Environmental Isotope Trace Of Groudwater In Yinchuan Plain

Based on field survy,we use environmental isotopes to analyze the recharge mechanism and cycle patterns of the groundwater in Yinchuan plain.The research results provide scientific base to realize the renewable property of groundwater and way to reasonable exploration,which is significant to mitigate the shortage of water resource.The results are summarized as following:(1) According to the environmental isotope dates of precipitation in Yinchuan plain,the paper clarifies the seasonal variation ofδ¹⁸O,the relationships betweenδ¹⁸O,precipitation and evaporation.It also establishes the Local Meteoric Water Line(LMWL), which is compared with the Global Meteoric Water Line(GMWL).Result shows that the precipitation is influenced by strong evaporation.(2) The paper also analyzes the distribution characteristics of environmental isotope in different water bodies:Yellow River water,lakes,single-layer structured phreatic water subsystem,multi-layer structured phreatic water subsystem,confined water,studies the main recharge of groundwater,discusses the relationship between these types of water in Yinchuan plain,and gets kinds of recharge percentage and discharge percentage:recharge percentage of single-layer structured phreatic water and multi-layer structured phreatic water,leakage recharge percentage between phreatic water and confined water,discharge percentage of drainage ditches.Results show that:the main source of groundwater supply of single-layer structured phreatic water subsystem in the area of piedmont acclivitous alluvial and flood plain is groundwater in base rock of Helan Mountain Eastern Region.The main source of groundwater supply of single-layer structured phreatic water subsystem in Yellow River alluvial fan in Qingtongxia and multi-layer structured phreatic water subsystem in the area of alluvial and flood plain is Yellow River water,leakage recharge percentage between phreatic water and confined water is 64.17%,discharge percentage of drainage ditches is 62%.(3) Isotope fractionation model is established to analyze the evaporation percentage of lakes,multi-layer structured phreatic water and drainage ditches from South to North. Conclusions are obtained that:influetion of evaporation on lakes and multi-layer structured phreatic water become larger and larger from South to North.(4) Inoder to recover the tritium concentration in precipitation from 1953 to 2004 for Yinchuan plain,interpolation method has been employed,and the tritium concentration in precipitation has been recovered.Then,exponential model is established to caculate the age of the phreatic water.The results show that the pheatic water has an active renewable property,for being renewed once in 48 years.At last,we use Vogel,Tamers,Pearson models to calculate the age of confined water,coming to the conclusion that the confined water in Yinchuan plain is paleogroundwater except in the recharge area and in the depression cone of deep groundwater,which has a very slow circulationg rate and low renewing capacity.