陇东黄土高原董志塬区地下水水化学特征与^(14)C年龄

Hydrogeochemical characteristics and radiocarbon dating of groundwater in the Dongzhi Tableland of Longdong Loess Plateau

研究陇东黄土高原董志塬区第四系地下水与马莲河沿岸地下水、地表水水化学离子分布、氢氧同位素特征与^(14)C年龄,了解董志塬区第四系地下水的水文地球演化规律与地下水补给来源.结果表明,董志塬第四系地下水总体矿化度较低,水质较好,主要由HCO_(3)-Ca型过渡到HCO_(3)-Ca-Na型水.水岩作用不强烈,受到阳离子交换反应和同离子效应影响,受蒸发浓缩作用的影响不大.董志塬地下水的δ^(2)H和δ^(18)O值在大气降水线下方且相对较贫,与现代大气降水多年加权平均特征值差异较大,说明地下水中存在有湿冷时期的古水补给成分,且来自现代大气降水补给的成分微乎其微.马莲河中下游地表水接受董志塬地下水泄流补给,马莲河源头处主要接受大气降水补给.^(14)C同位素的研究表明,董志塬深层地下水年龄在上千至上万年,结合氢氧同位素特征,认为董志塬区地下水中存在有晚更新世末期与全新世湿润时期的古降水成分.

The hydrochemical ion distribution, hydrogen and oxygen isotope characteristics and ^(14)C age of Quaternary groundwater in the Dongzhi Tableland and along the Malian River of Longdong Loess Plateau were analyzed to understand the hydrogeological evolution rules and groundwater recharge sources of the Quaternary groundwater. The results showed that the quaternary groundwater in Dongzhi Tableland had low salinity and good water quality, mainly having transferred from HCO_(3)-Ca type to HCO_(3)-Ca-Na type water. Water-rock reaction was not strong, and the groundwater could be affected by cation exchange reaction and the common-ion effect, with a weak effect from evaporation and concentration. The groundwater values of δ^(2)H and δ^(18)O in the Dongzhi Tableland were relatively poor and below the local meteoric water line, significantly different from the weighted characteristic value of modern atmospheric precipitation, indicating that the groundwater had paleo-water replenishment components during the wet and cold period, and the composition from modern atmospheric precipitation replenishment was very little. The stable isotope values of surface water in the middle and lower reaches of the Malian River were similar to those of the groundwater in the Dongzhi Tableland, and were on the same evaporation line, indicating that the middle and lower reaches of the Malian River accepted the recharge from the groundwater of the Dongzhi Tableland. Studies of ^(14)C isotopes indicated that the deep groundwater in the Dongzhi tablelands was tens of thousands of years old. Combined with the characteristics of hydrogen and oxygen isotopes,it was believed that the groundwater in the Dongzhi Tableland contained paleoprecipitation components from the late Pleistocene and Holocene humid periods.