石羊河流域地下水循环的同位素和地球化学演化特征

Isotopic and geochemical evolution characteristics of groundwater circulation in the Shiyang River Basin

石羊河流域是我国水资源开发程度最高的内陆河流域之一,是干旱区典型的水资源脆弱带,其生态环境问题日益严重,因此,研究石羊河流域地下水循环和地球化学演化规律具有重要意义.本研究从祁连山顶到红崖山水库沿径流剖面采集水样,对降水、地表水和地下水的水化学及同位素δ18O、δD进行分析,以揭示地下水的补给、径流和排泄规律.结果表明,地下水径流系统在向下游输送的过程中不断接受河流的渗漏补给和农田灌溉入渗补给,通过河床溢流、人工开采的形式排泄,盆地平原区地下水以垂向运动为主.盆地下游是地下水的主要排泄区,盆地北端地下水随基底抬升而上升溢出,转化为地表水排出.流域地下水从上游到下游矿化度逐渐升高,溶解性总固体(TDS)值在131～1750mg·L-1之间;水化学类型从HCO3--SO24-Ca2+-Mg2+型逐渐转化为SO24-HCO3--Mg2+-Ca2+型,呈现明显的分带特征.

Located in a typical vulnerable zone of water resources in arid area,Shiyang River Basin is one of the highest water resource development regions among inland river basins in China.With the worsening ecology,it is significant to investigate the groundwater circulation and geochemical evolution characteristics in Shiyang River Basin.In this study,water samples were collected from the top of the Qilian Mountains to Hongyashan Reservoir along the flow cross-section.Hydrochemistry and δ18O,δD of precipitation,surface water and groundwater were analyzed to reveal the groundwater recharge,runoff and discharge characteristics.The groundwater runoff system was recharged constantly by rivers leakage and irrigation water infiltration in the process of the runoff to the downstream,and was drained through the river overflow and pumping,with primarily a vertical movement.Downstream of the Basin was the main groundwater discharge area.Groundwater in the north of the Basin overflowed into surface water due to the basement uplift.The Total Dissolved Solids（TDS） values were between 131 and 1750 mg L^-1,gradually increasing along the flow direction.The hydrochemical types showed an obvious zonation from the upper to lower reaches,which gradually changed from HCO3^--SO4^2--Ca^2＋-Mg2＋ to SO4^--HCO3^--Mg^2＋-Ca^2＋.