中文摘要：

浮游植物是水生态系统的初级生产者,直接影响着水生态系统的结构、功能与稳定性。基于2012-2014年淮河流域沙颍河—淮干中游浮游植物和水质4次汛期和非汛期采集数据,利用物种优势度和多样性指数对浮游植物的时空分布进行表征,并利用冗余度分析、偏相关性分析等方法探索了淮河中上游流域的多种水环境因子对浮游植物时空分布的影响。结果表明,从时间变化上看,2012-2014年浮游植物密度呈现逐年递减趋势;从空间变化上看,物种丰度呈现从上游至下游逐渐减少趋势。从时空变化的影响因素上看,非汛期总磷和电导率影响最大,其解释度分别为：10.96%和8.36%;汛期总磷、总氮和氨氮影响最大,其解释度分别为9.47%、8.08%和6.96%。

英文摘要：

Phytoplankton is primary producer of aquatic ecosystem, and is also the main part of aquatic organism. The changes of phytoplankton assemblage strongly relate with water environmental factors. Spatial and temporal distribution of phytoplankton directly affects the structure and stability of the aquatic ecosystem. Moreover, the growth and abundance of phytoplankton are also the sensitive indicators to the river environment. The Huaihe River Basin is one of highly polluted basins in China. Many studies were focused on the flooding and water pollution controls, but paid less attention to the ecological restoration due to the shortages of ecological data. In our study, the upper and middle reaches of the Huaihe River Basin were selected as the study area. Phytoplankton species were investigated and identified for four times at ten stations from 2012 to 2014. The spatial distribution of phytoplankton was assessed by using the dominance and Shannon- Wiener indices. Moreover, the relationship between phytoplankton assemblages and water environment were detected and the main water environment variables were identified by using partial correlation analysis and redundancy analysis（RDA）. Finally, the contributions of key water environment variables on the phytoplankton assemblages were quantified individually. Results showed that：（1） the phytoplankton species and their densities reduced year by year. The species number decreased from 93 to 57, and the densities decreased from 1.64 × 109 cell /m3 to 7.36 × 108cell/m3from2012 to 2014. The abundance of phytoplankton in wet season was significantly higher than that in dry season, and the average abundance decreased from Zhaopingtai Station to Bengbu Station.（2） The key water environmental factors affected phytoplankton assemblages in the wet season were total phosphorus（TP）, total nitrogen（TN） and ammonium nitrogen（NH4-N）,and their contributions were 9.47%, 8.08% and 6.96%, respectively. In the dry season, total phosphorus（TP） and specific conduc