长江干流浮游植物群落结构空间异质性及其影响因素

Spatial Heterogeneity and Driving Factors of Phytoplankton Community Structure in the Main Stem of the Yangtze River

为探究长江干流浮游植物群落结构空间变化规律及区系组成特征,于2019年7~9月在长江干流设置了74个采样断面,并将其划分为源区、金沙江区、三峡库区、长江中游和长江下游5个区域进行浮游植物的调查研究。研究期间长江干流共鉴定浮游植物6门53属112种,源区、金沙江区、三峡库区和长江中游浮游植物种类组成均以硅藻门为主,且硅藻门种类在五个研究区域均占优势,如尖针杆藻(Synedra acus)、普通等片藻(Diatoma vulgare)、颗粒直链藻极狭变种(Melosira granulata var.Angustissima)等。干流全流域浮游植物平均密度为1.29×106cells/L,平均生物量为1.34 mg/L。各区域物种组成、硅藻商、多样性指数呈现明显的空间异质性,其中源区与其余各区域浮游植物物种均极不相似,仅中游与下游浮游植物物种中等相似;下游硅藻商显著高于其它区域(P<0.05),金沙江、三峡库区多样性指数均显著高于其它各区域(P<0.05)。基于Shannon-wiener (H’)、Margalef (d)、Pielou (J)生物多样性指数的水质评价结果表明:长江干流整体水质呈中污水平。Pearson相关性分析表明,水温(WT)、总氮(TN)、氨氮(NH3-N)是全流域浮游植物密度与生物量的主要影响因子,溶解氧(DO)是影响浮游植物多样性水平的最主要环境因素。我们的调查结果将提供“十年禁渔”计划实施前期的水生生物基础数据,为长江干流水域水生态管理和保护提供科学依据。

To explore the pattern of spatialvariations in phytoplankton community structure and the characteristics of floracomposition in the main stem of the Yangtze River basin, we set 74 sampling sectionsat five researchregions(i.e.,headwater region, Jinsha Riverregion, Three Gorge reservoir, middle and lower reaches of the Yangtze River) in the main stem to conduct the field survey on phytoplankton in July-September of 2019. A total of 112 species, belonging to 6 phyla in 53 genera, were identified during the survey. Bacillariophyta was the dominant taxa except the lower reach area. Diatoms were predominant at five research areas, e.g.,Synedra acus,Diatoma vulgare,Melosira granulata var. Angustissima. The mean density and biomass of phytoplankton throughout the main stem were 1.29×10~6 cells/L and 1.34 mg/L,respectively. Statisticallysignificant differences were foundin thespecies composition, Diatom Quotient and the diversity indices among five research areas. Specifically, the phytoplankton species in the headwater region were extremely dissimilar to those at other regions. The Diatom Quotient atthe lower reaches were significantly higher than those in other regions(P<0.05). The diversity indices in the Jinsha River area and Three Gorges Reservoir region were significantly higher than those atother regions(P<0.05). The indices of Shannon-Wiener diversity(H’),Margalef richness(D) and Pielou evenness(J) were employed to evaluate the ecological health of water bodies in the Yangtze River basin. The results show that the overall water quality in the main stem was amoderate pollution level. Pearson correlation analysis shows that WT(water temperature),TN(total nitrogen)and NH3-N(ammonium)were the primaryfactors affecting the densityand biomass of phytoplankton, while DO(dissolved oxygen)was the most important factor affecting the phytoplankton diversity. Our results will provide systematic basic data for the implementation of the “10-year Yangtze fishing ban”,and supply withscientific basis for the management and protection of aquatic ecology in the main stem of the Yangtze River.