NEWSFOCUS Three Gorges Dam: Into the Unknown A marvel of engineering, the Three Gorges Dam will start operating at full capacity later this year. Already under way is an epic experiment on how a dam impacts the environment YICHANG, CHINA—For millions of people in water levels below the dam. Recent IHB along the Yangtze River, the turbid waters surveys have found a sharp decline in carp of Asia’s longest river have long provided eggs and larvae downstream. “It’s a very an abundance of fish, including one kind bad sign,” Liu says. that locals are especially fond Carp are not the only Yangtze of: carp. But Yangtze fisheries species on the ropes. Fishers are are harvesting less than half the Online hauling in anything with fins and carp they were 5 years ago. sciencemag.org gills that they can net or lay hooks Thanks in no small measure to Podcast interview on, including the tiniest of fish to with the author of on April 15, 2009 the completion of the Three this article. feed aquaculture species such as Gorges Dam, the world’s biggest catfish or mandarin fish, IHB has dam, the outlook for the prized fish is grim. documented. The central government bans The Yangtze’s four major carp species— fishing on the Yangtze for 3 months each year, bighead, black, grass, and silver—spawn during spawning. But with vast stretches of when water levels rise during the summer the river in danger of being fished out, one of monsoon rains. “They need this stimulation,” China’ssenior ecologists, IHB’s Cao Wenxuan, says Liu Huanzhang, an ecologist at the Insti- last month made a bold public plea for a southern rivers to China’s parched north tute of Hydrobiology (IHB) of the Chinese 10-year moratorium for the entire Yangtze. (Science, 25 August 2006, p. 1034). But per- www.sciencemag.org Academy of Sciences (CAS) in Wuhan. Other troubles sapping the Yangtze’s vital- haps no endeavor has generated more debate Three Gorges reservoir, a 660-kilometer- ity include industrial effluents, raw sewage, on the economic and environmental trade- long serpentine lake that began to fill in and heavy boat traffic. But by greatly altering offs of megaprojects than the $25 billion 2003, has subtly altered seasonal variations ecosystems on the Yangtze’s middle reaches, Three Gorges venture in Yichang. the Three Gorges The main justification is flood control. By China’s Environmental Challenges Dam, which opera- regulating water flow, the dam is designed to tors plan to bring to prevent disastrous floods that have occurred Downloaded from China is waging a war on many fronts to stem environmental deterio- full capacity by the every decade or so; the worst in the last cen- ration while sustaining rapid economic growth. This special report end of the year, will tury was a flood in 1931 that the government examines three prominent ventures: 1. the world’s largest dam, which complicate attempts says killed 145,000 people and left 28 million is changing the ecology of a vast and fragile watershed (p. 628); to prevent a mighty homeless. (Unofficial tallies put the death toll 2. plans to restore the Qinghai-Tibetan Plateau (p. 633); and 3. Beijing’s river from becoming at 3 million people or more.) Also on the plus efforts to clean its notoriously foul air (p. 636). inhospitable to some side, the dam’s hydropower station is aquatic life forms. expected to generate 84.7 billion kilowatt- The Three Gorges hours per year of electricity, an amount equal Dam is one of several to that produced by burning 50 million tons of huge projects that are coal. And Three Gorges has eased navigation transforming China’s as the rising waters have eliminated treacher- environment. They ous shoals upstream. For these and other rea- include the recent sons, the State Council Three Gorges Project completion of the Construction Committee (CTGPC) has world’s highest rail- hailed the dam as “greatly beneficial” to the way across the environment. According to CTGPC vice Tibetan Plateau and a director Li Yong’an, “the project has brought plan to divert billions more ecological benefit than harm.” of cubic meters of But to many critics, Three Gorges is a water each year from bête noire. Besides worsening the plight of the Yangtze and other fish, the dam has fragmented habitats in a CREDIT: DU HUAJU/XINHUA PRESS/CORBIS 628 1 AUGUST 2008 VOL 321 SCIENCE www.sciencemag.org Published by AAAS CHINA’S ENVIRONMENTAL CHALLENGES | NEWSFOCUS Pulling out all the stops. Three Gorges is generating loads of electricity—and concern. on April 15, 2009 biodiversity hot spot, and it could erode voir area emits as submerged vegetation rots. group offered recommendations to a dozen inhabited islands in the Yangtze River delta. “Now that the dam is a