Transcript Fresh Water! - Falcon Science

Fresh Water!
Ch. 15
Of all the water on Earth, only 2.5% is considered
fresh water, or water with few dissolved salts most
of which is tied up in glaciers, ice caps, and
aquifers. This water is renewed and recycled as it
moves through the hydrologic cycle.
Guiding Questions
• What is water’s
importance to people
and to ecosystems?
• What are the major
types of freshwater
ecosystems?
• How do humans use
and alter freshwater
systems?
Describing Aquatic
Ecosystems
 Salinity: the amount of
dissolved salt present in
water. Ecosystems are
classified as salt water, fresh
water, or brackish
depending on salinity.
 Photosynthesis tends to be
limited by light availability,
which is a function of
depth and water clarity.
 Aquatic ecosystems are
either flowing or standing.
 Aquatic ecosystem zones:
photic, aphotic, benthic
Freshwater Ecosystems:
Ponds, Lakes, Inland Seas
 Salinity is less than 0.5 ppt
(parts per thousand)
 Ponds and lakes are
similar, except in size,
but inland seas contain
organisms adapted for
open water.
 Ponds and lakes are
divided horizontally
into zones: littoral
and limnetic
Freshwater Ecosystems:
Wetlands
 Areas of land flooded with
water at least part of the
year
 Include freshwater marshes,
swamps, bogs, and fens
 Wetlands prevent flooding,
recharge aquifers, filter
pollutants, and provide
habitats.
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
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Freshwater Ecosystems:
Rivers and Streams
 Bodies of surface water that
flow downhill, eventually
reaching an ocean or inland
sea
 Watershed: The area of land
drained by a river and its
tributaries
 Characteristics, such as
dissolved oxygen,
temperature, water speed,
organisms, and others,
change from source to
mouth.
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
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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
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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
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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
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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
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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
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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
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A typical dam
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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
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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
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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
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