| Selected Dadian Lake as research object,we had one investigation to physiochemical index and community structure of Metazoan zooplankton (including Rotifer、Cladocerans and Copepods) before and after in-situ dredging and ecological restoration composed of species composition、dominant species、density and biomass、diversity index and their correlation characteristics, in order to understand the trend of change of Metazoan zooplankton community structure after dredging and ecological restoration measures and accumulate biological data for restoration effect on lake eutrophication.The survey showed five parts below:1 Nutrient content of dadian lake decreased significantly,and water quality improved from standardⅤ~ inferiorⅤtoⅢ~Ⅳ(national surface water environmental quality GB3838-2002 standardin)after dredging restoration,up to the expected standard;Chlorophyll-a content decreased significantly,too.The state of nutrition was mesotrophic compared to eutrophication before dredging ,and algal bloom was in control. 2 One factor analysis of variance showed that there were significant differences (p <0.05) about the number of rotifer species between three sampling stages which were the initial ecological restoration、year 2008 and year 2009; The similarity coefficients of rotifer species between the three stages were 12.7%, 33.3%, 33.3%;Polyarthra trigla was always the first dominant species during all the sampling stages.The average density of rotifers during entire sampling time including Predredging stage、early restoration、year 2008 and year 2009 was 1990 ind./L, the average density at every stage was 3573 ind./L, 2929 ind./L,955 ind./L and 505ind./L;There was significant difference about rotifer density between year 2008 and year 2009 and that at early ecological restoration(p <0.05),and decreased by 69% and 81%;There was no significant difference between 2008 and 2009(p>0.05).The average biomass of rotifers during the whole sampling time including early restoration,2008 and 2009 was 1.64㎎/L, biomass at every stage was 1.27㎎/L,2.58㎎/L,1.05㎎/L,There was no significant difference about rotifer biomass between each stage (p <0.05).Species diversity and species richness index decreased significantly during the process of ecological restoration;There were significant and highly significant difference about species diversity index H’ and species richness index at different stages corresponding to seasonal differences(F=4.027,P <0.05;F = 9.979,P <0.01).3 16 species Cladocera were found in 2009,belonging to 4 families and 8 genera,6 species belong to 5 families and 5 genera during early ecological restoration;The dominant species in 2009 were Bosmina coregoni、Bosminopsis deitersi、Diaphanosoma leuchtenbergianum and Moina brachiata,and sum density of dominant species was 86.9 pencent of total density of all rotifers.During the early restoration time dominant species of Cladocera were Bosmina longirostris(Y=0.231)and Bosmina longirostris(Y = 0.054),and sum density of dominant species was 91.0 pencent of total density of all totifers at early restoration;Density and biomass of Cladocera during early restoration were 0.13 ind/L and 0.03㎎/L,10.2ind/L and 0.41㎎/L in 2009;Cladocera of lake in the process of ecological restoration were all of summer species.4 26 species planktonic copepods were found including Calanoida and Cyclopoida in 2009 belonging to 4 families and 11 genera.The dominant species were nauplius、Copepod larvae、thermocyclops taihokuensis,thermocyclops brevifurcatus;nauplius was the only dominant specie during early restoration and the dominance was 0.883;Breeding growing season of planktonic copepods dominant species in 2009 were all in summer;The total average density of the planktonic copepods during ecological restoration was 3 ind/L,and the peak month apeared in june and july 2009, the times peak appeared in the July 2006;There was no copepods found in March 2007;The average biomass of the total copepod during ecological restoration was 3.43㎎/L,peak apeared in July 2006,two sub-peaks September and Novenber 2006.Compared cladocera and copepod diversity index curves during the process of ecological restoration,the two curves presented complementary toppling "Mountain" appearance.5 Correlation analysis to metazoan zooplankton density、biomass and the water quality parameters.the results were as follows:the density of rotifer had a significant positive correlation with diversity index and nitrate nitrogen,had an extremely significant positive correlation with chlorophyll a,species diversity index;rotifer biomass had a significant positive correlation with chlorophyll a,had an extremely significant positive correlation with total phosphorus;density of Cladocera had an extremely significant positive correlation with nitrite nitrogen,and also had a significant positive correlation with dissoluble phosphorus; Cladocera density had an extremely negative correlation with permanganate index;Cladocera biomass had an extremely significant positive correlation with nitrite nitrogen,and also had a significant positive correlation with total phosphorus;Cladocera biomass had negative correlation with permanganate index;copepod density had an extremely significant positive correlation with dissoluble phosphorus, copepod density had a significant positive correlation with nitrogen and permanganate index;copepod biomass had an extremely significant positive correlation with dissoluble phosphorus,copepod biomass had a significant positive correlation with permanganate index.The conclusion were as follows,through comprehensive discussion about changes of water quality and the metazoan zooplankton before and after ecological restoration:1 The eutrophication state was better and water quality improved after bait-casting dredging and ecological restoration,which meaned that it was effective obviously at short notice about the effect of dredging and ecological restoration measures,but the long-term effect was to be determined.2 The lake water was still of eutrophication status after dredging repair,and dominant species of rotifers and cladoceras were still eutrophicative.3 There has been obvious succession phenomenon about composition of species rotifers after ecological restoration.4 Reproductive growth stage of dominant species of cladoceras were all in May to September during the process of ecological restoration,and were all summer species. Contractible ecological amplitude might be one characteristic of lakes after ecological restoration, compared to natural ones,and the ecological amplitude of cladoceras would recovery gradually along with the ecosystem stabilizing gradually.5 The proportion of rotifer、species、density, biomass decreased,and the proportion of Cladocera and Copepods increased;Small species (rotifers) reduced,large ones (Cladocera,copepods) increased,biodiversity increased,and the cyanobacterial blooms has been in control,which was similar to typical West Lake in Guangzhou;The survey also showed that it was effective through dredging and bioremediation against eutrophication and the adjustment of the aquatic community structure. |
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