Mrs. Dunkel
APES Chapter 13 Water: A Limited Resource
Key Points
Importance of Water
Details
Water is necessary for life. Humans are 70% water by weight. Only
3% of water is fresh and it is distributed unequally. We are using
over half of our accessible water so water shortages are
developing.
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Properties of Water
2 hydrogens and 1 oxygen. Polar: oxygen is negative and
hydrogens are positive. Hydrogen bond: contributes to high
melting/freezing point and high boiling point. High heat capacity:
ocean is able to moderate climate. Heat of vaporization: liquid to
gas takes heat with it  cooling effect. Universal solvent because
of polarity  problem with pollutants. Solid water floats. Ponds
freeze from top down.
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Hydrologic Cycle and
Fresh Water
Balance among water in ocean, land, and atmosphere. Renews
freshwater on land. ~98%of water has high salt concentration 
plants and animals need freshwater to live. Surface water:
precipitation on surface; streams, rivers, lakes, wetlands, etc.
Runoff: Movement of freshwater from precipitation to lakes,
rivers, etc.; renewable but finite. Drainage basin (watershed): land
that drains into a single river.
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Groundwater
Is the supply of fresh water under Earth’s surface that is stored in
underground aquifers  slowly seeps through rock and soil until is
reaches an impermeable layer. Related to surface water as
groundwater is eventually released into rivers, wetlands, etc.
Aquifers are underground caverns and porous layers of sand,
gravel, and rock in which groundwater is stored. 2 types:
unconfined (rocks above are porous so groundwater is
replenished. Upper limit is the water table) and confined or
artesian aquifers (groundwater stored between layers of
impermeable rock, often under pressure, not quickly refilled).
Considered nonrenewable due to the slow recharge time.
Summary:
Water is polar with 2 hydrogen bonds. This allows it to dissolve many chemicals, including pollutants.
We are using our small supply of freshwater at an unsustainable rate. Surface water is freshwater that
remains on Earth’s surface after precipitation. Groundwater is the supply of freshwater under Earth’s
surface. The water table is the upper surface of unconfined aquifers. Artesian (confined aquifers) are
groundwater between layers of impermeable rock that are not easily replenished.
Key Points
Water Use and Resource
Problems
Details
There is a huge disparity is daily water use among countries. A few
liters per day to several hundreds of liters per day. Agriculture requires
a lot of water. Total water use: irrigation (71%), industry (20%),
domestic and municipal use (9%).
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Too much water
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Floods of 2008
For 100s of years, Midwestern wetlands have been drained for
farmland, restricting the ability of wetlands to moderate the flooding.
Problems occur around Mississippi river in Missouri, Illinois, and Iowa.
Levees are built to protect many cities, but they are not fail proof.
Possible solutions including restoring some floodplains to their natural
condition and moving towns to higher ground.
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Too little water
Arid lands (deserts): fragile ecosystems where plant growth is restricted
by lack of precipitation. Semiarid lands: receive more precipitation than
deserts, but subject to frequent, long droughts. Irrigation is necessary
to grow food in these regions. Lands are also overgrazed so plants die
and ground is not able to absorb the water as well, leading to less
ground water.
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Aquifer depletion
Many locations are removing surface water with disastrous
consequences. Wetlands are drying up and estuaries become saltier
reducing local biodiversity and ecosystem health. Aquifer depletion:
removal of groundwater more rapidly than it can be recharged by
precipitation of melting snow. This can empty an aquifer. Aquifer
depletion can lead to subsidence (ground above it sinks, 33ft in 50 yrs in
San Joaquin Valley in CA).
Floodplains are areas bordering river channels that have the potential
to flood. Problems arise with people live in floodplains. Natural
vegetation helps absorb excess water during floods  clear cutting
contributes to flooding and erosion. Buildings and pavement don’t
absorb water  increased risk of flooding. Local governments are
restricting human development in flood plains.
Limestone bedrock can erode as water moves through it, causing
sinkholes (collapse of underground cave roof). When groundwater is
removed faster than it can recharge around coasts, saltwater intrusion
(movement of sea water into freshwater aquifers) can occur.
Summary:
Agriculture uses most of the available freshwater worldwide. Wetland removal and humans developing
floodplains has caused increased flooding damage. Aquifer depletion can lead to wetlands drying up,
saltier estuaries, subsidence, sinkholes, and saltwater intrusion.
Key Points
Details
Water Problems in US and Canada
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Surface Water
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Mono Lake
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Colorado River Basin
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Delaware: A state without water?
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Drought in Southeast
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Groundwater
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Ogallala Aquifer
Summary:
Key Points
Details
Global Water Problems
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Water and Climate Change
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Drinking-Water Problems
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Population Growth and Water Problems
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Sharing Water: Rhine River Basin
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Sharing Water: The Aral Sea
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Sharing Water: Volatile International Situations
Summary:
Key Points
Water Management
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Providing a Sustainable Water Supply
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The Columbia River
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The Missouri River
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Water Division Project
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Desalinization
Summary:
Details
Key Points
Water Conservation
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Reducing Agricultural Water Waste
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Reducing Industrial Water Waste
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Reducing Municipal Water Waste
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Impacts on Water Resources
You Can Make a Difference
Summary:
Details