3 6 Water Resources Water water everywhere and
- Slides: 29
3. 6 Water Resources Water, 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, and agriculture) Hydroelectric power Transportation (ships on lakes/rivers) Boundaries (states and nations)
Water Usage Pie Chart
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…) • Irrigation: 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
Washington Montana Oregon Idaho Wyoming North Dakota South Dakota Nebraska Nevada Utah Colorado California Kansas Oklahoma Arizona New Mexico Texas Highly likely conflict potential Substantial conflict potential Moderate conflict potential Unmet rural water needs Fig. 13 -5, p. 322
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 replenishable 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
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 Cheaper to extract than most surface waters Pollution of aquifers lasts decades or centuries Deeper wells are nonrenewable Fig. 13 -7, p. 325
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
Provides irrigation water above and below dam Provides water for drinking Reservoir useful for recreation and fishing Can produce cheap electricity (hydropower) Reduces downstream flooding of cities and farms Flooded land destroys forests or cropland displaces people Large losses of water through evaporation Deprives downstream cropland estuaries of nutrient-rich silt Risk of failure and devastating downstream flooding Disrupts migration and spawning of some fish Fig. 13 -13 a, p. 328
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 Fig. 13 -17, p. 332
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
Diverse ecological habitat Evapotranspiration Trees reduce soil erosion from heavy rain and wind Agricultural land Tree roots stabilize soil Forested Hillside Vegetation releases water slowly and reduces flooding Fig. 13 -25 a, p. 340
Tree plantation Roads destabilize hillsides Evapotranspiration decreases Overgrazing accelerates soil erosion by water and wind 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 After Deforestation Rapid runoff causes flooding Fig. 13 -25 b, p. 340
Three Big Ideas 1. One of the world’s major environmental problems is the growing shortage of freshwater in many parts of the world. 2. We can increase water supplies in water-short areas in a number of ways, but the most important way is to reduce overall water use and waste by using water more sustainably. 3. We can use water more sustainably by cutting water waste, raising water prices, slowing population growth, and protecting aquifers, forests, and other ecosystems that store and release water.
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