Water-salt Balance And Source Analysis Of The Lake In The Closed Area Of Horqin Sandy Land

The method of combining hydrogen-oxygen isotopes and hydrochemistry was used in this paper through field sampling and indoor testing,the hydrogen and oxygen isotope characteristics and hydrochemical characteristics of the lake water,shallow groundwater,middle groundwater,deep groundwater and precipitation in the small closed-flow lake basin of Horqin Sandy Land Agula Eco-hydrological Test Base were studied.Combined with the lake water level data,the water-salt balance of the lake was calculated.The main conclusions are as follows:1.The precipitation in the basin was weakly acidic fresh water,the isotope values were the most depleted,and the total ion concentration is minimum.The lake water was weakly alkaline brackish water,the isotope values were the most abundant,the total ion concentration is maximum.Groundwater in each layer was weakly alkaline fresh water,both the isotope values and the total ion concentration were located between the precipitation and the lake.Most groundwater isotope values were gradually negative from shallow to deep,and evaporation was weakened.2.In the time change,the ?D and ?18O values of the lake and all layers of groundwater in June was the highest,and they of the water except the deep groundwater in September was the lowest.The deep groundwater was the lowest in October,due to the suppy delay.In terms of hydrochemistry,the ion concentration of lake water and groundwater had no same regularity with time.In the spatial variation,with the flow of Lake water,evaporation-concentration effect became stronger.The ?D and ?18O values of the lake water were gradually positive,and the concentration of each ion increased except for Ca2+.The groundwater of each layer changed little along the path.This showed that the mixing of lake water and groundwater was not uniform in each section.3.The precipitation line in the basin was ?D=7.37?18O+0.84‰,located below the GMWL.It indicated that secondary evaporation occurred during precipitation and was mainly affected by continental air mass.The evaporation lines of lake water,shallow groundwater,middle groundwater and deep groundwater were ?D=5.65?18O-17.68‰,?D=5.82?18O-14.41‰,?D=6.18?18O-10.92‰,and ?D=7.05?18O-2.40‰.They were below LMWL and did not overlap,which reveals the precipitation evaporation is the smallest,and the lake water evaporation is the largest.4.Precipitation was SO42-Ca2+type,the lake water was HCO3-Na+ type,the shallow groundwater was HCO3--Ca2+and SO42--Ca2-type,the middle groundwater was HCO3--Na+and HCO3--Ca2+type,the deep groundwater was HCO3--Na+type.However,deep groundwater in May had HCO3--Ca2+type.It may be affected by the replenishment of soil water.According to the analyzing the control mechanism,shallow groundwater and lake water were both affected by varying degrees of rock weathering and evaporation-concentration.The medium and deep groundwater were mainly affected by rock weathering.Combined with the evaporation and lysing of the soil,it was found that the lake had both evaporation and soil lysing.The groundwater was mainly leached by soil,and the lysing effect from shallow to deep was getting stronger and stronger.According to the ion exchange analysis,it was known that the ion exchange of Ca2+?Na+occurd in the lake water and a part of the deep groundwater.5.The Na+and K+of the lake water and the groundwater in each layer were mainly derived from the dissolution of evaporite and the dissolution of potassium feldspar and albite.The Mg2+,Ca2+,HCO3-of groundwater mainly came from the dissolution of carbonate rocks,and a part of them derived from gpsum and anorthite.The Mg2+,Ca2+of the lake water mainly came from the dussoluution of silicate rock,carbonate rock and silphate rock.SO42-derived from the dissolution of gypsum and the dissolution of sulphate.Cl-was mainly derived from the dissolution of salt.6.Lake water is a mixed water between precipitation and groundwater.During the monitoring period,groundwater discharge accounted for 62.08%of the recharge of lake water,and precipitation accounted for 37.92%.7.Using the mass balance model of stable isotopes,the groundwater entering the lake was 602876 m3,and the slope flow was 193682 m3.Based on the chloride ion mass balance model,the chloride ion concentration in the stream into the lake was 146.31 mg/L.