Scale-dependence of temporal stability of surface-soil moisture in a desert area in northwestern China
Scale-dependence of temporal stability of surface-soil moisture in a desert area in northwestern China
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DOI：
10.1016/j.jhydrol.2015.05.015
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发表时间：
2015-08
影响因子：
6.4
通讯作者：
Pingping Zhang;M. Shao;Xingchang Zhang
中科院分区：
文献类型：
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作者：
Pingping Zhang;M. Shao;Xingchang Zhang
土壤水分是水文循环的重要组成部分，但在空间和时间上变化很大。作为优化土壤和水管理和有效的现场监测的工具，时间稳定性分析最近受到越来越多的关注。然而，时间稳定性的尺度依赖性却很少受到关注。2012年4月至10月，我们在中国西北部沙漠地区（40 km2）的187个采样点，利用Theta Probe对表层土壤（0 - 6 cm）水分进行了约每两周一次的测量，共进行了13次采样活动。我们通过重采样分析在6个采样间距和6个不同大小的采样区域（范围）下对样本进行分组，以分析在各种采样尺度下时间稳定性特征的变化，并测试在每个采样尺度下通过在有限数量的位置测量估计的田间平均含水量的准确性。增加间距对整体空间格局和个体位置的时间稳定性影响不大，而增加程度倾向于增加整体空间格局的时间稳定性，但降低个体位置的时间稳定性。在尺度较小的情况下，时间稳定性的特征易受尺度变化的影响。指数方程和幂方程能够很好地描述大部分时间稳定性参数与采样尺度之间的关系。确定的代表性的位置（RL）的数量的影响，样本量的范围比间距引起的样本量的变化更敏感。在所有采样尺度下，所选的RL集通过使用偏移估计准确地估计了整个研究期间的田间平均值，并且估计精度不受采样尺度的影响。增加间距并没有改变地形和土壤性质对时间稳定性的影响，而增加的程度往往会加强相对海拔和土壤有机碳含量的影响，但削弱饱和导水率的时间稳定性的影响。本研究有助于我们了解沙漠生态系统土壤水分的时间稳定性对采样尺度的依赖性，并将有助于整合不同空间尺度的信息和设计最佳的采样大小和策略，类似的研究。
Soil moisture is an important component in hydrological cycles but is highly variable in space and time. As a tool for optimal soil and water management and effective field monitoring, the analysis of temporal stability has recently received increasing interest. The scale dependence of temporal stability, however, has received little attention. We measured surface-soil (0–6 cm) moisture at 187 sampling locations in a desert region (40 km2) in northwestern China approximately every two weeks from April to October 2012 with a Theta Probe, for a total of 13 sampling campaigns. We grouped the samples by re-sampling analysis under six sampling spacings and six different sizes of sampling area (extents) to analyse the changes in the characteristics of temporal stability at the various sampling scales and to test the accuracy of the field-mean moisture content estimated by measurements at a limited number of locations at each sampling scale. Increasing the spacing had little influence on the temporal stability of both the overall spatial pattern and the individual locations, whereas increasing the extent tended to increase the temporal stability of the overall spatial pattern but to decrease the temporal stability at the individual locations. The characteristics of temporal stability were susceptible to changes in scale when extent was small. Exponential and power equations could well express the relationships between most of the parameters of temporal stability and sampling scale. The number of identified representative locations (RLs) was influenced by sample size and was more sensitive to changes in sample size caused by extent than by spacing. At all sampling scales, the sets of selected RLs accurately estimated the field mean for the entire study period by using offset estimates, and the estimate accuracy was not affected by sampling scale. Increasing the spacing did not change the influence of topography and soil properties on temporal stability, whereas increasing the extent tended to intensify the influence of relative elevation and soil organic carbon content but to weaken the influence of saturated hydraulic conductivity on temporal stability. This study contributes to our understanding of the dependence of temporal stability of soil moisture in desert ecosystems on sampling scale and will help the integration of information from different spatial scales and the design of optimal sampling sizes and strategies for similar studies.