[Phytoplankton Community Structure and Water Quality Assessment in Jialing River After the Impoundment of Caojie Reservoir].

The variation of phytoplankton community and the water quality in Jialing River after the impoundment of Caojie Reservoir was studied in this paper. There were 145 species of phytoplankton under the membership of 8 divisions and 74 genera. Bacillariophyta was the first dominant division, with a total of 57 species of 23 genera, accounted for 39. 3% of total phytoplankton species, followed by Chlorophyta, with 53 species of 28 genera and accounted for 36. 6%. Only 35 species of 23 genera belonged to Euglenphyta, Cryptophyta, Pyrrophyta, Chrysophyta, and Cyanophyta. The average phytoplankton abundance was 1. 82 x 10(5)cell . L-1, and the top three taxon of most abundant were Bacillariophyta, Cryptophyta and Pyrrophyta, accounted for 39. 2%, 29. 9%, and 24. 5% of total abundance, respectively. The cell abundance in spring was significantly higher than those in other seasons. The dominant species included Aulacoseria granulata, Melosira varians, Peridiniopsis niei, Komma caudata, Cryptomonas erosa etc., indicated by the dominant index. Excluded by cluster analysis, the influence on phytoplankton had initially emerged after the impoundment of Caojie Reservoir. The reservoir area could be divided into different ecological regions longitudinally after Caojie Reservoir impoundment, which had an important impact on the phytoplankton. Meanwhile, the phytoplankton and flow velocity between upstream and downstream of the dam significantly varied. Shannon-Wiener species diversity index, Margalef species richness index and Pielous evenness index ranged 2. 06 - 3. 55, 0. 76 - 1. 90 and 0. 50 - 0. 78, respectively. The evaluation results of phytoplankton community structure showed that the eutrophic state was at medium eutrophication level, while diversity analysis results indicated light to moderate pollution.