摘要
海洋区域蕴藏了丰富的天然气水合物资源,是地球上巨大的碳储库之一。当海洋环境发生变化时,部分水合物会分解释放出大量天然气,其向上运移过程中会发生厌氧或好氧氧化反应,从而减少由海洋向大气的碳排放量,起到消耗截流的作用。本文选取含烷烃好氧氧化菌的海底沉积物进行了水合物分解气的微生物好氧降解模拟实验,实验中用混合气(C_1+C_2+C_3)来模拟多组分水合物分解气。实验结果显示,在微生物作用下烃类混合气发生好氧氧化降解反应至消耗殆尽,反应优先顺序为C_1>C_2>C_3,降解速率C_1>C_2>C_3。且随着烃类组分含量的减少,其碳氢同位素组成发生了微生物降解分馏效应,并呈现出不同程度的富集趋势。C_1、C_2和C_3的碳同位素富集变化量分别为71.05‰、12.03‰和4.61‰,碳同位素分馏系数(εC)的平均值分别为-11.219‰、-2.951‰和-1.539‰;氢同位素富集变化量分别为368.64‰、156.00‰和111.97‰,氢同位素分馏系数(εH)的平均值分别为-56.092‰、-99.696‰和-73.303‰。可见,三者的碳位素富集程度C_1>C_2>C_3,而氢同位素富集程度C_2>C_3>C_1。此外,水合物分解气在微生物降解过程中气体成分组成及碳氢同位素特征发生了改变,对判别气体成因起到一定的干扰作用,因此,利用分解溢出气体样品进行气体溯源时需要适当考虑这一影响因素。
Natural gas hydrate,as an enormous carbon reservoir,is mainly embedded in subsurface marine sediments.A large amount of hydrocarbons may release from the marine regions where gas hydrate deposits occur.Anaerobic or aerobic oxidation of dissociated hydrocarbon gas in its upward migration may cause hydrocarbon consumption thus decrease the carbon emission to atmosphere.Here,we performed experimental measurements on the aerobic oxidation process using marine sediments containing aerobic hydrocarbon-oxidizing bacteria to simulate the process of aerobic biodegradation for hydrocarbons（C1＋C2＋C3）that decomposed from gas hydrate.The results show that the composition of methane,ethane and propane decreases together with carbon and hydrogen isotope fractionation during the aerobic consumption.An apparent preference for C1 over C2 and C3 is observed during oxidation.The rates of oxidation are also in an order of C1〉C2〉C3.At the same time,the carbon and hydrogen isotope of hydrocarbons show a various enrichment tendency.The enrichment amount of carbon isotope of C1,C2 and C3 are 71.05‰,12.03‰and4.61‰,and the average ofεCare-11.219‰,-2.951‰ and-1.539‰,respectively.The accumulation amount of hydrogen isotope are 368.64‰,156.00‰ and 111.97‰for C1,C2 and C3,as well as the average ofεHare-56.092‰,-99.696‰and-73.303‰for C1,C2 and C3,respectively.The enrichment degree of carbon and hydrogen isotope fractionation are in an order of C1C2C3 and C2〉C3〉C1,respectively.Therefore,the aerobic biodegradation of hydrocarbons decomposed from gas hydrate may interfere with the origin discrimination of gas hydrate since the aerobic oxidation makes the composition and carbon and hydrogen isotope fractionation of hydrocarbon changed.Therefore,the influential factor should be considered appropriately to genesis study on gas hydrate when using decomposed hydrocarbons in headspace analysis.
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
2017年第5期204-216,共13页
Marine Geology & Quaternary Geology
基金
国家自然科学基金项目(41406076)
中国地质调查局“天然气水合物测试技术与实验模拟”项目(DD2016026)
青岛海洋科学与技术国家实验室开放基金(QNLM2016ORP0203)
关键词
天然气水合物
分解气
好氧氧化反应
微生物降解
碳氢同位素分馏
gas hydrate
dissociated gas
aerobic oxidation
biodegradation
carbon and hydrogen isotopefractionation
