某石油污染地下水溶解性无机碳低异常的微生物地球化学成因探析

微生物地球化学作用往往导致石油污染场地地下水中溶解性无机碳(DIC)升高,而华北某石油污染场地地下水DIC低异常明显.为究其机理,在水文地球化学分析和16S rRNA基因高通量测序基础上,结合含水层结构及流场特征,剖析了地下水水化学和微生物两方面作用,辨识了地下水中DIC变异的主导因素,揭示了其中的生物地球化学作用的机理,发现该场地地下水DIC低异常可能与地下水中具有较高浓度钙镁离子和较高活性自养微生物有关,自养微生物代谢及诱导产生碳酸盐岩沉淀作用极可能是该场地地下水中DIC低异常的成因.推测机理为:Hydrogenophaga和Sedimentibacter等菌属微生物在氢化酶的作用下产氢气,Hydrogenophaga、Pseudomonas、Pseudoxanthomonas、Polynucleobacter等固碳微生物和产甲烷微生物利用氢气作为能源,将DIC合成有机碳,并产生碱性微环境,促使Ca~(2+)和Mg~(2+)与DIC反应形成碳酸钙镁沉淀.

Abnormally low dissolved inorganic carbon in petroleum contaminated groundwater caused by microbiological geochemistry

At petroleum contaminated sites, the interplay of microbiological and geochemical processes often causes the elevated level of dissolved inorganic carbon (DIC) in groundwater. However, abnormally low DIC has been found in a petroleum contaminated site located at North China Plain. To understand the underlying mechanism, we conducted a high throughput sequencing of 16S rRNA gene and a hydrogeochemical analysis, and examined the characteristics of local aquifer and groundwater flow to identify the factors and geochemical and microbiological mechanism dominating the variation in DIC levels. The results show that low DIC in the study site may be attributed to complex geochemical and microbiological processes associated with high concentration of Ca²⁺ and Mg²⁺ ions and active autotrophic bacteria in groundwater. The potential mechanism may be as follows:1 hydrogen-producing microorganisms, such as Hydrogenophaphaga and Sedimentibacter, produce hydrogen, which is then used as a source of energy by the autotrophic hydrogen-oxidizing bacteria, such as Hydrogenophaga, Pseudomonas, Pseudoxanthomonas, Polynucleobacter, to convert DIC into organic carbon, and 2the synthesis of organic carbon will result in an alkaline environment, which triggers the formation of calcium and magnesium carbonate precipitate.