Effects of special vertical layered water temperatures on algal bloom in Xiangxi Bay of Three Gorges Reservoir

The algal bloom occurs in some sections of Xiangxi Bay after the Three Gorges Reservoir(TGR) impounding.The spatiotemporal distribution of layered water temperature and algal bloom in 2008 was monitored.The results show that there was a weak stratification from March to April in TGR;the vertical temperature difference was only limited within about 1-2℃;and no algal bloom occurred in the main stream of TGR.There was a weak stratification in downstream of the bay because of the adverse slope density flow from the main stream of TGR and a strong stratification in upstream because of the process of bed down slope density current from the incoming flow with low water temperature.As a result,the grade of algal bloom in downstream of the bay was more serious than the upstream.There was high correlation coefficient between algal bloom occurring ratio and the water vertical stability ratio.The relationship between the algal bloom and the stratification can be summarized as the critical depth theory.