| Dongting Lake is one of the two largest fresh lakes in China. It can regulate flood storage and detention, degrade pollutants and regulate climate. Nowadays, the Dongting Lake has become polluted more and more seriously, and suffered enormously from eutrophication. Planktonic algae are considered as natural bioindicators because of their sensitive to the change of environment conditions and there exists a significant correlation between water environmental quality indicators.A sampled investigation was conducted on the species composition and population density of planktonic algae in East Dongting Lake in 2013~2014 to explore the temporal and spatial patterns of community structure and species diversity. The correlation between planktonic algae and environmental factors was discussed by Redundancy analysis(RDA). And it evaluates the water quality comprehensively by combining with biological and chemical indicators which provides a theoretical basis for water resource protecting and management in East Dongting Lake. The results show that :1. A total of 159 planktonic algae species(including varieties) were identified, belonging to 8 phyla and 65 genera in East Dongting Lake,The number of species and genera are higher the previous studies, especially for the diatom species.2. The mean density of the planktonic algae was 6.11×104 ind/L, and the average biomass was 0.20 mg/L, the average density and biomass were significant at 1% level between eight sampling points; the density and biomass of planktonic algae obtained in this survey are relatively lower than the previous studies.3. The dominant species mainly are Melosira varians, Scenedesmus carinatus, Euglena viridis, Cryptomonas erosa, etc., which showed a distinct seasonality.4. The average Shannon-Weiner diversity index was 4.11, ranged from 3.24 to 4.77, and the Margalef abundance index ranged from 3.50 to 7.32, with an average of 5.58. Both indices show a similar seasonality as March > November > June > September, indicating a higher species diversity in dry seasons than in wet seasons. The average Pieou evenness index of planktonic algae was 0.63, ranged from 0.40 to 0.74. The diversity index is lower at Baxianqiao and Bianshan, and highest at Jingjiangkou.5. The planktonic algae community can be roughly divided into 10 categories. The planktonic algal community structures are similar at sampling sites on the east side of the investigated area, all which are different from those on the west side of the Lake and the Xinqiang River. The dry seasons are also different from wet seasons in community structure.6. The sequencing of the correlations between the planktonic algae community structure and key water environmental factors was: DO>WT>CODMn>a-SAA> NH3-N>pH>Fluoride>Vol-P>COD>Cond>Hg, water environment factors analyzed by RDA explained 69.1% of accumulated variance of data to planktonic algae community structure. Monte Carlo significance test showed that planktonic algae community structure was most influenced by DO、WT、CODMn、a-SAA which were significant at 1% level, and less by pH and NH3-N. The six water environmental factors explained respectively 8.0%、7.5%、7.1%、7.0%、5.9%、5.5% of variance of data to planktonic algae communities structure.7. Based on criteria for evaluating trophic status, it can be concluded that East Dongting lake were both at low-grade polluted level during the year of 2013~2014. |
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