Stable hydrogen isotope ratios in soil constituents: New insights into the formation of organic matter and clay minerals

到目前为止，土壤中稳定氢同位素比值（δ 2 H值）的使用受到限制，因为土壤中的部分氢库与环境水分交换，不携带有意义的同位素信号。该部分需要与包含源和过程信息的不可交换部分分开。对于土壤有机质（SOM），可以使用脱矿质SOM与已知H同位素组成的沃茨的蒸汽平衡，而对于粘土矿物，可以在约100 ℃下脱气。200°C真空条件下分离交换性和非交换性H是常见的。以前的工作表明，SOM可能是快速处理通过微生物在糖酵解代谢过程中的C-结合H交换。粘土矿物在结构OH形成时保持环境水的δ 2 H值。我们建议研究（i）纳入环境水H到非交换性H部分（C-H键）在SOM和相关的同位素分馏过程中分解（ii）土壤粘粒部分是否可以用来确定土壤样品的起源和相对测年的泥质B（Bt）层的现代土壤和古土壤。我们将进行实验室和现场培养，建立粘土组分的蒸汽平衡，并分析全球土壤和部分过时的古Bt层的粘土组分。

The use of stable hydrogen isotope ratios (delta2H values) in soils has up to now been limited, because part of the H pool in soil exchanges with ambient moisture and does not carry a meaningful isotope signal. This part needs to be separated from the nonexchangeable part which contains source and process information. For soil organic matter (SOM), steam equilibration of demineralized SOM with waters of known H isotope composition can be used while for clay minerals degassing at ca. 200°C under vacuum is common to separate exchangeable and nonexchangeable H. Previous work has suggested that SOM may be rapidly processed through the microorganisms during which C-bound H is exchanged in the glycolytic metabolism. Clay minerals conserve the delta2H value of ambient water at the time of formation in structural OH. We propose to study (i) the incorporation of ambient water H into the nonexchangeable H fraction (C-H bonds) in SOM and the associated isotopic fractionation during decomposition (ii) whether the soil clay fraction can be used to determine the origin of a soil sample and for relative dating of argillic B (Bt) horizons of recent soils and palaeosols. We will conduct laboratory and field incubations, establish steam equilibration for clay fractions, and analyze clay fractions of a global set of soils and of partly dated palaeo Bt horizons.