Influence of soil structure and root water uptake strategy on unsaturated flow in heterogeneous media
Influence of soil structure and root water uptake strategy on unsaturated flow in heterogeneous media
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DOI：
10.1029/2011wr010651
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发表时间：
2012-02
影响因子：
5.4
通讯作者：
A. Kuhlmann;I. Neuweiler;S. Zee;R. Helmig
中科院分区：
文献类型：
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作者：
A. Kuhlmann;I. Neuweiler;S. Zee;R. Helmig
我们分析了土壤水力特性的空间变异性和植物根部吸水对不饱和水流的综合影响。对于此分析，我们使用简化的宏观根系吸水模型，该模型通常仅适用于均质或层状土壤，因此我们还确定它是否适用于多维异质介质。针对稳态和瞬态流动条件，分析了层状介质中压头均值和方差（一阶二阶矩近似）的解析解以及二维（2-D）自相关多高斯和非多高斯参数场的数值解。对于非高斯拓扑特征，如果忽略根部吸水量，对压力场的均值和方差几乎没有影响，我们测试如果考虑根部吸水量，影响是否显着。结果表明，在具有大片粗料的田地结构中，出现了在萎蔫点处具有压头值的局部区域；这些被湿材料包围。如果没有局部胁迫补偿机制，如果发生局部枯萎，则无法满足全局蒸腾需求。测试了各种补偿机制，这些补偿机制分别取决于饱和度、相对电导率或将全局吸收率的不足平均分配到无应力位置的策略。这些策略使全球实际蒸腾速率达到潜在值，并减少局部枯萎区域的形成。然而，枯萎区域仍然可能发生，并且可能是简化模型概念的产物，因为忽略了根与土壤的相互作用。因此，在异质介质中应谨慎使用根部吸水的简化宏观模型。
We analyze the combined effects of the spatial variability of soil hydraulic properties and the water uptake by plant roots on unsaturated water flow. For this analysis, we use a simplified macroscopic root water uptake model which is usually applied only for homogeneous or layered soil and therefore we also determine whether it is applicable for multidimensional heterogeneous media. Analytical solutions for mean and variance of pressure head (first‐order second‐moment approximations) in layered media and numerical solutions of two‐dimensional (2‐D) autocorrelated multi‐Gaussian and non multi‐Gaussian parameter fields are analyzed for steady state and transient flow conditions. For non‐Gaussian topological features, that have little influence on the mean and the variance of the pressure field if root water uptake is ignored, we test whether the influence is significant if root water uptake is accounted for. The results reveal that, in field structures with large patches of coarse material, local regions with pressure head values at the wilting point develop; these are surrounded by wet material. Without a compensation mechanism for local stress, the global transpiration demand is not met if local wilting occurs. Various compensation mechanisms are tested that depend, respectively, on the saturation, the relative conductivity or a strategy where the deficit in the global uptake rate is equally distributed to unstressed locations. The strategies lead to a global actual transpiration rate at the potential value and attenuate the formation of locally wilted areas. Wilted regions can, however, still occur, and may be an artifact of the simplified model concept as root‐soil interactions are neglected. Therefore simplified macroscopic models for root water uptake should be used with caution in heterogeneous media.