Research on the meteorological and hydrological factors of cyanobacteria bloom in Lake Dianshan

The high total nitrogen and phosphorus concentration of Lake Dianshan was the key nutrient supply for cyanobacteria bloom and resulted in the eutrophication.The ranges were 3.47～4.53 mg/L and 0.18～0.24 mg/L during 2007-2009,respectively.The results of MODIS images analysis showed that cyanobacteria bloom in Lake Dianshan increased during 2007-2009,and the frequencies were 3 d,6 d and 10 d,respectively.The results also showed that the main algae aggregation areas after bloom were the centre,the northeast and the east of the lake.The average water level of Lake Dianshan was higher and the water exchanging period extended from June to September,as a result of backwater effect from Huangpu River and Taipu River.The comparison results between the daily meteorological factors variations from July to September and that on the cyanobacteria bloom dates showed that,in summer,high temperature(24.2～30.5 ℃) and long illumination hours(more than 5.9 h) were likely to accelerate the proliferation rate of cyanobacteria;low air pressure(less than 1 015 hPa),low air velocity(slower than 2.2 m/s) and little precipitation were apt to accelerate the floating up rate of cyanobacteria;heavy precipitation and high air velocity would inhibit cyanobacteria bloom.The meteorological and hydrolgocial factors would play a key role in a prediction and early-warning system of lake cyanobacteria bloom,and also be an important part of building a risk prevention system.