Abstract:

The quality of water environment in the Fu River basin was decreasing, which caused more pressure on coastal water supply and even the ecological safety of Poyang Lake, and it was urgent to carry out ecological monitoring and evaluation of the whole basin to diagnose the risk of water ecology. Phytoplankton, as primary producers in the aquatic ecosystem, can characterize changes of the aquatic ecosystem. In response to the previous studies on the characteristics of phytoplankton communities in the Fu River, which were mainly focused on local areas such as the main stream and the estuary, an investigation of the water environmental factors and phytoplankton community structure of 40 sampling sites in the Fu River basin was carried out during the water period (July 2017), dry period (December 2017) and the normal water period (April 2018), taking the main stream and major tributaries of the Fu River as the target. Based on the species composition, dominant species, and the density and biodiversity of phytoplankton in the Fu River basin, the water ecological status was evaluated. As the same time, redundancy analysis (RDA) was used to investigate the relationship between dominant species of phytoplankton and water environmental factors to explore the relationship between dominant species of phytoplankton and water environmental factors in Fu River basin. Results showed that a total of 171 species from 7 phyla were detected in the Fu River basin, and the phytoplankton cell densities varied from 8.33×10⁵ to 4.43×10⁶ cell?L^?1, with Diatom, Chlorophyta and Cyanobacteria as the dominant taxa. There were 22 dominant species of phytoplankton, including 4 of Cyanobacteria, 12 of Diatoms, 1 of Cryptophyta and 5 of Chlorophyta, Aulacoseira granulata var. angustissima (O. Müller) Simonsen, Synedra Ehr. sp. and Scenedesmus quadricauda (Turp.) de Bréb.) were the perennial dominant species. Water temperature, nitrogen and phosphorus nutrients (Mainly PO₄^3?-P and NO₃^?-N) and organic matters (Mainly BOD₅ and COD_Mn) were important influences on the turnover of the dominant species of phytoplankton in the Fu River basin. Biological evaluation results showed that the Fu River basin was in an eutrophic state and medium pollution level during the water and dry period, and in a medium nutrition state and light pollution level in normal water period, with some sections in the medium pollution mainly concentrated in the main stream of Nancheng County and the downstream, tributaries of the urban section of Litan River and Chongren river. The ecological condition of the Fu River showed a downward trend in the past 10 years, and reducing nitrogen, phosphorus and organic pollution was the key to protect the water ecological environment in the Fu River Basin. Results of this study can provide a scientific basis for the water ecological of Fu River basin.

Key words: Fu river basin, phytoplankton, community structure, dominant species, aquatic ecological conditions evaluation

摘要：

抚河流域水环境质量呈下降趋势，给沿岸供水甚至鄱阳湖生态安全造成巨大压力，亟需开展全流域生态监测与评价，诊断水生态风险。浮游植物作为水生态系统的初级生产者，能表征水生态环境的变化。针对以往抚河浮游植物群落特征研究主要集中在干流和河口等局部区域，以抚河干流和主要支流为研究对象，于丰（2017年7月）、枯（2017年12月）、平（2018年4月）等3个水文期对抚河流域40个采样点的水环境因子及浮游植物群落结构进行了调查，结合浮游植物的种类组成、优势种、密度、生物多样性等对抚河流域水生态状况进行评价，运用冗余分析方法（Redundancy analysis，RDA），分析抚河流域浮游植物优势种与水环境因子的关系。结果表明：抚河流域共检出浮游植物7门171种，浮游植物细胞密度变化范围为8.33×10⁵－4.43×10⁶ cell?L^?1，优势类群以硅藻、绿藻和蓝藻为主，颗粒沟链藻极狭变种（Aulacoseira granulata var. angustissima (O. Müller)Simonsen）、针杆藻（Synedra Ehr. sp.）、四尾栅藻（Scenedesmus quadricauda (Turp.) de Bréb.）为抚河常年优势种。水温、氮磷营养盐（主要是正磷酸盐、硝氮）以及有机物（主要是五日生化需氧量、高锰酸盐指数）是影响抚河流域浮游植物优势种更替的重要影响因子。生物学评价结果表明，丰水期和枯水期，抚河水体处于富营养状态和中污染水平，平水期，抚河水体处于中营养状态和轻污染水平，但干流的南城县城河段以及下游，支流黎滩河、崇仁河的城市河段处于中污染水平。近10年，抚河水生态状况呈下降趋势，削减流域氮磷、有机物污染是抚河流域水生态环境保护的关键。研究结果可为抚河流域水生态环境保护提供科学依据。

关键词: 抚河流域, 浮游植物, 群落结构, 优势种, 水生态状况评价