太湖不同湖区夏季蓝藻生长的营养盐限制研究

Nutrient limitation of cyanobacterial growth in different regions of Lake Taihu in summer

采集太湖6个湖区水样,利用营养盐添加,现场培养实验研究了水华蓝藻在不同湖区水体中生长的氮、磷限制情况和蓝藻的生长潜力.结果表明,梅梁湾水体只有氮、磷同时添加才对蓝藻生物量具有显著的促进作用,表明该湖区水华蓝藻的生长不仅存在磷限制,而且存在明显的氮限制.在太湖西部河口区、竺山湾和贡湖湾,蓝藻对单独的氮添加没有反应,而单独磷添加和氮磷同时添加对蓝藻生长具有同样的促进作用,表明磷是这些区域藻类生长的主要限制因子.东太湖水体不论氮磷单独还是同时添加对蓝藻生长均没有促进作用,表明存在氮磷以外的限制因子.氮磷供应充足的情况下,梅梁湾和西部河口区水体培养的蓝藻生长速率最高,表明这两个水域蓝藻的生长潜力最大,氮磷输入极易刺激蓝藻大量增殖,这在一定程度上解释了为什么蓝藻水华在这两个区域更为严重.蓝藻在贡湖湾和胥口湾水体中生长速率较低,在东太湖水体中的生长速率最低,因此这些水域的蓝藻增殖潜力较低.

An in situ nutrient enrichment bioassay was conducted using surface lake water collected from six stations of Lake Taihu.The objective of the study was to investigate nutrient limitation of growth of phytoplankton,much of which was dominated by cyanobacteria,in different areas of the lake.The results showed that in Meiliang Bay（station 3）,phytoplankton biomass（Chl a） increased significantly with combined addition of nitrogen（N） and phosphorus（P）,with no significant effect from individual additions of N or P separately,suggesting that nutrient limitation of these two nutrients may be tightly coupled.In the river transition zone in the western area of the lake（station 10）,and in Zhushan Bay（station 16） and Gonghu Bay（station 13#）,chl a in the N aloneaddition treatments did not increase significantly compared to the initial chl a,but P addition treatments（both ＋P and ＋NP） led to significantly higher chl a concentrations than the control,reflecting N-replete and P-deficient biomass in these three areas.In the eastern part of the lake（station 24）,additions of N and P individually and together did not stimulate growth compared with the control,suggesting factors other than N and P may limit phytoplankton growth.Under conditions where N and P produced cells that were replete in these nutrients,phytoplankton growth rates in Meiliang Bay and the estuary zone in the western bank were highest（0.3d-1）,suggesting growth potential is largest in these two zones.This may help to explain why there are severe cyanobacterial blooms in these zones.Phytoplankton growth rates were lower（0.11 d-1 and 0.15 d-1,respectively） under nutrient replete conditions in Gonghu Bay and Xukou Bay,and losses occurred with nutrient additions in the eastern part of the lake,suggesting phytoplankton growth potential is low in these zones.