作为地层中含量最多和分布最广的金属元素、生化性质活泼的变价元素和生命必需元素，铁（Fe）不仅是衡量地下水质量的指标之一，也是环境地球科学关注的主要元素，甚至是多种元素地球化学循环的纽带，因此备受关注。已有证据表明，全球范围内部分地下水中铁的含量在近些年有升高趋势，且与环境中溶解性有机质（DOM）含量的升高密切相关。然而，铁和碳元素的地球化学循环均极其复杂，而且彼此相偶联，并被环境功能微生物介导，导致溶解性有机质和铁的相互作用尤其是在氧化还原界面上耦合转化的机理尚不明确，相互作用对含水介质中铁的动员作用也不清楚。这不仅影响对地下水化学和水质演化规律的预测，也限制了以含铁矿物为核心的地下水污染自然衰减修复技术的应用。本研究以典型的高浓度铁地下水分布区——松花江河漫滩试验场地研究区，联合应用野外调查、动力学控制实验、微观表征、室内动态渗流实验、理论计算和水文地球化学模拟等手段和方法，揭示了含水层中溶解性有机质和含铁矿物之间的相互作用及其对铁释放的影响。该结果证明铁和碳元素的地球化学循环是互相影响的，含水介质中的铁（氢）氧化物作为氧化剂有氧化地下水中还原性污染物的潜力，并且铁在溶解性有机质与活性矿物的相互作用下向地下水中释放。本研究丰富了铁-碳反应循环及其环境效应方面的研究成果，进一步推进了水化学和水质演化预测，也可推动含铁矿物在地下水污染监控式自然衰减修复技术中的应用。主要研究成果如下：（1）研究区河岸过滤带氧化还原环境、理化指标及微生物作用强度等分布存在较大差异。含水介质中总Fe含量范围为6.9~31.2 g/kg，Fe的形态和含量主要赋存在EFC-Fe中，其含量分布特征与垂向上的酸碱度和氧化还原环境相关，其中FeMnOx-Fe和OM-Fe的地球化学活性相对较强，能够通过还原溶解等作用使铁从固相进入地下水中。由于河岸过滤带强烈的水力交换作用导致含水介质中的微生物群落结构呈现出显著差异，同时，微生物的种类丰度和多样性指数也展现出明显的空间异质性。含水介质中铁氧化菌（IOB）参与地下水中Fe²⁺的生物转化和循环，介质中优势菌种的功能与活性与地下水环境协同演化，说明地下水入渗过程中Fe发生了生物地球化学转化。（2）与仅通过天然地下水作用获得的Fe浓度相比，DOM的存在显著激活了含水介质中Fe的活性，从而使地下水中Fe的浓度呈指数级增加。添加大分子有机物的实验组比小分子有机物实验组Fe释放的效果更为显著，过程中含铁矿物作为氧化剂，有机物作为还原剂，发生了一系列氧化还原作用。实验初期浸出液中Fe²⁺是优势铁物种（Fe²⁺/总Fe>0.5），之后Fe³⁺成为系统中的优势铁物种。DOM还能改变介质中Fe的形态，促进了介质中FeMnOx-Fe、Carb-Fe和EXC-Fe向水环境的释放，同时向OM-Fe和RES-Fe转化，这种现象在微生物作用下更为显著。含水介质中铁的活化作用受到微生物的正面影响，非生物介导下L-trp、FA和HA处理组中沉积物的变化质量与EFC-Fe的占比分别为14.6%、39.2%和40%，生物介导下与EFC-Fe的占比分别为32.7%、40%和45%，微生物介导下Fe的活化作用更为彻底。（3）不同深度含水介质中Fe释放的浓度曲线呈现出相似的变化趋势，且随着含水介质深度增加，粒径逐渐变大，Fe的单位释放量逐渐变小。单因素影响实验结果表明，酸性环境（pH=3.0）和碱性环境（pH=12.0）、温度升高、低DO分压、DOM浓度升高和外加离子浓度的升高的条件下Fe的活化作用更为明显，其中，碱性和低DO分压环境氧化还原作用显著，能促进更多的Fe²⁺转化为Fe³⁺，反之则抑制。方差分析的结果显示模型的分析判定系数（R²）为0.9731，基于响应曲面法识别出影响Fe释放的主控因子为pH、DOM浓度、DO和温度，pH与DOM浓度和DO与温度这两对因素间的交互作用显著影响Fe的释放。（4）DOM与自然界中铁矿物间的反应机制表明，实验过程中DOM为土壤氧化铁矿物的还原作用提供了碳源，而氧化铁表面的活性位点又引起有机质的分子组成转化及重新构型。pH对DOM的去除有显著影响，低pH的环境下DOM的降解效率更高，有利于DOM的吸附和进一步氧化。反应后的矿物表面覆盖了大量的C元素，Fe、C和O元素发生了动态团聚，DOM在矿物表面的分布方式表明二者间的络合作用主要是生成内圈络合物。反应后有机物的FTIR光谱显示发生反应的主要官能团包括C=C，C=O、C-H、N-H、C-O和COOH。此外，DOM与矿物反应过程中同时存在协同和拮抗，Fe释放的同时DOM发生了分解和腐殖化，高O/C分子被分解为低O/C的化合物，该过程为Fe的释放提供了微观的证据，同时也为地下水污染中铁基材料的研发和应用提供理论基础。（5）动态土柱模拟实验结果表明，氧化还原环境指标的空间变化影响了地下水的水化学特征，淋滤过程中DOM使Fe从非溶解态向溶解态转变被释放到地下水中。不同实验条件下Fe释放浓度的变化和分布特征相似，垂向上从上到下呈现出随采样深度而升高的趋势。Fe的释放浓度依赖于沉积物、DOM和功能微生物之间的平均接触时间和进水浓度。受接触时间和有机物浓度效应影响，2.4 L/d和1200 mg/L淋滤条件下Fe的释放能力分别增强26.7%和64.4%，Fe²⁺→Fe³⁺的转化率分别增强15.3%和23.2%。给水的有机成分控制着浸出液中Fe的浓度，EEM-PARAFAC分析将数据集聚类为6个有机质组分分量模型，地下水中Fe的浓度与原水中的荧光参数（HIX、BIX和FIX）呈正相关，表明与微生物代谢有关的腐殖质组分对Fe的释放具有主导作用。低流速和高进水浓度的条件强化了渗滤过程中的还原环境，从而使土柱内Fe的还原作用与一些功能性的优势微生物的数量和空间分布特征之间存在较强的相关性。反应后IOB和有机物降解细菌的平均累积相对丰度分别下降了11.2%、20.4%和16.9%、21.1%。PHREEQC模拟结果显示，模拟系统启动7.5年后，研究区地下水应出现铁污染。（6）结合研究内容，本文提出了DOM与介质中Fe的相互作用过程中存在的三种还原机制：Fe-DOM表面络合物可认为是配体控制溶解的前驱体，DOM可通过形成内圈络合物提高Fe的水溶性，从而导致了含Fe矿物表面的Fe脱离；Carb-Fe，EXC-Fe和FeMnOx-Fe的氧化还原溶解也是含水介质中Fe活化进入到地下水中的重要原因；在有机物的影响下，微生物介导的铁氧化物还原溶解与沉淀过程可能是系统内Fe元素释放的关键机制。

As the most abundant and widely distributed metallic element, biochemically active variable element, and essential element, iron (Fe) is not only one of the indicators of groundwater quality, but also one of the major elements of concern to environmental geosciences, and even a link in the geochemical cycling of various elements, and thus attracts much attention. There is evidence that Fe levels in some groundwaters have been increasing globally in recent years and are strongly correlated with elevated levels