Source identification of Lingshui Spring using GIS-based hydrochemistry and environmental isotopic methods

Multiple methods were used in this study in an attempt to identify the boundary and source of the Lingshui Spring,a karst spring in Wuming County of Nanning City.Hydro chemical data from the karst springs,boreholes,and epikarst springs possibly distributed in the Lingshui drainage area were collected in dry and rainy seasons.The hydro-chemical causes for different karst water were distinguished in the CaCO3-CO2-H2O equilibrium system.It was discovered that the chemical equilibrium system was influenced by CO2 partial pressures,pollution,and the existing conditions of groundwater.The analysis of the environmental isotope indicates that the isotopes δ2H and δ18O in the rainwater of the study area were affected by season and altitude.The variation of isotopes in groundwater was weakened by the mixed process in the aquifer.The average contents of δ2H and δ18O were almost equal to those of rainfall in summer,indicating that the rainfall infiltration recharge mostly occurred in summer.The GIS technique was used to divide the watersheds of the surface water system,based on which the groundwater drainage area was identified.The drainage area of the Lingshui Spring was found to be 697?km2,of which 126?km2were buried karst and the rest were covered karst.