The Study on Groundwater Recharge and Evolution in Northwestern China

The recharge and evolution of groundwater in the Wuwei Basin were investigated using chemical indicators, stable isotopes, and radiocarbon data. The results showed that the concentrations of Na+ and K+ in the groundwater were controlled by the dissolution of halite and sylvite from fine-grained sediments, whereas the increase of Na+ and Cl- was not in accordance with a ratio of 1:1, indicating that the dissolution of halite and sylvite barely affected the concentrations of Na+ and K+ in groundwater. Meanwhile, HCO3- was the dominant ion with a decreased ratio in the groundwater. The SO42-/Cl- ratio decreased with the sample profile from Southwest to Northeast due mainly to the increases of Cl concentration. The Cl- was enriched in the hydrodynamic sluggish belt, and thus the Ca2(+)/Cl- ratio decreased with the enhancement of Cl-. In addition, the delta O-18 and delta H-2 values of groundwater gradually increased from Southwest to Northeast along the flow path. Compared with the isotopic values of precipitation, the heavy isotopic values were strongly depleted in the groundwater samples, suggesting that the recharge of groundwater in the plain region was very limited from precipitation. Moreover, the groundwater in the phreatic aquifer was younger water with H-3 values from 47 to 71 a.BP, while the groundwater age in the confined aquifer was 1000-5800 BP evidenced by the C-14 values between 48 and 88 pmc. These results suggested that the recharge duration of the groundwater was from the late Pleistocene or early Holocene. These results might have important significance for inter-basin water allocation and groundwater management of the Wuwei Basin.