黄土高原水蚀风蚀交错带小流域土壤水分季节变化特征与主控因素

土壤水分是黄土高原水蚀风蚀交错带生态环境恢复的关键因子,具有明显的时空异质性。以水蚀风蚀交错带的代表性流域—老爷满渠小流域为对象,采用网格法(50 m×50 m)共布设了73个样点,原位观测0—5 m土壤含水率,共测定23次(2013年6月至2019年10月),通过获取每个样点的环境因子,结合经典统计、地统计、随机森林等方法,分析了小流域尺度不同土层深度(每层1 m,共5层)土壤含水率的季节变化特征与影响因素。结果表明:不同土层土壤含水率的空间分布特征和季节性变化规律不同;对于0—1 m土层,土壤含水率在夏季和冬季之间存在显著性差异(p0.05),而对于1 m以下土层,春季平均土壤含水率高于其他季节,但不显著;无论在何种季节,不同土地利用方式、壤土与砂土间的土壤含水率在3 m以上土层均存在显著差异(p0.05),而阴、阳坡的土壤含水率在所有土层均存在显著差异(p0.05);在不同季节,土壤含水率与容重和砂粒呈负相关,与其他环境因子(有机碳含量、黏粒、粉粒、有机碳密度、土地利用、坡向、土壤质地和pH)呈正相关;除有机碳密度和黏粒较为稳定外,土壤含水率与环境因子的相关性均随土层深度增加呈减少趋势;环境因子对土壤含水率空间变异的整体相对贡献表现为土壤性质地形土地利用。研究结果可为研究区深层土壤水资源管理、土壤水文观测与模拟、植被优化布局等提供参考。

Seasonal Changes of Soil Water Content and Controlling Factors in a Small Watershed in the Water-wind Erosion Crisscross Region of the Loess Plateau

Soil water is the key factor of eco-environmental restoration in the water-wind erosion crisscross region of the Loess Plateau, which demonstrates a great temporal and spatial heterogeneity. In this study, the representative LaoYeManQu watershed in the water-wind erosion crisscross region was selected as the research area, and 73 sampling points were set up with a grid of 50 m×50 m. From June 2013 to October 2019, 23 in-situ observations of soil water content (SWC) in 0-5 m profile was carried out by using neutron probe, and the environmental factors of each sampling point were collected simultaneously. Combined with classical statistics, geostatistics, and random forest, the seasonal variation characteristics and controlling factors of SWC at different soil layers (5 layers in total, one layer per meter) in the watershed were investigated. The results showed that the distribution characteristics and seasonal variations of SWC for soil layers differed. For the 0-1 m soil layer, the mean SWC between summer and winter was significant different (p < 0.05); while below 1 m, the mean SWC in spring was higher than that in other seasons, but it was not significant. In the soil layers above 3 m, significant differences were found in SWC among different land uses and between loam and sandy soil for four seasons (p < 0.05). For each soil layer, the SWC between shady and sunny slopes also differed significantly in different seasons (p < 0.05). SWC in all seasons was negatively correlated with soil bulk density and sand content, and positively correlated with other measured factors. With the increasing of soil depth, the correlations between SWC and measured factors generally decreased except soil organic carbon density and clay content. The factors contributing to SWC variation were soil properties, topography, and land use in sequence. These results could provide reference for the management of deep soil water resources, soil hydrological observation and simulation, and vegetation optimization in the study area and other similar regions characterized by the water and wind erosion crisscross.