The Spatiotemporal Distribution Of Toxic Microcystis And The Detection Of Microcystin In Dianchi Lake

Dianchi Lake,the largest freshwater lake in yunnan-guizhou plateau,was known as the "plateau pearl".With the rapid development of economy,a large number of industrial and living wastewater poured in Dianchi Lake,which led to the very serious eutrophication and the frequent occurrence of algal blooms in recent years and have been influence on the surrounding environment and residents.Microcystin was secondary metabolites produced by toxic cyanobacteria,which posed a serious health risk to animal and humans.The aim of this study was to investigate the type and concentration of microcystin,the spatial and temporal distribution in the abundance of toxic and total Microcystis genotypes in Dianchi Lake.The water samples of Haigeng and Caohai in Dianchi Lake were taken once a month for about a year and eleven sites distributed widely across the Dianchi Lake were also sampling in summer.Firstly,the temperature,pH,transparency,potassium permanganate index,total nitrogen,total phosphorus and chlorophyll-a of water samples were tested.The results showed that the water quality of Dianchi Lake was in the light eutropher which favorable for the growth of cyanobacteria.The annual average chlorophyll-a concentration of Haigeng and Caohai were 0.348 mg/L and 0.271 mg/L,respectively.On the spatial and temporal distribution,chlorophyll-a concentrations in summer were higher than in winter and were higher in the north-eastern part of Dianchi Lake than the other waters.The concentration of chlorophyll-a was very significantly positive correlated with the water temperature,pH,permanganate index and the content of total phosphorus,which was significant positive correlated with total nitrogen and was very significantly negative correlated with transparency.Secondly,the results showed that the microcystin-producing cyanobacteria genus was Microcystis in Dianchi Lake by PCR detection.On the basis of quantification by real-time PCR analysis,the annual average copy number of mcyE gene in Haigeng and Caohai were 7.73×106 copies/mL and 2.42×107 copies/mL,respectively;And these of PC-IGS gene were 2.64×107 copies/mL and 6.06×107 copies/mL,respectively.Caohai was higher than Haigeng on mcyE and PC-IGS gene copy number.Within the scope of the whole lake,the maximum and smallest mcyE gene copy number were Haigeng and Baiyukou,respectively.And the maximum and smallest PC-IGS gene copy number were Jianqiao and Baiyukou,respectively.The mcyE and PC-IGS gene copy number could reflect toxic Microcystis and total Microcystis population.The ratio between toxic Microcystis and total Microcystis population was 12.22%?72.63%.On the spatial and temporal distribution,toxic Microcystis and total Microcystis in summer were higher than in winter,in north-eastern part of Dianchi Lake higher than others.Correlation analysis showed a strong positive relationship between toxic Microcystis,total Microcystis,water temperature,pH,permanganate index,the total phosphorus and chlorophyll-a concentration,but strong negatively with transparency.Finally,microcystins in water samples were detected by HPLC.The results showed that main microcystin types were MC-RR and MC-YR.MC-LR was detected at individual sampling point.Microcystins were able to detect with different levels all the half year.The annual average microcystins concentration of Haigeng and Caohai were 0.381 mg/L and 0.334 mg/L,respectively.On the spatial and temporal distribution,microcystins concentration in summer were higher than that in winter,in the bottom were higher than that in the surface,in Haigeng were higher than Caohai.Only microcystin concentration in Guanyinshanxi sampling point was greater than 1?g/L.Microcystin concentrations were lower than 1 ?g/L under WHO regulations standard.However,drinking water containing MC was still potentially harmful to humans and animals.Correlation analysis also showed a strong positive relationship between microcystins concentration,water temperature,pH,permanganate index,total phosphorus,chlorophyll-a,the mcyE and PC-IGS gene copy number,but microcystins concentration were strong negatively with transparency.The research investigated the spatial and temporal distribution of chlorophyll-a,toxic Microcystis,total Microcystis and microcystins in Dianchi Lake,types and concentration of microcystin.The correlation of chlorophyll-a,toxic Microcystis,Microcystis group,microcystin and environmental indicators were analyzed.The method of molecular biology about microcystin detection was established.It provided a good theoretical basis to monitor and manage microcystins.