산샤댐 건설로 인한 북부 동중국해의 연별 해양환경 변화

Abstract

The northern East China Sea ecosystem during summer has been influenced by the input of the Changjiang Dilluted Water (CDW) created from a mixture of Changjiang freshwater with seawater. About 80% of the total discharged freshwater from rivers around the Yellow and East China Seas have been supplied by the Changjiang River. The Three Gorges Dam (TGD) in the middle of the Changjiang River has been constructed until 2009 primarily for preventing flooding downstream. We examined the water mass properties of CDW, the distribution of nutrients and suspended sediments, and the effect on the lower trophic ecosystem in the northern East China Sea (ECS) during summer in 2007 to 2009. We observed that CDW moved to eastward as a patch in the northern ECS. The distribution patterns of the CDW patches were different in every summer. The concentrations of nitrate and phosphate in CDW were relatively higher than that in the surrounding water. On the contrary, silicate concentrations were low, which probably resulted from a remarkable reduction of the suspended sediments in the Changjinag River after the TGD impoundment. Phytoplankton biomass and primary production showed an increasing trend in the area of relatively strong CDW influence. This indicated that high nutrient concentrations dissolved in CDW formed a favorable condition for the growth of phytoplankton. So far as our studies indicated, CDW has obviously been responsible for the changes in marine ecosystem of the northern ECS during summer period. It is predicted that the ocean environments and their ecosystems in the ECS will be changed by controlling water flow through the TGD.