Three Gorges Dam is affecting ocean life.Oceanographic surveys suggest that China's Three Gorges Dam Three Gorges Dam, 607 ft (185 m) high and 7,575 ft (2,309 m) long, on the Chang (Yangtze) River, central Hubei prov., China, 30 mi (48 km) W of Yichang. The largest concrete structure in the world, the dam was constructed from 1994 to 2006. is already influencing biological productivity in the East China Sea, even though the structure is still under construction. The dam, on the Yangtze River Yangtze River Chinese Chang Jiang or Ch'ang Chiang River, China. Rising in the Tanggula Mountains in west-central China, it flows southeast before turning northeast and then generally east across south-central and east-central China to the East China , will be the world's largest when it begins full-scale operations later this decade (SN: 5/24/03, p. 323). The first phase of filling the dam's reservoir was completed in June 2003. That impoundment An action taken by the president in which he or she proposes not to spend all or part of a sum of money appropriated by Congress. The current rules and procedures for impoundment were created by the Congressional Budget and Impoundment Control Act of 1974 (2 U.S.C.A. of water and the material it carries is affecting the food chain in the East China Sea, one of the world's largest fisheries, says Louis A. Codispoti, a chemical oceanographer at the University of Maryland's Horn Point Laboratory in Cambridge. The surface waters of the East China Sea receive much less nutrient-rich sediment than they did before the dam was built, says Codispoti. Measurements taken just downstream of the dam a few months after it was filled suggest that the river there carries just 20 percent of the sediment that it did previously. That trend deprives diatoms diatoms a series of unicellular algae, microscopic in size, with cell walls containing silica. Members of the family Diatomaceae. Their remains accumulate as geological deposits and are mined. See diatomaceous earth. , a group of marine microorganisms consumed by larger animals, of the silicon they need to build their shells. As a result, diatom diatom (dī`ətŏm', -tōm'), unicellular organism of the kingdom Protista, characterized by a silica shell of often intricate and beautiful sculpturing. Most diatoms exist singly, although some join to form colonies. populations have crashed. In August 2003, their numbers in the East China Sea were only 14 percent what they had been 5 years earlier. Diatom populations showed a slight recovery in 2004, says Codispoti. However, a continued dearth of sediment may trigger a significant shift in the balance of organisms at the base of the food chain, he and his colleagues speculate in the April 16 Geophysical Research Letters Geophysical Research Letters is a publication of the American Geophysical Union. GRL is the organization's only letters journal. Since its introduction in 1974, GRL has published only short research letters, typically 3-5 pages long, which focus on a specific discipline or .--S.P. |
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