Abstract: 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 Grescent Moon Spring continues to decline and water environment is getting worsening. At present，the main research objects on the Grescent 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 hydrogeologic 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 be concluded that this high flowrate causes the rapid water alterations of the Grescent Moon Spring and groundwater to reach the water-salt balance by the determination of twelve samples’ isotopes and sedimentary characteristics in the Quaternary 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 hydrochemical indexes of the spring are controlled by both groundwater formed from the filtered water after artificial recharge and groundwater from the south area. 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 paleogeography 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，detailed 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 hydrochemical index reveals the hydrodynamic relationship between spring region groundwater and regional groundwater. This paper also further demonstrates the spring formation mechanism and provides scientific foundation for emergency controlling measures.

Key words: the Grescent Moon Spring, groundwater, hydrochemistry, water-salt balance