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

9708487长期以来，含水层生物地球化学中最基本的问题之一涉及溶质运移和地球化学过程与微生物活动相结合影响氧化还原分带的时空变化的机制。我们将在被石油碳氢化合物污染的浅层砂质含水层中研究这些机制，该含水层表现出在季节性时间尺度上不同的氧化还原带状分布。该地点氧化还原分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，并检验关于(1)控制地下水从一个带到另一个带的反应和(2)控制氧化还原带的空间和时间维度的因素的假设。结合这三个学科的信息，通过野外和实验室研究，将建立氧化还原带状演化的三维、瞬时反应流动和输运模型。这项跨学科研究的目标是：(1)定量评估影响特定区域内氧化还原过程的水文地质、地球化学和微生物制约因素；(2)利用这些制约因素确定描述地下水从一个区域向另一个区域演化的反应集合；(3)将反应集合与动态流动和运移模型相结合，以模拟过去对现场不同氧化还原带规模的观测，并比较地下水水文事件的预测和观测结果，例如长期的高水位或低水位。这些目标将通过实地采样(季节性和事件)、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模拟来实现。这些方法的独特方面包括：(1)结合地球物理和水文地质数据来估计含水层性质；(2)利用16S rRNA核酸探针杂交来确定微生物多样性、脂肪酸甲酯分布和16S rDNA限制分析(ARDRA)来确定群落结构；(3)根据H2气体浓度估计氧化还原状态；(4)使用现场采样器和实验来评估矿物-微生物相互作用；以及(5)在反应流动和传输模型中结合地球化学反应和微生物反应集，以定量解释研究地点观察到的水化学。这一办法将使每个学科受益，因为它将更好地了解导致在原始含水层和受污染含水层中进行氧化还原分区的物理、化学和生物过程之间的相互作用，并将提供对设计适当的采样、监测和补救方法有价值的基本信息。这项建议是应环境地球化学和生物地球化学征集NSF 96-152的要求提交的，由地球科学部和环境生物学部共同资助。

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.