Fingerprint Fluorescence Spectroscopy Analysis Of The Release Process Of Cyanobacteria's Extracellular Organic Matter During The Blooming Period

In the cyanobacterial blooms,cyanobacteria proliferate excessively and release a large amount of extracellular organic matter(EOM)into the water,which can easily cause serious water pollution and threaten drinking water supply security.In addition,the algae toxins and odorants contained in the EOM pose a serious threat to human health.It is an urgent task to continuously monitor the concentration of EOM released by algae in water bodies,especially for the algae toxins and odorants,which to provide early warning of possible drinking water safety accidents.However,due to the complex composition of EOM and large differences in components,the total amount of dissolved organic carbon(DOC)monitoring cannot indicate the content of specific harmful components.The concentration of algae toxins and odorants in the water is extremely low,and it is difficult to effectively perform continuous on-line monitoring with existing means.In this paper,three dimensional excitation-emission matrix(3 DEEM)fluorescence spetra and PARAFAC models were used to investigate the fluorescence characteristics of EOM released by Microcystis aeruginosa cultivated in the lab and actual water samples collected from Taihu Lake during the cyanobacterial blooms.The dynamic release of EOM components and their correlations were also studied.Meanwhile,the correlations between the components of the EOM and the concentration of the algae toxins were analyzed,and those components which were significantly related to the concentration of the algae toxins were screened out.And further Granger causality tests were used to screen out components that are significantly correlated with the algal toxins in time series.The conclusions are as follows:1.For lab-cultivated Microcystis aeruginosa,3 DEEM fluorescence spectra of dissolved extracellular organic matter(dEOM)in growth phase only show tryptophan-like peak T and marine humic-like peak M.In stationary phase,peak M disappeared gradually.And in the decay phase,the tryptophan-like peak S and the humic-like peaks A and C appeared besides the peak T..During the whole growth phases,there are S,T,A,and C four peaks in the bound extracellular organism(bEOM).For the actual water samples from Taihu Lake,there are four peaks in the 3DEEM fluorescence spectra of dEOM,namely peak S,T,A,and C.The tyrosine-like peak D appeared in bEMbesides the peak T,A,and C.2.Analysis of PARAFAC showed that the dEOM and bEOM of Microcystis aeruginosa cultured in laboratory can be divided into two components,namely tryptophane-like and humic-like,and the concentration of tryptophan-like is higher than humic-like.The dEOMin actual water samples from Taihu Lake can be divided into three components,component 1 is tryptophan-like,and component 2 includes both tyrosine-like and tryptophan-like,component 3 is humic-like.bEOM in actual water samples from Taihu Lake also can be divided into three components,which are tryptophane-like,tyrosine-like and humic-like.Protein-like which include tryptophane-like and tyrosine-like is main component for dEOM and bEOM.3.The concentrations of dEOM and bEOM from laboratory-cultured Microcystis aeruginosa are significantly correlated(P<0.05),and the concentration of each component in bEOM is significantly higher than that in dEOM.It is concluded that EOM may exists in the form of bEOM at first,then falls off from the cell membrane and changes to the form of dEOM.At the end of the stationary phase,cell lysis leads to structural instability of the cell membrane,and fatty acids in the membrane is converted to humus-like substances,the content of humic-like in the bEOM rapidly increases whith the concentration of algae does not change significantly,which can be used as a signal for early warning of water quality safety.4.The content of each component and DOC concentration of dEOMin Taihu Lake are higher than that of bEOM.Due to the influence of the input of exogenous organic substances,DOC and dEOM,bEOM do not show significant correlation with chlorophyll-a,but there is a significant correlation between DOC and dEOM,bEOM normalized by chlorophyll-a.The correlation between dEOM and DOC is better than that of bEOM,therefore dEOM can be used as an important parameter for evaluating DOC in water.5.Due to the influence of different growth phases of algae,there is no significant correlation between chlorophyll a and algae toxin in Taihu Lake,and there is no significant correlation between DOC and the concentration of dEOM and bEOM.But the dEOM,bEOM components and DOC concentration normalized by chlorophyll-a correlated well with algal toxins,and dEOM components significantly correlated with the algal toxin(P<0.05).Granger causality test results show that More fractions in bEOM were the Granger cause of algal toxins in time series compared to that in dEOM.Therefore,the bEOM content are more suitable for the prediction of the algae toxin content in the water.In conclusion,there is a dynamic relationship between the EOM component and the algae toxin in Taihu Lake.Moreover,bEOM components correlate with algal toxin on time-series,which can be used as important parameters to predict the concentration of algae toxin.Combined with three dimensional excitation-emission matrix,it can be used to retrieve and predict the concentration of algae toxin in real time,which is meaningful for early warning of drinking water safety.