巴丹吉林沙漠及其东南边缘地区水化学和环境同位素特征及其水文学意义

通过对巴丹吉林沙漠东南部湖水和南缘地区地下水离子化学成分及其环境同位素分析,初步探讨了沙漠地区湖水和地下水之间补给的关系。沙漠湖水的离子化学特征显示沙漠东南部湖泊的演化趋势:微咸湖-咸水湖-盐水湖。显著不同的盐度、CO₃^2-和HCO₃^-含量以及地质资料都表明,沙漠北部较大的湖泊和东南部的湖泊被一地形上的褶皱隆起阻隔而形成了不同的地下水补给体系。环境同位素的分析结果表明,巴丹吉林沙漠东南部的湖泊和地下水与沙漠东南边缘地区的地下水有着相似的蒸发趋势,暗示南缘地区的地下水和沙漠东南部地区湖泊之间存在一定的联系。同其他干旱地区地下水的同位素结果进行对比显示,雅布赖地区和沙漠地区的地下水应该是埋深较浅的地下潜水。因本次研究结果不支持单一远源或者深层地下水补给的观点,故推断沙漠东南部地区以及南缘地区的地下水主要是当地雨量丰沛时期的降水及南缘低山降水下渗补给的。

ENVIRONMENTAL ISOTOPES AND WATER CHEMISTRY IN THE BADAIN JARAN DESERT AND IN ITS SOUTHEASTERN ADJACENT AREAS,INNER MONGOLIA AND THEIR HYDROLOGICAL IMPLICATIONS

The Badain Jaran Desert,the third largest sand sea in China,lies in Western Inner Mongolia from 39°20'N to 41°30'N,and 99°48'E to 104°14'E.Obviously different from other large deserts in the world,the desert is characterized by high dunes and permanent lakes within the dune field.In this study,the chemistry and isotopic compositions of groundwater and lake water samples,collected at 37 sites in the interior of the desert and its southeast margin,are analyzed.In the field,we measured water temperature,pH and TDS.Laboratory analysis included Na⁺,K⁺,Ca²⁺,Mg²⁺,Li⁺,NH⁺4,Cl-,SO^2-₄,NO-₃,F-,H2PO-₄,CO₂^-₃,HCO^-₃,δ¹⁸O and δ2H.In desert lakes,pH varies between 8.5 and 11.0 while the content of total dissolved solids(TDS)varies between 1.02g/L and 398.20g/L.Based on TDS,the desert lakes can be di￣vided into three types:brackish-water lake,salty water lake and salina.Most of desert lakes belong to Na^-Cl^-(SO₄)type of water.pH in groundwater of southeastern margin varies between 7.0 and 9.0.TDS in groundwater of southeastern margins is <12g/L.Most of groundwater samples belong to Na-(Ca)-(Mg)-Cl-(SO4)-(HCO3)type.Values of deuterium(δD)and oxygen-18(δ¹⁸O)in our study area vary over a large range,in desert lakes:1.8‰-5.9‰ for δ¹⁸O,-32.0‰--5.3‰ for δD;in desert groundwater:-3.9‰--1.7‰ for δ¹⁸O,-38.7‰--26.5‰ for δD;in groundwater of southeastern margin:-10.6‰--3.9‰ for δ¹⁸O,-91.1‰--45.1‰ for δD.By analyzing environmental isotope and ion chemistry in the desert lakes and groundwater of the Badain Jaran Desert and in its southeastern margin,we discuss the relationship between lakes and groundwater in the desert area.Referring to the salinity,the content of CO₂^-₃ and HCO^-₃ and geological data,the big northern lake group is different from the southeastern lake group in the desert,because a fold belt lies inbetween.The isotopes indicate the lakes and groundwater in southeast desert have a similar evaporation trend with the groundwater in the southeast margin of the desert,whose vaporing slope is 4.21.It implies there would have some kind of contact between groundwater in the margin and lakes of southeastern desert.The isotope shows that the groundwater in the desert and Yabulai area should be phreatic water which have a high water table.Therefore,we conclude that the groundwater in the southeastern part of the desert and southern margin are mainly recharged by precipitation of local rainfall and groundwater in the adjacent south mountains.