浮游植物对湖泊水体生态重建的响应——以太湖五里湖大型围隔示范工程为例

Response of phytoplankton to ecological restoration in eutrophic lakes:an experimental large enclosure in Wuli Lake,Lake Taihu

根据太湖五里湖湾生态重建大型围隔示范工程的现场观测结果,分析了湖泊生态重建措施对浮游植物的影响,结果显示:(1)在生态重建的第一年,尽管生态重建区内种植了大量水生植物,水体氮磷含量也有较大幅度的下降,水体透明度也被提高了近一倍,但是藻类却大量生长,并暴发了蓝藻水华;第二年,生态重建区的环境条件逐渐对藻类(包括蓝藻和其中的微囊藻)产生了抑制作用,开始出现藻类生物量下降趋势;表明生态重建措施(以水生植被重建为中心的生态系统重建组合措施)可以在较短时间内(当年)建立起一定规模的水生植物群落,有效降低水体氮磷营养盐,提高水体透明度,但要在较短时间内(2年内)完善一个较大的水生态系统结构、有效降低藻类生物量(特别是夏季)有一定困难．(2)尽管氮磷营养盐对水体藻类总量增加有较大影响,但并不是蓝藻大量暴发的决定因素,上行作用力对蓝藻的控制(bottom-up effort)表现弱于下行作用力(top-down effort)．(3)较低的TN/TP比值(15．9-35．6．平均30．5)既是蓝藻水华暴发的原因,也是其作用的结果,其可能有利于蓝藻的大量暴发．(4)生态重建措施较大幅度地改善了水环境,但并没有显著提高藻类多样性指数(Shannon index),因此,单凭藻类多样性指数并不能完全反映水环境改善状况,在评价水环境质量方面需要结合其它多种指标进行综合评估．

Response of phytoplankton to ecological restoration was evaluated based on the results of an experimental large enclosure in eutrophic Wuli Lake of Lake Taihu, China. The results indicated that in the first year of restoration, algal biomass significantly increased, and cyanobacteria blooms broke out although the coverage of aquatic plant was up to 55% ; TN and TP were significantly decreased, and secchi depth was enhanced by 100% or so. In the next year, algal growth, including cyanobacteria and Microcystis, was inhibited in certain extent with improvement of environment in enclosure compared with that in the lake area （ outside enclosure, a control area）. The result showed that response of phytoplankton to ecological restoration was a slow process. Higher TN and TP were not decisive factors for the breakout of cyanobacteria biomass though the increase of total algal biomass was caused by higher nutrition （TP）. Bottom-up effort was weaker than top-down effort. The lower TN to TP ratio possibly facilitated cyanobacteria growth, which was the cause and the result of cyanobactefia growth. In addition, the algal diversity index （Shannon index） was not totally indicating aquatic environment improvement status. It was suggested that it needed to integrate many factors for evaluating the trend of ecosystem.