While organic matter (OM) interactions in the water column prevent iron (Fe) precipitation and sedimentation, Fe also acts as a precursor of aggregation and a vector of OM to sediments. This study aims to characterize Fe–OM interactions to understand the role of Fe in promoting aggregation and transport of OM. Samples of Fe and OM were collected from water, settling material, and sediment along a gradient starting from the inlet and continuing offshore within a boreal lake. Fe speciation was determined using X-ray absorption spectroscopy (XAS), and the chemical composition of OM was assessed using Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT IR) and Nuclear magnetic resonance spectroscopy (NMR). The results show a decrease in Fe and OM concentrations in the water column with increasing distance from the inlet. Winter sampling revealed a shift in Fe speciation from dominance of organically complexed Fe to an increase in Fe(oxy)hydroxide, accompanied by a loss of aromatic and carboxylate function of OM. Summer sampling revealed no significant changes along the gradient, with Fe(oxy)hydroxide and carbohydrates dominating the water phase. Interestingly, settling particles and surface sediments were dominated by Fe(oxy)hydroxides and aliphatic OM. We propose that phototransformation may be an important process that influences the interaction between Fe and OM and, as a consequence, their fate along the spatial gradient. Our study suggests a photochemically induced loss of carboxylate groups, reflected by an increased carbohydrate-to-carboxylate ratio along the gradient, particularly in winter, and generally lower levels during summer. Loss of carboxylate function promotes the formation of Fe(oxy)hydroxides, which in turn, facilitates the aggregation and sinking of OM, particularly aliphatic components. These insights contribute to a broader understanding of carbon cycling and storage in lakes. Future studies should assess the significance of photochemical processes to OM burial and it how may change given trends in Fe and OM in northern regions.

虽然水柱中的有机物 （OM） 相互作用会阻止铁 （Fe） 沉淀和沉淀，但 Fe 也是聚集的前体和 OM 到沉积物的载体。本研究旨在表征 Fe-OM 相互作用，以了解 Fe 在促进 OM 聚集和运输中的作用。Fe 和 OM 的样品是从水、沉降材料和沉积物中收集的，沿着从入口开始一直延伸到北方湖内的近海的梯度。使用 X 射线吸收光谱 （XAS） 确定 Fe 形态，并使用漫反射红外傅里叶变换光谱 （DRIFT IR） 和核磁共振光谱 （NMR） 评估 OM 的化学成分。结果表明，随着与入口距离的增加，水柱中的 Fe 和 OM 浓度降低。冬季取样显示，Fe 形态从有机络合 Fe 的主导转变为氢氧化铁的增加，伴随着 OM 的芳香族和羧酸盐功能的丧失。夏季取样显示沿梯度没有显着变化，Fe（氧）氢氧化物和碳水化合物在水相中占主导地位。有趣的是，沉降颗粒和表面沉积物以氢氧化铁和脂肪族 OM 为主。我们提出光转化可能是一个重要的过程，它影响 Fe 和 OM 之间的相互作用，因此影响它们沿空间梯度的命运。我们的研究表明，光化学诱导的羧酸盐基团损失，反映在沿梯度的碳水化合物与羧酸盐比率增加上，尤其是在冬季，而夏季的水平通常较低。 羧酸盐功能的丧失促进了 Fe（氧基）氢氧化物的形成，这反过来又促进了 OM 的聚集和下沉，尤其是脂肪族成分。这些见解有助于更广泛地了解湖泊中的碳循环和储存。未来的研究应评估光化学过程对 OM 埋藏的重要性，以及鉴于北部地区 Fe 和 OM 的趋势，它可能会如何变化。