水利工程对长江河口生态环境的影响

我国对长江水资源的开发利用．如在干流和支流上已建和在建的许多大大小小的水利工程．特别是规模宏伟的三峡大坝建设和南水北调工程．将显著改变长江的水、沙动态，改变营养物质的输移特征，不仅直接影响下游河道的水文、水环境条件．而且对远离工程的河口生态环境也将产生显著和潜在的影响。分析了由于上游蓄水和引水造成的河流径流量减少、季节分配变化而对水体营养物质输移能力和水体自净能力的影响，以及因上游来水来沙量减少对河口生态环境和生物多样性的影响。水文因素是沼泽湿地和滨海湿地形成和发育的重要环境因素。上游建坝蓄水以后．洪水的消除或洪泛次数减少削弱了河流与湿地之间的联系，造成湿地逐渐萎缩，甚至大面积丧失，生物食物链中断，生物多样性和生产力下降。人海径流量减少将造成海水沿河上溯，盐水入侵河道，并污染地下水，滩地土壤发生盐渍化。河流携带泥沙能力下降，将导致三角洲从淤积型向侵蚀型转化，海岸线蚀退。水利工程对河口生态环境的影响是长期的、缓慢的、潜在的和极其复杂的，并且往往是上游各水利工程的叠加作用。因此在工程建设前后研究分析河口生态环境可能或已经遭受的影响，对生态环境的变化进行长期的跟踪、监测和评价，可为今后水利工程建设和生态环境保护提供理论依据和研究基础。

IMPACT OF WATER CONSERVANCY PROJECT ON ECOSYSTEM AND ENVIRONMENT OF THE YANGTZE RIVER ESTUARY

The development and utilization of Yangtze River water resources, such as many small and big, being built and having constructed water conservancy projects, especially the world largest Three Gorges Dam and the South-to-North Water Transfer Works, will remarkably change the moving state of water and silt, alter the trans-portation amount of nutrients, which affects not only the hydrology and environment of waterway in the middle and lower reaches, but also has a notable or latent effect on the faraway ecosystem and environment of the Yangtze River estuary. In this paper, the authors analyzed the effect of runoff decrease and seasonal distribution variation on nutrients carrying and water self- purification, and on the eco-environment and diversity of living beings after water storage and transfer in the upper reaches. Hydrological condition is a main factor affects the form and development of marsh and coast wetlands. The construction of dam in the upper reaches eliminates floods strength or reduces the happen rate of floods,that weakens the relationship between river and wetlands, gets rise in the loss of wetlands. The result of it is the food chain of organisms broke off, and the diversity of living beings and productive forces descend. The decrease of runoff causes the upstream of seawater, and makes an intrusion of salt, which pollutes the groundwater and salifies the beach soil. When the silt carried by river comes down, the delta will shift from the state of deposition to that of incursion and the sea shore will be eroded and re-tired . The influences of water conservancy projects on ecosystem and environment of river estuary are long-term, slowly, potential and extremely complicated, and are comprehensive effects of all projects on them. Following the tracks of projects, monitoring, evaluating and analyzing the response of river estuary will provide a scientific basis for the protection of ecological environment of later construction of water conservancy projects.