Main Characteristics And Genetic Mechanism Of Lakes And Groundwater In Badain Jaran Desert

This paper has been studied with lakes and groundwater in the southeast of Badain Jaran Desert,guided by the theory of groundwater system and water circulation,and based on a large number of field survey,monitoring and sampling data.The main conclusions are as follows.(1)The analysis of dynamic characteristics o f representative lakes and groundwater shows that the groundwater in desert area is driven by the terrain elevation difference and the runoff is generally from the South East to the North West.The lake mainly receives groundwater recharge,which is the minimum discharge point of local groundwater flow system,and lakes do not change the direction of groundwater flow.Evaporation is the main controlling factor of water level change,and precipitation has lagging effect on recharge of lakes and groundwater.(2)The spatial distribution and evolution of hydrochemical characteristics of groundwater and lakes are studied by means of mathematical statistics,systematic cluster analysis,difference analysis and Piper trilinear nomograph.The results show that the water chemical properties of various water bodies are very different.The water in the bedrock fissure or fractures of clastic rock in Beida and Yabulai mountains are highly mineralized.The degree of phreatic water mineralization in the Quaternary loose sand gravel layer along the piedmont gully is lower.And TDS of groundwater in the hinterland of desert is generally lower and the water quality is better.The salinity of the lake increases from southeast to northwest in space.(3)The formation and evolution mechanism of groundwater chemistry is discussed by using Gibbs diagram and ion correlation.The chemical formation of shallow groundwater in the study area is mainly controlled by strong evaporation and concentration,followed by rock weathering and lixiviation,and deep well water and rising spring are mainly affected by rock weathering and lixiviation.Groundwater generally evolves from rock weathering to evaporation concentration.The main leaching minerals in ground water are rock salt and mirabilite,but the lixiviation of aluminosilicate minerals,calcite,dolomite and gypsum is less,and the cation exchange is common.(4)The distribution characteristics of hydrogen and oxygen stable isotopes and tritium isotopes in groundwater and lakes are analyzed.The evaporation line of phreatic water and lake water in desert area are both deviate from the local meteoric water line(LWML),which reflects the isotopic dynamic fractionation effect of evaporation and causes heavy isotope enrichment.The intersections between the lower left side of the desert phreatic evaporation line and LMWL are close to the groundwater samples distributed along the valley,which proves that the groundwater in the desert area has a similar source of replenishment with this part of phreatic water in the periphery of desert.The content of tritium in the groundwater on the periphery of the desert is generally high,mainly from the recharge of atmospheric precipitation,while the tritium in the groundwater on the inland of desert is generally low,indicating that the runoff time of groundwater from the supply area to the discharge area is longer.The high level of tritium in the hinterland of the desert area indicates that the precipitation has also supplied the groundwater.(5)It is conjectured that the main source of groundwater recharge in the desert area is the flood of ice melting spring water and the short time strong precipitation in summer in the peripheral mountainous area,the rapid influx along the channel of the valley to the edge of the desert.And the precipitation in the hinterland of desert area also has a recharge effect on the groundwater.