Analysis Of The Relationships Between Occurrence Of Cyanobacteria Bloom And Meteorological Factors For Building Forecasting Model Of Cyanobacteria Bloom In Dianchi Lake

Previous studies have shown that cyanobacteria bloom mainly is caused by excessive reproduction and aggregation in the form of some nutrients(such as TN,TP,pH),climate,and hydrological conditions.However,under the current stable condition of water quality,the anniversary cyanobacteria bloom in Dianchi Lake seems that the main driver could be the meteorological factors.In order to further address the regularity between meteorological factors and occurrence of cyanobacteria bloom in Dianchi Lake,the relationships between cyanobacteria bloom and meteorological factors which were obtained from four stations observed at 09 to 12 AM every day ware analyzed.Then,the main sites and factors were identified by the binary logistic regression model and the remote sensing data and ground meteorological data from year 2010 to 2011.Afterward,a forecasting model of the occurrence of cyanobacteria bloom was built.This model can be used to precisely predict and forecast the occurrence of cyanobacteria bloom,and to reduce the impact of the cyanobacteria bloom,which had significance ecological and environmental consequences.Based on the above analysis,the results indicate that:(1)The monthly frequency of cyanobacteria bloom is significantly correlated with monthly average temperature,minimum temperature,cumulative sunshine of hours,cumulative rainfall and average wind speed.However,it has no significantly relations with maximum temperature and atmospheric pressure.Among the meteorological factors,monthly wind speed had the highest negative correlation coefficient(-0.783),which indicates that the frequency of cyanobacteria bloom was closely related to monthly wind speed at Dianchi Lake.(2)The most important daily influencing meteorological factor is wind speed.The stepwise regression accuracy by used comprehensive meteorological factors was 94.3%,and factors entered the model ware not consistent at the same site and time.The improved accuracy rate of the model indicated that the daily occurrence of cyanobacteria bloom was related to the comprehensive function of meteorological factors at different sites and times.(3)The accuracy of the prediction models of single factor and comprehensive meteorological factors is higher than 75%.The integrated meteorological factors and the average wind speed model also had higher prediction accuracy.Based on the prediction of the single factor model of the occurrence of cyanobacteria bloom,the critical value of the minimum temperature is 16.4℃ by Kunming Station at 09AM,average temperature is 18.5℃ by Chenggong station at 09AM,average wind speed is 2.2m/s by 4 sites at 11AM,wind direction angle was 66 degrees by 4 sites at 11AM.(4)Wind field was simulated by WRF(Weather Research and Forecasting)model.The result shows that near surface mainly had two types of wind field,they are divergence and weak easterly wind field,when the cyanobacteria bloom occurred(or before)at Dianchi Lake.Divergent wind field structure was a local vertical circulation,which updraft over the shores of the lake and downdrafts above the water body.The descending branch of the circulation formed divergent wind over the lake,leading to smaller wind speed near the divergence center,which was very conducive to the accumulation and occurrence of cyanobacteria blooms.The structure of weak easterly wind field was a weak partial east wind over Dianchi Lake.When the east wind reached the west of Dianchi Lake,it was blocked by the Western Hills.On the one hand,the climbed phenomenon of updrafts increased the upward movement,on the other hand,the horizontal wind speed was reduced,which was conducive to the occurrence of cyanobacteria bloom.