Collaborative Research: Humics and Iron Redox Reactions in Bangladesh Aquifer

合作研究：孟加拉国含水层中的腐殖质和铁氧化还原反应

• 批准号: 0738910
• 负责人: Diane McKnight
• 金额: $ 36.79万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-03-01 至 2012-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738910&HistoricalAwards=false
• 关键词: Collaborative; Research; Humics; Iron; Redox

Collaborative Research: Humics and Iron Redox Reactions in Bangladesh AquiferY. Zheng, D. Nemergut and D. McKnightElevated concentrations of arsenic (As) in groundwater in many sedimentary aquifers have been observed to occur under anoxic conditions, posing significant threats to human health in some regions of the world. Microbial reduction of As-bearing Fe(III)-oxides has been invoked to explain the enrichment of As, although the mechanisms of Fe(III)-oxide reduction are not fully resolved. One potentially important factor in microbial Fe(III)-oxide reduction is the availability and abundance of complex organic molecules called humic substances which can shuttle electrons between microbes and Fe(III)-oxides. This study evaluates the role of electron-shuttling by humic substances in FeIII-reduction and subsequent As release in Bangladesh aquifers over a variety of chemical, spatial and seasonal gradients. The chemistry of the seasonally variable recharge is hypothesized to structure microbial communities. The microbes, in turn, are hypothesized to regulate local rates of Fe reduction through electron shuttling by humics, ultimately influencing As release to the aquifer. The study seeks to ascertain if Fe(III) oxide reduction is enhanced by electron shuttling of humic substances during recharge to the shallow aquifer, and if electron shuttling is limited in the generally organic-poor sediment further down the flow path . The study takes place in Araihazar, Bangladesh, where the shallow aquifer has shown a range of As concentrations and recharges rates. In addition to assaying the chemical (pH, Eh, DO, nitrate, Fe, Mn, sulphate) and redox properties (FeII/FeIII, AsIII/AsV) of water and sediment, the study employs fluorescence spectroscopy to evaluate redox state of humics in the field and molecular phylogenetic methods for microbial community characterization. Sediment electron shuttling capacities will also be measured using incubation initiated in the field. This study provides critical data (e.g., proxies for concentrations of electron shuttling compounds and microbial community shifts) to enhance the understanding of the mechanisms of Fe(III) reduction in a system where seasonal flooding, agriculture, and human waste are simultaneously influencing carbon dynamics. Because of the many important natural biogeochemical consequences of Fe-reduction, our study will have implications for other deltaic environments far beyond the interpretation of As mobility.

合作研究：孟加拉含水层中的腐殖酸和铁氧化还原反应。Zheng，L.等，中国粘蝇D. Nemergut和D.据观察，在缺氧条件下，许多沉积含水层的地下水中砷（As）浓度升高，对世界某些地区的人类健康构成重大威胁。微生物还原的As轴承Fe（III）氧化物已被援引来解释富集的As，虽然Fe（III）氧化物还原的机制还没有完全解决。微生物Fe（III）-氧化物还原中的一个潜在重要因素是称为腐殖物质的复杂有机分子的可用性和丰度，其可以在微生物和Fe（III）-氧化物之间穿梭电子。本研究评估的作用，电子穿梭腐殖物质在FeIII还原和随后的释放在孟加拉国含水层在各种化学，空间和季节梯度。季节性变化的补给的化学假设结构微生物群落。反过来，微生物，假设通过电子穿梭腐殖酸调节当地的Fe还原率，最终影响作为释放到含水层。这项研究旨在确定，如果铁（三）氧化物的还原是加强电子穿梭的腐殖物质在补给过程中的浅含水层，如果电子穿梭是有限的，在一般的有机质贫乏的沉积物进一步下降的流动路径。这项研究发生在孟加拉国的Araihazar，那里的浅层含水层显示出一系列的As浓度和补给率。除了分析水和沉积物的化学（pH值，Eh，DO，硝酸盐，铁，锰，硫酸盐）和氧化还原特性（FeII/FeIII，AsIII/AsV），本研究采用荧光光谱法来评估氧化还原状态的腐殖酸在现场和微生物群落特征的分子系统发育方法。沉积物电子穿梭能力也将使用在现场启动的孵化来测量。该研究提供了关键数据（例如，电子穿梭化合物和微生物群落转移的浓度的代理），以提高对Fe（III）减少机制的理解，在一个系统中，季节性洪水，农业和人类废物同时影响碳动态。由于许多重要的自然生态地球化学的后果，铁还原，我们的研究将有影响其他三角洲环境远远超出了作为流动性的解释。