Influence Of Disturbance On The Vertical Distribution Of Microcystis And Its Mechanism

With the discharge of industrial and agricultural wastewater containing a large amount of nitrogen and phosphorus,the eutrophication of water bodies is becoming increasingly serious.As a secondary disaster of water eutrophication,water blooms not only damages the structure and function of water ecosystem,but also poses a threat to human safety and health.The blooms in most Chinese eutrophic water bodies are Microcystis blooms,which is a type of water bloom with high health risks.Through the bibliometric analysis of literature related to Microcystis bloom,it can be found that the current studies related to the Microcystis bloom mainly focus on the proliferation of algal cells,the relationship between bacteria and algae and the harm caused by the production of toxins.The vertical distribution and vertical migration of algal cells in the water column are of little concern.To study the effect of disturbance on the vertical distribution of Microcystis and its mechanism will help us to further understand the mechanism of water bloom outbreaks,so as to better prevent and treat water blooms.In this study,two different floating microcystis species,Microcystis FACHB-1028 and Microcystis FACHB-1757,were selected.We used ventilation to provide perturbation.We set up four groups of experiments,which are non-ventilation,the ventilation rate is 100 mL·min-1,300 mL·min-1and 600 mL·min-1 respectively.Our purpose is to investigate the effect of ventilation disturbance on the vertical distribution of different floating microcystis species and its influencing mechanism.The main conclusions are as follows:(1)For non-floating Microcystis FACHB-1028,ventilation disturbance activated the vertical migration of algal cell and its vertical distribution pattern changed,but it did not change regularly with the increase of ventilation disturbance rate.For floating Microcystis FACHB-1757,in the control group,algal cell mainly floated on the surface layer of the water.Ventilation disturbance disrupted the floating pattern of the surface and promoted the vertical distribution of Microcystis to be uniform.With the increase of ventilation rate,the layer with the highest content of Microcystis in the water column migrated from the upper layer to the lower layer.(2)For the non-floating Microcystis FACHB-1028,ventilation significantly increased the value of ?(P<0.05),but the change in ventilation rate had no significant effect on the the algal cells' ? value.Ventilation also significantly increased the Fv/Fm value of algal cells(P<0.05),and in the absence of light,the Fv/Fm of algal cells showed an increasing trend with the increase of ventilation rate.For floating Microcystis FACHB-1757,ventilation also significantly increased ? and Fv/Fm values of algal cells(P<0.05),but the change of ventilation rate did not affect the ? and Fv/Fm of algal cells.(3)For the non-floating Microcystis FACHB-1028,in the F3 layer,the ventilation caused the reduce of the absolute value of the Zeta potential.Overall,the ventilation had no significant effect on the Zeta potential of the algal cells.For floating Microcystis FACHB-1757,ventilation caused the absolute value of Zeta potential of algal cells to increase significantly.(4)For the non-floating Microcystis FACHB-1028,on the one hand,the protein content of the algal cells first increased and then decreased with the increase of the rate of ventilation.On the other hand,compared to the non-ventilation,the ventilation caused the sugar content of the algal cells to decrease.However,changes in the rate of ventilation did not affect the sugar content of the algal cells.For floating Microcystis FACHB-1757,on the one hand,when there is light,compared with in the ventilation rate of 100 mL·min-1 and 300 mL·min-1,in the ventilation rate of 600 mL·min-1,the content of cellular proteins and sugars was relatively high.On the other hand,changes in ventilation rate did not affect the cellular protein and sugar content in the absence of light.(5)For the non-floating Microcystis FACHB-1028 and floating Microcystis FACHB-1757,ventilation disturbance did not affect the peak position of Raman spectroscopy,that is,they did not affect the species of chlorophyll and carotenoids synthesized by the algal cells.However,ventilation disturbance affected the intensity of the peaks in the Raman spectrum,that is,they affected the content of chlorophyll and carotenoids in the algal cells.Based on the above results,it can be concluded that the ventilation disturbance affects the vertical distribution of non-floating Microcystis FACHB-1028 and floating Microcystis FACHB-1757.For non-floating Microcystis FACHB-1028,ventilation disturbance affects the vertical distribution of algal cells mainly by affecting the Fv/Fm value,the ? value,and sugar synthesis of algal cells.Ventilation disturbance activates the vertical migration of non-floating microcystis FACHB-1028 algae cells.The vertical distribution pattern changes,but it does not change regularly with the increase of ventilation disturbance rate.For floating Microcystis FACHB-1757,ventilation disturbance affects the vertical distribution of algal cells mainly by affecting the Fv/Fm value,the ? value,and the electrical performance of the algal cells.Ventilation disturbance breaks the surface floating situation and promotes the vertical distribution of Microcystis to be uniform.With the increase of ventilation rate,the layer with the highest content of Microcystis in the water column migrates from the upper layer to the lower layer.