of dissolved organic matter (DOM) in the environment. However, the geochemical cycles of both Fe and carbon elements are extremely complex and coupled to each other and mediated by environmentally functional microorganisms, leading to unclear mechanisms of coupled transformations of DOM-Fe interactions especially at redox interfaces, and the role of the interactions in mobilizing iron in aqueous media is not known. This not only affects the prediction of groundwater chemistry and water quality evolution patterns, but also limits the application of natural attenuation remediation techniques for groundwater contamination centered on iron-bearing minerals.In this study, the Songnen Plain, a typical distribution area of high Fe groundwater, was taken as the study area, and field investigation, kinetic control experiments, microscopic characterization, indoor dynamic seepage experiments, theoretical calculations, and hydrogeochemical simulations were jointly applied to reveal the interactions between DOM and Fe-bearing minerals in the aquifer and their effects on the Fe release in the aquifer. This result demonstrates that the geochemical cycling of elements Fe and C interact with each other and that Fe (hydrogen) oxides in aqueous media have the potential to act as oxidizing agents to oxidize reducing contaminants in groundwater, and Fe is released into groundwater under the interaction between DOM and active minerals. This study enriches the research results on Fe-C coupled cycle and its environmental effects, it also further promotes the prediction of hydrochemistry and water quality evolution, and may also promote the application of Fe-bearing minerals in groundwater contamination monitoring-based natural attenuation remediation technology. The main research results are as follows:(1) There are differences in the distribution of redox environment, physicochemical indicators and intensity of microbial action in the riparian filtration zone in the study area. The total Fe content in the water-bearing medium ranges from 6.9 to 31.2 g/kg, and the morphology and content of Fe are mainly endowed in EFC-Fe, and the distribution characteristics of the content are related to the acidity and alkalinity of the vertical upward and the redox environment, among which the geochemical activity of FeMnOx-Fe and OM-Fe is relatively strong, and it is able to make the Fe enter into the groundwater from the solid phase by reducing and dissolving and other actions. The microbial community structure of the aquatic media was significantly different due to the strong hydraulic exchange effect in the riparian filtration zone, and the abundance and diversity of microbial species showed strong spatial heterogeneity. Typical IOBs in the aquatic media were involved in the biotransformation and cycling of Fe²⁺ in the sediment and groundwater, and the function and activity of dominant bacterial species in the media evolved synergistically with the groundwater environment, suggesting that biogeochemical transformations of iron occurred in the infiltration process of the groundwater.