Upriver habitats—including a critical refuge created when construction began on the Three Gorges Dam—are now at risk from a series of new projects.

YONGSHAN, CHINA—Among the hundreds of fish species that call the upper Yangtze River home is the largemouth bronze gudgeon. The species spawns in the rapids of this rocky waterway—also known as the Jinsha River—which descends from the Tibetan Plateau through the mountains of western China. Its eggs and larvae are kept afloat by the swift current until they hatch and mature hundreds of kilometers downstream. “They have evolved to live in fast-flowing rivers,” says Cao Wenxuan, an ecologist at the Instituteof Hydrobiology at the Chinese Academy of Sciences (CAS) in Wuhan.

But with dozens of new dams planned for the Yangtze system, that habitat will soon change. Last month, preparatory work began on the controversial Xiaonanhai Dam, with more projects to follow. Within a few years, the Jinsha will slow to a sluggish pace and its temperature will drop as a series of large dams release cold bottom water from their reservoirs into the river. Along with other endemic fish species, the largemouth bronze gudgeon may spawn up to 3 months later, and soon after, its eggs and larvae may sink to the bottom and die from lack of oxygen. For species already threatened by the Three Gorges Dam downriver, Cao says, the new series of hydropower dams will “take away their last refuge.”

Last year, the central government solidified plans to increase China's reliance on non–fossil fuel energy from the 2010 level of 8% to 15% of the energy mix by 2020. Nearly two-thirds of that target will come from hydropower—an increase on par with adding nearly one Three Gorges Dam a year. “The scale of hydropower development in China is simply off the charts,” says Edward Grumbine, an environmental policy researcher at CAS's KunmingInstituteofBotany in Yunnan Province. Ecologists say China's hydropower push will threaten already-taxed ecosystems in the upper Yangtze.

Central to the spurt of construction is a 770-kilometer-long stretch of the lower Jinsha River flowing through Sichuan and Yunnan provinces. Last June, China announced an injection of $63.4 billion for hydropower in the region to cover four massive dams with a total capacity of 43,000 MW. “It's worrying to see so many proposed large dams, one immediately after another,” says Zhang Xiaodong, deputy director of the China Earthquake Networks Center in Beijing.

In addition, three large dams are under construction and five are planned on the 560-kilometer-long middle Jinsha, with more planned for the 960-kilometer-long upper reach. At a combined height of 2 kilometers, the dams will convert “the rapidly flowing Jinsha River into a series of stepped lakes with few free-flowing sections,” says Liao Wengeng, deputy director of the National Research Center for Sustainable Hydropower Development (NRCSHD) in Beijing. Also tagged for development are Yangtze tributaries such as the Yalong, Min, and Dahu rivers.

As construction of the Three Gorges Dam got under way in the 1990s, ecologists submitted petitions to the central government calling for an upstream reserve to protect fish populations. The result was the Upper Yangtze River Rare and Endemic Fish Reserve, a 500-kilometer-long protected stretch of river that includes 350 kilometers of the Yangtze mainstream. The reserve became a critical habitat for some 190 fish species—including the critically endangered paddlefish and the Yangtze sturgeon (Science, 1 August 2008, p. 628).

In 2005, officials sliced off 150 kilometers of the upriver portion to make way for the Xiangjiaba and Xiluodu dams. Now the Xiaonanhai Dam will chip away at the reserve even further. At a cost of $3.8 billion, the dam is expected to generate 1750 MW of electricity at its completion. Officials in Chongqing, the municipality overseeing the project, say that it will alleviate power shortages and boost the local economy. But it will also create a nearly 100-kilometer-long reservoir in the heart of the upstream protected area.

For years, ecologists have voiced fierce opposition against the Xiaonanhai Dam. But the battle was lost last December, when China's State Council green-lighted Chongqing's request to shrink the reserve. Road building and other preparation began 29 March. Critics like Fan Xiao, chief engineer at the Sichuan Bureau of Geology and Mineral Resources in Chengdu, fear that Xiaonanhai will pave the way for two additional upstream dams proposed by Sichuan authorities in the reserve area. And that could mean the end for the paddlefish, the Yangtze sturgeon, and other endemic fish: “The reserve would exist only in name,” he says.

Geological minefield

Driving on the narrow road clinging to a cliff above the Jinsha River is not for the fainthearted. It circles mountains that have risen out of tens of millions of years of thrusting and folding of Earth's crust, overlooking a steep valley carved by the roaring river. Scars left by recent landslides cut across facing slopes.

