长江干流湖北段浮游藻类群落结构特征

Community Structure of Phytoplankton in the Mainstream of the Yangtze River in Hubei

2014年5—6月期间,对长江干流西起宜昌三江桥东至黄梅新洲江段共57个样点的浮游藻类群落特征进行调查。结果显示,浮游藻类群落组成中,蓝藻(Cyanophyta)4科11属,绿藻(Chlorophyta)8科17属,硅藻(Bacillariophyta)10科30属140余种。硅藻的种类组成最丰富,主要优势属是小环藻(Cyclotella spp.),其后依次为隐藻(Cryptophyta)、蓝藻和绿藻。硅藻所占比例从上游到下游逐渐降低,而隐藻所占比例则逐渐增加,蓝藻和绿藻变化趋势不明显。从细胞密度来看,宜昌三江口到枝城大桥(A江段)各样点浮游藻类细胞密度相对较低,平均约为3.0×106L-1;松滋河口到中洲洄水处(B江段)所有样点细胞密度均相对较高,平均为7.4×106L-1;洞庭湖大桥到黄梅新洲(C江段)水体透明度显著下降,细胞密度最低。不同流态水体中浮游藻类组成明显不同。中等流速水体中硅藻占据绝对优势,平均比例高达70.0%。缓流水体中硅藻比例(47.2%)与隐藻比例(37.5%)相近,而隐藻是急流水体中的优势门类。综合细胞密度、Shannon-Weaver多样性指数和Pielou均匀度指数的结果,长江干流湖北段水质主要处于贫中营养状态。

Community structure of the phytoplankton in the mainstream of the Yangtze River in Hubei was investigated during May to June, 2014. A total of 57 sampling sites were laid out between the Sanjiang Bridge of Yichang and Xinzhou of Huangmei for sampling of phytoplankton. Results show that 11 genera of 4 families of Cyanophyta, 17 genera of 8 fami-lies of Chlorophyta and 140 species 30 genera of 10 families of Bacillariophyta were gathered and identified. Bacillariophy-ta, dominated with Cyclotella, was the most abundant in the phytoplankton community and followed by Cryptophyta, Cya-nophyta and Chlorophyta. With the water flowing from upstream to downstream, the proportion of Bacillariophyta reduced gradually, while the proportion of Cryptophyta increased and the proportions of Cyanophyta and Chlorophyta are remained almost unchanged. The average cell density was the highest at the sampling sites between the estuary of the Songzi River and the Zhongzhou River bend (Section B) (about 7. 4×106 L-1), lower between Shanjiangkou and the Zhicheng Bridge (Section A) (3. 0×106 L-1) and the lowest between the Dongting Lake Bridge and Xinzhou (Section C). Composition of the phytoplankton varied significantly with velocity of the flow. In the water moderate in flowing velocity, Bacillariophyta dominated, accounting for as high as 70. 0%, in the water low in flowing velocity, Cryptophyta and Bacillariophyta did, being quite close in proportion, 47. 2% and 37. 5%, respectively, while in the water, rapid in flowing velocity, Crypto-phyta became the dominant one. Taking into account comprehensively the cell density,the Shannon-Weaver biodiversity in-dex and the Pielou evenness index of the phytoplankton, it can be concluded that this section of the Yangtze River is poorly or moderately eutrophied in water quality.