This lecture will help you understand:

2. This lecture will help you understand: • Water and the hydrologic cycle • Water’s distribution on Earth • Freshwater ecosystems • Use and alteration of freshwater systems • Problems of water supply and solutions • Problems of water quality and solutions • How wastewater is treated

3. Plumbing the Colorado River • The 2,330 km Colorado River begins in the Rocky Mountains and trickles into the Gulf of California • Dams and irrigation provide water to millions of people in 7 states • Las Vegas, Nevada, is growing rapidly, and needs more water • The other states are allowing Las Vegas to drill for underground water, even though it threatens the area’s ecology and people

4. Freshwater systems • Water may seem abundant, but drinkable water is rare • Freshwater = relatively pure, with few dissolved salts • Only 25% of Earth’s water is fresh • Most freshwater is tied up in glaciers and ice caps

5. Rivers and streams wind through landscapes • Water from rain, snowmelt, or springs forms streams, creeks, or brooks • These merge into rivers, and eventually reaches the ocean • Tributary = a smaller river slowing into a larger one • Watershed = the area of land drained by a river and its tributaries

6. Rivers shape the landscape • If there is a large bend in the river, the force of the water cuts through the land • Oxbow = an extreme bend in a river • Oxbow lake = the bend is cut off and remains as an isolated, U-shaped body of water

7. A river may shift course • Floodplain = areas nearest to the river’s course that are flooded periodically • Frequent deposition of silt makes floodplain soils fertile • Riparian = riverside areas that are productive and species-rich • Water of rivers and streams hosts diverse ecological communities

8. Wetlands include marshes, swamps, and bogs • Wetlands = systems that combine elements of freshwater and dry land • Freshwater marshes = shallow water allows plants to grow above the water’s surface • Swamps = shallow water that occurs in forested areas • Can be created by beavers • Bogs = ponds covered in thick floating mats of vegetation • A stage in aquatic succession

9. Wetlands are valuable • Wetlands are extremely valuable for wildlife • They slow runoff • Reduce flooding • Recharge aquifers • Filter pollutants • People have drained wetlands, mostly for agriculture • Southern Canada and the U.S. have lost more than half of their wetlands

10. Lakes and ponds are ecologically diverse • Lakes and ponds are bodies of open, standing water • Littoral zone = region ringing the edge of a water body • Benthic zone = extends along the entire bottom of the water body • Home to many invertebrates • Limnetic zone = open portions of the lake or pond where the sunlight penetrates the shallow waters • Profundal zone = water that sunlight does not reach • Supports fewer animals because there is less oxygen

11. A typical lake

12. Lakes vary in their nutrients and oxygen • Oligotrophic lakes and ponds = have low nutrient and high oxygen conditions • Eutrophic lakes and ponds = have high nutrient and low oxygen conditions • Eventually, water bodies fill completely in through the process of succession • Inland seas = large lakes that hold so much water, their biota is adapted to open water

13. Groundwater plays a key role • Groundwater = any precipitation that does not evaporate, flow into waterways, or get taken up by organisms • Groundwater makes up one fifth of the Earth’s freshwater supply • Aquifers = Porous sponge-like formations of rock, sand, or gravel that hold groundwater • Zone of aeration = pore spaces are partially filled with water • Zone of saturation = spaces are completely filled with water • Water table = boundary between the two zones • Aquifer recharge zone = any area where water infiltrates Earth’s surface and reaches aquifers

14. A typical aquifer

15. There are two categories of aquifers • Confined or artesian = water-bearing, porous rocks are trapped between layers of less permeable substrate (i.e., clay) • Is under a lot of pressure • Unconfined aquifer = no upper layer to confine it • Readily recharged by surface water • Groundwater becomes surface water through springs or human-drilled wells • Groundwater may be ancient: the average age is 1,400 years

16. 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

17. Water is unequally distributed across Earth’s surface • Different regions possess vastly different amounts of groundwater, surface water, and precipitation • Many areas with high population density are water- poor and face serious water shortages

18. Water is distributed unevenly in time, too • Monsoon seasons bring concentrated storms • Half a region’s annual rain may fall in a few hours • People erect dams to store water

19. Climate change will cause water shortages • Climate change will cause • Altered precipitation patterns • Melting glaciers • Early season runoff • Intensified droughts • Flooding • Increasing probability that there will be still less water for more people

20. How we use water • We have achieved impressive engineering accomplishments to harness freshwater sources • 60 % of the world’s largest 227 rivers have been strongly or moderately affected • Dams, canals, and diversions • Consumption of water in most of the world is unsustainable • We are depleting many sources of surface water and groundwater

21. 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

22. Different types of water use • Consumptive use = water is removed from an aquifer or surface water body, and is not returned • Non-consumptive use = does not remove, or only temporarily removes, water from an aquifer or surface water • Electricity generation at hydroelectric dams

23. We have erected thousands of dams • Dam = any obstruction placed in a river or stream to block the flow of water so that water can be stored in a reservoir • 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

24. A typical dam

25. China’s Three Gorges Dam • The dam, on the Yangtze River, is the largest in the world • 186 m (610 feet) high, 2 km (1.3 mi) wide • Its reservoir stretches for 616 km (385 mi) • Provides flood control, passage for boats, and electricity

