中文摘要：

弄清三峡水库蓄水后干支流生境演变规律及其生态环境影响对保障三峡水库正常运行具有重要意义。通过整理5年的监测数据,掌握三峡水库干流水温变化规律,分析干流湖沼学特征并讨论干流发生水华的风险。结果表明,三峡水库干流水温季节性变化显著,年际变化范围为9～27℃;水温在3-5月出现弱分层现象,表底温差最大为2.5℃。3-5月干流混合层深度最低可小于10m,浮力频率（N2）整体大于5×10-5 s-2,属于过渡型分层水体,有一定的水华风险;其他时间水体均为完全混合水体,临界层受泥沙含量影响低于1m,不会发生藻类水华。整体来看,三峡水库干流属于典型的河流型水体,浮游植物生长受到水流限制,采用浮力频率法更能反映三峡水库水体的实际情况。

英文摘要：

It is important to understand the changes of the habitat and their ecological effects in the TGR after the Three Gorges Dam.In this paper,a five-year data is analyzed to study the thermal stratification,limnological changes and risk of algal bloom in the mainstream of the TGR.The results indicate that the water temperature seasonally change from 9℃to 27℃.From March to May,there is a sick thermal stratification,the temperature difference between surface and bottom layer is less than 2.5 ℃ and the mixing depth is also less than 10 m.As the buoyant frequency（N2）exceeds 5×10-5 s-2,the water body can be considered as a transitional water between the stratified and full mixing type during that period,there will be a little risk of algal bloom.The rest of the year,the mainstream is a full mixing water with a euphotic depth of less than 1m,and had no algal bloom.In conclusion,the mainstream of the TGR was a typical river-type reservoir,in which the phytoplankton growth was limited by the water flow.The parameter of N2 can be more accurate for the TGR to determine its water body type.