Phytoplankton diversity in backwater area of the Pengxi River in the Three Gorges Reservoir before and after 156 m impoundment

为了解156 m蓄水前后三峡水库次级河流藻类多样性变化特征,对2007年7月至2008年1月澎溪河回水区的藻类种群结构的变化进行连续监测.基于三峡水库水位调度特点,将监测期划分为蓄水前、中、后三个时段,即7-9月、10月、11月至翌年1月,应用Shannon-Weaver多样性指数H'对藻类多样性进行评价,通过Connell中度扰动假说理论结合优势藻种探讨蓄水过程水动力变化及藻类多样性的变化特征.结果表明:2007年7-9月蓄水前H'均值为3.466±0.317,10月蓄水期则降为3.246±0.338,而11月蓄水后高水位阶段H'均值上升为3.431±0.352.蓄水前澎溪河回水区具有河流型特征,流量与降雨作为主要的物理扰动因子影响水体扰动强度,进而引起多样性变化.10月蓄水期间水位突升、流量骤降导致水体扰动强度加剧,较蓄水前藻类多样性下降.自11月蓄水后的高水位阶段,降雨较小、流量趋于稳定,水体扰动降低,多样性回升并维持在相对稳定的状态.;In order to analyze the phytoplankton diversity in the backwater area of Pengxi River before and after the impoundment of the Three Gorges Reservoir (TGR) to the water level of 156 m, the variation of algae community of Pengxi River had been observed from July 2007 to January 2008. According to the water level variation in TGR, the time was divided into three periods:July-September, October and November-January. The algae diversity of five sites in Pengxi River was assessed using Shannon-Weaver diversity index H'. Moreover, the Connell's intermediate disturbance hypothesis was applied to analyze the impact on algae diversity caused by hydrodynamic conditions' variation during the impoundment process. Before 156 m impoundment, the mean H' index was 3.466 ± 0.317, declined to 3.246 ± 0.338 in October and recovered to 3.431 ± 0.352 during the high water level period. Before impounding, the Pengxi River was of riverine-type, with flow and rainfall being the main physical disturbance factors affected the disturbance intensity and algae diversity. As a result of water level suddenly risen and the flow severely droppen, the disturbance intensity increased compared with the impounding period. After 156 m impounding, the Pengxi River was at the high water phase, the less rainfall and stable flow reduced the physical disturbance, so the H' index recovered and maintained at a relatively stable state.