Effect Of Fluctuating Light Cycle On Growth And Chlorophyll Fluorescence Of Typical Algae In Water Source Reservoirs

To explore the effects of internal waves on the algae growth in simulated water environment,the typical algae of Microcystis aeruginosa and Chlorella vulgaris in stratified source water reservoirs were taken as study objects.Using an experimental device with adjustable light intensity based on single chip,the algae growth and photosynthesis were experimentally investigated under various light intensity conditions.Five light conditions were set for low,medium and high average light intensity cases,which were the static light group(SL)without internal wave,the fluctuating light under internal wave with different cycles(10min FL,1h FL,and 6h FL),and the average light intensity group(AL)under internal waves conditions.The main conclusions are as follows:(1)The vertical reciprocate motion of algae was analyzed under internal waves,the average light intensity(AL)during one periodand the static light(SL)intensity at the water depth of equilibrium circle were calculated theoretically,and the calculation results showed AL is always greater than SL.(2)Under low light intensity in deep waters,affected by internal waves,the growth rates and algae densities of Microcystis aeruginosa and Chlorella vulgaris were both significantly increased.Compared with the SL group,the algae densities of Microcystis aeruginosa for 6h FL(Fluctuation period of 6h),1h FL and 10 min FL groups were increased by 35.4%,24.1% and 8.8% respectively,the algae densities of Chlorella vulgaris for 6h FL,1h FL and 10 min FL groups were increased by 30.4%,22.1% and15.6%,respectively.(3)Under medium light intensity in waters with medium depth,affected by internal waves,the growth rates and algae densities of Microcystis aeruginosa and Chlorella vulgaris had a certain degree of increase.Compared with the SL group,the algae densities of Microcystis aeruginosa for 6h,1h and 10 min FL groups were increased by10.7%,25.4% and 7.9%,respectively,the algae densities of Chlorella vulgaris for 6h FL,1h FL and 10 min FL groups were increased by 4.9%,23.4% and 6.0%,respectively.(4)Under high light intensity in shallow waters,affected by internal waves,the growth rates and algae densities of Microcystis aeruginosa and Chlorella vulgaris varied in complex characteristics.Compared with the SL group,the algae densities of Microcystis aeruginosa for 6h FL,1h FL and 10 min FL groups were decreased by19.3%,-5.1% and 9.4%,respectively,the algae densities of Chlorella vulgaris for 6h FL,1h FL and 10 min FL groups were decreased by 20.5%,4.8% and 16.9%,respectively.(5)Under low average light intensity conditions,compared with the AL groups,.The algae densities of Microcystis aeruginosa for 6h FL,1h FL and 10 min FL groups were increased by 28.3%,18.2% and 7.7%,respectively,the densities of Chlorella vulgaris for three groups were increased by 23.5%,14.0% and 5.0%,respectively.(6)Under medium average light intensity conditions,compared with the AL groups,the densities of Microcystis aeruginosa for 6h FL,1h FL and 10 min FL groups were decreased by 8.2%,-3.9% and 10.6%,respectively,the densities of Chlorella vulgaris for three groups were decreased by 4.6%,-10.0% and 5.5%,respectively.(7)Under high average light intensity conditions,compared with the AL groups,the densities of Microcystis aeruginosa for 6h FL,1h FL and 10 min FL groups were decreased by 17.1%,-8.2% and 6.7%,respectively,the densities of Chlorella vulgaris for three groups were decreased by 6.3%,-7.1% and 3.1%,respectively.(8)Under each light condition,basically,the Fv/Fm,YII and rETR values varied in the similar way to the algal density,but opposite to carotenoid content.