| With the change of climate,accelerated eutrophication of water and rising salt level of inland water have set a remarkable effect on the freshwater phytoplankton.A device that can isolate and control algae in the surface area of a lake is proposed in this paper to solve the problem of algae blooms in lake and reservoir.Moreover,to investigate the effect on physiological characteristics of freshwater phytoplankton under the rising salty environment,Chlorella vulgaris,Microcystis aeruginosa and Melosira varians were researched and continuous cultured at raw water and salinity as 1.0g/L,3.0 g/L and 5.0g/L respectively.Chlorophyll a synthesis,cell multiplication,change of antioxidant index,chlorophyll fluorescence parameters and cell membrane permeability of the three kinds of freshwater algae were researched in the study and the difference of their adaptability between them was also analyzed.The main conclusions are as follows:(1)A device that has algae isolation and suppression function in the area of lake was proposes,which accelerates the subsidence of the algae particles into the bottom of the reservoir under the action of the aeration system and the shading net.Algae died due to the disappearance of light in the dark water and stopped photosynthesis,thereby reducing the number of algae particles entering the water tower to decrease the cost of water treatment.(2)As salinity increase of inland water,the growth,proliferation and chlorophyll a synthesis of the three kinds of freshwater algae have been inhibited in varying degrees;when salinity condition was above 3.0 g/L,cell division ratio gradually declined and rate of chlorophyll a synthetic also fell rapidly.It was indicated that increasing salinity can significantly inhibit the growth of freshwater algae,and the higher the salinity,the stronger the inhibition.(3)The increase of salinity caused SOD activity and MDA content in algae cells to rise,and the higher the salinity,the higher the peak of SOD activity,the higher the average content of the MDA.It was indicated that rising salt level led to the increase of intracellular free radicals,which enhanced cell oxidation of lipid membrane and then produced certain damage to the cell membrane structure;and the higher the salinity,the more serious the damage to the cell membrane.Meanwhile,salinity increases caused changes in chlorophyll fluorescence parameters,such as photochemical quenching coefficient qP reduced and non-photochemical quenching coefficient NPQ increased.It showed that rising water salt reduce the photosynthetic activity and elevated salinity probably caused some damage to the photosynthetic structure of algae cells.(4)When salinity increased to above 3.0g/L,it had a significant inhibitory effect on the growth of three algae.The relative attenuation of Chlorella vulgaris was the highest,reaching 34.6%,followed by Melosira varians,Microcystis aeruginosa was the smallest.Meanwhile,the ratio of cell division was similar as that.Therefore,it was speculated that Microcystis aeruginosa had the strongest adaptability to rising salinity,followed by Melosira varians and Chlorella vulgaris did the weakest.If the trend of salinity increase was difficult to reverse,freshwater algal system might turn from multi-algae system into salt-tolerant algae system,and the diversity of ecosystem was likely to be lost.(5)Changes in cell membrane permeability and cell damage of salinity is directly related.The rise of salinity increased the permeability of Chlorella vulgaris cell membrane,and there was almost no recovery ability under the condition of higher salinity.The recovery of Melosira varians and Microcystis aeruginosa was below 3.0 g/L,but 5.0 g/L when the cell membrane was also serious damage.The difference probably related to the protection of mucilage outside the cell of Microcystis aeruginosa and catenulate glial layer structure of Melosira varians. |
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