Estimation of shallow groundwater ages and circulation rates in the Henan Plain, China: CFC and deuterium excess methods

CFC age and deuterium excess methods were applied to the estimation of groundwater circulation rates in the Quaternary shallow groundwater system of the Henan Plain. The results provide a basis for groundwater renewability evaluation. The spatial distribution of CFC age shows that the groundwater system mainly comprises modern water, less than 50 a. The groundwater of less than 30 a was in the piedmont zone of the Taihang, Funiu, and Dabie Mountains, indicating short groundwater residence times, and fast groundwater cycling, with circulation rates of 27-31 m/d. Groundwater cycling along the Yellow River was also rapid because of exchange with the Yellow River. The circulation rates were 34-54 m/d. In the areas around Tongxu, Shangqiu, Taikang, Xiangcheng, in the middle of the study area, and east of Huaxian-Changyuan and Xixian, Gushi in the south, groundwater age was 30-40 a, suggesting a longer groundwater residence time. The groundwater cycle in these areas was slower than in the piedmonts, and the area along the Yellow River. The circulation rates were 15-26 m/d. In the areas of Luyi, Yongcheng, Zhumadian, Xincai and Huaibin, the groundwater age was older than 40 a, with the longest residence times and slowest circulation rates (similar to degrees 12 m/d). The correlation between groundwater age and deuterium excess averages for the northern, central, southern shallow groundwater systems and the < 30 a, 30-40 a, > 40 a groundwater age divisions was strong (R = 0.9714), showing that the groundwater residence time embodied by the deuterium excess parameter was consistent with groundwater age estimated using the CFC method.