Formation and dynamics of organo-mineral associations in redoximorphic soils

氧化还原型土壤的形成以氧化和还原条件的周期性变化为特征。铁锰氧化物的还原溶解和随后的氧化再形成导致了这些土壤中特征性的积累和贫化区以及矿物转化。我们申请的项目的目的是追溯有机矿物组合的形成和动态，即，受地下水影响的氧化还原型土壤中矿物质和有机相的变化。特别强调调查铁和锰的氧化物，在溶解有机物的存在下形成。有机物影响铁氧化物的结构特性，并通过与矿物相的相互作用而稳定分解。我们假设老化的铁氧化物氧化还原循环过程中更多的结晶相，其中对有机物的反应性的变化。我们假设优先吸附的芳香族化合物和空间分化的铁和锰氧化物连同相关的有机质。我们的目的是研究在溶解有机物质存在下矿物的原位形成，即，他们的关联，在高空间分辨率。这些有机-矿物协会的化学组成将其特征在于纳米尺度的二次离子质谱（NanoSIMS）在亚微米尺度和形态的Fe和Mn的X射线吸收光谱法（XANES/EXAFS）在微米尺度。有机-矿物协会的形成将在研究中进行调查，越来越复杂和接近自然的条件：从实验室研究的有机-矿物协会的形成和性质的矿物混合物作为模型基质的研究与未受干扰的Bg层的天然土壤的实地研究，在Bg层的石灰性潜育土，在那里我们将收集有机-矿物协会原位形成。利用13 C-和15 N-标记的有机模型物质和土壤大气中的18O_2，将实验中新形成的有机-无机组合与较老的成土组合区分开来，这将有助于理解以前不清楚的氧化还原敏感的金属氧化物与土壤中C循环之间的关系。鉴于铁和锰氧化物的高反应性，它也解释了其他污染物和营养物质的循环。

Formation of redoximorphic soils is characterized by a periodical change of oxidizing and reducing conditions. Reductive dissolution and subsequent oxidative re-formation of Fe and Mn oxides causes characteristic accumulation and depletion zones and mineral transformations in these soils.The aim of the project we apply for is to retrace formation and dynamics of organo-mineral associations, i.e., changes of the mineral and organic phase, in redoximorphic soils, which are affected by ground water. Special emphasis is laid on investigating Fe and Mn oxides, which form in the presence of dissolved organic matter. Organic matter affects structural properties of Fe oxides and is stabilised towards decomposition by interactions with the mineral phase. We postulate ageing of Fe oxides during redox cycles to more crystalline phases, the reactivity of which towards organic matter changes. We postulate preferential sorption of aromatic compounds and the spatial differentiation of Fe and Mn oxides together with the associated organic matter. We aim at studying the in-situ formation of the minerals in the presence of dissolved organic substances, i.e., their associations, at high spatial resolution. The chemical composition of these organo-mineral associations will be characterized by nano-scale secondary ion mass spectrometry (NanoSIMS) at the sub-micron scale and the speciation of Fe and Mn by X-ray absorption spectroscopy methods (XANES/EXAFS) at the micron scale. The formation of organo-mineral associations will be investigated in studies with increasing complexity and near-natural conditions: from laboratory studies on formation and properties of organo-mineral associations in mineral mixtures as model substrates over studies with undisturbed Bg horizons of natural soils to field studies in the Bg horizon of a Calcaric Gleysol, where we will collect organo-mineral associations formed in situ. The differentiation of newly formed organo-mineral associations in the experiments from older pedogenic ones will be achieved by using 13C- and 15N-labelled organic model substances and 18O2 in the soil atmosphere.This project will contribute to the understanding of previously unclear correlation between redox-sensitive metal oxides and the C cycle in soils. Given the high reactivity of Fe and Mn oxides, it also accounts for the cycles of further contaminants and nutrients.