S

3.6 Water ResourcesWater, water everywhere and not a drop to drink!

Connections between water resources and food resources

Earth’s water budget

Only 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 water The remaining 1% is lakes rivers swamps and in the

atmosphere

Human Uses for Fresh water Domestic water ( drinking, washing, cleaning) Irrigation Industry (manufacturing, mining, andagriculture) Hydroelectric power Transportation (ships on lakes/rivers) Boundaries (states and nations)

Water usage by category

Virtual Water Use

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).

Solutions• Reduce domestic use of fresh water (shorter showers/wash cars

less…)• Drought resistant crops• Closed pipes instead of open canals• Reduce farming contamination (pesticides• and fertilizers). • Force industry to remove pollutants from wastewater

Case Study: The Colorado River: An Over tapped Resource

1,429 miles through 7 U.S. states

Supplies water and electricity ~30 million people in USA and Mexico

Heavily dammed for electricity and agriculture (14 dams)

80% used for irrigation and cattle ranching

Downstream (in Mexico) can dry up completely some years and lead to droughts.

Salinity problems prevent irrigation in Mexico

Dried river causes loss of biodiversity

The Colorado River Basin

Fig. 13-1, p. 317

Aerial View of Glen Canyon Dam Across the Colorado River and Lake Powell

Fig. 13-2, p. 317

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, rice Water use subsidized by government

Reservoirs Leak water into ground below Lose much water through evaporation Fill up with silt load of river, depriving delta Could eventually lose ability to store water and create

electricity States must conserve water, control population, and slow urban

development

Water Shortages Will Grow Dry climates Drought Too many people using a normal supply of water Wasteful use of water 30% earth’s land area experiences

severe drought Potential conflicts/wars over water

Refugees from arid lands Increased mortality

Fig. 13-5, p. 322

Washington

OregonMontana

North Dakota

Idaho South DakotaWyoming

NevadaNebraska

Utah Colorado Kansas

California Oklahoma

Arizona New Mexico

Texas

Highly likely conflict potentialSubstantial conflict potentialModerate conflict potentialUnmet rural water needs

Natural Capital Degradation: Stress on the World’s Major

River Basins

Fig. 13-6, p. 323

Is Extracting Groundwater the Answer? Groundwater is Being Withdrawn Faster Than It Is Replenished Most aquifers are renewable Aquifers provide drinking water for half the world Water tables are falling in many parts of the world, primarily

from crop irrigation

Water: A Replenishable Resource India, China, and the United States

Three largest grain producers Over pumping aquifers for irrigation of crops Small farmers drilling tube wells Effect on water table

Saudi Arabia Aquifer depletion and irrigation

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

Is Building More Dams the Answer?

Main goal of a dam and reservoir system

Capture and store runoff Release runoff as needed to control:

Floods Generate electricity Supply irrigation water Recreation (reservoirs)

Advantages and Disadvantages of Dams

Advantages Reduce flooding Zero emissions electricity production

Disadvantages Displaces people with reservoir Impaired ecological services of rivers Loss of plant and animal species Can cause other streams and lakes to dry up

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 evaporationProvides

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

Fig. 13-13b, p. 328

Powerlines

Reservoir

Dam

IntakePowerhouse

Turbine

Is irrigation the answer? Case Study: The Aral Sea Disaster Large-scale water transfers for irrigation stops flow of

water into the Aral Sea Less Water = Increase in salinity Fish population declines Water pollution Restoration efforts

More efficient irrigation Dam built to help raise lake level

Natural Capital Degradation: The Aral Sea, Shrinking Freshwater Lake

Is Desalination the Answer? Desalination- Removing Salt from Seawater

Distillation: evaporate water, leaving salts behind

Reverse osmosis, microfiltration: use high pressure to remove salts

Problems: Very Costly, Kills Organisms, Creates Briny Wastewater

14,450 plants in 125 countries Saudi Arabia: highest number

The Search for Improved Desalination Technology

Desalination on offshore ships Solar or wind energy

Use ocean waves for power Build desalination plants near electric power plants

Deforestation Above China’s Yangtze River Contribute to Erosion and Floods

Fig. 13-26, p. 341

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

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