26. Drawbacks of the Three Gorges Dam • Cost $25 billion to build • Is flooding 22 cities and the homes of 1.13 million people • Submerging 10,000-year-old archaeological sites • Drowning farmland and wildlife habitat • Tidal marshes at the Yangtze’s mouth are eroding • Pollutants will be trapped • China will spend $5 billion to build sewage treatment plants

27. Benefits: Power generation Emission reduction Crop irrigation Drinking water Flood control Shipping New recreational opportunities Drawbacks: Habitat alteration Fisheries declines Population displacement Sediment capture Disruption of flooding Risk of failure Lost recreational opportunities Benefits and drawbacks of dams

28. Some dams are being removed • Some people feel that the cost of dams outweighs their benefits • They are pushing to dismantle dams • Rivers with dismantled dams • Have restored riparian ecosystems • Reestablished fisheries • Revived river recreation • 500 dams have been removed in the U.S. • Property owners who opposed the removal change their minds once they see the healthy river

29. Dikes and levees are meant to control floods • Flooding is a normal, natural process • Floodwaters spread nutrient-rich sediments over large areas • Floods also do tremendous damage to property • Dikes and levees (long, raised mounds of earth) along the banks of rivers hold rising waters in channels • The U.S. Army Corps of Engineers has constructed thousands of miles of levees • Levees can make floods worse by forcing water to stay in channels and overflow

30. We divert – and deplete – surface water People have long diverted water to farm fields, homes, and cities The once mighty Colorado River has been extensively dammed and diverted

31. The Colorado River is heavily diverted • What water is left after all the diversions comprises just a trickle into the Gulf of California • On some days, water does not reach the gulf • Diversion has drastically altered the river’s ecology

32. The Aral Sea Once the fourth-largest lake on Earth It has lost more than 80% of its volume in just 45 years The two rivers leading into the Aral Sea were diverted to irrigate cotton fields Consequences of a shrinking sea 60,000 fishing jobs are gone Pesticide-laden dust from the lake bed is blown into the air The cotton cannot bring back the region’s economy

33. Can the Aral Sea be saved? People may have begun saving the northern part of the Aral Sea

34. Inefficient irrigation wastes water • Today, 70% more water is withdrawn for irrigation than in 1960 • The amount of irrigated land has doubled • Crop yields can double

35. Most irrigation is highly inefficient • Only 45% of water is absorbed by crops via “flood and furrow” irrigation • Overirrigation leads to waterlogging, salinization, and lost farming income • Most national governments subsidize irrigation • Water mining = withdrawing water faster than it can be replenished

36. Areas where water use exceeds supply

37. We are depleting groundwater • Groundwater is easily depleted • Aquifers recharge slowly • 1/3 of world population relies on groundwater • As aquifers become depleted • Water tables drop • Salt water intrudes in coastal areas • Sinkholes = areas where ground gives way unexpectedly • Some cities (Venice, Mexico City) are slowly sinking • Wetlands dry up

38. Ground Water Depletion

39. Ground Water Depletion These pictures show a reach of the Santa Cruz River south of Tucson, Arizona. In the 1942 picture vegetation is growing in the riparian (river bank) area the river, indicating that sufficient water in the soil existsed at a level that plant roots could access it. The same site in 1989 shows that the riparian trees have largely disappeared as a result of lowered groundwater levels.

40. Ground Water Depletion Chicago-Milwaukee area - Chicago has been using groundwater since at least 1864 and groundwater has been the sole source of drinking water for about 8.2 million people in the Great Lakes watershed. This long-term pumping has lowered groundwater levels by as much as 900 feet.

41. Ground Water Depletion This photograph shows that the ground level in California’s San Joaquin Valley has been lowered about 30 feet in 50 years by groundwater depletion. This aquifer has lost about 20 cubic miles of water in the last seven years.

42. Ground Water Depletion Map

43. Ground Water Depletion-The Making of a Sinkhole

44. Ground Water Depletion Sink Holes

45. 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 • Show video

46. Solutions can address supply or demand • We can either increase supply or reduce demand • Lowering demand • Politically difficult in the short term • Offers better economic returns • Causes less ecological and social damage • Increasing supply • Water can be transported through pipes and aqueducts • It can be forcibly appropriated from weak communities

47. Desalinization “makes” more water • Desalinization = the removal of salt from seawater or other water of marginal quality • Distilling = hastens evaporation and condenses the vapor • Reverse osmosis = forces water through membranes to filter out salts • Desalinization facilities operate mostly in the arid Middle East • It is expensive, requires fossil fuels, and produces concentrated salty water

48. The world’s largest reverse osmosis plant • Near Yuma, Arizona • Intended to reduce the salinity of irrigation runoff • Too expensive to operate and closed after 8 months

49. Agricultural demand can be reduced • Look first for ways to decrease agricultural demand • Lining irrigation canals • Low-pressure spray irrigation that spray water downward • Drip irrigation systems that target individual plants • Match crops to land and climate • Selective breeding and genetic modification to raise crops that require less water

50. Residential demand can be reduced • Install low-flow faucets, showerheads, washing machines, and toilets • Water lawns at night, when evaporation is minimal • Eat less meat • Xeriscaping = landscaping using plants adapted to arid conditions