Isotope ratios of nonexchangeable hydrogen in soils from different climate zones
Isotope ratios of nonexchangeable hydrogen in soils from different climate zones
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DOI：
10.1016/j.geoderma.2009.12.005
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发表时间：
2010-03
期刊：
影响因子：
6.1
通讯作者：
M. Ruppenthal;Y. Oelmann;W. Wilcke
中科院分区：
文献类型：
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作者：
M. Ruppenthal;Y. Oelmann;W. Wilcke
全球降水中氢同位素的分馏导致降水中氢浓度随纬度、海拔和大陆性的增加而持续降低。因此，植物光合作用或成土黏土矿物新生过程中消耗的当地降水、土壤和地下水往往具有空间诊断性的δ2H值。我们假设块状土壤中同位素不可交换H的δ2H值（由土壤有机质（SOM）中的c键H和成土黏土矿物中o键H的不可交换部分组成）分别与生物质生产和黏土矿物形成地点和时间的当地降水平均δ2H值相关。我们先用已知同位素组成的水平衡土壤样品，然后用元素分析仪-同位素比质谱仪（EA-IRMS）进行δ2H分析，以确定土壤中同位素不可交换氢的δ2H值。我们分析了来自不同气候带（温带、亚北极和热带）的12个表土样品。土壤非交换性氢的δ2H值在−75‰~−167‰之间。土壤非交换性氢的δ2H值与预测样点年平均降水δ2H值高度相关（r=0.89, p<0.001）。西伯利亚土壤非交换性H的δ2H值比中欧土壤的δ2H值大80‰，这直接对应了中欧和西伯利亚降水年平均δ2H值的差异。我们的研究支持了局部降水平均H同位素组成是大块土壤中非交换性H同位素组成的主要控制的假设。由于土壤有机质和成土黏土矿物的非交换性氢的δ2H值主要由全球降水的δ2H值决定，因此无论土壤有机质和黏土矿物的精确含量如何，大块土壤样品的δ2H分析都是有意义的。
The fractionation of H isotopes in global precipitation leads to a continuous decrease in2H concentrations of precipitation with increasing latitude, altitude and continentality. Thus, the local precipitation, soil and ground water used by plants for photosynthesis or consumed during neoformation of pedogenic clay minerals often have a spatially diagnostic δ2H value. We hypothesize that the δ2H value of isotopically nonexchangeable H in bulk soil (composed of C-bonded H in soil organic matter (SOM) and the nonexchangeable fraction of O-bonded H in pedogenic clay minerals) is correlated with the mean δ2H value of local precipitation water at the place and time of biomass production and clay mineral neoformation, respectively. We equilibrated soil samples with water of known isotopic composition prior to δ2H analysis with an Elemental Analyzer-Isotope Ratio Mass Spectrometer (EA-IRMS) to determine the δ2H value of isotopically nonexchangeable H in soil. We analyzed 12 topsoil samples from different climate zones (temperate zone, subarctic zone and tropics). The δ2H values of nonexchangeable H in soil ranged from −75‰ to −167‰. The δ2H values of nonexchangeable H in soil were highly correlated with predicted average annual δ2H values of local precipitation at the sampling sites (r=0.89, p<0.001). The δ2H values of nonexchangeable H in soils from Siberia were up to 80‰ depleted in2H compared to soils from Central Europe, which directly corresponds to the difference in average annual δ2H values of precipitation from Central Europe and Siberia. Our study supports the hypothesis that the average H isotope composition of local precipitation is the primary control of the isotopic composition of nonexchangeable H in bulk soils. Since δ2H values of nonexchangeable H in SOM and pedogenic clay minerals are both primarily determined by δ2H values of global precipitation, δ2H analyses of bulk soil samples are meaningful irrespective of the precise fractions of SOM and clay minerals in soil.