从同位素和水化学成分对比看沙漠地区湖泊水补给来源——以鄂尔多斯盆地木凯淖湖为例

The Source of Lake Water Supply from the Comparison of Isotopic and Hydrochemical in Desert Area:Taking Mukainao Lake in Ordos Basin as an Example

在自然和人为因素影响下,沙漠地区湖泊面积萎缩成为影响地区经济发展和生态环境质量的主要因素。本文以鄂尔多斯盆地内封闭型木凯淖湖为例,采用氢氧稳定同位素方法和水化学特征法,统计了湖水稳定同位素δ18O和δD特征,并同降水和地下水进行对比分析,揭示湖水补给来源,初步查明沙漠地区湖泊萎缩原因。研究发现,井水样品平均值为δ18O为-8.29‰,δD为-62.86‰,湖周围浅层地下水δ18O平均值为-7.2‰,δD为-57.46‰。湖水同位素数据因采样时间段的不同(7月,10月)表现出不同特征。7月份暴雨后δ18O平均值为-13.84‰,δD为-99.61‰,与暴雨前的湖水样品相比明显贫化,与暴雨同位素丰度(平均δ18O/‰为-13.2‰,δD为-93.56‰)一致。10月湖水蒸发线δD=5.1δ18O-14,比7月蒸发线δD=4.19δ18O-8.4斜率小,蒸发减弱。湖周围浅层地下水和中浅层井水同位素平均值相近,浅层地下水部分存在蒸发,蒸发线与湖水蒸发一致。夏季湖水同位素值远大于地下水同位素值,可回归到雨水线上,推测夏季湖水主要由降水补给。10月份湖水数值回归后与地下水一致,显示地下水和湖水密切相关,证明秋季湖水由地下水补给。

Under the influence of natural and human factors,the shrinking of Lake area in desert area has become the main factor affecting regional economic development and ecological environment quality.Taking the closed mukainao Lake in Ordos Basin as an example,the stable isotope δ18O and δD characteristics of lake water were statistically analyzed by using hydrogen and oxygen stable isotope method and hydrochemical characteristics method,and compared with precipitation and groundwater,the source of lake water supply was revealed,and the causes of Lake shrinkage in desert area were preliminarily identified.The results show that the averageδ18O andδD of well water samples near the study area are-8.29‰and-62.86‰,while the averageδ18O andδD of shallow groundwater around the Mukainao Lake are-7.2‰and-57.46‰.The isotopic data of Mukainao Lake water show corresponding characteristics due to different sampling periods.so,theMukainao Lake is divided into two groups:the lake water in July and the lake water in October.After heavy rain in July,the averageδ18O andδD are-13.84‰and-99.61‰,which are obviously depleted compared with the lake water samples before heavy rain.The evaporation line of Mukainao Lake in October isδD=5.1δ18O-14,which is smaller than the slope of the evaporation lineδD=4.19δ18O-8.4 in July.average values of isotopes in shallow groundwater and middle-shallow well water around the Mukainao Lake are similar,the evaporation also exists in shallow groundwater,and the evaporation line is consistent with evaporation of Mukainao Lake.Isotopes of the lake water in summer are far enriched in groundwater and can return to rainwater line.It is speculated that Mukainao Lake water in summer is mainly composed of precipitation.The regression of lMukainao Lake water value in October is consistent with groundwater,which shows the close relationship between groundwater and lake water,Combined with local precipitation data,it can be known that the main recharge of the lake water in autumn is the groundwater.