Fundamental Research On Growth Influencing Factors And Control Of Microcystis Aeruginosa

This article first tracked and investigated the water quality,algae species,and zooplankton in a surface water zone and a reclaimed water zone of a landscape water body in Xi'an.Through a comparative study,the bottom-up and top-down effects of phytoplankton in the surface water zone and the reclaimed water zone were understood.A laboratory scale experiment was conducted to determine proportion and concentration of different forms of nitrogen at different temperatures,as well as the effects of phosphorus concentration and zooplankton on the growth of Microcystis aeruginosa.Finally,the control effect of micro-nano aeration on algae was studied.The above research can provide an important basis for the control and management of eutrophication of landscape water bodies.The research mainly obtained the following results and conclusions:?1?In the landscape waters surveyed,the water quality status of surface water zone and reclaimed water zone throughout the year were both mesotrophic levels.The nitrogen in surface water zone and reclaimed water zone mainly exists in the form of nitrate nitrogen,accounting for 70.46%and 68.90%of the annual total nitrogen concentration,respectively.The phosphorus is dominated by organic phosphorus,and phosphate accounts for only 39.29%and 35.91%of the annual total phosphorus concentration,respectively.The annual average values of the algae density and Chl-a of the reclaimed water zone were 1.27 times and 1.28 times of surface water zone,respectively.?2?10 species of algae were detected in the surface water replenishment area and 14 species of algae were detected in the reclaimed water zone.Microcystis aeruginosa was the dominant algae species in both waters,accounting for 72.39%and87.56%of the total algae density in the surface water zone and the reclaimed water zone.Only a few zooplankton species were detected in the urban landscape waters,of which28 species of zooplankton were detected in the surface water zone,and 30 species of zooplankton were detected in the reclaimed water zone.Rotifers were the dominant zooplankton in both water bodies,accounting for 97.33%and 95.60%of the average number of total zooplankton,as well as 76.84%and 80.24%of the biomass of total zooplankton in the surface water zone and the reclaimed water zone.The annual average values of the number and biomass of total zooplankton in the reclaimed water zone were 4.21 times and 6.03 times that in the surface water zone,respectively.?3?Based on PCA,RDA and Pearson analysis of one-year water quality data,it is known that the influence of the bottom-up effect is greater than that of the top-down effect in landscape water.Therefore,to improve the landscape effect of urban water bodies,attentions should be paid to the control of supplementary water quality.When reclaimed water is used to supply landscape water,phosphorus concentration is the key to control water quality.?4?The culture of Microcystis aeruginosa was carried out at temperatures of10?,15?,20?,25?,30?and the ratio of NO₃^--N/NH₄⁺-N at 5:0,4:1,3:2,2:3,1:4,PO₄^3--P concentration at 0.2 mg/L and 0.1 mg/L in the laboratory experiments.The response of Microcystis aeruginosa to nitrogen and phosphorus was determined by concentration,form and proportion of nitrogen and phosphorus as well as temperature.So the concentration of nitrogen and phosphorus in landscape water replenishment should be seasonally regulated according to temperature change.Compared with nitrogen,phosphorus had a greater effect on the growth and proliferation of Microcystis aeruginosa.In addition,it was found that Microcystis aeruginosa gave priority to the use of NH₄⁺-N in the process of growth,and NO₃^--N was utilized only when the concentration of NH₄⁺-N in water was low to a certain concentration.However,the absorption of phosphorus by Microcystis aeruginosa was not affected by the form and proportion of nitrogen.?5?The SOD activity can reflect the stress of exogenous stimulation on Microcystis aeruginosa.The SOD activity of Microcystis aeruginosa at 10?was the highest,while the SOD activity at 25?was the lowest,indicating that the low temperature of 10?had the greatest stress to Microcystis aeruginosa,while 25?was more beneficial to the growth of Microcystis aeruginosa than other temperatures.Under the condition that the concentration of PO₄^3--P was 0.1 mg/L,the ratio of NO₃^--N/NH₄⁺-N was 3:2 at 15?,the SOD activity reached the peak,which indicated that the coupling of temperature and nutrition had the greatest stress on Microcystis aeruginosa.At 20?,the SOD activity was the highest in the case of PO₄^3--P=0.1 mg/L,NO₃^--N/NH₄⁺-N=4:1,and the Microcystis aeruginosa declined.Therefore,PO₄^3--P=0.1mg/L,NO₃^--N/NH₄⁺-N=3:2 at 15?and PO₄^3--P=0.1 mg/L,NO₃^--N/NH₄⁺-N=4:1 at20?are more favorable for the control the growth of Microcystis aeruginosa than other conditions.?6?A micro-nano aeration was used to control algae in a laboratory-scale experiment,where the micro-nano aeration of the landscape water body was carried out for a total of 120 minutes and stopped for 5 hours every 40 minutes of aeration.During the aeration process,the dissolved oxygen concentration increased at first and then decreased,and the nitrogen and phosphorus concentration did not change significantly.However,the removal rates of total algae density and Microcystis aeruginosa were34.46%and 49.71%,respectively.The results show that micro-nano aeration has a certain control effect on algae,especially Microcystis aeruginosa in landscape water.