Distribution characteristics of phytoplankton functional groups and their relationship with environmental factors in Taihu Basin

太湖流域地处长江下游,水系发达,是典型的平原水网地区,为明确空间和环境因子对太湖流域浮游植物功能类群分布的影响,本研究于2019年8—9月期间比较太湖流域包括河流、湖泊和水库的85个采样点的浮游植物、空间和环境特征. 首次利用"人工智能图像识别技术",并结合传统人工镜检,共鉴定浮游植物250个分类单位,隶属于9门13纲28目57科110属,以绿藻门(45.6%)、硅藻门(19.2%)和蓝藻门(16.4%)为主. 共划分功能类群31个,包括M、D、J、S1、C、Y、F、P、MP、H1、SN、W1、G、K和TB共15个优势功能类群. 结果表明:1)太湖流域不同水体功能类群组成差异显著,差异主要来自M、J、S1、Y、P、H1类群;2)浮游植物功能类群分布具有一定的空间异质性,以太湖为中心向外形成3个聚类组,物种组成类型依次为蓝藻型、蓝藻-绿藻-硅藻型、绿藻-硅藻-蓝藻型,主要贡献类群依次为M、S1类群,M、S1、P、J类群,P、S1、J、D、C类群;3)在太湖流域,相对于环境因子而言,空间因子对浮游植物功能类群组成的影响更大. RDA分析表明,COD_Mn、NO₃^--N、TN、SD、pH值和DO与太湖流域浮游植物优势功能类群呈显著相关. 过去十年,以控源截污为主导的环境管理政策已在太湖流域取得显著成效,但是对于以M、S1类群水华为特征的夏季太湖流域而言,蓝藻水华防控仍是必须面对的难题,有机污染物和氮的控制仍是关注重点,不同水体类型和浮游植物功能类群因地制宜的管控模式仍是关键.;The study area locates in the Taihu Basin, and it spans across three provinces (Jiangsu, Zhejiang, Anhui) and the Shanghai Administrative Region. We sampled at 85 sites during Aug. and Sep. 2019, including lakes, rivers, streams and reservoirs, to investigate the effects of spatial and environmental factors on the distribution characteristics of phytoplankton functional groups (PFG) in Taihu Basin. A total of 250 phytoplankton taxa, belonging to 9 phyla, 13 classes, 28 orders, 57 families and 110 genera, were identified by the artificial intelligence image recognition technology for the first time, combined with traditional microscopy. The phytoplankton species composition was dominated by Chlorophyta (45.6%), followed by Bacillariophyta (19.2%) and Cyanophyta (16.4%). According to the PFG classification method, 31 functional groups were identified, respectively, with dominant function groups including M, S1, C, D, Y, G, MP, P, J, SN, F, TB, K, H1 and W1. The results showed that: 1) There were significant differences in the PFG composition among different water bodies in Taihu Basin, mainly from M, J, S1, Y, P and H1 groups; 2) The PFG distribution in Taihu Basin showed certain spatial heterogeneous, and three cluster groups were found. Moreover, the corresponding species composition types are Cyanophyta, Cyanophyta-Chlorophyta-Bacillariophyta and Chlorophyta-Bacillariophyta-Cyanophyta. The dominant groups are M and S1 groups, M, S1, P, j groups, P, S1, J, D and C groups, respectively; 3) Spatial factor plays a major role in the formation of phytoplankton community than environmental factor in Taihu Basin. Redundant analysis showed that COD_Mn, NO₃^--N, TN, SD, pH and DO were the main environmental factors affecting the PFG distribution. Over the past decade, the environmental management policy led by source pollution control has achieved remarkable results in the Taihu Basin; however, more effective prevention and control methods are expected to propose for controlling cyanobacterial blooms in the future, and the control of organic pollutants and nitrogen should be paid more attention for aquatic ecological management in Taihu Basin during summer. More importantly, appropriate aquatic ecological management mode should be adopted to deal with different water types and different PFGs.