Abstract Describing and mapping soil water content (SWC) distribution are required to understand and explain the hydrological phenomena at various spatial scales. Soil drought in the hilly and gully regions of Loess Plateau reduces agricultural production and plants biomass, which has attracted great attention but few studies associated it with the gullied terrain. To understand the SWC distribution pattern in the slope–gully system, we established a cross-section transect for SWC observation across a permanent gully and acquired 23 occasions of SWC data in the periods from October 2014 to September 2018. The standardized beta coefficient in stepwise multiple linear regression was employed to determine the strength of the effect of the selected variables (soil textural separates, soil depth, relative height, distance to the gully and saturated hydraulic conductivity) on SWS distribution. Spectral and cross-spectral analysis were performed on the time series of SWC to evaluate the cyclical behavior and the similarity for adjacent sites, respectively. The following results were obtained: First, the SWC distribution had a bilateral asymmetrical pattern across the gully, which constituted a specific and detailed content of spatial variability of SWC. Second, soil water storage in the slope–gully system was primarily affected by soil texture, meanwhile, the effect of distance to the gully was stronger than that of soil depth. Third, the SWC of the adjacent pair sites presented consistent periodic behavior. The cross-spectral analysis indicated a dissimilar pattern for soil layer of 0–60 cm and deep synchrony for the other depth layers. In conclusion, the gully edge effect aggravated the SWC status in the south bank and caused a bilateral asymmetrical pattern in the slope–gully system. These results improved our knowledge on the complicated distribution of SWC in the gullied region. Moreover, the results indicate that ignoring the nearby areas of a permanent gully in a catchment is inappropriate when investigating soil water resources.

中文翻译：

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沟壑边缘对永久性沟壑土壤水分分布格局的初步研究

摘要 描述和绘制土壤含水量 (SWC) 分布需要理解和解释不同空间尺度的水文现象。黄土高原丘陵沟壑区土壤干旱减少了农业生产和植物生物量，引起了广泛关注，但与沟壑地形相关的研究较少。为了解斜坡-沟壑系统中SWC的分布格局，我们建立了一条永久性沟壑的SWC观测横断面，采集了2014年10月至2018年9月23次SWC数据。采用多元线性回归来确定所选变量（土壤质地分离、土壤深度、相对高度、SWS 分布上到沟渠的距离和饱和导水率）。对 SWC 的时间序列进行光谱和交叉光谱分析，以分别评估相邻站点的循环行为和相似性。得到以下结果：首先，SWC分布在整个沟壑上呈现双边不对称格局，构成了SWC空间变异性的具体而详细的内容。其次，坡沟系统的土壤储水量主要受土壤质地的影响，而沟沟距离的影响强于土层深度。第三，相邻对站点的 SWC 呈现一致的周期性行为。交叉光谱分析表明 0-60 cm 土壤层的不同模式和其他深度层的深度同步。综上所述，沟壑边缘效应加剧了南岸的 SWC 状态，并导致斜坡-沟壑系统的双边不对称格局。这些结果提高了我们对沟壑区 SWC 复杂分布的认识。此外，结果表明，在调查土壤水资源时，忽略流域内永久性沟渠附近的区域是不合适的。