| Cyanobacteria blooms are one of the most important water environmental problems facing the world.Artificial mixing is considered to be one of the most effective methods for controlling cyanobacterial blooms.Artificial mixing such as aeration has been used as a measure to prevent cyanobacterial blooms in eutrophic lakes and reservoirs for many years.However,this approach has not always been successful.Therefore,this study explored the influence of aeration on the growth,physiology and competitive ability of Microcystis.It has a deeper understanding of the outbreak mechanism of cyanobacteria bloom and provides a theoretical basis for bloom management.In order to improve the ability of controlling cyanobacteria blooms by artificial disturbance,the laboratory experiment was combined with field experiment to control cyanobacteria blooms by mobile aeration in shallow fish ponds with extremely high nutrient content.The main conclusions of this thesis are as follows:(1)When the turbulence dissipation rate was 4×10-8 m2 s-3-1×10-7 m2 s-3,the formation of Microcystis colony was promoted,while the disturbance above 1×10-7 m2 s-3 was not conducive to the formation of Microcystis colony.The lower the aeration intensity,the lower the content of toxic Microcystins.(2)Our results demonstrated that Scenedesmus was more resistant to the turbulence than Microcystis in the absence of sediment.In the presence of sediment,S.obliquus was promoted,while M.aeruginosa was inhibited under all aeration conditions.The highest inhibition rate of M.aeruginosa was identified under the condition of low-intensity aeration in the nighttime with small sediment addition,which was 89.2%.Our results indicated that aeration induced turbulence could be used to mitigate the cyanobacteria blooms,particularly under the small sediment particle size condition.In the mixed culture,the growth of Microcystis was inhibited by Scenedesmus in all treatments with aeration regardless of the presence of sediment,and the low-intensity aeration in the daytime could promote the inhibition.Furthermore,artificial mixing could be an effective measure to promote a shift in phytoplankton composition from cyanobacteria to green algae.(3)A self-designed moving aeration device was employed to control cyanobacterial blooms in an extremely eutrophic shallow pond.The results showed that,except for ammonia(NH3-N)concentration,there were no significant differences in the mean values of total phosphorus(TP),total nitrogen(TN),nitrate(NO3--N),phosphate(P2O53-)and p H between the two ponds.In the second year of the experiment,Cyanobacteria was the dominant phytoplankton phylum in the control pond,comprising up to 70%of the total community.However,in the treated pond,the maximum proportion of Cyanobacteria was just 30%,while the proportions of Bacillariophyta and Chlorophyta reached approximately 80%.Moreover,Microcystis was the dominant genus in the control pond,while Scenedesmus and Pediastrum became dominant in the treated pond in the second year.The biomass in the treated pond was almost reduced to half of that in the control pond in the second year.The occurrence of blooms was eliminated in the treated pond in the second year,while cyanobacterial blooms still occurred frequently in the control pond.Similarly,the Microcystis colony size decreased substantially in the treated pond in the second year.The results suggest that moving aeration is an environmentally friendly method of controlling cyanobacterial blooms in shallow fish ponds. |
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