黄土高原区域尺度地下水稳定同位素特征及其指示意义

Characteristics and Indicative Significance of Groundwater Stable Isotopes in the Loess Plateau at the Regional Scale

为深入认识黄土高原区域尺度地下水补给规律,于2019年7月对13个主要流域地下水(浅层)进行系统采集与稳定同位素测定,分析地下稳定同位素的空间分布特征及影响因素,再结合区域降水稳定同位素资料,揭示地下水补给的来源和方式.结果表明,地下水稳定同位素的区域分布趋势不明显,但存在流域差异(P<0.001),随流域年均降水量增加而变贫化;与降水稳定同位素相比,地下水稳定同位素普遍贫化,与雨季(7~9月)降水相似,指示地下水补给存在季节效应,雨季降水是其主要补给季节,并发现地下水补给季节性与流域年均降水量和叶面积指数相关;地下水lc-excess普遍为负值,流域平均值介于−4.3‰~−0.7‰,指示不同流域地下水补给方式不同(基质流与优先流的比例),未来需要将饱和区(地下水)和非饱和区(土壤)结合起来进行具体量化分析.研究结果可提升对黄土高原地下水补给规律的科学认知,以期为区域层面地下水资源可持续管理提供科学依据.

Regional groundwater recharge is a critical scientific issue for sustainable groundwater resource development and management.However,spatial variations in groundwater recharge in the Loess Plateau(LP)remain poorly understood.To fill this knowledge gap,a systematic sampling campaign and stable isotope analysis were carried out for groundwater(shallow aquifer)in 13 major catchments during July 2019.The main objectives of this study were:①to understand the spatial distribution and influencing factors of stable isotopes in groundwater and②to reveal the groundwater recharge sources and pathways and their spatial variations,combined with the precipitation stable isotope datasets.Stable isotopes in groundwater had poor spatial variations at the regional scale;however,they became isotopically depleted with the increase in annual average precipitation on the catchment scale(r=−0.87).Compared with the stable isotope of precipitation,stable isotopes of groundwater were generally depleted and were similar to the precipitation of the rainy season(July⁃September).These together indicated that there was pronounced seasonality of groundwater recharge,and the main recharge period was the rainy season.In particular,the recharge seasonality index(δP/G)was closely related to the catchment's average annual precipitation(r=−0.77)and leaf area index(r=−0.63).In addition,groundwater lc-excess was generally negative,with the catchment-mean value ranging from−4.3‰to−0.7‰.Hydrologically,this indicated that groundwater recharge pathways(ratio of matrix flow vs.preferential flow)were different among these catchments,which should be quantitatively determined by combining the saturated zone(groundwater)and the unsaturated zone(soil)in future work.Our findings can improve the understanding of groundwater recharge in LP and provide a scientific basis for sustainable management of groundwater resources at the regional scale.