The Hydrogeochemical Feature And Enrichment Characteristics Of Nitrogen In Groundwater In The Turpan-Hami Area,Xinjiang

Due to the seriously shortage of water resources in the Turpan-Hami area,Xinjiang,which is located in Northwestern China,groundwater has become the main water supply.In recent years,more and more people pay attention to the shortage of water resources in the area.The high TDS and the enrichment characteristics of nitrogen has caused lots of impacts on the economic development and ecological environment in the area.Therefore,studying on the hydrogeochemical characteristics and origins of nitrogenenrichmentis of scientific significance,which can gain knowledge for the development and protection of regional groundwater.Based on the hydrogeological data in the study area,we conducted some fieldwork and collectedsome groundwater samples.Combining with the hydrochemical,hydrogen,oxygen and nitrogen stable isotopes measurements,the hydrogeochemical characteristics,the distribution and originsof nitrogen in groundwater ofthe Turpan-Hami area were analyzed in this study.Besides,by using the method of CMB,the cumulative age of TDS and nitrogen in the groundwater was calculated.The results are as followings:(1)In the Hami area,the hydrochemical types gradually evolved from the Cl·SO₄-Na to Cl-Na along the groundwater flow path.In the study,TDS is mainly concentrated in 4 g/L?100 g/L.The concentration of groundwater chemical components gathered along the flow path,leaching and evaporation play important role on the hydrochemical evolution,and the evaporation was the dominant processfor groundwater hydrochemical evolutionin Turpan-Hami area.(2)All the points of groundwater samples lie below the GMWL and are far away from the line.A linear regression line was fitted using the data of?D and?¹⁸O of all samples,representing an evaporation line with R²=0.924.It shows that the main recharge source of groundwater is from atmospheric precipitation with low value of deuterium excess,indicating the groundwater in study area has experienced strong evaporation and concentration effects.(3)The concentration variationsof nitrate,nitrite,ammonia are consistent with that of TDS.The formation of high level nitrogen in groundwater is consistent to that of Cl^-,Na⁺and SO₄^2-,which is mainly affected by strong evaporation.(4)The?¹⁵N-NO₃^-ranges from-0.6‰to+31‰and mainly fall in the range of+4.1‰to+19.3‰,the?¹⁸O-NO₃^-is about+16.3‰to+37.4‰.The vaule of?¹⁵N-NO₃^-and?¹⁸O-NO₃^-in most groundwater samples is in the range of atmospheric precipitation.The originof nitrate is mainly from atmospheric precipitation,no obvious transformation of three nitrogen occurred in the groundwater.(5)The infiltration rate of atmospheric precipitation range from 0.14 to 2.39mm/a,and the average value of the rate is 1.278mm/a.The cumulative age of groundwater in the typical study area is from 57.11 to 337.87a.