresh water
Groundwater 0.592
Biota 0.0001
Rivers 0.0001
Lakes 0.007
0.014
Fresh water 2.6
Atmospheric water vapor 0.001
Oceans and saline lakes 97.4
Ice caps and glaciers 1.984
Soil moisture 0.005
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Major Water Compartments

• 1. Oceans
• Together, oceans contain more than 97 of all
  liquid water in the world.
• Contain 90 of worlds living biomass
• Moderate earths temperature
• Gulf Stream carries 100X more water than all
  rivers on earth.
• Average residence time of water in the ocean is
  about 3,000 years

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Major Water Compartments

• 2. Glaciers, Ice, and Snow
• 2.4 of worlds water is classified as fresh.
• 90 is frozen in glaciers, ice caps, and
  snowfields
• As recently as 18,000 years ago, one-third of
  continental landmass was covered by glacial ice
  sheets.
• Now, Antarctic glaciers contain nearly 85 of all
  ice in the world.
• Greenland, together with ice floating around the
  North Pole, is another 10.

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Major Water Compartments

• 3. Groundwater
• Second largest reservoir of fresh water
• Infiltration - process of water percolating
  through the soil and into fractures and permeable
  rocks
• Zone of aeration - upper soil layers that hold
  both air and water
• Zone of saturation - lower soil layers where all
  spaces are filled with water
• Water table - top of zone of saturation

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Infiltration
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Groundwater

• Aquifers - Porous layers of sand, gravel, or rock
  lying below the water table.
• Aquifers are separate from groundwater they are
  usually isolated by layers of rock.
• Artesian Well Directly tapes into an aquifer as
  a source of water.

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Groundwater

• The recharge zone is an area where water
  infiltrates and refills an aquifer.
• Recharge rate is often very slow, depending on
  the size of the recharge zone and how often it
  rains there.

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Major Water Compartments

• Rivers and Streams
• Precipitation that does not evaporate or
  infiltrate into the ground runs off the surface,
  back toward the sea.
• Best measure of water volume carried by a river
  is discharge (cfs).
• The amount of water that passes a fixed point in
  a given amount of time

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Major Water Compartments

• Lakes and Ponds
• Ponds are generally considered small bodies of
  water shallow enough for rooted plants to grow
  over most of the bottom.
• Lakes are inland depressions that hold standing
  fresh water year-round.
• Both ponds and lakes will eventually fill with
  sediment, or be emptied by an outlet stream.

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Major Water Compartments

• Wetlands
• Play a vital role in hydrologic cycle
• Lush plant growth stabilizes soil and retards
  surface runoff, allowing more aquifer
  infiltration.
• Disturbance reduces natural water-absorbing
  capacity, resulting in floods and erosion in
  wet periods, and less water flow the rest of the
  year.
• Half of U.S. wetlands are gone.
• Can hold excess water during flooding.

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Major Water Compartments

• The Atmosphere
• Among the smallest water reservoirs
• Contains lt 0.001 of total water supply
• Has most rapid turnover rate
• Provides mechanism for distributing fresh water
  over landmasses and replenishing terrestrial
  reservoirs

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Water Availability and Use

• Renewable Water Supplies
• Made up of surface runoff plus infiltration into
  accessible freshwater aquifers
• About two-thirds of water carried in rivers and
  streams annually occurs in seasonal floods too
  large or violent to be stored effectively for
  human use.

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Drought Cycles

• Every continent has regions of scarce rainfall
  due to topographic effects or wind currents.
• Water shortages have most severe effect in
  semiarid zones where moisture availability is the
  critical factor in plant and animal
  distributions.
• U.S. seems to have 30 year drought cycle.
• Dust Bowl in 1930s

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Drought Cycles

• Much of Western U.S. is still plagued by drought
  and overexploitation of limited supply of water.
• El Nino plays an important role in determining
  when North America has drought.
• Global warming may make droughts more frequent
  and severe.

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Water Consumption

• Withdrawal - total amount of water taken from a
  source
• Consumption - fraction of withdrawn water made
  unavailable for other purposes (not returned to
  its source)
• Degradation - Change in water quality due to
  contamination making it unsuitable for desired
  use. Much water that is not consumed is
  nevertheless polluted.

