| Qingcaosha Reservoir given more attention because of its important function value has the best water quality in Shanghai, in the west north of Changxing Island. Planktonic algae plays a key role in the variation of water quality and ecosystem succession. In this survey between January 2014 and December 2015, 11 monitoring sites of Qingcaosha Reservoir was carried out monthly to monitor the planktonic algae and water quality indexes, summarizing planktonic algae of species composition, biomass distribution, the succession of the dominant species, community structure characteristics, combined with the diversity index, analyzed community succession and distribution, and combined with the data of water quality indicators, to investigate the response of phytoplankton and various environmental factors, so as to objectively reflect the present situation of the reservoir ecosystem. The main results are as follows: 1. Species composition of planktonic algaeDuring the period of investigation, A total of identified were 257 species and varieties of planktonic algae in Qingcaosha Reservoir, belonging to 86 genera and 7 phyla. Among them, 39 genera and 121 species of Chlorophyta, 15 genera and 35 species of Cyanophyta, 28 genera and 77 species of Bacillariophyta, 7 genera and 17 species of Euglenophyta. Pyrrophyta, Chrysophyta and Xanthophyta were less, respectively 3, 1, 3 species. Chlorophyta algae were the most, accounting for the total number of species 47.08%; Bacillariophyta and Cyanophyta, respectively, were accounted for the total number of species of algae 29.96% and 13.62%. During two years, the species number of algae showed rising trend, in spring and summer the most abundant species. In autumn and winter were relatively less, especially in four seasons. There were at least in winter which the temperature were the lowest,. Besides, Chlorophyta algae for to every season occupied absolute advantage. 2. Temporal and spatial variation of standing crop of planktonic algaeThe average annual density of planktonic algae were(499.43±322.10)×104cell/L and(1451.28±648.61)×104cell/L, showing rising trend. In two years, the annual variation of planktonic algae density showed higher in spring and summer, lower in autumn and winterthe generally. But algae density in 2014 had the significantly differences than 2015. In 2014~2015, the average annual biomass of planktonic algae in the reservoir was(0.8951± 0.6030) mg/L and(4.6837±5.1175) mg/L, which showed rising trend. The variation of biomass also showed that lager in autumn and winter than in spring and summer generally in two years. Algal biomass in 2014 had the significantly differences than 2015. In addition, the algae were less affected by the hydrodynamic conditions in the surface waters so that the existing differences between the two sites were not significantly different. 3. Temporal and spatial variation of diversity index of planktonic algaeThe average value of H’, D and J of planktonic algae were(1.57±0.57),(0.50±0.18) and(1.49±0.42), respectively. Seasonal variation of the Shannon-Wiener diversity index, Pielou uniformity index and Margalef richness index was consistent, showed the seasonal trend was lager in summer and autumn and lower in winter and spring. The three indexes of horizontal distribution were not significantly different between every site in 2014, but H’, J values showed a very significant difference, D value showed significant differences in 2015. H’, J values of each season in 2015 were relatively lower than 2014, but the D value of each season was relatively higher than 2014. 4. Composition and seasonal variation of dominant speciesThere were 32 dominant species in the community structure of planktonic algae, which belonged to 21 genera and 4 phyla. Dominant species group composition was similar in two years, the top four dominance of algae: Cyclotella sp., Aphanothece stagnina, Tribonema sp., Merismopedia minima, Microcystis incerta, Pseudanabaena sp., Cyclotella sp., Ankistrodesmus falcatus var. mirabilis and Klebsormidium scopulinum were the common dominant species. Comparing with the data of 2014, the dominant species were substantially reduced in 2015, and the seasonal variation was less obvious than in 2014. As a whole, the dominant species were more in summer and autumn than in winter and spring. The majority of dominant species groups was Cyanophyta and Chlorophyta. Dominant species groups were showed the characteristics of more Cyanophyta in summer, autumn and more Chlorophyta in spring, summer. Algae of Bacillariophyta and Xanthophyta became dominant species more likely in spring and summer. 5. Relationship between community structure of planktonic algae and environmental factorsRedundancy Analysis showed that planktonic algae density was positively correlated with water temperature, conductivity and negatively correlated with p H, TN in 2014. Planktonic algae density positively correlated with TP, TN, CODMn and negatively correlated with transparency, dissolved oxygen in 2015. Pearson correlation analysis showed that planktonic algae density and biomass were significant or extremely significant positive correlation with water temperature, p H, TP, CODMn, and were significant and extremely significant negative correlation with TN, dissolved oxygen in 2014. Planktonic algae density and biomass were significant and very significant negative correlation with water temperature, and was significant or extremely significant positive correlation with p H, TP, TN, CODMn in 2015. From two kinds of statistical analysis, it was concluded that the phytoplankton community structure was mainly affected by water temperature, nutrient salt, CODMn, dissolved oxygen, transparency. Other factors affected the number and distribution of algae to a certain extent. |
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