(2) The presence of DOM significantly activated the activity of Fe in the aqueous medium compared to the Fe concentration obtained only through the action of natural groundwater, which led to an exponential increase in the concentration of Fe in the groundwater, and the experimental group with the addition of large-molecule organics was more effective in releasing Fe than the experimental group with small-molecule organics, with a series of redox actions occurring during the process, in which iron-containing minerals acted as oxidizing agents and organics acted as reductants. Fe²⁺ was the dominant Fe species in the leachate at the beginning of the experiment (Fe²⁺/total Fe > 0.5), after which Fe³⁺ became the dominant Fe species in the system. DOM also altered the morphology of Fe in the medium, and DOM facilitated the release of FeMnOx-Fe, Carb-Fe, and EXC-Fe from the medium to the aqueous environment, with a simultaneous conversion to OM-Fe and RES-Fe, and this phenomenon results were more significant under microbial action, and the activation of Fe in aqueous media was positively influenced by microbes, with 14.6%, 39.2%, and 40% of the changed mass of sediment to EFC-Fe in the abiotic-mediated L-trp, FA, and HA treatment groups, respectively, and 32.7%, 40%, and 45% of the biologically mediated to EFC-Fe, respectively, with microbial The activation of Fe was more complete under microbial mediation.(3) The concentration profiles of Fe release from aqueous media of different depths showed similar trends, and the particle size of Fe gradually became larger and the unit release gradually became smaller with the increase of the depth of aqueous media. The results of one-factor influence experiments showed that the activation of Fe was more obvious in acidic (pH=3.0) and alkaline (pH=12.0) environments, elevated temperature, low DO partial pressure, elevated DOM concentration, and elevated concentration of externally applied ions, among which, alkaline and low DO partial pressure environments had a significant redox effect, which could promote the conversion of more Fe²⁺ to Fe³⁺, and vice versa, which was inhibited. The results of the analysis of variance show that the analysis judgment coefficient (R²) of the model is 0.9731. Based on the response surface methodology, the main controlling factors affecting the release of Fe were identified as pH, DOM concentration, DO, and temperature, and the interactions between the pairs of factors, namely, pH and DOM concentration, and DO and temperature, significantly affected the release of Fe.(4) The mutual feeding mechanism between DOM and iron minerals in nature suggests that DOM provides a carbon source for the reduction of soil iron oxide minerals during the experiments, while the active sites on the surface of iron oxides cause the transformation of the molecular composition and reconfiguration of the organic matter. The pH had a significant effect on the removal of DOM, and the degradation of DOM was more efficient at low pH, which favored the adsorption and further oxidation of DOM. The surface of the reacted minerals was covered with a large amount of elemental C. Dynamic agglomeration of elements Fe, C and O occurred, and the way DOM was distributed on the mineral surface indicated that the complexation between the two was mainly