Abstract:

To clarify the pollution sources and the influence on algae bloom(cyanobacterial blooms)in Lake Taihu,the third largest fresh water lake of China,the spatiotemporal pattern of water environmental indicators of the lake,such as transparency,permanganate index,nitrogen and phosphorus concentrations,and chlorophyll concentration,was analyzed based on the monthly investigating data in 32 sample sites during 2005 to 2007.The spatial different among different areas of the lake was significant.The inflow mouths of several rivers in the northwest of the lake contented a lot of nutrients,which the permanganate index was several times higher than the east part of the lake.This reflected the strong influence of external pollution  on the lake eutrophication and northwest catchments were the main contributor of nutrients of Taihu.The water quality of the lake was also highly varied seasonally.Total nitrogen concentrations,for instance,were averagely doubled in winter and spring than those in summer and autumn,however,total phosphorus and chlorophyll  showed significantly high values during May to September.During summer,chlorophyll  concentration showed a significant positive relationship with total nitrogen,total phosphorus concentration and with permanganate index,which suggested that the nutrients and organic pollution during summer have promoting influence on cyanobacterial bloom.The research suggested that both the morphological characteristics(for example,large surface area combined with extreme shallowness,the distribution of inflow rivers)and the external input from northwest of the lake were the main reasons of the spatiotemporal eutrophic pattern of Lake Taihu.It also indicated that external pollution still was the main reason for the development of cyanobacterial blooms in Taihu.Strictly control and efficiently decrease the external pollution was the first step and the only choice for bloom control.And,to solve the cyanobacterial bloom of the lake,the external pollution from northwest of the lake must be controlled efficiently first.

Key words: Lake Taihu/cyanobacterial bloom/ eutrophication/ external source pollution