浅水湖泊浮水植物芡实收割对浮游植物群落的影响

浅水湖泊生态系统正遭受广泛而强烈的人为干扰，但是对收割水生植物干扰的研究甚少。于2019年8月对芡实过度生长的陈瑶湖进行通道式分区收割工程，分析了收割芡实（Euryale ferox）前后不同处理组浮游植物群落的变化。研究期间共鉴定出浮游植物6门47属72种，其中收割前63种，收割后71种。收割后浮游植物的细胞密度和生物量均高于收割前，分别增加了39.78%和5.09%。收割芡实导致陈瑶湖浮游植物群落为由蓝藻-绿藻-硅藻-隐藻群落转变为蓝藻-绿藻-硅藻群落。其中蓝藻细胞密度和生物量显著高于收割前（P<0.05），归因于有害蓝藻（铜绿微囊藻Microcystis aeruginosa、水华束丝藻Aphanizomenon flos-aquae、小颤藻Oscillatoria tenuis、卷曲鱼腥藻Dolicospermum circinale、小席藻Phormidium tenu）的增加。收割还导致了硅藻群落由附生型向浮游型硅藻的转变，表现为尖针杆藻（Ulnaria acus）减少，而颗粒直链藻极狭变种（Aulacoseira granulata var.angustissima）、梅尼小环藻（Cyclotella meneghiniana）增加。在芡实收割过程中，未收割组和河道的浮游植物群落结构在时空分布上无显著性差异（P>0.05），但收割组在收割后的不同阶段内差异较为明显，其细胞密度和生物量随着收割实验的结束逐渐降低。浮游植物与环境因子的相关性分析表明，水生植被覆盖度、总磷、总氮、溶解氧和叶绿素a浓度是影响浮游植物细胞密度和生物量变化的主要环境因子。综合陈瑶湖水质状态，本研究认为收割芡实并不能缓解浅水湖泊富营养化状况，研究结果为浅水湖泊水生植被的管理提供理论依据。

Effects of harvest of floating plants Euryale ferox on phytoplankton community in shallow lakes

Shallow lake ecosystems are suffering from the extensive and intense anthropogenic disturbances, but little research has been conducted on harvesting macrophyte disturbance. In this study, a passage zoned harvesting project was conducted in August 2019 in Euryale ferox overgrown Lake Chenyao, and changes in phytoplankton communities in different treatment groups before and after harvesting of E. ferox were analyzed. A total of 72 species of 6 families, 47 genera and 72 genera of phytoplankton were identified during the study, including 63 species before and 71 species after harvest; the cell density and biomass of phytoplankton were higher after harvest than before, increasing by 39.78% and 5.09%, respectively. The harvest of E. ferox led to the change of phytoplankton community from cyanobacteria-green algae-diatom-cryptoalgae community to cyanobacteria-green algae-diatom community. The relative proportion of cyanobacteria was significantly higher than that before harvest (P<0.05), showed the increase of harmful cyanobacteria (Microcystis aeruginosa, Aphanizomenon flos-aquae, Oscillatoria tenuis, Dolicospermum circinale and Phormidium tenu). Harvesting also led to the transformation of diatom community from epiphytic to planktonic diatoms, with the decrease of Ulnaria acus and the increase of Aulacoseira granulata var. angustissima and Cyclotella meneghiniana. During E. ferox harvesting, there was no significant difference in the spatial and temporal distribution of phytoplankton community between the unharvested group and the river channel (P>0.05), but there were obvious differences in different stages after harvesting in the harvested group, and their cell density and biomass decreased gradually with the end of harvesting project. Correlation analysis between phytoplankton and environmental factors showed that aquatic vegetation coverage, total phosphorus, total nitrogen, dissolved oxygen and chlorophyll a concentration were the main environmental factors affecting the changes of phytoplankton cell density and biomass. Based on the water quality status of Lake Chenyao, this study concluded that harvesting E. ferox did not alleviate the eutrophication condition of shallow lakes, and the results of the study provided a theoretical basis for the management of aquatic vegetation in shallow lakes.