| The problem of water resources and water environment is very serious in the process of rapid development of present society.The study of hydrogen and oxygen stable isotopes in water and hydrochemical characteristics can reveal the present situation of water environment and water circulation mode in a basin,which is beneficial to the rational utilization and protection of water resources.Heihe is located in Zhouzhi Country,Xi'an City,Shaanxi Province,and it is an important water source of Xi'an.The problems of water resources and water environment affect the lives of local people.In view of this,we choose the catchment area of Heihe in Xi'an as the study area.The precipitation,river water and groundwater samples were collected from September 2014 to August 2016 in the basin.We use the data of hydrogen and oxygen stable isotopes,physicochemical index and water chemistry,combine with the regional hydrological and geological survey data,and according to the meteorological data analysis the samples characteristics of stable isotopes and hydrochemical.The main conclusions are as follows:(1)The values of hydrogen and oxygen isotopes in precipitation in catchment area of Xi'an Heihe are high in spring and low in summer and autumn.The range of isotope fluctuation in spring is the largest,which is related to the complex water vapor source and the change of temperature.The local meteoric water line of the whole year in the basin is 8D=7.38?18O+8.78(R2=0.97).The slopes of the meteoric water lines in different seasons are different,which indicates that the water vapor has undergone different degrees of evaporation fractionation.The ?16O in precipitation has a significant correlation with temperature in spring and has no correlation in the whole year.The rainfall effect of ?16O in precipitation in summer is the most significantU and the effect is weak in the whole year.The values of ?16O decrease with altitude and the decreasing rate is 2‰ per 1000m.The values of the deuterium surplus of the precipitation are high in autumn and winter,and the values in spring and summer are quite low.The slopes and intercepts of the river water and groundwater evaporation lines are much smaller than the local meteoric water line of the basin,which indicates that the waters have suffered strong evaporation.The hydrogen and oxygen isotopes of the river water both have smaller ranges,which indicates that each supply source have a certain regulating effect to the river water isotope.In addition,the ?18O of river water also has a certain elevation effect.The changes of the groundwater hydrogen and oxygen isotopes are the most stable,which indicates the influence factors of groundwater are relatively single.The variations of groundwater in different years are quite different,which shows the groundwater is influenced by precipitation and river water greatly.(2)The conductivity and ion concentration of precipitation in the source area of Heihe Basin in Xi'an are quite low,which indicates that the quality of atmospheric precipitation in the basin is cleaner.The major anion and cation of precipitation are SO42-and Ca2+.The ion concentration in dry season is high and in wet season is low.The correlation analysis and principal component analysis indicate the sources of precipitation can be divided into anthropogenic source,marine source and terrestrial source.In all of the ions,NO3-,SO42-and NH4+ represent anthropogenic source,which accounted for 30.73%;Na+ and Cl-represent marine source,and Ca2+ and Mg2+represent terrigenous contribution.The river water presents weak alkalinity.The values of conductivity and solubility of solid are low,which indicates the quality of river water is clean.The variations of ion concentration along the river don't increase or decrease individually,which indicates that the river water is influenced by complex factors.The major anion and cation of the river water are HCO3-and Ca2+.The graph of piper three line shows the river water chemistry type is Ca2+—Mg2+—HCO3-.Combined with the analysis of Gibbs map,we know that the river water of the Heihe catchment area in Xi'an is mainly controlled by carbonate rock weathering.The correlation between the ion concentration and the ratio of the ions shows that Ca2+ and Mg2+ are mainly derived from the weathering of limestone and dolomite.SO42-may come from gypsum weathering and human activities.Na+ and K+ are mainly derived from feldspar weathering,and precipitation and human activities also have a certain impact to the ion source at the same time.The Cl-in river water may from precipitation and agricultural activities.NO3-is mainly from the use of nitrogen fertilizer and biomass burning.(3)There is a close relationship between atmospheric precipitation,river water and groundwater in the catchment area of Heihe,Xi'an.Through the analysis of stable isotopes,we can get that precipitation is the final recharge source of river water and groundwater.In the basin,the river water has a certain response to the precipitation,and there is a good synchronism between groundwater and river water.We use the mixed model of two terminal element based on ?16O and Cl-parameters,and the two terminal element mixed model calculation method based on mass conservation to estimate the supply proportion of river in different seasons in the catchment area of Heihe Xi'an.The result is that the proportion of precipitation recharge in summer and autumn accounted for 71.63%and 53.33%respectively,and the proportion of groundwater recharge in winter and spring accounted for 86.74%and 69.83%respectively.We use mass balance method to estimate the ion transport ratio of precipitation to river water in autumn according to the water chemical characteristics.The ion contribution rate of Na+?K+?Mg2+?Ca2+ and SO42-to the river water in autumn are 52.95%?1.54%?8.32%?0.37%and 2.39%respectively.The average ion contribution of precipitation to the river water is 13.11%. |
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