山西太岳山小流域土壤水分空间异质性及其影响因子

以山西太岳山华北落叶松林地为主的小流域作为研究对象,采用地统计学方法结合地理信息系统(GIS)技术手段,研究了接石沟小流域土壤水分(0—60cm)的空间变异特征,以及植被分布和地形因子对其影响规律。结果表明:在时间稳定性的前提下,土壤水分含量和变异系数随土层加深逐渐降低。三层土壤水分半方差函数的最优拟合模型为球状模型,变程范围在1.1—1.4 km,均具有强烈的空间自相关性,其中0—20 cm和20—40 cm层土壤水分的空间异质性程度高于40—60 cm土层,以中间层的结构因素占总变异比例最大。自然结构因素(地形、母质、植被和土壤等)对不同土层土壤水分的总空间变异性起主导作用(81.4%—91.3%),而随机因素(取样误差、人为干扰等)的影响相对较小(8.7%—18.6%)。沿着集水线由西-东方向,从边缘的土壤水分高值斑块区逐渐过渡到明显的低值斑块区,梯度变化明显。研究发现,在植被覆盖异质性小的山地,土壤水分的空间异质性主要由地形因素引起,具体表现为其与坡向指数(TRASP)、坡度、海拔和土壤有机碳、全氮呈极显著相关关系(P0.01),而与植被指数(NDVI)呈弱的负相关关系。叠加分析显示,在阴坡、坡度较缓(15°)及高海拔叠合的区域土壤水分含量较高。研究结果可为山地人工林构建和植被恢复中土壤水资源的利用以及水分管理策略的制定提供理论依据。

Factors influencing spatial heterogeneity of soil moisture content in a small catchment of Mount Taiyue, Shanxi Province

Soil moisture is a hydrological characteristic that plays a crucial role in the soil-plant-atmosphere continuum. The spatial distribution of soil moisture and factors that influence this distribution are extremely important to many ecological processes, especially in temperate mountain forest regions such as those in northern China. Nonetheless, little is known about soil moisture heterogeneity in typical subalpine forest lands or the controlling factors of soil moisture change. In this study, soil moisture content (SMC) was measured for depths of 0 to 60 cm in a typical watershed forest, dominated by Larix principis-rupprechtii, in Taiyue Mountain, Shanxi Province. We used Geographic Information System (GIS) data and geostatistical methods to examine the spatial heterogeneity of SMC and the factors (i.e., vegetation and topography) that influence it. SMC and its coefficient of variation (CV) decreased with increasing soil layer depth, exhibiting high to moderate variation under an assumption of time stability. At this small watershed scale, the best-fit model for SMC of the three layers (0-20 cm, 20-40 cm, and 40-60 cm) is the spherical model; the spatial autocorrelation distance ranged from 1.1 to 1.4 km. The distribution of SMC has strong spatial autocorrelation in all three layers. The degree of spatial heterogeneity of soil moisture in the 0-20 cm and 20-40 cm soil layers was higher than that in 40-60 cm layer. The structural characteristics of the middle layer accounted for the largest proportion of the total variation. Spatial variability of soil moisture was mainly (81.4% to 91.3%) controlled by natural structure factors such as topography, parent material, vegetation properties, and soil properties, while the influences of random factors such as sampling error, human disturbance, plant root distribution, and absorption were relatively small (8.7% to 18.6%). Moran''s I values indicated that soil moisture had moderately aggregated distributions (0.44-0.51) across soil depths. The overall trend of SMC spatial distribution gradually transitioned from high to low values from west to east along with the waterline, an obvious gradient change. We also found that the spatial heterogeneity of soil moisture was mainly controlled by terrain factors in this mountainous catchment with homogeneous vegetation cover. Spatial variability of soil moisture was significantly correlated with topographic factors (such as aspect, slope, and elevation) and soil chemical properties (such as soil organic carbon and total nitrogen) (P < 0.01). However, it was weakly and negatively correlated with the normalized difference vegetation index (NDVI). Overlay analysis suggested that SMC was relatively high in regions where the three attributes of shady slope, smooth slope (<15 degrees), and high altitude overlapped. Moreover, soil moisture variation nearly matched the color depth change in a superimposed terrain map. Taken together, the results of this study provide data for planning the use of soil water resources in artificial vegetation restoration and construction of temperate subalpine forests and a theoretical basis for devising water management strategies.