Distribution of Phytoplankton Communities and Chlorophyll Fluorescence Characteristics in Urban Lakes of Nanchang in Summer

目的：旨在探讨夏季城市内湖水华形成过程中浮游植物群落结构及其光合生理响应特征，揭示水华形成的光合机制，为城市湖泊藻华的监测与防控提供科学依据。方法：本研究以南昌市黄家湖不同水深为对象，采用分层采样技术，并结合显微镜定量分析与PHYTO-PAM原位叶绿素荧光测定，解析浮游植物群落结构与叶绿素荧光参数的响应规律。结果：研究表明：(1) 夏季水华期共鉴定浮游植物36种，以蓝藻(Microcystis sp., Anabaena sp., Oscillatoria等)和绿藻(Chlorella vulgaris, Scenedesmus sp.)为优势种。群落的香农指数由非水华期的2.23显著下降至1.88，蓝藻丰度显著增加38.06% (其中微囊藻占比36.71%)，但生物量减少75.56%，群落多样性明显降低。(2) 水华群落的光合最大效率Fv/Fm值(0.149)显著低于非水华期(0.423)，其中蓝藻表现出更高的光耐受力(Fv/Fm = 0.321)，远高于硅藻(Fv/Fm = 0.126)；(3) 快速光响应曲线显示水华藻类的光适应参数α及电子传递速率最大值rETRmax分别下降39.78%和62.79%，但随水深增加逐步恢复的趋势。结论：蓝藻凭借更强的光合生理适应性，成为夏季城市湖泊水华的主导生物；而过强的光抑制效应则显著降低群落的光合效率，增加表层水体的生态风险。Objective: The aim is to explore the structure of phytoplankton communities and their photosynthetic physiological response characteristics during the formation process of summer urban lake blooms, revealing the photosynthetic mechanisms behind bloom formation, and providing a scientific basis for monitoring and controlling algal blooms in urban lakes. Methods: This study focused on different water depths of Huangjia Lake in Nanchang City, using a stratified sampling technique combined with quantitative analysis under a microscope and in situ chlorophyll fluorescence measurement with PHYTO-PAM to analyze the response patterns of phytoplankton community structure and chlorophyll fluorescence parameters. Results: The study shows that: (1) A total of 36 phytoplankton species were identified during the summer bloom period, with cyanobacteria (Microcystis sp., Anabaena sp., Oscillatoria, etc.) and green algae (Chlorella vulgaris, Scenedesmus sp.) being the dominant species. The Shannon index of the community significantly decreased from 2.23 during non-bloom periods to 1.88, with cyanobacteria abundance significantly increasing by 38.06% (of which Microcystis accounted for 36.71%), but biomass decreased by 75.56%, leading to a noticeable decline in community diversity. (2) The maximum photosynthetic efficiency Fv/Fm of the bloom community (0.149) was significantly lower than that during non-bloom periods (0.423), with cyanobacteria exhibiting higher light tolerance (Fv/Fm = 0.321), far exceeding diatoms (Fv/Fm = 0.126); (3) Rapid light response curves showed that the light adaptation parameters α and the maximum electron transport rate rETRmax of blooming algae decreased by 39.78% and 62.79%, respectively, but showed a recovery trend with increasing water depth. Conclusion: Cyanobacteria, with stronger photosynthetic physiological adaptability, become the dominant organisms of urban lake blooms in summer; while the excessively strong light inhibition effect significantly reduces the community’s photosynthetic efficiency, increasing the ecological risk of surface water.