鄂尔多斯高原潜水同位素特征及其成因分析

Isotope Characters of Shallow Groundwater and Their Formation in the Ordos Plateau

西北干旱半干旱区地下水的补给来源和方式仍没有统一的认识。通过对比鄂尔多斯高原不同水体氢氧稳定同位素特征,发现鄂尔多斯高原潜水的δD、δ^(18)O平均值(-71.75‰,-9.64‰)相对于当地降水均值(-65.00‰,-8.79‰)偏负。通过综合分析区内气候特点、地下水补给方式、潜水位动态等方面因素,认为潜水δD、δ^(18)O偏负现象与干旱地区降水的雨量效应和季节性冻土冻融作用下降水入渗补给地下水过程有关。δD、δ^(18)O值偏负的大降水补给地下水的能力较强,可能使潜水δD、δ^(18)O值偏负;冻土冻融条件下δD、δ^(18)O值偏负的冬季降水有效入渗补给能力较强,是潜水δD、δ^(18)O值偏负的另一可能原因。研究表明,利用氢氧稳定同位素研究干旱半干旱区地下水的补给来源和方式,需要考虑不同降水条件及冻土冻融作用下地下水补给能力的差异及其对地下水同位素组成的影响。

Groundwater recharge in arid and semiarid areas in northwest China is still under debate currently.Hydrogen and oxygen stable isotopes in different water bodies showed that the mean values of δD and δ^（18）O in shallow groundwater（-71. 75‰,-9. 64‰） were depleted more than the mean values of precipitation（-65. 00‰,-8. 79‰） in the Ordos Plateau. According to the combined analysis with local climate,groundwater recharge patterns and groundwater dynamic change of shallow groundwater level,it was considered that the depleted mean values of δD and δ^（18）O in shallow groundwater were probably attributed to the effect of precipitation and soil water infiltration during the freezing-thawing periods of seasonal frozen soil in arid and semiarid areas. Groundwater recharge capacity in heavy rain was high,which possibly caused the depleted values of isotopes in shallow groundwater. The high recharge capacity of winter precipitation under soil freezing-thawing was another possible reason. The study revealed that the difference of groundwater recharge capacity caused by different conditions of precipitation and freezing-thawing of frozen soil must be taken into account when hydrogen and oxygen isotopes are used to study groundwater recharge.