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

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

Turnover time Time it takes water to enter and leave a part of a system Water in oceans= years Water is icecaps= years Water in ground= 300 years Water in atmosphere = 9 days Water in rivers = days

Oceanic Conveyer belt

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

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…) 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

Fig. 13-5, p. 322 Washington Oregon Montana North Dakota Idaho South Dakota Wyoming Nevada Nebraska Utah Colorado Kansas California Oklahoma Arizona New Mexico Texas Highly likely conflict potential Substantial conflict potential Moderate conflict potential Unmet 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 AdvantagesDisadvantages 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 a, p. 328 Provides irrigation water above and below dam Flooded land destroys forests or cropland and displaces people Large losses of water through evaporation Provides 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 b, p. 328 Powerlines Reservoir Dam Intake Powerhouse 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 Fig , 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 , p. 341

Fig a, 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 flooding Forested Hillside

Fig b, 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

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.