[Study on seasonal characteristics of thermal stratification in lacustrine zone of Lake Qiandao].

Lake Qiandao is a typical subtropical man-made reservoir in China. The investigation on the seasonal and vertical dynamics of water temperature, dissolved oxygen (DO), pH value, turbidity, photosynthetic available radiation (PAR) and chlorophyll a was conducted in 2011 in order to find out the physical characteristics of Lake Qiandao. The average surface water temperature ranged from 10.4 to 32.7 degrees C. A monomictic thermal stratification was observed in Lake Qiandao, initiating in April and lasting until December. The results showed that thermal stratification had influences on vertical distribution of DO, pH value, turbidity, PAR and chlorophyll a. Very strong stratification of DO was found, inducing lower oxygen concentration in the thermocline layer and temporal hypoxia in the bottom water. The maximum turbidity was found in the thermocline layer and the precipitation affected the surface turbidity value. Moreover, the chlorophyll a concentration was higher in the surface water and lower in the bottom water as found in this study, implying that water quality was affected by stratification. Besides, the maximum photosynthesis rate and algal growth rate were found at the depth 5-10 m below the water surface. Therefore, the results can provide theoretical support for the sampling and analysis of algal blooms in Lake Qiandao.