The Study Of Hydrogen And Oxygen Isotopic And Hydrochemical Characteristics Of Water In Yinchuan Plain

Yinchuan plain is located in the arid areas,northwest of China,where the economic development is seriously restricted by water resource.Increasing human activities leads to the dramatically increase of the groundwater exploitation,and underground water level decreased significantly.The shortage and unreasonable utilization of groundwater resources have became the key factors to restrict the sustainable economic development of Yinchuan.Clarify the resource of surface water and groundwater in the Yinchuan plain,and its renovation rate,grasping the mechanism of available water supply,drainage and water quality variation is the foundation of developing and managing of water resource.Combining with previous atmospheric precipitation isotope data,the research utilizes the environmental isotope and hydrochemical technology to analysis hydrogen and oxygen isotopic,cations&anions of different water bodies of the Yinchuan plain,which were sampled in winter and summer separately 208 water samples were analysed in this study,and the main conclusions are as below:?1?According to the meteorological and isotopic data of former study,the equations of meteoric water line?LMWL?in Yinchuan?including the whole year,summer and winter?are established as?D=7.22×?¹⁸O+5.5??D=9.12×?¹⁸O+17.84??D=8.39×?¹⁸O+20.34.The slope and intercept of the LMWL are lower than the global meteorological water line?GMWL?,which reflects the significant evaporation of the northwest arid region.The slope and intercept of winter is similar to those of summer,but the?¹⁸O??D values showed a significant seasonal variations.The regression analysis of precipitation isotopes and meteorological data of different seasons,rainfall effect were more significant during June to September,as well as temperature effect was more significant during dry October to May.In addition,the isotopic value of rainfall in summer is more positive than winter,reflecting the conversion of water vapor sources in different seasons.?2?Due to the precipitation and other water supplies,evaporation,the?¹⁸O??D value of surface water and groundwater in the study area generated different intensity of isotope fractionation.The?¹⁸O??D value of the lake water,pool water,ditch water,canal water,groundwater is partial light in turn.The equation of evaporation line of each water body was obtained by linear regression of the sampling point data,the evaporation line of the Yellow River:?D=4.69×?¹⁸O-22.87?R²=0.85?;the canal water:?D=5.78×?¹⁸O-14.05?R²=0.87?;the lake:?D=5.78×?¹⁸O-14.05?R²=0.87?;the pool water:?D=4.72×?¹⁸O-25.49?R²=0.97?;the gutter water:?D=4.92×?¹⁸O-24.11?R²=0.93?;and the groundwater:?D=5.64×?¹⁸O-16.39?R²=0.89?.?3?The surface water,groundwater isotope data analysis results show that:the d-?¹⁸O is negatively related,the?¹⁷O-?¹⁸O is positively related,and?¹⁸O??¹⁷O?d?¹⁷O-excess exist significant seasonal difference.Moreover,the?¹⁸O??¹⁷O?d-excess values of different water bodies in different seasons is not consistent.It embodies that the?¹⁸O??¹⁷O value of Yellow River water,canal water are more positive in winter,and the pool water,lake water,drain water,groundwater are more positive in summer.It indicates that the evaporation of pool water,lake water,ditch water and groundwater is stronger in summer.The excessive deuterium value of pool and the Yellow River water are more positive in winter.The lake water,canal water and ground water are different.Due to the secondary evaporation of lake and pond water in summer,the d value are more negative.However,the seasonal differences of ¹⁷O-excess in different water bodies were identical,which were more negative in January.?4?The physical and chemical parameters of water shows that surface water and groundwater are both neutral and alkaline.Na⁺is the dominant cation of surface water and groundwater,and there are differences in anions in different water bodies.Different water ions have different seasonal differences.TDS and salinity in different water bodies from low to high followed by yellow water,groundwater,drainage water,pond water,lake water,ditch water.The ditch water have a high content of Cl^-,reflecting the human activities on water pollution.The TDS of the Yellow River water increases gradually from Qingtongxia to Shizuishan.It is caused by water diversion and waste water discharge from Yinchuan area.?5?The study of water ion correlation analysis,chemical types and sources shows that the hydrochemical types of the Yellow River,canal water,lake water,pool water are relatively simple,and the ditch water,groundwater are more diversification,which indicates a more complicated water source.The ionic sources of surface water and groundwater are mainly controlled by evaporative crystallization and rock weathering.Part of the groundwater is rich in Cl^-and SO₄^2-,which indicates the salt infiltration from soil through irrigation water and ditch water.?6?The synthetic analysis of the characteristics of surface water and groundwater show that the Yellow River water is the main recharge source of canal water,lake water,pool water,drain water,and groundwater.The water supply source of lake water,pool water and canal water are relatively simple,and the source of ditch water and groundwater are more diversified.The Yellow River water is used to recharge the groundwater,and the groundwater is absorbed into the Yellow River through the drainage ditch after evaporation processes.In addition to the replenishment of the Yellow River,the groundwater also has the infiltration of atmospheric precipitation,the infiltration of canal water and ditch water.Overall,the hydraulic connections between different water bodies are intimate in the Yinchuan plain.The Yellow River irrigation effects not only the amount of water resources in the study area,but also the water quality of different water bodies.