三峡成库后香溪河库湾底栖动物群落演变及库湾纵向分区格局动态

水库生态系统演替是水库生态学研究及水库管理过程中都比较关注的问题。三峡水库自2003年6月成库以来,有关水库生态系统演替的研究却鲜见报道。以三峡水库香溪河库湾底栖动物为研究对象,分析了自2003年8月—2010年7月3个不同蓄水阶段底栖动物群落的演变状况,并对库湾纵向分区格局的动态变化进行了探讨。结果表明,水库蓄水后,摇蚊科和颤蚓科成为第一批定殖者,并以摇蚊科为主;随后,颤蚓科中的霍甫水丝蚓逐渐成为优势类群;直到2004年4月仙女虫科的肥满仙女虫与霍甫水丝蚓共同主导群落。一期蓄水后约1a,底栖动物密度和物种数呈现出明显的增长趋势,空间上呈现出"中间高、两头低"的格局。库湾总体密度于2006年4月达到最高值,高达24146个/m2。二期蓄水导致底栖动物总密度显著降低,而三期蓄水后则变化相对较小。随着时间的增长,库湾底栖动物偶见种出现的频率逐渐降低,群落逐渐趋于稳定。基于TWINSPAN(two-way indicator species analysis)的分析,一期蓄水后期,香溪河库湾纵向上底栖动物群落结构呈现出稳定的分区格局,库湾中部区域呈现出相同的群落类型,无季节变化;而自二期蓄水开始,库湾纵向上大部分样点的群落类型发生改变,表明二期蓄水的干扰较强;之后呈现出季节性波动,此种格局与水位的季节波动相关联,表明三峡水库底栖动物逐渐适应水库周期性的调度,群落结构呈现稳定的季节性周期波动。

Macroinvertebrate succession and longitudinal zonation dynamics in Xiangxi Bay, after impoundment of the Three Gorges Reservoir

Studying the succession of reservoir ecosystems is of great importance to both freshwater ecosystem research and reservoir management. However, little research has been reported regarding the succession of the Three Gorges Reservoir ecosystem after its impoundment in June 2003. In the present study, we analyzed the macroinvertebrate succession and reservoir zonation of Xiangxi Bay, a tributary of the Three Gorges Reservoir, from August 2003 to July 2010 in different impoundment stages. We found that Chironomidae and Tubificidae were the first to colonize after the first impoundment, with Chironomidae as the main group. Limnodrilus hoffmeisteri dominated the community gradually, and Nais inflata established itself as an additional dominant species from April 2004. The total macroinvertebrate density and richness increased from the first stage, exhibited a spatial pattern of "high in the middle and low in the two edges". The density peaked in April 2006 (24,146 ind./m²), declined remarkably after the second stage of impoundment, and changed slightly after the third stage. Fewer rare species were observed in the third stage than in the other two stages, which indicated that the community became more stable gradually. Two-way indicator species analysis revealed a stable zonation pattern during the first stage; however, the community type changed during the second stage, which implied that the stage was associated with strong disturbance. Afterward, we observed seasonal fluctuations in the community type, which was coupled to seasonal fluctuations of the water level. This indicated that the macroinvertebrate assemblage gradually adapted to the periodic reservoir operation of the Three Gorges Reservoir and that the community structure exhibited stable periodic fluctuations.