Phytoplankton Community Structure and Biodiversity at Lushanxihai Reservoir in Summer and Autumn

The study of phytoplankton community structure is one of the core areas of lake ecological research,providing important information on biological resources and the ecological status of lakes. In this study,we investigated the community structure of phytoplankton in Lushanxihai Reservoir,analyzed seasonal and spatial variations,as well as the biodiversity of the phytoplankton community. The data collected were used to evaluate the water quality of Lushanxihai Reservoir. Lushanxihai,a large reservoir( 308 km2) located in the northwest of Yongxiu county,Jiangxi province,provides important social functions including drinking water supply,tourism,aquaculture and water for industry and agriculture. During the summer( August) and autumn( October) of 2012,samples were collected at eighteen sites( S1- S4 in open water,S5- S12 in the transition zone and S13- S18 near the inlet). Phytoplankton samples for qualitative analysis were collected using plankton nets and identified by optical microscopy.Water samples from the surface and bottom were collected using glass bottle for four times and mixed in a 10 L container. A 1 L portion of the well-mixed water was removed for quantitative analysis and the phytoplankton was concentrated to 25 mL by settling for 24 h. Eight phyla,including 86 species,were found in Lushanxihai Reservoir.Chlorophyta was the dominant phylum and included 43 species,accounting for 59. 43% of the total phytoplankton species,followed by Bacillariophyta( 17 species) and Cyanophyta( 14 species),accounting for 19. 54% and16. 09%,respectively. Of the 86 species observed,14 species from four phyla were dominant during the investigation and included Chlamydomonas reinhardi,Palmellaceae mucosa,Anabaena oscillarioides,Cryptomonas ovate and Chroomonas acuta. The overall mean value of phytoplankton density was 2. 20 × 106 cell /L( range,4. 28 × 105-5. 17 × 106 cell /L),with a mean summer value of 3. 15 × 106 cell /L and mean autumn value of 1. 25 × 106 cell /L.The average biomass was 2. 90 mg /L( range,1. 24- 7. 01 mg /L),with a mean summer value of 3. 90 mg /L and mean autumn value of 1. 89 mg /L. The Shannon-Wiener diversity index,Pielou evenness index and Margalef richness index were 2. 84- 4. 45,0. 63- 0. 89,1. 46- 3. 69,respectively. Phytoplankton density,biomass and species richness varied by season in Lushanxihai Reservoir,higher in summer and lower in autumn,but the biodiversity indices of phytoplankton were higher in autumn than summer. No obvious spatial variation in species diversity and community structure were observed in Lushanxihai Reservoir. The data collected during this study indicates good water quality in Lushanxihai Reservoir with water quality in the transition zone of higher quality in summer and water quality in the lacustrine zone higher in autumn.