Schaub Monika, Seth Barbara, Alewell Christine
Institute of Environmental Geosciences, University of Basel, Bernoullistrasse 30, CH-4056 Basel, Switzerland.
Rapid Commun Mass Spectrom. 2009 Jan;23(2):313-8. doi: 10.1002/rcm.3871.
The stable oxygen isotope signature (delta(18)O) of soil is expected to be the result of a mixture of components within the soil with varying delta(18)O signatures. Thus, the delta(18)O of soils should provide information about the soil's substrate, especially about the relative contribution of organic matter versus minerals. As there is no standard method available for measuring soil delta(18)O, the method for the measurement of single components using a high-temperature conversion elemental analyser (TC/EA) was adapted. We measured delta(18)O in standard materials (IAEA 601, IAEA 602, Merck cellulose) and soils (organic and mineral soils) in order to determine a suitable pyrolysis temperature for soil analysis. We consider a pyrolysis temperature suitable when the yield of signal intensity (intensity of mass 28 per 100 microg) is at a maximum and the acquired raw delta(18)O signature is constant for the standard materials used and when the quartz signal from the soil is still negligible. After testing several substances within the temperature range of 1075 to 1375 degrees C we decided to use a pyrolysis temperature of 1325 degrees C for further measurements. For the Urseren Valley we have found a sequence of increasing delta(18)O signatures from phyllosilicates to upland soils, wetland soils and vegetation. Our measurements show that the delta(18)O values of upland soil samples differ significantly from wetland soil samples. The latter can be related to the changing mixing ratio of the mineral and organic constituents of the soil. For wetlands affected by soil erosion, we have found intermediate delta(18)O signatures which lie between typical signatures for upland and wetland sites and give evidence for the input of upland soil material through erosion.
土壤的稳定氧同位素特征（δ¹⁸O）预计是土壤中具有不同δ¹⁸O特征的各组分混合的结果。因此，土壤的δ¹⁸O应能提供有关土壤基质的信息，特别是关于有机质与矿物质的相对贡献。由于没有可用于测量土壤δ¹⁸O的标准方法，因此采用了使用高温转换元素分析仪（TC/EA）测量单一成分的方法。我们测量了标准物质（国际原子能机构601、国际原子能机构602、默克纤维素）和土壤（有机土和矿质土）中的δ¹⁸O，以确定适合土壤分析的热解温度。当信号强度的产率（每100微克质量数28的强度）达到最大值，且所获取的原始δ¹⁸O特征对于所用标准物质是恒定的，并且土壤中的石英信号仍然可忽略不计时，我们认为该热解温度是合适的。在1075至1375摄氏度的温度范围内对几种物质进行测试后，我们决定使用1325摄氏度的热解温度进行进一步测量。对于乌尔塞伦山谷，我们发现从页硅酸盐到高地土壤、湿地土壤和植被，δ¹⁸O特征呈递增序列。我们的测量表明，高地土壤样品的δ¹⁸O值与湿地土壤样品有显著差异。后者可能与土壤中矿物质和有机成分混合比例的变化有关。对于受土壤侵蚀影响的湿地，我们发现其δ¹⁸O特征介于高地和湿地典型特征之间，这证明了高地土壤物质通过侵蚀输入。
