Environmental Problems, Their Causes, and Sustainability 1

Aquifers provide drinking water for about one-fourthof the world’s people. In the United States, waterpumped from aquifers supplies almost all of the drinkingwater in rural areas, one-fifth of that in urban areas,and 43% of irrigation water.Relying more on groundwater has advantagesand disadvantages (Figure 15-15). The good news is thataquifers are widely available and are renewablesources of water as long as the water is not withdrawnfaster than it is replaced and as long as the aquifers donot become contaminated.The bad news is that water tables are falling inmany areas of the world as the rate of pumping out water(mostly to irrigate crops) exceeds the rate of naturalrecharge from precipitation. The problem of fallingwater tables sneaks up on us because we cannot see ithappening. The first sign is shallow wells going dry,followed by loss of water from deeper wells if the watermining process continues. Covering aquifer rechargeareas with urban development also contributesto aquifer depletion.The world’s three largest grain-producing countries—China,India, and the United States—are overpumpingmany of their aquifers. In 2002, China announceda massive project to pump surface waterAdvantagesGood source ofwater for drinkingand irrigationAvailable yearroundExists almosteverywhereRenewable if notoverpumped orcontaminatedNo evaporationlossesCheaper toextractthan mostsurface watersT rade-OffsWithdrawing GroundwaterDisadvantagesAquifer depletionfrom overpumpingSinking of land(subsidence) whenwater removedPolluted aquifersunusable fordecades or centuriesSaltwater intrusioninto drinking watersupplies near coastalareasReduced water flowsinto streams, lakes,estuaries, andwetlandsIncreased cost,energy use, andcontamination fromdeeper wellsFigure 15-15 Trade-offs: advantages and disadvantages ofwithdrawing groundwater. Pick the single advantage and disadvantagethat you think are the most important.through three huge aqueducts from the Yangtze Riverin China’s water-rich south to the country’s arid north.The water will help grow more food and slow aquiferdepletion in the North China Plain. This project is tobegin in 2005 but will not be completed until 2050. Environmentalistsare concerned about its potentiallyharmful ecological impacts.In the United States, groundwater is being withdrawnat four times its replacement rate. The most seriousoverdrafts are in parts of the huge Ogallala Aquifer,underlying eight states in the arid high plains fromsouthern South Dakota to central Texas (Case Study,p. 320) and in parts of the arid Southwest (Figure 15-16,p. 320). Serious groundwater depletion is also takingplace in California’s water-short Central Valley, whichsupplies about half the country’s vegetables and fruits.Do you live in any of the blue areas in Figure 15-16 or ina similar area in another country where groundwater isbeing withdrawn faster than it is replenished?Saudi Arabia is as water-poor as it is oil-rich. Itgets about 70% of its drinking water at a high cost fromthe world’s largest desalination complex on its easterncoast. The rest of the country’s water is pumped fromdeep aquifers, most as nonrenewable as the country’soil. Yet this water-short nation wastes much of itsscarcest resource with large numbers of fountains,swimming pools, and countless irrigation sprinklersthat suck nonrenewable water from deep undergroundand let precious water evaporate into the hot,dry desert air. Hydrologists estimate that because ofthe rapid depletion of its fossil aquifers, most irrigatedagriculture in Saudi Arabia may disappear within 10to 20 years.According to water resource expert Sandra Postel,about 480 million people are being fed with grainproduced with eventually unsustainable water miningfrom aquifers. This example of the tragedy of thecommons is expected to increase as irrigated areas areexpanded to help feed 2.5 billion more people projectedto join the ranks of humanity between 2004and 2050.In addition to limiting future food production,overpumping aquifers is increasing the gap betweenthe rich and poor in some areas. As water tables drop,farmers must drill deeper wells, buy larger pumps,and use more electricity to run the pumps. Poor farmerscannot afford to do this and end up losing theirland and either working for richer farmers or migratingto cities already crowded with poor people strugglingto survive.Withdrawing lots of water sometimes allows thesand and rock in aquifers to collapse, causing the landabove the aquifer to subside or sink. Once an aquiferbecomes compressed, recharge is impossible. Since1950, some spots above aquifers in California’s heavilyfarmed San Joaquin Valley has sunk or subsided morethan 50 meters (160 feet).http://biology.brookscole.com/miller14319