Effects of Thermal Stratification on Spring Blooms in Xiangxi Bay of the Three Gorges Reservoir

Frequent spring blooms have been observed in tributary bays of the Three Gorges Reservoir(TGR) since its initial filling.In order to identify the primary factor controlling spring blooms,a field monitoring plan was carried out in Xiangxi Bay,the largest tributary of TGR head area in spring 2010.The environmental factors such as water temperature,Secchi depth,underwater illumination and nutrients were monitored.The results showed that the sudden decrease of mixing depth resulting from the development of thermal stratification was the direct and primary contributor to the onset of spring blooms(Pearson correlation coefficient of the ratio of euphotic depth to mixing depth(Zeu/Zmix) and chlorophyll-a(Chl-a) is 0.934,P0.01).The significant response of spring blooms to thermal stratification indicates that Critical Depth model can be applied to tributary bays of TGR,which will provide important references for the investigators and managers who are working on the prediction and control of algal blooms in the bays.