中文摘要：

2008年4月3日08：00—4日08：00在三峡水库香溪河库湾5个监测点对拟多甲藻（Peridiniopsissp．）进行了24h连续监测，以研究拟多甲藻的昼夜垂直迁移特性，并解释拟多甲藻水华表层水体表观颜色昼夜变化的原因．结果表明：拟多甲藻在12m水深以上水柱中存在明显的周期性昼夜垂直迁移特性，00：00—16：00拟多甲藻向表层水体迁移并聚集，最大上移速度约为2m／h；16：00—00：00拟多甲藻向下部水体迁移，最大下移速度约为4m／h；拟多甲藻的昼夜垂直迁移是导致拟多甲藻水华表层水体表观颜色不断变化的主要原因．水体中各层叶绿素a质量浓度[ρ（Chla）]昼夜变化较大，用单层ρ（Chla）不足以评价藻类水华暴发程度；均深叶绿素a质量浓度[ρ（A．D．Chla）]的昼夜变化不大，能够综合表征藻类迁移水柱中藻类的现存量，可以作为河道型水库拟多甲藻水华暴发程度的评价指标．

英文摘要：

To study the diurnal vertical migration of Peridiniopsis sp. , continuous monitoring （time interval on the order of an hour） was conducted at five profiles in the Xiangxi Bay of the Three Gorges Reservoir from 08：00 April 3rd to 08：00 April 4th in 2008. The causes of diel variation of apparent color of surface water containing Peridiniopsis sp. bloom were attempted to explain. The vertical distribution of Peridiniopsis sp. biomass changed regularly throughout day and night within the upper 12 m. Peridiniopsis sp. rose and accumulated to the surface water with the highest speed of approximately 2 m/h between 00：00 and 16：00, and sank between 16：00 and 00：00 with the highest speed of approximately 4 m/h, which resulted in the diel variation of apparent color of surface water containing Peridiniopsis sp. bloom. The biomass of Chla in a certain layer changed too much over day and night to evaluate the extent of the algal bloom. The A. D. Chla mass concentration at different depths was suggested to judge the degree of an algae bloom, because it changed little in 24 h and indicated algae standing crops in algae migration water column.