阊江上游河道整治底质粒径变化对鱼类群落多样性的影响

Effects of River Realignment and Sediment Grain Size Change on Fish Community Diversity in the Upstream Changjiang

河床基质为溪流鱼类的重要栖息地。为研究溪流河道整治后基质组成变化对鱼类群落结构产生的影响及其作用机制,在阊江上游选取急流浅滩与缓流浅滩两种典型溪流生境,对比分析了两种生境河道整治前后鱼类群落结构的变化及其主要原因。结果表明,采集鱼类数量由河道整治前的24种降低至整治后的17种,但前后不存在显著性差异(P>0.05);鱼类群落优势种由河道整治前的5种降低至整治后的3种。河道整治前鱼类群落的Shannon-Weiner指数、Simpson指数、Margalef指数和Pielou均匀度指数分别为1.623~2.253,0.715~0.866,1.680~3.109和0.652~0.813;整治后分别为1.120~1.679,0.528~0.724,1.444~2.695和0.508~0.722。除春季和秋季整治后的Margalef指数高于整治前,其余各季节,河道整治前的多样性和均匀性指数均要高于整治后(P<0.05)。主要原因在于河道整治后河床基质粒径及粒径多样性降低、流态减少等使生境异质性降低。因此,建议在河道整治过程中避免选择性清除大粒径基质及裁弯取直等,以维持河床基质的多样性,从而防止或降低施工带来的不利影响。

River-bed and various substrata provide diverse habitats for fish. With the purpose of revealing varies of fish assemblage which caused by changes of bottom substrate after river realignment, the difference of fish communities were compared before and after the river regulation in two typical habitats of the upstream Changjiang in 2017 and 2019, and the two habitats are the fast flowing riffle(depth<0.3 m, velocity>0.3 m/s) and slow flowing river(depth<0.4 m, velocity<0.3 m/s). The result indicates that there is no significant difference(P>0.05) in the number of fish species between the two surveys, though fishes in collection decreased from 24 to 17 species after the river realignment. However, fish community diversity and evenness are decreased significantly after the river realignment(P<0.05) except for the Marglef richness index in spring and summer. The values of Shannon-Weiner index, Simpson index, Margalef richness index and Pielou evenness index were 1.623-2.253, 0.715-0.866, 1.680-3.109, 0.652-0.813 before the river regulation, 1.120-1.679, 0.528-0.724, 1.444-2.695, 0.508-0.722 after the river regulation, respectively. It was also found that the diameter of substrate on the riverbed decreased significantly(P<0.05), and so did the diversity of particle size. We speculated that the variations of fish community can be attributed to the decrease of habitat heterogeneity which is closely associated with riverbed structure. Therefore, to maintain the habitat heterogeneity, the selective removal of big size river-bed substrate should be avoided in the process of river realignment.