黄土区小流域土壤容重和饱和导水率的时空动态特征

土壤水力性质是评估降水入渗、径流发生以及土体可蚀性的重要参数。研究小流域尺度土壤水力性质的时空动态特征,对于以小流域为基本单元的黄土高原综合治理具有直接意义,有助于加深对相关生态水文过程的理解。以陕西省神木县六道沟老叶满渠小流域为对象,进行50 m×50 m网格布点(共73个样点),2014年8-10月期间每月测定1次表层土壤容重和饱和导水率,结合经典统计学与地质统计学的方法研究容重和饱和导水率的时空变化规律。结果表明:1)小流域尺度容重的月际变化趋势较为一致,整体呈正态分布规律,饱和导水率的月际变化强烈,呈偏态分布;容重较饱和导水率变化范围较小,变异程度较低;2)小流域尺度容重和饱和导水率在8-10月的半方差可用指数模型进行最优拟合,两者均表现出中等程度的空间依赖性;Kriging插值图表明小流域容重总体差异性较小,而饱和导水率差异显著;8-10月,西坡局部区域、坡顶的容重呈逐月增大趋势,而饱和导水率呈减小趋势;3)Pearson相关性分析表明,8-10月单次测定的容重和饱和导水率之间的相关性不明显;在同一土壤类型下(干润砂质新成土)表现出极显著的负相关关系(P0.01)。

Spatio-temporal characteristics of soil bulk density and saturated hydraulic conductivity at small watershed scale on Loess Plateau

Abstract: Surface soil bulk density (BD) and saturated hydraulic conductivity are two of important parameters to assess rainfall infiltration, runoff formation and soil erosion. But little research has been done at a watershed scale. On the Loess Plateau of China, investigations on the spatio-temporal changes of BD and saturated hydraulic conductivity at a small watershed scale are essential for regional ecological restoration and may enrich our understanding on the related eco-hydrolgical processes. In this study, we measured BD and saturated hydraulic conductivity in August, September, and October of 2014 at 73 sites that were pre-located by using Global Positioning System in a 50 m × 50 m grid at the LaoYeManQu watershed on the wind-water erosion crisscross region of the Chinese Loess Plateau. Using classical statistical and geostatistical methods, we characterized and compared the spatial and temporal changes of BD and saturated hydraulic conductivity. The semivariograms and kriging method included in the geostatistical method were used to reflect the visual variation among different months from August to October. Results showed that: 1) Among the three months, BD had a normal distribution and exhibited a time stability while saturated hydraulic conductivity had a skewed distribution and varied greatly. BD variation was smaller than that of the saturated hydraulic conductivity at the watershed scale. 2) Semivariograms of BD and saturated hydraulic conductivity from August to October could be best fitted by an isotropic exponential model. Both BD and saturated hydraulic conductivity exhibited a moderate spatial dependence. Distribution maps produced by kriging indicated pronounced spatial patterns of BD and saturated hydraulic conductivity at the small watershed-at the slope top and the western part of the watershed, BD demonstrated an increasing trend while saturated hydraulic conductivity decreased gradually from August to October. 3) Pearson correlation analysis showed that correlations between BD and saturated hydraulic conductivity at each measured time from August to October were weak (r<0.4); while, for the same soil type (dry sandy entisol) in the watershed, BD was correlated with saturated hydraulic conductivity negatively at the significant level of 0.01 and for aeolian soils the correlation was not significant. Our results suggested that different soil types in the watershed may change the overall correlation between BD and saturated hydraulic conductivity of the three months. Understanding the spatial and temporal variation of BD and saturated hydraulic conductivity would increase the accuracy in modeling and predicting rainfall infiltration, soil water and solutes movement at the watershed scale.