Community Structure Characteristics of Phytoplankton and Water Quality Assessment in Cascade Reservoirs in Hongshui River Drainage in Autumn

Species composition, density and biomass, spatial distribution and biodiversity of phytoplankton were investigated in six cascade reservoirs in Hongshui River, including Longtan Reservoir, Yantan Reservoir, Dahua Reservoir, Bailongtan Reservoir, Letan Reservoir and Qiaogong Reservoir in autumn in 2010. In total, 64 species algae, being classified into 6 phyla, were identified in taxonomy. The results showed that species in Bacillariophyta were dominated in the phytoplankton community, followed by members in Chlorophyta and Cyanophyta. There were 31 species(accounting for 48.44%) in Bacillariophyta, 17 species representing 26.56% in Chlorophyta and 10 species(accounting for 15.63%) in Cyanophyta. Also, 2 species in Pyrrophyta, 2 species in Chrysophyta and 2species in Rhodophyta were observed, accounting for 3.13% for each. The dominance index analysis revealed that members in Bacillariophyta were found to be the dominant phytoplankton species in the six cascade reservoirs in Hongshui River, followed by species in Chlorophyta and Cyanophyta. The phytoplankton density in each cascade reservoir was ranged from 3.41×105ind./L to 5.90×105ind./L, with the maximal density of 5.90 ×105ind./L in Bailongtan Reservoir, and the minimum of 3.41 ×105ind./L in Qiaogong Reservoir. The phytoplankton biomass in each cascade reservoir was varied from 0.55 mg/L to 2.70 mg/L, with the maximum of 2.70 mg/L in Longtan Reservoir and the minimum of 0.55 mg/L in Dahua Reservoir, with Shannon-Wiener diversity index from 2.03 to 2.88, and Pielou evenness index from 0.52 to 0.95. The similarity index of phytoplankton composition was ranged from 0.34 to 0.72, with the minimum in Dahua Reservoir and Bailongtan Reservoir, and the maximum in between Longtan Reservoir and Qiaogong Reservoir.The water quality was shown to be mesotrophic-oligotrophic in Logntan Reservoir and oligotrophic in other five reservoirs according to the evaluation standards of algal biological index.