Effects Of Different Inorganic Nitrogen Sources On The Growth Of Microalgae And The Production And Emission Of Greenhouse Gases In Water Body

Greenhouse effect and water eutrophication are the global environmental problems at present.Nitrogen plays an important role in water eutrophication and greenhouse gas production.Exist in various forms of nitrogen in the environment,including inorganic nitrogen forms including ammonium nitrogen,nitrate nitrogen and nitrate nitrogen,different aquatic biological characteristics of inorganic nitrogen absorption and utilization of differences,but different in the process of the transformation of inorganic nitrogen in water will directly or indirectly affect carbon dioxide,nitrous oxide and methane and other greenhouse gases,therefore,research on inorganic nitrogen forms on the relationship between the algae growth and greenhouse gas of rich nitrogen environment effect and the conversion of data is important.In this study,the effects of different inorganic nitrogen sources on the growth of Microcystis aeruginosa and Chlorella vulgaris were studied by light culture experiments in laboratory and outdoor natural water.The effects of different forms of inorganic nitrogen on the production and emission of greenhouse gases such as carbon dioxide,methane,nitrous oxide,as well as the changes of dissolved greenhouse gas concentrations in different depths of water were studied through outdoor water culture experiments.Laboratory light culture set up three kinds of inorganic nitrogen treatment,240 mg/L respectively ammonium nitrogen treatment,240 mg/L nitrate nitrogen treatment and 240 mg/L and nitrite nitrogen treatment,and the natural outdoor water culture experiment set up four kinds of inorganic nitrogen treatment,240 mg/L respectively ammonium nitrogen treatment,240 mg/L nitrate nitrogen,240 mg/L nitrite nitrogen treatment and three kinds of amount of inorganic nitrogen,(ammonium nitrogen,nitrate nitrogen and nitrate nitrogen are 80 mg/L),and set up a surface depth processing,50 cm and 100 cm,3 processing.The results of this study are as follows:(1)In the laboratory incubator treatment,nitrate nitrogen and nitrite nitrogen can promote the growth of Microcystis aeruginosa and Chlorella vulgaris,and nitrate nitrogen is better than nitrite nitrogen,while ammonium nitrogen is not conducive to or even inhibits the growth of both algae,and inhibits the growth of Microcystis aeruginosa more than Chlorella vulgaris;During the whole experiment,the pH value of nitrate nitrogen and nitrite nitrogen treatment was greater than 9.0,and the concentration of gas carbon dioxide in the culture flask was lower.However,the pH value of ammonium nitrogen treatment was lower,and the pH value was lower than 7.0 in the late experiment,and the concentration of gas carbon dioxide in the culture flask was higher.In the outdoor culture treatment,the promotion effect of nitrite nitrogen treatment on the growth of algae in natural water was obviously stronger than that of nitrate nitrogen treatment,and the growth condition of algae was the best in the late experiment under the same amount of inorganic nitrogen treatment,while the inhibition effect of ammonium nitrogen treatment on the growth of algae was obvious.Nitrate nitrogen and nitrite nitrogen treatments had higher dissolved oxygen content,higher pH value,and lower dissolved carbon dioxide content in water,while the other two treatments were on the contrary.(2)In the outdoor culture treatment,the number of species decreased from 19 to 9,10,6and 7,respectively,after the addition of ammonium nitrogen,nitrate nitrogen,nitrite nitrogen and the same amount of inorganic nitrogen,and the number of dominant species increased while the number of species decreased in all inorganic nitrogen treatments.Microcystis is the dominant algae species in the treatment with vigorous growth of algae.(3)The ammonium nitrogen is mainly converted to nitrite nitrogen in water,but the amount of conversion is smaller than that of ammonia volatilization.When pH is greater than8.0,the loss of ammonia volatilization is extremely high.The dissolved amount of carbon dioxide in water with different inorganic nitrogen was negatively correlated with pH,and the content of free carbon dioxide in water with higher pH was less.(4)In this experiment under aerobic conditions,nitrate nitrogen does not promote the production of nitric oxide in water,ammonium nitrogen and nitrate nitrogen are of nitrous oxide to produce a certain role in promoting,and the amount of ammonium nitrogen,nitrate nitrogen and nitrite nitrogen treatment can obviously promote the production of nitrous oxide,especially in the later period,The concentration of nitrous oxide in water increased exponentially;Similarly,nitrate nitrogen does not promote the emission of nitrous oxide,while the same amount of ammonium nitrogen,nitrate nitrogen and nitrite nitrogen can significantly promote the emission of nitrous oxide.The emission flux of nitrous oxide(y)is significantly positively correlated with the concentration of dissolved nitrous oxide(x)in water,as follows:y=-25.21+0.3279x(n=28,R~2=0.9612,p<0.0001).The cumulative emissions of nitrous oxide were 30.66±10.98 mg,6.56±2.02 mg,1.20±0.61 mg and 0.055±0.051 mg under three inorganic nitrogen equalization treatments,nitrite nitrogen treatment,ammonium nitrogen treatment and nitrate nitrogen treatment,respectively.(5)The concentration of dissolved carbon dioxide in water treated with ammonium nitrogen is higher than that of other treatments,and the concentration of carbon dioxide in nitrite nitrogen treatment is the lowest.In general,all treatments are in a state of absorption of carbon dioxide,the carbon dioxide emission flux(y)was significantly correlated with the dissolved carbon dioxide(x)in water,and the two were in line with the y=-41.80+0.6543 x(n=28,R~2=0.1753,p<0.05)model.All the treatments were carbon dioxide absorption sinks.The cumulative absorption of carbon dioxide under three treatments of inorganic nitrogen equalization,nitrite nitrogen,ammonium nitrogen and nitrate nitrogen were 1744.17±687.71mg,741.93±312.00 mg,563.17±185.14 mg and 361.44±129.98 mg respectively.(6)Different ammonium nitrogen content processing,its electrical conductivity,inorganic nitrogen,total nitrogen,pH,solubility of carbon dioxide and nitrous oxide and carbon dioxide and nitrous oxide emission flux index differences,but there is no difference between the above indexes between different depth,different depth between the solubility of carbon dioxide content and solubility nitric oxide has nothing to do with the depth of the water.