Comparison Study Of Community Structure Of Phytoplankton Between Inside And Outside Of Bio-manipulation Pen And Demonstration Project Area In Lake Gehu

Gehu Lake is the second largest lake in southern Jiangsu Taihu Lake Basin, the total area of the lake is 137km2.It has a very important geographical location. Gehu has a variety of functions such as water source, irrigation, transport, tourism and aquaculture. Since the 1990 s to 2006,Because of the pollution from industry, agriculture and aquaculture, Gehu Lake eutrophication was very serious. So the government attaches great importance to Gehu Lake and carried out a series of measures. For example,through the stocking filter feeding fish(Hypophthalmichthys molitrix and Aristichys mobilis)in bio- manipulation pen to control the outbreak of Cyanobacteria;There were ecological dredging and submerged plant restoration projects in demonstration project area. C urrently, there are a lot of research on phytoplankton and zooplankton of Gehu Lake, Some academics have also discussed the influences of silver carp and bighead in Bio- manipuation Pen on The C ladocerans and Zoobenthos. But the comparison study of phytoplankton between inside and outside of bio- manipulation pen and demonstration project area in Lake Gehu has not been reported. From July 2013 to June 2014, comparative experiment was carried out to study the community structure of phytoplankton in three regions of Lake Gehu. The three regions include demonstration project area, inside and outside of bio- manipulation pen. the effects on improving eutrophic water was also been involved, it can provide scientific basis for the protection of ecological system and Ecological Regulation Project in Lake Gehu.The main results were as below:1.During July 2013 and June 2014, 139 species of phytoplankton belonging to 7 phyla, 77 genera were observed in the inside of bio- manipulation pen of Lake Gehu; 137 species of phytoplankton belonging to 7 phyla, 72 genera were observed in the outside of bio- manipulation pen of Lake Gehu; 117 species of phytoplankton belonging to 6 phyla, 69 genera were observed in the demonstration project area of Lake Gehu. Three regions have 110 same species, The main species in three regions were Cyanobact eria,Chlorella and Diatoms. The species between inside and outside of bio-manipulation pen were very similar, the species between inside of bio- manipulation and demonstration project area were medium similar, the species between outside of bio- manipulation and demonstration project area were medium similar.2.The average annual density of phytoplankton of inside and outside of bio- manipulation pen and demonstration project area were(3201.07 ±2236.63)×104 cell ?L-1 and(4359.23±2574.36)×104 cell?L-1 and(454.89 ±313.48)× 104 cell ?L-1. The order of density as: outside of bio- manipulation pen > inside of bio- manipulation pen> demonstration project area. LSD from multiple comparison showed that density of phytoplankton were significant difference between inside and outside of bio- manipulation pen(P<0.05).Extremely significant difference was found between inside of bio- manipulation pen and demonstration project area(P<0.01), outside of bio- manipulation pen and demonstration project area(P<0.01).3.The average annual biomass of phytoplankton of inside and outside of bio- manipulation pen and demonstration project area were(3201.07 ±2236.63)×104 cell ?L-1 and(6.0041±7.2080)mg?L-1 and(7.6721±7.7090)mg?L-1 and(1.3979±1.3503)mg?L-1. The order of biomass as: outside of bio- manipulation pen > inside of bio- manipulation pen> demonstration project area. Biomass of phytoplankton exist extremely significant differences between inside of bio- manipulation pen and demonstration project area(P<0.01), outside of bio-manipulation pen and demonstration project area(P<0.01).There was no significant difference between inside and outside of bio- manipulation pen.4. The average value of Shannon-Wiener diversity of phytoplankton in inside and outside of bio- manipulation pen and demonstration project area were 2.41±0.41 and 2.46±0.40 and 2.22±0.49. There was no significant difference between three regions.The average value of Pielou evenness index of phytoplankton in inside and outside of bio- manipulation pen and demonstration project area were 0.66±0.10 and 0.66±0.11 and 0.71±0.13. There was no significant difference between three regions. The average value of Margalef species richness index of phytoplankton in inside and outside of bio- manipulation pen and demonstration project area were 2.26±0.39 and 2.40±0.48 and 1.46±0.40. There was significant difference between three regions(F=45.724,P<0.01).5. There were 11 dominant species of phytoplankton in inside of bio- manipulation pen, 9 dominant species of phytoplankton in outside of bio- manipulation pen and 5 dominant species of phytoplankton in demonstration project area. The main dominant species inside and outside of bio-manipulation pen throughout the year were: Microcystis incerta, in demonstration project area were Melosira granulate var. angustissima.6. RDA and Pearson showed that water temperature(WT)、C hl.a and CODMn, werethe main environmental variables affecting the community structure of phytoplankton.7. The order of standing crop as: outside of bio-manipulation pen > inside of bio- manipulation pen> demonstration project area. The mian dominant species in inside and outside of bio- manipulation pen were Cyanobacteria, and in demonstration project area there was no dominant species of Cyanobacteria. This showed that in demonstration project area the cyanobacteria blooms were under control, water quality has been improved. The water quality in inside of bio- manipulation pen was slightly better than the water quality in outside of bio- manipulation pen. This showed bio- manipulation pen has a certain effect.