Application of chloride tracer method to study residual flux of precipitation in areas around Huangqihai

Soil samples from three profiles were collected in the areas around Huangqihai by hand drill. The TDS value and chloride concentration of fifty soil water were determined and the basic principle of the calculation of mean chloride concentration, residual flux and chloride cumulative age was introduced. From TDS value and chloride concentration profiles, it is concluded the TDS distribution is almost different from the one of chloride concentration in each soil profile because of different ions having different migration rule. Through the calculation, the weighted mean chloride concentrations in three profiles are 59.04g/m³, 58.59g/m³ and 174.82g/m³, corresponding to the residual flux of 1.88mm/a, 1.90mm/a and 0.64mm/a, which only account for 0.50%, 0.51% and 0.17% of annual precipitation, respectively. The weighted mean chloride concentration is inversely proportional to the residual flux and the chloride cumulative ages in three profiles are 440, 293 and 725 years. It is proposed that the local precipitation is not the main recharge source of the groundwater in areas around Huangqihai.