文件名称：Reduction of primary production and changing of nutrient ratio in the East China sea
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更新时间：2013-05-04 02:37:47
The Three Gorges;ecology
The Changjiang (Yangtze) River, the fifth largest river in the world in terms of water discharge, empties into the northwest corner of the East China Sea (ECS), one of the largest fisheries in the world. Annual water discharge reaches 924.8 109 m3 y1 , and the nutrient flux of inorganic nitrogen (N), phosphate (P) and silicate (Si) is 6.1 1010 , 7.7 108 , and 9.4 1010 mole y1 , respec- tively [Tian et al., 1993; Liu et al., 2003; Duan et al., 2000]. Fresh water discharge before 2003 peaked between June and August, during which time the mixing of fresh water and seawater forms the Changjiang Diluted Water (CDW) zone in the ECS [Beardsley et al., 1985; Gong et al., 1996; Chen et al., 2003]. The CDW generally has a salinity of less than 31 psu, and as being influenced by the southwest monsoon, it is widely distributed throughout a trapezoidal region within the 60-m isobath between the latitudes of 27 and 32N (Figure 1). This traditionally nutrient-rich (TNR) region has been characterized by high primary productivity (PP), which develops beyond the turbid zone associated with the river mouth [Gong et al., 2003]. For this reason, the ECS has become an extremely rich fishing ground and an important sink for atmospheric CO2 [Tsunogai et al., 1999; Peng et al., 1999; Chen and Wang, 1999]. [3] Notwithstanding the wealth and the importance of the ECS, the construction of the Three-Gorges Dam (TGD) was begun in 1994 about 2000 km upstream from the mouth of the Changjiang River, with the first filling stage of the reservoir completed in June 2003. Slated to begin full-scale operations in 2009, this dam will be the largest dam in the world. The TGD will have important positive effects, such as controlling flooding, aiding navigation, and hydroelec- tricity, but it will also change sediment loading, seasonality of flow rate and nutrient flux to coastal area (W. C. Jones and M. Freeman, Schiller Institute Great Infrastructure Projects, Three Gorges Dam, 2005, available at http:// www.schillerinstitute.org/economy/phys_econ/phys_ econ_3_gorges.html, hereinafter referred to as Jones and Freeman, 2005). According to previous high-frequency investigations, high PP usually appears in the TNR region of the ECS between June and August (i.e., flood season) due to high nutrient loading and appropriate growth con- ditions [Gong et al., 2003]. However, there is little pub- lished data to show how the ecosystem of the TNR region in the ECS is affected by the construction of the TGD. In this paper, we will report the preliminary response of the ECS’s ecosystem to the construction of TGD, especially in terms of shifts in river discharge, nutrient flux, sediments loading, PP, and phytoplankton species shift. This paper will also help in our understanding of how marine ecosystems are influenced by giant dam construction.