基于地表景观信息的黄土小流域土壤干燥化识别

Soil moisture is the key limiting factor for plant growth and ecological restoration in the semi-arid areas. Drought and excessively soil water consumption by vegetation restoration without scientific guidance have become an important limitation for ecological restoration in the Loess Plateau. Identifying the soil desiccation based on surface landscape information and regulated soil desiccation mechanism is an important and urgent problem for current study. The Longtan watershed, which is located in Dingxi City of Gansu province is selected as study area. The temporal variation and spatial distribution of soil desiccation is planned to be studied by field observation, statistical methods, spatial analysis, and model calculation. The influence of landscape structure and landscape pattern on soil desiccation will be identified in this study. Furthermore, the quantitative influence of surface landscape information (such as vegetation dynamics, topographical features and soil properties) on spatial-temporal variation of soil desiccation will be revealed. The method of soil desiccation identification would be developed based on multiple surface landscape information in geographical information system. The soil desiccation characteristics would be quantitatively identified by surface landscape information and methods of control soil desiccation would be discussed. This study will provide scientific guidance for the sustainable utilization of soil moisture and the spatial pattern optimization of vegetation restoration.

土壤水分是半干旱地区植被生长和生态恢复的关键限制因子。缺乏科学指导的植被建设布局和恢复方式导致的土壤干燥化是黄土高原生态恢复面临的一个重要限制因素，深入研究地表景观信息对干燥化的识别方法，探讨土壤干燥化的调控机制尤为迫切和必要。本项目以位于典型半干旱黄土丘陵区的甘肃定西龙滩流域为例，通过野外定位监测，结合经典统计、空间分析和模型计算等手段，揭示土壤干燥化的时间动态特征和空间分异规律。阐明景观结构、空间格局对土壤干燥化时空分异的影响，揭示植被动态、地形特征和土壤属性等地表景观信息对土壤干燥化的作用机制及其定量表达关系。在GIS中构建耦合地表多元景观信息的土壤干燥化时空动态识别方法，通过地表景观信息对土壤干燥化进行识别。该项研究将为黄土高原土壤水资源的可持续利用和植被恢复的空间格局优化提供科学依据。

土壤干燥化及其时空分异是地表多重因子共同作用的结果。本项目以半干旱黄土小流域为例，通过不同深度土壤水分的长期定位监测，结合植被群落、地形和景观格局，在点位—坡面—流域尺度上系统研究了土壤干燥化的时间动态和空间分异规律、地表景观对土壤干燥化的作用过程、以及植被格局与土壤水分时空分异的耦合关系。主要得出以下结论：（1）降雨对不同植被类型土壤水分的补给效率存在显著差异，定量识别了黄土丘陵区典型植被土壤水分有效补给的降雨阈值；（2）人工植被下深层土壤水分已经没有明显的季节变化和年际变化，降水增加并不能有效增加深层土壤水分，而干旱却能显著降低深层土壤水分，加剧土壤干燥化程度；（3）大规模人工植被恢复改变了坡面尺度不同层次土壤水分的空间分异规律，地形是表层土壤水分的重要影响因素，而地上生物量成为深层土壤水分空间分异的决定因素，大规模人工植被恢复也降低了土壤水分的空间异质性；（4）地表植被叶片特征受前一年土壤水分的影响更为明显，与当年降水关系并不显著，植被群落特征对土壤水分的响应存在时滞性。在坡面和流域尺度上，植被结构决定了土壤水分状况，而植被的空间布局则决定了土壤水分的时空分异特征。