Distribution Characteristics Of Microcystins In Water And Sediment Of Meiliang Bay,Lake Taihu

Cyanobacteria blooms in natural waters are increasingly frequent,and the presence of MCs can be detected in 50%to 75%of cyanobacteria blooms,posing a great threat to the safety of aquatic ecosystem and human health.So,in this paper,Meiliang Bay,a serious cyanobacteria bloom area in Lake Taihu was taken as the research area,carrying out a great deal of field investigation and research.From November 2017 to August 2018,inside and outside MCs of water,as well as MCs of sediment were analyzed,combining time and space distribution characteristics.the vertical distribution characteristics of MCs in surface water,overlying water,interstitial water and surface sediment ranged from 1 to 10 cm were the key reseaches during the breakout of cyanobacteria blooms?May 2018 to November 2018?.The composition ratio and spatial and temporal variation characteristics of the three main MC isomers in the water inside and outside the cell,as well as in the sediments were analyzed and discussed in detail,revealing the seasonal succession rule and spatial distribution pattern characteristics of MCs in algal lakes,and evaluating the role of non-biological environmental factors in the spatial and temporal distribution of MCs.The main conclusions are as follows:1?During the investigation,the total intracellular concentration of MCs in Meiliang Bay ranged from 8.60 ng/L to 21237.60 ng/L.The concentration of MC-LR ranged from 2 ng/L to 15839.2 ng/L,and all can be detected in water Phytoplankton bodies.The concentration ranges of MC-RR and MC-YR were 2³013.65 ng/L and0²422.8 ng/L respectively,and the detection rate were 100%and 83.33%respectively.The total intracellular MCs concentration in autumn,spring and summer was significantly higher than that in winter?p<0.05?,but there was no significant difference in the total intracellular MCs concentration between spring,summer and autumn.The total concentration range of extracellular MCs in water was 6.60⁶57.56ng/L,and the concentration range of MC-LR was 6.60⁴55.81 ng/L,which can be detected in water body during four seasons.The concentration range of MC-RR was0¹23.56 ng/L,and the detection rate was 79.17%.The concentration range of MC-YR was 0⁷8.19 ng/L,and only 1#sample point was undetected in Augest during summer.The total extracellular MCs concentration in autumn was significantly higher than that in winter and summer?p<0.05?,while there was no significant difference in the total extracellular MCs concentration between winter,spring and summer.For intracellular and extracellular MCs,MC-LR is a major isomer,average relative abundance were 78.46%and 76.58%,respectively,both difference is not big,in addition,for intracellular MCs,the MC-LR relative abundance was higher in May?84.67%?than that in February?71.33%?slightly.For extracellular MCs,the relative abundance of the MC-LR changed little over time.The Person correlation analysis results showed that intracellular MCs,MC-LR,MC-RR were positively correlated with TN,TP,COD_Mn,and Chl-a?p<0.01?,respectively,and MC-YR was positively correlated with TP,COD_Mn,and Chl-a?p<0.01?,and positively correlated with TN?p<0.05?.Extracellular MCs,MC-LR,MC-RR,MC-YR were positively correlated with TP,COD_Mn,and Chl-a?p<0.01?,respectively,and MCs,MC-RR,MC-YR were positively correlated with TN?p<0.05?,and MC-LR was positively correlated with TN?p<0.01?.2?During the investigation,the total content of MCs in the surface sediments of Meiliang Bay in Lake Taihu ranged from 2.20 ng/g to 1111.30 ng/g,and the content of MC-LR ranged from 1.70 ng/g to 913.23 ng/g,which could be detected in the surface sediments.The content range of MC-RR was 0¹7.43 ng/g,with a low detection rate of 83.33%.The content range of MC-YR was 0.5¹80.65 ng/g,and the detection rate was 100%.The total MCs