甘肃梨园河流域地下水来源及其水化学特征

通过分析水化学与氢氧稳定同位素的关系，研究梨园河流域地下水的补给机理和水化学演化规律。地下水总溶解固体（TDS）自西南向东北递增，最大值为1 258 mg/L。沿流程方向，深层地下水的水化学类型由Ca-HCO₃→Ca-Mg-HCO₃、Mg-SO₄→Na-SO₄型。浅层地下水的水化学类型由Ca-HCO₃→Mg-HCO₃-SO₄→Mg-SO₄型。地表水的水化学类型无分异，主要为Ca-HCO₃型。深层和浅层地下水沿途均发生了水岩融滤作用。Na⁺含量沿程增大，一是地下水中Ca²⁺与岩石中Na⁺发生阳离子交换作用，二是硅酸盐矿物的风化作用产生Na+。Phreeqc软件模拟显示，深层地下水中方解石先沉淀后溶解；CO₂、石膏、白云石和岩盐溶解。浅层地下水中，方解石由不饱和逐渐变为饱和；石膏、岩盐一直溶解。地下水的δ²H和δ¹⁸O值大部分位于大气降水线上方，反应了山区现代降水或雪冰融水通过出山地表径流补给，交替更新快，且深层地下水向上补给浅层地下水和地表水。地表、地下水相互转化是该区水循环的主要特征。

The Sources and Hydrochemical Properties of Groundwater in the Liyuan River Basin, Gansu Province

The Liyuan River Basin is located in an arid inland in northwest China and it is an important agricultural area in the Hexi Corridor,Gansu Province.As a tributary stream of the Heihe River,the Liyuan River is of significance in promoting economic and ecological development in the Zhangye Basin.The ecosystem in the region is highly vulnerable and strongly affected by the hydrochemical composition of water.For this reason,it is necessary to monitor the hydrochemical evolution in this area so as to avoid the degeneration of the local ecological environment.As surface water resources are limited,groundwater has gradually become as an indispensable water source in people’s daily life and agriculture.A lack of understanding of the mechanisms of groundwater evolution may lead to unwise utilization of groundwater,and thus have a negative impact on local sustainable development may be resulted in.In this paper,the relationships between hydrochemical properties and stable isotopes were analyzed.The transformation of surface water and groundwater was lucubrated so as to provide the government with decisional support concerning groundwater conservation.It was assumed that groundwater flowed in the same path from the southwest to the northeast based on considering the flow direction of the Liyuan River.The results showed that the TDS values of groundwater increased from the southwest to the northeast.The highest TDS value was 1 258 mg/L,which was too high for drinking use;this was the result of water-rock interaction and the salinization caused by the infiltration of irrigation water.Along with the flow path,the hydrochemical type of deep groundwater changed from Ca-HCO3 to Ca-Mg-HCO3,Mg-SO4 and Na-SO4,that of shallow groundwater changed from Ca-HCO3 to Mg-HCO3-SO4 and Mg-SO4,and that of surface water remained as Ca-HCO3 without change.Among the hyrdochemical changes,the increasing content of Na+ was the most apparent.There were two reasons for the increase of Na+ content along the flow path: the first was that Ca2+ in groundwater exchanged with Na+ in minerals in the cation-exchange process,and the second was the weathering of silicate minerals that produced Na+.The results simulated with Phreeqc software identified that there were the main water-rock interactions in groundwater along the flow path.In deep groundwater,calcite was precipitated at first,and then dissolved;whereas CO2 gas,gypsum,dolomite and halite were dissolved.In shallow groundwater,calcite was dissolved at first,and then precipitated,while gypsum and halite were dissolved.The modeling results were the evidences of the hydrochemical processes.The tracer elements of 2H and 18O in water molecules were used in this paper to analyze the water resources and recharge patterns.By comparing the δ18O-δ2H relation line of surface water and groundwater,global meteoric water line(GMWL) and local meteoric water line(LMWL),it was concluded that groundwater was recharged by precipitation or snowmelt water via surface runoff from the mountain area.Deep groundwater migrated upward to recharge shallow groundwater and surface water.