额尔古纳河流域秋季浮游植物群落结构特征

2008年8-9月对额尔古纳河流域5个重要水体呼伦湖、乌兰泡、二卡湿地、伊敏河和哈乌尔河进行浮游植物调查，结果显示：1）共鉴定浮游植物8门82属177种（含变种），以绿藻和硅藻种类最多，绿藻有36属77种，占43.5%，硅藻21属54种，占30.5%；其次是蓝藻，13属26种，占14.7%；裸藻4属11种，占6.2%；其他藻类仅占5.1%；2）在呼伦湖共有64属121种，乌兰泡47属88种，二卡湿地62属116种，伊敏河41属59种，哈乌尔河32属54种；优势度分析显示：呼伦湖与乌兰泡优势种为蓝藻和绿藻，二卡湿地为硅藻与隐藻，伊敏河与哈乌尔河为硅藻；蓝藻个体密度在乌兰泡与呼伦湖最大，分别为5.17?106 ind./L和4.01?106 ind./L，而硅藻密度则在二卡湿地、伊敏河与哈乌尔河占优势，分别为1.40?106 ind./L、1.84?105 ind./L与4.89?105 ind./L；此外，聚类分析显示5个水体的浮游植物群落按结构特征可分为两大类；3）与历史记录相比，呼伦湖的优势种转变为细胞较小的坚实微囊藻(M. firma)与不定微囊藻(M. incerta)，这种小型化的趋势表明呼伦湖水体富营养化程度加剧；4）综合多种指标对水质状况进行评估：呼伦湖、乌兰泡为中-富营养水体，二卡湿地为中营养水体，伊敏河与哈乌尔河属于贫-中营养水体。

Community structure characteristics of phytoplankton in argun River Drainage Area in autumn

Argun River drainage area locates on the northeast of Inner Mongolia, adjacent to Mongolia and Russia. It has very limited biodiversity information. In recent years, with the rapid regional economic development and climate change,its aquatic ecosystem faces many serious challenges,such as water quality degradation, eutrophication and decrease of wetland size. Phytoplankton is a major contributor to primary productivity in aquatic ecosystem. Species, density and biomass of phytoplankton have been widely used to evaluate and monitor ecosystem health. In August-September 2008, the phytoplankton samples were collected from 26 locations in Argun River drainage area, which includes Hulun Lake, Wulan Lake, Erka Wetland, Yimin River and Hawuer River. A total of 177 species belonging to 82 genera in 8 phyla were identified, Chlorophyta (77 species of 36 genera), Bacillariophyta(54 species of 21 genera), and Cyanophyta (26 species of 13 genera) dominated the phytoplankton communities, and 20 other species were also identified from Euglenophyta,Cryptophyta,Dinophyta,Chrysophyta and Xanthophyta. 121 species of 64 genera were found in Hulun Lake,88 species of 47 genera in Wulan Lake,116 species of 62 genera in Erka Wetland, 59 species of 41 genera in Yimin River and 54 species of 32 genera in Hawuer River. The dominant species in Hulun Lake and Wulan Lake belonged to Cyanophyta and Chlorophyta, while Bacillariophyta had an apparent dominance in Erka Wetland, Yimin River and Hawuer River. Cryptophyta also had an important role in Erka Wetland. It had high cyanobacterial density in Wulan Lake(5.17×10⁶ ind./L) and Hulun Lake (4.01×10⁶ ind./L), while high density diatoms in Erka Wetland(1.40×10⁶ ind./L), Yimin River (1.84×10⁵ ind./L)and Hawuer River(4.89×10⁵ ind./L). Result from hierarchical cluster analysis showed that community structures of phytoplankton in lakes and wetland, rivers were different. Moreover, compared to a former study in the corresponding season in 1988, Hulun Lake had fewer species and less biomass than 1988, and higher density, and higher percentage of diatoms in biomass. Dominant species belonging to Microcystis in Hulun Lake had changed from M. aeruginosa and M. flos-aquae to M. firma and M. incerta which two have a smaller cell size. The average individuals' size also tended to diminish in Hulun Lake, those phenomena suggested eutrophication increased. Based on the species composition, density, and biomass, it suggested that Hulun Lake and Wulan Lake were in meso-eutrophic status, Erka Wetland in mesotrophic status, Yimin River and Hawuer River in oligo-mesotrophic status.