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Water Use is Increasing

• Many societies have always treated water as an
  inexhaustible resource.
• Natural cleansing and renewing functions of
  hydrologic cycle do not work properly if systems
  are overloaded or damaged
• Renewal of water takes time
• Rate at which we are now using water makes
  conservation necessary

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Quantities of Water Used

• Human water use has been increasing about twice
  as fast as population growth over the past
  century, but impact varies with location.
• Canada withdraws less than 1 of its renewable
  supply per year.
• In Israel, groundwater and surface water
  withdrawals equal more than 100 of the renewable
  supply. Obviously, this is not sustainable.

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Agricultural Water Use

• Water use is divided into agriculture, domestic
  use and industrial use.
• Worldwide, agriculture claims about two-thirds of
  total water withdrawal and 85 of consumption.
• Aral Sea, once the fourth largest inland body of
  water in world, has been drained.
• Lake Chad in northern Africa went from 400,000
  sq. km to less than 1,000 sq. km.

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Exhibit A

• During the late 1940s, Joseph Stalin proposed a
  plan in the Soviet Union to prevent a repeat of
  drought-caused famine in 1947 that killed nearly
  a million people.
• A wide variety of ideas were implemented during
  the next two decades.

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• A network of irrigation canals were built to
  divert water from two rivers into a desert
  region, to encourage the cultivation of crops
  such as rice, wheat, and cotton.
• The rivers normally fed into the Aral Sea.

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The Aral Sea

• In the 1950s, the Aral sea was one of the four
  largest lakes in the world, with an area of
  26,300 square miles.
• The entire lake was part of the U.S.S.R., in the
  countries that today are Kazakhstan and
  Uzbekistan.

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Irrigation Canals

• The irrigation canals were poorly built and
  uncovered, allowing about half of the water to
  evaporate or leak into the surrounding soil.
• The Aral sea, deprived of its main water supply,
  began to shrink in 1961.

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Aral Sea
Satellite imagery of the Aral Sea shrinkage from
1961-2011.
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Water Use

• Consumption Water that is withdrawn and no
  longer available for use because it has
  evaporated, been consumed by animals or plants,
  or discharged to a different location.

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Water Use in Agriculture

• Irrigation can be inefficient.
• Flood or furrow irrigation
• Half of water can be lost through evaporation.
• Flood irrigation used to remove salts from field,
  but salt contaminates streams
• Sprinklers have high evaporation.
• Drip irrigation releases water near roots,
  conserving water.

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Quantities of Water Used

• Water use has been increasing twice as fast as
  population growth over past century.
• Worldwide, agriculture claims about 70 of total
  water withdrawal.
• In many developing countries, agricultural water
  use is extremely inefficient and highly
  consumptive.
• Worldwide, industry accounts for about 25 of all
  water use.
• Cooling water for power plants is single largest
  industrial use.

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Water Withdrawal
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Typical Household Water Use in U.S.
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FRESHWATER SHORTAGES

• Areas that consume more water than typically
  falls as precipitation are considered to have
  water stress.

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Freshwater Shortages

• U.N. estimates a billion people lack access to
  safe drinking water.
• 2.6 billion lack acceptable sanitation.
• At least 45 countries, mostly in Africa and the
  Middle East, are considered to have serious water
  stress.
• Water shortages could lead to wars as population
  grows and climate change dries up some areas. An
  underlying cause of the Darfur genocide is water
  scarcity.

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Freshwater Shortages

• Privatization of public water supply in Bolivia
  sparked a revolution that overthrew the
  government in 2000.
• Multinational corporations are moving to take
  control of water supplies in many countries.
• Global warming may make water shortages much
  worse in many parts of the world.

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A Precious Resource

• Currently, 45 countries cannot meet the minimum
  essential water requirements of their citizens.
• Will increase to 60 countries by 2050.

