(EGB) Understanding and Modeling Hydrogeological, Microbiological, and Geochemical Processes that Control Groundwater Redox Zonation

含水层生物地球化学中最基本的问题之一是溶质运移和地球化学过程与微生物活动结合影响氧化还原带时空变化的机制。我们将在受石油烃污染的浅层砂质含水层中研究这些机制，该含水层在季节时间尺度上表现出不同的氧化还原带。该地点氧化还原带的动态性质使我们能够研究水文地质、地球化学和微生物过程之间的相互作用，并测试关于(1)控制地下水从一个区域到另一个区域演化的反应和(2)控制氧化还原带时空维度的因素的假设。通过现场和实验室研究，结合三个学科的耦合信息，构建氧化还原带演化的三维瞬态反应流和输运模型。这项跨学科研究的目标是：(1)定量评估在给定区域内影响氧化还原过程的水文地质、地球化学和微生物限制；(2)利用这些约束条件来确定描述地下水从一个区域到另一个区域演化的一系列反应；(3)将反应集与动态流动和输运模型相结合，模拟场址各氧化还原带的尺度，并比较地下水水文事件的预测和观测结果，如长时间的高水位或低水位。这些目标将通过现场采样（季节和事件）、实验室分析和实验、现场水文地质、微生物和地球化学分析以及水文地球化学建模来实现。该方法的独特之处在于：(1)结合地球物理和水文地质资料估算含水层性质；(2)采用16S rRNA核酸探针杂交测定微生物分子量、脂肪酸甲酯谱和16S rDNA限制性内切分析（ARDRA）测定群落结构；(3)根据H2气体浓度估算氧化还原状态；(4)利用原位采样器和实验评估矿物与微生物的相互作用；(5)结合反应流输模型中的地球化学反应集和微生物反应集，定量解释研究点观测到的水化学。这种方法将通过提高对导致原始和受污染含水层氧化还原带的物理、化学和生物过程之间相互作用的理解使每个学科受益，并将为设计适当的采样、监测和补救方法提供有价值的基本信息。该提案是根据环境地球化学和生物地球化学招标NSF 96-152提交的，由地球科学部和环境生物部联合资助。

9708487 Long One of the most fundamental issues in aquifer biogeochemistry concerns the mechanisms by which solute transport and geochemical processes combine with microbiological activity to influence spatial and temporal variations in redox zonation. We will examine these mechanisms in a shallow sandy aquifer contaminated with petroleum hydrocarbons, which has exhibited redox zonation that varies on seasonal time scales. The dynamic nature of redox zonation at this site allows us to examine the interaction among hydrogeological, geochemical, and microbiological processes, and test hypotheses regarding the (1) reactions that govern groundwater evolution from zone to zone and (2) factors which control the spatial and temporal dimensions of redox zones. By coupling information gained from the three disciplines, through field and laboratory research, a three-dimensional, transient reactive flow and transport model for the evolution of redox zonation will be constructed. The goals of this interdisciplinary study are to (1) quantitatively assess hydrogeologic, geochemical and microbiological constraints that influence redox processes within a given zone; (2) use these constraints to identify sets of reactions that describe the evolution of groundwater from one zone to another; and (3) integrate the reaction sets with a dynamic flow and transport model to simulate past observations regarding the dimensions of various redox zones at the site, as well as compare the predicted and observed outcome of groundwater hydrologic events such as prolonged periods of high or low water table. These goals will be achieved through field sampling (seasonal and event), laboratory analysis and experimentation, in-situ hydrolgeological, microbiological, and geochemical analyses, and hydrogeochemical modeling. Unique aspects of the methods include: (1) combining geophysical and hydrolgeological data to estimate aquifer properties; (2) using 16S rRNA nucleic acid probe hybridization to determine microbial abu ndance, fatty acid methyl ester profiles and 16S rDNA restriction analysis (ARDRA) to determine community structure; (3) estimating redox state from H2 gas concentrations; (4) assessing minerals-microbial interactions using in-situ samplers and experiments; and (5) combing geochemical and microbiological reaction sets in a reactive flow and transport model to quantitatively account for observed water chemistry at the study site. This approach will benefit each discipline through improved understanding of the interaction among physical, chemical and biological processes that lead to redox zonation in both pristine and contaminated aquifers, and will provide fundamental information valuable to the design of appropriate sampling, monitoring and remediation methodologies. This proposal was submitted in response to the Environmental Geochemistry and Biogeochemistry solicitation NSF 96-152, and is being funded jointly by the Divisions of Earth Sciences and Environmental Biology.