reality, I hope we bodies in China and at the United Nations www.sciencemag.org The impoundment of 39.3 billion cubic can manage it well,” says Niu Wenyuan, chief but did not receive a single response. “It was meters of water has destabilized slopes, scientist of China’s sustainable development a sad story,” says Chen. heightening risk in a landslide-prone strategy program and a counselor of the State Chinese scientists insist they are open to region, while the sheer weight of all that Council. A wealth of data on the Yangtze’s outside views and determined to confront the water has heaped strain on seismic faults. fragile condition has been posted to a colossal project’s mixed legacy. “Researchers The rising waters have also uprooted more CTGPC-run Web site, www.tgenviron.org. want to tell the truth,” says Wu. than 1 million people and submerged entire The findings are expected to guide priorities Downloaded from communities. Another 4 million of the of a $7.3 billion monitoring and mitigation A fading pulse 16 million people living in the reservoir program over the next 12 years. In the 1930s, engineers identified the pictur- area may have to be relocated in coming “Humanity deserves the opportunity to esque Three Gorges region straddling Hubei years, officials revealed last fall. learn some lessons from this engineering and Sichuan provinces as an ideal spot for a In China, public debate about the dam’s exercise,” says Chen Jiquan, a landscape dam to dwarf all others. The original idea was dark side is muted. But for scientists, the myr- ecologist at the University of Toledo in to tame the Yangtze’s periodic floods, but iad effects of Three Gorges are fair game. The Ohio. In 2000, Chen led a 12-person delega- planning sputtered until the early 1980s, when government has sanctioned an ambitious pro- tion from the Society for Conservation Biol- China’s energy needs grew more intense. gram to monitor the Yangtze and the Three ogy to China to assess Three Gorges. The “They thought this large dam would solve a lot Gorges reservoir area, which at of problems,” says Chen. Then-Premier Li 58,000 square kilometers is big- Well bred. A female Peng, a water engineer by training, pushed ger than Switzerland. “We’re jiangzhu and her two hard for Three Gorges, and in 1984 CAS studying the changing land- babies at IHB. began an environmental impact assessment. scape,” says Wu Bingfang, whose After weighing the pros and cons, the 8-year- team at CAS’s Institute of Remote long review gave Three Gorges the thumbs- Sensing Applications (IRSA) in up. Construction started in 2003—to the dis- Beijing is using satellite imagery may of many scientists. “I felt there were seri- to follow how the dam impacts its ous problems. My opinion was to wait 20 or surroundings. They also intend to 30 years,” says Niu. estimate how much methane and In May 2006, some 26,000 workers com- CREDIT: DING OF WANG COURTESY other greenhouse gases the reser- pleted a Great Wall for the Yangtze: a concrete www.sciencemag.org SCIENCE VOL 321 1 AUGUST 2008 629 Published by AAAS NEWSFOCUS barrier 185 meters tall and 2.3 kilometers Yangtze just 38 kilometers downstream, and Although millions of lab-bred finger- long. The reservoir had begun filling 3 years it would have been “impossible” to build a lings have been released into the Yangtze in earlier and has risen from its original low big enough passage for the primary species the past 2 decades, most young sturgeon water mark of 62 meters to the present that would have benefited from it, the Chi- captured in the Yangtze delta are wild, 156 meters. By December, engineers expect nese sturgeon (Acipenser sinensis). suggesting that the wild population is cop- to have finished installing the last five of It turns out, however, that Chinese stur- ing reasonably well, Liu says. Over the past 26 hydropower turbines. geon may still have a future on the Yangtze. 3 years, the Yangtze River Fisheries For ships to move upstream, they must The ancient species spends much of its life Research Institute in Jingzhou has released traverse five locks stacked like a staircase at at sea, migrating upriver to spawn. The orig- sturgeon into the Three Gorges reservoir to the dam’s northern end that raise craft more inal sturgeon spawning areas were hundreds see if the fish can thrive exclusively in fresh than 100 meters. Migratory fish don’t have a of kilometers upstream of Three Gorges. water. Early results are discouraging, says chance. “There was serious debate about The fish has been blocked from reaching the institute’s Wei Qiwei, because the reser- whether to build a passage for fish,” says those areas since Gezhouba Dam rose in voir ecosystem is changing as the river slows Liu.