Phytoplankton community structure and water ecological assessment in the Three Gorges Reservoir

Abstract

2020年是长江禁渔开局之年,三峡库区作为长江的重要生态屏障,其水生态环境健康对长江大保护的实施具有重要意义。本文于2020年8月、11月及2021年1月、4月在三峡库区干支流共设置19个断面探究浮游植物群落结构特征,并利用生物量、多样性指数、综合营养状态指数和浮游植物Q指数等多种评价方法评价三峡库区水生态健康并分析其影响因素。结果表明:(1)三峡库区共鉴定出浮游植物8门105属266种,年平均丰度为6.4×10⁴ cells/L,年平均生物量为0.038 mg/L。不同季节优势种组成不同,变异直链藻(Melosira varians Agardh)、骨条藻(Skeletonema spp.)、脆杆藻(Fragilaria spp.)为全年优势种。(2)三峡库区共划分24个功能群,B、D、MP、S1、P、Y为优势功能群。RDA分析表明,电导率、总氮、化学需氧量、总磷、pH、总溶解性固体与三峡库区四季功能群呈现显著关系。(3)相较于丰度、生物量和多样性水质评价结果,浮游植物Q指数更适用于三峡库区水生态评价,显示三峡库区干流水生态环境总体较好,但春、夏两季支流浮游植物丰度、生物量显著升高和浮游植物Q指数的降低在一定程度上影响了干流水生态健康,成为三峡库区面临的主要风险。因此更应充分做好支流水华监测、预警,充分利用干流水生态调度,保障三峡库区水生态环境健康。;The year 2020 is the first year of the 10-year fishing ban in the Yangtze River. As an important ecological barrier of the Yangtze River, the water ecological environment health of the Three Gorges Reservoir (TGR) is of great significance to the implementation of the Yangtze River protection. Nineteen sites were set in the main and tributaries of the TGR in year 2020 (August and November) and 2021 (January and April) to explore the composition of phytoplankton community, and multiple assessment methods such as biomass, diversity index, comprehensive trophic status index and phytoplankton Q index were used to evaluate the water ecological health of the TGR area and analyze its influencing factors. The results showed that: (1) The 266 taxa of phytoplankton belonging to 105 genera in 8 phyla were identified,the average annual density was 6.4×10⁴ cells/L and an average annual biomass was 0.038 mg/L. The composition of dominant species varied seasonally. Melosira varians Agardh, Skeletonema spp. and Fragilaria spp. were the dominant species all year round. (2) The phytoplankton in the TGR was classified into 24 functional groups, of which B, D, MP, S1, P and Y were the dominant functional groups. Redundant analysis showed that Cond, total nitrogen, COD, total phosphorus, pH and total dissolved solid were the main environmental factors affecting the functional groups in the TGR. (3) Compared with the assessment results of density, biomass and the diversity of water quality, phytoplankton Q index were more suitable for the assessment of water ecology in the TGR. Results showed that the water ecological environment of the main stream in the TGR area was generally good. However, the significant increases of the density, biomass and the decrease of phytoplankton Q index in spring and summer tributaries would affect the water ecological health of the main stream to a certain extent, which had become the main risks for the TGR area. Therefore, we should make full use of the monitoring and early warning of tributary bloom and take advantage of the water ecological dispatch of the main stream to ensure the water ecological environment health of the whole TGR area.