黑河张掖段浮游植物群落结构及其与环境因子的关系

为探究黑河张掖段浮游植物群落季节动态及其与环境因子的相互关系，于2017年对黑河张掖段10个断面进行4个季度的采样调查，共计检出浮游植物8门80属316种，其中蓝藻门、绿藻门和硅藻门种类分别占总种类数的10.75%、15.22%和68.35%.水环境因子中，温度、电导率、盐度、溶解氧和叶绿素a浓度时空变化显著，总氮、总磷浓度则随着海拔降低而呈现显著升高的趋势.调查期间，黑河张掖段浮游植物密度在0.92×10⁴~116.67×10⁴ cells/L之间，从上游到下游呈现明显的递增趋势.优势种主要集中在硅藻门，包括扇形藻（Meridion sp.）、弧形峨眉藻（Ceratoneis arcus）、极小曲壳藻（Achnanthes minutissimum）、延长等片藻细弱变种（Diatoma elongatum var.tenuis）、尖针杆藻（Synedra acus）、简单舟形藻（Navicula simplex）、谷皮菱形藻（Nitzschia palea）、变异直链藻（Melosira varians）、普通等片藻（Diatoma vulgaris）、肘状针杆藻（Synedra ulna）等，此外，在河段优势种中，中下游出现蓝藻门的微囊藻（Microcystis sp.）（优势度为0.025）、绿藻门的四尾栅藻（Scenedesmus quadricauda）（优势度为0.020）、隐藻门的尖尾蓝隐藻（Chroomonas acuta）和卵形隐藻（Cryptomonas ovata）（优势度为分别为0.045和0.032）种类.4个季度Shannon-Wiener多样性指数（H''）均值分别为2.65、2.76、2.89和2.44，Pielou均匀度指数（E）均值为0.93、0.90、0.91和0.87，Margalef丰富度指数（d）均值为1.73、1.77、2.00和1.31.随着海拔的降低，浮游植物H''和d显著升高，而E变化范围相对平稳.结合水体营养盐指标、浮游植物及多样性指数等指标对水质评价，黑河张掖段水质总体呈无污染或轻度污染到轻中度污染状态，且中游污染程度加剧.RDA与Pearson相关性分析结果表明，水体氮磷营养盐、温度、海拔是影响黑河张掖段浮游植物群落结构及动态的关键因素，而在河段下游，电导率、盐度也是影响浮游植物群落结构的主要环境因子.

Relationship between the structure of phytoplankton community and environmental factors in the Zhangye section of Heihe River

In order to investigate the various seasonal dynamics of the phytoplankton community and the correlation with environmental factors in the Zhangye section of Heihe River, the samples of the phytoplankton and the aquatic environment from 10 different river segments were assessed in 2017. A total of 316 species belonging to 8 divisions and 91 genera including the variants were identified to be mainly composed of the Chlorophyta, Cyanophyta and Bacillariophyta in the proportions of 10.75%, 15.22% and 68.35%, respectively. The environmental factors such as the temperature, conductivity, salinity, dissolved oxygen and chlorophyll-a displayed significant temporal and spatial changes, while the total nitrogen and total phosphorus showed a significant increase with the decrease in altitude. During the survey period, the density of the phytoplankton in the Zhangye section of Heihe River was 0.92×10⁴-116.67×10⁴ cells/L, with the existence of a significant increasing trend from upstream to downstream. The dominant species mainly belonged to Bacillariophyta and included Meridion sp., Ceratoneis arcus, Achnanthes minutissimum, Diatoma elongatum var. tenuis, Synedra acus, Navicula simplex, Nitzschia palea, Melosira varians, Diatoma vulgaris, Synedra ulna etc. In addition, it was found that Chlorophyta species Microcystis smithii (McNaughton index Y was 0.025), Cyanophyta species Scenedesmus quadricauda (Y value was 0.020) and Cryptophyta species Chroomonas acuta and Cryptomonas ovata (Y values were 0.045 and 0.032, respectively) were prominent in the middle and lower reaches of the river. With reference to the algal diversity in four quarters, the averages of Shannon-Wiener index (H'') were 2.65, 2.76, 2.89 and 2.44, while Pielou evenness index (E) were 0.93, 0.90, 0.91 and 0.87 and Margalef diversity index (d) were 1.73, 1.77, 2.00 and 1.31, respectively. With the decrease in altitude, the H'' and d were seen to increase significantly while the range of E remained relatively stable. Through the comprehensive evaluations of the water physicochemical index together with the density of algae and their diversity, the water quality in the Zhangye section of Heihe River was found to range from being unpolluted to light or moderately polluted. However, the levels of pollution in the middle reaches appeared to be aggravating. Meanwhile, the results of redundancy analysis and Pearson analysis for the relationship between the phytoplankton and the environmental factors showed that the factors such as total nitrogen, total phosphorus, temperature and elevation played a key role in affecting the structure and dynamics of the phytoplankton community in the Zhangye section of Heihe River. In the downstream regions of the river, factors such as conductivity and salinity were found induce a similar effect on the phytoplankton community structure.