多级闸坝对大型底栖动物群落日漂流规律的影响

河流中底栖动物的漂流模式是维持群落动态稳定的重要因素，闸坝改变了河流原有的水文节律，阻隔了底栖动物纵向漂流的连续性，闸坝对河流大型底栖动物群落的影响机制是近年来河流纵向格局维持研究的热点问题.2018年8月选择神农架国家级保护区的九冲河，在上游参照点(S1)、第一级电站取水口下游(S2)和第二级电站取水口下游(S3)布设3个样点开展24 h的日漂流监测，研究多级闸坝对大型底栖动物漂流类群、漂流节律和β生物多样性的变化.结果表明:①九冲河漂流的主要优势类群为蜉蝣目和毛翅目.②受堰坝阻隔影响，各样点漂流最优势物种发生了变化，S1样点为四节蜉(Baetis sp.)，S2样点为花翅蜉(Baetiella sp.)，S3样点为舌石蛾(Glossosoma sp.).③尽管各样点仍然以双峰型漂流模式为主，但参照点S1为“alternans”型的夜漂流，而坝下S2和S3样点则为“bigeminus”型的夜漂流，前者漂流密度的最大值出现在黎明前，而后者则为日落后.④坝下(S2和S3)漂流底栖动物的物种数明显低于参照点(S1)，单因素方差分析表明闸坝阻隔具有显著的累积效应，3个样点漂流底栖动物的生物量之间存在差异显著(P < 0.05)，漂流密度在参照点S1和坝下(S2和S3)的差异显著(P < 0.05).⑤基于Bray-Curtis相似性的聚类分析表明，S2样点群落发生了明显的分化，其日间样品均与S3样点聚为一类，而夜间样品全部与S1样点聚为一类.⑥采用无度量多维度标定排序(NMDS)进行的β多样性分析表明，S1样点漂流群落的昼夜差异性最小，S3样点的差异性最大.研究显示，九冲河小水电梯级开发造成了漂流型大型底栖动物群落结构、漂流规律和β生物多样性发生变化，3个样点的漂流优势类群发生改变，β多样性的变化随梯级闸坝呈现明显的累积效应，从长期来看会对河流生态系统的稳定性和生态功能造成深远影响. 

Effects of Multiple Runoff Dams on Diel Drift Mechanisms of Macroinvertebrate

Drift patterns play an important role in sustaining the dynamic stability of macroinvertebrate communities in the lotic ecosystems. The construction of dams changes the natural flow pattern of rivers and causes the longitudinal discontinuity of macroinvertebrate drift. The impact mechanisms of dams on the macroinvertebrate community highlight the research interests in the longitudinal patterns of river ecosystems. In order to study the effect of multiple runoff dams on the drifted taxa of macroinvertebrates, diel drift patterns and beta diversity variations, the drifted macroinvertebrates were collected from three sampling sites in the Jiuchong River, a typical mountainous river located in Shennongjia Reserve in August 2018. The first site (S1) located at the head of the river was selected as the reference site, and second site (S2) located at the downstream of the first runoff dam, and the third site (S3) located at the downstream of the second runoff dam. The results show that Ephemeroptera and Trichoptera were the dominant drifted taxa in the Jiuchong River. The effects of dams caused the changes of the most dominant taxa. The most dominant taxa were the Baetis sp., Baetiella sp. and Glossosoma sp. at the sites S1, S2 and S3, respectively. Even though the bimodal patterns happened at night for all the sampling sites, the drift pattern of 'alternans' changed to 'bigeminus' from S1 to S2 and S3. The former peak drift density happened before dawn, while the later happened after sunset. The taxa richness was lower in the upstream S1 than the downstream sites (S2 and S3) of the dams. By using the One-way ANOVA, the biomass was significantly different among the three sampling sites (P < 0.05). The density was significantly different between the up S1 and downstream sites (S2 and S3) (P < 0.05). Those differences indicated the cumulative effects of multiple dams on the biomass and density of the drift macroinvertebrate. The communities of S2 site were separated into the daytime group and nighttime group according to the cluster analysis based on the Bray-Curtis similarities. The samples of the daytime group were clustered into site S3, and the samples from nighttime group were clustered into site S1. The beta diversity showed that the variations of the drifted community composition were the smallest at the S1 site and the largest at the S3 site by using nonmetric multidimensional scaling (NMDS) analysis. Our studies showed that effects of multiple dams on the drifted community compositions, diel drift patterns and beta diversity variations in the Jiuchong River. The most dominant taxa of drift macroinvertebrate changed at three sampling sites. The beta diversity at the downstream sites of dams represented the cumulative effects. The multiple runoff dams had an extensive and far-reaching impact on the stability and function of river ecosystem.