毛乌素沙地土壤水分冻融入渗机理及同位素效应研究

According to previous studies, the values of δD, δ18O of shallow groundwater in the Mu Us Desert are more negative than the mean value of precipitation. This phenomenon reveals probably that part of groundwater is recharged by soil water infiltration from seasonal frozen soil during the freezing and thawing periods. To verify the hypothesis, we carried out researches in the Mu Us Desert and rely on the Field Observation and Research Base of MLR. The project will carry out lysimeter tests to analyze the relationship between rainfall, soil water and groundwater and study the effect of water storage regulation of frozen soil on groundwater recharge. Through in-situ tests on the moisture movement in a two-dimensional cross-section, the patterns of soil water infiltration during thawing periods are identified in order to understand the mechanism of soil water infiltration under the freezing and thawing process on net groundwater recharger. Through collection and measurement of δD, δ18O values of different water samples, isotopic effects in transformation process of precipitation, soil moisture and groundwater are studied in order to find the reason of why the values of δD, δ18O of shallow groundwater in the Mu Us desert are more negative. This project reexamines the contribution of water infiltration to groundwater recharge during the freezing and thawing periods from the perspective of isotopes, which provides a new thinking and a new perspective for study of groundwater recharge in arid and semi-arid areas. The research results can provide a basis for the evaluation of groundwater resources in arid and semi-arid areas. It has important scientific significance and practical values in the field of ecological environment protection.

前期研究发现，毛乌素沙地潜水δD、δ18O值较降水均值偏负，推断是由季节性冻土冻融作用下水分入渗补给地下水造成。为验证假设，拟依托位于毛乌素沙地的国土资源部野外科学观测基地，开展如下研究：（1）通过野外地渗仪试验，分析冻融期降水-土壤水-地下水相互转化关系，研究冻土蓄水调节作用对降水入渗补给过程的影响；（2）通过剖面二维水分运移原位试验，识别消融期土壤剖面二维水分入渗模式，探究其对地下水补给的影响机制；（3）通过采集和测定不同水体δD、δ18O值，分析冻土冻融条件下降水-土壤水-地下水转化过程的同位素效应，阐明潜水δD、δ18O值偏负机理。本申请从同位素角度重新审视冻融期水分入渗对地下水补给的贡献，为揭示干旱半干旱区地下水补给机理提供新视角和新思路。研究成果可为干旱半干旱区地下水资源评价提供依据，在生态环境保护等领域也有重要科学意义和应用价值。

前期研究发现，毛乌素沙地潜水δD、δ18O值较降水均值偏负，推断是由季节性冻土冻融作用下水分入渗补给地下水造成。为验证假设，拟依托位于毛乌素沙地的国土资源部野外科学观测基地，开展如下研究：（1）通过野外原位监测试验，分析冻融期降水-土壤水-地下水相互转化关系，研究冻土蓄水调节作用对降水入渗补给过程的影响；（2）通过剖面二维水分运移原位试验，识别消融期土壤剖面二维水分入渗模式，探究其对地下水补给的影响机制；（3）通过采集和测定不同水体δD、δ18O值，分析冻土冻融条件下降水-土壤水-地下水转化过程的同位素效应，阐明潜水δD、δ18O值偏负机理。收集整理了前期鄂尔多斯盆地北部毛乌素沙地范围内布设的30余组潜水动态监测孔监测数据，对地下水位动态特征、动态类型、影响因素及动态曲线对冻土冻融作用的响应作了深入分析研究。在野外原位试验场选取典型土壤剖面，引入高密度电法物探技术，开展了冻融期剖面二维水分运移原位监测试验，有效识别了消融期土壤剖面二维水分优势流入渗模式，探究了其对地下水补给的影响机制；建立了土壤水分温度监测系统，开展土壤水分冻融入渗野外原位监测试验，深入认识了冻融期土壤水、地下水的相互转化规律及其对入渗补给的影响控制作用。通过系统采集并测试分析降雨、雪水、土壤水和地下水同位素组分，分析了不同水体同位素特征及相互关系，解答了毛乌素沙地潜水δD、δ18O 值偏负原因，并识别和量化了地下水补给的季节性差异，从同位素角度重新审视冻融期水分入渗对地下水补给的贡献，为揭示干旱半干旱区地下水补给机理提供新视角和新思路。研究成果可为干旱半干旱区地下水资源评价提供依据，地下水补给季节性差异的定量揭示在气候变化影响及生态环境保护等领域也有重要科学意义和应用价值。