Selection And Evaluation Of Suitable Media Of Common Bloom Dominant Algae

Microalgae are a common class of single-celled photosynthetic organisms,including prokaryotic algae and eukaryotic algae,which are widely found in marine and freshwater water bodies.In recent years,with the proposal of global climate change,eutrophication of water bodies,and carbon neutrality,it has attracted great attention in various fields,and microalgae has become one of the hot spots in the research of scholars and engineering and technology communities.On the one hand,eutrophicationic water bodies cause algal blooms,affect the sensory traits of water bodies,and cause dissolved oxygen in water bodies to decrease and harmful algal toxins to accumulate,thereby destroying the ecological stability of water bodies and damaging their ecological functions;on the other hand,microalgae produce a carbon sequestration effect by photosynthesis absorbing CO₂,and the carbon sink of water bodies is largely achieved by microalgae,and carbon reservoirs can be formed in water bodies and sediments.In addition,microalgae have great potential and value in the treatment of wastewater,the production of high-value products and even the field of power generation.All of the above researches are based on the life activity and biomass accumulation of microalgae.At present,there are about50,000 kinds of microalgae in nature,with a wide variety of species,and there are significant differences in the environmental conditions of their living conditions and the demand for nutrients and trace elements theoretically.Most of the indoor culture studies of microalgae are carried out using only a few mediums such as BG11.In fact,there are flaws in methodology,which is debatable,whether such cultivation conditions are suitable for the growth of microalgae of different phylums,and whether the experimental results obtained can truly reflect the physiological and ecological process of microalgae.In this paper,based on the mixed algae species of water blooms of Gaoyang Lake in Pengxi River Basin of the Three Gorges Reservoir Area in the summer of 2021,mixed algae cultures were first conducted to explore the growth characteristics of algae samples in five common media,resulting in media that are more suitable for several common bloom dominant algae.Based on the experimental results of the previous step,the pure algae were cultivated by adjusting the nitrogen concentration,phosphorus concentration and basic culture medium to obtain the relatively suitable culture conditions for the bloom dominant algae.And the most suitable culture conditions were obtained by changing the nitrogen concentration and phosphorus concentration of the most suitable medium,the microalgae were investigated to determine which nutrients were more sensitive under pure culture conditions.The main conclusions obtained are as follows:（1）Mixed algae samples obtained during the summer blooms of the Pengxi River were cultured using five common media,BG11,BBM,F/2,M11 and SE,the Microcystis aeruginosa reached a larger cell density than other media at the end of culture in M11 and BG11 media;In F/2,SE and BBM medium,Eudorina sp.culture ended with a bigger cell density than other media,and Cagal algae cells are significantly larger in F/2 medium than in other media;Anabaena variabilis reached a higher cell density than other medium at the end of culture in BG11 and SE medium.（2）The results of pure culture experiments showed that the optimum concentrations of nitrogen and phosphorus in Microcystis aeruginosa were 144.1 mg/L and 27.7 mg/L respectively,in Anabaena variabilis were 247.1 mg/L and 50.0 mg/L,respectively,in Eudorina sp.were 144.1 mg/L and 50.0 mg/L respectively.In terms of trace element composition,Microcystis aeruginosa prefered the trace element composition and concentration of BG11 medium,while BBM medium and F/2 medium exhibited inhibition on Microcystis aeruginosa.The Anabaena variabilis also prefered the trace element composition and concentration of BG11 medium,and can better adapted to SE media and BBM medium with higher concentrations of heavy metal elements,which indicated that the Anabaena variabilis was more tolerant of heavy metals than the Microcystis aeruginosa.Eudorina sp.prefered the trace element composition and concentration of SE medium,and F/2 medium showed significant inhibition to it.（3）Under the above suitable medium conditions,in terms of specific growth rate,the limiting factor of Microcystis aeruginosa was phosphorus concentration,and its specific growth rate was negatively correlated with nitrogen concentration,positively correlated with phosphorus concentration,and more sensitive to changes in phosphorus concentration.The limiting factor for the Anabaena variabilis was nitrogen concentration,its specific growth rate increased with increased nitrogen concentration,decreased with increased phosphorus concentration,and it was more sensitive to changes in phosphorus concentration.Nitrogen and phosphorus concentrations are not the limiting factors of Eudorina sp.,its specific growth rate was reduced with an increase in nitrogen concentration.Regardless of whether the phosphorus concentration increased or decreased,the specific growth rate decreased,when the phosphorus concentration ranged from 45.6 mg/L to 54.4 mg/L,Eudorina sp.was more sensitive to changes in nitrogen concentration,outside this range,it was more sensitive to changes in phosphorus concentration.（4）The results showed that the optimal medium scheme for Microcystis aeruginosa was based on BG11 medium,with an adjusted nitrogen concentration of 115.3 mg/L and a phosphorus concentration of 33.3 mg/L;The optimal medium regimen for the Anabaena variabilis was the adjusted BG11 medium with nitrogen and phosphorus concentration of 296.5 mg/L and 40.0 mg/L,respectively;The relatively suitable medium protocol for Eudorina sp.was based on SE medium,with an adjusted nitrogen concentration of 115.3 mg/L and a phosphorus concentration of 50.0 mg/L.