Soil Particle Transport and Mixing Near a Hillslope Crest: 1. Particle Ages and Residence Times
Soil Particle Transport and Mixing Near a Hillslope Crest: 1. Particle Ages and Residence Times
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DOI：
10.1029/2017jf004315
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发表时间：
2018-05-01
影响因子：
3.9
通讯作者：
Doane, Tyler H.
中科院分区：
文献类型：
--
作者：
Furbish, David Jon;Roering, Joshua J.;Doane, Tyler H.
我们检验了土壤颗粒年龄和停留时间的概率元素，从它们进入机械活动的土柱开始测量，重点放在山坡顶端附近的稳定条件下，在存在侵蚀的情况下，颗粒稳定地进入和穿过固定厚度的土壤覆盖层。我们的目标是阐明颗粒轨迹的几何形状和扰动驱动的混合与颗粒进入和离开土壤元素的表面布置有关的后果。我们引入了粒子运动的欧拉-拉格朗日描述来描述具有叠加深度依赖混合的非均匀(二维)平均运动的影响。对于弱混合，颗粒停留时间和年龄的概率分布的形式和矩是不同的，并且在很大程度上由土单元内颗粒平均运动的几何形状控制。平均颗粒年龄系统地小于平均停留时间。这些分布只有在良好混合系统的理想化极限下才会收敛到均值相等的指数形式。这一分析为考虑粒子风化和化学损失与停留时间和年龄的关系以及描述示踪剂的时空结构提供了基础，例如宇宙成因核素浓度和光激发发光粒子年龄，这些都与粒子混合所揭示的信息有关。
We examine probabilistic elements of soil particle ages and residence times measured from their entry into the mechanically active soil column, focusing on steady conditions near a hillslope crest, where particles steadily move into and through a soil mantle with fixed thickness in the presence of erosion. Our objective is to clarify consequences of the geometry of the particle trajectories and disturbance-driven mixing in relation to the arrangement of the surfaces through which the particles enter and leave the soil element. We introduce an Eulerian-Lagrangian description of particle motions to characterize effects of a nonuniform (two-dimensional) mean motion with superimposed depth-dependent mixing. With weak mixing, the forms and moments of the probability distributions of particle residence times and ages are distinct and are largely controlled by the geometry of the mean particle motion within the soil element. The average particle age is systematically less than the average residence time. These distributions converge to exponential forms with equal means only in the idealized limit of a well-mixed system. The analysis provides the foundation for considering particle weathering and chemical losses in relation to residence times and ages and for describing the spatiotemporal structure of tracers, for example, cosmogenic nuclide concentrations and optically stimulated luminescence particle ages, in relation to what these reveal about particle mixing.