Experimental Simulation Study On The Density Forecast Of Microcystis Aeruginosa In Taihu Lake

Cyanobacteria in Taihu Lake were mainly composed of Microcystis aeruginosa.The emphasis of cyanobacteria bloom controlling in Taihu lied in prevention.And the prevention need the support of forecasting technology.In recent decades,domestic and overseas scholars had been working hard to study the algal forecasting technology.However,the expected effects had never been reached.The reason was the unclearness of the algal bloom mechanism.In the past 10 years,Guo Weihua and others at Chongqing University revealed the vernalization and its mechanism of Microcystis aeruginosa.The outbreak mechanism of Microcystis aeruginosa,namely rapid propagation mechanism,was solved along with it.Reproductive capacity of Microcystis aeruginosa was regulated by temperature.High temperature for growth could depress its rapid multiplication.And high temperature of dormancy may even make the multiplication ceased.However,both of the two effects could be relieved by low inducing temperature.The recovering degree of reproductive capacity largely depended on the intensity and time of low inducing temperature which Microcystis aeruginosa was exposed.Greater recovery of reproductive capacity meant a faster multiplication for Microcystis aeruginosa.It could be known from the rapid propagation mechanism of Microcystis aeruginosa that,for the outbreak of Microcystis aeruginosa in Taihu,low temperature in winter was the precondition,and the growth temperature and light were the necessary conditions.Therefore,this mechanism was the theoretical basis for algal density forecasting of Microcystis aeruginosa bloom in Taihu,and had also become the theoretical basis for this research.After the understanding of the vernalization and rapid propagation mechanism of Microcystis aeruginosa in Taihu,how to predict the density of algae in outbreak was a very important and key problem.This problem had been troubling the research team for a long time.Until recently,the algal density forecasting technology route was proposed by the research team according to the principle of vernalization in Microcystis aeruginosa.That was: at the beginning of spring,samples of Microcystis aeruginosa need be collected from the site and analysed growth rate for forecasting;when forecasting of temperature and light suitable for its bloom,samples of Microcystis aeruginosa need be collected from the site and measured in density;finally,forecasting density of Microcystis aeruginosa during its bloom.Although the proposed technical route was theoretically feasible,the actual guidance effect of prediction work need to be verified by experiments.The validation experiments were consisted of 4 low-temperature treatment processes,and 2 different illumination experiments were conducted after each treatment.There were totally 8 experimental groups in validation experiments.The main results and conclusions of this study were as follows.(1)Microcystis aeruginosa in Taihu Lake had the effect of vernalization after the low-temperature induction.The optimum induction temperature was 16~18 ?.(The growth temperature of Microcystis aeruginosa in Taihu was 21~39 ?,and the suitable temperature zone was 27~35 ?.The high temperature of dormancy was 40~43 ?,and the high temperature of death was more than 45 ?.)After low induction temperature,the demand for strong or weak light in growth would change in Microcystis aeruginosa in Taihu Lake.(2)Three criteria for algae density forecasting were proposed: the accuracy index I of the forecast results need to be more than 0.6,that was,the forecast results were within 60%~140% of the growth algae density(standard 1);the probability Q of I?0.6 need to be more than 60%(standard two);the continuous days of I?0.6 and Q?60% need to be more than 2 days(standard three).Three criteria were used to evaluate the effect of algae density forecasting.(3)Results of the evaluation: There were 5 experimental groups whose accuracy index of forecasting I was more than 0.6 in 6 days.Which represented that most of the forecasting results were within 60%~140% of the density measured,according with the evaluation standard one.As the forecasting algal density in the range of 60% to 140% of the growth,forecasting results of 8 experimental groups during 6 days had an occurrence rate(Q)more than 62.5%.Which tallied with evaluation standard two.The number of consecutive days of I ?0.6 and Q?60% was 6,more than 2.Which met with evaluation standard three.Therefore,it was feasible to forecast the density of Microcystis aeruginosa in Taihu with the technical route above during its bloom.(4)Technical route for density forecasting of Microcystis aeruginosa: at the beginning of spring,samples of Microcystis aeruginosa need be collected from the site and analysed growth rate for forecasting;when forecasting of temperature and light suitable for its bloom,samples of Microcystis aeruginosa need be collected from the site and measured in density;finally,forecasting density of Microcystis aeruginosa during its bloom.