Coupling and competitiveness of iron-, sulfate-, and CO2-reduction along gradients

生物地球化学梯度与有机物和污染物周转的相关性还知之甚少。本研究旨在识别和量化的相互作用的不同氧化还原过程沿着梯度。铁，硫酸盐还原和产甲烷的相互作用将在控制批次和柱实验中进行研究。将评估限制使用这些电子受体的可及性和能量产率的因素，如铁氧化物的钝化，铁氧化物上硫化氢的再氧化。然后将描述这些限制对特定过程的竞争力的影响。将特别关注以前以铁和硫酸盐还原条件为特征的系统中产甲烷条件的演变。由于产甲烷条件主要是从微生态位演化而来，因此建立了研究微生态位存在、演化和稳定性的方法。为此，将使用Gibbs自由能计算、同位素分馏和示踪剂测量以及代谢中间体（小样本池大小）和终产物（大样本池大小）的质量平衡的组合。将比较使用微电极（毫米级），溶质和气体（厘米级）和质量流平衡（柱/反应器级）的微取样装置在不同尺度上测量这些参数，以表征有机物降解途径和电子流的单位体积。特别感兴趣的将是氧化还原活性腐殖物质对所涉及的终端电子接受过程的竞争力的影响，无论是作为电子穿梭或直接提供电子接受能力。这将使用荧光光谱和平行因子分析（PARAFAC）的获得的光谱进行研究。我们期望，研究结果将提供一个基础，以改善反应输运模型的厌氧过程在含水层和沉积物。

The relevance of biogeochemical gradients for turnover of organic matter and contaminants is yet poorly understood. This study aims at the identification and quantification of the interaction of different redox processes along gradients. The interaction of iron-, and sulfate reduction and methanogenesis will be studied in controlled batch and column experiments. Factors constraining the accessibility and the energy yield from the use of these electron acceptors will be evaluated, such as passivation of iron oxides, re-oxidation of hydrogen sulfide on iron oxides. The impact of these constraints on the competitiveness of the particular process will then be described. Special focus will be put on the evolution of methanogenic conditions in systems formerly characterized by iron and sulfate reducing condition. As methanogenic conditions mostly evolve from micro-niches, methods to study the existence, evolution and stability of such micro-niches will be established. To this end, a combination of Gibbs’ free energy calculations, isotope fractionation and tracer measurements, and mass balances of metabolic intermediates (small pool sizes) and end products (large pool sizes) will be used. Measurements of these parameters on different scales using microelectrodes (mm scale), micro sampling devices for solutes and gases (cm scale) and mass flow balancing (column/reactor scale) will be compared to characterize unit volumes for organic matter degradation pathways and electron flow. Of particular interest will be the impact of redox active humic substances on the competitiveness of involved terminal electron accepting processes, either acting as electron shuttles or directly providing electron accepting capacity. This will be studied using fluorescence spectroscopy and parallel factor analysis (PARAFAC) of the gained spectra. We expect that the results will provide a basis for improving reactive transport models of anaerobic processes in aquifers and sediments.