Study The Effects Of Ecological Restoration Project Of Lianghewan Bay On Structures Of Phytoplankton Community

Gonghu Bay is used as one of mainly water-supply source sites for Wuxi, the coast city, situated on the north-east of Taihu lake, where cyanobacterial bloom accumulated by the currents driven with south or south-west wind in summer, resulting in water quality so deteriorate that it could not be drunk. An ecological-restoration engineering of wetland was constructed in Lianghewan of Gonghu Bay to prevent and control the pollution of cyanobaterial bloom.In order to evaluate the spatial and temporal variation of phytoplankton community structure in Tai Lake and their relationship with environmental factors and also to analysis the impact of ecological restoration project on phytoplankton, an investigation was carried out from March2010to February2011. In this period,21sampling sites were selected and the samples were taken once a month. The species composition, density variation, dominated species, bio-diversity indexes were studied and the main results as follow:1. There were67of8phyla including108species that were identified, of which Chlorophyta,52species of31genera, accounting48.1%of the total phytoplankton species, Bacillariophyta(23species of18genera), Euglenophyta(14species of5genera), Cyanophyta(8species of8genera), is accounting for21.3%、13.0%、7.4%of the total phytoplankton species respectively. In spring and winter the dominated species were mainly Asterionella Formosa, Melosira granulate and Cyclotella meneghiniana. In summer the dominated species were mainly Microcystis aeruginosa, Anabaena flos-aquae which is easy leading to water bloom. In autumn, dominated species were mainly Cryptomonas ovata, Chroomonas acuta.2. The seasonal succession of phytoplankton assemblages in Lianghewan Bay is as follow:in spring and winter Bacillariophyta are the dominant populations; when it is coming to the late spring and the early summer the dominant assemblages are Bacillariophyta and Chlorophyta; into the summer and autumn Cyanophyta is the dominant populations; with the arrival of winter the importance of Bacillariophyta is rising again.3.The abundance of phytoplankton in Lianghe Bay ranged from106.0X104to89938.4X104cells/L with only one peaks in a year.. The maximum and minimum abundance of phytoplankton were founded in the summer (on July27th) and in the spring (on March15th) seperatively. The phytoplankton density from high to low is summer, autumn, winter and spring.4. Spatial distribution of phytoplankton is influenced by wetland ecosystem restoration project and the water bloom as well. Exception of the interval of water bloom, the phytoplankton density did not differ between each sampling sites. The phytoplankton density of havest phytoplankton channel is higher than that of outside the project, and more than that of control area, that of project area is minimum during this time. The results of statistics analysis show that the algal density in project area was significantly less than that of other area with SPSS software.5.The average of Shannon-Wiener indexes, Margalef indexes and uniformity indexes were2.69、2.82and0.45in project area,2.34、2.24and0.40in control area,2.42、2.35and0.40in without project area. The results revealed that the biodiversity in project area was higher than the other areas.6. The results illustrate that the ecological effecs of wetland restoration project is the great resistant against phytoplankton density increase and algal biodiversity decrease in project area during the bloom (from June to September).