Case Study Sharing the Chattahooc he e Beginning from a small spring in north-ern Georgia's Blue Ridge Mountains, the Chattahoochee River provides drinking wa-ler, irrigation, hydropower, wildlife habitat, and recreation ior millions of people. As It tumbles down from the mountains. the Chattahoochee is a clean, cool, swift-flowing stream, a popular destination for fishing, swimming, and boating. Far downstream , the Chattahoochee joins the Flint to form the Apalachicola River. which flows across tile Florid Panhandle into Apalachicola Bay. In he GUlf of Mexico. Together, Ihe Apalachicola. Chal1ahoochee, and Rint (ACF) watershedsupports rich and diverse ecosys-tems. including valuable marine fisheries for oysters, shrimp, and finfish. But between the mountains and the sea. e Cnattahoocnee River passe s through Atlanta, where it und rgoes dramatic changes. M anta IS one of America's fastest-growing cities. Expanding suburbs and industries crowd the Chattahoochee's banks, produc-Ing runoff of silt. salts. and yard fertilizers that washInto he river. Growing numbers of households and industries with-draw water from the river, Wllich becomes lovller, slower, and warmer. Additional contaminants mix with remaining water---oils, metals. and dust from city streets and storm sewers, as well as cbtorine and other contaminants from sewage treatment plants. The warm, shallow, turbid water holds less oxygen and supports fewer of the river's native plants and animals. The Environmental Protection Agency has named the 100 kill of the Chattahoochee south of Atlanta one of the five most pol-lutedriversegments in the United States. In an effort to force action, the EPA has levied millions of dollars in ilnes on Atlanta for polluting the river. Atlanta dilutes 118 contaminated waters by releasing more clean water from reservoirs upstream, but the city govemment says lilli e can be done to prevent widespread runoff from the large and growing city. These diffuse sources of po llu-tants, running off of roads. yards. and parking lots. can be much harder to control than localized sources . such as factory pipe outlets. MeanWhile, Alabama and Florida complain that Georgia is teking too much water. They say the 2.3 billion liters (600 million gal) of water withdrawn each year' in Georgia is needed downstream for homes. industries. and farms. Low river flows and contaminated water also threaten wildlife, shipping, and recreation.The Apalachicola Bay is particularly endangered. Pollution, reduced river flow, and increasing salinity in the estuary jeopardize the bay's multimillion-dollar-per-year fishing and ourism industries. Atlanta recognized the looming prob-lem of water supp lies in the 1970s, and the city hasbeen wo rking with the Army Corps of Engineers to develop additional water supplies. In 2004 Georgia began working on a com prehensive state water plan. which is scheduled to be completed in four yea s. Ecologists worry that wildlife and biodiversity won't be adequa tely represented in this plan-ning. Meanwhile, hydrologists point out that climate change could result in moreerratic, less dependable rainfall in the future (chapter 9). If river flows become more unpredictable as a result, water manage-ment could become an even more urgent and difficul concern. In the United States, water shortages have long been a western problem. ',viti, growing cities in California and other western states struggling to acquire enough water without destroymq river ecosys-tems. But like Atlanta. many growi 19 metropclitan areas in other regions are increasingly competing with other users for water. Around the world, cities are experiencing water shortages, while pollution makes the water we do have less useful. TIle United Nations warns that water supplies are likely to become one of the most p essing environmenta issues of tile twenty-first century'. By 2025 we-thirds of all humans co liel be living in countries where water resources are Inadequate. In this chapter. we'll 1001<at where our fresh water comes from, what we do v'lith it, and how we can protect its quality and extena its usefulness. EOF IA RiSingin the moun tains of northern Georgia. the Chattahoochee flows south through Atlanta before jOining the Rint to form the Apalachicola River. WATER RESOURCES Water is a marvelous substancc-i-flowing. swirling. seeping. con-xtantly moving from sea to land and back again. It shapes the earth's surfa .e and moderate" our climate. Water is essential for life. It is the medium in which all living processes occur (chap-ter 2), Water dissolves nutrients and distributes them to cells. reg-ulates body temperature, supports structures. and removes waste products. About 60 percent or your body is water. You could sur-vive for weeks without rood, but only a few days without water. Water also is needed for agriculture. industry. transportalion. and a host of other human uses. In short. clean freshwater is 0 11e of our most vital natural resources, The hydrologic cycle constantly redistribu tes water The water we lise cycles endlessly through the environment. TIle total amount of water on our planet is immense-i-morc than 1040-1 million krn : (370 billion billion gal) (table IIl.I), This water CHAPTER 10 \)(lmer: Resour c-, and I'ollution 233TABLE 10 .1 Units of Water Measurement One cubic kilometer (km'') equals 1 billion cubi c meters (m3). 1 trillion liters. or 264 billion ga l. One acre-fool is the amou nt of water required to c over an acre of gro und1 ft deep. This is equivalent to 325,851 ga l. or 1.2 mil-lion liters . or 1.234 01 3 , approximately the amount consumed annually by a family of four in the Un ited Stales. One cubic foot per sec ond of river flow eq uals 28 .3 liters per sec-ond, or 449 gal per minute. evaporates from moist surfaces, falls us rain or snow, passes through livinr; organisms. and return s to the ocean in a process known as the hydrologic cycle (sec liu. 2.19). Every year. about 500.000 knr', or a layer 1.4 m thick. evaporates from the oceans. More than 90 percent of that moisture falls back on the ocean. The '17.000 kill" carried onshore joins SO Ill C 72,000 knr' that evaporate from lakes. rivers. soil, and plants 10 become our annual,