| Qiandao Lake, located in the west part of Zhejiang province, is a typical subtropical deepwater reservoir formed since the Xin’anjiang dam completed in1959. To explore the water characteristic in the reservoir, an on-site survey including water temperature, dissolved oxygen and chlorophyll-a concentration at6sites was carried out every month from January to December of2012. Based on the monitoring data, this paper analyzed vertical hierarchical structure and discussed the characteristics of the water body stratification. The results indicated that the water temperature of upper-middle layer had significant seasonal variation in Qiandao Lake, which was affected by the temperature, showing high in summer and low in winter. However, the water temperature of lower layer indicated no seasonal variation about10degrees. Qiandao Lake had different thermocline throughout the year, which showed enhanced-stable-weakened-disappeared life cycle as the seasons changed. DO distribution characteristics showed significant vertical and seasonal difference. In winter, DO values were high but no significant difference in the vertical except the dam site. In summer, DO values showed greater vertical difference than spring and autumn, and the maximum DO values in Jinshan, Santan Island and the dam sites were found in euphotic layer. Affected by water temperature and other factors chlorophyll-a concentration exhibited high in summer and low in winter. Correlation analysis showed there was significant relationship among DO, water temperature and chlorophyll-a. In summer, the positive linear correlation was found between DO and water temperature, and the temperature themal stratification of DO is a key factor in the vertical distribution. The highest coefficient of chlorophyll-a was exhibited in spring and summer, mainly due to the photosynthesis of the phytoplankton especially in the euphotic layer, resulting in increasing content of DO. |
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