CHAPTER 10

1. CHAPTER 10 Water: Hydrologic Cycle and Human Use

2. Aral Sea The former Soviet Union was responsible for the death of the Aral Sea in Central Asia Once the fourth largest lake on Earth Look at the photos on p. 245 Two rivers were tapped for irrigation for cotton The Aral Sea began to shrink Lack of freshwater inflow = too salty for fish to live The commercial fishery collapsed 60,000 fishermen lost their jobs Windblown salt and dust cause asthma and cancer

3. Water: a vital resource Water is fundamental to life 97% of all water is salt water (oceans, seas) 67% of fresh water is bound up in ice caps and glaciers (at present) and less than 1% of all water on Earth exists in accessible lakes, wetlands, rivers, groundwater

4. Freshwater is a renewable resource Streams, rivers, ponds, lakes, swamps, estuaries, groundwater, bays, oceans, and the atmosphere represent ecosystem capital (goods and services) Water is used for so many purposes: drinking, industries, irrigation, energy, transportation, recreation, waste processing And water modifies the climate Humans have constructed huge infrastructures to control water: Dams, canals, reservoirs, aqueducts, sewer systems Treatment plants, water towers, pipelines, irrigation Desalinization plants

5. Differences in availability

6. Future challenges Consider: Water quantity Water quality

7. The hydrologic cycle

8. Precipitation varies by location/season

9. Rain shadow Moisture-laden trade winds encounter mountain ranges The deflected air rises and cools and precipitation occurs on the windward side of the mountains Air crossing the mountains warms and picks up moisture Deserts occur on the leeward sides of mountains Rain shadow: the dry region downwind of a mountain range Causes the severest deserts in the world For example, Death Valley, east of the Sierra Nevada mountains in California

10. Groundwater vs. “surface water” Precipitation can either soak into the ground (infiltration) or run off the surface Runoff flows into streams and rivers, eventually reaching oceans or inland seas Watershed: all the land area that drains into a particular stream or river Surface waters: ponds, lakes, streams, rivers, etc. on the Earth’s surface Groundwater is our main source of drinking water in this area.

11. Groundwater and the water table Groundwater is like a slow-moving, underground river It lies on top of an impervious layer of rock or clay Aquifer: porous rock or gravel through which groundwater moves Recharge area: the area where water enters an aquifer (may be miles away from where water leaves the aquifer) Water table: the upper surface of groundwater Wells are dug below the water table to allow groundwater to seep into the well

12. Human impacts on the hydrologic cycle Changes to Earth’s surface Changes to Earth’s climate Atmospheric pollution Withdrawals for human use

13. Cleared land affects the hydrologic cycle Removing vegetation causes a sudden influx of water (and sediment) into rivers and streams. Causing floods, pollutants from erosion, and less groundwater recharge Wetlands naturally store and slowly release water Destruction leads to flooding and polluted waterways Wetlands dry up during droughts In 2008, Iowa had massive flooding due to filling wetlands and converting tallgrass prairies to plowed fields

14. Uses of water Worldwide, the largest use is for irrigation Then industry and direct human use Most increases in withdrawal are due to increases in agriculture (see next slide) Agriculture accounts for about 70% of freshwater consumption in the U.S., with ________________ being the main use.

15. Regional usage of water

16. Sources of water 37% of domestic water comes from groundwater sources 63% comes from surface water (rivers, lakes, reservoirs) Rural people in developing nations get water where they can Wells, rivers, lakes, rainwater Women often have to walk long distances to get water Water in developing nations is often polluted with waste. Remember: 1 in 6 people use polluted water.

