Impacts of water conservancy projects on estuarine ecological environment

摘要

The domestic water resources utilization and development have achieved certain results, such as the large and small water conservancy projects built along the stem stream of Yangtze River and the Yellow River or along their tributaries. Among these water conservancy projects, the Three Gorges Dam is the most magnificent. However, the water conservancy projects will change the ecological environment of estuary, including water, dynamic state of sediment, and nutrient substance. All these changes will have direct impact on the hydrological condition of downstream river. The fundamental reason of the impact of water conservancy projects on estuary environment, aquatic ecosystem, shrink of river delta, salt-water encroachment and coastline erosion is the changes of hydrological condition caused by water conservancy projects. Therefore, it is necessary to track and monitor the aquatic ecosystem before and after water conservancy projects, getting a clear understanding of the relationship among hydrologic condition, water quality, silt and biomass, determining the relevant hydrologic conditions of rivers, lakes, wetland and estuary as well as the mutual relationship among aquatic ecosystems, so as to legally and rationally develop and utilize river resources. The paper analyzes the impacts of the decrease of river runoff and changes of seasonal distribution which are caused by upstream impoundment and water diversion on the transporting capacity of nutrient substance in the water and the self-purifying capacity of water, besides the impact of the decreasing upstream water and sediment on estuarine environment and biodiversity is also taken into account.