Spatial and Temporal Distribution Dynamics of Phytoplankton in Muye Lake and their Relationship with Environmental Factors

Muye Lake,in the central district of Xinxiang city,Henan Province,with an area of 1. 1x105m2,is a public place of leisure and entertainment for local people and is important ecologically. The phytoplankton community in Muye Lake,including the succession of spatial and temporal distribution,population composition,dominant species,and their relationship with the environmental factors,all reflect the water quality and lake dynamics. From September 2012 to August 2013,the structure of the phytoplankton community and associated environmental factors were analyzed monthly in Muye Lake. The relationship between the phytoplankton community and environmental factors was characterized based on the results. Five sample sites were selected,representing the upstream river channel,confluence,shoreline,pelagic zone and the downstream channel of the lake. Phytoplankton samples for qualitative analysis were collected with 25 μm plankton nets and fixed in 4% formaldehyde. 1 L samples for quantitative analysis were collected 0. 5m below the surface and concentrated to 30 ml by settling for 48 h. Phytoplankton was identified using a microscope. The water temperature( WT),transparency( SD),pH and dissolved oxygen( DO) were measured at the sample site and the chemical oxygen demand( CODCr),total phosphorous( TP),total nitrogen( TN),NH+4-N,NO-3-N,and chlorophyll a( Chl-a) were measured in the laboratory within 48 h. A total of 147 species of phytoplankton belonging to 87 genera were identified,including 6 species of Xanthophyceae,6species of Cryptophyta,4 species of Chrysophyta,4 species of Pyrrophyta,57 species of Chlorophyta,23 species of Euglenophyta,29 species of Bacillariophyta and 18 species of Cyanophyta. The phytoplankton density ranged from7. 4 × 107 to 9. 1 × 107 cell /L,with the highest value of 16 × 107 cell /L observed during the summer of 2013. The phytoplankton community was dominated by Chlorophyta and Bacillariophyta in autumn,winter and spring,accounting for 32. 2% and 23. 9% of the total phytoplankton in autumn,39. 2% and 24. 5% in winter,40% and51. 7% in spring. The density of Cyanophyta was the highest in summer,comprising 83% of the total phytoplankton. During the study values of the Shannon index in autumn,winter,spring and summer were 1. 3,1. 27,1. 06,0. 48 and the Pielou evenness index also decreased from 0. 35 to 0. 175,indicating that water quality of Muye Lake was declining continuously from the fall of 2012 to the summer of 2013. Pearson correlation analysis showed that temperature,CODCr,SD,NO-3-N and Chl-a were the environmental factors most affecting phytoplankton density in Muye Lake. There was a significant positive relationship between average phytoplankton density and Chl-a,CODCr,and temperature( P 0. 05). Phytoplankton density also displayed a positive correlation with TN,TP,and NH+4-N and a negative correlation with SD and NO-3-N.