石羊河流域水化学演化与地下水补给特征

Chemical Evolution and Recharge Characteristics of Water Resources in the Shiyang River Basin

以地球化学和包气带氯质量平衡技术相结合,通过腾格里沙漠包气带沙芯记录和石羊河流域地下水、地表水地球化学的研究,探讨中国西北干旱区地下水补给历史及其气候特征和地下水地球化学演化规律。石羊河流域水化学在天然状态下具有水平分带性,上游地表水矿化度小于360mg l,下游达1000mg l;武威盆地洪积扇地下水主要为HCO3-SO4型水,至民勤终端湖演变为Cl-SO4型水,矿化度相应由500mg l增加为17g l左右。在腾格里沙漠的一个钻孔剖面记录了过去930年以来的补给量变化过程及其所反映的气候波动特征,氯质量平衡法计算的地区补给量平均仅为1 26mm,从剖面完整的记录可以将930aBP气候划分为4个干期和3个湿期。

Based on geochemical technology and chloride mass balance method, a case study of unsaturated zone profile in the Tengger desert and groundwater in the Shiyang river basin has been taken up in order to understand groundwater recharge process and geochemical evolution in arid area of the Northwest China. The trends of the major elements both in the groundwater and river follow a progressive sequence of geochemical evolution. The total dissolved solid in the river from Mountains is about 360 mg/l, and it is more than (1 500)mg/l in the Plain. Groundwater quality is good in the middle and upper reach of the river while high salinity in the Minqin basin. The chemicals are evolved from alkali-sulphate type in the recharge area to alkali-sulphate-chloride type along the river flow. In sedimentary rock, sulphate ions are derived from gypsum of anhydrite in the deep marlaceous matrix. High concentration of Na and SO_4^(2-) in comparison with Ca^(2+) and Cl^- are indicative of dissolution of Glauber's salt. The recharge of precipitation to groundwater in the arid zone is estimated to be 1.26 mm yr^(-1), giving a mean rainfall of 110mm. The climatic change events of 10～20 years duration were well preserved in the unsaturated zone profile. There are three wet phases and four dry episodes in the recent 930 years according to the peaks and troughs of recharge rate calculated through chloride concentration and moisture content.