To understand the spatial and temporal variation characteristics of blue algae in summer in Lake Dianshan,the phytoplankton in Lake Dianshan from June to September in 2009 was surveyed. It found 11 genera and 28 species blue algae in total. Microcystis,Oscillatoria and Chroococcus were the main composition communities of blue algae in Lake Dianshan in summer. In the survey period,the average density of blue algae in Lake Dianshan was 16.48×106 cells/L which changed during 1.01×106-59.76×106 cells/L. The characteristics were:September July August June. The mass propagation and aggregation of Microcystis in September caused that the water blooms phenomenon in the partial water areas was serious. In the space,the average density of blue algae in the west and southwest parts of Lake Dianshan was bigger than in the east and southeast. When the nutritive matter was sufficient,the temperature was the main factor which affected the generation and disappearance of blue algae water blooms. The wind direction was also an important factor which affected the distribution of blue algae.
To understand the relationship between the spatial-temporal variations of phytoplankton primary productivity and its environmental factors in Dianshan Lake, monthly survey was carried out from April, 2009 to March, 2010, with the method of white and black bottles. The result shows that seasonal variation of primary productivity (calculated according to carbon, following the same) is summer [0.95 g x (m3 x d)(-1)] > winter [0.83 g x (m3 x d)(-1)] > spring [0.77 g x (m3 x d)(-1)] > autumn [0.62 g x (m3 x d)(-1). From the flat distribution, primary productivity is higher in northern and southern parts than that in east and west, with no significant differences in each point (p > 0.05). From the vertical distribution, phytoplankton light availability is an important limiting factor. Primary production of 0. 3 m underwater is higher than that of 0.5 m. However, primary production of 0.3 m level in summer is lower because of light inhibition. Seasonal changes in primary productivity may be due to phytoplankton community structure and replacement of the dominant species. There are significantly positive correlation between Chlorophyll a (Chl-a) and phytoplankton density with primary productivity (p < 0.01), and Chl-a has better correlation with primary productivity. Phytoplankton biomass shows a positive reaction to its productivity and may preliminary provide a reference for the number of phytoplankton.
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