10:29:47 am, Categories: Earth Science, Environment, Global Warming and Climate Change, Politics and Science, Public Policy, 624 words
By the end of this week, the Chinese government expects to pour the last concrete for the enormous Three Gorges Dam on the Yangtze River. Partially operational since 2003, the dam will be fully operational in 2009, according to the confident officials, bringing to a close more than a decade's worth of construction.
The nearly 8,000 foot long dam towers roughly 800 feet over the river below and will generate as much as 10 percent of China's current energy needs--more than 18,000 megawatts--in addition to improving navigation and reducing flooding, according to its champions. That's good news as far as China's ever-rising greenhouse gas emissions go since it derives the majority of its power from dirty coal-fired plants (although this is somewhat counterbalanced by the methane-emissions of microbes breaking down organic material in the reservoir behind the spillway). Of course, that percentage is set to decline precipitously as Chinese electricity demand rises, note its critics. And that is just the first of many charges.
In addition to flooding more than 1,000 archaeological sites with its sinuous 370-mile reservoir, Three Gorges has already begun to have an impact downstream. Since 1998 Taiwanese scientists have been measuring nutrient flows and plankton blooms in the East China Sea into which the river empties--home to a vital and vibrant fishing ground. The Yangtze used to discharge enough water to dilute the sea in the summer, but by August 2003--two months after the first filling phase of the reservoir--that fresh water influx had disappeared.
And it has not reappeared in subsequent years, according to research published in the April 15 issue of Geophysical Research Letters. In fact, the size of the pool of diluted seawater has shrunk to just the mouth of the river. "In July 2004, when water discharge would have reached its maximum, the area of the [pool] still had not regained its former size prior to the filling of the reservoir," the researchers write.
The dam has also choked off the supply of sediment to the ocean and thus the supply of critical nutrients. This has given scientists an unprecedented chance to study the impacts of a dam on its downstream marine ecosystem. "Dinoflagellates that normally occurred in the coastal zone had almost disappeared within a few months of the filling of the reservoir," the scientists write. "Meanwhile, flagellates, such as prymnesiophytes, cryptophytes and chrysophytes had become the dominant species." After all, the Colorado River--dammed and drained repeatedly by the U.S.--no longer flows all the way to its mouth in Mexico, leaving ecosystem estimates to historians rather than marine biologists.
This ecosystem transformation may or may not be responsible for a host of strange phenomena in the East China Sea, including an invasion of giant jellyfish that is disrupting the coastal fisheries of Japan. But it is clear that the dam will have wide-ranging impacts For one thing, a host of subsidiary dams will need to be built, some in even more ecologically sensitive regions than Three Gorges, to prevent the giant dam from silting up in short order.
Silt may be just one of the dam's environmental foes, however. Researchers at the Chinese Academy of Sciences recently revealed that the Tibetan glaciers that feed Asia's rivers--the Yellow, Mekong, Ganges and Indus rivers, in addition to the Yangtze--are shrinking by 7 percent every year. The 60,000 square miles of glaciers on the so-called "roof of the world" are halving every decade--with subsequent effects on the rivers they feed--thanks to a two degree Fahrenheit rise in average temperatures in the region. The scientists called it an "ecological catastrophe" in the making and the loss of one enormous dam and a rich fishery may be the least of it. More than 300 million Chinese rely on glacier melt for survival. No dam can hold back that flood of discontent.
Posted by David Biello
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