Studies On Community Structure Of Macrobenthos And Related Physical And Chemical Facrors In Dianshan Lake

Dianshan Lake located in junction of Jiangsu and Shanghai. It is the largest freshwater lake in Shanghai as well as the water resources protected field and main channel in Huangpujiang river. The water quality and hydrology has a vital role to have safe drinking water in Shanghai. In the past several years, the water quality of Dianshan Lake had been deteriorated, of which the index of water quality decreased fromâ…¡-grade level to V-grade level or inferior V-grade level. Therefore, experimental projects that control eutrophication and prevent algal blooms were built by integrating biological treatment technology and inner pollution control technology in typical water areas of Dianshan Lake since 2008. A series of experimental projects should be executed in order to find practical techniques of eutrophication controling.Macrobenthos is an important component of wetland ecosystems, it has great significance to understand the structure, function and evolution of wetland ecosystems. This paper reports that macrobenthos species composition, community structure characteristics, biomass and spatial distribution, relations between various types of macrobenthos and the main environmental ecological factors, as well as water quality conditions of the Dianshan Lake is evaluated. The paper also reveals the pollution condition of sediment and the distribution characteristics of pollutants of Dianshan Lake, and heavy metal environment risk is evaluated by the potential ecological risk index method, and further analyzes the relationship between the heavy metal pollution and macrobenthos distribution.In order to evaluate the achieved of ecological restoration projects of Dianshan Lake. In this paper, enclosure ecosystem had been established as the research object at south shore of Dianshan Lake for more comprehensive process to evaluate species composition, community structure characteristics, biomass and spatial distribution, relations between various types of macrobenthos and the main environmental ecological factors of macrobenthos during the ecological restoration. Hoping for eutrophication control, ecological restoration experimental project, environmental management and protection of Dianshan Lake of Shanghai provide scientific theory and basis. The main results are as follows:1. Community structure of macrobenthos and water quality assessment in Dianshan Lake The community structure and biodiversity of macrozoobenthos were investigated in Lake Dianshan of Shanghai from August 2008 to June 2010. We recorded 32 species from 15 families,9 orders,7 classes and 3 phyla among the 17 sampling stations of which 20 species were molluses,3 species were polychaetas,3 species were oligochaetes,3 species were acquatic insects and 3 species were others. The average density and biomass of macrozoobenthos were 85.6ind./m2 and 103.71 g/m2. There were 10 dominant species and they were Bellamya aeruginosa, Bellamya purificata, Corbicula fluminea, Limnoperna lacustris, Corophium sp, Limnodrilus hoffmeisteri, Tubifex tubifex, Tanypus chinensisi, Nephtys oligobranchia, Novaculina chinensis. Compared with the previous data, molluse species, the average density and biomass had been reduced and the dominant species had a greater changes. Water quality was assessed using both physical and chemical analyses, including Shannon-Winener index, Sinpson index, Margalef index, Pielou index. These analyses indicated that water quality of Lake Dianshan was mesotrophic. Cluster analysis and one-way analysis of similarity (ANOSIM) classified the 17 stations into five groups with significant differences. According to the pearson correlation analysis results, there was a highly significant positive correlation between SD, NH3-N and density of polychaeta. DO, NH3-N, TN significant correlated positively to density of oligochaete; FC highly significant correlated positively to density of molluse. Between each group also has a certain correlation.2. The distribution of heavy metals in surface sediment of Dianshan Lake and its correlations with macrobenthosIn the present study, the contents of seventeen heavy metals were determined using X-ray fluorescence spectrometry in Lake Dianshan sediment and their spatial distribution characters were analyzed. Hakanson's methodology was applied to determine the degree of contamination and the ecological risk of six heavy metals:Cd, As, Pb, Cu, Cr and Zn. The results showed that according to the contents, these heavy metals in the surface sediments followed the order as Al>Fe>K>Na>Ca>Mg>Ti>Mn> Zr>Zn>Sr>Rb>Cu>Cr>Pb>Ni>As; The potential ecological risk index showed that the heavy metals pollution risk was moderate in the Lake Dianshan sediments; According to the impacting extent of potential ecological risk, the pollutants could be ranged as:Cu>As>Pb>Ni>Cr>Zn. The community structure and biodiversity of macrobenthos were investigated and additionally the correlations among the heavy metals and Macrobenthos were analyzed. The results showed that except Cr there were highly significant positive correlations between the contents of the heavy metals; The contents of Cu, Zn and the potential ecological risk indexes of Cd, RI highly correlated positively to density of Oligochaete; Shannon-Wiener index and Margalef index had highly negative correlations with the contents of Pb and Ni.3. Effects of recovery and reestablishment of submerged macrophytes on macrobenthos in Dianshan LakeThe community structure and biodiversity of macrozoobenthos were investigated in ecological zone alongshore 318 Road of Lake Dianshan of Shanghai from August 2009 to June 2010. We recorded 25 species from 14 families,8 orders,7 classes and 3 phyla among the 6 sampling sites of which 23 species were in the enclosures and 15 species were in the adjacent sampling sites. The average density of macrozoobenthos were 73.54ind./m2,91.82ind./m2 and the average biomass of macrozoobenthos were 93.71g/m2,54.23g/m2 in the enclosures and the adjacent sampling sites. Water quality was assessed by using bio-diversity index. These analyses indicated that water quality of the enclosures was mesotrophic and water quality is better in enclosures than those in the adjacent sampling sites. Correlation analysis was employed to identify the relationship between community structure of macrozoobenthos and environmental factors of in the enclosures and the adjacent sampling sites. It was proved that total phosphorus(TP), Suspended solids(SS) were significant factors influencing community structure of macrozoobenthos. Community structure of macrozoobenthos had a significant change and biodiversity index of macrozoobenthos had increased significantly after the reestablishment of submerged macriphytes. It was found that there was a significant positive correlation between biomass of submerged macrophytes and biomass of macrozoobenthos.