Research On Water Level Dynamic Characteristics And Water Recharge Sources Of The Lake Area In The Badain Jaran Desert

Northwest arid area is one of three major components of China's physical geographical regionalization,where its ecological environmental protection is very important to realize the sustainable development of social economy in this region and a larger spatial scale.With the increasing demand for water resources from social development,groundwater in the region have continuously been over-exploited,which has caused a series of ecological and environmental problems.As one of main geographic units in Northwest arid area of China,the exploitation of natural resources and the stabilization of natural ecosystems in the Badain Jaran Desert are of great significance to the desert hinterland,surrounding areas,and even the entire arid region of Northwest arid area.In recent years,desert groundwater has become one of water sources in surrounding areas.In order to promote rational use of water resources in arid areas and avoid ecological destruction of the desert hinterland and the surrounding environment,it is necessary to carry out research on occurrence regularities and supply sources of desert groundwater resources.In this study,groundwater level and lake level data in 2011-2018 were gathered from nineteen groundwater level observation points and ten lake level observation points laid out in grid form in the hinterland of the Badain Jaran Desert,and two groundwater level observation points in the Tengger Desert.The study investigated dynamic characteristics of groundwater level and lake level at a long time scale and a large space scale by time series analysis method,and qualitatively analized the main recharge source of groundwater.Meanwhile,combined with precipitation data from an automatic weather observation station in the hinterland of the Badain Jaran Desert,lateral net replenishments and precipitation infiltration replenishments were calculated by groundwater level fluctuation method to clarify the impact of precipitation on groundwater level in the desert hinterland,and quantified the contribution of different water sources on replenishing groundwater in the Badain Jaran Desert.Main results and conclusions are as follows:(1)Groundwater in the Badain Jaran Desert is mainly derived from seasonal icesnow melting water in Mount Qilian.Controlled by distribution of deep water flowing fault channels between the Tibet Plateau and the Alxa Plateau,groundwater is mainly supplied from southeast and southwest of the desert.In recent years,affected by premature melting of snow and ice caused by climate warming in Mount Qilian,times that groundwater level reached its peak and valley values were generally earlier than before,moving forward by 9.8 days and 23 days,respectively.(2)The exploitation of water resources in the Hexi Corridor and the undulation of desert terrain determined the type of groundwater changes from stable to unstable,from the southeast to the northwest,and the annual variation amplitude of groundwater level gradually increases,ranging from 26.3 to 178.1 cm.The large annual variation amplitude of groundwater level in local area of the desert hinterland is related to strong intensity tourism activities in relevant lake basins.(3)Shallow groundwater,human activities,spring water,and salinity of lakes have all affected the fluctuation process of lake water level.The annual periodic variation of lake water level is controlled by the seasonal fluctuation of groundwater level.It peaks in April and decreases to valley in October-November,which is lagging with respect to the change in groundwater level.Human activities and spring water supply in lake basins have a great impact on extreme phases of lake water level,which makes it different from groundwater level on temporal variation laws,and changes spatial distribution patterns of extreme phases in the region.Human activities also cause the phenomenon that lake water level is higher than groundwater level.(4)Controlled by ice and snow melting from Mount Qilian,lateral net replenishments of groundwater in the desert hinterland has been relatively stable for many years and presents seasonal characteristics.In spring,the lateral net replenishment began to increase,reaching the maximum in summer,ranging from 8.9 to 20.0 mm / d,and gradually decreasing in autumn and winter.(5)The shallower groundwater level in the desert hinterland,the more sensitive it is to precipitation events.Precipitation can recharge shallow groundwater with a burial depth of less than 1.4m,with the infiltration amount is less than about 2 orders of magnitude of the lateral net recharge.Precipitation infiltration replenishments decreases with the increase in burial depth,the maximum is 0.8mm,and the largest precipitation infiltration recharge coefficient is 0.4.Precipitation cannot effectively replenish deeper groundwater in lake basins and aquifers in Megadunes.For groundwater with a burial depth greater than 1.4m,observed water level fluctuations may be caused by evapotranspiration or formation and release of the trapped gas.