to generate inner-circle complexes. FTIR spectra of the reacted organic matter showed that the major functional groups that reacted included C=C, C=O, C-H, N-H, C-O, and COOH. In addition, there were both synergistic and antagonistic processes during the reaction of DOM with the minerals, and Fe release was accompanied by DOM decomposition and humification, with the high O/C molecules being decomposed into low O/C compounds, a process that provides microscopic evidence, at the same time, it also provides a theoretical basis for the research and application of iron-based materials in groundwater pollution.(5) The results of dynamic soil column simulation experiments show that the spatial variation of redox environmental indicators affects the hydrochemical characteristics of groundwater, and that the DOM releases Fe from the solid form to groundwater during the leaching process, and the spatial distributions of Fe releases under different experimental conditions are somewhat similar, with a tendency to increase vertically with the increase in sampling depth. The Fe release concentration was dependent on the average contact time and influent concentration between sediment, DOM and functional microorganisms. The Fe release capacity was enhanced by 26.7% and 64.4% for 2.4 L/d and 1200 mg/L leach conditions, respectively, and the Fe²⁺→Fe³⁺ conversion was enhanced by 15.3% and 23.2%, respectively, as affected by the effects of contact time and organic matter concentration. The organic composition of the feed water controlled the concentration of Fe in the leachate. EEM-PARAFAC analysis clustered the dataset into six component models of organic matter fractions, the concentration of Fe was positively correlated with the fluorescence parameters (HIX, BIX and FIX) in the raw water, which indicated that humus fractions related to microbial metabolism had a dominant role in the release of Fe, the conditions of low flow rate and high influent concentration strengthened the reduction environment in the infiltration process, and the content of functional dominant bacterial species and the The spatial distribution characteristics correlated well with the reduction of Fe. The average cumulative relative abundance of IOB and organic matter-degrading bacteria decreased by 11.2%, 20.4% and 16.9%, 21.1%, respectively, after the reaction. PHREEQC modeling results indicate that iron contamination should occur in groundwater in the study area 7.5 years after the modeling system is activated.(6) Combined with the study, this paper proposes three possible reduction mechanisms during the interaction of DOM with Fe in the medium: the Fe-DOM surface complex can be considered as a precursor for ligand-controlled solubilization, and DOM can increase the aqueous solubility of Fe through the formation of inner-circle complexes, which results in the detachment of Fe from the surface of Fe-bearing minerals; Redox dissolution of Carb-Fe, EXC-Fe, and FeMnOx-Fe is the main release mechanism for Fe migration from aquifer media to groundwater; microbial-mediated reductive dissolution and precipitation of Fe oxides in the presence of organic matter may be the main mechanism for Fe release in the system.