[Temporal and Spatial Distribution of Environmental Factors and Phytoplankton During Algal Bloom Season in Pengxi River, Three Gorges Reservoir].

Planktonic algae and Related Environmental Factors were monitored during the period of algal blooms season in 2014 (Spring April 17 and summer 27 July) in Pengxi river, Three Gorges Reservoir. Mathematical statistical tools were used to analyze the community structure of planktonic algae in Pengxi River with its environmental factors. The results of sampling in spring showed that except the estuary site, S1 and the site close by, S2, the waters stratified, but without epilimnion, only had metalimnion and hypolimnion; the upstream sites had larger temperature difference between water layers than did the downstream ones; from all the 8 sampling sites from estuary to upstream, water depth, and the temperature, pH, conductivity, dissolved oxygen, chlorophyll a, TN and TP of the surface layer (0-0.5 m deep) were significantly different (ANOVA, P < 0.05). 25 species (genus) of planktonic algae were identified. The abundance of species ranged from 2.76 x 10⁴ cell · L⁻¹ to 145.8 x 10⁴ cell · L⁻¹. Ceratium hirundinella was the main dominant species, and Anabaena sp. was the sub-dominant species. Algal bloom in upstream sampling sites S7 (63.4 x 10⁴cell · L⁻¹) and S8 (145.8 x 10⁴cell · L⁻¹)were relatively serious in spring. Temperature of water, pH , conductivity, dissolved oxygen and NO₃⁻ were the key regulatory factors for phytoplankton abundance based on redundancy analysis ( RDA). The results of sampling in summer showed similar stratification trends among sites; the depth of the same 8 sampling sites, and their surface layer's temperature of water, turbidity, redox potential, pH, water depth, conductivity, chlorophyll a, NH₄⁺, NO₃⁻, total nitrogen and total phosphorus were significantly different (ANOVA, P < 0.05). 46 species (genus) of phytoplanktonic algae were identified. The abundance ranged from 9.56 x 10⁴ cell · L⁻¹ to 278.88 x 10⁴ cell · L⁻¹. Phormidium sp. was the main dominant species, and Anabaena sp. was the sub- dominant algae. Algal bloom at the lower part of the river, S2 (216.44 x 10⁴ cell · L⁻¹), S3 (278.88 x 10⁴ cell · L⁻¹) and S4 (108.12 x 10⁴ cell · L⁻¹) were relatively serious in summer. Turbidity, depth of water, TN, oxidation-reduction potential, conductivity and dissolved oxygen were the key regulatory factors for phytoplankton abundance based on RDA. Stratification had important effect on algal bloom formation.