17. Water in the developing world

18. Glen Canyon Dam

19. Dams have enormous impacts Valuable freshwater habitats (waterfalls, rapids, fish runs) are lost The waterway below the diversion is deprived of water Fish and other aquatic organisms are directly impacted Wildlife is adversely affected (e.g., food chains) Wetlands dry up and waterfowl die Fish (e.g., salmon) cannot swim upstream to spawn or downstream to return to the ocean Large dams often displace a million or more people

20. Three Gorges Dam

21. Floods Dams help prevent devastating floods Many areas have increased flood frequency and severity Erosion and reduced infiltration from deforestation and cultivation “Sponge effects” of forests helps prevent floods Deforestation in the Himalayan foothills causes extreme flooding in Bangladesh India’s Koshi River broke through dirt levees Caused massive floods and stranded a million people The breach came because of massive silt deposition

22. Impacts of falling water tables Falling water tables are the simplest indication that groundwater withdrawals exceed recharge rates Falling water tables are common throughout the world Groundwater fills spaces in the ground Helping support overlying rock and soil Land subsidence: gradual settling of the land Causes building foundations, roadways, and pipes to crack

23. Sinkholes A sinkhole: a kind of land subsidence Results when an underground cavern is drained of its supporting groundwater and suddenly collapses Sinkholes can occur unexpectedly Most occur in the southeastern U.S. 4,000 sinkholes have formed in Alabama alone They have occasionally “consumed” buildings, livestock, sections of highways

24. Sinkhole

25. Saltwater intrusion In many coastal areas, springs of outflowing groundwater lie under the ocean High water tables keep pressure in the aquifer, so wells normally yield fresh water Lowering the water table reduces pressure, allowing salt water to flow into wells. This is called saltwater intrusion. This is a serious problem in many European countries along the Mediterranean coast

26. Saltwater intrusion

27. Water stewardship The water supply can meet human needs for fresh water But increasing populations create increasing water demand Developing countries may lack good infrastructure (wells, water-treatment systems, dams) To eradicate hunger, water use will have to double An unacceptable and impossible scenario Only five possibilities exist to meet future water needs where water for agriculture dominates demand

28. Desalting seawater Desalination: desalting of seawater for domestic use 13,000 desalination plants exist in 120 countries Especially in the Middle East Smaller plants use microfiltration (reverse osmosis [RO]) Water is forced through a fine membrane to remove salt Large plants use distillation (evaporation and condensation) Waste heat from power plants may be used Desalination costs two to four times what most U.S. citizens pay Desalinized water costs about $2 for 1,000 gallons

29. Tampa Bay leads the way in the U.S. The Tampa Bay seawater desalination plant was completed in 2008 The first U.S. plant built for a primary water source It uses salty cooling water from a power plant It produces 25 million gallons per day (MGD) It costs $2.50/1,000 gallons (groundwater = $1/1,000 gallons) Most people in the U.S. can afford desalinized water But costs are too high for most agricultural use The world’s largest plant is in the United Arab Emirates It produces 215 MGD (2,500 gallons/second)

30. Using less water People in developing nations use 1 gallon/person/day for all their needs, including cooking and washing A typical person in the U.S. uses 100 gal per day This does not even include irrigation of food crops. Don’t think how much water we need and where we get it Think how much water is available and how can we best use it The rate of water use has dropped because of conservation

31. Conserving water in agriculture Agriculture is the largest user of fresh water 40% of crops are grown in irrigated soil Current flood or center-pivot irrigation wastes huge amounts of water Evaporation, percolation, runoff The drip irrigation method uses pipes with holes to drip water at the base of each plant Wastes less water, retards salinization, increases yields

32. Drip irrigation

33. Why don’t farmers switch to drip irrigation? 99% of world irrigation is still by traditional flood or center-pivot methods It is cheaper to use traditional methods than switch The U.S. government pays $400/acre in subsidies But collects only 10% of the costs in water fees Farmers pay almost nothing for water It makes financial sense to use the cheapest (but most wasteful) system Reducing subsidies would encourage water conservation through using more efficient irrigation technologies

34. Municipal systems Each person in a modern home uses 100 gallons/day Mostly for washing and removing wastes (flushing toilets, taking showers, doing laundry) It will be expensive and impractical to get more water through traditional reservoirs and wells The only practical alternative is to save water Cities provide free faucet repair and low-flow showers Xeriscaping: planting plants that don’t require watering

35. A flush world In 1997 it became illegal to sell 6-gallon commodes New toilets use 1.6 gallons or even less water 50 million U.S. low-flow toilets save 600 million gallons/day It is wasteful to use high-quality water to water lawns or flush toilets Gray water: slightly dirtied water from sinks, showers, tubs, and laundry tubs can be safely used in toilets, for watering lawns, washing cars Some treated water is higher quality than river and lake water