content of surface sediments in autumn and winter were significantly higher than those in spring and summer.There was no significant difference in total MCs content between autumn and winter,as well as spring and summer.For MCs in sediments,MC-LR was the main isomer type in surface sediments,accounting for 76.58%on average,followed by MC-YR accounting for19.75%on average,and MC-RR accounting for only 3.67%on average.In the surface sediments,MCs,MC-LR,MC-RR and MC-YR were positively correlated with EMCs,ERR and EYR?p<0.01?,respectively,and MCs,MC-LR,MC-YR were positively correlated with ELR?p<0.01?,MC-RR was positively correlated with ELR?p<0.05?.MCs,MC-LR,MC-RR,MC-YR were positively correlated with IMCs and ILR?p<0.05?,respectively,and were positively correlated with IRR?p<0.01?.There was no correlation between MCs,MC-LR,MC-YR and IYR,while MC-RR was positively correlated with IYR?p<0.05?.In addition,MCs,MC-LR,MC-YR were positively correlated with H₂O-P?p<0.05?,and MC-RR,MC-YR were positively correlated with albite?p<0.05?.3?For the extracellular MCs concentration,in the early stage of cyanobacteria outbreak?May 2018?,the concentrations of MC-LR,MC-RR and MC-YR in interstitial water were significantly higher than those in surface water and overlying water?p<0.05?,and the concentrations of MC-LR,MC-RR and MC-YR in the surface water at each point were slightly higher than those in the corresponding point.In the middle stage of cyanobacteria outbreak?August 2018?,the concentrations of MC-LR,MC-RR and MC-YR in the overlying water were significantly higher than those in the surface water and overlying water?p<0.05?,and there was no significant difference between the concentrations of MC-LR,MC-RR and MC-YR in the surface water and the interstitial water.In the later stage of cyanobacteria outbreak?November 2018?,the concentrations of MC-LR,MC-RR and MC-YR in overlying water were significantly higher than those in surface water and interstitial water?p<0.05?,and there was no significant difference between the concentrations of MC-LR,MC-RR and MC-YR in surface water and interstitial water.For intracellular MCs concentration,during the cyanobacteria outbreak?May 2018^November 2018?,the concentrations of MC-LR,MC-RR and MC-YR in surface water were significantly higher than those in the overlying water?p<0.05?.In the early stage of cyanobacteria outbreak?May 2018?,the content range of MC-LR in surface sediments of 1¹0 cm was 0.60²6.95 ng/g,the content range of MC-RR was 0⁰.90 ng/g,and the content range of MC-YR was 0⁸.10 ng/g.The detection rates of MC-LR,MC-RR,and MC-YR were 100%,70%,and 91.67%,respectively.In the middle stage of cyanobacteria outbreak?August 2018?,the content range of MC-LR in surface sediments of 1¹0 cm was 0.54⁸8.50 ng/g,the content range of MC-RR was 0¹.60ng/g,and the content range of MC-YR was 0.45²5.90 ng/g.The detection rates of MC-LR,MC-RR and MC-YR were 100%,81.67%and 100%,respectively.In the later stage of the cyanobacteria outbreak?November 2018?,the content range of MC-LR in surface sediments of 1¹0 cm was 0.45⁸11.50 ng/g,the content range of MC-RR was 0.47⁶.79 ng/g,and the content range of MC-YR was 0.45¹61.47 ng/g.The detection rates of MC-LR,MC-RR and MC-YR were all 100%.For MC-LR and MC-YR,the contents of MC-LR and MC-YR in the surface sediments from 1 to 10cm presented a declining trend as a whole with the increase of sediment depth,and the nonlinear fitting curve?y?28?a?x^b?showed that the declining trend could be well fitted,but the MC-RR content did not change much with the increase of sediment depth.In addition,the concentrations of MC-LR,MC-RR,and MC-YR in the overlying sediment water without external sources and in the dark decreased with time.Linear fitting curve?y?28?a?10?b?x?can fit it well.The R² of the curves after MC-LR,MC-RR,and MC-YR fitting reached 0.856,0.927,and 0.876,respectively.