Study On Methane Oxidation Rate And Carbon Isotope Fractionation In Bohai Sea Sediments

The Bohai Sea contains a large number of oil and gas resources,and its main component is greenhouse gas methane.The impact of natural factors or human factors can cause its leakage and migration,and it will have a negative impact on the environment.During the leakage and migration of methane on the seabed,microorganisms can oxidize most of the methane,thereby reducing the damage to the environment.With the continuous destruction of the atmospheric environment and the global warming,the microbial oxidation of greenhouse gases methane has important implications for reducing the increase of greenhouse gases.Therefore,the rate of microbial oxidation of methane and the carbon and hydrogen isotope fractionation process are important prerequisites for a deep understanding of the relationship between marine ecological environment and global climate change,which have important theoretical and reference values.In order to better understand the rules of methane oxidation and isotope separation in the sediments of the Bohai Sea,the Bohai Sea sediments were selected as experimental raw materials for laboratory simulation of degradation experiments,which using gas chromatography and chromatography-isotope ratio mass spectrometry.The results are as follows:(1)The results of batch oxidation experiments based on different oxygen contents showed that the residual methane content in the anaerobic oxidation test group of the four groups at different temperatures during the test up to 160 days remained at about 90%.The methane in the aerobic oxidation experiment group will completely oxidized the methane in the device at a higher temperature,that is,the oxidation of methane in Bohai Sea sediments is dominated by aerobic oxidation.In the low-temperature 4°C experimental group,both aerobic oxidation and anaerobic oxidation were basically stagnant,indicating that the activity of microorganisms at low temperatures was inhibited and the life metabolic activities were stopped.In the experiment,the residual content of methane decreased by about 10%,which was mainly due to the dissolution and adsorption of sediment and broth in the device.(2)Simulating the oxidative decomposition of methane degradation in the free state of the seabed through continuous oxidation experiments.The results show that the average oxidation rate of methane does not increase significantly when the temperature was increased from 10°C to 15°C.However,when the temperature rose to 28°C,the average oxidation rate increases by about 77%,that is,the lower the temperature,the more harmful the methane oxidation is.When the gas flow rate was increased from 50?L/min to 150 ?L/min,the average oxidation rate of methane increased by about 90%,that is,the increase of the gas flow rate was conducive to the increase of the oxidation reaction rate.The experiment also found that the fractionation effect of methane carbon and hydrogen isotopes is mainly regulated by oxidation temperature,and the degree of fractionation is positively correlated with temperature,ie,temperature is an important factor in affecting methane oxidation rate and isotopic fractionation rules.(3)By detecting the content changes of the by-products carbon dioxide during the aerobic experiment of microorganisms,the results showed that the carbon dioxide content gradually increased until the maximum of about 0.14 ?mol after a certain period of time.Then it began to gradually decrease,reaching a minimum of about 0.04 ?mol at 110 days,and within the next 70 days,the change in carbon dioxide content entered a homeostasis and remained stable at about 0.04 ?mol.This may be due to the dissolution of carbon dioxide or to the precipitation of Ca2+.(4)The results of the batch oxidation experiment and the low-speed continuous oxidation experiment show that the average oxidation rate of the batch oxidation test at28°C is 1.14 ?mol/g·day,and the average oxidation rate of the continuous oxidation at28°C is 1.05 ?mol/g ·day,the oxidation rate is relatively close.In the two oxidation modes of “batch oxidation” and “low-speed continuous oxidation”,the methane carbon isotope fractionation coefficients are-14.401 and-17.982 respectively,and the methane hydrogen isotope fractionation coefficients are-99.285 and-92.514,respectively.The fractionation coefficient is also similar.Therefore,the two oxidation methods are relatively close and there are no major differences.