梯级堰作用下芙蓉溪浮游植物春秋季群落结构及其驱动因素研究（英文）

Study on the phytoplankton community structure and its driving factors in Furong Creek during spring and autumn under the influence of cascade weirs

摘要

【目的】筑堰改变河流水力特性，影响河流浮游植物群落结构以及水生态系统健康水平。为探究梯级堰建设下芙蓉溪浮游植物春秋季群落结构及其驱动因素的非线性响应关系。【方法】于2023—2024年在芙蓉溪开展了浮游植物群落结构及相关环境要素的调研，重点分析了芙蓉溪同一枯水期内秋春两季浮游植物营养物质浓度及生物量变化状况，通过冗余分析筛选影响浮游植物群落结构的关键影响因子，使用MIKE 11模型拟合了河道内水动力变化状况，结合总氮和高猛酸盐指数，构建了浮游植物多样性指数与水动力因子的GAM模型，拟合了梯级堰优化布置后的浮游植物多样性变化状况。【结果】结果显示：芙蓉溪浮游植物Shannon-Wiener多样性指数全年均值为2.79,整体处于轻度污染状态，鉴定出浮游植物8门95属239种：绿藻门是芙蓉溪全年浮游植物的主要构成门类，其次为硅藻门和蓝藻门，浮游植物春秋两季细胞丰度变化范围为3.11~20.64 mg/L和0.23~6.31 mg/L,浮游植物群落结构季节性演替明显，相较于秋季，春季蓝藻门的相对丰度在全河段显著降低，而金藻门和甲藻门在部分点位显著上升，并形成水华现象，造成浮游植物多样性水平显著下降。全年水域优势种为链形小环藻(Cyclotella catenata)、小球藻(Chlorella vulgaris)、双对栅藻(Scenedesmus bijuga)、四尾栅藻(Scenedesmus quadricauda)、尖尾蓝隐藻(Chroomonas acuta)、卵形隐藻(Cryptomonas ovata)和啮蚀隐藻(Cryptomonas erosa)。冗余分析(RDA)表明，水动力因子(v、h)和水体环境因子(TN、COD_Mn)是浮游植物种群结构的显著影响因子。【结论】结果表明：芙蓉溪春季的水环境营养物质浓度、浮游植物生物量和密度远高于秋季，结合水动力因子和环境因子构建的GAM模型可以有效地反应浮游植物多样性指数与驱动因素间的非线性关系，在春季营养物质浓度提升的情况下，溢流堰形成的低流速和高水深的生境条件，会导致浮游植物Shannon-Wiener指数降低，富营养化风险加剧，而合理的梯级堰布设方案将会提高浮游植物多样性水平，降低河流富营养化风险。本研究结果有助于深化理解河流梯级筑堰引发的河流生态环境效应。

Abstract

[Objective] The construction of weirs changes the hydraulic characteristics of rivers and affects the structure of phytoplankton communities and the health of aquatic ecosystems in the river. This study aims to explore the nonlinear response relationship between phytoplankton community structure and its driving factors in spring and autumn in Furong Creek under the construction of cascade weirs. [Methods] The structure of phytoplankton communities and related environmental factors were investigated in Furong Creek from 2023 to 2024. This study focused on the analysis of the changes of nutrient concentrations and biomass of phytoplankton in autumn and spring within the same dry season in Furong Creek. Redundancy analysis was used to identify the key factors influencing the structure of phytoplankton communities. The MIKE 11 model was employed to simulate the hydrodynamic changes in the river. Combined with total nitrogen and permanganate index, a GAM model of phytoplankton diversity index and hydrodynamic factors was developed, and the change of phytoplankton diversity after the optimized layout of the cascade weirs was fitted. [Results] The result showed that the annual average value of Shannon-Wiener diversity index of phytoplankton in Furong Creek was 2. 79, which was in a state of mild pollution. A total of 239 species from 95 genera in 8 phyla were identified. Among the phytoplankton, Chlorophyta was the dominant group throughout the year in Furong Creek, followed by Bacillariophyta and Cyanophyta. The cell abundance of phytoplankton ranged from 3. 11 to 20. 64 mg/L and from 0. 23 to 6. 31 mg/L in spring and autumn, which indicated a clear seasonal succession of phytoplankton community structure. Compared with autumn, the relative abundance of Cyanophyta significantly decreased in spring across the whole river section, while Chrysophyta and Dinophyta showed significant increase at some monitoring sites, leading to water bloom phenomenon and a noticeable decline in the diversity of phytoplankton. The dominant species in the water bodies throughout the year were Cyclotella catenata, Chlorella vulgaris, Scenedesmus bijuga, Scenedesmus quadricauda, Chroomonas acuta, Cryptomonas ovata, and Cryptomonas erosa. Redundancy analysis(RDA) showed that hydrodynamic factors(v, h) and water environmental factors(TN, COD_Mn) were the main influencing factors of phytoplankton community structure. [Conclusion] The result show that the nutrient concentration, phytoplankton biomass, and density in Furong Creek in spring are significantly higher than in autumn. The GAM model, constructed by combining hydrodynamic and environmental factors, can effectively reflect the nonlinear relationship between phytoplankton diversity index and its driving factors. In spring, with an increase in nutrient concentration, the habitat conditions of low flow speed and high water depths formed by overflow weirs will lead to a decrease in the Shannon-Wiener index of phytoplankton and an intensified risk of eutrophication. However, a reasonable layout scheme of cascade weirs will improve the diversity of phytoplankton and reduce the risk of eutrophication in the river. The findings of this study can help deepen the understanding of the ecological and environmental effects of cascade weir construction in the river.

关键词

梯级堰 / MIKE 11模型 / 冗余分析 / GAM模型 / 影响因素

Key words

cascade weirs / MIKE 11 model / redundancy analysis / GAM model / influencing factors

基金资助

国家重点研发项目(2022YFC3204200)

国家重点研发项目(2022YFC3204204)

国家自然科学基金青年科学基金项目(52409100)