| Longjing Lake is a typical small mountainous urban lake. In order to explore the features and the distribution of plankton and zoobenthos, 12 mensual samplings and monitorings were conducted from January to December in 2014. The main monitoring indexes were phytoplankton, zooplankton and zoobenthos. The results were analysed by diversity indexes, correlation analysis(CA), principal components analysis(PCA), hierarchical cluster analysis(HCA) and redundancy analysis(RDA) to find out the extents of environmental factors′effects and the regularities of spatial distribution. After that, a combined method was used for the ecological assessment of water quality and trophic level based on the results of the aforementioned analysis.① 137 taxa of phytoplankton were identified, which belonged to 66 genera of 8 phyla. The yearly average biomass was 7.30×107ind./L. The biomass of Cyanophyta ranked the first. And the number of species of Chlorophyta was the largest. According to the computing results of dominances, there were 3 annual dominant taxa which included Oscillatoria, Ankistrodesmus and Cryptomonas. And the annual dominant species were Oscillatoria subtillissima, Ankistrodesmus spirlis and Cryptomonas ovate. The amount of species was the largest in winter and the fewest in summer. On the contrary, the biomass was the largest in summer amd the fewest in winter. The yearly average values of Shannon-Wiener diversity index(H), Margalef richness index(D) and Pielou evenness index(J) were 2.29±0.99, 2.75±0.76 and 0.55±0.23 respectively. The results of HCA and PCA showed that 8 sampling sites were divided into 3 groups. On the basis of SD, p H and DO, RDA divided 8 sites into 3 groups. And according to the correlations between different taxa and environmental factors, the 66 genera were divided into 4 groups.② 62 species and genera of zooplankton were identified, among which there were Rotifera 27 genera, Protozoa 20 genera, Copepoda 9 species, Cladocerans 4 genera and Nematomorpha only 1 genus. The yearly average biomass was 1252.34 ind./L. Both of the biomass and the number of species of Rotifera ranked the first. According to the computing results of dominances, there were 6 annual dominant taxa which included Asplanchna, Polyarthra, Difflugia, Trichocerca, Keratella and Brachionus. And the annual dominant species were Asplanchna girodi, Polyarthra dolichoptera, Difflugia globulosa, Trichocerca pusilla and Brachionus angularis. The amount of species was the largest in spring and summer and the fewest in winter. The biomass was the largest in autumn and the fewest in winter. The yearly average values of H, D and J were 2.26±0.51, 2.60±0.58 and 0.79±0.06 respectively. The results of HCA and PCA indicated that 8 sampling sites were divided into 3 groups. On the basis of SD, p H, DO and water temperature, RDA divided 8 sites into 3 groups. And according to the correlations between different taxa and environmental factors, the 62 species and genera were divided into 4 groups.③ 26 genera of zoobenthos were identified, which belonged to 18 families of 3 phyla. The yearly average biomass was 11.57 ind./m2. Both of the biomass and the number of species of Arthropoda were far beyond the other two phyla. Palaemonidae was the only one annual dominant taxon whose dominance reached 0.79. And the annual dominant species was Macrobrachium nipponensis. The amount of species was the largest in spring and summer and the fewest in winter. The biomass was the largest in summer and the fewest in winter. The yearly average values of H, D and J were only 0.26±0.16, 0.25±0.12 and 0.19±0.13 respectively. The results of HCA and PCA showed that 8 sampling sites were divided into 3 groups. On the basis of EC, p H, DO, ORP and water temperature, RDA divided 8 sites into 3 groups. And according to the correlations between different taxa and environmental factors, the 18 families were divided into 3 groups.④ Based on the analysis of annual data and the combined method, the results indicated that the water quality of Longjing Lake was moderately polluted and the trophic level was eutrophication in general in 2014.In conclusion, the community structure and distribution characteristics of plankton and zoobenthos can reflect the water quality and trophic level of Longjing Lake comprehensively and objectivedly. And we also can find out the dynamic change of water and environmental effects that accumulated and added together for a long time by analysing monitoring results. These are meaningful for constucting and maintaining the healthy aquatic ecosystems. |
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