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.

协作研究：孟加拉国水上动物的Humics和铁氧化还原反应。 Zheng，D。Nemergut和D. McKnightelele浓度在许多沉积含水层中的地下水中的砷浓度（AS）都在缺氧条件下发生，对世界某些地区的人类健康构成了重大威胁。尽管未完全解决Fe（III） - 氧化物还原的机理，但已调用了含氧Fe（III） - 氧化物的微生物还原以解释AS的富集。微生物Fe（III） - 氧化物还原的一个潜在重要因素是，称为腐殖质物质的复杂有机分子的可用性和丰度可以在微生物和Fe（III） - 氧化物之间穿梭电子。这项研究评估了腐殖质物质在孟加拉国含水层中释放的腐殖质在feiii-Reduction中的作用，并在各种化学，空间和季节性梯度上发挥作用。假设季节性可变充电的化学性能是结构微生物群落的。反过来，假设微生物可以通过humics通过电子穿梭来调节局部降低局部降低速率，最终会影响到含水层的释放。该研究旨在确定Fe（III）氧化物还原是否会通过充电到浅水含水层时的腐殖质物质的电子穿梭来增强，并且如果电子穿梭在通常的有机贫困沉积物中受到限制。该研究在孟加拉国的Araihazar举行，浅水含水层显示了一系列的AS浓度和补给率。除了测定水和沉积物的化学物质（pH，EH，DO，MN，MN，MN，硫酸盐，硫酸盐，硫酸盐，硫酸盐，硫酸盐，硫酸盐，ASIII/ASV）外，该研究还采用荧光光谱来评估田间的氧化还原状态，以评估田间的氧化还原状态，用于微生物群体群体群体的特征。泥沙电子穿梭能力也将使用田间启动的孵育来测量。这项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），以增强对季节性洪水，农业和人类废物的系统降低机制的理解，同时影响碳动力学。由于减少额外的许多重要的自然生物地球化学后果，我们的研究将对其他三角洲环境产生影响，远远超出了对流动性的解释。