Quantitative estimation of groundwater recharge ratio along the riparian of the Yellow River.

Quantitative estimation of groundwater recharge is crucial for limited water resources management. A combination of isotopic and chemical indicators has been used to evaluate the relationship between surface water, groundwater, and rainfall around the riparian of the Yellow River in the North China Plain (NCP). The ion molar ratio of sodium to chloride in surface- and groundwater is 0.6 and 0.9, respectively, indicating cation exchange of Ca(2+) and/or Mg(2+) for Na(+) in groundwater. The δD and δ(18)O values in rainfall varied from -64.4 to -33.4‰ and from -8.39 to -4.49‰. The groundwater samples have δD values in the range of -68.7 to -58.0‰ and δ(18)O from -9.29 to -6.85‰. The δ(18)O and δD in surface water varied from -8.51 to -7.23‰ and from -64.42 to -53.73‰. The average values of both δD and δ(18)O from surface water are 3.92‰ and 0.57‰, respectively, higher compared to groundwater. Isotopic composition indicated that the groundwater in the riparian area of the Yellow River was influenced by heavy rainfall events and seepage of surface water. The mass balance was applied for the first time to estimate the amount of recharge, which is probably 6% and 94% of the rainfall and surface water, respectively.