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Dams and Diversions

• Before 1900 there were 250 high dams in the
  world today there are more than 45,000.
• In the U.S. dams are built by Army Corps of
  Engineers and Bureau of Reclamation
• Provide cheap hydroelectric power
• Jobs
• Reduce flooding
• Allow farming on lands that would otherwise be
  too dry

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Dams and Diversions

• On the downside, dams
• Drown free flowing rivers
• Submerge farmlands and towns
• Block fish migration e.g. salmon
• Change aquatic habitats for native species
• Can sometimes fail, causing catastrophe
• Johnstown flood (city just east of Pittsburgh,
  PA) killed 2,200 people when dam broke.
• Dam failure in China killed 230,000.

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Dams and Diversions

• Tide of public opinion is turning
• Army Corps of Engineers announced in 1998 that it
  would no longer be building large dams and would
  be removing some older dams to restore natural
  habitat
• Sediment carried by rivers eventually fills up
  dams
• Lakes behind dams lose huge amounts of water
  through evaporation and seepage
• Downriver habitats lose nutrients and the beaches
  disappear as sediment is no longer available

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Dams and Diversions

• Diversion projects can dry up rivers
• Yellow River in China is dry 226 days per year
  due to diversions
• Colorado River in the U.S. is so depleted that
  most of the year no water reaches the mouth of
  the river in the Sea of Cortez
• Mono Lake has been depleted to send water to Los
  Angeles. Salinity of water doubled, killing the
  brine shrimp that fed huge flocks of migratory
  birds

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Mono Lake in California

• Diversion of water from the lake to Los Angeles
  has shrunk the lake by 1/3, exposing these towers
  where calcium- rich springs once entered the lake.

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Depleting Groundwater

• Groundwater is the source of nearly 40 of fresh
  water in the U.S.
• On a local level, withdrawing water faster than
  it can be replenished leads to a cone of
  depression in the water table.
• Heavy pumping can deplete an aquifer.
• Ogallala Aquifer
• Underlies 8 states between Texas and North Dakota
• Wells have dried up and whole towns are being
  abandoned
• Will take thousands of years to refill

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The Ogallala Aquifer
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Depleting Groundwater

• Withdrawing large amounts of groundwater in a
  small area causes porous formations to collapse,
  resulting in subsidence (settling).
• Sinkholes form when an underground channel or
  cavern collapses. Results in permanent loss of
  aquifer.
• Saltwater intrusion can occur along coastlines
  where overuse of freshwater reservoirs draws the
  water table low enough to allow saltwater to
  intrude.

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Saltwater Intrusion
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Increasing Water Supplies

• Seeding Clouds
• Condensation nuclei
• Desalination - removing salt from ocean water or
  brackish water to get fresh water
• Most common methods are distillation and reverse
  osmosis.
• Three to four times more expensive than most
  other sources

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Domestic Conservation

• Estimates suggest we could save as much as half
  of domestic water usage without change in
  lifestyle
• Largest domestic use is toilet flushing
• Can use low volume toilets or waterless
  composting
• Anaerobic digesters use bacteria to produce
  methane gas from waste
• Significant amounts of water can be reclaimed and
  recycled.
• Purified sewage effluent
• San Diego pumps water from sewage plant directly
  into drinking reservoir

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Price Mechanisms and Water Policy

• Through most of U.S. history, water policies have
  generally worked against conservation.
• In well-watered eastern states, water policy was
  based on riparian use rights.
• In drier western regions where water is often a
  limiting resource, water law is based primarily
  on prior appropriation rights.
• Fosters Use it or Lose it policies, where if
  you conserve you lose your rights to the water

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Price Mechanisms and Water Policy

• In most federal reclamation projects, customers
  were only charged for immediate costs of water
  delivery.
• Dam and distribution system costs were
  subsidized.
• Underpriced water in some areas amounted to a
  subsidy of 500,000 per farm per year.
• Growing recognition that water is a precious and
  finite resource has changed policies and
  encouraged conservation across the U.S.

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Price Mechanisms and Water Policy

• Charging a higher proportion of real costs to
  users of public water projects has helped
  encourage conservation.
• Conservation has been successful. U.S. today
  uses 10 less water than in 1980 but has 37
  million more people.