(November 7, 2008) The pool behind the controversial Three Gorges Dam (1, 2) on the Changjiang (Yangtze) River in Hubei Province, China, will top off at 175 m above sea level next winter (2008 to 2009) (“Three Gorges Dam: Into the unknown,” R. Stone, News Focus, 1 August, p. 628). With this flood level, former cities, homes, and farm fields of about 1.5 million people will be seasonally under water, and a set of new unique ecosystems will develop. The extent of the impact of this unprecedented amount of wetland underwater,the potential ecological systems that will result on the borders of this reservoir, and possible approaches to minimize the impacts or enhance ecological services are mostly unknown.
Flooding in the pool behind the Three Gorges Dam will extend up to 300 km upstream, almost to the city of Chongqing. The affected area with the most impact on human settlements is on the Pengxi River; it is in this region that a city of 300,000, Kaixian, has actually been relocated to higher grounds. The Pengxi River valley includes 5500 ha of land that will now be seasonally flooded, some for 6 months. Approximately 5% of this newly flooded land is former urban area.
Opportunities exist for optimizing ecosystem services through application of ecological engineering (3). Algal blooms, mainly with Peridiniopsis sp., were widespread in the pools during flooding in 2008, so nutrient management will need consideration. Conventional agriculture can be practiced during periods of low water level on the riparian slopes, with one major exception—no fertilizers should be used, as they will exacerbate the pool eutrophication the next spring. Nor will fertilizers be needed. Sedimentation of nutrients, especially phosphorus, will be significant during flooding, and an agriculture more harmonious with the new conditions might flourish. Cascading terraced ponds and wetlands such as those at the Honghe River (4) are another approach for retaining the water as it recedes, while reducing nutrient loss to the river system. Mudflats will be abundant near or at the river in summer, providing ideal habitat for shorebirds and other wading birds. Commercial enterprises for food production can be designed to utilize the pulsing water. Fish-net systems could be used to capture fish as the flood pulse recedes.
We agree with Stone that there will be a new, though perhaps uneasy, equilibrium between the Three Gorges Dam and its reservoir area in the next several decades as nature adapts with new emerging ecosystems.
WILLIAM J. MITSCH,1* JIANJIAN LU,2 XINGZHONG YUAN,3 WENSHAN HE,2 LI ZHANG1
1Wilma Schiermeier Olentangy River Wetland Research Park, The Ohio State University, Columbus, OH 43202, USA. 2Chongxi Wetland Research Centre, East China Normal University, Shanghai 200062, China. 3College of Resources and Environmental Science, Chongqing University, Chongqing 400044, China.
William J. Mitsch, Science Magazine, November 7, 2008
Categories: Three Gorges Probe