| In recent years,the impact of cyanobacterial blooms on many water bodies such as ponds and lakes has received widespread attention.In this study,the most representative cyanobacteria Microcystis blooms in eutrophic water bodies were investigated,and the effects of light and bloom concentration on cyanobacterial blooms were investigated under the appropriate aeration disturbance intensity,and the study on the control of cyanobacterial blooms by shading and aeration disturbance was carried out in situ in ponds.The study has important theoretical and practical significance for controlling cyanobacterial blooms in ponds.This study is divided into three main components as follows,including:(1)To study the effect of different aeration disturbance intensity on the community structure of Microcystis under low light conditions,continuous aeration disturbance experiments were conducted in a glass greenhouse in the summer of 2021,with aeration gradients of 0 m~3/h,0.045 m~3/h,0.185 m~3/h and 0.64 m~3/h,corresponding to treatments I,II,III and IV,respectively,and the area above the aeration experiment was covered with The shading net was used to form a low light condition,and each treatment obtained98.9% shading relative to outdoor light.The water temperature during the experiment ranged from 21.87 ± 0.24°C to 32.07 ± 0.33°C.The initial chlorophyll a(Chla)concentration of algae was 1367 μg/L,total nitrogen concentration was 34.03 mg/L,and total phosphorus concentration was 2.45 mg/L.The evaporated water was supplemented with tap water during the experiment.During the experiment,Chla concentrations decreased significantly(P < 0.01)in treatments II,III and IV,and all showed the result of succession of Microcystis to other algae.Treatment I,which was not disturbed by aeration,was still dominated by Cyanobacteria and Microcystis as the most dominant genus,followed by Phormidium;Treatment II was dominated by Chlorella,followed by Cyclotella,and treatments III and IV were dominated by Nitzchia,a diatom.Nitzchia was the most dominant genus in treatments III and IV,with 85.80% ± 3.82% and68.56% ± 13.55% of wet mass,respectively,and Chlorella was the second most dominant genus in treatment IV with 23.11% ± 9.48%.The results showed that under the shading rate of 98.9%,the continuous aeration disturbance of the three treatments effectively inhibited the growth of Microcystis while promoting the succession of algal community structure.The treatment with aeration disturbance intensity of 0.185 m~3/h was the most favorable for the succession of Microcystis to diatoms,while the treatments with aeration disturbance intensity of 0.045 m~3/h and 0.640 m~3/h promoted the succession of Microcystis to diatoms and green algae at the same time.(2)To investigate the effects of shading and cyanobacterial bloom concentration on cyanobacterial blooms,especially algal community structure,under continuous aeration disturbance,a regulation experiment of cyanobacterial phylum Microcystis blooms was conducted in a glass greenhouse from June 24 to August 3,2021.The experiment was an orthogonal experiment with 2 algal concentrations and 2 light gradients.The initial concentrations of Microcystis blooms were divided into low(treatments I and III)and high(treatments II and IV)according to the initial concentration of Chla,where the concentrations were 384.32 and 736.21 μg/L,and treatments I,II and III and IV corresponded to low light(shading of 99.4%)and strong light conditions(shading of72.8%),respectively.During the experiment,Chla concentration decreased in all treatments,ranking from IV > III > II > I(P < 0.01),and all of them showed the succession of Microcystis to other algae.Among them,treatments I and II under low light conditions appeared to have diatoms of the phylum Nitzchia as the most dominant genus,with their wet mass percentage reaching 90.48% ± 9.29% and 93.64% ± 2.28%,respectively.In treatments III and IV,the cyanobacterial phylum was still the most dominant,and treatment III showed the most dominant genus of Phormidium,followed by Microcystis and Nitzchia;treatment IV showed the most dominant genus of Microcystis,followed by Nitzchia and Phormidium.The results showed that the light intensity and the concentration of cyanobacterial bloom both affected the succession of algal community structure in cyanobacterial bloom under continuous aeration disturbance,and the shading rate of 99.4% could effectively inhibit the growth of cyanobacterial bloom with high concentration and promote its succession to diatoms.(3)The results of the indoor study showed that the growth and community structure of Microcystis blooms could be influenced by appropriate shading under suitable aeration disturbance intensity,and the purpose of regulating Microcystis blooms was achieved.In situ control of cyanobacterial blooms in aquaculture ponds in Mao Town,Songjiang District,Shanghai,China was initiated in early July 2022 to investigate the effect of aeration disturbance under suitable shading conditions on the control of cyanobacterial blooms and community structure in situ in ponds.Ponds 1#and 2# with the same geographical location,size(2 m × 50 m × 100 m),orientation and culture conditions were selected for the study.The shading area was 10×50m and the shading rate was 81.3% and 79.6% respectively.Three study sites were selected under the shading net,sites I,II and III were 10 m,25m and 40 m away from the long side of the pond respectively,and each site was 5m away from the wide side of the pond.Point III in both ponds was continuously disturbed by aeration using an impeller-type aerator with the same operating power of 750 W.The experiment was conducted for a total of57 days.During the experiment,the Chla concentration and cyanobacterial facultative wet mass concentration of each point in both ponds tended to decrease,and the decrease was significant(P < 0.05)in point III,while more Chlorella.evolved in point III of pond 1# and more Euglena and Chlorella.evolved in point III of pond 2#.The results showed that in the combined study of shading and aeration in this experiment,the reduction of light intensity weakened the cyanobacterial bloom dominance at each site as a whole,which led to the succession of non-cyanobacterial dominant genera at each site,while the aeration disturbance significantly inhibited the growth of cyanobacterial bloom and played a significant role in the in situ control of cyanobacterial bloom. |
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