环境条件变化下滇池冬春季节浮游植物的演替特征

富营养化和气候变暖是影响浮游藻类结构组成以及物候学等特征的两大重要环境条件。为探讨在人为干预和全球变化影响下富营养化湖泊滇池浮游植物的演替特征,2017-2019年2个冬春季在滇池选择北(D1)、中(D2)、南(D3)3个采样点对浮游植物群落进行监测。研究结果表明,滇池浮游植物在冬春季呈现与以往不同的演替特征。第一、滇池在冬春季仍以蓝藻占优势,但优势种组成发生了变化。蓝藻中占主要生物量的是微囊藻,而且,惠氏微囊藻(Microcystis wesenbergii)取代铜绿微囊藻(Microcystis aeruginosa)占绝对优势。近20年来(2001-2019年),滇池冬春季微囊藻优势种经历了从铜绿微囊藻到绿色微囊藻(Microcystis viridis)再到惠氏微囊藻的转变。在水温较低的2-3月份,蓝藻生物量比例下降,绿藻和硅藻生物量比例上升,在此时期,香农威纳指数也相对升高。第二,束丝藻(Aphanizomenon)和鱼腥藻(Anabaena)的物候特征发生了改变。曾经春季的优势水华藻种束丝藻提前在秋季出现,且2018年秋季峰值较2017年约提前2周。2018年春季鱼腥藻在滇池北部发生了小型的水华,取代了往年发生束丝藻水华的现象,2019年春季鱼腥藻没有出现较高的生物量,但仍在春季达到峰值,其峰值约提前1周出现。本研究结果为揭示在全球变化和人为干预影响下湖泊冬春季节浮游植物群落演替特征及响应策略提供了基础数据支撑。

Winter and Spring Succession of the Phytoplankton Community in Dianchi Lake under the Influences of Human Intervention and Global Warming

Eutrophication and climate warming are affecting the structure and phenology of phytoplankton. In the past two decades, large scale cyanobacterial blooms have occurred frequently in Dianchi Lake, but water quality in Dianchi Lake is gradually improving due to pollution control. Since 2016, the water quality status of Dianchi Lake has improved from inferior Class V to Class V and the trophic level index (TLI) has decreased by 4.8%. In recent years, global warming has been strengthening and the average temperature of Dianchi Lake is clearly increasing, with the largest increase in winter. To explore the effects of human intervention and climate change on Dianchi Lake, seasonal succession of the phytoplankton community was investigated. Samples were collected at three sites in Dianchi Lake, D1 (north), D2 (central) and D3 (south) during winter and spring of 2017, 2018 and 2019. Water environmental parameters were monitored simultaneously, including total nitrogen (TN), total phosphorous (TP), chlorophyll a (Chl a), pH, conductivity and water temperature. Redundancy analysis (RDA) and Pearson correlation analysis were used to analyze the relationship between phytoplankton cell density and the environmental factors. The winter-spring successional characteristics of the phytoplankton community were found to be shifting. Cyanobacteria were still dominant in Dianchi Lake, but the dominant species had changed. Microcystis still made the largest contribution to cyanobacterial biomass, but M. wesenbergii replaced M. aeruginosa as the absolute dominant species. In the 20 years from 2001 to 2019, during winter and spring, the dominant species in Dianchi Lake shifted from M. aeruginosa to M. viridis and then to M. wesenbergii. From February to March, when water temperature is low, the relative biomass of cyanobacteria decreased, while those of Chlorophyta and diatoms increased. During this period, the Shannon Weiner index increased proportionately. The phenology of Aphanizomenon and Anabaena is also shifting. Aphanizomenon, formerly the dominant bloom-forming species in spring, appeared early, in autumn. However, the peak biomass of Aphanizomenon in autumn 2018 was about 2 weeks earlier than that in autumn 2017. A small Anabaena bloom occurred in the northern part of Dianchi Lake in spring 2018, replacing the previous Aphanizomenon bloom. Anabaena did not have a higher biomass in spring 2019, but still peaked in the spring, about a week earlier. Based on these findings, we concluded that the composition and phenological characteristics of the winter-spring phytoplankton community in in Dianchi Lake have changed as a result of nutrient reduction and climate change.