| Macrozoobenthos is the important part of the aquatic ecosystem, and plays an irreplaceable role in the material circulation, energy flowing, biological production and information transfer. It reflects the healthy status of the entire aquatic ecosystem. There was research systematically the species composition, spatial distribution, seasonal change and biodiversity of macrozoobenthos in Lake Gehu, and analysed the relationship between community structure of macrozoobenthos and environmental factors in Lake Gehu. Assess the pollution of Lake Gehu. To provides a scientific basis for ecological restoration and comprehensive management of Gehu Lake. The main results are as follows:1. A survey on macrozoobenthos was conducted seasonally to reveal the community characteristics of macrozoobenthos and their relationship with aquatic environmental factors at 20 sampling sites in the Lake Gehu from 2013 to 2014. A total of 25 macrozoobenthos species including 3 species (12% of total) of Mollusca,12 species (48%) of Chironomidae,4 species (16%) of Oligochaeta,4 species (16%) of Crustacean were identified. The dominant species were Limnodrilus hoffmeisteri, Branchiuras owerbyi, Tanypus chinensis, and Propsilocerus taihuensis. Density and biomass of Chironomid larvae and Oligochata had significant spatial and seasonal changes. The denity of Limnodrilus hoffmeisteri at the south was significantly higher than the north (P<0.05), and the denity of Tanypus chinensis at the south was significantly than the centre (P<0.05). The denity and biomass of Oligochata in the winter was significantly than the summer, and the biomass of Oligochata in the winter was significantly than the autumn (P<0.05). The biodiversity index of macrozoobenthos was very small. The values of Shannon-Wiener diversity index, Margalef species richness index, Pielou index, FBI and BPI suggested that the Lake Gehu was of moderate to serious pollution.2. A survey on 14 aquatic physicochemical parameters were monitored monthly to reveal the community characteristics of macrozoobenthos and their relationship with aquatic environmental factors at 20 sampling sites in the Lake Gehu from July 2013 to December 2014. The 14 aquatic physicochemical parameters were analysed by PCA. The spatial distribution and seasonal variation of main aquatic factors were analyzed. The water quality of the Lake was assessed based on the comprehensive nutrition state index. The main influence aquatic factors on the community structure of macrozoobenthos in Lake Gehu was TN, NH4+ -N, NO3- -N, T, TP, PS and DO. And the primary aquatic physicochemical parameters had significant spatial and seasonal changes. The concentration of TN and NO3--N at the north was significantly higher than the centre (P<0.05), and the centre was significantly higher than the south (P<0.05). The concentration of TP at the centre was significantly higher than the south (P<0.05). The concentration of DO at the south was significantly higher than the centre (P<0.05), and the centre was significantly higher than the north (P<0.05). The concentration of NO3- -N in the spring was significantly higher than the autumn (P<0.05). The concentration of TN in the winter was significantly higher than the autumn (P<0.05). The concentration of NH4+-N in the winter was significantly higher than the summer and autumn (P<0.05). And the concentration of DO in the winter was significantly higher than the summer (P<0.05). The results showed that Lake Gehu is in the eutrophic state according to comprehensive nutrition state index.3. This study investigated the horizontal distribution characteristics of nutrients and heavy metals (Zn, As, Cr, Cu, Ni, Pb, Cd and Hg) in January,2014, and assessed the potential ecological risk of Lake Gehu. It was found that the average contents of TN and TP were 2207.94 and 708.62 mg·kg-1, respectively. TN and TP contents of the sediments at the centre were significantly higher than the north (P<0.05), while TN content at the south was also significantly higher than the north of Lake Gehu (P<0.05). The average contents of Zn, As, Cr, Cu, Ni, Pb, Cd, Hg were 766.59,350.66,307.98, 59.54,122.67,168.97,2.34,0.41 mgkg-1, respectively. The content of Cu at the centre was significantly higher than the north (P<0.05), and Zn content at the centre was significantly greater than the south of Lake Gehu (P<0.05), however the difference of other heavy metals content at these three areas were not significant. Furthermore, the obvious correlation between elements and granularity was only found in the aspect of TP, Cu and Hg. The comprehensive pollution index (PI) indicated that the Lake Gehu was heavily polluted, especially the centre and south areas. The potential ecological risk index (RI)showed that Cd, As and Hg had caused serious pollution in Lake Gehu while the other heavy metals only induced slightly or medium pollution. According to the contribution of Cd, As and Hg to RI, it was concluded that the sediments in Lake Gehu was at a serious potential ecological risk.4. The relationship between macrozoobenthos and environmental factors at 20 sites on the Lake Gehu was studied by correlation analysis. The results showd that the the density and biomass of Oligochata there were significant negative correlation between the concentration of TN znd NO3--N. The density of Chironomid larvae was highly significant positive correlation with the water temperature, and it was highly significant negative correlation with the content of TN, NO3--N and Zn. The biomass of Chironomid larvae was significant positive correlation with the water temperature, and it was highly significant negative correlation with the concentration of TN and NO3--N, and it was significant negative correlation with the content of TP and Zn. The taxa of Chironomid larvae were highly significant positive correlation with the water temperature, and it was significant negative with the content of TN and Zn, and it was highly significant negative correlation with the concentration of NO3--N. The density, biomass and taxa of Crustacean were significant positive correlation with the content of Cr. The content of Cd was significant negative correlation with the Shannon-Wiener diversity index. Overall analysis indicated that TN and NO3--N in the water and Zn and Cd in the surface sediment played a key role in the community structure characteristics of the macrozoobenthos in the Lake Gehu. The environmental variables could better explainthe changes of main macrobenthic species. |
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