荒漠绿洲过渡带白刺灌丛沙堆土壤水分空间分布及入渗特征

摘要

本研究选取民勤荒漠绿洲过渡带白刺灌丛沙堆3个演化阶段：雏形阶段（流动白刺沙堆）、沙堆形成阶段（发育20年，半固定白刺沙堆）和结皮与土壤形成阶段（发育40年，固定白刺沙堆）为研究对象，采用空间代替时间的方法，研究不同类型沙堆土壤物理属性对水分空间分布及入渗的影响，探索白刺灌丛沙堆土壤水分运行规律，为绿洲荒漠过渡带防护林体系优化配置、绿洲生态安全管理奠定理论基础。结果表明，1）土壤紧实度和结皮厚度：固定白刺沙堆＞半固定白刺沙堆＞流动白刺沙堆。2）表层土壤密度流动、半固定、固定白刺沙堆分别为2．32，2．30，1．95 g／cm3；最大持水量、毛管持水量、田间持水量和总孔隙度大小为：固定白刺沙堆＞半固定白刺沙堆＞流动白刺沙堆，而深层土壤各因子变化不稳定。3）在干旱季节，固定、半固定和流动白刺沙堆分别以0，70，150 cm 土层含水量最小，50，130，110 cm 土层含水量最大；在多雨季节，表层土壤含水量波动幅度较大，深层土壤含水量基本保持不变。4）不同演化阶段沙堆降雨量与累计入渗量之间存在显著的正相关性（P ＜0．01）。其中固定、半固定白刺沙堆随降雨事件的发生立即开始入渗，流动白刺沙堆当降雨量达到临界降雨量后才开始入渗。在降雨量相同情况下，当降雨量大于0．12 mm 时，累积入渗量依次为：固定白刺沙堆＞半固定白刺沙堆＞流动白刺沙堆。%This study utilized Nitraria tangutorun nebkhas vegetation growing in a desert-oasis ecotone in Minqin to investigate space distribution of soil moisture content and the influence of soil physical properties, particularly soil hardness and crust thickness on water distribution and infiltration of the three evolutionary stages of soil formation;stable sand dune,sand dune formation and moving sand.The aim was to explore the effect of N .tangutorun nebkhas on soil moisture and to establish a theoretical foundation for protective systems for oasis-desert ecotones.The results as follows:1)Soil hardness and crust thickness were highest in the stable dune,intermediate in forming dunes and least in moving sand.2 )Soil surface bulk density was 2.32,2.30 and 1.95 g/cm3 in moving sand,forming dunes and stable dunes respectively;maximum water holding capacity,capillary water content,field capacity and total porosity was highest in the stable dune,inter-mediate in the forming dune and least in the moving sand.Soil physical properties in the subsurface layer were variable in all dune formation stages.3)In the dry season,the lowest soil moisture contents occurred in soils from forming dunes and moving sand at 0,70,150 cm depth,maximum soil moisture occurred at 50,130,110 cm;in the rainy season,surface soil moisture content fluctuated while soil moisture at depth was relatively stable.4)There were significant correlations between rainfall and infiltration in all three stages of soil forma-tion (P <0.01 ).Water infiltration after rainfall events occurred immediately instable and forming dune soils whereas infiltration in moving sand only occurred when rainfall reached a critical threshold;with rainfall grea-ter than 0.12 mm,infiltration was highest in the stable dune,intermediate in forming dune and least in moving sand.