Dynamic characteristics of nutrients in Xiangxi Bay and converse impact from mainstream in drainage period of the Three Gorges Reservoir

Key words: 
• Three Gorges Reservoir /
• drainage period /
• nutrient /
• converse influence

Abstract: In order to study the impact of the main stream of the Three Gorges Reservoir（TGR） on dynamic characteristics of nutrients in Xiangxi Bay（XXB）,the flow features and chlorophyll a, total nitrogen(TN),total phosphorus(TP) as well as soluble silicate(D-Si) were continuously monitored to inquiry the temporal-spatial dynamics. During the TGR drainage period,the water flows of XXB could be mainly generalized as a densitystratified flow in different directions along depth and the water of main stream flow backward into the Bay in the form of density current. The particular flow of XXB during drainage period provides the hydrodynamic basis for the nutrient transport，and the converse effects of reservoir main stream play a significant role on the supply of nutrients for XXB. From the estuary to the end of the backwater zone, nitrogen and silicon diminished under the influence of the main stream，the spatial distribution of phosphorus was mainly affected by the upper reaches in contrast with nitrogen and silicon; the concentrations of chlorophyll a showed a rising trend from the estuary to the end of backwater zone，and the scope of water bloom contracted to upstream, which indicated that water bloom of XXB downstream was restricted by converse influence of main stream in the drainage period of the TGR.