黄土丘陵小流域土壤水分的时空变异特征——半变异函数

Spatiotemporal Variability of Soil Moisture in Small Catchment on Loess Plateau——Semivariograms

结合地理信息系统 (GIS) ,利用地统计学方法研究了黄土丘陵沟壑区小流域土壤水分的空间结构特征及其季节变化规律。结果表明 :土壤水分具有较高的分维数 ,表现出强烈和中等程度的空间自相关。 1对平均土壤水分来说 ,基台值 (空间总变异 )的季节变化与其相反 ,在干旱季节 ,土壤水分的基台值高 ;湿润季节 ,基台值降低 ;而在极端干旱条件下 ,土壤含水量接近凋萎系数 ,土壤水分变异程度降低。变程的季节变化在干旱季节数值高 ,湿润季节变程小 ,且变程变化在 1 35～ 1 60 m之间。块金值 (随机变异 )变化在 0 .2和 1 .5,季节变化格局并不明显 ,与平均土壤含水量的季节变化具有某些相似性。2对剖面土壤水分来说 ,在整个观测期内 ,基台值 (不包括 5 cm土壤水分 )随剖面深度增加而增加。变程随土壤深度并不显示明显的趋势而呈现波动变化 ,其变化幅度 60～ 1 60 m,差异近 3倍。块金值随土壤深度也无明显格局 ,但其倾向于基台值高 ,块金值也高。土壤水分的空间结构特征及其季节变化能从土地利用、地形。

At present, using geostatistics for studying on these variables with random and structure is becoming one of the main spatial analytical methods within the field of environmental sciences. In hilly areas of Loess Plateau, due to the importance of soil moisture, many researchers have studied on its spatial variability and relationships between land use and topography using descriptive methods. However, studies on that the spatiotemporal variability of soil moisture using geostatistics are still inadequate in this area. In this paper, we use geostatistics combined with GIS to determine and quantify the spatial and temporal variability of soil moisture. The results indicated that soil moisture exhibited high fractal dimensions and clear spatial autocorrelation. For mean soil moisture of 0~70 cm, the seasonal changes of the sills were opposite to the mean soil moisture. During dry season, the spatial heterogeneity of soil moisture was high, and the sills showed high level. During wet and extremely conditionds, the sills decreased and were low. The ranges varying between 135 m and 160m were high during dry season and low during wet season. The nuggets, random variance, ranged from 0 2 to 1 5, and did not exhibit apparent seasonal pattern and loosely mimiced mean soil moisture. For profile soil moisture, the sills except for 5 cm increased with soil depth during whole observation period. The ranges varying between 60m and 160 m did not show the systemic change with depth. However, the ranges of soil moisture of 45 cm and 70 cm exhibited little fluctuation compared to 5 cm, 15 cm and 25 cm during study period. After a significant rain event, the changes of the sills and ranges with depth became more complicated. The nugget showed no clear pattern with depth, and tended to high value with high sill and low value with low sill. These suggest that the processes for influencing on profile soil moisture pattern were convoluted, and their relative roles were different during the observation period. The spatial dependence and seasonal variability of soil moisture were interpreted by land use, topography, precipitation and soil physical attributes. Their relative roles of influencing on soil moisture depended on different seasons.