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题名: 水稻土中铁的微生物厌氧氧化还原循环对砷运移的影响
作者: 王兆苏
学位类别: 硕士
答辩日期: 2010
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 朱永官
关键词: 铁的厌氧生物氧化还原循环 ; 依赖硝酸盐的铁氧化菌 ; 异化铁还原菌 ; ; 水稻土
中文摘要:       水稻是地球上最重要的农作物,全球拥有1.43亿公顷的种植面积,而且其中75%是淹水种植。在水稻土系统中存在不同的好氧-厌氧界面:表层(几毫米)水稻土和根际水稻土分别由于大气溶解氧和根系放氧而形成的好氧环境,而其他土体为厌氧环境。在这个特殊的生态环境中,铁离子由于具有活跃的价态变化,在水稻土不同的环境微区中,进行活跃的氧化还原生物化学反应。而铁矿作为普遍存在于环境中的一种矿物,是影响砷迁移转化的重要因素。 本文通过富集培养的手段探讨砷污染水稻土中铁的氧化还原循环,及对As迁移的影响。 1.水稻土中铁的微生物厌氧氧化还原循环对砷运移的影响 本研究证明了水稻土中存在铁的厌氧生物化学循环:三价铁(人工合成针铁矿)在厌氧条件下被逐渐还原成二价铁(约6.48 mmol·L-1);铁还原过程结束并外源添加硝酸根(2.5 mmol·L-1)时,培养基中新生的二价铁在依赖于硝酸根的铁氧化菌的作用下被氧化(7天内80%被氧化);当提供新的电子供体5 mmol·L-1乙酸钠时,生物合成的铁矿重新被还原。在铁氧化还原循环过程中,随着铁的还原,培养基中砷的浓度不断增加(增加了约40 ng·L-1),反之,当铁逐渐氧化的同时不断地吸附固定培养基中的砷,达到砷释放之前的浓度水平(约10 ng·L-1)。在铁的厌氧氧化阶段,铁氧化的同时硝酸根被还原,培养基中积累了约1.2 mmol·L-1 NH4+和0.35 mmol·L-1 NO2-。因此,厌氧水稻土中可以进行完整的铁氧化还原循环,同时这个循环过程耦合了氮和砷的迁移转化。 2.微生物铁还原对砷运移的影响 异化铁还原菌群既可以利用溶解态的柠檬酸铁也可以利用难溶的水合铁矿沉淀,而柠檬酸铁的还原效率明显高于水合铁矿(约相差15 mmol·L-1)。在以柠檬酸铁为铁源的含砷培养过程中,As(V)对于异化铁还原菌群铁还原过程具有一定的抑制作用,而溶液中的As浓度随着柠檬酸铁还原产生沉淀而显著降低。 3.微生物铁氧化对砷运移的影响 外源添加的As(III)在依赖硝酸盐的铁氧化菌群的铁氧化过程中氧化生成As(V),并且被生成的铁氧化物吸附共沉淀;而As(III)对Fe(II)的氧化具有一定的抑制作用。因此,微生物的铁氧化过程对降低As污染对人体健康的风险有着重要的意义。
英文摘要:       The rice paddy microcosm is a useful system for the description and prediction of microbiological and biogeochemical processes in wetland habitats. Oxygen deplete rapidly in a few millimeters beneath the soil surface, leaving the bulk soil anoxic. However, oxygen is considered to leak from aerenchymatous tissue in rice creating an oxic rhizosphere within the anoxic bulk soil. Microbially catalyzed, anaerobic Fe(II) oxidation represents a biological mechanism promoting the reoxidation of Fe(II) in anoxic environments, potentially contributing to a dynamic, anoxic Fe redox cycle by microorganisms. The precipitation of biogenic Fe(III) oxides provides a mechanism for the immobilization of heavy metals and metalloids through coprecipitation or physical envelopment or reactive surface with an adsorptive affinity for anions and cations. The enrichment culture of paddy microorganisms was used to investigate the potential microbially mediated anaerobic redox cycling of iron and the effect on arsenic mobility by the cycling. The redox cycling of iron was simulated by the enrichment as follows: 1) Goethite (Fe(III)) was reduced immediately following inoculation of Artificial Groundwater medium (AGW) with paddy under anaerobic condition; 2) addition of NO3- after Fe(III) reduction ceased resulted in the immediate oxidation of Fe(II) coupled to reduction of NO3-.3) the fresh Fe(III) minerals originated from the nitrate dependent iron oxidation were reduced again when new electron donor of acetate was supplied to the enrichment. Arsenic was released when iron minerals were reduced, and it was immobilized by absorbing to minerals when Fe(II) was oxidized. Nitrate reduction was coupled to Fe(II) oxidation during anaerobic oxidation of Fe(II), which resulted in the accumulation of NH4+ and NO2-. These results indicated that the paddy contained microorganisms which were capable of dissimilatory Fe(III) and oxidation of Fe(II) with reduction of NO3-, which potentially drove the microbially mediated redox cycling of iron, and which significantly affected the transformation of N and As. The enrichment culture of dissimilatory ferric iron reducers could both utilize soluble citrate ferric and solid HFO. The reduction efficiency of ferric citrate was higher than HFO.The citrate ferric was used as iron source and the bacteria cultured in medium with As(V). The utilization of citrate ferric and quantity of total As were monitored. The results indicated that As(V) could inhibit the reduction of citrate ferric, and the As concentration in the solution was significantly decreased with the production of precipitate. The NO3-depended Fe-oxidizing bacteria were enriched from paddy rice and inoculated under anaerobic circumstance to observe the effect of Fe(II)-oxidizing process on As mobility. The results mainly showed that in Fe(II)-oxidizing process, As(III) was oxidized to As(V) and was co-precipitated by the Fe(III) oxide generated. The oxidizing rate of Fe(II) was restrained by As(III).
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/35045
Appears in Collections:中澳联合土壤环境研究室_学位论文

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Recommended Citation:
王兆苏. 水稻土中铁的微生物厌氧氧化还原循环对砷运移的影响[D]. 北京. 中国科学院研究生院. 2010.
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