Critics fear that China's hydropower expansion will collide with this stark topography. Crisscrossed with active faults hundreds of kilometers long, the region is “much more geologically complex than the Three Gorges,” says geologist Guo Shunmin of the China Earthquake Administration's Instituteof Geology in Beijing. Earthquakes of magnitude 7 or 8 are not uncommon. “A lot of the reservoirs will have active faults beneath them,” he adds.

Given that some evidence links construction of the Zipingpu Dam to the 2008 Wenchuan earthquake (see sidebar, p. 291), “there should be studies on the effect of water impoundment on active faults beneath the [Jinsha area] reservoirs,” says Hu Xianming, a geophysicist at the Sichuan Seismological Bureau's Instituteof Reservoir-Induced Seismicity Research in Chengdu. The current safety evaluation, however, involves only surveys to avoid building dams on active faults.

Compounding the problem is the up to 2 meters in precipitation the Jinsha region gets every year. In monsoon season, torrential rains can tear apart steep slopes. Massive landslides have blocked the Jinsha for days at a time in the past, says Yang Yong, director of the environmental group the Hengduanshan Society in Chengdu.

Changes in water temperature will be stark as well. The 278-meter-high Xiluodu Dam will cool water temperature by an average of 1.5°C for the months of March through September, according to the project's environmental impact assessment (EIA). Deep reservoirs stratify water into layers of different temperature, with the coldest near the bottom. Water from the cold bottom layer will be released downstream, Liao says. Most fish species spawn in April or May, when the water warms to 16°C to 18°C. After the four dams on the lower Jinsha are built, the EIA says, downstream portions of the river won't reach such temperatures until 2 to 3 months later. That will “hamper fish reproduction,” Liao says. He points to the Three Gorges Dam: With spawning delayed by over a month, downstream carp populations have been decimated.

The problems brought on by that earlier dam are well documented. The river dolphin, or baiji, has been functionally extinct since 2007, and ecologists fear that the finless porpoise, or jiangzhu, may soon follow it.

Also of concern is silt accumulation: Sediment retention in the reservoir means the clearer downstream water can cut the riverbed deeper and lower water levels in lakes fed by the Yangtze. In January, Poyang Lake, China's largest freshwater lake, was hit by the worst drought in 6 decades: the water level dropped to a mere 8 meters, and much of the lake has become a plain of cracked mud. Such problems will snowball with “a cascade of upstream dams,” Liao says.

A stacked deck

Some hydrologists say that optimizing dam operation could alleviate problems with downstream water supply. But many are unconvinced. With so many new dams, says Guo Qiaoyu, director of The Nature Conservancy's Yangtze River project, “it will be extremely difficult to ensure proper coordination between provinces and companies that operate the dams.”

With the new hydropower boom, criticism of China's EIA process is mounting. By law, dams cannot be constructed in nature reserves or their buffer zones. But the government is all too willing to redraw the boundaries to accommodate hydropower projects, some say. The Xiaonanhai Dam in particular, Guo says, is “yet another example of the country's disregard for the environment.”

Critics say EIA committee members are often paid for their services by dam projects and deliver favorable assessments in order to be invited back. “The EIA is just about friends evaluating each other's projects,” says Wang Mingna, a hydrologist at the Chinese Instituteof Water Resources and Hydropower Research in Beijing. Scientists' warnings “often fall on deaf ears,” adds ecologist Yang Junxing of CAS's KunmingInstituteof Zoology.

Adding bias to the schedule, ecologists say, are rules that allow developers to start preparing for a proposed dam while project assessment is still under way. And EIAs are too narrow, examining projects in isolation, points out He Daming, an ecologist at Yunnan University, Kunming. “Even if the impact of individual dams is acceptable,” he says, “the cumulative effects of stacking dams on top of one another could still be catastrophic.”

The science ministry is funding research that takes additive impacts into account. The Ministry of Water Resources, meanwhile, may soon improve the EIA process, says Yu Xuezhong, chief engineer at the NRCSHD.

But such measures may come too late for the upper Yangtze's beleaguered fish species. Ecologists are scrambling to set aside small sanctuaries—in small tributaries near their current habitats, for example. The goal, Cao says, is to “save as many fish species as we can. All we can hope for is to slow down the extinction rate.”

(Source: http://www.sciencemag.org/content/336/6079/288.full?sid=694ef542-5e55-4e21-a4a6-a4160b6f4ab1)