Soil water depletion by oak trees and the influence of root water uptake on the moisture content spatial statistics
Soil water depletion by oak trees and the influence of root water uptake on the moisture content spatial statistics
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橡树土壤水分消耗及根系吸水对含水量空间统计的影响
DOI：
10.1029/96wr03978
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发表时间：
1997
影响因子：
5.4
通讯作者：
R. Oren
中科院分区：
文献类型：
--
作者：
G. Katul;Philip Todd;D. Pataki;Z. Kabala;R. Oren
在一个直径为3.1 m的封闭顶室中，使用土壤水分和压力的三维测量网格以及树木蒸腾的测量，研究了橡树土壤水分吸收的时空统计结构。利用时域反射仪（TDR）测量的含水量、电阻块测量的土壤水压力和紧凑型恒水头渗透仪测量的饱和导水率，首次估算了该试验箱的土壤水力特性。然后，提出了利用土壤水压力的无量纲统计措施，并用于评估横向流对垂直流的相对重要性。根据测量的土水压力的统计特性，发现垂直流至少比侧向流大一个数量级，因此使用一维流近似连续性。利用连续性和白金汉-达西垂直通量关于空间平均含水量状态的一阶泰勒级数展开，推导出空间平均含水量随时间变化的近似关系，并用TDR测量进行检验。尽管TDR测得的含水量的空间变异系数很大（这也被证明与大规模田间实验的报告值相当），但发现两个单独干燥循环的平均含水量预测值和测量值之间具有良好的一致性。利用泰勒级数通量展开的近似方法，推导出空间含水率方差随时间变化的相似关系。由此产生的方差预算被用来评估的作用，根系吸水水分含量的空间变异性。结果发现，根系吸水分量，这是由于根系吸水和水分含量的空间扰动之间的协方差，是可比的土壤水力特性和土壤水分再分配的贡献。在这项研究中的主要发现之一是，根系吸水是中央的水分含量的空间方差消散，特别是在干燥的土壤水分条件。这些结果使用Monte Carlo模拟进行了进一步研究。
The space‐time statistical structure of soil water uptake by oak trees was investigated in a 3.1‐m‐diameter closed top chamber using a three‐dimensional measurement grid of soil moisture and pressure, and measurements of tree transpiration. Using the time domain reflectometery (TDR) measured moisture content, resistance block measured soil water pressure, and a compact constant head permeameter measured saturated hydraulic conductivity, the soil hydraulic properties for the chamber were first estimated. Then, dimensionless statistical measures that utilize the soil water pressure were proposed and used to assess the relative importance of lateral to vertical flow. On the basis of the measured statistical properties of the soil‐water pressure, it was found that the vertical flow is at least an order of magnitude larger than the lateral flow, and thus a one‐dimensional flow approximation to continuity was utilized. Using continuity and a first‐order Taylor series expansion of the Buckingham‐Darcy vertical flux about the spatial mean moisture content state, an approximate relation for the time variation of the spatial mean moisture content was derived and tested with the TDR measurements. Despite a large spatial coefficient of variation in the TDR measured moisture content (which was also shown to be comparable to reported values from larger‐scale field experiments), good agreement between mean moisture content predictions and measurements were found for two separate drying cycles. The approximate Taylor series flux expansion was utilized for deriving an analogous relation for the time variation of the spatial moisture content variance. The resultant variance budget was used to assess the role of root water uptake on the spatial variability of moisture content. It was found that the root uptake component, which resulted from a covariance between the root water uptake and moisture content spatial perturbations, is comparable to the contribution from soil hydraulic properties and soil water redistribution. One of the main findings in this study is that root water uptake is central to the moisture content spatial variance dissipation especially for dry soil moisture conditions. These results were further investigated using Monte‐Carlo simulations.