| Due to the rapid development of industrial modernization and agricultural science and technology,a large amount of pesticides and industrial wastewater flow into the water body,resulting in a substantial increase in the level of nutrients in the water body,and the phenomenon of eutrophication in the water body.Eutrophic water bodies are often suitable environments for the growth and reproduction of cyanobacteria.In addition to the increase in water temperature brought about by global warming,cyanobacteria blooms frequently occur in eutrophic water bodies.Nowadays,the large number of cyanobacteria blooms have brought great threats to the water ecosystem and the health of humans and animals.The management of water eutrophication and the control of cyanobacteria blooms have become a major environmental problem that needs to be solved urgently.In the treatment of cyanobacteria blooms,there are roughly three methods,physical,chemical and biological.Among them,the use of protozoa in the biological method to control harmful algae is an environmentally friendly means of algae control.This method is based on the fact that protozoa are the main herders of phytoplankton in natural water bodies,and many protozoa produce harmful algae.Algae toxins are well tolerated and can even effectively degrade algae toxins.As the nutrient level based on nitrogen and phosphorus and warming are key environmental factors that affect the outbreak and intensity of cyanobacteria blooms,it is unclear whether and how the use of protozoan grazing to control cyanobacteria blooms is affected by the fluctuations of these environmental factors.This paper has carried out a series of researches around the above-mentioned scientific issues,and obtained the following results:1)The effect of changes in nitrogen concentration at room temperature on the removal of Microcystis aeruginosa by Ochromonas gloeoparaNitrogen is the main constituent element of chloroplasts and has a direct impact on the photosynthesis and growth of algae.This experiment studied the effect of changes in nitrogen concentration at room temperature on the removal of M.aeruginosa by O.gloeopara.The experiment set six nitrogen concentrations of 0.5,1,2,4,8,16 mg/L.Before the start of the experiment,the O.gloeopara and M.aeruginosa were "nitrogen starved" twice respectively,and then pre-adapted twice in a preset nitrogen concentration environment for 14 days,and then the formal grazing experiment was started.Experiments have found that nitrogen content significantly affects the removal of M.aeruginosa by O.gloeopara.In the grazing group with 0.5-4.0 mg/L nitrogen,the began of the decline of the M.aeruginosa population increases with the increase in nitrogen content,and when the nitrogen content is higher than It tended to be stable after 4.0 mg/L.In the absence of O.gloeopara,the environmental capacity and population growth rate of the M.aeruginosa population showed an increasing trend with the increase of nitrogen level,and stabilized when the nitrogen concentration was higher than 8.0 mg/L.In the absence of M.aeruginosa,the photosynthetic activity and the population growth rate of P.vulgaris did not change significantly within the range of the measured nitrogen concentration,indicating that the measured nitrogen level has no significant effect on its photosynthetic autotrophic ability.The above results show that the nitrogen content mainly affects the algae control efficiency of M.aeruginosa by affecting the growth of M.aeruginosa.The high nitrogen environment promotes the growth of M.aeruginosa and therefore delays the removal of M.aeruginosa by O.gloeopara.2)The effect of changes in phosphorus concentration at room temperature on the removal of M.aeruginosa aeruginosa by O.gloeoparaAt present,most lakes in my country are of the types that are relatively affected by phosphorus.In eutrophic water bodies,the increase of phosphorus concentration will cause cyanobacteria to occupy an absolute advantage in the succession of phytoplankton communities.In this experiment,six phosphorus concentrations were set at 25°C,namely 0.02,0.1,0.5,1,2,and 4 mg/L.The experiment was conducted in BG-11 with six phosphorus concentrations.Before the start of the experiment,the brown flagella and M.aeruginosa were "phosphorus starved" twice,and then preadapted twice in a preset phosphorus concentration environment for 14 days,and then the formal grazing experiment was started.The experimental results show that the O.gloeopara can effectively eliminate M.aeruginosa under all phosphorus concentration treatments.When the phosphorus concentration is 0.5-4 mg/L,as the phosphorus concentration increases,the time to clear M.aeruginosa by O.gloeopara will be shortened by about three days.Under the condition that there is no Microcystis aeruginosa in the phosphorus concentration of 0.02-1 mg/L,the population of O.gloeopara will increase with the increase of phosphorus concentration,and show a stable trend after2 mg/L.In the absence of O.gloeopara,the population of M.aeruginosa will increase with the increase of phosphorus concentration in the range of 0.02-2 mg/L phosphorus.The above results indicate that the change of phosphorus content at room temperature increases the biomass of the O.gloeopara population and strengthens the grazing capacity of M.aeruginosa,thus shortening the grazing time.3)The response of O.gloeopara to remove the nitrogen concentration of M.aeruginosa under high temperatureSummer is the season of high incidence of cyanobacterial blooms,because the temperature in summer will rise,leading to the increase of water body temperature.Studies have shown that high temperature is beneficial to the growth of algae.Based on the experimental results in Chapters 2and 3,the O.gloeopara clearing M.aeruginosa has a greater response to nitrogen concentration,and the clearing completion time is shorter.Therefore,this chapter will study the response of O.gloeopara to the nitrogen concentration in the removal of M.aeruginosa under high temperature.In this experiment,six nitrogen concentrations of 0.5,1,2,4,8,and 16 mg/L were set at a high temperature of 30°C.Before the start of the experiment,the O.gloeopara and M.aeruginosa were "nitrogen starved" twice respectively,and then pre-adapted twice in a preset nitrogen concentration environment for 14 days,and then the formal feeding experiment was started.The final experimental results show that the O.gloeopara treated with nitrogen concentration under high temperature can effectively eliminate M.aeruginosa within 5 days,and the nitrogen concentration increases with the nitrogen concentration in the range of 1-16 mg/L.The removal time of M.aeruginosa will be extended.In the end,the reduction rate of M.aeruginosa reached more than 99%.There is no obvious trend in the population of O.gloeopara within the nitrogen concentration range set by the experiment,but the population of M.aeruginosa can increase with the increase of nitrogen concentration.The above results show that the nitrogen concentration at high temperature mainly affects the algae control efficiency of M.aeruginosa by affecting the growth of M.aeruginosa.High nitrogen concentration promotes the growth of M.aeruginosa,thus prolonging the removal of M.aeruginosa by O.gloeopara time.In summary,O.gloeopara are good predators of M.aeruginosa in natural water bodies.Even under the environmental conditions of external nutrients and temperature changes,the O.gloeopara can effectively complete the removal of M.aeruginosa.This provides a theoretical basis for the use of protozoa to achieve biological control of algae,to understand more about the response of the relationship between protozoa and cyanobacteria to changes in elements,and to predict the effect of protozoa on algae control under different eutrophication backgrounds. |
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