毛乌素沙地土壤水分热驱动入渗模式研究

The hydrogen and oxygen stable isotopic compositions of shallow groundwater in Mu Us desert are depleted from mean value of precipitation. This phenomenon reveals that part of groundwater is supplied by soil-water thermodynamic downward movement. This provides a new thinking and a new perspective for study of precipitation infiltration mechanism, especially of the infiltration induced by low intensity precipitation and dew in desert and sand coved region. To further explore the water cycle mechanism indicated by the phenomenon, this project select the typical aeolian sand region and carry out field experiments of soil evaporation and thermaldynamic infiltration. Numerical modeling for coupling hydro-thermal- geochemistry-isotope simulation will be done for the need of quantitative analysis. The aim of the project is to find the reason of why hydrogen and oxygen stable isotopic compositions of shallow groundwater in Mu Us desert are depleted, and reveal the contribution of vapor movement for soil-water in unsaturated zone. The main water sources of soil water in Mu Us desert are low intensity precipitation and dew. The potential recharge effect of these waters to groundwater is very important for the desert region. Thus the study of soil-water hydrodynamic downward movement has significant meaning in both hydrology and geochemistry for arid and semi-arid areas of Western China.

毛乌素沙地潜水氢氧稳定同位素相对于降水均值发生贫化，初步认为该现象是由土壤水以气态形式向下运移补给地下水造成。这为从气态水运移的角度研究低强度降水入渗机理提供了新视角和新思路。本申请拟采用土面蒸发实验和热驱动入渗实验对非饱和带水分运移过程进行再现和观测，并通过水-热-溶质-同位素耦合模拟进行定量分析，确定近地表热驱动水分运移模式，查明热驱动条件下气态水的下行深度和下行净通量，评价低强度降水对地下水的潜在补给作用，进而揭示近地表非饱和带热驱动水分运移机理，探究潜水氢氧稳定同位素贫化的原因。这项研究对沙漠和风积沙覆盖区地下水的补给机理具有重要的理论意义，对准确评价西北干旱-半干旱地区地下水资源量具有重要的实际意义。

毛乌素沙地潜水氢氧稳定同位素相对于降水均值发生贫化，初步认为该现象是由土壤水以气态形式向下运移补给地下水造成。这为从气态水运移的角度研究低强度降水入渗机理提供了新视角和新思路。本次研究采用蒸发实验和原位热驱动入渗实验对非饱和带水分运移过程进行再现和观测，并通过同位素模拟进行定量分析，确定近地表水分运移以热驱动为驱动力，查明热驱动条件下气态水的下行深度为90cm，进而确定潜水氢氧稳定同位素贫化的原因主要为热驱动条件下气态水下行冷凝所致。通过同位素转化模型的拓展，进一步确定了鄂尔多斯盆地降水补给地下水的最低单次降水强度为6.2mm，对准确评价西北干旱—半干旱地区地下水资源量具有重要的实际意义。