敦煌月牙泉域沉积环境及泉湖水化学成因分析

Strata sedimentary environment and hydrochemistry cause of Lake Grescent Moon Spring in Dunhuang

在系统分析月牙泉水文地质条件的基础上,通过野外示踪实验和地下水调查采样,结合地下水同位素研究和第四纪沉积学特征分析的方式,对区域地下水运移规律和泉域地下水径流特征进行了研究,对月牙泉地下水水化学特征及其成因进行了深入分析,对党河地表水人工回灌入渗后形成的新的地下水流与南部地下水双重补给月牙泉进行了进一步论证,并提出了该区域第四纪浅层含水层风力沉积、河流沉积成因和地下水流速之间的关系:风积砂含水层为月牙泉域地下水快速径流提供了良好的径流条件,使泉湖水与周边地下水快速循环,月牙泉周边地下水水-盐循环均衡,是月牙泉淡水湖形成的重要因素之一。

The Dunhuang Grescent Moon Spring is surrounded by three sides of desert, and freshwater spring lake was formed owning to groundwater overflow. The Grescent Moon Spring is renowned in the wide world as the desert and the spring coexistence. In recent decades, because of the influence of the nature factor and the artificial factor, water level of the Greseent Moon Spring continues to decline and water environment is getting worsening. At present, the main research objects on the Greseent Moon Spring are the variation of water leverl and water quantity of spring region groundwater and regional groundwater. Therefore, based on the analysis of its hydrogeol0gic conditions, the sedimentary environments and hydrochemistry characteristic were investigated and deeply analyzed. First, it has been verified by the field tracer test, which chose ammonium molybdate as the indicator. The test shows that the shallow groundwater flowrate is much greater than the velocity of percolation of complete aquifer. It can he conclud- ed that this high flowrate causes the rapid water alterations of the Greseent Moon Spring and groundwater to reach the water-salt balance by the determination of twelve samples＇ isotopes and sedimentary characteristics in the Qua- ternary period in this region, and it is also the most essential factor for the emergence of the Grescent Moon Spring in the desert region. On that basis, the research on regional groundwater migration regularity and characteristics of groundwater runoff of spring region were carried out, demonstrating that hydroehemical indexes of the spring are con- trolled by both groundwater formed from the filtered water after artificial recharge and groundwater from the south ar- ea. In this paper, the relation of the causes of wind deposition in the Quaternary shallow aquifer, fluvial deposition and groundwater flow velocity was demonstrated for the first time. In the spring region, depositional environment of the Quaternary loose stratum is multi-phase deposition, and vertical distribution of groundwater aquifers is obvious. Aeolian sands aquifer provides the good condition for the high flow velocity of groundwater and the rapid alternation of the water in the spring. On the other hand, knowledge is gained from studying hydrochemistry characteristics of the spring and its surrounding area, and gives some informative and powerful evidence on the causes resulting in the great differences between lake water and its surounding groundwater in hydrochemistry index. On the impact of pa- leogeography and sedimentary environment, the water channel swung and shrank, making the sediments contain tiny grain of material in certain areas. Relatively poor ground water runoff condition and strong evaporation lead to high-sodium in aquifer and poor water quality in the peripheral areas of Grescent Moon Spring Lake. To sum up, de- tailed sedimentary environment of spring area can provide strong support for the further study of groundwater flowing and hydrochemistry characteristics in this region; the research of the cause of hydroehemical index reveals the hy- drodynamic relationship between spring region groundwater and regional groundwater. This paper also further dem- onstrates the spring formation mechanism and provides scientific foundation for emergency controlling measures.