Effects Of Calcium And Magnesium Ions On The Colony Formation Of Microcystis Aeruginosa Under Hydrodynamic Action

Water eutrophication intensified with the rapid development of economic,the outbreak frequency and intensity of cyanobacteria blooms increased.The cyanobacteria bloom in natural water is mainly in the form of Microcystis aeruginosa colony.Microcystis aeruginosa colony plays an important role in the the formation of bloom water.The formation of Microcystis aeruginosa bloom affected by many factors,but the effect of hydrothermal and calcium-magnesium on the formation of Microcystis aeruginosa colony is unclear.The aim of this study is to investigate the effects of Ca and Mg on the formation of Microcystis aeruginosa colony under the hydrodynamic action.The main results of this study are as follows:(1)Under the hydrodynamic action,the Ca and Mg ions contribute to the formation of Microcystis aeruginosa colony.Compared with the low concentration calcium and magnesium ion culture medium,the high concentration calcium and magnesium ion culture medium morphological characteristics of Microcystis aeruginosa colony are more obvious.In the high and low calcium and magnesium ion culture medium,the hydrodynamic action all promoted the formation of Microcystis aeruginosa colony.The morphological characteristics of Microcystis aeruginosa colony are most obvious at the flow rate of 15 cm/s.The number of cells in the largest population of Microcystis aeruginosa in the experimental group with the high and low concentration calcium and magnesium ion was 280 and 210 cells,respectively.The maximum range of microcystis population in the experimental group was 0.6~0.82 and 0.52~0.74,respectively.The maximum proportion of large population(>20 cells)in the high and low concentration calcium and magnesium ion experimental groups is about 43% and 35%,respectively.(2)Under the hydrodynamic action,the Mg ion plays a more important role in the formation of Microcystis aeruginosa colony.There is no significant inhibition of Microcystis aeruginosa colony formation in the experimental group without calcium ion.The colony morphological characteristics are most obvious at the flow rate of 25 cm/s.But the formation of Microcystis aeruginosa colony is significantly inhibited by the magnesium-free experiment group under hydrodynamic action,and the Microcystis colony is smaller and less than the non calcium ion experimental group.In the calcium-free experimental group and the magnesium-free experimental group,the maximum number of cells in the Microcystis colony is 200 and 90 cells,respectively.The maximum proportion of the number of cells in the Microcystis colony is 0.41~0.65 and 0.33~0.48,respectively.In the calcium-free and magnesium-free experiments,the maximum proportion of Microcystis aeruginosa large colony(>20 cells)is about 31% and 20%,respectively.(3)Under the hydrodynamic action,the pH value of the culture medium in the high and low concentration calcium-magnesium ion and the calcium-free culture medium increased with the increase of the culture time.In the magnesium-free experiment group,the pH value of the culture medium decreased significantly with the increase of culture time,the increase of the culture medium pH value changed the Microcystis cell characteristics and promoted the formation of Microcystis colony.(4)Hydrothermal action of calcium and magnesium ions promote the secretion of extracellular polysaccharides of Microcystis aeruginosa,is conducive to the formation of Microcystis colony.The unit cell extracellular polysaccharide content of Microcystis aeruginosa in the each experimental group is higher than that static control group.In each experimental group,the unit cell extracellular polysaccharide content of Microcystis aeruginosa in the growth period is higher than that in logarithmic growth period.At the appropriate water flow rate,the unit cell extracellular polysaccharide content of Microcystis aeruginosa is the lowest.Microcystis aeruginosa secrete more extracellular polysaccharides in the external environment to reduce the impact of the external environment on their own,to adapted the changes of the environment.